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Kathavate, V. S., K. Eswar Prasad, Mangalampalli S. R. N. Kiran, and Yong Zhu. "Mechanical characterization of piezoelectric materials: A perspective on deformation behavior across different microstructural length scales." Journal of Applied Physics 132, no. 12 (September 28, 2022): 121103. http://dx.doi.org/10.1063/5.0099161.
Повний текст джерелаАнотація:
Piezoelectric materials (PEMs) find a wide spectrum of applications that include, but are not limited to, sensors, actuators, semiconductors, memory devices, and energy harvesting systems due to their outstanding electromechanical and polarization characteristics. Notably, these PEMs can be employed across several length scales (both intrinsic and extrinsic) ranging from mesoscale (bulk ceramics) to nanoscale (thin films) during their applications. Over the years, progress in probing individual electrical and mechanical properties of PEM has been notable. However, proportional review articles providing the mechanical characterization of PEM are relatively few. The present article aims to give a tutorial on the mechanical testing of PEMs, ranging from the conventional bulk deformation experiments to the most recent small-scale testing techniques from a materials science perspective. The advent of nanotechnology has led materials scientists to develop in situ testing techniques to probe the real-time electromechanical behavior of PEMs. Therefore, this article presents a systematic outlook on ex situ and in situ deformation experiments in mechanical and electromechanical environments, related mechanical behavior, and ferroelectric/elastic distortion during deformation. The first part provides significant insights into the multifunctionality of PEM and various contributing microstructural length scales, followed by a motivation to characterize the mechanical properties from the application's point of view. In the midst, the mechanical behavior of PEM and related mechanical characterization techniques (from mesoscale to nanoscale) are highlighted. The last part summarizes current challenges, future perspectives, and important observations.
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Tao, Ran, Kirk Rice, Anicet Djakeu, Randy Mrozek, Shawn Cole, Reygan Freeney, and Aaron Forster. "Rheological Characterization of Next-Generation Ballistic Witness Materials for Body Armor Testing." Polymers 11, no. 3 (March 8, 2019): 447. http://dx.doi.org/10.3390/polym11030447.
Повний текст джерелаАнотація:
Roma Plastilina No. 1 (RP1), an artist modeling clay that has been used as a ballistic clay, is essential for evaluation and certification in standards-based ballistic resistance testing of body armor. It serves as a ballistic witness material (BWM) behind the armor, where the magnitude of the plastic deformation in the clay after a ballistic impact is the figure of merit (known as “backface signature”). RP1 is known to exhibit complex thermomechanical behavior that requires temperature conditioning and frequent performance-based evaluations to verify that its deformation response satisfies requirements. A less complex BWM formulation that allows for room-temperature storage and use as well as a more consistent thermomechanical behavior than RP1 is desired, but a validation based only on ballistic performance would be extensive and expensive to accommodate the different ballistic threats. A framework of lab-scale metrologies for measuring the effects of strain, strain rate, and temperature dependence on mechanical properties are needed to guide BWM development. The current work deals with rheological characterization of a candidate BWM, i.e., silicone composite backing material (SCBM), to understand the fundamental structure–property relationships in comparison to those of RP1. Small-amplitude oscillatory shear frequency sweep experiments were performed at temperatures that ranged from 20 °C to 50 °C to map elastic and damping contributions in the linear elastic regime. Large amplitude oscillatory shear (LAOS) experiments were conducted in the non-linear region and the material response was analyzed in the form of Lissajous curve representations with the values of perfect plastic dissipation ratio reported to identify the degree of plasticity. The results show that the SCBM exhibits dynamic properties that are similar in magnitude to those of temperature-conditioned RP1, but with minimal temperature sensitivity and weaker frequency dependence than RP1. Both SCBM and RP1 are identified as elastoviscoplastic materials, which is particularly important for accurate determination of backface signature in body armor evaluation. The mechanical properties of SCBM show some degree of aging and work history effects. The results from this work demonstrate that the rheological properties of SCBM, at small and large strains, are similar to RP1 with substantial improvements in BWM performance requirements in terms of temperature sensitivity and thixotropy.
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Oliver, W. C., and G. M. Pharr. "Measurement of hardness and elastic modulus by instrumented indentation: Advances in understanding and refinements to methodology." Journal of Materials Research 19, no. 1 (January 2004): 3–20. http://dx.doi.org/10.1557/jmr.2004.19.1.3.
Повний текст джерелаАнотація:
The method we introduced in 1992 for measuring hardness and elastic modulus by instrumented indentation techniques has widely been adopted and used in the characterization of small-scale mechanical behavior. Since its original development, the method has undergone numerous refinements and changes brought about by improvements to testing equipment and techniques as well as from advances in our understanding of the mechanics of elastic–plastic contact. Here, we review our current understanding of the mechanics governing elastic–plastic indentation as they pertain to load and depth-sensing indentation testing of monolithic materials and provide an update of how we now implement the method to make the most accurate mechanical property measurements. The limitations of the method are also discussed.
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Anton, Hadăr, Baciu Florin, Voicu Andrei-Daniel, Vlăsceanu Daniel, Tudose Daniela-Ioana, and Adetu Cătălin. "Mechanical Characteristics Evaluation of a Single Ply and Multi-Ply Carbon Fiber-Reinforced Plastic Subjected to Tensile and Bending Loads." Polymers 14, no. 15 (August 7, 2022): 3213. http://dx.doi.org/10.3390/polym14153213.
Повний текст джерелаАнотація:
Carbon fiber-reinforced composites represent a broadly utilized class of materials in aeronautical applications, due to their high-performance capability. The studied CFRP is manufactured from a 3K carbon biaxial fabric 0°/90° with high tensile resistance, reinforced with high-performance thermoset molding epoxy vinyl ester resin. The macroscale experimental characterization has constituted the subject of various studies, with the scope of assessing overall structural performance. This study, on the other hand, aims at evaluating the mesoscopic mechanical behavior of a single-ply CFRP, by utilizing tensile test specimens with an average experimental study area of only 3 cm2. The single-ply tensile testing was accomplished using a small scale custom-made uniaxial testing device, powered by a stepper motor, with measurements recorded by two 5-megapixel cameras of the DIC Q400 system, mounted on a Leica M125 digital stereo microscope. The single-ply testing results illustrated the orthotropic nature of the CFRP and turned out to be in close correlation with the multi-ply CFRP tensile and bending tests, resulting in a comprehensive material characterization. The results obtained for the multi-ply tensile and flexural characteristics are adequate in terms of CFRP expectations, having a satisfactory precision. The results have been evaluated using a broad experimental approach, consisting of the Dantec Q400 standard digital image correlation system, facilitating the determination of Poisson’s ratio, correlated with the measurements obtained from the INSTRON 8801 servo hydraulic testing system’s load cell, for a segment of the tensile and flexural characteristics determination. Finite element analyses were realized to reproduce the tensile and flexural test conditions, based on the experimentally determined stress–strain evolution of the material. The FEA results match very well with the experimental results, and thus will constitute the basis for further FEA analyses of aeronautic structures.
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Oliver, Warren C., and George M. Pharr. "Nanoindentation in materials research: Past, present, and future." MRS Bulletin 35, no. 11 (November 2010): 897–907. http://dx.doi.org/10.1557/mrs2010.717.
Повний текст джерелаАнотація:
The method we introduced in 1992 for measuring hardness and elastic modulus by nanoindentation testing has been widely adopted and used in the characterization of mechanical behavior at small scales. Since its original development, the method has undergone numerous refinements and changes brought about by improvements to testing equipment and techniques, as well as advances in our understanding of the mechanics of elastic-plastic contact. In this article, we briefly review the history of the method, comment on its capabilities and limitations, and discuss some of the emerging areas in materials research where it has played, or promises to play, an important role.
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Lang, Anna, Oliver Focke, and Axel S. Herrmann. "Mechanical Behavior of Loops with Small Diameters." Key Engineering Materials 742 (July 2017): 374–80. http://dx.doi.org/10.4028/www.scientific.net/kem.742.374.
Повний текст джерелаАнотація:
To meet the comprehensive requirements of lightweight design, a material minded design method will be aimed. A fiber minded solution for load application in fiber reinforced plastics are loop joints, which are mainly applied for introducing high concentrated tensile loads, e.g. in mountings for rotor blades, or in pre-tensioned supporting structures. Usually, these loop joints consist of, diameters in centimeter scale. Miniaturized loop joints with diameters in millimeter scale are applied in transition structures for carbon reinforced plastic-aluminum multi material designs. Factors of miniaturization influencing the mechanical behavior are decoupled for tensile testing. Data from computer tomography provides information on the failure behavior of loop joints. To validate the non-destructive test method microsections will be used.
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Sancaktar, Erol. "Constitutive Behavior and Testing of Structural Adhesives." Applied Mechanics Reviews 40, no. 10 (October 1, 1987): 1393–402. http://dx.doi.org/10.1115/1.3149541.
Повний текст джерелаАнотація:
Material characterization of structural adhesives in the bulk and bonded forms is discussed. Constitutive relations used for describing stress–strain data are reviewed. The difficulties associated with adhesive characterization in the bonded form are cited. Common testing procedures for adhesive characterization in the bulk and bonded forms are reviewed. In presenting the constitutive relations used in material characterization of structural adhesives, deformation theories introduced by Hencky are reviewed first. The modifications made in this theory to render it rate dependent and bilinear are discussed and applications to adhesive characterization are cited. Application of linear viscoelasticity, mechanical model characterization, and its use in describing the dependence of adhesive and cohesive strengths on rate, temperature, and bond thickness are presented. The time–temperature superposition principle and three-dimensional stress–strain relations in integral and differential operator forms are reviewed. Frequent assumptions for dilatation and distortion operations are presented. Procedures for describing nonlinear viscoelastic behavior are reviewed. It is pointed out that the extent of nonlinearity is dependent on both the stress level and the time scale. The use of nonlinear spring and dashpot elements, nonlinear differential operators, and perturbation of elastic and viscous coefficients are cited. Prandtl’s incremental theory of plasticity and its extension in the form of over-stress theory is presented. The incorporation of this over-stress idea into the viscoelastic mechanical model characterization is discussed. The modified Bingham model and the Chase–Goldsmith model developed in this fashion and their application to adhesive material characterization are presented. The use of empirical relations for the description of creep behavior is discussed. Prediction of shear behavior based on bulk tensile data is demonstrated. It is suggested that characterization of adhesive behavior in the bonded form should include the application of stress analysis, fracture mechanics, polymer chemistry and surface analysis techniques. In testing bonded samples the use of thick adherend symmetric single lap geometry or napkin ring test geometry is advised and it is suggested that the specimens should be prepared with the same surface preparation and cure techniques.
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Vogel, D., R. Ku¨hnert, M. Dost, and B. Michel. "Determination of Packaging Material Properties Utilizing Image Correlation Techniques." Journal of Electronic Packaging 124, no. 4 (December 1, 2002): 345–51. http://dx.doi.org/10.1115/1.1506698.
Повний текст джерелаАнотація:
Thermo-mechanical reliability in advanced electronic packaging requires new materials testing approaches. The necessary understanding of the impact of very local material stressing on component reliability leads to the need of materials testing and characterization on microscopic scale. For example, defect initiation and propagation in multilayer structures as in WLP and flip chip technology, the influence of material migration to mechanical behavior or defect development in ultra-thin silicon dies often are not well understood. A key for micro materials testing and characterization is the measurement of strains and displacements inside microscopic regions. Correlation techniques (e.g., microDAC, nanoDAC) are one of the promising tools for that purpose. Their application potentials to micro testing for electronic packaging materials are demonstrated in the paper. More in detail, CTE measurement and crack testing are discussed. First attempts for testing under AFM conditions and their results are considered.
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Liu, Dong, Peter Heard, Branko Šavija, Gillian Smith, Erik Schlangen, and Peter Flewitt. "Multi-scale characterization and modelling of damage evolution in nuclear Gilsocarbon graphite." MRS Proceedings 1809 (2015): 1–6. http://dx.doi.org/10.1557/opl.2015.433.
Повний текст джерелаАнотація:
ABSTRACTIn the present work, the microstructure and mechanical properties of Gilsocarbon graphite have been characterized over a range of length-scales. Optical imaging, combined with 3D X-ray computed tomography and 3D high-resolution tomography based on focus ion beam milling has been adopted for microstructural characterization. A range of small-scale mechanical testing approaches are applied including an in situ micro-cantilever technique based in a Dualbeam workstation. It was found that pores ranging in size from nanometers to tens of micrometers in diameter are present which modify the deformation and fracture characteristics of the material. This multi-scale mechanical testing approach revealed the significant change of mechanical properties, for example flexural strength, of this graphite over the length-scale from a micrometer to tens of centimeters. Such differences emphasize why input parameters to numerical models have to be undertaken at the appropriate length-scale to allow predictions of the deformation, fracture and the stochastic features of the strength of the graphite with the required confidence. Finally, the results from a multi-scale model demonstrated that these data derived from the micro-scale tests can be extrapolated, with high confidence, to large components with realistic dimensions.
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Field, J. S., and M. V. Swain. "Determining the mechanical properties of small volumes of material from submicrometer spherical indentations." Journal of Materials Research 10, no. 1 (January 1995): 101–12. http://dx.doi.org/10.1557/jmr.1995.0101.
Повний текст джерелаАнотація:
The stress/strain behavior of bulk material is usually investigated in uniaxial tension or compression; however, these methods are not generally available for very small volumes of material. Submicrometer indentation using a spherical indenter has the potential for filling this gap with, possibly, access to hardness and elastic modulus profiles, representative stress/strain curves, and the strain hardening index. The proposed techniques are based on principles well established in hardness testing using spherical indenters, but not previously applied to depth-sensing instruments capable of measurements on a submicrometer scale. These approaches are now adapted to the analysis of data obtained by stepwise indentation with partial unloading, a technique that facilitates separation of the elastic and plastic components of indentation at each step and is able to take account of the usually ignored phenomena of “piling up” and “sinking in”.
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Kchaou, Mohamed, Amira Sellami, Jamal Fajoui, Recai Kus, Riadh Elleuch, and Frédéric Jacquemin. "Tribological performance characterization of brake friction materials: What test? What coefficient of friction?" Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology 233, no. 1 (March 25, 2018): 214–26. http://dx.doi.org/10.1177/1350650118764167.
Повний текст джерелаАнотація:
This article describes and explains the tribological tests and methods for the evaluation of the performance of the brake friction materials. It starts by discussing the particularities of these materials and the variation of characterization tests, which can experimentally simulate many aspects of brake situation but with a large field of tribo-test, from standard to specific protocol. Examples of preparation, procedures, instrumentation, and analysis results for the tribological aspect testing ranging from the scale of vehicle braking performance (by methods including inertia dynamometers, Krauss testing, friction assessment screening test, and Chase testing) to simplified test using reduced-scale prototypes for small-sample friction, are explained. A particular attention is attributed to the discussion of the viability of the friction coefficient report in relation to the material properties and brake compound performance. At the end of this article, the guarantee of the performance output or ranking evaluated by such experimental methods is discussed.
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Gavin, H. P., R. D. Hanson, and F. E. Filisko. "Electrorheological Dampers, Part II: Testing and Modeling." Journal of Applied Mechanics 63, no. 3 (September 1, 1996): 676–82. http://dx.doi.org/10.1115/1.2823349.
Повний текст джерелаАнотація:
Electrorheological (ER) materials develop yield stresses on the order of 5–10 kPa in the presence of strong electric fields. Viscoelastic and yielding material properties can be modulated within milli-seconds. An analysis of flowing ER materials in the limiting case of fully developed steady flow results in simple approximations for use in design. Small-scale experiments show that these design equations can be applied to designing devices in which the flow is unsteady. More exact models of ER device behavior can be determined using curve-fitting techniques in multiple dimensions. A previously known curve-fitting technique is extended to deal with variable electric fields. Experiments are described which illustrate the potential for ER devices in large-scale damping applications and the accuracy of the modeling technique.
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Guo, Y. B., and A. W. Warren. "Microscale Mechanical Behavior of the Subsurface by Finishing Processes." Journal of Manufacturing Science and Engineering 127, no. 2 (April 25, 2005): 333–38. http://dx.doi.org/10.1115/1.1807853.
Повний текст джерелаАнотація:
Hard turning, grinding, and honing are common finishing processes in today’s production. The machined subsurface undergoes severe deformation and possible microstructure changes in a small scale subsurface layer <20μm. Mechanical behavior of this shallow layer is critical for component performance such as fatigue and wear. Due to the small size of this region, mechanical behavior of this shallow layer is hard to measure using traditional material testing. With the nanoindentation method, mechanical behavior (nanohardness and modulus) at the microscale in subsurface was measured for AISI 52100 and AISI 1070 steel components machined by hard turning, grinding, and honing. The test results show that white layer increases nanohardness but decreases modulus of a turned surface. Nanohardness and modulus of the ground surface are slightly smaller than the honed one in the subsurface. However, grinding produces higher nanohardness and modulus in near-surface <10μm than honing, while honing produces more uniform hardness and modulus in the near-surface and subsurface, and would improve component performance. Nanohardness and modulus of the machined near-surface are strongly influenced by strain hardening, residual stress, size-effect, and microstructure changes.
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Ishikawa, Tatsuya, Etsuo Sekine, and Seiichi Miura. "Cyclic deformation of granular material subjected to moving-wheel loads." Canadian Geotechnical Journal 48, no. 5 (May 2011): 691–703. http://dx.doi.org/10.1139/t10-099.
Повний текст джерелаАнотація:
This paper describes a new testing method to examine the mechanical behavior of railroad ballast subjected to repeated train passages on ballasted track. Two types of cyclic loading tests, namely a single-point loading test and a moving-wheel loading test, were performed with small-scale models of ballasted track. Next, a “multi-ring shear apparatus” was developed as a type of torsional simple shear apparatus, and the applicability of a newly proposed multi-ring shear test to an element test of railroad ballast subjected to moving-wheel loads was examined by comparing the results of multi-ring shear tests with those of small-scale model tests. As a result, it was recognized that cumulative strain obtained from multi-ring shear tests is almost equivalent to the one derived from small-scale model tests. Moreover, it was revealed that the difference between loading methods has a considerable influence on the cyclic plastic deformation of railroad ballast because settlement in a moving-wheel loading test was much larger than the one in a single-point loading test. These results lead to the conclusion that a multi-ring shear test has an excellent applicability to the estimation of deformation behavior of granular materials subjected to moving-wheel loads.
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Kaiser, Trent M. V. "Post-Yield Material Characterization for Strain-Based Design." SPE Journal 14, no. 01 (March 1, 2009): 128–34. http://dx.doi.org/10.2118/97730-pa.
Повний текст джерелаАнотація:
Summary Conventional material specifications and test methods were developed to support load-based designs in which inelastic deformations are relatively small and yield strength is the primary material factor governing design. However, in strain-based designs where substantial portions of the structure soften under post-yield deformation, more detailed characterization of the post-yield material behavior is required. This paper presents a framework for describing the post-yield properties of metals (including strain-rate dependence of yield strength) a testing method for measuring post-yield strength in terms of strain and strain rate, and an analytical basis for extrapolating measured properties to static conditions for strain-based design and quality assurance (QA). Introduction Typical test specifications for determining the mechanical properties of oil-country tubular goods (OCTG) were developed to provide an index of mechanical strength to support common load-based design methods. Advancing recovery techniques impose conditions on many well structures that exceed the limits of these methods and the material characterizations on which they are founded. Among these new techniques are those used to recover heavy oil. While typical conditions in heavy-oil reservoirs appear benign, enhanced-oil-recovery (EOR) methods such as thermal stimulation and ultrahigh sand production create some of the most challenging conditions for well structures. Imposed deformations commonly exceed the yield limit of the material, therefore post-yield material characteristics govern much of the structural response. Industry-standard material tests provide only limited characterization of post-yield behavior, particularly at strain levels near the yield point (both pre- and post-yield). Furthermore, test strain rates can affect the measured material strength significantly. Field loading usually occurs at much lower rates and is then sustained for extended periods. A method for characterizing post-yield material properties is, therefore, desired to adequately support designs for such applications. This paper proposes a new basis for characterizing mechanical steel properties that provides the static strength and stiffness over the post-yield strain range. Relaxation characteristics are interpreted from testing, and local stiffness properties are provided. Although static properties are inferred, the test and interpretation basis allows the tests to be executed in a relatively brief time frame, making it possible to apply the method in QA programs to confirm post-yield properties for strain-based designs. A test apparatus built to implement the material-characterization protocol is presented, and sample results are provided to demonstrate the method.
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Gowda, Arun, David Esler, Sandeep Tonapi, Annita Zhong, K. Srihari, and Florian Schattenmann. "Micron and Submicron-Scale Characterization of Interfaces in Thermal Interface Material Systems." Journal of Electronic Packaging 128, no. 2 (February 14, 2006): 130–36. http://dx.doi.org/10.1115/1.2188952.
Повний текст джерелаАнотація:
One of the key challenges in the thermal management of electronic packages are interfaces, such as those between the chip and heat spreader and the interface between a heat spreader and heat sink or cold plate. Typically, thermal interfaces are filled with materials such as thermal adhesives and greases. Interface materials reduce the contact resistance between the mating heat generating and heat sinking units by filling voids and grooves created by the nonsmooth surface topography of the mating surfaces, thus improving surface contact and the conduction of heat across the interface. However, micron and submicron voids and delaminations still exist at the interface between the interface material and the surfaces of the heat spreader and semiconductor device. In addition, a thermal interface material (TIM) may form a filler-depleted and resin-rich region at the interfaces. These defects, though at a small length scale, can significantly deteriorate the heat dissipation ability of a system consisting of a TIM between a heat generating surface and a heat dissipating surface. The characterization of a freestanding sample of TIM does not provide a complete understanding of its heat transfer, mechanical, and interfacial behavior. However, system-level characterization of a TIM system, which includes its freestanding behavior and its interfacial behavior, provides a more accurate understanding. While, measurement of system-level thermal resistance provides an accurate representation of the system performance of a TIM, it does not provide information regarding the physical behavior of the TIM at the interfaces. This knowledge is valuable in engineering interface materials and in developing assembly process parameters for enhanced system-level thermal performance. Characterization of an interface material between a silicon device and a metal heat spreader can be accomplished via several techniques. In this research, high-magnification radiography with computed tomography, acoustic microscopy, and scanning electron microscopy were used to characterize various TIM systems. The results of these characterization studies are presented in this paper. System-level thermal performance results are compared to physical characterization results.
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Meng, Qing Li, and Min Zheng Zhang. "Nonlinear Performance Simulation of RC Structures with Small-Scaled Model in Earthquake Simulation Test." Advanced Materials Research 243-249 (May 2011): 3717–29. http://dx.doi.org/10.4028/www.scientific.net/amr.243-249.3717.
Повний текст джерелаАнотація:
For small-scale RC structure model in earthquake simulation test, the material behavior of the model is hard to resemble the prototype well so that the model cannot simulate correctly the nonlinear performance of the prototype. On the basis of the dynamic similitude of mechanical behavior between common concrete and micro-concrete which derive from mechanical behavior tests, the simplified equivalent dynamic similitude relations, which are applicable to the nonlinear performance simulation with small-scale RC structure models in the earthquake simulation tests, have been proposed. By the numerical simulation of earthquake simulation tests and the deviation analysis, the dynamic simulation experimental method has been verified. In addition, for small-scaled RC model, to consider the similitude harmony between concrete and reinforcement used in the model, by adjusting the reinforcement and stirrup, or the effective section height (h0) and hoop spacing etc., simple element testing, shaking table test and numerical simulation were carried out to verify this model design method. Thus, it’s realizable that the small-scaled RC model can simulate correctly the nonlinear performance of the prototype.
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Wei, Kai, Jian Hua Xia, Naotaka Kimura, Taiki Nakamura, Zhi Juan Pan, Guo Qiang Chen, Byoung Suhk Kim, and Ick Soo Kim. "Tensile Strength of Single Electrospun Nanofibers." Advanced Materials Research 175-176 (January 2011): 294–98. http://dx.doi.org/10.4028/www.scientific.net/amr.175-176.294.
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Researchers have paid much attention to small-scale natural fibers among the biological materials to seek innovative methods in order to create new high performance materials. Recently, spider dragline silk fibers are being studied because of their unique combination of high strength to weight ratio and high extensibility, which leads to a tough and lightweight fiber. Biomimetic fibers based on spider silk have been a focus of research for the past decade. However, there are still many unanswered questions about the mechanisms by which silk achieves its unique mechanical properties, as well as challenges in mechanical testing of electrospinning silk nanofibers which are often hindered by both small diameters and limited material availability. A method to characterize local mechanical behavior in small diameter nanofibers was developed to both improve understanding of structure-property in natural fibers and provide a method for comparing mechanical behavior in natural and electrospinning fibers.
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Viale, Nicola, Federico Accornero, Giuseppe Lacidogna, and Giulio Ventura. "AE Characterization of Brick Masonry Walls Mechanical Behavior: The Case-Study of Alessandria and Boves Barracks." Key Engineering Materials 817 (August 2019): 563–70. http://dx.doi.org/10.4028/www.scientific.net/kem.817.563.
Повний текст джерелаАнотація:
IIn the present study, Acoustic Emission (AE) monitoring technique is applied in order to characterize the brick masonry of two important military buildings located in Northern Italy: the barracks of Alessandria and Boves. The internal brick masonry walls of the two barracks object of the study are tested by two double flat-jack systems, in order to analyze the compressive strength of the structural material. Flat-jack testing is a versatile and powerful technique that provides significant information on the mechanical properties of historical constructions. The first applications of this technique on some historical monuments clearly showed its great potential. The flat-jack test method is only slightly destructive, and when double jacks are used, this test works according to the same principle as a standard compressive test. The difference is that it is performed in situ and the load is applied by means of two flat-jacks instead of the loading platens. During the tests, the stress-strain relationship of the masonry is determined by gradually increasing the pressure applied by the flat-jacks in the course of three loading-unloading cycles. Moreover, AE technique is coupled to the flat-jack testing, in order to assess the extent of damage in the masonry texture. Thus, AE technique makes it possible to highlight critical phenomena and fracture mechanics scale effects in the masonry by identifying the critical conditions, not entrusted to an analysis of the loading process (compression or shear), rather depending primarily on the distribution and evolution of crack patterns.
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Chuluunbat, Turbadrakh, Andrii G. Kostryzhev, and Olexandra Marenych. "Investigation of X80 Line Pipe Steel Fracture during Tensile Testing Using Acoustic Emission Monitoring." Key Engineering Materials 794 (February 2019): 21–27. http://dx.doi.org/10.4028/www.scientific.net/kem.794.21.
Повний текст джерелаАнотація:
The acoustic emission (AE) monitoring technique is widely used in mechanical and materials research for detection of plastic deformation, fracture initiation and crack growth. However, the quantitative dependences of the AE signal parameters on material fracture parametersare not completely understood. This paper presents recent research results on AE monitoring of the fracture behavior of X80 line pipe steel, a critically important material for the oil and gas transportation industry.Fracture of this steel was studied using tensile testing of small scale specimens coupled with AE monitoring and high speed video camera. The dependence of fracture behavior and AE parameters on loading conditions (strain rate and presence or absence of a notch) was investigated. The AE parameters were analyzed using the “Average Hit” features and “Wave Form and Power Spectrum” methodologies. The fracture surface was characterized using scanning electron microscopy and a dependence of the AE parameters on the average void size has been obtained.
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Nsom, Blaise, and Noureddine Latrache. "USE OF SPATIOTEMPORAL DIAGRAMS TO CHARACTERIZE A SILO DISCHARGING PROCESS." Transactions of the Canadian Society for Mechanical Engineering 37, no. 1 (March 2013): 53–70. http://dx.doi.org/10.1139/tcsme-2013-0004.
Повний текст джерелаАнотація:
To get a better knowledge of discharging flows of ensiled granular materials, a small scale silo was designed and built. It is equipped with a flat bottom and it has a rectangular cross section. Moreover, it is entirely transparent for image processing purpose. First of all, a physical and mechanical characterization of wood granules (inert materials) was performed using a shear box testing. Then, silo emptying flows were generated. Flow regimes and flow rate were determined using spatiotemporal diagrams extracted from images of the free surface of the ensiled material. The same method was then used to measure the flow rate of discharging flows of soya, colza and rye seeds which were characterized in a previous study. For each material studied, the flow rate measured with this non intrusive method was successfully compared with a direct method consisting in weighing a volume of grains discharged during a unit time and with Berveloo’s formula.
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Wu, Chenglin, Congjie Wei, and Yanxiao Li. "In Situ Mechanical Characterization of the Mixed-Mode Fracture Strength of the Cu/Si Interface for TSV Structures." Micromachines 10, no. 2 (January 25, 2019): 86. http://dx.doi.org/10.3390/mi10020086.
Повний текст джерелаАнотація:
In situ nanoindentation experiments have been widely adopted to characterize material behaviors of microelectronic devices. This work introduces the latest developments of nanoindentation experiments in the characterization of nonlinear material properties of 3D integrated microelectronic devices using the through-silicon via (TSV) technique. The elastic, plastic, and interfacial fracture behavior of the copper via and matrix via interface were characterized using small-scale specimens prepared with a focused ion beam (FIB) and nanoindentation experiments. A brittle interfacial fracture was found at the Cu/Si interface under mixed-mode loading with a phase angle ranging from 16.7° to 83.7°. The mixed-mode fracture strengths were extracted using the linear elastic fracture mechanics (LEFM) analysis and a fracture criterion was obtained by fitting the extracted data with the power-law function. The vectorial interfacial strength and toughness were found to be independent with the mode-mix.
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Arguelles, Andrea P., Olivia Cook, Nancy Huang, Christopher M. Kube, and Allison Beese. "Ultrasonic nondestructive characterization and its role in the development and implementation of additive manufacturing processes." Journal of the Acoustical Society of America 152, no. 4 (October 2022): A93. http://dx.doi.org/10.1121/10.0015654.
Повний текст джерелаАнотація:
Advancements in manufacturing processes, such as metal 3D printing, are deeply reliant on our understanding of the resulting internal features and microstructures that dictate material behavior. Microstructure characterization is often relegated to techniques that require extensive sample sectioning and surface preparation, which are inherently limited to a small portion of the bulk material. In this presentation, I will show how elastic wave propagation methods (namely, ultrasonic testing) can be combined with physics-based models to extract microstructural parameters in fit-for-service parts. Example results are given for binder jet printed metals (namely, stainless steel 316 and SS316 infiltrated with bronze) where microstructure is characterized over large volumes nondestructively. These methods are correlated to both destructive metrics of microscale features and mechanical properties, which are linked to processing conditions and sample geometry. Finally, I will provide a broader outlook for the impact these techniques may have on the development and implementation of quality assurance protocols for additively manufactured parts.
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VanLandingham, M., J. Villarrubia, G. Meyers, and M. Dineen. "Advancing Nanoscale Indentation Measurements Toward Quantitative Characterization of Polymer Properties." Microscopy and Microanalysis 6, S2 (August 2000): 1108–9. http://dx.doi.org/10.1017/s1431927600038034.
Повний текст джерелаАнотація:
The ultimate objective of instrumented indentation testing is to obtain absolute measurements of material properties and behavior. To achieve this goal, accurate knowledge of the shape of the indenter tip is required. For indentation measurements involving sub-micrometer scale contacts, accurate knowledge of the tip shape can be difficult to achieve. In this presentation, a technique referred to as blind reconstruction is applied to the measurement of tip shapes of indenters used with the atomic force microscope (AFM) to indent polymeric materials.The AFM has been used recently to make nanoscale indentation measurements and is particularly useful for evaluating the mechanical response of polymeric materials. These measurements can be made using AFM cantilever probes and operating the AFM in force mode with some modifications to account for lateral tip motion. Because the AFM was not specifically designed as an indentation device, other complications can arise due to instrumental uncertainties such as piezo hysteresis, piezo creep, and photodiode nonlinearities.
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Martín-Montal, Jordi, Jesus Pernas-Sánchez, and David Varas. "Experimental Characterization Framework for SLA Additive Manufacturing Materials." Polymers 13, no. 7 (April 2, 2021): 1147. http://dx.doi.org/10.3390/polym13071147.
Повний текст джерелаАнотація:
Additive manufacturing (AM) is driving a change in the industry not only regarding prototyping but due to the ease of including printed parts in final designs. Engineers and designers can go deeper into optimization and improvements of their designs without drawbacks of long manufacturing times. However, some drawbacks such as the limited available materials or uncertainty about mechanical properties and anisotropic behavior of 3D printed parts prevent use in large-scale production. To gain knowledge and confidence about printed materials it is necessary to know how they behave under different stress states and strain-rate regimes, and how some of the printing parameters may affect them. The present work proposes an experimental methodology framework to study and characterize materials printed by stereolithography (SLA) to clarify certain aspects that must be taken into account to broaden the use of this kind of material. To this end, tensile and compression tests at different strain rates were carried out. To study the influence of certain printing parameters on the printed material behavior, samples with different printing angles (θ = [0–90]) and different printing resolution (layer height of 50 and 100 µm) were tested. In addition, the effects of curing time and temperature were also studied. The testing specimens were manufactured in the non-professional SLA machine Form 2 from Formlabs® using resin called Durable. Nevertheless, the proposed experimental methodology could be extended to any other resin.
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Burnham, Tom. "Seasonal Load Response Behavior of a Thin Portland Cement Concrete Pavement." Transportation Research Record: Journal of the Transportation Research Board 1819, no. 1 (January 2003): 251–61. http://dx.doi.org/10.3141/1819b-32.
Повний текст джерелаАнотація:
The mechanistic-empirical pavement design methods currently under development have demonstrated a need for seasonal material and load response behavior characterization. The seasonal dynamic load strain response of a thin [5-in. (127-mm)], low-cost, portland cement concrete pavement at the Minnesota Road Research Project was examined. Environmental and load-related factors to be considered in this type of study are described. For the truck speeds used, analysis found minimal effects on measured dynamic strain. Nonlinear temperature profiles in the slabs prompted the use of the temperature-moment concept in the analysis. For the approach side of the joint in the slabs, during periods with unfrozen base and subgrade layers, there is only a small increase in the dynamic strain response with decreasing temperature-moment. Average dynamic strain responses range from 50 to 80 microstrain, with little difference in magnitude between the 80,000-lb (355-kN) and 102,000-lb (453-kN) loadings. For the leave side of the joints in the slabs, there is a larger increase in dynamic strain response with decreasing temperature-moment. In addition, the 102,000-lb load response is nearly 60% larger than the 80,000-lb load response for large negative temperature-moments. Recommendations for improving dynamic load testing of pavements are given.
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Lee, C. F., and T. J. Shieh. "Theory of Endochronic Cyclic Viscoplasticity of Eutectic Tin/Lead Solder Alloy." Journal of Mechanics 22, no. 3 (September 2006): 181–91. http://dx.doi.org/10.1017/s1727719100000824.
Повний текст джерелаАнотація:
AbstractIn this paper, a theory of Endochronic cyclic viscoplasticity of eutectic Tin/Lead (60Sn/40Pb) solder alloy under cyclically thermomechanical strain histories had been established. Under the conditions of isotropic and inelastically incompressible small deformation, the constitutive equation of deviatoric behavior was expressed as:here and the strain rate dependent intrinsic time scale and . Employing the experimental cyclic shear stress-strain curves of various testing temperature and frequency, all temp. dependent material parameters and ; and the temp.-freq. dependent material function were determined for temp. between 213K and 423K and freq. between 0.3Hz and 0.01Hz. Predicative capability of the theory were then challenged by a set of experiments with complicate strain history such as (i) Fast in tension/Slow in compression constant strain amplitude cyclic tests (ii) Slow-Fast-Slow constant amplitude cyclic tests. Through the excellent computational results, the present theory demonstrated that it can, not only play a vital role in the area of electronic solder mechanics, but also meet the needs of reliability analysis and life assessment in the electronic/photoelectronic packagings.
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Santana, Clóvis Veloso de, Yêda Vieira Póvoas, Deborah Grasielly Cipriano da Silva, and Francisco de Assis Miranda Neto. "Recycled gypsum block: development and performance." Ambiente Construído 19, no. 2 (April 2019): 45–58. http://dx.doi.org/10.1590/s1678-86212019000200307.
Повний текст джерелаАнотація:
Abstract The gypsum plaster waste is still faced a serious economic and environmental problem. Considering the high volume and the destination often inadequate. Intending to provide a mitigating alternative, this research intends to develop blocks that incorporate the industrial gypsum plaster waste through reverse logistics. For this, a physic-chemical recycling process of gypsum plaster waste was carried out on an industrial scale and the developed material was characterized in anhydrous and fresh state. Then, blocks were made with the recycled material and characterized according to NBR 16495 (ABNT, 2016). After its characterization, the material was evaluated for its mechanical performance when used in walls, regarding the tests of suspended vertical loads and hard and soft body impact, according to the guidelines included in the performance standard NBR 15575-4 (ABNT, 2013). The walls constituted with the developed material showed satisfactory performance, having, in some cases, presented superior performance in comparison to the conventional walls of gypsum blocks, according to results presented by the Technical Assessments Document - DATEC nº 27 (2015). Finally, small walls of the recycled gypsum block and gypsum glue were elaborated to verify the compressive behavior. Regarding these verifications, it was noticed that the small walls obtained good resistive capacity.
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Xu, Chen, Zeeshan Ahmad, Asghar Aryanfar, Venkatasubramanian Viswanathan, and Julia R. Greer. "Enhanced strength and temperature dependence of mechanical properties of Li at small scales and its implications for Li metal anodes." Proceedings of the National Academy of Sciences 114, no. 1 (December 19, 2016): 57–61. http://dx.doi.org/10.1073/pnas.1615733114.
Повний текст джерелаАнотація:
Most next-generation Li ion battery chemistries require a functioning lithium metal (Li) anode. However, its application in secondary batteries has been inhibited because of uncontrollable dendrite growth during cycling. Mechanical suppression of dendrite growth through solid polymer electrolytes (SPEs) or through robust separators has shown the most potential for alleviating this problem. Studies of the mechanical behavior of Li at any length scale and temperature are limited because of its extreme reactivity, which renders sample preparation, transfer, microstructure characterization, and mechanical testing extremely challenging. We conduct nanomechanical experiments in an in situ scanning electron microscope and show that micrometer-sized Li attains extremely high strengths of 105 MPa at room temperature and of 35 MPa at 90 °C. We demonstrate that single-crystalline Li exhibits a power-law size effect at the micrometer and submicrometer length scales, with the strengthening exponent of −0.68 at room temperature and of −1.00 at 90 °C. We also report the elastic and shear moduli as a function of crystallographic orientation gleaned from experiments and first-principles calculations, which show a high level of anisotropy up to the melting point, where the elastic and shear moduli vary by a factor of ∼4 between the stiffest and most compliant orientations. The emergence of such high strengths in small-scale Li and sensitivity of this metal’s stiffness to crystallographic orientation help explain why the existing methods of dendrite suppression have been mainly unsuccessful and have significant implications for practical design of future-generation batteries.
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Capa, Vicente E., F. Javier Torrijo, Pedro A. Calderón, and Carlos Hidalgo Signes. "Geotechnical Characterization of Quito’s North-Central Zone as Applied to Deep Excavation in the Urban Setting." Sustainability 15, no. 10 (May 19, 2023): 8272. http://dx.doi.org/10.3390/su15108272.
Повний текст джерелаАнотація:
This paper describes an in-depth soil characterization study in the La Carolina financial district of Quito (Ecuador). As there was very little information available on the geotechnical structure of Quito’s volcanic soil, particularly in this area, where large-scale property development has taken place, the aim was to provide information on soil parameters to engineers working on large geotechnical and civil engineering projects based on the results of a thorough and comprehensive study of such properties. A series of field tests were performed at three different sites, where thin-walled tube samples were collected for lab testing to estimate the index properties and mechanical parameters. These index properties were then combined with conventional two-way drainage oedometer tests and stress-path triaxial testing to evaluate compressibility, stiffness and strength. The subsoil was found to be partly composed of slightly overconsolidated volcanic soils. X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) analyses were also conducted to determine mineralogical and microstructural features and evaluate their influence on the mechanical behavior of the volcanic soil. This type of research is frequently applied to the study of landslides in urban environments, where it is essential to understand their failure mechanisms, especially in slopes generated by the construction of important engineering works. Therefore, based on this geotechnical characterization study, parameters were subsequently determined for the Mohr–Coulomb (MC), Hardening Soil (HS), and Hardening Soil with Small-Strain Stiffness (HSsmall) soil constitutive models, and these were applied to a numerical study of the Soil Nailing system behavior for the construction of a five-level underground car parking structure of an important building located in the north-central sector of the city of Quito. It was verified that the HSsmall and HS constitutive soil models better reproduce the behavior of this type of structure. Finally, the multiple geotechnical parameters determined in this study significantly contribute to the analysis of these structures in this soil type.
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Abdel-Rahman, M. A., Alaa Aldeen Ahmed, and Emad A. Badawi. "Testing Natural Aging Effect on Properties of 6066 & 6063 Alloys Using Vickers Hardness and Positron Annihilation Lifetime Techniques." Defect and Diffusion Forum 303-304 (July 2010): 107–12. http://dx.doi.org/10.4028/www.scientific.net/ddf.303-304.107.
Повний текст джерелаАнотація:
The aim of this work was to produce a high strength 6xxx series Aluminum alloy by adjusting the processing conditions, namely solutionizing and natural aging. It consists of heating the alloy to a temperature at which the soluble constituents will form a homogeneous mass by solid diffusion, holding the mass at that temperature until diffusion takes place, then quenching the alloy rapidly to retain the homogeneous condition. In the quenched condition, heat-treated alloys are supersaturated solid solutions that are comparatively soft and workable, and unstable, depending on composition. At room temperature, the alloying constituents of some alloys tend to precipitate from the solution spontaneously, causing the metal to harden in about four days. This is called natural aging. The mechanical characterization of heat treatable 6xxx (Al-Mg-Si-Cu based) 6066, 6063 wrought aluminum alloys was studied. Their effects were investigated in terms of microstructure using positron annihilation lifetime technique and mechanical properties by hardness measurements. The hardness is the Resistance of material to plastic deformation, which gives it the ability to resist deformed when a load is applied. The greater the hardness of the material, the greater resistance it has to deformation. Hardness measurement can be defined as macro-, micro- or nano- scale according to the forces applied and displacements obtained. Micro hardness is the hardness of a material as determined by forcing an indenter such as a Vickers indenter into the surface of the material under 15 to 1000 gf load; usually, the indentations are so small that they must be measured with a microscope. During this work we are monitoring the effect of natural aging on the properties of positron lifetime and Vickers hardness parameters. The Vickers hardness of 6066 alloy has a maximum value(80) after (10)days of quenching at 530 which is the solution temperature of this alloy .the hardness of 6063 alloy has a maximum value (40) after (14)days of quenching at 520 which is the solution temperature of this alloy. The hardness which is conformed to the references.
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Ingole, S., A. Schwartzman, and H. Liang. "In Situ Investigation of Nanoabrasive Wear of Silicon." Journal of Tribology 129, no. 1 (June 27, 2006): 11–16. http://dx.doi.org/10.1115/1.2372764.
Повний текст джерелаАнотація:
Investigation of abrasive wear at the nanometer-length scale is presented on single crystalline (001) and amorphous silicon. Experiments were performed using nanoindentation and nanoscratch approaches. Surface characterization was carried out using an atomic force microscope. Results show that both materials behave quite differently from each other during indentation and scratch. Specifically, amorphous silicon is proven to be more unstable during scratching than single crystal silicon. The comparison of in situ and ex situ normal displacement was made. Evidence was found on the hysteretic and viscoplastic behavior of amorphous silicon in nanoscratch that is also seen in indentation. Furthermore, it is found that this material is unstable under stress within small scales. Indications of phase transformation, (reverse) densification, and transition of elastic-plastic deformation are seen. These observations, enabled on silicon using an in situ and nanometer length scale process, are fundamentally different from the understanding of conventional abrasive wear.
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Dong, Yue, Suya Liu, Johannes Biskupek, Qingping Cao, Xiaodong Wang, Jian-Zhong Jiang, Rainer Wunderlich, and Hans-Jörg Fecht. "Improved Tensile Ductility by Severe Plastic Deformation for Nano-Structured Metallic Glass." Materials 12, no. 10 (May 16, 2019): 1611. http://dx.doi.org/10.3390/ma12101611.
Повний текст джерелаАнотація:
The effect of severe plastic deformation by high-pressure torsion (HPT) on the structure and plastic tensile properties of two Zr-based bulk metallic glasses, Zr55.7Ni10Al7Cu19Co8.3 and Zr64Ni10Al7Cu19, was investigated. The compositions were chosen because, in TEM investigation, Zr55.7Ni10Al7Cu19Co8.3 exhibited nanoscale inhomogeneity, while Zr64Ni10Al7Cu19 appeared homogeneous on that length scale. The nanoscale inhomogeneity was expected to result in an increased plastic strain limit, as compared to the homogeneous material, which may be further increased by severe mechanical work. The as-cast materials exhibited 0.1% tensile plasticity for Zr64Ni10Al7Cu19 and Zr55.7Ni10Al7Cu19Co8.3. Following two rotations of HPT treatment, the tensile plastic strain was increased to 0.5% and 0.9%, respectively. Further testing was performed by X-ray diffraction and by differential scanning calorimetry. Following two rotations of HPT treatment, the initially fully amorphous Zr55.7Ni10Al7Cu19Co8.3 exhibited significantly increased free volume and a small volume fraction of nanocrystallites. A further increase in HPT rotation number did not result in an increase in plastic ductility of both alloys. Possible reasons for the different mechanical behavior of nanoscale heterogeneous Zr55.7Ni10Al7Cu19Co8.3 and homogeneous Zr64Ni10Al7Cu19 are presented.
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Huang, Yuanchen, Yunpeng Zhu, Carlos Alberto Cimini, and Sung Kyu Ha. "Characterization of moisture effect on static and fatigue performance of epoxy resin using thin-film specimen on dynamic mechanical analyzer." Journal of Composite Materials 51, no. 3 (July 28, 2016): 303–14. http://dx.doi.org/10.1177/0021998316644851.
Повний текст джерелаАнотація:
A novel method of characterizing moisture effect on mechanical performance of epoxy resin is presented in this paper. A 50-µm-thick layer of cured epoxy resin was fabricated and cut into strips of 4 mm wide and 30 mm long as specimens to be tested on a dynamic mechanical analyzer equipped with thin-film tension clamp. Static tension and force-controlled tension–tension fatigue tests were first carried out using thin-film specimens made from Momentive 135/137 and BASF 5400/5440 epoxy resin systems without applying moisture, and results were compared with those obtained using conventional dog-bone specimens to validate the proposed testing method. Another batch of thin-film specimens were then immersed into deionized water, and the weight gain was recorded regularly until full saturation to obtain the absorption curve. Static and fatigue tests were performed using thin-film specimens made from BASF 5400/5440 with 55% and 100% saturation of moisture respectively, to evaluate moisture-induced material degradation. The aging effect on BASF 5400/5440 caused by cyclic water immersion and drying process was also assessed by performing static and fatigue tests using fully dried thin-film specimens after aging. It was concluded that the combination of thin-film specimen and dynamic mechanical analyzer would yield as good measurements of tensile strength and fatigue life as conventional dog-bone specimen does, and the small thickness of thin-film specimen would greatly reduce the time to reach a certain level of moisture content, facilitating further studies on effect of moisture ingression on polymeric matrix composites using multi-scale approaches.
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Orozco, Gustavo, Laura Villegas, and José Jaime García. "Mechanical Behavior of Bamboo Species Guadua angustifolia under Compression along the Thickness of the Culm." Key Engineering Materials 600 (March 2014): 49–56. http://dx.doi.org/10.4028/www.scientific.net/kem.600.49.
Повний текст джерелаАнотація:
The bamboo species Guadua angustifolia is a natural functionally graded material with a high potential to help solving the housing deficit in Latin American countries. Bamboo plantations also play an important role to help reducing the devastation of tropical forests. Many studies have demonstrated the excellent mechanical properties of bamboo along the length of the culm. However, other properties like the strength under circumferential tension and shear are low and the associated types of failure are fragile. Therefore, longitudinal fissures are often initiated in the structural joints which avoid taking advantage of the high resistance along the longitudinal direction. To the best of our knowledge, no study has been devoted to study the mechanical behavior of bamboo along the thickness of the culm or radial direction. This characterization may be crucial to improve the performance of the joints in bamboo structures. The aim of this study was to determine the strength and the Young ́s modulus of Guadua angustifolia along the radial direction. Thus, 27 small hexahedral elements of approximately 11 mm × 6 mm × 7 mm were tested under compression along the thickness of the culm. The stress-strain curves depicted a typical ductile behavior with an average failure strain of 37.8 ± 5.4 %. The failure was characterized by fissures on planes parallel to the fibers and forming angles in the range 35° - 55° with respect to the axis of loading. The secant Young ́s modulus and the radial strength were equal to 44.50 ±9.60 MPa, and 18.50 ±4.20 MPa respectively and there was no significant difference with position along the culm. The initial Young ́s modulus was equal to 96.73 ±52.30 MPa, 37.00 ±24.35 MPa and 48.90 ±7.31 MPa for the bottom, middle and upper portions of the culm and there was a significant difference (p=0.025) between the bottom and middle locations. The high variations of the initial Young ́s modulus may be explained by the irregular form of the surfaces of contact with the testing machine, that were not cut perfectly flat in order to preserve the intact material. These experiments show that Guadua behaves as a ductile material under compression along the thickness of the culm. This property may be used to improve the efficiency of structural joints by applying radial compression.
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Tutumluer, Erol, Dallas N. Little, and Sung-Hee Kim. "Validated Model for Predicting Field Performance of Aggregate Base Courses." Transportation Research Record: Journal of the Transportation Research Board 1837, no. 1 (January 2003): 41–49. http://dx.doi.org/10.3141/1837-05.
Повний текст джерелаАнотація:
The International Center for Aggregates Research Project 502 focused on pavement layers of unbound aggregate proper representation in mechanistic pavement models. The research team developed models for resilient and permanent deformation behavior from the results of triaxial tests conducted at the Texas Transportation Institute and the University of Illinois. The studies indicate that the unbound aggregate base (UAB) material should be modeled as nonlinear and cross-anisotropic to account for stress sensitivity and the significant differences between vertical and horizontal moduli and Poisson’s ratios. Field validation data were collected from a full-scale pavement test study conducted at Georgia Tech. The validation of the anisotropic modeling approach was accomplished by analyzing conventional flexible pavement test sections using the GT-PAVE finite element program to predict responses to load in the UAB layer and comparing these predicted responses to the measured values. Laboratory testing of the aggregate samples was conducted at the University of Illinois, and characterization models were developed for the stress-sensitive, cross-anisotropic aggregate behavior. With nonlinear anisotropic modeling of the UAB, the resilient behavior of pavement test sections was successfully predicted for a number of response variables. In addition, the stress-sensitive, cross-anisotropic representation of the base was shown to greatly reduce the horizontal tension computed in the granular base compared with a linear isotropic representation.
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Brynk, Tomasz, Francisco Javier Perosanz Lopez, and Alec McLennan. "Increase of nuclear installations safety by better understanding of materials performance and new testing techniques development (MEACTOS, INCEFA-SCALE, and FRACTESUS H2020 projects)." EPJ Nuclear Sciences & Technologies 8 (2022): 42. http://dx.doi.org/10.1051/epjn/2022033.
Повний текст джерелаАнотація:
Research to better understand the phenomena influencing materials and components’ performance is important for increasing the safety of Generation II and III nuclear plants. A crucial step for improving nuclear safety is the development of new experimental techniques that can provide the necessary data. The three H2020 projects presented in this paper, MEACTOS (2017–2022), INCEFA-SCALE (2020–2025), and FRACTESUS (2020–2024), cover the steps needed to realize those safety improvements. The goal of the MEACTOS project is to improve the resistance of critical locations, including welds, to environmentally-assisted cracking through optimizing surface machining and treatments. The project is currently in its final stage, and the complete analysis of the data is finished. The objective of INCEFA-SCALE is to improve predictions of component fatigue lifetime when subjected to Environmentally-Assisted Fatigue (EAF). The strategy consists of producing guidance on how to appropriately accommodate variable amplitude and plant-relevant loading in EAF assessments. Increasing the understanding of the EAF mechanism based on substantial testing, characterization, and analysis program will support the INCEFA-SCALE strategy. The FRACTESUS project will validate the use of miniaturized compact tension specimens by comparing the results of master curve-oriented fracture toughness tests performed with small and large specimens. The round-robin exercises will use irradiated and non-irradiated Reactor Pressure Vessel (RPV) materials. The material selection process is complete in time for the project to enter the testing phase. The output of the project will be beneficial from a long-term operation perspective and a saving in the material amount needed for RPV surveillance programs. Even though each project is devoted to different research areas, common aspects are clearly visible. All three projects investigate phenomena that are relevant to the performance and safe operation of the nuclear plant. Moreover, each project will provide valuable databases and analyses of test results for materials relevant to components in the nuclear plant. The output of these projects will be of great value to the nuclear industry. This paper presents the current progress for each project, emphasizing the common research domains between the projects.
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Wei, B., and K. Komvopoulos. "Nanoscale Indentation Hardness and Wear Characterization of Hydrogenated Carbon Thin Films." Journal of Tribology 118, no. 2 (April 1, 1996): 431–38. http://dx.doi.org/10.1115/1.2831320.
Повний текст джерелаАнотація:
An experimental investigation of the surface topography, nanoindentation hardness, and nanowear characteristics of carbon thin films was conducted using atomic force and point contact microscopy. Hydrogenated carbon films of thickness 5, 10, and 25 nm were synthesized using a sputtering technique. Atomic force microscopy images obtained with silicon nitride tips of nominal radius less than 20 nm demonstrated that the carbon films possessed very similar surface topographies and root-mean-square roughness values in the range of 0.7–1.1 nm. Nanoindentation and nanowear experiments performed with diamond tips of radius equal to about 20 nm revealed a significant enhancement of the hardness and wear resistance with increasing film thickness. High-resolution surface imaging indicated that plastic flow was the dominant deformation process in the nanoindentation experiments. The carbon wear behavior was strongly influenced by variations in the film thickness, normal load, and number of scanning cycles. For a given film thickness, increasing the load caused the transition from an atomic-scale wear process, characterized by asperity deformation and fracture, to severe wear consisting of plowing and cutting of the carbon films. Both the critical load and scanning time for severe wear increased with film thickness. Below the critical load, the wear rate decreased with further scanning and the amount of material worn off was negligibly small, while above the critical load the wear rate increased significantly resulting in the rapid removal of carbon. The observed behavior and trends are in good qualitative agreement with the results of other experimental and contact mechanics studies.
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Wei, B., and K. Komvopoulos. "Nanoscale Indentation Hardness and Wear Characterization of Hydrogenated Carbon Thin Films." Journal of Tribology 117, no. 4 (October 1, 1995): 594–601. http://dx.doi.org/10.1115/1.2831521.
Повний текст джерелаАнотація:
An experimental investigation of the surface topography, nanoindentation hardness, and nanowear characteristics of carbon thin films was conducted using atomic force and point contact microscopy. Hydrogenated carbon films of thickness 5, 10, and 25 nm were synthesized using a sputtering technique. Atomic force microscopy images obtained with silicon nitride tips of nominal radius less than 20 nm demonstrated that the carbon films possessed very similar surface topographies and root-mean-square roughness values in the range of 0.7–1.1 nm. Nanoindentation and nanowear experiments performed with diamond tips of radius equal to about 20 nm revealed a significant enhancement of the hardness and wear resistance with increasing film thickness. High-resolution surface imaging indicated that plastic flow was the dominant deformation process in the nanoindentation experiments. The carbon wear behavior was strongly influenced by variations in the film thickness, normal load, and number of scanning cycles. For a given film thickness, increasing the load caused the transition from an atomic-scale wear process, characterized by asperity deformation and fracture, to severe wear consisting of plowing and cutting of the carbon films. Both the critical load and scanning time for severe wear increased with film thickness. Below the critical load, the wear rate decreased with further scanning and the amount of material worn off was negligibly small, while above the critical load the wear rate increased significantly resulting in the rapid removal of carbon. The observed behavior and trends are in good qualitative agreement with the results of other experimental and contact mechanics studies.
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D’Alessandro, Antonella, Filippo Ubertini, Enrique García-Macías, Rafael Castro-Triguero, Austin Downey, Simon Laflamme, Andrea Meoni, and Annibale Luigi Materazzi. "Static and Dynamic Strain Monitoring of Reinforced Concrete Components through Embedded Carbon Nanotube Cement-Based Sensors." Shock and Vibration 2017 (2017): 1–11. http://dx.doi.org/10.1155/2017/3648403.
Повний текст джерелаАнотація:
The paper presents a study on the use of cement-based sensors doped with carbon nanotubes as embedded smart sensors for static and dynamic strain monitoring of reinforced concrete (RC) elements. Such novel sensors can be used for the monitoring of civil infrastructures. Because they are fabricated from a structural material and are easy to utilize, these sensors can be integrated into structural elements for monitoring of different types of constructions during their service life. Despite the scientific attention that such sensors have received in recent years, further research is needed to understand (i) the repeatability and accuracy of sensors’ behavior over a meaningful number of sensors, (ii) testing configurations and calibration methods, and (iii) the sensors’ ability to provide static and dynamic strain measurements when actually embedded in RC elements. To address these research needs, this paper presents a preliminary characterization of the self-sensing capabilities and the dynamic properties of a meaningful number of cement-based sensors and studies their application as embedded sensors in a full-scale RC beam. Results from electrical and electromechanical tests conducted on small and full-scale specimens using different electrical measurement methods confirm that smart cement-based sensors show promise for both static and vibration-based structural health monitoring applications of concrete elements but that calibration of each sensor seems to be necessary.
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Punyamueang, Suttirat, and Vitoon Uthaisangsuk. "Determination of Stress-Strain Curve of Dual Phase Steel by Nanoindentation Technique." Key Engineering Materials 658 (July 2015): 195–201. http://dx.doi.org/10.4028/www.scientific.net/kem.658.195.
Повний текст джерелаАнотація:
The advanced high strength (AHS) steels, for example, dual phase (DP) steels, transformation induced plasticity (TRIP) steels and complex (CP) steels principally exhibit multiphase microstructure features. Thus, mechanical behavior of the constituent phases significantly affects the resulting overall properties of such AHS steels. Novel material characterization techniques on micro- and nano-scale have become greatly more important. In this work, stress-strain response of the DP steel grade 1000 was determined by using the Nanoindentation testing. The DP steel showed the microstructure containing finely distributed martensite islands of about 50% phase fraction in the ferritic matrix. The nano-hardness measurements were firstly performed on each individual phase of the examined steel. In parallel, finite element (FE) simulations of the corresponding nano-indentation tests were carried out. Flow curves of the single ferritic and martensitic phases were defined according to a dislocation based theory. Afterwards, the load and penetration depth curves resulted from the experiments and simulations were compared. By this manner, the proper stress-strain responses of both phases were identified and verified. Finally, the effective stress-strain curve of the investigated DP steel could be determined by using 2D representative volume element (RVE) model.
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Ziolkowski, L. A., N. C. S. Mykytczuk, C. R. Omelon, H. Johnson, L. G. Whyte, and G. F. Slater. "Arctic gypsum endoliths: a biogeochemical characterization of a viable and active microbial community." Biogeosciences 10, no. 11 (November 27, 2013): 7661–75. http://dx.doi.org/10.5194/bg-10-7661-2013.
Повний текст джерелаАнотація:
Abstract. Extreme environmental conditions such as those found in the polar regions on Earth are thought to test the limits of life. Microorganisms living in these environments often seek protection from environmental stresses such as high UV exposure, desiccation and rapid temperature fluctuations, with one protective habitat found within rocks. Such endolithic microbial communities, which often consist of bacteria, fungi, algae and lichens, are small-scale ecosystems comprised of both producers and consumers. However, the harsh environmental conditions experienced by polar endolithic communities are thought to limit microbial diversity and therefore the rate at which they cycle carbon. In this study, we characterized the microbial community diversity, turnover rate and microbe–mineral interactions of a gypsum-based endolithic community in the polar desert of the Canadian high Arctic. 16S/18S/23S rRNA pyrotag sequencing demonstrated the presence of a diverse community of phototrophic and heterotrophic bacteria, archaea, algae and fungi. Stable carbon isotope analysis of the viable microbial membranes, as phospholipid fatty acids and glycolipid fatty acids, confirmed the diversity observed by molecular techniques and indicated that present-day atmospheric carbon is assimilated into the microbial community biomass. Uptake of radiocarbon from atmospheric nuclear weapons testing during the 1960s into microbial lipids was used as a pulse label to determine that the microbial community turns over carbon on the order of 10 yr, equivalent to 4.4 g C m−2 yr−1 gross primary productivity. Scanning electron microscopy (SEM) micrographs indicated that mechanical weathering of gypsum by freeze–thaw cycles leads to increased porosity, which ultimately increases the habitability of the rock. In addition, while bacteria were adhered to these mineral surfaces, chemical analysis by micro-X-ray fluorescence (μ-XRF) spectroscopy suggests little evidence for microbial alteration of minerals, which contrasts with other endolithic habitats. While it is possible that these communities turn over carbon quickly and leave little evidence of microbe–mineral interaction, an alternative hypothesis is that the soluble and friable nature of gypsum and harsh conditions lead to elevated erosion rates, limiting microbial residence times in this habitat. Regardless, this endolithic community represents a microbial system that does not rely on a nutrient pool from the host gypsum cap rock, instead receiving these elements from allochthonous debris to maintain a more diverse and active community than might have been predicted in the polar desert of the Canadian high Arctic.
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Ziolkowski, L. A., N. C. S. Mykytczuk, C. R. Omelon, H. Johnson, L. G. Whyte, and G. F. Slater. "Arctic Gypsum Endoliths: a biogeochemical characterization of a viable and active microbial community." Biogeosciences Discussions 10, no. 2 (February 8, 2013): 2269–304. http://dx.doi.org/10.5194/bgd-10-2269-2013.
Повний текст джерелаАнотація:
Abstract. Extreme environmental conditions such as those found in the polar regions on Earth are thought to test the limits of life. Microorganisms living in these environments often seek protection from environmental stresses such as high UV exposure, desiccation and rapid temperature fluctuations, with one protective habitat found within rocks. Such endolithic microbial communities, which often consist of bacteria, fungi, algae and lichens, are small-scale ecosystems comprised of both producers and consumers. However, the harsh environmental conditions experienced by polar endolithic communities are thought to limit microbial diversity and the rate at which they cycle carbon. In this study, we characterized the microbial community diversity, turnover, and microbe-mineral interactions of a gypsum-based endolithic community in the polar desert of the Canadian high Arctic. 16S/18S rRNA pyrotag sequencing demonstrated the presence of a diverse community of phototrophic and heterotrophic bacteria, algae and fungi. Stable carbon isotope analysis of the viable microbial membranes, as phospholipid fatty acids and glycolipid fatty acids, confirmed the diversity observed by molecular techniques and indicated that atmospheric carbon is assimilated into the microbial community biomass. Uptake of radiocarbon from atmospheric radioweapons testing during the 1960s into microbial lipids was used as a pulse label to determine that the microbial community turns over carbon on the order of 10 yr, equivalent to 4.4 g C m−2 yr−1 gross primary productivity. SEM micrographs indicated that mechanical weathering of gypsum by freeze-thaw cycles leads to increased porosity, which ultimately increases the habitability of the rock. In addition, while bacteria were adhered to these mineral surfaces there was little evidence for microbial alteration of minerals, which contrasts with other gypsum endolithic habitats. While it is possible that these communities turn over carbon quickly and leave little evidence of microbial-mineral interaction, an alternative hypothesis is that the soluble and friable nature of the gypsum and harsh conditions lead to elevated erosion rates, limiting microbial residence times in this habitat. Regardless, this endolithic community represents a microbial system that does not rely on a nutrient pool from the host gypsum cap rock, instead receiving these elements from allochthonous debris to maintain a more diverse and active community than might have been predicted in the polar desert of the Canadian high Arctic.
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Sebastian, Ann Rose, Md Golam Kaium, Yeonwoong Jung, and Ethan Ahn. "Centimeter-Scale MoS2 Thin Films As a Temperature Sensor." ECS Meeting Abstracts MA2022-01, no. 12 (July 7, 2022): 867. http://dx.doi.org/10.1149/ma2022-0112867mtgabs.
Повний текст джерелаАнотація:
Backgrounds/Introduction Transition-metal dichalcogenides (TMDs) is an atomically-thin semiconducting material family, exhibiting unique physical and multi-functional properties. Despite the great promises in flexible electronics, the practical adoption of TMDs in a wider variety of far-reaching application domains, including high-temperature applications such as automobiles and aircrafts, still requires TMDs to be prepared at a larger scale and tailor-researched to the needs of a specific application. In this work, molybdenum disulfide (MoS2), one of the most widely studied TMD materials, is synthesized at a centimeter-scale by sulfurizing the transition metal seed layer (Mo) in a CVD (chemical vapor deposition) reactor, and comprehensively characterized to explore MoS2’s potential as the next-generation temperature sensor. Key Results: Fig. 1 depicts both the schematic drawing (1a) and the transmission electron microscope (TEM) image (1b) of few-layer MoS2 thin films grown on a SiO2/Si substrate by the CVD process described in our earlier work [1]. As seen in the figure, 2D MoS2 layers were successfully grown in a planar direction with their basal planes parallel to the growth substrates. The horizontal growth of few-layer MoS2 thin films (thicknesses of less than 5 nm) was achieved by precisely controlling the thickness of the metal seed layer (Mo). We first investigated the Raman characteristics of our centimeter-scale (2cm x 2cm), CVD-grown MoS2 thin films at varying temperatures (from 26°C to 206°C) in Fig. 2. It is clearly seen that both E2g (out-of-plane vibration modes at ~ 383 cm-1) and A1g (in-plane vibration modes at ~ 408 cm-1) characteristic peaks appeared in the temperature-dependent Raman measurement. Since these peak positions are known to be strongly dependent on materials or external parameters (e.g., thickness, mechanical strain, charge transfer), observing any notable change in the peak position at varying conditions can lead to discovery of MoS2’s novel functionality. The overall trend of red shift (i.e., decrease of Raman shift) with an increase in temperature observed in Fig. 3 is in good agreement with what has been already reported for an exfoliated single-layer MoS2 flake [2]. This has been attributed to either charge transfer from the substrate (doping effect) or compressive strain resulted from thermal expansion coefficient mismatch between MoS2 and the substrate. In order to further elucidate the physical mechanism while examining the potential of MoS2 to become a temperature sensor of the RTD (resistance temperature detector) type, we carefully measured the conductivity vs. temperature characteristics by using the temperature controller-attached probe station (Figs. 4 and 5). Firstly, a clear trend of increase in electrical conductivity with temperature indicates the semiconducting nature of our MoS2 thin films (Fig. 4). More importantly, Fig. 5 suggests that electronic transport in the temperature range of room temperature to about 300°C follows an Arrhenius behavior, implying a variable-range hopping mechanism [3]. Table 1 summarizes the temperature coefficient (cm-1/°C, measured from Raman) and the activation energy (eV, measured from the Arrhenius plot). Significance: Previously, researchers have studied the temperature dependence of electrical conductivity for exfoliated MoS2 flakes (either undoped [4] or doped [5]). These methods may not be best suited for temperature sensing applications because of the small areal size and lack of tight control on the thickness. This work significantly advances the field by demonstrating the temperature-induced modulation of spectroscopic and electrical transport characteristics of a relatively large-area MoS2 thin film. References: Jung, Y., Shen, J., Liu, Y., Woods, J. M., Sun, Y., & Cha, J. J. (2014). Metal seed layer thickness-induced transition from vertical to horizontal growth of MoS2 and WS2. Nano letters, 14(12), 6842-6849. Taube, A., Judek, J., Jastrzębski, C., Duzynska, A., Świtkowski, K., & Zdrojek, M. (2014). Temperature-dependent nonlinear phonon shifts in a supported MoS2 monolayer. ACS applied materials & interfaces, 6(12), 8959-8963. Mukherjee, S., Biswas, S., Ghorai, A., Midya, A., Das, S., & Ray, S. K. (2018). Tunable optical and electrical transport properties of size-and temperature-controlled polymorph MoS2 nanocrystals. The Journal of Physical Chemistry C, 122(23), 12502-12511. Garadkar, K. M., Patil, A. A., Hankare, P. P., Chate, P. A., Sathe, D. J., & Delekar, S. D. (2009). MoS2: Preparation and their characterization. Journal of Alloys and Compounds, 487(1-2), 786-789. El Beqqali, O., Zorkani, I., Rogemond, F., Chermette, H., Chaabane, R. B., Gamoudi, M., & Guillaud, G. (1997). Electrical properties of molybdenum disulfide MoS2. Experimental study and density functional calculation results. Synthetic Metals, 90(3), 165-172. Figure 1
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Dufva, Olli, Tiina Kelkka, Shady Awad, Nodoka Sekiguchi, Heikki Kuusanmäki, Emma I. Andersson, Samuli Eldfors, et al. "Exome Sequencing of Aggressive Natural Killer Cell Leukemia and Drug Profiling Highlight Candidate Driver Pathways in Malignant Natural Killer Cells." Blood 126, no. 23 (December 3, 2015): 700. http://dx.doi.org/10.1182/blood.v126.23.700.700.
Повний текст джерелаАнотація:
Abstract Background Natural killer (NK) cell malignancies are rare lymphoid neoplasms characterized by aggressive clinical behavior and poor treatment outcomes. Clinically they are classified as extranodal NK/T-cell lymphoma, nasal type (NKTCL) and aggressive NK cell leukemia (ANKL). Both subtypes are almost invariably associated with Epstein-Barr virus (EBV). Recently, genomic studies in NKTCL have identified recurrent somatic mutations in JAK-STAT pathway molecules STAT3 and STAT5b as well as in the RNA helicase gene DDX3X in addition to previously detected chromosomal aberrations. Here, we identified somatic mutations in 4 cases of ANKL in order to understand whether these entities share common alterations at the molecular level. To further establish common patterns of deregulated oncogenic signaling pathways operating in malignant NK cells, we performed drug sensitivity profiling using NK cell lines representing ANKL, NKTCL and other malignant NK cell proliferations. We aimed to identify sensitivities to agents that selectively target components of pathways required for survival of malignant NK cells in an unbiased manner. Methods Exome sequencing was performed on peripheral blood or bone marrow of ANKL patients using the NK cell negative fraction or other healthy tissue as control. Profiling of drug responses was performed with a high-throughput drug sensitivity and resistance testing (DSRT) platform comprising 461 approved and investigational oncology drugs. The NK cell lines KAI3, KHYG-1, NKL, NK-YS, NK-92, SNK-6 and YT and IL-2-stimulated and resting NK cells from healthy donors were used as sample material. All drugs were tested on a 384-well format in 5 different concentrations over a 10,000-fold concentration range for 72 h and cell viability was measured. A Drug Sensitivity Score (DSS) was calculated for each drug using normalized dose response curve values. Results The ANKL patients displayed mutations in genes reported as recurrently mutated in NKTCL, such as FAS, TP53, NRAS, STAT3 and DDX3X. Additionally, novel alterations in genes previously implicated in the pathogenesis of NKTCL were detected. These included an inactivating mutation in INPP5D (SHIP), a negative regulator of the PI3K/mTOR pathway and a missense mutation in PTPRK, a negative regulator of STAT3 activation. Interestingly, the total number of nonsilent somatic mutations in 3 out of 4 ANKL patients (97, 82 and 45) was remarkably high compared to other hematological malignancies analyzed in our variant calling pipeline. Analysis of drug sensitivities in NK cell lines showed a close correlation between all cell lines and a markedly higher correlation with those of IL-2 stimulated than resting healthy NK cells, suggesting that malignant NK cells may share a common drug response pattern. Furthermore, in an unsupervised hierarchical clustering the NK cell lines formed a distinct group from other leukemia cell lines tested (Fig. A). Among pathway-selective compounds (namely, kinase inhibitors and rapalogs), the drugs most selective for malignant NK cells fell into two major categories: PI3K/mTOR inhibitors (e.g. temsirolimus, buparlisib) and inhibitors of aurora and polo-like kinases such as rigosertib and GSK-461364 (Fig. B). JAK inhibitors (e.g. ruxolitinib, gandotinib) and CDK inhibitors (e.g. dinaciclib) showed strong efficacy in both malignant NK cells and IL-2 activated healthy NK cells. Conclusions Our exome sequencing results suggest that candidate driver alterations affecting similar signaling pathways underlie the pathogenesis of ANKL as has been reported in NKTCL. Drug sensitivity profiling highlights the PI3K/mTOR pathway as a potential major driver of malignant NK cell proliferation, whereas JAK-STAT signaling appears to be essential in both healthy and malignant NK cells. Components of these pathways harbored mutations in our small cohort of ANKL patients and have been shown to be deregulated by mutations or other mechanisms in previous studies, underlining their importance as putative drivers. The systematic large-scale characterization of drug responses also identified these pathways as potential targets for novel therapy strategies in NK cell malignancies. Figure 1. (A) Unsupervised hierarchical clustering based on drug sensitivity scores (DSS) of NK, AML, CML and T-ALL cell lines. (B) Scatter plot comparing DSS of malignant NK cell lines (average) and healthy IL-2 stimulated NK cells. Figure 1. (A) Unsupervised hierarchical clustering based on drug sensitivity scores (DSS) of NK, AML, CML and T-ALL cell lines. (B) Scatter plot comparing DSS of malignant NK cell lines (average) and healthy IL-2 stimulated NK cells. Disclosures Mustjoki: Novartis: Honoraria, Research Funding; Bristol-Myers Squibb: Honoraria, Research Funding; Pfizer: Honoraria, Research Funding.
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Garman, Christina, Natalie Bindert, Adhira Sunkara, Leocadia Paliulis, and Donna M. Ebenstein. "Deformation Mapping in Micro- and Nanoscale Fibers." MRS Proceedings 1185 (2009). http://dx.doi.org/10.1557/proc-1185-ii04-02.
Повний текст джерелаАнотація:
AbstractSmall-scale natural fibers are among the biological materials being studied by researchers seeking innovative methods to create new high performance materials. For example, spider dragline silk fibers are being studied because of their unique combination of high strength-to-weight ratio and high extensibility, which leads to a tough and lightweight fiber. Biomimetic fibers based on spider silk have been a focus of research for the past decade. However, there are still many unanswered questions about the mechanisms by which silk achieves its unique mechanical properties, as well as challenges in mechanical testing of biomimetic silk fibers (which is often hindered by both small diameters and limited material availability). A method to characterize local mechanical behavior in small diameter fibers was developed to both improve understanding of structure-property relationships in natural fibers and provide a method for comparing mechanical behavior in natural and biomimetic fibers. The deformation mapping technique described in this paper, which utilizes a piezoelectric micromanipulator with pulled glass tips, an inverted microscope with attached camera, and an image processing MATLAB program, is also applicable to the characterization of other micro- and nanoscale fibers where local deformation mechanisms may be of interest (e.g., for mechanical characterization of electrospun fibers).
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Hosemann, Peter, Erich Stergar, Andrew T. Nelson, C. Vieh, and Stuart A. Maloy. "Nanostructured Engineering Alloys for Nuclear Application." MRS Proceedings 1298 (2011). http://dx.doi.org/10.1557/opl.2011.492.
Повний текст джерелаАнотація:
ABSTRACTIn advanced nuclear applications, high temperature and a corrosive environment are present in addition to a high dose radiation field causing displacement damage in the material. In recent times it has been shown that Nanostructured Ferritic Alloys (NFA’s) such as advanced Oxide Dispersion Strengthened (ODS) steels are suitable for this environment as they tolerate high dose irradiation without significant changes in microstructure or relevant mechanical properties.Ion beam irradiation is a fast and cost effective way to induce radiation damage in materials but has limited penetration depth. Therefore, small scale mechanical testing such as nanoindentation and micro compression testing in combination with FIB based sample preparation for micro structural characterization has to be performed allowing a full assessment of the materials’ behavior under radiation environment. In this work two different ODS materials have been irradiated using proton and combined proton and He beams up to 1 dpa at different temperatures. Nanoindentation and LEAP measurements were performed in order to assess the changes in properties of these alloys due to irradiation. The same techniques were applied to intermetallic nanostructured alloys in order to investigate the effectiveness of the metal-intermetallic interface to provide defect sinks for He and radiation damage. It was found that irradiation can cause the formation of intermetallic particles even at room temperature while increasing the material strength significantly.
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Mota-Santiago, Pablo, Jonas Engqvist, Stephen Hall, Roberto Appio, Maxime Maghe, Gautham Sathikumar, Matti Ristinmaa, and Tomás S. Plivelic. "In situ biaxial loading and multi-scale deformation measurements of nanostructured materials at the CoSAXS beamline at MAX IV Laboratory." Journal of Applied Crystallography 56, no. 4 (June 30, 2023). http://dx.doi.org/10.1107/s1600576723005034.
Повний текст джерелаАнотація:
Characterization of the mechanical response of polymers and composite materials relies heavily on the macroscopic stress–strain response in uniaxial tensile configurations. To provide representative information, the deformation process must be homogeneous within the gauge length, which is a condition that is rarely achieved due to stress concentration or inhomogeneities within the specimen. In this work, the development of a biaxial mechanical testing device at the CoSAXS beamline at MAX IV Laboratory is presented. The design facilitates simultaneous measurement of small- and wide-angle X-ray scattering (SAXS/WAXS), allowing assessment of the microstructural configuration before, after and during the continuous deformation process at multiple length scales. The construction also supports multiple deformation conditions, while guaranteeing stability even at high loads. Furthermore, the mechanical experiments can be complemented with spatially resolved mesoscopic surface deformation measurements using 3D-surface digital image correlation (DIC). Polycarbonate (PC) was used to demonstrate the varied material response to multi-axial deformation, as PC is isotropic with a high glass transition temperature (∼150°) and high strength. As a result, a clear correlation between full-field methods and the microstructural information determined from WAXS measurements is demonstrated. When a uniaxial load is applied, homogeneous strain regions could be observed extending perpendicular to the applied load. When a secondary axial load was added (biaxial mode), it was observed that high strain domains were created near the centre of the sample and at the boundaries after yield. With increased strain, the deformation in the main deformation direction also increases. Mechanical reliability was demonstrated by carrying out static loading of polyacrylonitrile-based carbon fibre (CF) bundles. As a result, the nonlinear stiffening behaviour typically observed in CFs was seen, while no evidence of the creation of new voids during loading was observed. The results support the reliability and broad applicability of the developed technique.
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"Mechanical Behavior of ARC Welding using Different Flux Materials." International Journal of Innovative Technology and Exploring Engineering 9, no. 2 (December 10, 2019): 4344–49. http://dx.doi.org/10.35940/ijitee.b7736.129219.
Повний текст джерелаАнотація:
To perform welding process on the material under varying conditions with different flux materials, different welding parameters and further subjecting the material to various suitable tests such as tensile test, hardness test, optical tests and study the characteristics of the material under testing. The tests conducted on the welded work piece it is proposed the suitable parameters under which welding of greater precision can be performed. it is also analyzed the working conditions under which the selected work piece material of stainless steel grade 304 would deviate from its desired characteristics. From the results of the tests it is able to determine the conditions that would reduce the characteristics of the welded work piece. Thus it can be further used for reference when the welding process is done on the same material of stainless steel of grade 304. The electrodes that were chosen for this project were selected by the criteria of widely used and chief material in the welding of various grades of stainless steel. The composition of the chemicals that constitute the electrodes were tribiologically analyzed and studied. The need for high precision welding in large scale as well as small scale industries is relatively high as the threshold for errors in such areas are greatly undesirable. The results of this study would greatly contribute to the reduction of errors and defects in the welding operation.
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El-Nimr, Maher Taha, Ali Mohamed Basha, Mohamed Mohamed Abo-Raya, and Mohamed Hamed Zakaria. "Structural behavior of small-scale reinforced concrete secant pile wall." World Journal of Engineering, March 17, 2022. http://dx.doi.org/10.1108/wje-11-2021-0651.
Повний текст джерелаАнотація:
Purpose To predict the real behavior of the full-scale model using a scale model, optimized simulation should be achieved. In reinforced concrete (RC) models, scaling can be substantially more critical than in single-material models because of multiple reasons such as insufficient bonding strength between small-diameter steel bars and concrete, and excessive aggregate size. Overall, there is a shortfall of laboratory and field-testing studies on the behavior of secant pile walls under lateral and axial loads. Accordingly, the purpose of this study is to investigate the validity and the performance of the 1/10th scaled RC secant pile wall under the influence of different types of loading. Design/methodology/approach The structural performance of the examined models was evaluated using two types of tests: bending and axial compression. A self-compacting concrete mix was suggested, which provided the best concrete mix workability and appropriate compressive strength. Findings Under axial and bending loads, the failure modes were typical. Where the plain and reinforced concrete piles worked in tandem to support the load throughout the loading process, even when they failed. The experimental results were relatively consistent with some empirical equations for calculating the modulus of elasticity and critical buckling load. This confirmed the validity of the proposed model. Originality/value According to the analysis and verification of experimental tests, the proposed 1/10th scaled RC secant pile model can be used for future laboratory purposes, especially in the field of geotechnical engineering.