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1
Mohammad, Noor. "Desiccation Cracking Behaviour in Thin Bentonite Layers." Thesis, The University of Sydney, 2020. https://hdl.handle.net/2123/22231.
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This thesis investigates the behaviour of desiccation cracks in thin bentonite layers under different conditions (initial water content, layer thickness, temperature and mixtures with kaolinite). For this, a comprehensive series of experiment was conducted as well as some theoretical models were developed. The theoretical model was developed based on the critical cracking thickness following the principles of linear elastic fracture mechanics (Chapter 4). This model was then used in the following chapters and validated with the experimental investigations. Also, hydraulic properties of the cracked soil mass were modelled and the effects of cracks on hydraulic conductivity and water retention properties were shown. In the experimental investigations, firstly, the combined effects of initial water content and layer thickness were studied in a phase diagram to observe the behaviour of desiccation cracks (Chapter 5). It was found that critical cracking thickness could be an important factor in distinguishing cracked and non-cracked samples in the phase diagram. Characteristics of cracks (crack density, total crack length, average crack length and crack width) increase with increasing layer thicknesses as well as initial water contents. The effects of temperature (Chapter 6) and mixtures of bentonite-kaolinite (Chapter 7) on desiccation cracking were investigated in the phase diagram developed in Chapter 5. At higher temperatures, the critical thickness of a clay layer ould be decreased. Results of bentonite-kaolinite mixture demonstrated that the phase boundary shifted to increase the critical thickness of the clay layers of mixtures containing less bentonite (i.e. more kaolinite). Crack morphology was also affected by the change in temperatures and properties of the mixtures. In summary, this study shows some understanding of desiccation cracking behaviour and could provide insights for better design of clay liners, which often at risk of desiccation problem.
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Steadman, David Lawrence. "Growth-arrest behavior of small fatigue cracks." Diss., Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/11731.
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Xue, Yibin. "Three dimensional interface cracks in anisotropic bimaterials." Diss., Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/17273.
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Kaul, Vivek. "Tracking and detection of cracks using minimal path techniques." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/37214.
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The research in the thesis investigates the use of minimal path techniques to track and
detect cracks, modeled as curves, in critical infrastructure like pavements and bridges. We
developed a novel minimal path algorithm to detect curves with complex topology that may
have both closed cycles and open sections using an arbitrary point on the curve as the sole
input. Specically, we applied the novel algorithm to three problems: semi-automatic crack
detection, detection of continuous cracks for crack sealing applications and detection of crack
growth in structures like bridges. The current state of the art minimal path techniques only
work with prior knowledge of either both terminal points or one terminal point plus total
length of the curve. For curves with multiple branches, all terminal points need to be known.
Therefore, we developed a new algorithm that detects curves and relaxes the necessary user
input to one arbitrary point on the curve. The document presents the systematic development
of this algorithm in three stages. First, an algorithm that can detect open curves with
branches was formulated. Then this algorithm was modied to detect curves that also have
closed cycles. Finally, a robust curve detection algorithm was devised that can increase the
accuracy of curve detection. The algorithm was applied to crack images and the results of
crack detection were validated against the ground truth. In addition, the algorithm was also
used to detect features like catheter tube and optical nerves in medical images. The results
demonstrate that the algorithm is able to accurately detect objects that can be modeled as
open curves.
5
Hejman, Ulf. "On initiation of chemically assisted crack growth and crack propagation paths of branching cracks in polycarbonate." Licentiate thesis, Malmö högskola, Teknik och samhälle, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:mau:diva-7790.
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Stress corrosion, SC, in some cases gives rise to stress corrosion cracking, SCC, which differs from purely stress intensity driven cracks in many aspects. They initiate and grow under the influence of an aggressive environment in a stressed substrate. They grow at low load and may branch. The phenomenon of SCC is very complex, both the initiation phase and crack extension itself of SCC is seemingly associated with arbitrariness due to the many unknown factors controlling the process. Such factors could be concentration of species in the environment, stress, stress concentration, electrical conditions, mass transport, and so on.In the present thesis, chemically assisted crack initiation and growth is studied with special focus on the initiation and branching of cracks. Polycarbonate plates are used as substrates subjected to an acetone environment. Experimental procedures for examining initiation and branching in polycarbonate are presented. An optical microscope is employed to study the substrate.The attack at initiation is quantified from pits found on the surface, and pits that act as origin for cracks is identified and the distribution is analysed. A growth criterion for surface cracks is formulated from the observations, and it is used to numerically simulate crack growth. The cracks are seen to coalesce, and this phenomenon is studied in detail. Branching sites of cracks growing in the bulk of polycarbonate are inspected at the sample surface. It is found that the total width of the crack branches are approximately the same as the width of the original crack. Also, angles of the branches are studied. Further, for comparison the crack growth in the bulk is simulated using a moving boundary problem based algorithm and similar behaviour of crack branching is found.
6
Karim, Md Rezaul. "Transient response of laminated composites with subsurface cracks." Diss., The University of Arizona, 1988. http://hdl.handle.net/10150/184541.
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The dynamic response of subsurface cracks in fiber reinforced composites is analytically studied. The response of layered half-space and three-layered plate with two interface cracks excited by a plane SH-wave and line load respectively are studied by formulating the problem as integral equations in the frequency domain. The governing equations along with boundary, regularity and continuity conditions across the interface are reduced to a coupled set of singular integral equations by using Betti's reciprocal theorem along with the Green's functions. In addition, the transient response of an orthotropic half-space with a subsurface crack subjected to inplane line load at an arbitrary angle is analyzed. Two new Green's functions for the uncracked medium are developed and used along with the representation theorem to derive the scattered field. Satisfaction of the traction free condition at the crack surfaces gives rise to a system of singular integral equations. Singular integrals involved in the analysis are computed numerically by removing the poles. Part of the integrals containing the poles are then obtained analytically by using residue theorem. The solution of singular integral equations are obtained by expanding the unknown crack opening displacements (COD) in terms of a complete set of Chebychev polynomials. The problem is first solved in the frequency domain, the time histories are then obtained numerically by inverting the spectra via Fast Fourier Transform (FFT) routine. Numerical results are presented for isotropic and anisotropic materials for several different crack geometries. The results show significant influence of crack geometries and material properties on the COD and surface response of composites.
7
Venkateswaran, Anuradha. "Role of cracks in creep of brittle, polycrystalline, structural ceramics." Diss., Virginia Polytechnic Institute and State University, 1985. http://hdl.handle.net/10919/49951.
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An analytical study was conducted of the effect of cracks on creep of polycrystalline, brittle structural ceramics. Two independent mechanisms of contribution of cracks were defined. The mechanism of elastic creep by crack growth represents the rate of increase in strain, with time, resulting from the time-dependent decrease in elastic moduli of the material, due ·to crack growth. The mechanism of crack-enhanced creep provides a measure of the increase in creep rate over that in an identical but crack-free material, due to the local stress field associated with the cracks and the resultant transfer of stress to the adjacent, crack-free material. Creep rates due to these mechanisms were quantified for simple crack geometries. It was shown that the contribution of cracks can result in an idealized 4-stage creep curve for a brittle, polycrystalline ceramic, in contrast to the conventional 3-stage creep curve for metals. The four stages consist of a primary or crack incubation period, a secondary sigmoidal region resulting from growth of microcracks along grain boundary facets, a tertiary or crack-enhanced stage associated with arrested microcracks, and a quarternary stage comprising crack linkage and coalescence. It was demonstrated that the formation and growth of cracks during creep can result in apparent power-law creep, positive grain size dependence of the creep rate, and grain size-dependent creep activation energy. It can also account for observations of decreasing creep rate with increasing time in constant load creep tests, anomalous stress relaxation behavior in structural ceramics, significantly higher creep rates in tension tests than in compression tests, and discrepancy between diffusion coefficients inferred from creep studies and measured in diffusivity experiments.
A simple model was presented for the effect of cracks on creep rate in bending, based on the time-rate of change of curvature of a bend specimen.
Analysis of the effect of cracks on creep was extended to a general state of multiaxial stress, through matrix formulation of stress, creep rate, and creep compliance tensors. Derivation of components of the creep compliance tensor from analogs in elasticity was demonstrated for crack-enhanced creep, for uniaxial and uniform triaxial tension, for simple crack geometries. It was demonstrated that materials containing cracks can exhibit a finite rate of creep under hydrostatic tension, in contrast to a corresponding creep rate of zero in crack-free materials.
Recommendations are made for analysis and interpretation of experimental creep data for structural ceramics.Ph. D.
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8
Patel, Akshay Mahesh. "Growth of small fatigue cracks in PH 13-8 Mo stainless steel." Thesis, Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/18185.
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Clements, Harold William. "An analysis of stress absorbing membrane interlayers used to inhibit tensile fatigue reflective cracking." Thesis, University of Ulster, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.342402.
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Miller, Douglas Dwight. "Stress intensity factors for circumferential part-through cracks from holes in hollow cylinders subjected to tension and bending loads." Thesis, Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/16055.
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Awal, Mohammad A. 1959. "Transient response of delamination, intersecting and transverse cracks in layered composite plates." Thesis, The University of Arizona, 1989. http://hdl.handle.net/10150/276955.
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A numerical method is developed to determine the dynamic behavior of delamination and transverse cracks in multilayered plates. The plate is subjected to a time dependent antiplane shear stress field which is acting on the plate surfaces. The interaction of waves diffracted at the crack tip with those reflected at the plate boundaries and transmitted at the material interface makes the problem very complicated, so analytical study of this problem cannot be carried out with our present state of knowledge; hence the problem is solved numerically. The finite element equations are obtained by variational calculus applied in the frequency domain. Thus time intregration schemes are avoided, but time dependent response can still be obtained after inverting the frequency dependent response spectra numerically by Fast Fourier Transform (FFT) routine. Another advantage of the frequency domain analysis is that the resonance frequency can be easily detected from the sharp peaks of the response spectra. The numerical difficulty associated with the singular behavior of the stress field near the crack tip has been avoided by using quarter point elements. The numerical results obtained from this investigation are compared with analytical results to verify the accuracy of the method.
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Bernica, Andrew. "Rational load rating of deck-girder bridges with girder end shear cracks in reverse orientation." Thesis, Kansas State University, 2016. http://hdl.handle.net/2097/32559.
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Master of ScienceCivil Engineering
Hayder Rasheed
Reverse diagonal shear cracking at the supports of many reinforced concrete girders is a phenomenon affecting a number of KDOT’s low-volume bridges built in the early-to-mid 1900’s. This phenomenon is not addressed in the AASHTO Bridge Design Manual (2002) or ACI specifications. This study investigates the causes of this cracking and creates BRIDGE (Bridge Rating of Inclined Damage at Girder Ends), an Excel-based software to determine the load rating of a user specified bridge exhibiting reverse diagonal shear cracking at the girder supports. A user-interface is created which allows a user to create a grillage model of an existing bridge and to place various rating trucks on the bridge. Equivalent flexibility analysis is used to distribute the truck live loads from within the deck panels to the surrounding girders and diaphragms. Stiffness matrices are utilized to find the nodal displacements then the reactions at the girder supports caused by the truck live loads and bridge dead load. These reactions are checked against RISA software models to test the accuracy of the stiffness matrix application. ABAQUS FE models and Mohr’s circle stress distribution is used to find the driving and clamping forces on the crack. These forces are caused by resolving the dead and live load reactions and the friction force generated between the concrete girder and the rusty steel bearing pad along the shear crack orientation. These clamping and driving forces are used, along with the simplified modified compression field theory to determine the shear capacity of each girder at the reverse cracks. A modified version of Equation 6B.4.1 from the Manual for Bridge Evaluation (2011) is used to find the operating and inventory rating factors for the bridge.
13
Piyasena, Ratnamudigedara, and n/a. "Crack Spacing, Crack Width and Tension Stiffening Effect in Reinforced Concrete Beams and One-Way Slabs." Griffith University. School of Engineering, 2003. http://www4.gu.edu.au:8080/adt-root/public/adt-QGU20030606.165418.
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An analytical method for determining the crack spacing and crack width in reinforced concrete beams and one-way slabs is presented in this thesis. The locations and the distribution of cracks developed in a loaded member are predicted using the calculated concrete stress distributions near flexural cracks. To determine the stresses, a concrete block bounded by top and bottom faces and two transverse sections of the beam is isolated and analysed by the finite element method. Two types of blocks are analysed. They are: (i) block adjacent to the first flexural crack, and (ii) block in between successive cracks. The calculated concrete stress distribution adjacent to the first flexural crack is used to predict the locations of primary cracks (cracks formed at sections where the stresses have not been influenced by nearby cracks). The concrete stress distributions in between successive cracks, calculated for various crack spacings and load levels, are used to predict the formation of secondary cracks in between existing cracks. The maximum, minimum and the average crack spacing at a given load level are determined using the particular crack spacing that would produce a concrete tensile stress equal to the flexural strength of concrete. The resulting crack width at reinforcement level is determined as the relative difference in elastic extensions of steel and surrounding concrete. The accuracy of the present method is verified by comparing the predicted spacing and width of cracks with those measured by others. The analytical method presented in this thesis is subsequently used to investigate the effects of various variables on the spacing and width of cracks, and the results are presented. These results are used to select the set of parameters that has the most significant effect. A parametric study is then carried out by re-calculating the spacing and width of cracks for the selected parameters. Based on the results of this parametric study, new formulas are developed for the prediction of spacing and width of cracks. The accuracy of these formulas is ascertained by comparing the predicted values and those measured by other investigators on various types of beams under different load levels. The calculated stress distributions between successive cracks are also used to develop a new method of incorporating the tension stiffening effect in deflection calculation. First, curvature values at sections between adjacent cracks are determined under different load levels, using the concrete and steel stresses. These results are used to develop an empirical formula to determine the curvature at any section between adjacent cracks. To verify the accuracy of the new method, short-term deflections are calculated using the curvature values evaluated by the proposed formula for a number of beams, and the results are compared with those measured by others.
14
Piyasena, Ratnamudigedara. "Crack Spacing, Crack Width and Tension Stiffening Effect in Reinforced Concrete Beams and One-Way Slabs." Thesis, Griffith University, 2003. http://hdl.handle.net/10072/366060.
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An analytical method for determining the crack spacing and crack width in reinforced concrete beams and one-way slabs is presented in this thesis. The locations and the distribution of cracks developed in a loaded member are predicted using the calculated concrete stress distributions near flexural cracks. To determine the stresses, a concrete block bounded by top and bottom faces and two transverse sections of the beam is isolated and analysed by the finite element method. Two types of blocks are analysed. They are: (i) block adjacent to the first flexural crack, and (ii) block in between successive cracks. The calculated concrete stress distribution adjacent to the first flexural crack is used to predict the locations of primary cracks (cracks formed at sections where the stresses have not been influenced by nearby cracks). The concrete stress distributions in between successive cracks, calculated for various crack spacings and load levels, are used to predict the formation of secondary cracks in between existing cracks. The maximum, minimum and the average crack spacing at a given load level are determined using the particular crack spacing that would produce a concrete tensile stress equal to the flexural strength of concrete. The resulting crack width at reinforcement level is determined as the relative difference in elastic extensions of steel and surrounding concrete. The accuracy of the present method is verified by comparing the predicted spacing and width of cracks with those measured by others. The analytical method presented in this thesis is subsequently used to investigate the effects of various variables on the spacing and width of cracks, and the results are presented. These results are used to select the set of parameters that has the most significant effect. A parametric study is then carried out by re-calculating the spacing and width of cracks for the selected parameters. Based on the results of this parametric study, new formulas are developed for the prediction of spacing and width of cracks. The accuracy of these formulas is ascertained by comparing the predicted values and those measured by other investigators on various types of beams under different load levels. The calculated stress distributions between successive cracks are also used to develop a new method of incorporating the tension stiffening effect in deflection calculation. First, curvature values at sections between adjacent cracks are determined under different load levels, using the concrete and steel stresses. These results are used to develop an empirical formula to determine the curvature at any section between adjacent cracks. To verify the accuracy of the new method, short-term deflections are calculated using the curvature values evaluated by the proposed formula for a number of beams, and the results are compared with those measured by others.Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Engineering
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Pierola, Javier. "Three dimensional stress intensity factor for large arrays of radial internal surface cracks in a cylindrical pressure vessel." FIU Digital Commons, 1993. http://digitalcommons.fiu.edu/etd/2514.
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The objective of this study is to present the mode I stress intensity factor distribution (SIF) along the crack-front for a wide array of semicircular and semi-elliptical surface cracks inside of a pressurized thick-walled cylinder. A three-dimensional finite element package ANSYS is used to evaluate the SIF for multicracked cylinder with number of cracks from n=1 to 128, the ratio of crack-depth to the wall thickness a/t=0.05 to 0.6, the ellipticity of the crack (the crack-depth to the semi-crack length) a/c=0.2 to 1.5, the ratio of the outer to the inner radius ro/ ri=2.
A substructuring technique is introduced which solved a coarse model meshed with ten-node isoparametric elements and applied the resulting displacements in the boundary surface of a submodel which is built employing singular elements along the crack-front to produce the 1/√r singularity . The SIF is evaluated using nodal-displacement method.
To validate the modeling and analysis procedure of the present results various configurations were solved using this method and compared to other finite element solutions. The present results were in very good agreement: less than 5 % comparing with Raju and Newman's results and within 8 % of Kirkhope's results.
An empirical equation to calculate the maximum SIF, was developed in this study. The equation was obtained by nonlinear fitting of the finite element results and the error was within ± 5.7 %.
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Maritz, Jaco-Louis. "An investigation into the use of low volume - fibre reinforced concrete for controlling plastic shrinkage cracking." Thesis, Stellenbosch : Stellenbosch University, 2012. http://hdl.handle.net/10019.1/19983.
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Thesis (MScEng)--Stellenbosch University, 2012.ENGLISH ABSTRACT: Plastic shrinkage cracking (PSC) in concrete is a well-known problem and usually occurs within the first few hours after the concrete has been cast. It is caused by a rapid loss of water from the concrete, either from the surface through evaporation or through absorption by dry subgrade or formwork in contact with the concrete and results in an overall reduction in concrete volume. If this volume reduction or shrinkage is restrained, plastic shrinkage cracks can occur. Plastic shrinkage cracks create an unsightly appearance on the concrete surface which reduces the quality of the concrete structure. These cracks also develop weak points in the concrete which can be widened and deepened later on by drying shrinkage and thermal movement. As a result harmful substances may enter the cracks causing accelerated concrete deterioration. These cracks may also expose the steel reinforcement causing it to corrode more aggressively. Consequently, the aesthetic value, serviceability, durability and overall performance of the concrete will be reduced. Therefore it is important to consider methods of limiting PSC. One of these methods is the addition of low volumes of polymeric fibres to concrete to reduce PSC. However, the application of this low volume fibre reinforced concrete (LV-FRC) is not clearly understood since there is a lack of knowledge and guidance available for the use of LV-FRC. The objective of this study is to gain a full understanding of PSC behaviour in conventional concrete and LV-FRC by investigating the effects of evaporation and bleeding as well as the effect of various fibre properties on PSC. The following significant findings were attained: A basis for a crack prediction model in conventional concrete was developed using the average differences in cumulative evaporation and cumulative bleeding to create a crack prediction value (CPV). This preliminary model showed that there exists a certain CPV range (-0.2 to 0.4 kg/m2 for this study) where a slight decrease in the CPV results in a significant PSC reduction. It also showed that if the CPV falls outside this range, varying the bleeding or evaporation conditions will have very little effect on the PSC. A study on the fibre properties in LV-FRC showed that there exist certain limits to the fibre volume, length and diameter where a further increase or decrease in value will have no or little effect on reducing PSC. It also showed that the effect of the fibres depend on the level of severity of PSC. The knowledge gained from this investigation can serve as a basis for the design of a model that can predict the risk of PSC in conventional concrete and specify preventative measures needed to reduce this risk. It also provides information that can be used to develop guidelines for the effective use of LV-FRC.
AFRIKAANSE OPSOMMING: Plastiese krimp krake (PKK) in beton is `n bekende probleem en vorm gewoonlik binne die eerste paar uur nadat die beton gegiet is. Dit word veroorsaak deur die vinnige waterverlies vanuit die beton, óf deur verdamping vanaf die beton oppervalk óf deur absorpsie van `n droeë grondlaag of bekisting wat in kontak is met die beton. Dit veroorsaak `n algehele vermindering in beton volume. As hierdie krimping van die beton beperk word, kan plastiese krimp krake ontstaan. PKK skep 'n onooglike voorkoms van die beton oppervlakte en verlaag die kwaliteit van die beton struktuur. Hierdie krake tree ook op as swak plekke in die beton wat later kan verbreed of verdiep deur droogkrimping en termiese beweging. Gevolglik kan skadelike stowwe vanuit die omgewing die krake binnedring wat lei tot versnelde agteruitgang van die beton. Hierdie krake kan ook die staalbewapening ontbloot wat veroorsaak dat dit vinniger roes. Gevolglik verminder die estetiese waarde, diensbaarheid, duursaamheid en algehele prestasie van die beton. Daarom is dit belangrik om metodes te ondersoek vir die beperking van PKK. Een van hierdie metodes is die byvoeging van lae volumes polimeer vesels tot beton om PKK te verminder. Die toepassing van hierdie lae volume - vesel versterkte beton (LV-VVB) word egter nog nie volledig verstaan nie as gevolg van 'n algemene gebrek aan kennis en riglyne vir die gebruik van die LV-VVB. Die doel van hierdie studie is om 'n volledige begrip van PKK gedrag in normale beton asook LV-VVB te kry. Dit word behaal deur die effek van verdamping en bloei op PKK sowel as die effek van verskillende vesel eienskappe op PKK te ondersoek. Die volgende noemenswaardige bevindinge is bekry. • Die basis van 'n kraak voorspellingsmodel vir gewone beton is ontwikkel deur gebruik te maak van die gemiddelde verskil tussen die kumulatiewe verdamping en die kumulatiewe bloei om 'n kraak voorspellingswaarde (KVW) te vorm. Hierdie voorlopige model toon dat daar `n sekere KVW interval ontstaan (-0,2 tot 0,4 kg/m2 vir hierdie studie) waar slegs 'n effense vermindering in die KVW 'n geweldige vermindering in die PKK tot gevolg het. Dit dui ook aan dat, indien die KVW buite hierdie interval val, ʼn verandering in die bloei of verdamping toestande `n baie klein invloed op die PKK het. 'n Studie oor die vesel eienskappe in LV-VVB het gewys dat daar sekere grense is aan die vesel volume, lengte en deursnee waardes, waar 'n verdere toename of afname in waarde min of geen effek het op die vermindering van PKK nie. Dit wys ook dat die effek van die vesels grotendeels afhanklik is van die risiko vlak vir PKK. Die kennis wat uit hierdie ondersoek opgedoen is, kan dien as 'n basis vir die ontwerp van 'n model wat die risiko van PKK in gewone beton kan voorspel en daarvolgens besluit op 'n voorkomingsmaatsreël om hierdie risiko te verminder. Dit bied ook inligting wat gebruik kan word om riglyne te ontwikkel vir die effektiewe gebruik van LV-VVB.
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Gerber, Johan Andries Kritzinger. "Characterization of cracks on ultra thin continuously reinforced concrete pavements." Thesis, Stellenbosch : University of Stellenbosch, 2011. http://hdl.handle.net/10019.1/6772.
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Thesis (MScEng (Civil Engineering))--University of Stellenbosch, 2011.ENGLISH ABSTRACT: The southbound screener lane of the Heidelberg Traffic Control Centre received structural improvements by means of an ultra thin continuously reinforced concrete pavement (UTCRCP) overlay. This experimental overlay forms part of the South African National Roads Agency Limited’s innovative highway repair strategy on existing pavements that have exceeded design life. The primary objective of this study was to characterize the UTCRCP overlay with regard to crack spacing formation under accelerated pavement testing (APT). Characterization comprised of empirical modelling techniques, statistical analysis, non destructive testing and software simulations. Pavement deflection responses were empirically and linear elastically converted to input parameters. These parameters were used in the mean crack spacing prediction model of the Mechanistic-Empirical Pavement Design Guide (M-E PDG). Observed cracking under APT was recorded and analyzed by means of descriptive statistics. The outcome of the M-E PDG’s mean crack spacing and the statistics of the observed cracking were evaluated against cncPave simulations. Initial shrinkage crack formations ranged from 500 mm to 900 mm, with a mean spacing of 695 mm. Subsequent secondary cracking reduced the segments, delineated by initial cracking, to intervals consisting of 100 mm to 350 mm. A statistical analysis of the observed cracking indicated that traffic had little effect on the transverse crack spacing formation. The observed cracks yielded a mean spacing of 296 mm, compared to the 186 mm of the M-E PDG mean crack spacing calculation. cncPave simulations indicated that the expected range of cracking would fall between 237 mm and 350 mm with a probability of 50% that crack spacing would exceed 265 mm. The 50th percentile of the observed cracks resulted in a spacing of 233 mm. The APT project was limited to a single test section. No pavement failures occurred during the APT project. A total of 2.8 million 80 kN load repetitions were applied to the UTCRCP. However circular crack formations regarded as a punchout development have formed on the UTCRCP test section. Circular cracks formed around weaknesses in the pavement system. The prediction of these punchout formations incorporates the mean crack spacing result. Occurrence of mean crack spacing forms part of a crack spacing distribution defined by a range. Therefore designing a punchout prediction model for UTCRCP should include the characteristics and range of the crack pattern and not merely the mean crack spacing value. Key Words: UTCRCP, APT, Mean Crack Spacing, Punchout, Descriptive Statistics, cncPave, M-E PDG, Transverse Cracks, Dense Liquid Foundation, Elastic Solid Foundation.
AFRIKAANSE OPSOMMING: Die suidwaartse moniteerings laan van die Heidelberg Verkeersbeheer Sentrum, het strukturele verbetering ondergaan deur die konstruksie van ‘n ultradun aaneen-gewapende betonplaveisel (UDAGBP) wat dien as ‘n deklaag. Hierdie eksperimentele deklaag is deel van die Suid-Afrikaanse Nasionale Paaie Aggentskap Beperk (SANRAL) se vernuftige deurpadherstelstrategie vir bestaande deurpaaie waarvan die ontwerplewe verstryk het. Die primêre doel van hierdie studie is om die UDAGBP te karakteriseer, met betrekking tot kraakspasiëring, deur middel van Versnelde Plaveisel Toetsing (VPT). Die karakteriseringsproses het bestaan uit empiriese moduleringstegnieke, statistiese ontleding, nie-destruktiewe toetsmetodologieë en sagtewaresimulasies. Die plaveiseldefleksiegedrag is empiries en linieêr elasties ontleed en omgeskakel na invoerparameters. Hierdie parameters is gebruik in die peilingsmodel vir gemiddelde kraakspasiëring van die Meganisties-Empiries Plaveisel Ontwerpsgids (M-E POG). Waargenome kraakspasiëring na die afloop van VPT is opgeteken en deur middel van beskrywende statistiek ontleed. Die resultate van die M-E POG se gemiddelde kraakspasiëring en die statistiese ontleding van die waargenome krake is geëvalueer teenoor cncPave simulasies. Aanvanklike krimpingskrake het gevorm met wisselende kraakspasiëring tussen 500 mm en 900 mm met ‘n gemiddelde spasiëring van 695 mm. Daaropvolgende krake het die aanvanklike segmente, wat gevorm het tydens die aanvanklike krimpingskrake, verkort na intervalle van 100 mm tot 350 mm. ‘n Statistiese ontleding van die waargeneemde krake het aangedui dat verkeer weinig ‘n aandeel het in die dwarskraak-vormingsproses. Die waargenome krake het ‘n gemiddelde spasiëring van 296 mm in vergelyking met 186 mm van die M-E POG se gemiddelde kraakspasiëring berekening. cncPave simulasies het aangedui dat die verwagte kraakspasiëringsgrense tussen 237 mm en 350 mm is en ‘n 50% waarskynlikheid dat die kraakspasiëring meer as 265 mm is. Die VPT projek is beperk tot ‘n enkele toetsseksie. Geen plaveiselfalings is waargeneem gedurende die VPT projek nie. In totaal was 2.8 miljoen as-lasherhalings aangewend op die UDAGBP. Daar het egeter sirkelvormige kraakformasies, wat beskou word as ponsswigting, ontwikkel op die UDAGBP toetsseksie. Sirkelvormige kraakpatrone het gevorm rondom swak plekke in die plaveisel. Die peilingsmodelle van hierdie ponsswigting maak gebruik van die gimiddelde kraakspasiëringsresultaat. Die verskynsel van gemiddelde kraakspasiëring in hierdie studie is deel van ‘n kraakspasiëringsverdeling, gedefinieerd deur ‘n spasiëringsgrens. Daarom moet die kraakspasiëringskarakteristieke en spasiëringsgrense in ag geneem word in die ontwerpsproses van ‘n UDAGBP ponsswigting-peilings-model, nie slegs die waarde van die gemiddelde kraakspasiëring nie. Sleutel woorde: UDAGBP, VPT, Gemiddelde Kraakspasiëring, Ponsswigting, Beskrywende Statistiek, cncPave, M-E POG, Transversale Krake, Digte Vloeistof Fondasie, Elasties- Soliede Fondasie.
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Ahn, Byung Ki. "Interfacial Mechanics in Fiber-Reinforced Composites: Mechanics of Single and Multiple Cracks in CMCs." Diss., Virginia Tech, 1997. http://hdl.handle.net/10919/29791.
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Several critical issues in the mechanics of the interface between the fibers and matrix in ceramic matrix composites (CMCs) are studied. The first issue is the competition between crack deflection and penetration at the fiber/matrix interface. When a matrix crack, the first fracture mode in a CMC, reaches the interface, two different crack modes are possible; crack deflection along the interface and crack penetration into the fibers. A criterion based on strain energy release rates is developed to determine the crack propagation at the interface. The Axisymmetric Damage Model (ADM), a newly-developed numerical technique, is used to obtain the strain energy in the cracked composite. The results are compared with a commonly-used analytic solution provided by He and Hutchinson (HH), and also with experimental data on a limited basis.
The second issue is the stress distribution near the debond/sliding interface. If the interface is weak enough for the main matrix crack to deflect and form a debond/sliding zone, then the stress distribution around the sliding interface is of interest because it provides insight into further cracking modes, i.e. multiple matrix cracking or possibly fiber failure. The stress distributions are obtained by the ADM and compared to a simple shear-lag model in which a constant sliding resistance is assumed. The results show that the matrix axial stress, which is responsible for further matrix cracking, is accurately predicted by the shear-lag model.
Finally, the third issue is multiple matrix cracking. We present a theory to predict the stress/strain relations and unload/reload hysteresis behavior during the evolution of multiple matrix cracking. The random spacings between the matrix cracks as well as the crack interactions are taken into account in the model. The procedure to obtain the interfacial sliding resistance, thermal residual stress, and matrix flaw distribution from the experimental stress/strain data is discussed. The results are compared to a commonly-used approach in which uniform crack spacings are assumed.
Overall, we have considered various crack modes in the fiber-reinforced CMCs; from a single matrix crack to multiple matrix cracking, and have suggested models to predict the microscopic crack behavior and to evaluate the macroscopic stress/strain relations. The damage tolerance or toughening due to the inelastic strains caused by matrix cracking phenomenon is the key issue of this study, and the interfacial mechanics in conjunction with the crack behavior is the main issue discussed here. The models can be used to interpret experimental data such as micrographs of crack surface or extent of crack damage, and stress/strain curves, and in general the models can be used as guidelines to design tougher composites.Ph. D.
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Rhymer, Donald William. "Stress Intensity Solutions of Thermally Induced Cracks in a Combustor Liner Hot Spot Using Finite Element Analysis." Diss., Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/7515.
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Thermally cycling a thin plate of nickel-based superalloy with an intense in-plane thermal gradient, or hot spot, produces thermally induced crack growth not represented by classic thermo-mechanical fatigue (TMF). With the max hot spot temperature at 1093 C (2000 F) of a 1.5 mm thick, 82.55 mm diameter circular plate of B-1900+Hf, annular buckling and bending stresses result during each thermal cycle which drive the crack initiation and propagation. A finite element analysis (FEA) model, using ANSYS 7.1, has been developed which models the buckling and as well as represents the stress intensity at simulated crack lengths upon cool down of each thermal cycle. The model approximates the out-of-plane response at heat-up within 5% error and a difference in the final displacement of 0.185 mm after twelve thermal cycles. Using published da/dN vs. Keff data, the number of cycles needed to grow the crack to the experimental arrest distance is modeled within 1 mm. The number of cycles to this point is within 5 out of 462 in comparison to the experimental test.
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Yavas, Ozgur. "Effect Of Welding Parameters On The Susceptibility To Hydrogen Cracking In Line Pipe Steels In Sour Environments." Master's thesis, METU, 2006. http://etd.lib.metu.edu.tr/upload/2/12608074/index.pdf.
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In this study, hydrogen induced cracking (HIC) behavior of welded steels used in petroleum lines under sour petroleum environments was investigated. The testing environment in NACE TM0284-2003 standard was used in order to simulate sour petroleum environment.
In order to investigate behavior of welding parameters, used in pipe production, on HIC, welds were done with different line energies. Two different API X-65 steels were used in welding operations. The specimens taken from welded zones were tested in testing environment. The specimens were examined metallographically. Crack lengths were measured with a computer program. The results obtained were discussed in view of metallurgical and welding parameters aspects.
The result obtained from this investigation led to a general conclusion that, the metallurgical parameters of steels used in pipe production were more important than welding parameters regarding their effect on HIC. It was shown that the composition and microstructural grain size of steels were in
direct relation to HIC.
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Bolivar, Vina José. "Experimental study of the behavior of colonies of environmentally-assisted short cracks by digital image correlation, acoustic emission and electrochemical noise." Thesis, Lyon, 2017. http://www.theses.fr/2017LYSEI059/document.
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Ce travail s’inscrit dans le contexte d’une meilleure prédiction de la durée de vie de structures soumises au risque d’amorçage et de propagation de fissures multiples de corrosion sous contrainte (CSC). Ainsi, en développant une méthodologie expérimentale originale basée sur des mesures conjointes de corrélation d’images numériques (DIC), d’émission acoustique (EA) et de bruit électrochimique (EN), et leur analyse, ce travail vise à contribuer à l’amélioration de la compréhension des mécanismes impliqués dans le développement de colonies de fissures courtes de CSC qui interagissent entre elles, et à la simulation du comportement de cette colonie. Le choix de conditions optimales de traitement thermique d’un alliage base-Ni et de pH d’une solution de polythionate, a permis la maitrise des paramètres géométriques et morphologiques de colonies de fissures intergranulaires, qui ont été investiguées par DIC grâce à l’optimisation d’une préparation de surface adaptée. Les différentes phases de propagation d’une fissure unique et d’une colonie de fissures ont été identifiées, de même que les mécanismes associés, par des expérimentations et analyses réalisées en 2D et en 3D. Cette approche expérimentale innovante a permis de poser les bases d’une approche numérique puis de la valider. Un focus particulier a été porté sur l’EN au travers d’une analyse critique des perturbations engendrées par le bruit de l’instrumentation et par l’asymétrie du système d’étude. Les limitations de la technique pour son application à l’étude quantitative de la corrosion sous contrainte ont été évaluées sur la base des résultats de l’étude. Une transposition de la démarche expérimentale à hautes pressions et températures est proposée comme perspective à court terme de ce travail, qui permet également d’envisager la prise en compte de différents modes de propagation des fissures en lien avec la microstructure du matériau dans l’approche numériqueThis work concerns with the current needs of enhancing the tools used for predicting the remnant lifetime of structures subjected to the risk of initiation and propagation of multiple stress corrosion cracks (SCC). The approach consists in developing an original experimental methodology based on joint measurements of digital image correlation (DIC), acoustic emission (EA) and electrochemical noise (EN). The final objective is to contribute to both the understanding of the mechanisms involved in the development of interacting short stress corrosion cracks and to the modeling of the colony behavior. The choice of optimal conditions for the heat treatment of a Nickel-base alloy and for the pH of a polythionate solution allowed controlling the morphological parameters of intergranular cracks colonies, which were investigated by DIC owning to an optimized suitable surface treatment. The different propagation stages of a single crack and some colonies were identified, together with the involved mechanisms, through experiments and analyses performed in 2D and 3D. This innovative experimental approach allowed settling the basements of the numerical modeling and validating it. A particular attention was focused on EN measurements through a critical analysis of the perturbations generated by the instrumental noise and the asymmetry of the studied system. The limitations of the technique for its application to the quantitative study of SCC were evaluated on the basis of the present results. A transposal of the experimental approach towards high temperature and pressure conditions of test was finally proposed as a short-term prospect of this work, also allowing considering other modes of crack propagation linked to the material microstructure in the numerical approach
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Kluyts, Grant. "Investigation of the effect of selected polypropylene fibres and ultra-fine aggregate on plastic shrinkage cracks on South African roads." Thesis, Nelson Mandela Metropolitan University, 2005. http://hdl.handle.net/10948/174.
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Plastic shrinkage cracks, although not inherently structurally debilitating, expose the reinforcement in low-volume reinforced concrete roads to deleterious substances, which may reduce its effectiveness leading ultimately to structural failure. In un-reinforced low-volume concrete road these cracks appear unsightly and cause the road user an unpleasant riding experience. Many researchers believe that plastic shrinkage crack development remains a concern to the concrete industry, occurring in particularly large–area pours such as low-volume concrete roads, and therefore requires further research to understand their formation and minimization. This study reports findings on the effectiveness of oxyfluorinated polypropylene fibres to control plastic shrinkage cracks, and the effect the addition of ultra-fine material has on the formation and/or propagation of these cracks. Findings indicate that low volume dosages (2 kg/m³), of oxyfluorinated polypropylene fibre significantly reduced the formation of plastic shrinkage cracks under test conditions. Furthermore, that the addition of ultra-fine material in excess of 63 kg/m³ increased the formation and/or development of plastic shrinkage cracks.
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Swindeman, Michael James. "A Regularized Extended Finite Element Method for Modeling the Coupled Cracking and Delamination of Composite Materials." University of Dayton / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1324605778.
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Franceschini, André Schwarz. "Avaliação do fenômeno de união de trincas induzidas pelo hidrogênio e sua influência na integridade estrutural de um vaso de pressão." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2011. http://hdl.handle.net/10183/29062.
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Componentes e equipamentos utilizados na indústria petroquímica estão suscetíveis a presença de descontinuidades e, por esta razão, diversas pesquisas são desenvolvidas com o intuito de aprimorar e criar novos métodos para evitar, remediar ou controlar estas, de forma a não causarem um dano à integridade estrutural. Neste trabalho é avaliado um conjunto de trincas induzidas pelo hidrogênio (TIH), através do método de elementos finitos, com a finalidade de verificar o fenômeno de união das suas extremidades formando uma trinca contínua do tipo SWC (Stepwise Cracking). Também se verifica a influência do conjunto de trincas à integridade da estrutura com base na metodologia Fitness for Service (FFS) através do uso dos diagramas de avaliação de falhas (FAD – Failure Assessment Diagram) indicados pelas normas API-579 / ASME FFS-1 e BS 7910 além do procedimento CEGB-R6. Os resultados mostram que o efeito de interação entre as extremidades é intenso quando estas se encontram próximas umas das outras, confirmando assim a tendência de união das fissuras. Também se constata que o fenômeno é fortemente influenciado pela pressão interna presente nas TIH, esta causada pela presença de hidrogênio. Em relação à aceitabilidade das descontinuidades, é observado que os resultados da avaliação são influenciados pela maneira como a descontinuidade é caracterizada.Components and equipments of the petrochemical industry are susceptible to the presence of flaws and, for this reason, several studies are developed aiming to improve and create new methods to avoid, remedy and control these flaws in order they will not cause any integrity damage. In this work a cluster of Hydrogen Induced Crack (HIC) is assessed, using the finite element method, with the goal to verify the union phenomena in their tips forming a Stepwise Cracking (SWC) flaw. Also is verified the influence of the cluster to the integrity of the structure based on the Fitness for Service methodology, using the Failure Assessment Diagrams indicated by the Standards API-579 / ASME FFS-1 and BS 7910, also the CEGBR6 procedure. The results show that the interaction effect among the tip of the cracks is considerably intense when they are near to each other, confirming the tendency of union among them. Also this phenomenon is strongly influenced by the internal pressure in the HIC, caused by the presence of atomic Hydrogen diffused in the structure. In relation to the flaw assessment, it is observed that results are strongly influenced on how the flaw is characterized.
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Heideklang, René. "Data Fusion for Multi-Sensor Nondestructive Detection of Surface Cracks in Ferromagnetic Materials." Doctoral thesis, Humboldt-Universität zu Berlin, 2018. http://dx.doi.org/10.18452/19586.
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Ermüdungsrissbildung ist ein gefährliches und kostenintensives Phänomen, welches frühzeitig erkannt werden muss. Weil kleine Fehlstellen jedoch hohe Testempfindlichkeit erfordern, wird die Prüfzuverlässigkeit durch Falschanzeigen vermindert. Diese Arbeit macht sich deshalb die Diversität unterschiedlicher zerstörungsfreier Oberflächenprüfmethoden zu Nutze, um mittels Datenfusion die Zuverlässigkeit der Fehlererkennung zu erhöhen.
Der erste Beitrag dieser Arbeit in neuartigen Ansätzen zur Fusion von Prüfbildern. Diese werden durch Oberflächenabtastung mittels Wirbelstromprüfung, thermischer Prüfung und magnetischer Streuflussprüfung gewonnen. Die Ergebnisse zeigen, dass schon einfache algebraische Fusionsregeln gute Ergebnisse liefern, sofern die Daten adäquat vorverarbeitet wurden. So übertrifft Datenfusion den besten Einzelsensor in der pixelbasierten Falscherkennungsrate um den Faktor sechs bei einer Nutentiefe von 10 μm.
Weiterhin wird die Fusion im Bildtransformationsbereich untersucht. Jedoch werden die theoretischen Vorteile solcher richtungsempfindlichen Transformationen in der Praxis mit den vorliegenden Daten nicht erreicht. Nichtsdestotrotz wird der Vorteil der Fusion gegenüber Einzelsensorprüfung auch hier bestätigt.
Darüber hinaus liefert diese Arbeit neuartige Techniken zur Fusion auch auf höheren Ebenen der Signalabstraktion. Ein Ansatz, der auf Kerndichtefunktionen beruht, wird eingeführt, um örtlich verteilte Detektionshypothesen zu integrieren. Er ermöglicht, die praktisch unvermeidbaren Registrierungsfehler explizit zu modellieren. Oberflächenunstetigkeiten von 30 μm Tiefe können zuverlässig durch Fusion gefunden werden, wogegen das beste Einzelverfahren erst Tiefen ab 40–50 μm erfolgreich auffindet. Das Experiment wird auf einem zweiten Prüfkörper bestätigt.
Am Ende der Arbeit werden Richtlinien für den Einsatz von Datenfusion gegeben, und die Notwendigkeit einer Initiative zum Teilen von Messdaten wird betont, um zukünftige Forschung zu fördern.Fatigue cracking is a dangerous and cost-intensive phenomenon that requires early detection. But at high test sensitivity, the abundance of false indications limits the reliability of conventional materials testing. This thesis exploits the diversity of physical principles that different nondestructive surface inspection methods offer, by applying data fusion techniques to increase the reliability of defect detection. The first main contribution are novel approaches for the fusion of NDT images. These surface scans are obtained from state-of-the-art inspection procedures in Eddy Current Testing, Thermal Testing and Magnetic Flux Leakage Testing. The implemented image fusion strategy demonstrates that simple algebraic fusion rules are sufficient for high performance, given adequate signal normalization. Data fusion reduces the rate of false positives is reduced by a factor of six over the best individual sensor at a 10 μm deep groove. Moreover, the utility of state-of-the-art image representations, like the Shearlet domain, are explored. However, the theoretical advantages of such directional transforms are not attained in practice with the given data. Nevertheless, the benefit of fusion over single-sensor inspection is confirmed a second time. Furthermore, this work proposes novel techniques for fusion at a high level of signal abstraction. A kernel-based approach is introduced to integrate spatially scattered detection hypotheses. This method explicitly deals with registration errors that are unavoidable in practice. Surface discontinuities as shallow as 30 μm are reliably found by fusion, whereas the best individual sensor requires depths of 40–50 μm for successful detection. The experiment is replicated on a similar second test specimen. Practical guidelines are given at the end of the thesis, and the need for a data sharing initiative is stressed to promote future research on this topic.
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Zubillaga, Eceiza Lierni. "Experimental and analytical study of delamination caused by free-edges and matrix cracks in laminated composites." Doctoral thesis, Universitat de Girona, 2014. http://hdl.handle.net/10803/284759.
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In the last decades, the use of laminated composites, such as Carbon Fiber Reinforce Polymer has increased in many industrial sectors. Different failure mechanisms different damage mechanism can appear in laminated composites. Among the different damage mechanisms, delamination or interlaminar failure is the one that reduces the load-carrying capacity of composite structures and may compromise structural integrity. Nowadays, the prediction of delamination can be done using computational tools that involve high computational costs, limiting their applicability in the initial stages of the design of new structural components. In this work, quick-analysis tools for delamination predictions are proposed. Two different sources of delamination have been studied: free-edge and matrix-crack induced delamination. A methodology to predict both types of induced delamination is proposed and it has been validated with experimental resultsEn los últimos años se ha incrementado el uso de materiales compuestos en diferentes campos de la tecnología. Este tipo de materiales presentan varios tipos de fallo, siendo uno de ellos la deslaminación o fallo interlaminar. La deslaminación puede reducir la capacidad de carga de los compuestos y puede comprometer la integridad estructural. En la actualidad, se puede predecir la deslaminación mediante herramientas numéricas, pero estas implican un alto coste computacional que imposibilita su utilización en las primeras etapas del diseño de un componente estructural. En esta tesis se aborda esta problemática, proponiendo métodos de cálculo de bajo coste computacional que permiten predecir la deslaminación en las primeras etapas del diseño estructural. Se han desarrollado métodos de análisis para dos distintos tipos de deslaminación: por efectos de borde y provocada por grietas en la matriz, y se han validado mediante una campaña experimental
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Some, Liene. "Automatic image-based road crack detection methods." Thesis, KTH, Geodesi och satellitpositionering, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-189245.
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Pavement crack detection is an important procedure in road maintenanceand traffic safety. Traditionally, the road inventory was performed by field inspection, now it is replaced by the evaluation of mobile mapping system images. The acquired images are still a significant source of temporal condition of thepavement surface. The automatisation of crack detection is highly necessarybecause it could decrease workload, and therefore, maintenance costs. Two methods for automatic crack detection from mobile mapping imageswere tested: step by step pixel based image intensity analysis, and deep learning. The objective of this thesis is to develop and test the workflow for the streetview image crack detection and reduce image database by detecting no-cracksurfaces. To examine the performance of the methods, their classification precisionwas compared. The best-acquired precision with the trained deep learningmodel was 98% that is 3% better than with the other method and it suggeststhat the deep learning is the most appropriate for the application. Furthermore, there is a need for faster and more precise detection methods, and deep learningholds promise for the further implementation. However, future studies areneeded and they should focus on full-scale image crack detection, disturbingobject elimination and crack severity classification.
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Ter-Onvanessian, Benoît. "Etude comparative de différents superalliages base Ni pour ressorts de systèmes de maintien." Thesis, Toulouse, INPT, 2011. http://www.theses.fr/2011INPT0021/document.
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Les systèmes de maintien situés sur les structures assemblages-combustibles des réacteurs nucléaires à eau sous pression (REP) sont constitués d'un empilement de lames qui agissent à la fois, comme élément accommodant les incompatibilités thermiques résultant des différences de coefficients de dilatation Acier, alliages de zirconium et principalement, comme système permettant de limiter les effets hydrodynamiques induits par le passage du fluide caloporteur à travers les assemblages. Actuellement, l'alliage 718 est le matériau constitutif de ces ressorts à lames. Il présente les performances en service nécessaires et suffisantes pour répondre aux sollicitations de ces systèmes ainsi qu'aux exigences des autorités de sûreté (dans les conditions actuelles de fonctionnement des REP). Or, dans le cadre de l'augmentation des performances générales des assemblages combustibles, l'emploi d'autres matériaux, dont les propriétés de relaxation sous flux neutronique sont supérieures à celles du 718, est envisagé par AREVA. Les matériaux étudiés sont principalement des superalliages base Ni, tels que les nuances 625+ et 725 qui à l'instar de l'alliage 718 durcissent par précipitation de phases secondaires, ainsi que des nuances d'alliage 718 riche en Molybdène. Cependant, bien que ces nouveaux matériaux présentent une relaxation sous flux neutronique améliorée, ils doivent répondre également à un cahier des charges strict, propre à leur utilisation en centrale : des propriétés mécaniques équivalentes, une bonne résistance à la corrosion sous contrainte (CSC) et une bonne résistance à la fragilisation par l'hydrogène (FPH) en milieu primaire de REP. Chacune de ces propriétés a été étudiée avec attention dans le double but de comparer ces matériaux entre eux et afin de cerner les paramètres clés contrôlant leur différence de comportement aussi bien en CSC qu'en FPHHold-down systems used in the fuel assembly of Nuclear Pressurized Water Reactor (PWR) are constituted by stiff springs. The role of the hold-down springs is to ensure the bond between the fuel assembly and the lower plate of the intern structure of the core, thus holding down the assembly on the bottom plate of the reactor, during all the exploitation and maintenance periods. Nowadays, alloy 718 is the constitutive material of these hold-down springs. Its properties in terms of mechanical behaviour, corrosion resistance… fill in the specifications required for such application in the present service conditions. However, in order to improve the common efficiency of fuel assemblies, the upgrading of their design as well as the use of new materials are advocated by the nuclear power plant company, AREVA. Though other Ni-base superalloys known for their good behaviour under neutronic radiation can be proposed as new materials, those superalloys must fill in all the application specifications in order to substitute alloy 718. So, sufficient mechanical properties, good resistance to Stress Corrosion Cracking (SCC) and good resistance to Hydrogen Embrittlement (HE) are also required to allow the replacement. All of these properties are carefully studied with the double aim to characterize and compare different superalloys, and to determine key parameters governing the SCC and HE behaviours of such alloys in primary water of PWR
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Hamdi, Jabrane Khalil. "Modélisation explicite de l’initiation et la propagation de fractures." Thesis, Université de Lorraine, 2017. http://www.theses.fr/2017LORR0353/document.
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L’étude du comportement des roches nécessite de comprendre leur réponse sous diverses sollicitations. L’étude énergétique de l’endommagement des roches est indispensable pour prédire les phénomènes dynamiques. Ces phénomènes sont dus au développement de fissures dans les roches soumises à des fortes contraintes initiales et induites. La fissuration est une forme de dissipation d’énergie qui permet de rétablir l'équilibre du milieu. L’objectif de la thèse est de modéliser la fissuration dans les milieux rocheux dans la perspective d’étudier le comportement des ouvrages souterrains à grande profondeur. Le développement des modèles capables de représenter la fissuration, la coalescence des fissures et leur interaction avec des fractures préexistantes est indispensable. De la littérature, il ressort deux principales approches théoriques et numériques de modélisation de la fissuration : continue et discrète. Une synthèse critique de ces approches nous a conduit à retenir l’approche discrète et plus particulièrement le code Yade dans le cadre de cette thèse. Ce code permet de simuler explicitement la fissuration avec ou sans fractures pré-existantes. Des développements ont été effectués afin de tenir compte des différentes formes d’énergie intervenant dans le comportement des roches soumises à des sollicitations. En particulier une corrélation entre l’énergie de fissuration numérique et l’activité microsismique observée sur des échantillons en laboratoire en compression. Les différentes composantes énergétiques explicitées puis implémentées dans Yade sont : le travail externe, l’énergie potentielle, l'énergie élastique, l’énergie de frottement, l’énergie de fissuration, l'énergie cinétique et l’énergie dissipée en amortissement. La validation de l’approche énergétique a été réalisée grâce à la simulation des essais de laboratoire. L’évolution des différentes composantes énergétiques a permis de vérifier que le bilan des énergies est correctement évalué. Le bilan énergétique a également été vérifié à échelle de structures en simulant l’excavation souterraine d’un Mine-by Experiment (URL Manitoba). L’extension de la zone endommagée induite par l’excavation prédite numériquement a été comparée à celle observée in-situ autour du Mine-by Experiment. Il a été constaté que l’endommagement prédit est similaire à celui observé dans les directions des contraintes initiales mineure et majeure. Par ailleurs la formulation énergétique permet d’étudier numériquement les processus de fissuration des roches. Wassermann (2006) a réalisé des essais de compression uniaxiale et triaxiale sur des échantillons de minerai de fer lorrain. Nous avons modélisé ces essais. La comparaison qualitative des événements acoustiques et des énergies de fissuration issues respectivement des essais et des simulations numériques a montré des tendances similaires. Par contre, la comparaison d’un point de vue quantitatif a montré que le nombre des événements acoustiques numériques est plus important que celui déterminé expérimentalement. L’énergie dissipée par fissuration numérique est également plus importante que celle obtenue sur les essais. Cette différence est expliquée par le fait que les capteurs du dispositif expérimental ne détectent pas tous les événements acoustiques. Les résultats obtenus pourront permettre de mieux comprendre les cinétiques des phénomènes dynamiques dans les ouvrages souterrains profonds. Une autre application a consisté à modéliser un pilier de mine de fer de Joeuf (Lorraine). Le modèle numérique montre deux modes de fissuration dans le pilier : (a) écaillage en peau de pilier, (b) deux bandes de rupture s’initiant du mur et toit du pilier pour se propager vers le cœur du pilier. Ce travail offre de bonnes perspectives pour mieux comprendre la propagation de la fissuration à plus grande échelle mais aussi de progresser dans la recherche de corrélation entre la géomécanique et la géophysiqueThe study of rock mass behavior requires the understanding of their response under various loadings. The study of rock damage from an energetic point of view is essential in order to predict dynamic phenomena. These phenomena are due to the development of cracks in rocks subjected to strong initial and induced stresses. Fracturing is a form of energy dissipation that restores the balance of the involved medium. The aim of the thesis is to model rock cracks and study the behavior of underground structures at great depths. The development of models able to simulate the fracturing, the coalescence of cracks and their interaction with pre-existing fractures is essential. In the literature, there are two main theoretical and numerical approaches for crack modeling: continuous and discrete. A detailed analysis of these approaches has led us to choose the discrete approach and more particularly the code Yade. This code enables to simulate explicitly cracks propagation with or without pre-existing fractures. Developments have been made to evaluate the different forms of energy involved in rock behavior. In particular, a correlation between the cracks energy determined numerically and the microseismic activity observed in laboratory samples has been performed. The various energy components developed and then implemented in Yade are: external work, potential energy, elastic energy, friction energy, cracks energy, kinetic energy and damping energy. Validation of the energy approach was carried out by simulating laboratory tests. The evolution of the various energy components permits to verify that the energy balance is correctly evaluated. The energy balance was also verified at a structure scale by simulating the underground excavation of a Mine-by Experiment (URL Manitoba). The extension of the damaged zone induced by excavation and predicted by numerical simulations was compared with that observed in-situ around the Mine-by Experiment. It has been found that the predicted and the observed damage are similar in the directions of initial minor and major initial stresses. In addition, the energy formulation enables to study numerically the fracturing process of rocks. Wassermann (2006) performed uniaxial and triaxial compression tests on samples of iron ore from Lorraine. We have modeled these tests. The qualitative comparison of acoustic events and cracks energies determined from tests and numerical simulations showed similar trends. On the other hand, the quantitative comparison showed that the number of numerical acoustic events is greater than the number of experimental acoustic events. Also, the energy dissipated by cracks determined numerically is greater than the energy measured in the tests. This difference is explained by sensors accuracy of the experimental device, which are not able to detect all the generated acoustic events. The results obtained will allow us to better understand the dynamic phenomena in the deep underground structures. Another application consisted in modeling an iron ore pillar of Joeuf (Lorraine). The numerical model shows two modes of cracking in the pillar: (a) flaking of pillar wall, (b) two breaking bands initiating from the wall and the roof of the pillar to propagate towards his core. This provides good perspectives for better understanding cracks propagation at a larger scale, also to progress in the understanding of the correlation between geomechanics and geophysics
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Lieboldt, Matthias, and Viktor Mechtcherine. "Medientransport durch Verstärkungsschichten aus textilbewehrtem Beton." Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2009. http://nbn-resolving.de/urn:nbn:de:bsz:14-ds-1244045285527-10721.
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In den durchgeführten Versuchsreihen wurden die Wasserabsorption sowie die Gas- und Wasserpermeabilität sowohl an gerissenen als auch rissfreien Prüfkörpern aus textilbewehrtem Beton (TRC) untersucht. Eine deutliche Steigerung der Wasseraufnahme bei Proben mit unbeschichteten Textilien konnte mit Zunahme der Garnfeinheit beobachtet werden. Bei den gerissenen Proben besteht eine ausgeprägte Abhängigkeit der Transportraten von Flüssigkeiten und Gasen zu den relevanten Risscharakteristika (kumulative Risslänge, Rissbreite). Weiterhin sind Selbstheilungseffekte von feinen Rissen infolge einer zyklischen Wasserbeaufschlagung beobachtet worden. Hierbei kam es zu einer deutlichen Reduzierung der Transportraten sowohl für Wasser als auch für Gase. Eine speziell entwickelte Permeabilitätsmesskammer zur Durchführung von In- Situ-Messungen ermöglicht Untersuchungen zum Stofftransport unter axialer Zugbelastung bei verschiedenen Dehnungszuständen.
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Cai, Qingbo. "Finite element modelling of cracking in concrete gravity dams." Thesis, Pretoria : [s.n.], 2007. http://upetd.up.ac.za/thesis/available/etd-01302008-160623.
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Nejadi, Shamsaddin Civil & Environmental Engineering Faculty of Engineering UNSW. "Time-dependent cracking and crack control in reinforced concrete structures." Awarded by:University of New South Wales. School of Civil and Environmental Engineering, 2005. http://handle.unsw.edu.au/1959.4/22440.
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Due to the relatively low tensile strength of concrete, cracks are inevitable in reinforced concrete structures. Therefore, studying the cracking behaviour of reinforced concrete elements and controlling the width of cracks are necessary objectives both in research and in design. The introduction of higher strength reinforcing steel has exacerbated the problem of crack control. Using higher strength steel, means less steel is required for a given structure to satisfy the strength requirements. The stiffness after cracking is reduced and wider crack widths will occur under normal service loads. Unserviceable cracking may encourage corrosion in the reinforcement and surface deterioration, and may lead to long term problems with durability. Indeed excessive cracking results in a huge annual cost to the construction industry because it is the most common cause of damage in concrete structures. In this study cracking caused by both shrinkage and external loads in reinforced concrete members is examined experimentally and analytically. The mechanisms associated with cracking and the factors affecting the time-varying width and spacing of both direct tension cracks due to restrained shrinkage deformation and flexural cracks due to the combined effects of constant sustained service loads and shrinkage are examined. Laboratory tests on eight fully restrained slab specimens were conducted for up to 150 days to measure the effects of drying shrinkage on the time-dependent development of direct tension cracks due to restrained deformation. The effect of varying the quantity, diameter, and spacing of reinforcing steel bars was studied. In addition, an analytical model previously developed without experimental verification by Gilbert (1992) to study shrinkage cracking was modified and recalibrated. A second series of tests on twenty four prismatic, singly reinforced concrete beams and slabs subjected to monotonically increasing loads or to constant sustained service loads for up to 400 days, were also conducted. The effects of steel area, steel stress, bar diameter, bar spacing, concrete cover and shrinkage were measured and quantified. An analytical model is presented to simulate instantaneous and time-dependent flexural cracking. The tension chord model (Marti et al, 1998) is modified and used in the proposed model to simulate the tension zone of a flexural member and the time-dependent effects of creep and shrinkage are included. The analytical predictions of crack width and crack spacing are in reasonably good agreement with the experimental observations.
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Dorfman, Susannah M. "Permeability modifying processes : thermal cracking and crack healing of geomaterials." Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/114114.
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Thesis: S.B., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2005.Cataloged from PDF version of thesis. Pages 29-37, 42 and 46 not in original thesis.
Includes bibliographical references (pages 44-48).
We explored two complementary mechanisms for change in porosity and permeability of geomaterials: thermal cracking and crack healing by diagenesis. A suite of thermal cracking experiments was performed on andesite plugs from the geothermal field in Awibengkok, Indonesia. Permeability (k) and specific storage capacity were measured by the oscillating flow method in a wide range permeameter, at room temperature, with effective pressures between 15 MPa and 95 MPa, before and after thermal cracking. The samples were cracked at 150 and 300 °C and ambient pressure. Andesite samples have low permeability, on the order of 10-²⁰ M² . With increased pressure, permeability is reduced by a factor of two. Contrary to expectations, thermal cracking reduced the permeability of this material by an order of magnitude. We also examined a set of samples from crack healing experiments performed on Sioux quartzite by M. Messar. In these experiments the quartzite permeability fell by three orders of magnitude within a few days when the samples were saturated with water and heated to temperatures from 300 to 500 °C and pressures from 25 to 200 MPa. In order to correlate Messar's permeability measurements and experimental conditions with visual observations of the pore structure (mainly consisting of grain boundary cracks), we took scanning electron microscope micrographs of the samples. We then counted the intersections of test lines with healed and unhealed cracks. This yielded a set of measurements of the crack area per volume of the quartzite. We found that the final permeability of the samples was related to the area per volume of unhealed cracks by a power relation. Combining the findings from the two sets of experiments, it seems that cracking and healing effects due to the ambient temperature and pressure in geothermal fields such as Awibengkok could eliminate any permeability through grain boundary scale cracks within a matter of days.
by Susannah Dorfman.
S.B.
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Nguyen, Olivier T. Ortiz Michael. "Cohesive models of fatigue crack growth and stress-corrosion cracking /." Diss., Pasadena, Calif. : California Institute of Technology, 2002. http://resolver.caltech.edu/CaltechETD:etd-12032004-161201.
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Agustini, Márcia Cristine. "Crackin' the code of post-race." reponame:Repositório Institucional da UFSC, 2013. https://repositorio.ufsc.br/xmlui/handle/123456789/122783.
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Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro de Comunicação e Expressão, Programa de Pós-Graduação em Inglês: Estudos Linguísticos e Literários, Florianópolis, 2013.Made available in DSpace on 2014-08-06T17:22:07Z (GMT). No. of bitstreams: 1 325938.pdf: 1366756 bytes, checksum: 08b1972334b52728fa8f574a3b9e0053 (MD5) Previous issue date: 2013
Abstract : The last decades has seen a shift in racial thought in the U.S. The discourses vary from the statement that the U.S. has moved beyond race to the post-racial neoliberalist discourse in which 'essential' identities are fragments of a social past and its continuance has the function of renewing race and racism. As these discourses gain ground in the U.S. society, the issue of fighting racism becomes more slippery. The present investigation analyzes the meanings attached to the rebirth of novels that deals with the concept of passing for white in this period and its relation with the fragmentation of the color line. More specifically, the aim of this dissertation is to unveil the forms through which No Telephone to Heaven, Caucasia, and The Girl Who Fell from the Sky respond to the discourses of racial liberalism and Critical Realism. Drawing upon Santiago?s concept of in-betweenness and Butler's concept of performativity, this dissertation sought to analyze the novels chosen as rich sources of insight about the changing racial thought in the U.S.
As últimas décadas registraram uma mudança no pensamento racial nos Estados Unidos. Os discursos variam da afirmação de que os Estados Unidos transcendeu a questão racial ao discurso neoliberalista pós-racial que considera identidades 'essenciais' como fragmentos de um passado social e sua continuação apenas renova os conceitos de raça e racismo. A medida que esses discursos se tornam dominantes nos Estados Unidos, a questão do combate ao racismo se torna mais incerta. A presente investigação analisa os significados ligados ao reaparecimento de romances que lidam com o conceito de 'passar por branco' neste período e sua relação com a fragmentação da ?color line?. Mais especificamente, o objetivo deste estudo é investigar a forma que No Telephone to Heaven, Caucasia, and The Girl Who Fell from the Sky respondem aos discursos de liberalismo racial e Realismo Crítico. Com base no conceito de ?entre-lugar? de Santiago e o conceito de performatividade de Butler, esta tese procurou analisar as novelas escolhidas como fontes ricas de compreensão do pensamento racial nos Estados Unidos.
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Mackay, F. G. "The application of the J-integral to stress corrosion cracking." Thesis, University of Newcastle Upon Tyne, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.384084.
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Foulkes, Michael David. "Assessment of asphalt materials to relieve reflection cracking of highway surfacings." Thesis, University of Plymouth, 1998. http://hdl.handle.net/10026.1/2576.
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The thesis investigates the mechanisms and restraints which influence transverse crack propagation through the bituminous surfacings of semi-flexible pavements. These pavements incorporate continuously laid cement bound roadbases which, during curing, crack into slabs of varying length, ranging from 4-25m. Reciprocal crack growth can occur in the surfacing, known as 'reflection cracks', located through stresses concentrated at the discontinuities within the roadbase . Three mechanisms have been identified and are described as contributing to reflection crack propagation. They have been analysed independently although the majority of conclusions drawn are applicable to their combined action. Their relative importance will vary with respect to pavement geometry, material properties, environmental conditions and traffic intensity. The first mechanism, 'tensile fatigue', induces crack propagation vertically upward through the surfacing. Tensile strains are developed during daily and ru1nual fluctuations of temperature, which cause expansion and contraction of the cement bound roadbase. This mechanism is most prominent on pavements with thin surfacings and long slab lengths. The rate of crack growth is dependent on the range of temperature within the roadbase , slab length, thermal characteristics of the roadbase material and resistance of the surfacing to this form of fatigue . A model has been developed based on a combination of results from an extensive testing programme, the use of fracture mechanics theory and computer simulation of the condition. The results quantify the resistance shown by conventional bituminous mixes to reflection cracking in terms of their mix parameters. Also considered are the use of stress relieving membranes, reinforcement material and modified binders to inhibit crack growth. The second mechanism, 'tensile yield' is also thermally induced but associated with cold weather conditions. Temperature gradients through the pavement structure induce warping and contraction within the uppermost layers. Tensile strains developed at the surface can, under U.K. winter temperatures, exceed the ultimate yield strain of the wearing course material. Preliminary. investigations of four pavements constructed in the early 1970's to motorway specifications indicate that reflection cracking will initiate at the surface if the yield strain, as defined through tensile creep tests, is reduced through binder oxidization to a value of 0.5%. This mechanism will operate on pavements with greater structural layer thicknesses and is only partially dependent on slab length. The influence of a further mechanism, 'shear fatigue' induced through trafficking of the pavement, has been shown to be confined to the acceleration of crack growth in the final stages of propagation unless a breakdown of interlock occurs between adjoining roadbase slabs.
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La, Saponara Valeria. "Crack branching in cross-ply composites." Diss., Georgia Institute of Technology, 2001. http://hdl.handle.net/1853/11973.
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Brooker, Timothy Nicholas. "The determination of crack propagation rates of reflection cracking through asphalt surfacings." Thesis, University of Plymouth, 1986. http://hdl.handle.net/10026.1/2791.
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A large proportion of the U.K. highway network constructed in the 1960's and 1970's contains lean concrete roadbase with bituminous surfacing. Pavements containing relatively high strength lean concrete have rarely required structural maintenance (thick overlay or reconstruction) but have required maintenance because of reflection cracking where the surfacing cracks above cracks in the lean concrete. The time of appearance of this cracking is very variable (2-20 years). Field observations indicate that roadbase transverse crack spacings are often greater than 5m. Reflection cracking at these long spacings can be caused by thermal stresses, This project identifies conditions under which ther<ral reflection cracking will occur and develops a predictive model that allows estimation of the combined effect of thermal and traffic stresses. Finite element analyses indicate that initial crack development is likely to be caused by thermal stresses and final cracking will be assisted by traffic stresses. A temperature model has been developed to determine roadbase daily temperature range and surfacing temperature on a mean monthly basis. Thermal reflection cracking is considered to result from daily cycle fatigue rather than an extreme low temperature mechanism. A test rig has been developed to apply cyclic crack opening movements and simulative tests have been accelerated to 0.1Hz by using a "bitumen stiffness" fatigue criterion., Finite element results, displacements recorded during tests and tensile creep tests to determine mix stiffness, enable dc/dN and K 1 values and material constants (A, n) to be determined. This fracture mechanics interpretation of test results serves as the basis of the predictive model for thermal reflection cracking that is consistent with observations from an untrafficked road. The combined estimate of thermal and traffic stresses cannot however explain reflection cracking at<5m spacings. This cracking apparently initiates at the surface and is probably influenced by other mechanisms.
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Lozano-Perez, Sergio. "TEM crack tip investigations of SCC." Thesis, University of Oxford, 2002. http://ora.ox.ac.uk/objects/uuid:7e503ff9-782a-4f74-b184-dddaa96e03e2.
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Over the last few years, TEM has become a powerful technique to study cracks and specially crack tips. However, the number of publications including TEM results has not grown as it was expected. The main reason for this might be difficulties in the sample preparation. In this work we present a novel FIB sample preparation technique which has proved to be an ideal tool for preparing cross sectional samples containing crack tips. The morphology of intergranular stress corrosion cracking (IGSCC) has been investigated in Alloy 600 subjected to constant load and slow strain rate tests in simulated primary circuit pressurized water reactor conditions. Cracks were observed to nucleate at high-angle grain boundaries and propagate to depths of a few tens of micrometer along such boundaries, still in the initiation stage. Electron diffraction, energy dispersive x-ray (EDX) and electron energy loss spectroscopy (EELS) have been used to identify the different corrosion products and precipitates. Elemental mapping was employed to reveal changes in composition in the crack tip area. Major observations at cracks and grain boundaries include: the presence of different oxides in different locations, differences in grain boundary oxides and open crack/free surface oxides. These observations suggest that IGSCC involves oxygen diffusion through a porous oxide region along grain boundaries to the bare metal. This is a novel concept that offers an alternative to previous mechanisms proposed in the literature e.g. H embrittlement, slip-dissolution, etc., for which no supporting evidence has been found.
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Desjarlais, Justin J. "An Examination of Crack Growth in Wood-FRP Bonds." Fogler Library, University of Maine, 2007. http://www.library.umaine.edu/theses/pdf/DesjarlaisJJ2007.pdf.
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Hamm, Richard William. "A multi-regime model comparison for constant amplitude small crack behavior in Ti-6A1-4V." Thesis, Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/16831.
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Baah, Prince. "Cracking Behavior of Structural Slab Bridge Decks." University of Akron / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=akron1417539467.
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Keller, Wesley John. "Effect of Environmental Conditions and Structural Design on Linear Cracking in Virginia Bridge Decks." Thesis, Virginia Tech, 2004. http://hdl.handle.net/10919/31936.
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Chloride-induced corrosion of reinforcing steel is widely accepted as the primary cause of premature deterioration in concrete bridge decks (Brown, M.C., 2002). Since linear cracking in concrete cover can potentially accelerate chloride ingress to the depth of the reinforcing steel, there is reason to believe that severity of deck cracking can significantly influence the time to first repair and/or rehabilitation of the bridge deck.
Surface width, orientation, and length of cracks in 38 Virginia bridge decks were investigated in order to characterize the general distribution of deck cracking in the commonwealth of Virginia. Crack data was correlated to structural/material design parameters and environmental exposure conditions in order to determine significant predictor-response relationships. The majority of surveyed bridge decks were divided into four classifications of deck type based on superstructure type and construction era, either 1968-1971 or 1984-1991. Surveyed bridge decks that did not fit into any of the four classifications were used to form more generalized subsets. These larger subsets were used to determine if significant influence factors could be translated to broader classifications of bridge decks.
Transverse beam spacing, annual average daily truck traffic (AADTT), resistivity of the deck concrete, chloride exposure, and the percentage of concrete clear cover depths less than or equal to 38mm (1.5 in) were all determined to have a significant correlation with linear deck cracking.Master of Science
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Stonkus, Rimantas. "Failure resistance of high-cycle loaded welded joints." Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2012. http://vddb.laba.lt/obj/LT-eLABa-0001:E.02~2012~D_20120223_134248-35614.
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The dissertation investigates the problems of welded joints resistance to fracture, affected by high-cycle load. The object of research is mechanical state of welded joints, formed in construction elements, in which the fracture process begins because of high-cycle load. Examination of fracture mechanism is important to ensure the design and running durability of large-size elements. Detailed analysis and interpretation allows to choose better calculation methodology for welded joints. The main aim of dissertation – to investigate the process of fracture in butted welded joints, which are loaded high-cyclically, to improve calculating methodology according to consistent patterns of crack formation, propagation, stop and complete fracture, defined by experimental analytical researches. The dissertation consists of an introduction, five chapters, summary of results, references and list of author’s publications on dissertation subject. The introduction reveals the investigated problem, the topicality of the issue, the object of research, describes the aim and tasks of the paper, research methodology, scientific novelty, the practical significance of the results examined in the paper and defended propositions. The introduction ends in presenting the author’s publications on dissertation subject and reports in conferences. The first chapter covers the literature review. It reviews the research works closely related to the dissertation topic and presents the topicality and problems... [to full text]Disertacijoje nagrinėjamos suvirintųjų jungčių atsparumo irimui problemos, veikiant daugiacikliam apkrovimui. Tyrimo objektas yra suvirintųjų jungčių mechaninis būvis, susidarantis konstrukcijos elementuose, kuriuose dėl apkrovos daugiacikliškumo prasideda irimo procesas. Suirimo mechanizmo nagrinėjimas yra svarbus didelių gabaritų detalių projektiniam ir eksploataciniam ilgalaikiškumui užtikrinti. Detali analizė ir interpretacija leidžia parinkti tinkamesnę suvirintųjų jungčių skaičiavimo metodiką. Pagrindinis disertacijos tikslas – ištirti irimo procesus suvirintuose sandūriniuose sujungimuose, apkrautuose daugiacikliškai, patobulinti skaičiavimo metodiką pagal plyšio susidarymo, plitimo, sustojimo ir visiško suirimo dėsningumus, nustatytus eksperimentiniais analitiniais tyrimais. Disertaciją sudaro įvadas, penki skyriai, rezultatų apibendrinimas, naudotos literatūros ir autoriaus publikacijų disertacijos tema sąrašai. Įvade aptariama tiriamoji problema, darbo aktualumas, aprašomas tyrimų objektas, formuluojamas darbo tikslas bei uždaviniai, aprašoma tyrimų metodika, darbo mokslinis naujumas, darbo rezultatų praktinė reikšmė, ginamieji teiginiai. Įvado pabaigoje pristatomos disertacijos tema autoriaus paskelbtos publikacijos ir pranešimai konferencijose bei disertacijos struktūra. Pirmasis skyrius skirtas literatūros analizei. Jame apžvelgiami moksliniai darbai, glaudžiai susiję su disertacijos tematika, pateikiama daugiaciklio stiprumo suvirintuose komponentuose aktualijos... [toliau žr. visą tekstą]
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Hassan, Tasnim. "NUMERICAL STUDY OF TRANSIENT RESPONSE OF AN INTERFACE-CRACK IN A TWO LAYERED PLATE (ANTI-PLANE, STRESS INTENSITY FACTOR)." Thesis, The University of Arizona, 1985. http://hdl.handle.net/10150/275474.
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Yao, Lan. "Experimental and numerical study of dynamic crack propagation in ice under impact loading." Thesis, Lyon, 2016. http://www.theses.fr/2016LYSEI043/document.
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Les phénomènes liés au comportement à la rupture de la glace sous impact sont fréquents dans le génie civil, pour les structures offshore, et les processus de dégivrage. Pour réduire les dommages causés par l'impact de la glace et optimiser la conception des structures ou des machines, l'étude sur le comportement à la rupture dynamique de la glace sous impact est nécessaire. Ces travaux de thèse portent donc sur la propagation dynamique des fissures dans la glace sous impact. Une série d'expériences d'impact est réalisée avec un dispositif de barres de Hopkinson. La température est contrôlée par une chambre de refroidissement. Le processus dynamique de la rupture de la glace est enregistré avec une caméra à grande vitesse et ensuite analysé par des méthodes d'analyse d'images. La méthode des éléments finis étendus complète cette analyse pour évaluer la ténacité dynamique. Au premier abord, le comportement dynamique de la glace sous impact est étudié avec des échantillons cylindriques afin d'établir la relation contrainte-déformation dynamique qui sera utilisée dans les simulations numériques plus tard. Nous avons observé de multi-fissuration dans les expériences sur les échantillons cylindriques mais son étude est trop difficile à mener. Pour mieux comprendre la propagation des fissures dans la glace, des échantillons rectangulaires avec une pré-fissure sont employés. En ajustant la vitesse d'impact on aboutit à la rupture des spécimens avec une fissure principale à partir de la pré-fissure. L'histoire de la propagation de fissure et de sa vitesse sont évaluées par analyse d'images basée sur les niveaux de gris et par corrélation d'images. La vitesse de propagation de la fissure principale est identifiée dans la plage de 450 à 610 m/s ce qui confirme les résultats précédents. Elle varie légèrement au cours de la propagation, dans un premier temps elle augmente et se maintient constante ensuite et diminue à la fin. Les paramètres obtenus expérimentalement, tels que la vitesse d'impact et la vitesse de propagation de fissure, sont utilisés pour la simulation avec la méthode des éléments finis étendus. La ténacité d'initiation dynamique et la ténacité dynamique en propagation de fissure sont déterminées lorsque la simulation correspond aux expériences. Les résultats indiquent que la ténacité dynamique en propagation de fissure est linéaire vis à vis de la vitesse de propagation et semble indépendante de la température dans l'intervalle -15 à -1 degrésThe phenomena relating to the fracture behaviour of ice under impact loading are common in civil engineering, for offshore structures, and de-ice processes. To reduce the damage caused by ice impact and to optimize the design of structures or machines, the investigation on the dynamic fracture behaviour of ice under impact loading is needed. This work focuses on the dynamic crack propagation in ice under impact loading. A series of impact experiments is conducted with the Split Hopkinson Pressure Bar. The temperature is controlled by a cooling chamber. The dynamic process of the ice fracture is recorded with a high speed camera and then analysed by image methods. The extended finite element method is complementary to evaluate dynamic fracture toughness at the onset and during the propagation. The dynamic behaviour of ice under impact loading is firstly investigated with cylindrical specimen in order to obtain the dynamic stress-strain relation which will be used in later simulation. We observed multiple cracks in the experiments on the cylindrical specimens but their study is too complicated. To better understand the crack propagation in ice, a rectangular specimen with a pre-crack is employed. By controlling the impact velocity, the specimen fractures with a main crack starting from the pre-crack. The crack propagation history and velocity are evaluated by image analysis based on grey-scale and digital image correlation. The main crack propagation velocity is identified in the range of 450 to 610 m/s which confirms the previous results. It slightly varies during the propagation, first increases and keeps constant and then decreases. The experimentally obtained parameters, such as impact velocity and crack propagation velocity, are used for simulations with the extended finite element method. The dynamic crack initiation toughness and dynamic crack growth toughness are determined when the simulation fits the experiments. The results indicate that the dynamic crack growth toughness is linearly associated with crack propagation velocity and seems temperature independent in the range -15 to -1 degrees
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Wu, Yi, and 吳奕. "Post-crack and post-peak behavior of reinforced concrete members by nonlinear finite element analysis." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2006. http://hub.hku.hk/bib/B37006447.
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Arne, Kevin C. "Crack depth measurement in reinforced concrete using ultrasonic techniques." Thesis, Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/51914.
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Concrete is the most widely used construction material in the world, so the assessment of damage in concrete is critical from the point of view of both safety and cost. Of particular interest are macro cracks that extend through the concrete cover of the reinforcement, which can potentially expose the reinforcement to corrosive elements. The high density of scatterers such as aggregate and voids in concrete makes quantitative imaging with coherent ultrasound difficult. As an alternative, this research focuses on diffuse energy based ultrasonic methods rather than coherent ultrasonic methods for crack depth assessment. Two types of ultrasonic measurements were made on real cracks formed under four point bending: one that focuses on time of flight measurements from an impactor; while the other uses the arrival time of maximum energy in a diffuse field excited by an impulsive load from a transducer. Each of these ultrasonic techniques is used to interrogate a macro crack in a concrete beam, and the results are compared to determine their accuracy and robustness. The actual crack depth is determined using direct surface measurements and a destructive dye-injected approach with drilled cores. The results suggest that the diffusion method, using a maximum energy approach, more accurately estimates the crack than visual inspection and impact echo methods, which overestimate the depth.
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Barbe, Andre. "A critical assessment of crack growth criteria in unidirectional composites." Thesis, Virginia Polytechnic Institute and State University, 1985. http://hdl.handle.net/10919/90908.
Full textAbstract:
The problem examined is an infinite anisotropic layer with a through crack at arbitrary orientation, subjected to uniform in-plane remote loading. The purpose of this study is to gain a better understanding of several theoretical models for predicting the direction of crack propagation and the level of load causing crack extension, and to present a new model for predicting the critical load. The discussed models are particularly examined in detail with regard to the physical parameters affecting the results. Comparison is made with available experimental results. It is shown that the normal stress ratio theory provides good agreement with experimental crack growth direction, independent of physical parameters, and that the newly proposed traction ratio theory predicts well the critical load causing crack extension.M.S.