Dissertations / Theses on the topic 'Strain release'

Thesis (M.S.)--West Virginia University, 2006.
Title from document title page. Document formatted into pages; contains xv, 133 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 126-133).

This study developed and analyzed a modification of the blister test permitting nearly constant strain energy release rate testing of adhesive bonds. The work consisted of three parts; (1) development of the testing technique to evaluate strain energy release rate and to record the time dependent nature of the fracture process, (2) numerical analysis of the constrained blister test to determine the applicability of an approximate solution for several materials, and (3) development of an. analytical technique to evaluate the strain energy release rate for relatively stiff specimens.

Master of Science

The objective of this thesis is to develop and demonstrate techniques for self-deployment of origami-based mechanical systems achieved through internal strain-energy storage and release, with special application to medical implant devices. The potential of compliant mechanisms and related origami-based mechanical systems to store strain-energy make them ideal candidates forapplications requiring an actuation or deployment process, such as space system arrays and minimally invasive surgical devices. The objective of this thesis is achieved by first categorizing differentdeployment methods in origami-based, deployable mechanisms and then further exploring the use of strain energy to facilitate actuation in deployable mechanisms. With this understanding inplace, there are opportunities using strain energy to develop new approaches to deploy particular mechanical systems. These origami-based mechanisms have the ability to improve devices in themedical field. This work contributes to the knowledge base of self actuating deployable structures in origami-based mechanical systems by developing design concepts and models for strain energystorage and release. By developing the foundational characteristics for self-actuation, the work will be demonstrated thorough applications in medical implant devices.

Composite materials together with adhesive-bonding have been increasingly used in the aviation industry. Delamination is among the critical failure modes in fiber-reinforced laminated composite structures including adhesive-bonded assemblies. This thesis presents an analytical approach by taking into account the first-ply failure in adhesive-bonded composite joints subjected to axial tension. The ASTM D3165 standard test specimen geometry is followed for model development derivations. The field equations, in terms of displacements within the joint, are formulated by using the first-order, shear-deformable, laminated plate theory together with kinematics relations and force equilibrium conditions. The stress distributions for the adherends and adhesive are determined after the appropriate boundary and loading conditions are applied and the equations for the field displacements are solved. The equivalent forces at the tip of the prescribed interlaminar crack are obtained based on interlaminar stress distributions. The strain energy release rate of the crack is then determined by using the virtual crack closure technique (VCCT). The system of second-order differential field equations is solved to provide the adherend and adhesive stresses using the symbolic computation tool, Maple 9.52. Finite element analyses using the J-integral as well as the VCCT are performed to verify the developed analytical model. Finite element analyses are conducted using the commercial finite element analysis software ABAQUS 6.5-1. Results determined using the analytical method are shown to correlate well with the results from the finite element analyses.
Thesis [M.S] - Wichita State University, College of Engineering, Dept. of Aerospace Engineering

Chloride ion induced corrosion of reinforcing steel in concrete bridge decks has become a major problem in the United States. Latex modified concrete (LMC), low slump dense concrete (LSDC) and hot-mix asphalt membranes (HMAM) overlays are currently some of the most used rehabilitation methods. Epoxy coated reinforcing steel (ECR) was developed and promoted as a long term corrosion protection method by the Federal Highway Administration (FHWA). However, recent evidence has suggested that ECR will not provide adequate long term corrosion protection. The Reynolds Metals Company has developed an aluminum bridge deck system as a proposed alternative to conventional reinforced steel bridge deck systems. The deck consists of a polymer concrete overlay and an aluminum substrate. The purpose of this investigation is to evaluate the bond durability between the overlay and the aluminum substrate after conditioning specimens in various temperature and humidity conditions. The average critical strain energy release rate, Gcr, for each specimen was measured using a modified mixed mode flexure (MMF) test. In this investigation the strain energy release rate is a measure of the fracture toughness of the interface between the polymer concrete overlay and the aluminum substrate. The different environmental conditionings all had a significant effect on the bond durability. Specimens conditioned at 30 degrees C [86 degrees F], 45 degrees C [113 degrees F] and 60 degrees C [140 degrees F] at 98 % relative humidity all showed a decrease in interfacial bond strength after conditioning. A decrease in the interfacial bond strength was also observed for the specimens conditioned in freezing and thawing cycles as well as specimens conditioned in a salt water soak. Of the exposure conditions used in this investigation, the only one that showed an increase in the bond strength was drying the specimens continuously in an oven at 60 degrees C [140 degrees F].
Master of Science

Proton exchange membrane fuel cells typically consist of stacks of membrane electrode assemblies sandwiched between bipolar plates, effectively combining the individual cells in series to achieve the desired voltage levels. Elastomeric gaskets are commonly used between each cell to insure that the reactant gases are isolated; any failure of a fuel cell gasket can cause the reactants to mix, which may lead to failure of the fuel cell. An investigation of the durability of these fuel cell seals was performed by using accelerated characterization methods. A hydrocarbon sealant was tested in five different environments to simulate fuel cell conditions. Viscoelastic properties of these seals were analyzed using momentary and relaxation compressive stress tests. Material properties such as secant modulus at 100% strain, tensile strength, and strain at failure were determined using dog-bone samples aged at several different imposed strains and aging times in environments of interest. Tearing energy was evaluated using trouser test samples tested under different rates and temperatures after various environmental aging conditions. Additionally, tearing tests were conducted on samples tested in liquid environment. A viscoelastic and mechanical property characterization of these elastomeric seals under accelerated aging conditions could help understand the behavior and predict durability in the presence of mechanical and environmental loading. Additionally, the effects of confinement have been evaluated for a bonded joint with varying thickness along the bonded direction. The Dreaming project is a glass art project in Fredrick, MD which incorporates such a varying thickness joint where thermal expansion of the adhesive has caused the glass adherend to break and debonding of the sealant. To examine this joint design, finite element analysis has been used to determine the effects of thermal expansion on such a complex geometry. Nine different test geometries have been evaluated to determine the effect of confinement coupled with thermal expansion on joint design with an elastomeric adhesive. Once evaluated, design changes were performed to try to reduce the loading while maintaining the general joint design. Results of this analysis can be used to determine the effects of confinement on a complex elastomeric joint.
Master of Science

The objective of this study is to evaluate the bond durability of an epoxy-based polymer concrete wearing surface bonded to aluminum bridge decks. In the bridge design, an aluminum alloy bridge deck is used with a polymer concrete wearing surface. A modified mixed mode flexure fracture test was developed to assess the bond durability of specimens aged in the following environmental conditionings: 30°C [86°F], 98% RH; 45°C [113°F], 98% RH; 60°C [140°F], 98% RH; freezing and thawing; salt (NaCl) water soak; and 60°C [140°F], dry. The exposure times varied from none to twelve months. The critical strain energy release rate (Gc) of the bond was determined using a compliance technique. In spite of considerable scatter in the data, the results suggested that the interfacial bond toughness had been degraded by exposure conditions. The aging appeared to affect the polymer concrete overlay (silica aggregates/epoxy bond) as well. Fracture analysis and finite element modeling were completed for linear elastic behavior. Analytical and numerical solutions were in reasonably good agreement. Characterization of the bridge components and failure specimens were accomplished using analytical measurements including thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA). Techniques employed in the surface analysis included x-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM).
Master of Science

Road administrators have to make decisions regarding the maintenance and rehabilitation of many existing jointed Portland Cement Concrete (PCC) pavements in the road network. Since these pavements are in general expensive to rehabilitate, agencies often opt for overlaying the deteriorated PCC pavement with Hot Mix Asphalt (HMA), resulting in a composite pavement. Unfortunately, the tensile stresses and strains at the bottom of the overlay developed from the movement of the joints, which are caused by the traffic and the changes in temperature, will create cracks on the surface known as reflective cracking. Reflective cracking can reduce the life of a pavement by allowing water or other particles to get into the underlying layers, which causes the pavement structure to lose strength. To improve the performance of the composite pavement, road agencies have studied mitigations techniques to delay the initiation and propagation of those cracks reflected from the PCC joints and cracks. Traditionally, these studies have relied only on laboratory testing or nondestructive tests. This dissertation expands the traditional approach by adding full-scale Accelerate Pavement Testing (APT) to a laboratory effort to investigate enhanced asphalt overlays that delay the initiation and propagation of cracks reflected from the PCC joints. The study was organized into three complementary experiments. The first experiment included the first reflective cracking study of hot-mix asphalt (HMA) overlays over jointed Portland cement concrete pavements (PCCP) conducted at the Virginia APT facility. A Heavy Vehicle Simulator (HVS) was used to compare the reflective cracking performance of a Stone Matrix Asphalt (SMA) control mix with a modified mix with a synthetic fiber. The discussion includes the characterization of the asphalt mixes, the pavement structure, construction layout, the equipment used, the instrumentation installed, and lessons learned. Results showed that the fiber-modified mix had a higher resistance to fracture, which increases the pavement life by approximately 50%. The second experiment compared the cracking resistance of the same control and modified mixes in the laboratory. Four cracking resistance tests were performed on each mix. These four tests are: (1) Indirect Tensile Asphalt Cracking Test (IDEAL-CT), which measures the Cracking Test index (CTindex); (2) Semicircular Bend Test-Illinois (SCB-IL), which measures the critical strain energy release rate (Jc); (3) Semicircular Bend-Louisiana Transportation Research Center (SCB-LTRC), which measures the Flexibility Index (FI); and (4) Overlay Test (OT), which measures the Cracking Propagation Rate (CPR). The results from the four tests showed that the fiber-modified mix had a better resistance to cracking, confirming the APT test results. The laboratory assessment also suggested that the IDEAL-CT and SCB-IL test appear to be the most practical for implementation. The third phase evaluated the performance of mixes designed with a high content of Reclaimed Asphalt Pavement (RAP) and an enhanced asphalt-rubber extender, which comprises three primary components: plain soft bitumen, fine crumb rubber and an Activated Mineral Binder Stabilizer (AMBS). The experiment evaluated the fracture resistance of nine mixes designed with different rates of recycled asphalt pavement (RAP) and asphalt-rubber, compare them with a traditional mix, and propose an optimized mixture for use in overlays of concrete pavements. The mixes were designed with different rates of RAP (15, 30, 45%) and asphalt-rubber extender (0, 30, and 45%) following generally, the design requirements for an SMA mix in Virginia. The laboratory test recommended in the second experiment, IDEAL-CT and SCB-IL, were used to determine the fracture resistance of the mixes. The results showed that the addition of RAP decreases fracture resistance, but the asphalt-rubber extender improves it. A mix designed that replaced 30% of the binder with asphalt-rubber extender and 15% RAP had the highest resistance to fracture according to both. Also, as expected, all the mixed had a low susceptibility to rutting.
Doctor of Philosophy
Reflective cracking can reduce the life of a pavement by allowing water or other particles to get into the underlying layers, which causes the pavement structure to lose strength. To improve the performance of the composite pavement, road agencies have studied mitigations techniques that will delay the initiation and propagation of those cracks reflected from the PCC joints. Traditionally, these studies rely only on laboratory testing or nondestructive tests that will assist in the decision-making stage in a short time manner. This dissertation focusses on a reflective cracking study conducted through Accelerate Pavement Testing (APT) using a Heavy Vehicle Simulator (HVS) and laboratory testing. The first task used an HVS to evaluate reflective cracking of a Stone Matrix Asphalt (SMA) control mix and a modified mix with synthetic fiber. One lane was constructed with two layers of 1.5-inches of a control Stone Matrix Asphalt (SMA) mix and the second lane with an SMA mix modified with the synthetic fiber. Results from APT demonstrated that the modified SMA has a higher resistance to fracture which increases the pavement life by approximately 50%. The second task estimated the fracture resistance of the mixes studied in task one following the laboratory test: Indirect Tension Asphalt Cracking Test (IDEAL-CT), Texas Overlay Test (OT), Semi-Circular Bend-Louisiana Transportation Research Center (SCB-LTRC) and Semi-Circular Bend-Illinois (SCB-IL) to estimate the Cracking Test Index (CTindex), Cracking Propagation Rate (CPR), critical strain energy release rate (Jc) and Flexibility Index (FI), respectively. Results showed that the modified mix had a better resistance to cracking, confirming the APT test results. Specifically, CTindex results showed that the modified mix is more resistant than the control, with indices of 268.72 and 67.86. The estimated Jc indicated that less energy is required to initiate a crack for the control mix that achieved 0.48 kJ/m2 compared to the modified mix with synthetic fibers 0.54 kJ/m2. FI results for the control and fibers were 2.16 and 10.71, respectively. The calculated CPR showed that the control mix propagates a crack at a higher rate of 0.188 compared to the modified mix with a CPR of 0.152. The third phase evaluated the performance of mixes designed with a high content of Reclaimed Asphalt Pavement (RAP) and an enhanced asphalt-rubber extender, which comprises three primary components: plain soft bitumen, fine crumb rubber and an Activated Mineral Binder Stabilizer (AMBS). The experiment evaluated the fracture resistance of nine mixes designed with different rates of recycled asphalt pavement (RAP) and asphalt-rubber, compare them with a traditional mix, and propose an optimized mixture for use in overlays of concrete pavements. The mixes were designed with different rates of RAP (15, 30, 45%) and asphalt-rubber extender (0, 30, and 45%) following generally, the design requirements for an SMA mix in Virginia. The laboratory test recommended in the second experiment, IDEAL-CT and SCB-IL, were used to determine the fracture resistance of the mixes. The results showed that the addition of RAP decreases fracture resistance, but the asphalt-rubber extender improves it. A mix designed that replaced 30% of the binder with asphalt-rubber extender and 15% RAP had the highest resistance to fracture according to both. Also, as expected, all the mixed had a low susceptibility to rutting.

As hydrogel products are manufactured and used for applications ranging from biomedical to agricultural, it is useful to characterize their behavior and interaction with other materials. This thesis investigates the adhesion between two different solvated semi-interpenetrating polymer network (S-IPN) silicone hydrogels and a cyclo-olefin (COP) polymer through experimental, analytical, and numerical methods.

Interfacial fracture data was collected through the application of the wedge test, a relatively simple test allowing for the measurement of fracture properties over time in environments of interest. In this case, the test was performed at discrete temperatures within range of 4Ë C to 80Ë C. Two COP adherends were bonded together by a layer of one of the S-IPN silicone hydrogels. Upon the insertion of a wedge between the two adherends, debonding at one of the two interfaces would initiate and propagate at a decreasing rate. Measurements were taken of the debond length over time and applied to develop crack propagation rate versus strain energy release rate (SERR) curves. The SERR values were determined through the application of an analytical model derived for the wedge test geometry and to take into account the effects of the hydrogel interlayer. The time-temperature superposition principle (TTSP) was applied to the crack propagation rate versus SERR curves by shifting the crack propagation rates with the Williams-Landel-Ferry (WLF) equation-based shift factors developed for the bulk behavior of each hydrogel. The application of TTSP broadened the SERR and crack propagation rate ranges and presented a large dependency of the adhesion of the system on the viscoelastic nature of the hydrogels. Power-law fits were applied to the master curves in order to determine parameters that could describe the adhesion of the system and be applied in the development of a finite element model representing the interfacial fracture that occurs for each system. The finite element models were used to validate the analytical model and represent the adhesion of the system such that it could be applied to future geometries of interest in which the S-IPN silicone hydrogels are adhered to the COP substrate.

[Files modified per J. Austin, July 9, 2013 GMc]
Master of Science

A full numerical evaluation using Abaqus has been done for 2D and 3D Mode I and II delamination propagation (in composite materials). First the theory to explain all the mechanisms that are involved in delamination growth were developed, also the theory that Abaqus uses to solve the delamination process was explained. Furthermore, all the values that have been used were explained in detail, these values are difficult to find. Then, the results were obtained combining the delamination theory with Matlab. The parameters that have been analyzed are: critical strain energy release rate, the most relevant stresses around the delamination and the shape of the delamination tip. The numerical results are in accordance with the experimental results, thus, the simulations are able to predict the delamination growth.

Multi-layered electronic packages increase in complexity with demands for functionality. Interfacial delamination remains a prominent failure mechanism due to mismatch of coefficient of thermal expansion (CTE). Numerous studies have investigated interfacial cracking in microelectronic packages using fracture mechanics, which requires knowledge of starter crack locations and crack propagation paths. Cohesive zone theory has been identified as an alternative method for modeling crack propagation and delamination without the need for a pre-existing crack. In a cohesive zone approach, traction forces between surfaces are related to the crack tip opening displacement and are governed by a traction-separation law. Unlike traditional fracture mechanics approaches, cohesive zone analyses can predict starter crack locations and directions or simulate complex geometries with more than one type of interface. In a cohesive zone model, cohesive zone elements are placed along material interfaces. Parameters that define cohesive zone behavior must be experimentally determined to be able to predict delamination propagation in a microelectronic package. The objective of this work is to study delamination propagation in a copper/mold compound interface through cohesive zone modeling. Mold compound and copper samples are fabricated, and such samples are used in experiments such as four-point bend test and double cantilever beam test to obtain the cohesive zone model parameters for a range of mode mixity. The developed cohesive zone elements are then placed in a small-outline integrated circuit package model at the interface between an epoxy mold compound and a copper lead frame. The package is simulated to go through thermal profiles associated with the fabrication of the package, and the potential locations for delamination are determined. Design guidelines are developed to reduce mold compound/copper lead frame interfacial delamination.

Polymer electrolyte membrane (PEM) fuel cell (FC) stacks require elastomeric gaskets for each cell to keep the reactant gases within their respective regions[1]. If any gasket degrades or fails, the reactant gases can leak or mix with each other directly during operation or standby, affecting the overall operation and performance of the FC. The elastomeric gaskets used as FC seals are exposed to a range of environmental conditions, and concurrently, subjected to mechanical compression between the bipolar plates forming the cell. The combination of mechanical stress and environmental exposure may result in degradation of the seal material[2] over a period of time. In order to address the durability and make reliability predictions, the long-term stability of the gaskets in FC assemblies is critical. The aim of this study is to investigate the performance of elastomeric seals in a simulated FC environment in the presence of mechanical stresses. The overall scope of the study includes mechanical and viscoelastic properties characterization, and lifetime durability predictions based on an accelerated characterization approach. With the help of finite element analysis software, ABAQUS, a fixture was designed to perform strain-based accelerated characterization of seal material in air, deionized (DI) water, 50v/50v ethylene glycol/water solution, and 0.1M sulfuric acid solution. Dogbone samples were strained to different levels in the custom fixture and submerged in liquid solutions at 90°C and in air at 90°C and 120°C. It was observed that mechanical properties such as tensile strength, strain to break, 100% modulus, crosslink density, and tensile set degrade due to aging and the extent of change (increase or decrease) depends significantly on the strain level on the specimen. Trouser tear tests were conducted on reinforced specimens in air and deionized water (DI) to evaluate the tear resistance of an elastomeric seal material intended for proton exchange membrane fuel cells. Plots relating the crack growth rate with tearing energy were obtained at various temperatures and provided significant insight into the rate and temperature dependence of the tearing strength of the seal material. Stick-slip crack propagation was observed at all temperatures and loading rates, although the behavior was suppressed significantly at low loading rates and high temperatures. Crack growth rate versus tearing energy data at different temperatures was shifted to construct a master curve and an estimate on the threshold value of tear energy was obtained which may be helpful in designing components where material tear is of concern. Strain energy release rate (SERR) value, calculated using the J-integral approach for a pre-existing crack in ABAQUS, was used to estimate the crack growth rate in a given seal cross-section to predict lifetime. In order to assess the viscoelastic behavior and to investigate the long term stress relaxation behavior of the seal material, compression stress relaxation (CSR) tests were performed on molded seals, called as SMORS, over a range of environmental conditions using a custom-designed fixture. The effect of temperature and environment was evident on material property changes and presented in terms of momentary properties and stress relaxation behavior. Various mechanisms involved in material degradation, chain scission and crosslinking, were suggested and insights were gained into how cure state and level of antidegradants in a material dictate the material behavior during the first phase of environmental exposure leading to change in material properties. Ring samples made of silicone were also tested using the fixture to obtain insight additional into material degradation due to aging. Results presented from testing on SMORS showed a lot more variation in data as compared to neat silicone rings due to the complexity involved in making SMORS. For understanding the deformation behavior of an elastomeric seal and its sealing performance, finite element characterization of seal cross-section was carried out on O-ring and SMORS cross-section. The effect of a seal's layout on distribution and magnitude of contact stresses and contact width was investigated for the O-ring and the information obtained thereby helped to analyze a complex assembly such as SMORS, where several interfaces and boundary conditions are involved. Stress/strain profiles were generated to visualize their concentration and distribution in the seal cross-section. Frictionless and rough interfacial conditions between seal material and platens were assumed and it was found that its effect on contact width and peak contact pressure was insignificant. Results obtained from FEA on SMORS were validated through comparison with contact mechanics approach and experimental data and it was found that Lindley's equation correlates well with experimental data whereas ABAQUS overestimates the load values at a given compression. Lindley's approach may be used to develop contact pressure profiles that may help estimate peak contact pressure at a given time so leaking can be avoided.
Ph. D.

Cross-ply composite laminates can develop very high density of transverse cracks in the 90-layer under severe thermal and mechanical loading conditions. At such high crack densities, two adjacent cracks start to interact, and a stress gradient is created in the region between these cracks. Due to the presence of high stress gradients, thickness averaging of longitudinal stress becomes obsolete. Thus, a detailed analysis of stress state along the thickness direction becomes necessary to study growth conditions of fiber sized microcracks initiated at the interface between 0-layer and 90-layer. Stress analysis at various crack densities is carried out in this project using finite element analysis or FEM as the main tool. This analysis is coupled with strain energy release rate (ERR) studies for a microcrack which grows in transverse direction from one interface to the other. The growth of this microcrack is found to be strongly influenced by the stress gradients and a presence of compressive stresses along midplane under tensile loading conditions at high crack densities.

This study aims to aid many issues related to fatigue, namely biaxial loading, the definition of the finite geometry correction factor of the stress intensity factor and the understanding of the energy dissipation per fatigue crack growth. In our work, we are using the geometry correction factor definition that uses the ratio of external work introduced to the material. Using different biaxiality ratios varies the external work done, thus makes it possible for us to observe how the geometry correction factor handles this variation. The trend of strain energy release rate per crack growth is also investigated through biaxiality. Moreover, the common discussion of the effects of biaxiality on fatigue properties is aided with yet another study. For this purpose, cruciform shaped plate specimen from an aluminum alloy are manufactured and biaxially loaded. Crack growth is observed while load-to-displacement data is recorded to evaluate the external work done on the specimen. As a result, it is seen that biaxiality delays the fatigue failure. Crack growth rates decreases as the biaxiality increases for a given effective stress intensity factor. Making use of the work values for the calculation of the finite geometry correction factor handles the effects of biaxiality well. Strain energy release rate increases as the crack propagates, but there is no trend between strain energy release rate and biaxiality of the loading. In the future works, observing also the crack tip plasticity and trying out a wider range of biaxiality ratios with different types of material would result in more generalizable conclusions. Moreover, more repetitions of the fatigue tests would give more accurate values for the amount work introduced to the material with changing biaxiality.

Due to their ability to confer enhanced surface properties without compromising the properties of the substrate, coatings have become ubiquitous in heavy industrial applications for corrosion, wear, and thermal protection, among others. Kinetic Metallization (KM), a solid-state impact consolidation and coating process, is well-suited for depositing industrial coatings due to its versatility, low substrate heat input, and low cost. The ability of KM coatings to adhere to the substrate is determined by the quality of the interface. The purpose of this study is to develop a model to predict the interfacial quality of KM coatings using known coating and substrate properties. Of the various contributions to adhesion of KM coatings, research suggests that the thermodynamic Work of Adhesion (WAD) is the most fundamental. It is useful to define interfacial quality in terms of the critical strain energy release rate (GC) at which coating delamination occurs. Studies show that GC for a given interface is related to WAD. This study attempts to develop a theoretical model for calculating WAD and understand the relationship between GC and WAD. For a bimetallic interface between two transition metals, WAD can be theoretically calculated using known electronic and physical properties of each metal: the molar volume, V, the surface energy, γ, and the enthalpy of alloy formation, ΔHinterface; ΔHinterface is a function of the molar volume, V, the work function, φ, and the electron density at the boundary of the Wigner-Seitz cell, nWS.WAD for Ni-Cu and Ni-Ti interfaces were 3.51 J/m2 and 4.55 J/m2, respectively. A modified Four-point bend testing technique was used to experimentally measure GC for Ni-Cu and Ni-Ti specimens produced by KM. These tests yielded mean G­C values of 50.92 J/m2 and 132.68 J/m2 for Ni-Cu and Ni-Ti specimens, respectively. Plastic deformation and surface roughness are likely the main reasons for the large discrepancy between GC and WAD. At the 95% confidence level, the mean GC of the Ni-Ti interface is significantly higher than that of the Ni-Cu interface. Further testing is recommended to better understand the relationship between WAD and GC.

The objective of this study was to evaluate and develop an understanding of durability of an adhesive bonded system, for application in a future high speed civil transport (HSCT) aircraft structure. The system under study was comprised of Ti-6Al-4V metal adherends and a thermosetting polyimide adhesive, designated as FM-5, supplied by Cytec Engineered Materials, Inc. An approach based on fracture mechanics was employed to assess Ti-6Al-4V/FM-5 bond durability. Initially, wedge tests were utilized to find a durable surface pretreatment for the titanium adherends. Based on an extensive screening study, chromic acid anodization (CAA) was chosen as the standard pretreament for this research project. Double cantilever beam specimens (DCB) were then made and aged at 150° C, 177° C, and 204° C in three different environments; ambient atmospheric air (14.7 psia), and reduced air pressures of 2 psi air (13.8 KPa) and 0.2 psi air (1.38 KPa). Joints were aged for up to 18 months (including several intermediate aging times) in the above environments. The strain energy release rate (G) of the adhesive joints was monitored as a function of exposure time in the different environments. A 40% drop in fracture toughness was noted over the 18 month period, with the greatest degradation observed in samples aged at 204° C in ambient atmospheric air pressure. The loss in adhesive bond performance with time was attibutable to a combination of physical and chemical aging phenomena in the FM-5 resin, and possible degradation of the metal-adhesive interface(s). Several mechanical and material tests, performed on the bonded joints and neat FM-5 resin specimens, confirmed the above statement. It was also noted that physical aging could be "erased" by thermal rejuvenation, partially restoring the toughness of the FM-5 adhesive material. The FM-5 adhesive material displayed good chemical resistance towards organic solvents and other aircraft fluids such as jet fuel and hydraulic fluid. The results from the FM-5 adhesive and its bonded joints were compared and contrasted with VT Ultem and REGULUS polyimide adhesives. The FM-5 adhesive showed the best performance among the three adhesive systems. The effect of mode-mixity on the fracture toughness of the Ti-6Al-4V/FM-5 adhesive bonded system was also evaluated. DCB tests in conjunction with end-notched flexure (ENF) and mixed-mode flexure (MMF) tests, were used to fracture the bonded joints under pure mode I, pure mode II, and a combination of mode I and II loadings. The results showed that the mode I fracture toughness was twice as large as the mode II toughness. This was a rather surprising find, in sharp contrast to what several researchers have observed in the past. Our current understanding is that the crack path selection during the failure process plays a significant role in explaining this anomalous behavior. Finally, failure envelopes were generated for the titanium/FM-5 bonded system, both prior to and following thermal aging. These envelopes could serve as useful tools for engineers designing with Ti-6Al-4V/FM-5 bonds.
Ph. D.

An experimental evaluation of the mixed-mode fracture behavior of bonded composite joints is presented. Commonly used experimental techniques for characterizing the mode I, mixed-mode I/II, mode II, and mode III fracture behavior have been employed for the purpose of developing a fracture envelope to be utilized in the automotive design process. These techniques make use of such test geometries as the double cantilever beam (DCB), asymmetric double cantilever beam (ADCB), single-leg bend (SLB), end-loaded split (ELS), and split cantilever beam (SCB) specimens. Symmetric versions of the DCB, SLB, and ELS specimens produced mode mixities of 0°, 41°, and 90° respectively, while the testing of ADCB specimens allowed for mode mixities of 18°, 31°. Pronounced stick-slip behavior was observed for all specimen test geometries under both quasi-static and dynamic loading conditions. Due to the nature of the adhesive studied, a limited number of data points were obtained under mode I loading conditions. A significant increase in the number of measurable crack initiation events was observed for mixed-mode I/II loading conditions, where stick slip behavior was less pronounced. Additionally, a comparison of the measured fracture energies obtained under mixed-mode I/II loading conditions reveals that the addition of a small mode II component results in a decrease in the mode I fracture energy by roughly 50%, as the crack was driven to the interface between the adhesive layer and composite adherends. Furthermore, the propensity of debonds to propagate into the woven composite laminate adherends under mode II loading conditions limited the number of crack initiation points that could be obtained to one or two usable data points per specimen. A limited number of experimental tests using the SCB specimen for mode III fracture characterization, combined with a numerical analysis via finite element analysis, revealed a significant mode II contribution toward the specimen edges. Similarly, FE analyses on full bond width and half bond width SCB specimens was conducted, and results indicate that by inducing a bond width reduction of 50%, the mode II contribution is greatly decreased across the entire width of the specified crack front. To provide a means for comparison to results obtained using the standard DCB specimen, an alternative driven wedge test specimen geometry was analyzed, as this geometry provided a significant increase in the number of measurable data points under mode I loading conditions. A three-dimensional finite element analysis was conducted to establish ratios of simple beam theory results to those obtained via FEA, GSBT/GFEA, were of particular interest, as these ratios were used to establish correction factors corresponding to specific crack lengths to be used in correcting results obtained from an experimental study utilizing a driven wedge technique. Corrected results show good agreement with results obtained from traditional mode I double cantilever beam tests. Finally, bulk adhesive experiments were conducted on compact tension specimens to establish a correlation between adhesively bonded composite joint and bulk adhesive fracture behavior under mode I loading conditions. Measured fracture energy values were shown to gradually drop across a range of applied loading rates, similar to the rate-dependent behavior observed with both the DCB and driven wedge specimens. Application of the time-temperature superposition principle was explored to determine whether or not such techniques were suitable for predicting the fracture behavior of the adhesive studied herein. Good correlation was established between the fracture energy values measured and the value of tan d obtained from dynamic mechanical analysis tests conducted at corresponding reduced test rates.
Master of Science

Structural adhesives are widely used with great success, and yet occasional failures can occur, often resulting from improper bonding procedures or joint design, overload or other detrimental service situations, or in response to a variety of environmental challenges. In these situations, cracks can start within the adhesive layer or debonds can initiate near an interface. The paths taken by propagating cracks can affect the resistance to failure and the subsequent service lives of the bonded structures. The behavior of propagating cracks in adhesive joints remains of interest, including when some critical environments, complicated loading modes, or uncertainties in material/interfacial properties are involved. From a mechanics perspective, areas of current interest include understanding the growth of damage and cracks, loading rate dependency of crack propagation, and the effect of mixed mode fracture loading scenarios on crack path selection. This dissertation involves analytical, numerical, and experimental evaluations of crack propagation in several adhesive joint configurations. The main objective is an investigation of crack path selection in adhesively bonded joints, focusing on in-plane fracture behavior (mode I, mode II, and their combination) of bonded joints with uniform bonding, and those with locally weakened interfaces. When removing cured components from molds, interfacial debonds can sometimes initiate and propagate along both mold surfaces, resulting in the molded product partially bridging between the two molds and potentially being damaged or torn. Debonds from both adherends can sometimes occur in weak adhesive bonds as well, potentially altering the apparent fracture behavior. To avoid or control these multiple interfacial debonding, more understanding of these processes is required. An analytical model of 2D parallel bridging was developed and the interactions of interfacial debonds were investigated using Euler-Bernoulli beam theory. The numerical solutions to the analytical results described the propagation processes with multiple debonds, and demonstrated some common phenomena in several different joints corresponding to double cantilever beam configurations. The analytical approach and results obtained could prove useful in extensions to understanding and controlling debonding in such situations and optimization of loading scenarios. Numerical capabilities for predicting crack propagation, confirmed by experimental results, were initially evaluated for crack behavior in monolithic materials, which is also of interest in engineering design. Several test cases were devised for modified forms of monolithic compact tension specimens (CT) were developed. An asymmetric variant of the CT configuration, in which the initial crack was shifted to two thirds of the total height, was tested experimentally and numerically simulated in ABAQUS®, with good agreement. Similar studies of elongated CT specimens with different specimen lengths also revealed good agreement, using the same material properties and cohesive zone model (CZM) parameters. The critical specimen length when the crack propagation pattern abruptly switches was experimentally measured and accurately predicted, building confidence in the subsequent studies where the numerical method was applied to bonded joints. In adhesively bonded joints, crack propagation and joint failure can potentially result from or involve interactions of a growing crack with a partially weakened interface, so numerical simulations were initiated to investigate such scenarios using ABAQUS®. Two different cohesive zone models (CZMs) are applied in these simulations: cohesive elements for strong and weak interfaces, and the extended finite element method (XFEM) for cracks propagating within the adhesive layer. When the main crack approaches a locally weakened interface, interfacial damage can occur, allowing for additional interfacial compliance and inducing shear stresses within the adhesive layer that direct the growing crack toward the weak interface. The maximum traction of the interfacial CZM appears to be the controlling parameter. Fracture energy of the weakened interface is shown to be of secondary importance, though can affect the results when particularly small (e.g. 1% that of the bulk adhesive). The length of the weakened interface also has some influence on the crack path. Under globally mixed mode loadings, the competition between the loading and the weakened interface affects the shear stress distribution and thus changes the crack path. Mixed mode loading in the opposite direction of the weakened interface is able to drive the crack away from the weakened interface, suggesting potential means to avoid failure within these regions or to design joints that fail in a particular manner. In addition to the analytical and numerical studies of crack path selection in adhesively bonded joints, experimental investigations are also performed. A dual actuator load frame (DALF) is used to test beam-like bonded joints in various mode mixity angles. Constant mode mixity angle tracking, as well as other versatile loading functions, are developed in LabVIEW® for use with a new controller system. The DALF is calibrated to minimize errors when calculating the compliance of beam-like bonded joints. After the corrections, the resulting fracture energies ( ) values are considered to be more accurate in representing the energy released in the crack propagation processes. Double cantilever beam (DCB) bonded joints consisting of 6061-T6 aluminum adherends bonded with commercial epoxy adhesives (J-B Weld, or LORD 320/322) are tested on the DALF. Profiles of the values for different constant mode mixity angles, as well as for continuously increasing mode mixity angle, are plotted to illustrate the behavior of the crack in these bonded joints. Finally, crack path selection in DCB specimens with one of the bonding surfaces weakened was studied experimentally, and rate-dependency of the crack path selection was found. Several contamination schemes are attempted, involving of graphite flakes, silicone tapes, or silane treatments on the aluminum oxide interfaces. In all these cases, tests involving more rapid crack propagation resulted in interfacial failures at the weakened areas, while slower tests showed cohesive failure throughout. One possible explanation of this phenomenon is presented using the rate-dependency of the yield stress (commonly considered to be corresponding to the maximum traction) of the epoxy adhesives. These experimental observations may have some potential applications tailoring adhesive joint configurations and interface variability to achieve or avoid particular failure modes.
Ph. D.

Cílem této diplomové práce je lépe porozumět konceptu únavového poškození damage tolerance zmapováním všech možných vlivů na lomovou houževnatost vláknového kompozitu s polymerní matricí. Toho je dosaženo provedením zkoušek za různých podmínek (např. změna parametrů měření, mód zatížení, pořadí vrstev a materiál) a monitorováním odlišností v šíření trhliny. Na základě dat získaných během těchto testů je určena lomová houževnatost. Potenciální rozdíly jsou zkonzultovány a porovnány s ostatními vzorky.

The target of the ‘Green Overlays’ research was a cost effective, minimal disruption, sustainable and environmentally friendly alternative to the wholesale demolition, removal and complete reconstruction of the existing structural concrete pavement. The important problem of flexural resistance for strengthening concrete pavements with structural overlays has been scrutinised. A new mix design method for steel fibre reinforced, roller compacted, polymer modified, bonded concrete overlay has been proposed. The mixes developed were characterized of high flexural strength and high bond strength with the old concrete substrate. ‘Placeability’ and ‘compactability’ of the mix were two dominant issues during laboratory investigation. An innovative approach for establishing the relationship between Stress and Crack Face Opening Displacement for steel fibre reinforced concrete beams under flexure was developed. In addition, a new and simple method for calculating the interfacial Strain Energy Release Rate of both, a two-dimensional specimen and a three-dimensional model of the overlay pavement system were developed. This method can be readily and easily used by practicing engineers. Finally, a new test specimen and its loading configuration for measuring interfacial fracture toughness for concrete overlay pavements were established. The interfacial fracture toughness of a composite concrete beam, consisted of steel fibre-reinforced roller compacted polymer modified concrete bonded on conventional concrete and undergoing flexure, was assessed. In summary, this thesis presents four key findings: A new mix design method for steel fibre-reinforced roller compacted polymer modified concrete bonded on conventional concrete. A new method for establishing the fibre bridging law by an inverse analysis approach. A new, simplified method for calculating strain energy release rate at the interface of a composite beam. A new, innovative technique for calculating strain energy release rate at the interface of an overlaid pavement. The thesis contains a plethora of graphs, data-tables, examples and formulae, suitable for future researchers.

In 1993, to determine if wild-strain mallard releases could be used as a management practice to increase local mallard breeding populations, I released 2,344,4.5- week-old mallard ducklings (1,200 females and 1,144 males) to wetlands on 12,10.4-km2 sites (approximately 200 per site, 100 females, 100 males) in the North Dakota Prairie Pothole Region. I monitored the release sites to determine if any relationship existed between site characteristics and time of release to duckling survival estimates. I conducted breeding pair surveys during 1994 and 1995 on treatment and paired control sites to compare post-release population levels. Lastly, I analyzed return data and habitat use, and conducted behavioral experiments to determine if wild-strain mallards experienced higher mortality rates and if any observed differences could be explained by behavior. In 1994,1 observed 55 of the nasal saddled ducklings returning as adult fem ale to the release sites. In 1995, only 5 nasal saddled females were observed, both on treatment and control sites. No difference was observed hi breeding pair populations on treatment and control sites in 1994 (P = 0.18) and 1995 (P = 0.59). Hard-released wild-strain mallard females had lower survival rates than wild (P = 0.01) and modified gentle-release wild-strain females (P = 0.05). Ail wild-strain females were virtually eliminated from the population by year 4. This suggests that these buds may have been more vulnerable to predation and other mortality factors than wild females. Breeding wild and wild-strain mallard females reacted similarly to human approach, but when flushed, wild females flew farther than wild-strain females (P = 0.0002). Wetlands used by wild-strain females differed from wild females during breeding by type (P < 0.0001) and cover (P = 0.0003) classification. Wild-strain females selected larger, more permanent wetlands exhibiting less emergent vegetation than did wild counterparts. These differences may help to explain why wiki-strain mallard releases did not increase local breeding populations. The lack of band recoveries for wild-strain females during the latter years when viewed in the context of the observed behavioral differences suggests that these birds were unable to adapt to conditions in the wild.

The use of pop-up satellite archival tags (PSATs) eliminates many of the limitations associated with acoustic and conventional tags by using fishery-independent data collection and retrieval. Previous research techniques have provided information on longer-term movements, migrations, and behavior patterns, but there is still a need for additional tagging studies using tags with depth and light data and increased memory that will further define the short-duration activity patterns and habitat utilization of juvenile swordfish in the western North Atlantic. PSATs have been successfully used on other large pelagic fishes, but have yet to be used on juvenile swordfish. This study investigated two main topics: a) the post-release survival rates of juvenile swordfish after being released from the recreational rod-and-reel fishery and commercial swordfish buoy gear fishery in the Florida Straits, and b) the habitat utilization of juvenile swordfish following release. High-resolution PSAT technology was used to estimate the post-release survival of 16 individual juvenile swordfish captured with standard recreational or buoy fishing gear and techniques in the southeast Florida swordfish fishery. Analysis of release mortality estimates was done using the “Release Mortality” Program. Five of the fourteen reporting tags showed a mortality within 48 hours, for a release mortality rate of 35.7%. However, no common thread could be found among the five mortalities. Results of the Release Mortality program indicated that if the true mortality rate was 35.7%, approximately 1800 tags would have to be deployed to increase the precision of the mortality estimates to +/- 5% of the true value. The nine surviving fish varied in straight-line distance traveled and in direction, and could withstand a wide range of temperatures. A deterministic, periodic model was developed to fit to the data and describe the fishes’ habitat utilization. This model identified both diurnal and lunar signals in the data, confirming that juveniles do move vertically based on the daily cycle of the sun and the lunar cycle of the moon and that their diurnal movements are much greater than their lunar movements. The results of this study can be valuable to management practices in future stock assessments and decisions regarding mandatory release of undersized fish.

Caratteristica della fibrosi cistica (FC) è la colonizzazione del polmone da parte di batteri, in particolare Pseudomonas aeruginosa (Pa). Essa prevede l’instaurarsi di un’interazione batterio-ospite, la quale è mediata non solo dal contatto diretto con il microorganismo, solitamente ostacolato dalla presenza di dense secrezioni e dall’insediamento di ceppi mucoidi, ma anche dal rilascio di fattori specifici. Pa cresce nelle vie respiratorie di pazienti FC in condizioni di microaerobiosi. Quando le cellule epiteliali delle vie respiratorie FC sono state trattate con surnatante batterico ottenuto in seguito alla cultura del ceppo clinico AA2, cresciuto in aerobiosi e microaerobiosi, si è osservato in entrambi le condizioni un significativo aumento di IL-8 mRNA, a differenza del surnatante del ceppo di laboratorio PAO1 che non ha indotto alcuna significativa risposta pro-infiammatoria. Allo scopo di individuare fattori proteici rilasciati da Pa aventi attività pro-infiammatoria è stata applicato un approccio proteomico innovativo (MudPIT: Multidimensional Protein Identification Technology) che ha permesso di identificare 451 e 235 proteine nel surnatante di AA2 e PAO1 rispettivamente. L’analisi proteomica ha rivelato che varie proteine sono espresse e rilasciate in modo differente a seconda del ceppo, clinico o di laboratorio, e delle condizioni di coltura, aerobiche o microaerobiche. Tra queste, di particolare interesse, vi sono undici diverse proteasi che sono state trovate nel surnatante del ceppo AA2, mentre solo quattro sono stati rilevate nel surnatante del ceppo PAO1. Ecotin, un inibitore delle proteasi, è presente in quantità notevole nel surnatante di PAO1 rispetto a quello di AA2 ottenuti entrambi in microaerobiosi. Questi risultati sono stati confermati dai saggi di Western blot e zimogramma. Il livello di espressione delle proteasi e dell’inibitore ecotin nei due ceppi correla con l’attività pro-infiammatoria osservata in vitro. Solo nel 31% dei ceppi di Pseudomonas aeruginosa isolati da pazienti FC cronicamente infetti è stata osservata una discreta attività metalloproteasica mentre è state identificata in tutti gli isolati che derivano da pazienti FC infettati sporadicamente. Questi risultati suggeriscono che la tecnologia MudPIT può essere utile per dipanare la complessità del microambiente polmonare caratterizzato da infezione e infiammazione cronici e per facilitare l'identificazione delle molecole chiave coinvolte nell’interazione tra batterio Pa e vie respiratorie. Negli ultimi anni c’è stato un crescente interesse per l'utilizzo dell’antibiotico azitromicina (AZM) per il trattamento delle patologie polmonari in pazienti affetti da fibrosi cistica. L’azitromicina agisce quale inibitore della sintesi proteica nei batteri. Nonostante Pseudomonas aeruginosa risulti essere resistente all’azione del farmaco, la somministrazione del macrolide comporta in soggetti affetti da infezione cronica un miglioramento dell’intero quadro patologico. E’ stato suggerito che la modulazione dei fattori di virulenza di Pa sia correlata agli effetti benefici riscontrati nei pazienti FC. Abbiamo testato gli effetti dell’ azitromicina in relazione all’ isolato clinico AA2, per stabilire come questo farmaco potrebbe interferire con la produzione dei fattori di virulenza batterica. Abbiamo dimostrato che l'aumento di IL-8 mRNA in cellule epiteliali CF indotto dal surnatante prodotto dalla coltura di AA2 è stato significativamente ridotto quando il ceppo clinico è stato cresciuto in presenza di AZM, suggerendo che questo macrolide riduce la patogenicità di Pa. Nel tentativo di ottenere informazioni sull'identità delle molecole rilasciato dal ceppo clinico PA prima e dopo il trattamento con AZM abbiamo applicato la tecnologia MudPIT. Abbiamo trovato 12 proteine differenzialmente espresse e rilasciate nel surnatante di AA2 cresciuto in presenza e assenza dell’antibiotico. Una delle proteine di interesse è la metalloproteasi alcalina (APR) che viene down-regolata in presenza di AZM. E’ stato anche osservato che AZM diminuisce l'attività metalloproteasica e l’espressione di APR in surnatanti di isolati clinici di individui infettati sporadicamente, mentre nessun effetto è stato osservato nei surnatanti isolati di pazienti FC cronicamente infetti. Questi risultati sono stati validati per mezzo di zimogramma e Western blot. L'analisi MudPIT delle proteine rilasciate dal ceppo clinico AA2 cresciuto in assenza e in presenza di AZM suggerisce che tale macrolide possa diminuire l'espressione e il rilascio di fattori associati alla virulenza del batterio. Gli effetti dell’ AZM, inoltre, sull'espressione e il rilascio di fattori pro-infiammatori da ceppi clinici possono contribuire a spiegare i benefici clinici associati con la terapia del macrolide.
Colonization by Pseudomonas aeruginosa (Pa) is a hallmark of lung disease in cystic fibrosis (CF), where microaerobic conditions develop as a consequence of disease progression. Conditioned medium (CM) obtained from Pa clinical strain AA2, unlike the CM from laboratory strain PAO1, induces in airway epithelial cells IL-8 mRNA in both aerobic and microaerobic conditions. The effect was impaired by protease digestion. Shotgun proteomic analysis (Multidimensional protein identification technology: MudPIT) of conditioned medium of PAO1 and AA2 identified 451 and 235 individual proteins. Various proteins were found differentially regulated between strains and culture conditions. Among these eleven different proteases were found released by the AA2 strain, while fewer peptides of only four of them were detected in the PAO1 strain. Ecotin, a protease inhibitor, was found to be highly represented in PAO1 in comparison with AA2 grown in microaerobiosis. These results were confirmed by functional assay (zymography) and western blotting. The pattern of expression of several proteases and their inhibitor ecotin correlates with pro-inflammatory activity in vitro better than other candidate virulence factors. Only 31% of the Pa strains isolates from chronically infected CF patients expressed detectable metalloprotease activity while all the isolates derived from sporadically infected individuals scored positive (individual strains analyzed: 42, p<0.002). These results suggest that high-throughput approaches are critical to unravel the complexity of the pro-inflammatory microenvironment associated to the presence of Pa and to facilitate the identification of key molecules involved in Pa biology/pathology. There is considerable interest in the use of azithromycin (AZM) for the treatment of lung disease in patients with cystic fibrosis. Although its mechanism of action as an inhibitor of bacterial protein synthesis has been well established, it is less clear how AZM ameliorates the lung disease associated with P. aeruginosa, which is considered to be resistant to the drug. Modulation of Pa virulence factors was suggested as mechanism for AZM beneficial effects in CF patients. We tested the effects of azithromycin on clinical isolate AA2 to establish how this drug might interfere with the production of bacterial virulence factors that are relevant to the pathogenesis of airway disease in CF patients. We demonstrated that the increase of IL-8 mRNA in CF epithelial cells induced by CM from AA2 was significantly reduced when the clinical strain was grown in the presence of AZM, suggesting that this macrolide reduces Pa pathogenicity. In the attempt to gain information on the identity of the molecules released by Pa clinical strain before and after treatment with AZM we applied MudPIT. We found 5 upregulated and 7 downregulated proteins in CM from AA2 incubated with AZM. Peptides from the alkaline metalloproteinase precursor (APR) were less represented in CM derived from AA2 strain grown in presence of AZM than in those from the same strain cultured in absence of this macrolide. AZM was observed also to decrease the metalloprotease activity and APR expression in CM of Pa isolates derived from sporadically infected individuals while any effect was detected in CM of Pa isolates from chronically infected CF patients. These results was validated by means of zymography assay and western blot technique. The MudPIT analysis of released proteins from Pa clinical isolate grown alone and in presence of AZM gives suggestion on the macrolide ability to decrease the expression of substances that contributes to Pa virulence, such as alkaline metalloproteinase. The effects of AZM on the expression and release of selected polypeptides by Pa strains may help to explain the clinical benefits associated with macrolide therapy.

Biological invasions threaten the ecological integrity of natural ecosystems. Anthropogenic introductions of non-native species can displace native flora and fauna, altering community compositions and disrupting ecosystem services. One often-overlooked vector for such introductions is the release of aquarium organisms into aquatic ecosystems. Following detrimental aquarium-release invasions by the “killer alga” Caulerpa taxifolia, aquarium hobbyists and professions began promoting the use of other genera of macroalgae as “safe” alternatives. The most popular of these marine aquarium macroalgae, the genus Chaetomorpha, is analyzed here for invasion risk. Mitigation strategies are also evaluated. I found that the propensity for reproduction by vegetative fragmentation displayed by aquarium strains of Chaetomorpha poses a significant invasion threat—fragments of aquarium Chaetomorpha are able to survive from sizes as small as 0.5 mm in length, or one intact, live cell. Fragments of this size and larger are generated in large quantities in online and retail purchases of Chaetomorpha, and introduction of these fragments would likely result in viable individuals for establishment in a variety of geographic and seasonal environmental conditions. Mitigation of invasion risk was assessed in two ways—rapid response to a potential introduction by chemical eradication and prevention through safe hobbyist disposal. I tested the effectiveness of five chemicals used as algicides and found that acetic acid was highly effective at limiting survival and growth of aquarium Chaetomorpha. Chlorine bleach, copper sulfate and rock salt were effective at limiting growth but were inconsistent or ineffective in reducing survival of algal fragments. The algicide Sonar limited neither survival nor growth. If aquarium strains of Chaetomorpha are released, chemical eradication presents a viable management strategy, particularly through the use of acetic acid. A more cost-effective strategy, however, would be preventing introductions; thus safe alternatives to release were determined for hobbyist disposal of unwanted or excess aquarium Chaetomorpha. Here I present the minimum exposure durations necessary to induce full mortality of aquarium Chaetomorpha through boiling, microwaving, freezing, desiccation and exposure to freshwater. Hobbyist disposal by any of these methods would constitute safe alternatives to introduction of the alga into natural environments. Such preventative measures will inform outreach campaigns in order to limit the potential for aquarium-release introduction.
M.S.
Masters
Biology
Sciences
Biology

Doctor of Philosophy
Civil Engineering
Robert J. Peterman
A study was conducted to determine the effect of different concrete properties and prestressing steel indentation types on development length and flexural capacity of pretensioned members. Wires and strands commonly used in the manufacturing of prestressed concrete railroad ties worldwide were selected for the study. Thirteen different 5.32-mm-diameter prestressing wire types and six different strands (four, seven-wire strands and two, three-wire strands) were used to cast prisms with a square cross section. The ratio of concrete to prestressed steel in the test prism’s cross section was representable of typical concrete railroad ties. Thus, geometrical and mechanical properties of test prisms were representative of actual ties in the railroad industry. To understand the effect of concrete-release strengths and slumps on development length, all parameters were kept constant in the prisms except concrete-release strength and slump. To manufacture prisms with different release strengths, all four wires/strands were pulled and detensioned gradually when the concrete compressive strength reached 3500 (24.13 MPa), 4500 (31.03 MPa), and 6000 (41.37 MPa) psi. To determine the effect of different slumps on development length, prisms with different slumps of 3 in. (7.6 cm), 6 in. (15.2 cm), and 9 in. (22.9 cm) were manufactured and all other parameters were kept constant in prisms. All prisms were tested in three-point bending at different spans to obtain estimations of development length based on type of reinforcement, concrete-release strength, and concrete slump. Lastly, a design equation was developed based on experimental data for prediction of development length. In the last phase of load tests, cyclic-loading tests were conducted on the prisms manufactured with wires to evaluate the bond performance of wires with different indentation types under cyclic loading. A total of 210 load tests, including 14 cyclic tests, were conducted. The monotonic-load tests revealed a large difference in the development length of pretensioned concrete members manufactured with different wire/strand types and different concrete-release strengths. Also, the cyclic-load tests revealed a significant difference in bond performance of different wire types under cyclic loading compared to monotonic loading.

[ES] El uso masivo de plásticos sintéticos y su impacto medioambiental obliga a buscar alternativas biodegradables para el envasado de los alimentos,etapa necesaria para su adecuada conservación.Así mismo,la necesidad de incrementar la vida útil de los alimentos ha despertado gran interés en el desarrollo de materiales activos(antimicrobianos y antioxidantes)que mantengan su calidad y seguridad por más tiempo,mediante el uso de compuestos de origen natural,seguros para el consumidor.En este sentido,el desarrollo de materiales biodegradables activos para el envasado de alimentos constituye hoy en día un reto importante para la industria alimentaria.En la presente Tesis Doctoral,se ha estudiado la encapsulación de carvacrol mediante el electroestirado o extensión y secado de diferentes disoluciones poliméricas con carvacrol.Se han utilizado polímeros biodegradables portadores de diferente polaridad(almidón termoplástico:TPS,polivinil-alcohol:PVA, policaprolactona:PCL o ácido poliláctico:PLA)disueltos en el solvente adecuado,con el fin de obtener capas activas.Estas capas se han combinado con otras de polímeros con propiedades complementarias,para obtener laminados activos adecuados para el envasado de alimentos.Los laminados combinaron polímeros polares(TPS o PVA)y poliésteres no polares(PCL o PLA)incorporando el carvacrol en una de las capas.Se evaluó la cinética de liberación del activo,así como la acción antimicrobiana de los materiales obtenidos.Los laminados se caracterizaron en su funcionalidad como material de envase(prop. de barrera,mecánicas u ópticas)así como en su estructura y comportamiento térmico.Los estudios de encapsulación revelaron un mayor potencial encapsulante del carvacrol para los polímeros no polares(PCL;PLA),aunque el PVA mostró también una buena afinidad con el compuesto activo.La matriz de PVA mostró una mayor retención de carvacrol mediante electroestirado de sus disoluciones acuosas que por extensión y secado,sin necesidad de adición de tensoactivos como el Tween85.Para la encapsulación en PLA,se usaron mezclas binarias de solventes aptos para contacto con los alimentos(acetato de etilo y DMSO).En este caso,se obtuvo una mayor eficiencia encapsulante del PLA en los materiales obtenidos por extensión y secado que en los electroestirados.La cinética de liberación del carvacrol de las fibras de PCL explicó el mayor efecto antibacteriano contra E.coli,y el escaso efecto antilisteria.La velocidad de liberación del activo aumentó cuando disminuyó la polaridad de los simulantes alimentarios, mostrando una liberación completa en los sistemas apolares,pero solo hasta 75% en los sistemas acuosos,que requerirían una mayor proporción del activo en el envase para potenciar su efectividad.La combinación de láminas de TPS con fibras de PCL cargadas con carvacrol dio lugar a materiales con una permeabilidad al vapor de agua mejorada,en comparación con los films de almidón,sin efectos relevantes sobre las otras propiedades funcionales estudiadas.Cuando los laminados se probaron in vitro contra cepas G(+) y G(-) mostraron un efecto antibacteriano similar al de las fibras de PCL con carvacrol,pero retrasado en el tiempo.Los estudios de desintegración-biodegradación de los laminados almidón-PCL revelaron que las películas con carvacrol afectaron la actividad del inóculo del compost,disminuyendo ligeramente la biodegradabilidad de las películas,pero alcanzando valores de desintegración similares(75-80%)a las muestras libres de carvacrol.Se obtuvieron también laminados de PLA y PVA mediante la extensión y secado de disoluciones acuosas de PVA con carvacrol.La superficie del PLA fue sometida a aminolización a fin de mejorar la extensibilidad de las disoluciones acuosas.A pesar del incremento de la componente polar de la energía superficial del PLA y su mejorada humectabilidad con las soluciones de PVA,estas bicapas no mostraron una mejora significativa en las propied
[CAT] L'ús massiu de plàstics sintètics i el seu impacte mediambiental obliga a buscar alternatives biodegradables per a l'envasament dels aliments necessari per a la seua conservació.Així mateix,la necessitat d'incrementar la vida útil dels aliments ha despertat gran interés en el desenvolupament de materials actius(antimicrobians i antioxidants)que mantinguen la seua qualitat i seguretat per més temps,per mitjà de l'ús de compostos d'origen natural,segurs per al consumidor.En este sentit,el desenvolupament de materials biodegradables actius per a l'envasament d'aliments constituïx un repte important per a la indústria alimentària.En la present Tesi Doctoral,s'ha estudiat l'encapsulació de carvacrol per mitjà de l'electroestirat o extensió i assecat de diferents dissolucions polimèriques amb carvacrol.S'han utilitzat polímers biodegradables portadors de diferent polaritat(midó termoplàstic:TPS, polivinil-alcohol:PVA, policaprolactona:PCL o àcid poliláctic:PLA)dissolts en el solvent adequat,a fi d'obtindre capes actives.Estes s'han combinat amb altres de polímers amb propietats complementàries,per a obtindre laminats actius adequats per a l'envasament d'aliments.Els laminats van combinar polímers polars(TPS o PVA)i poliésters no polars(PCL o PLA)incorporant el carvacrol en una de les capes.Es va avaluar la cinètica d'alliberament de l'actiu,així com l'acció antimicrobiana dels materials obtinguts.Els laminats es van caracteritzar en la seua funcionalitat com a material d'envàs(propietats de barrera, mecàniques o òptiques),així com en la seua estructura i comportament tèrmic.Els estudis d'encapsulació van revelar un major potencial encapsulant del carvacrol per als polímers no polars(PCL i PLA),encara que el PVA va mostrar també una bona afinitat amb el compost actiu.La matriu de PVA va mostrar una major retenció de carvacrol per mitjà d'electroestirat de les seues dissolucions aquoses que per extensió i assecat,sense necessitat d'addició de tensioactius com el Tween 85.Per a l'encapsulació en PLA,es van usar mescles binàries de solvents aptes per a contacte amb els aliments(acetat d'etil i DMSO).Es va obtindre una major eficiència encapsulant del PLA en els materials obtinguts per extensió i assecat que en els electroestirats.La cinètica d'alliberament del carvacrol de les fibres de PCL va explicar el major efecte antibacterià contra Escherichia coli,i l'escàs efecte antilisteria.La velocitat d'alliberament de l'actiu va augmentar quan va disminuir la polaritat dels simulants alimentaris,mostrant un alliberament complet en els sistemes no polars, però només fins a un 75% en els sistemes aquosos,que requeririen una major proporció de l'actiu en l'envàs per a potenciar la seua efectivitat.La combinació de làmines de TPS amb fibres de PCL carregades amb carvacrol va donar lloc a materials amb una permeabilitat al vapor d'aigua millorada,en comparació amb els films de midó, sense efectes rellevants sobre les altres propietats funcionals.Quan els laminats es van provar in vitro contra ceps Gram(+) i Gram(-) van mostrar un efecte antibacterià semblant al de les fibres de PCL amb carvacrol,però retardat en el temps.Els estudis de desintegració-biodegradació dels laminats midó-PCL van revelar que les pel·lícules amb carvacrol van afectar l'activitat de l'inocule del compost,disminuint lleugerament la biodegradabilitat,però aconseguint valors de desintegració semblants(75-80%)a les mostres lliures de carvacrol.Es van obtindre també laminats de PLA i PVA per mitjà de l'extensió i assecat de dissolucions aquoses de PVA amb carvacrol.La superfície del PLA va ser sotmesa a aminolizatció a fi de millorar l'extensibilitat de les dissolucions aquoses.A pesar de l'increment de la component polar de l'energia superficial del PLA i la seua millorada mullabilitat amb les solucions de PVA,estes bicapes no van mostrar una millora significativa en les propietats mecàniques i de barrera
[EN] The massive use of synthetic plastics and their environmental impact makes necessary the search for biodegradable alternatives for food packaging. Likewise, the need to increase the shelf life of food has aroused great interest in the development of active materials (antimicrobial and antioxidant) that maintain food quality and safety for longer periods of time through the use of compounds of natural origin, safe for the consumer. In this sense, the development of active biodegradable materials for food packaging is both a major imperative and challenge for the food industry today. In the present Doctoral Thesis, the encapsulation of carvacrol has been studied by means of the electrospinning or casting of different polymeric solutions with carvacrol. Biodegradable polymers with different polarities (thermoplastic starch: TPS, poly(vinyl-alcohol): PVA, poly-(¿-caprolactone): PCL or poly(lactic acid): PLA) dissolved in the appropriate solvent have been used to obtain active layers. These have been combined with other polymers with complementary properties, to obtain active laminates suitable for food packaging. The laminates combined polar polymers (TPS or PVA) and non-polar polyesters (PCL or PLA) incorporating carvacrol in one of the layers. The release kinetics of the active ingredient was evaluated, as well as the antimicrobial action of the materials obtained. The laminates were characterized in their functionality as a packaging material (barrier, mechanical or optical properties), as well as in their structure and thermal behaviour. Encapsulation studies revealed a higher encapsulating potential of carvacrol for non-polar polymers (PCL and PLA), although PVA also showed a good affinity with the active compound. The PVA matrix showed a higher retention of carvacrol by electrospinning of its aqueous solutions than by casting, without the need for addition of surfactants such as Tween 85. For the encapsulation in PLA, binary mixtures of solvents suitable for food contact (ethyl acetate and DMSO) were used. A higher encapsulation efficiency of PLA was obtained in the materials produced by casting than by electrospinning. The carvacrol release kinetics of PCL fibres explained the higher antibacterial effect against Escherichia coli and the lower antilisterial effect. The release ratio of the active ingredient increased when the polarity of the food simulants decreased, showing a complete release in non-polar systems and only up to 75% in aqueous systems that would require a higher proportion of the active ingredient in the packaging material to enhance its effectiveness. The combination of TPS films with carvacrol loaded PCL fibres resulted in materials with improved water vapour permeabilities, compared to starch films, with no relevant effects on the other functional properties. When the laminates were tested in vitro against Gram (+) and Gram (-) strains, they showed a similar antibacterial effect to that of PCL fibres with carvacrol, but delayed in time. Disintegration-biodegradation studies of PCL-starch laminates revealed that carvacrol films affected the activity of the compost inoculum, slightly decreasing the biodegradability of the laminates, but reaching similar disintegration values (75-80%) to the carvacrol-free samples. PLA and PVA laminates were also obtained by casting aqueous PVA solutions with carvacrol. The surface of PLA was submitted to aminolization in order to improve the extensibility of the aqueous solutions. Despite the increase in the polar component of the PLA surface energy and its improved wettability with PVA solutions, these bilayers did not show significant improvement in mechanical and barrier properties over the PLA monolayers.
The authors would like to thank the Ministerio de Economia y Competitividad of Spain, for funding this study as part of projects AGL2013-42989-R and AGL2016-76699-R and predoctoral research grant # BES-2014-068100.
Tampau, A. (2020). Carvacrol encapsulation by electrospinning or solvent casting to obtain biodegradable multilayer active films for food packaging applications [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/140313
TESIS

碩士
元智大學
機械工程學系
91
Multi-layer structures are common in electronic package especially for the micro devices manufactured Via the semi-conductor processes or MEMS processes. Interfacial crack due to the delamination significantly weakens the multi-layer structure. It is desired to understand the interfacial fracture properties of the electronic packaging materials. In this research, four specimens named Doubled Cantilever Beam (DCB), End-Notched Flexure (ENF), Four-Point-Bending, and Three-Point-Bending are proposed to investigate the fracture toughness associated with modeⅠ,modeⅡ and mixed mode. Basing on the Bernoulli beam theory, the strain energy in a multi-layer beam is derived the strain energy before and after the propagation of the interfacial crack are calculated, lead to the determination of the strain energy release rate. The analytical results of strain energy release rate derived in this investigation are compared with the numerical results obtained from finite element method and literature’s report. The effects of material properties and thickness between the adjacent layers of interfacial crack are examined through the parametric study.

Polymer matrix composites are widely used as structural components in the aerospace industry and wind turbine industry etc. to take advantage of their unique mechanical properties and weight saving ability. Although there have been considerable developments in analyzing delamination growth and effects of voids on certain mechanical properties of composites, none of the present literatures investigates the effects of voids on delamination growth under compression. In this research, a parametric study is performed to investigate the effects of voids on delamination growth in composite laminates under compression. In composite structures, delamination would be created by eccentricities in structural load path, structural discontinuities, and during manufacturing and maintenance processes. Also, the service damage such as the impact of foreign objects may also result in delamination. In the Finite Element model developed, a through-width surface delamination is assumed, and void is placed in critical locations ahead of crack tip. Strain Energy Release Rate (SERR) is calculated by the Virtual Crack Closure Technique (VCCT) in order to study the delamination growth. It is found that the delamination front experiences a mixed-mode delamination behavior when local out-of-plane buckling occurs. During the loading, Mode II SERR increases monotonically while Mode I SERR increases first and then decreases as the delamination front starts to close. Meanwhile, Mode II SERR is found to be much larger than the Mode I component. The presence of void does not significantly alter the transverse displacement of the delaminated part. However, the presence of void increases the Mode II SERR, as well as the total SERR, and this increase depends on the size and location of void. For Mode I SERR, the effect of void is not that prominent.

碩士
元智大學
機械工程學系
94
Multi-layer structures are common in electronic package especially for the micro devices manufactured Via the semi-conductor processes or MEMS processes. As the multi-layer structures subject to uniform temperature change, the thermal stresses are induced due to the mismatch of the coefficients of thermal expansion between the adjacent layers. In this investigation, the longitudinal thermal stresses in the middle region of a bi-layer beam and a tri-layer beam are derived basing on the Euler-Bernoulli beam theory. The strain energy release rate of a bi-layer beam and a tri-layer beam with interfacial crack are derived basing on the theory of fracture mechanics. The analytical expressions of the longitudinal thermal stress and strain energy release rate are validated by the finite element method. The effect of Young’s modulus, coefficients of thermal expansion and thickness between the adjacent layers on the thermal stress and strain energy release rate are presented through parametric study.

碩士
高苑科技大學
高分子環保材料研究所
94
英文摘要 　　This study examined the feasibility of using polycaprolactone (PCL) and its composites (with Starch and/or HA) encapsulating cells of phosphate-solubilizing bacteria (PBS) for the development of biodegradable and “controlled-release” bacterial fertilizer. The PSB used in this work was able to degrade all the cell-release. Morphology observation indicates that severe disruption of the capsule structure occurred after incubation for 30-60 days. The biodegradability of the capsules decreased in the order of PCL/Starch (20Wt.%) > PCL alone > PCL/HA (20Wt.%). Similar trends were also observed for the decrease in enthalpy (△Hm), suggesting strong connections between biodegradability and the thermal properties. 　　Addition of Starch appeared to enhance the biodegradability of the capsules,whereas the HA-blended composites were less biodegradable. The amount and rate of cell release from cell-encapsulated PCL-based capsules were positively dependent on the biodegradability and on the decrease in the thermal enthalpy of melting. The cell-release profiles were, however, quite similar for all types of capsules. The outcome of this work seems to suggest that by proper manipulation of composite composition, controlled release of the bacterial fertilizer (i.e.,Bacillus sp. PG01 cells) may be achievable.

碩士
國立成功大學
微電子工程研究所碩博士班
100
Quantum confine Stark effect (QCSE) would reduce the efficiency of LEDs. To reduce the residual strain in the MQWs of LEDs, we fabricate three different strain-released LEDs. We use the electroluminescence (EL) to measure the emission wavelength and determine the strain of LEDs. It is well known that the QCSE is relative to the blueshift of emission wavelength. The blueshift of screening effect for LED A (Strain-released layer, n-GaN/u-InGaN SPS), LED B (Strain-released layer, LT n-GaN) and LED C (Strain-released layer, p-GaN/p-InGaN SPS) are 0.39 nm, 0.32 nm and 0.54 nm, respectively. External quantum efficiency of LED B is the largest, 10.3 mw with injection current 20 mA. However, the wall plug efficiency (WPE) droop of LED B is the smallest, which is attributed to its high junction temperature. Thus, the factor dominates in junction temperature is series resistance. Furthermore, the high series resistance would be attributed to the strain-released structure of LEDs.

碩士
國立虎尾科技大學
光電與材料科技研究所
101
In this thesis, the Al/AlN multiple-layer films were used as the strain release layers between glass substrate and AuSn eutectic metal. Due to a great amount of heterostructural interface change, it is beneficial to increase the material toughness, stop the fissure expansion, and enhance the abrasion resistance. In addition, Al is a soft metal with extraordinary ductility, and AlN, as a ceramic material, shows extremely high heat transfer coefficient and hardness. The integration of these two materials can form a structure that is applicable to create the strain release layers so as to enhance the later deposited film reliability. This study utilized sputtering to deposit one set, two sets, and three sets of Al/AlN multiple-layer films onto the glass substrates, and finalize an Al cap layer. After the aluminum film surfaces were chemically processed. The electroplating technique was used to prepare the required AuSn eutectic bonding layers. The optimized shear stress and bonding temperature were discussed for various release layers. It was found that the optimal bonding temperature and shear stress increased with increasing the number of film layers. Subsequently, the SEM and XRD analysis were performed on various films to find more the optimal eutectic phase ζ (Au5Sn). In the final, the photolithography was used to define the pattern of flip-chip LED bounding carrier. The encapsulated LED sample was operated at 20 mA, and the forward voltage was measured as 4.09 V.

In the first part, a new analytical approach, within the extended finite element (XFEM) framework, is proposed to compute Strain Energy Release Rates (SERRs) directly from Irwin's integral. Crack tip enrichment functions in XFEM allow for evaluation of integral quantities in closed form (for some crack configurations studied) and therefore results in an accurate and efficient method. The effects of high order enrichments, mesh refinement and the integration limits of Irwin's integral are examined in benchmark numerical examples. The results indicate that high order enrichment functions have significant effect on the convergence, in particular when the integral limits are finite. When the integral limits tend to zero, simpler SERR expressions are obtained and high order terms vanish. Nonetheless, these terms contribute indirectly via coefficients of first order terms. The analytical formulation is then extended to cracks in arbitrary orientations. Several benchmark examples are investigated including off-center cracks, inclined cracks and crack growth problems. On all these problems, the method is shown to work well, giving accurate results. Moreover, due to its analytical nature, no special postprocessing is required which leads to a fast approach to obtain Strain Energy Release Rates. Thus it is concluded that this method may provide a good alternative to the popular J-integral method. In the second part of the thesis, the stress-strain behavior of short single walled carbon nanotube (SWCNT) aggregates is investigated by a novel incremental constrained minimization approach. An AIREBO potential is used to model the interactions within and between CNTs. The idea is to homogenously disperse SWCNTs in the computational cell at random positions and orientations following spherical uniform distributions, and incrementally deform the cell while restraining the movement of atoms at the ends of nanotubes. The stress-strain response of the system is obtained in each loading direction and it is shown to converge to an isotropic behavior (a similar response in all directions) as the number of CNTs in the system increases. In addition, it is shown that the Young's modulus of the system increases linearly with the CNT aggregates density and the method agrees well with results obtained from molecular dynamics simulations running at near zero degrees kelvin, which are obtained at only a fraction of the CPU time required for MD methods.

The increasing demand for resources and depletion of near ground mineral resources caused deeper mining operations under high-stress and high-temperature rock mass conditions. As a results of this, strain burst, which is the sudden and violent release of stored strain energy during dynamic brittle failure of rocks, has become more prevalent and created considerable safety risks damaging underground infrastructures. This research focuses on the development of experimental methodologies to better understand the fundamental knowledge concerning the failure mechanism of strain burst and the influence of thermal damage, high confining pressure and various loading rate on the overall mechanical behaviour of highly brittle granitic rocks leading to strain burst. Strain burst is related to the elastic stored strain energy and how this stored energy is released during the unstable spontaneous failure. Therefore, it is significant to investigate the energy state during strain burst from the viewpoint of energy theory. In this sense, circumferential strain controlled quasi-static tests on Class II rocks over a wide range of confining pressures at different heat-treatment temperatures were conducted to capture the snap-back behaviour and calculate excess strain energy that is responsible for the spontaneous instability. A new energy calculation method associated with acoustic emission (AE) was developed to express the propensity of strain burst and investigate the post-peak energy distribution characteristics for brittle rocks under the coupling influence of confinement and temperature. In order to quantify the micro-crack density and reveal the micro-fracture characteristics of the brittle rocks exposed to various temperatures, scanning electron microscopy (SEM) analysis was also conducted. This is highly relevant to link the excess strain energy and the main failure mechanism triggering strain burst under high-temperature condition. The failure process of strain burst is the outcome of the unstable growth and coalescence of secondary micro-cracks. If the dissipative energy to grow pre-existing cracks and the secondary cracks is smaller than the elastic stored strain energy in rock masses, the residual strain energy will be released suddenly in the form of kinetic energy, resulting in ejecting high-velocity rock fragments. Therefore, understanding the crack initiation and propagation in rocks is of great concern for engineering stability and security. As an intrinsic property of rocks to resist crack initiation and propagation, the rock fracture toughness is the most significant material property in fracture mechanics. In this respect, the three-point bending method was applied using cracked chevron notched semi-circular bend (CCNSCB) granite specimens subjected to different temperatures under a wide range of loading rates in pure mode I. A suitable relation for the dimensionless stress intensity factor (𝑌∗) of SCB with chevron notch samples were presented based on the normalised crack length (𝛼) and half-distance between support rollers (𝑆/2). The minimum dimensionless stress intensity factor (𝑌𝑚𝑖𝑛∗) of CCNSCB specimens were determined using an analytical method, i.e., Bluhm’s slice synthesis method. In this study, the influence of thermal damage and loading rate on the quasi-static mode I fracture toughness and the energy-release rate using CCNSCB method was investigated. In the deep mining process, the rock mass is subjected to a dynamic disturbance caused by blasting, and mechanical drilling resulting in dynamic fractures in the forms of strain burst, slabbing, and spalling. The dynamic rock fracture parameters, including dynamic initiation fracture toughness and fracture energy which are an important manifestation of dynamic rock failure (strain burst) in deep underground engineering and they are of great practical significance to assess the dynamic fracture behaviour of deep rock masses. Since deep rock engineering operations in high temperature and high pressure environment is prone to strain burst, the influence of thermally induced damage on the dynamic failure parameters of granite specimens was investigated. The damage evolution of granitic rocks were studied over a wide range of loading rates to reveal the rate dependency of strain burst. Dynamic fracture toughness tests were carried out on granite under different temperatures and impact loadings using a Split Hopkinson Pressure Bar (SHPB) apparatus at Monash University. With dynamic force balance achieved in the dynamic tests, the stable-unstable transition of the crack propagation crack was observed and the dynamic initiation fracture toughness was calculated from the dynamic peak load. The thermal damage influence on strain burst characteristics of brittle rocks under true-triaxial loading-unloading conditions was investigated using the AE and kinetic energy analyses. A unique strain burst testing system enabling to simulate the creation of excavation at the State Key Laboratory for Geomechanics and Deep Underground Engineering in Beijing (China) was used to replicate strain burst condition. Time-domain and frequency-domain responses AE waves related to strain burst were studied, and the damage evolution was quantified by b-values, cumulative AE energy and events rates that can be used as warning signals to rock failure. The ejection velocities of the rock fragments from the free face of the granite specimens were used to calculate kinetic energies which can be used as an indicator for quantitatively evaluating the intensity of strain burst. Based on the energy evolution characteristics of brittle rocks under uniaxial and triaxial compression, true-triaxial loading-unloading and three-point bending, new strain burst proneness indexes and strain burst criterion were proposed. The effects of temperature, confinement and loading rate on strain burst proneness were discussed. This study aims to advance the understanding on underlying processes that govern the macro-behaviour of brittle rocks during strain burst and make use of this insight to further advance our current predictive capabilities of strain burst with references to large-scale underground mining. Using the developed experimental methodologies in this study, fractures around an excavation to reduce the amount of excess strain energy leading to strain burst can be determined and ultimately incipient strain burst in deep mines can be predicted avoiding potential hazards. Using the methodology for forecasting of strain burst in this research can be used for enhanced understanding of the design of rock support in strain burst-prone areas in deep mining activities. The findings of this study will facilitate achieving a better and comprehensive understanding of the damage process during strain burst in deep mines. This study underpins the development of better and more efficient prediction methods for strain burst which will lead to better planning guidelines and ultimately safer deep underground working conditions.
Thesis (Ph.D.) -- University of Adelaide, School of Civil, Environmental and Mining Engineering, 2019

碩士
國立臺灣大學
光電工程學研究所
96
In this research, we fabricate anodic alumina oxide (AAO) on GaN and InGaN/GaN quantum well (QW) structure. With the AAO technique, we can fabricate a thin aluminum oxide film with nano-pore array on the nitride structure, which is used as a mask to deposit metal nano-particle arrays on to study the surface plasmon (SP) characteristics, or to release the strain in the QW. Our first study is about the SP characteristics of a silver or gold nano-particle array on GaN template. We change the AAO process condition to control the hole diameter and interpore distance such that we can vary the particle size and density of the metal nano-particle array. We observe the SP absorption spectra and its resonance frequencies of different particle sizes and densities. The second study is about the strain relaxation phenomenon by fabricating nano-hole array patterns with the AAO technique on an InGaN/GaN QW structure. The effective strain relaxation, leading to the significant enhancement of emission efficiency and reduction of quantum-confined Stark effect (QCSE), in a high-indium InGaN/GaN QW structure via nano-pore fabrication on the sample surface with the anodic aluminum oxide technique is demonstrated. By generating nano-pores of 60 nm in size, 4.71 x 109 cm-2 in pore density, and a depth several nm above the QW, the internal quantum efficiency (IQE) can be increased by about three times and the QCSE is reduced by 2.5 times while the emission spectrum is blue-shifted by 14 nm in the green range. With this approach, it is possible to achieve a higher IQE and a smaller QCSE by relaxing the built-in strain of a higher-indium QW structure and blue-shifting its emission, when compared with a lower-indium sample of the same emission spectrum as the blue-shifted one.

Bioactive compounds released by proteolytic cleavage of milk proteins during milk fermentation have a role beyond their nutritional importance. The first research chapter in this thesis assessed the proteolytic activity of Lactobacillus helveticus strains ASCC 953, ASCC 474, ASCC 1188 and ASCC 1315, and their ability to release bioactive compounds with antioxidative and in vitro anticarcinogenic properties during incubation at 37°C in reconstituted skim milk. The performance of these strains was not affected by the pH decline during fermentation. Soluble extracts of milk fermented by L. helveticus strain ASCC 474 showed the highest free radical (1,1-diphenyl-2-picrylhydrazyl) (DPPH) scavenging activity after 12 h of fermentation; this was followed by a significant reduction of activity at 24 h compared with the other strains and control (untreated milk). Skim milk fermented by L. helveticus contained compounds with anti-colon cancer activity at levels that differed throughout fermentation. Growth inhibition activity (19.03–50.98%) was greatest in the extract obtained after 12 h of fermentation but had markedly declined (5.40–9.94%) by the end of fermentation. L. helveticus ASCC 1315 released compounds into the skim milk supernatant that exerted greater growth inhibition (50.98%) on the HT-29 colon cancer cell line than did the other strains. More importantly, these compounds had no significant inhibitory effect on normal, primary colon cells T4056. Although these results suggest that milk fermented by L. helveticus may release bioactive compounds with important multifunctional properties, the characteristics and activities of these compounds appear highly strain and fermentation time dependent. The second research chapter aimed to evaluate the effects of 28 days of cold storage on the release of antioxidative peptides in milk fermented by L. helveticus strain 1315 (L. 1315). Additional types of bioactivity including angiotensin-converting enzyme (ACE) inhibition and antimicrobial activities were also assessed. Further, samples were subjected to in vitro digestion to assess the fate of peptides during gastrointestinal (GI) passage. The antioxidative properties of fermented milk exerted significantly higher radical scavenging activity using DPPH, ABTS●+ 2,2′-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) reducing power and hydroxyl radical (●OH) assays after 14 days than at other time points, and were time dependent. However, these bioactivities diminished after exposure to in vitro digestive enzymes. Samples with the highest antioxidative activity were fractionated and purified, revealing the presence of nine peptides derived from beta casein (β-CN), as identified using liquid chromatography–tandem mass spectrometry (LC–MS/MS). The peptides KVLPVPQKAVPYPQ and SQSKVLPVPQKAVPYPQ exhibited the highest scavenging activity, in a dose-dependent manner. The last research chapter in this thesis describes the isolation and identification of potential antiproliferative peptides from milk fermented by L. helveticus 1315 on HT-29, and evaluation of the antioxidant and anti-colon cancer activities of these peptides after in vitro GI digestion. The mechanism of anti-colon cancer activity (apoptotic activity, caspace-3 and cell cycle arrest) was also assessed. A peptide fraction derived from fermented milk after 14 days of cold storage at 4oC had high anti-colon cancer activity on HT-29 cells using the MTS (3-(4,5-dimethylthiazol-2-yl)-5-(3- carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium) assay. Among the nine peptides identified in the fraction, KVLPVPQKAVPYPQ and SQSKVLPVPQKAVPYPQ derived from β-CN exhibited the highest antiproliferative activity. These two peptides were further subjected to in vitro GI digestion to determine their stability. The antioxidant activity of digested peptides was also assessed using DPPH and ABTS●+ assays, which revealed increased antioxidant activity and antiproliferative activity in HT-29 cancer cells through induction of apoptosis resulting in G2/M cell cycle arrest. These results indicate that these peptides and their derivatives after digestion have potential physiological effects that may be harnessed to manage oxidation-related diseases and disorders including cancers.

Calcific aortic valve disease (CAVD) is one of the most common causes of cardiovascular disease in North America. Mechanical factors have been closely linked to the pathogenesis of CAVD and may contribute to the disease by actively regulating the mechanobiology of valve interstitial cells (VICs). Mechanical forces affect VIC function through interactions between the VIC and the extracellular matrix (ECM). Studies have shown that the transfer of mechanical stimulus during cell-ECM interaction depends on the local material properties at hierarchical length scales encompassing tissue, cell and cytoskeleton. In this thesis, biomechanical tools were developed and applied to investigate hierarchical cell-ECM interactions, using VICs and valve tissue as a model system. Four topics of critical importance to understanding VIC-ECM interactions were studied: focal biomechanical material properties of aortic valve tissue; viscoelastic properties of VICs; transduction of mechanical deformation from the ECM to the cytoskeletal network; and the impact of altered cell-ECM interactions on VIC survival. To measure focal valve tissue properties, a micropipette aspiration (MA) method was implemented and validated. It was found that nonlinear elastic properties of the top layer of a multilayered biomaterial can be estimated by MA by using a pipette with a diameter smaller than the top layer thickness. Using this approach, it was shown that the effective stiffness of the fibrosa layer is greater than that of the ventricularis layer in intact aortic valve leaflets (p<0.01). To characterize the viscoelastic properties of VICs, an inverse FE method of single cell MA was developed and compared with the analytical half-space model. It was found that inherent differences in the half-space and FE models of single cell MA yield different cell viscoelastic material parameters. However, under particular experimental conditions, the parameters estimated by the half-space model are statistically indistinguishable from those predicted by the FE model. To study strain transduction from the ECM to cytoskeleton, an improved texture correlation algorithm and a uniaxial tension release device were developed. It was found that substrate strain fully transfers to the cytoskeletal network via focal adhesions in live VICs under large strain tension release. To study the effects of cell-ECM interactions on VIC survival, two mechanical stimulus systems that can simulate the separate effects of cell contraction and cell monolayer detachment were developed. It was found that cell sheet detachment and disrupted cell-ECM signaling is likely responsible for the apoptosis of VICs grown in culture on thin collagen matrices, leading to calcification. The studies presented in this thesis refine existing biomechanical tools and provide new experimental and analytical tools with which to study cell-ECM interactions. Their application resulted in an improved understanding of hierarchical valve biomechanics, mechanotransduction, and mechanobiology.

碩士
國立雲林科技大學
環境與安全工程系碩士班
95
The main ingredient of the liquefied natural gas is methane whose volume will become 600 times at 0℃ and 1 atm. Once little leaking out natural gas mix with air and have the chance to get heat, it will cause a terrible fire and explosion. Or a factory at a neighbor industrial estate has fire and the conductance of heat radiation make the temperature of the reserve tanks of the liquefied natural gas to the point, and there will be a explosion causing by mixing pressure releasing vapor and air. And the gas is lighter than air, so it could be on fire easily even far away from the fire source. Especially in such a high population density and highly developed of the oil and chemistry industry country like Taiwan, the releasing of poison matters might be a serious danger to a worker’s life and property, Therefore the purpose of the article is to quantify and estimate the risk of the releasing of the liquefied natural gas, and take some necessary emergency to control the damage of environment and personal health. The article will treat the safety of the LNG station in the process of manufacturing, reserving, and carrying, or the result of that there are some liquefied natural gas release or get fire. We use the software “ALOHA” to analyze the degree of damage, and USA risk management model “Rmp*Comp” to simulate the quantity of releasing and the degree of damage. According to the atmosphere condition and assumptive releasing condition, to analyse the worst-case scenario and alternative release scenarios. By considering with the different releasing distance between LNG reserve tanks and affiliated installations, we could have some reference of preliminary emergency to secure people. And we could spray, separate, or use water mitigation system to decease the damage caused by releasing. We could conclude that the degree of damage is influenced by releasing quantity, releasing condition, and the height of releasing source by simulating many scenarios. We suggest that the source management, maintain, and training plan should be noticed at the same time to reduce the danger. Or we should building emergency center to control the releasing condition and avoid influencing the neighbor a residential area or industrial estate.