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1
Choudhry, RS, Kamran A. Khan, Sohaib Z. Khan, Muhammad A. Khan e Abid Hassan. "Micromechanical modeling of 8-harness satin weave glass fiber-reinforced composites". Journal of Composite Materials 51, n.º 5 (28 de julho de 2016): 705–20. http://dx.doi.org/10.1177/0021998316649782.
Resumo:
This study introduces a unit cell-based finite element micromechanical model that accounts for correct post cure fabric geometry, in situ material properties and void content within the composite to accurately predict the effective elastic orthotropic properties of 8-harness satin weave glass fiber-reinforced phenolic composites. The micromechanical model utilizes a correct post cure internal architecture of weave, which was obtained through X-ray microtomography tests. Moreover, it utilizes an analytical expression to update the input material properties to account for in situ effects of resin distribution within yarn (the yarn volume fraction) and void content on yarn and matrix properties. This is generally not considered in modeling approaches available in literature and in particular, it has not been demonstrated before for finite element micromechanics models of 8-harness satin weave composites. The unit cell method is used to obtain the effective responses by applying periodic boundary conditions. The outcome of the analysis based on the proposed model is validated through experiments. After validation, the micromechanical model was further utilized to predict the unknown effective properties of the same composite.
2
Bergo, Sondre, David Morin, Tore Børvik e Odd Sture Hopperstad. "Micromechanical modelling of ductile fracture in pipeline steel using a bifurcation-enriched porous plasticity model". International Journal of Fracture 227, n.º 1 (29 de dezembro de 2020): 57–78. http://dx.doi.org/10.1007/s10704-020-00495-7.
Resumo:
AbstractIn this paper, we investigate the possibility of predicting ductile fracture of pipeline steel by using the Gurson–Tvergaard–Needleman (GTN) model where the onset of void coalescence is determined based on in situ bifurcation analyses. To this end, three variants of the GTN model, one of which includes in situ bifurcation, are calibrated for a pipeline steel grade X65 using uniaxial and notch tension tests. Then plane-strain tension tests and Kahn tear tests of the same material are used for assessment of the credibility of the three models. Explicit finite element simulations are carried out for all tests using the three variants of the GTN model, and the results are compared to the experimental data. The capability of the simulation models to capture onset of fracture and crack propagation in the pipeline steel is evaluated. It is found that the use of in situ bifurcation as a criterion for onset of void coalescence in each element makes the GTN model easier to calibrate with less free parameters, all the while obtaining similar or even better predictions as other widely used formulations of the GTN model over a wide range of different stress states.
3
Šittner, P., V. Novák, P. Lukáš e M. Landa. "Stress-Strain-Temperature Behavior Due to B2-R-B19′ Transformation in NiTi Polycrystals". Journal of Engineering Materials and Technology 128, n.º 3 (26 de fevereiro de 2006): 268–78. http://dx.doi.org/10.1115/1.2204945.
Resumo:
Thermomechanical behavior of superelastic NiTi wires undergoing sequential B2-R-B19′ martensitic transformation was investigated by two recently developed in-situ experimental methods (in-situ neutron diffraction and combined ultrasonic and electric resistance measurements) capable of detecting and recognizing the activity of various deformation/transformation processes in NiTi and theoretically by micromechanical modeling. An earlier model of SMA polycrystal transformation is further developed, so it accounts for the strains due to the R-phase related deformation processes in activated NiTi. A continuous variation of the rhombohedral distortion angle α of the R-phase structure with temperature and stress is newly introduced as a legitimate deformation mechanism. Simulation results for NiTi bars and wires exposed to three types of thermomechanical tests—mechanical loading at constant temperature, cooling under constant stress, and recovery stress tests are presented and confronted with results.
4
Sun, Tianyi, Jaehun Cho, Zhongxia Shang, Tongjun Niu, Jie Ding, Jian Wang, Haiyan Wang e Xinghang Zhang. "Deformation mechanism in nanolaminate FeCrAl alloys by in situ micromechanical strain rate jump tests at elevated temperatures". Scripta Materialia 215 (julho de 2022): 114698. http://dx.doi.org/10.1016/j.scriptamat.2022.114698.
5
Prasad, K. Nagendra, BR Srinivasa Murthy, A. Vatsala e T. G. Sitharam. "Yielding of sensitive clays: micromechanical considerations". Canadian Geotechnical Journal 35, n.º 1 (1 de fevereiro de 1998): 169–74. http://dx.doi.org/10.1139/t97-072.
Resumo:
Test results reported on several natural sensitive soils show significant anisotropy of the yield curves, which are generally oriented along the coefficient of earth pressure at rest (K0) axis. An attempt is made in this paper to explain the anisotropy in yielding from microstructural considerations. An elliptic pore, with particle domains aligned along the periphery of the pore, and with the major axis of the pore being oriented along the direction of the in situ major principal stress, is chosen as the unit of microstructure. An analysis of forces at the interdomain contacts around the ellipse is carried out with reference to experimentally determined yield stress conditions of one soil, and a yield criteria is defined. The analysis, with the proposed yield criteria, enables one to define the complete yield curve for any other soil from the results of only two tests (one constant eta compression test with eta close to eta sub K0, where eta is the stress ratio (= q/p) and eta sub K0 is the stress ratio corresponding to anisotropic K0 compression, and another undrained shear test). Predicted yield curves are compared with experimental yield curves of several soils reported in the literature.Key words: sensitive clays, yield criteria, anisotropy, microstructure.
6
Hu, Junfeng, Xi Deng, Xutong Zhang, Wen-Xue Wang e Terutake Matsubara. "Effect of Off-Axis Ply on Tensile Properties of [0/θ]ns Thin Ply Laminates by Experiments and Numerical Method". Polymers 13, n.º 11 (31 de maio de 2021): 1809. http://dx.doi.org/10.3390/polym13111809.
Resumo:
The effect of off-axis ply on the tensile properties of unbalanced symmetric [0/θ]ns laminates was explored through experimental and numerical analysis. Six CFRP [0/θ]2s plies with different off-axis angles θ were fabricated for tensile tests. In situ observations of the damage to the laminates were conducted to investigate the initiation and progressive growth of the laminates during the tension tests. The fiber fractures, crack initiation, and progressive propagation were analyzed by observing the free edge of the laminates, and the difference in damage behavior caused by different off-axis angles was investigated. All the six [0/θ]2s plies with off-axis angles θ ranging from 15° to 90° showed approximate linear stress–strain responses in the tensile tests. Matrix cracks were not observed prior to the final catastrophic failure in the off-axis layers of the [0/θ]2s laminates with a θ in the range of 15–60°. Finite element analysis (FEA) of the [0/θ]s plies was conducted using a 3D micromechanical model, in which matrix cracking and fiber-matrix debonding in the off-axis layer were simulated using a cohesive interface element. Three micromechanical crack-free, cohesive interface, and initial crack models were analyzed to predict the influence of the matrix cracks inside the off-axis layer on the damage behavior of the [0/θ]s laminates. The numerical results from the initial crack micromechanical model show a lower bound of the tensile strength of the [0/θ]s plies. A high stress concentration is observed adjacent to the cracked off-axis layer, inducing a tensile strength loss of about 20%.
7
Alfreider, M., M. Meindlhumer, V. Maier-Kiener, A. Hohenwarter e D. Kiener. "Extracting information from noisy data: strain mapping during dynamic in situ SEM experiments". Journal of Materials Research 36, n.º 11 (19 de janeiro de 2021): 2291–304. http://dx.doi.org/10.1557/s43578-020-00041-0.
Resumo:
Abstract Micromechanical testing techniques can reveal a variety of characteristics in materials that are otherwise impossible to address. However, unlike to macroscopic testing, these miniaturized experiments are more challenging to realize and analyze, as loading and boundary conditions can often not be controlled to the same extent as in standardized macroscopic tests. Hence, exploiting all possible information from such an experiment seems utmost desirable. In the present work, we utilize dynamic in situ microtensile testing of a nanocrystalline equiatomic CoCrFeMnNi high entropy alloy in conjunction with initial feature tracking to obtain a continuous two-dimensional strain field. This enables an evaluation of true stress–strain data as well as of the Poisson’s ratio and allows to study localization of plastic deformation for the specimen. We demonstrate that the presented image correlation method allows for an additional gain of information in these sophisticated experiments over commercial tools and can serve as a starting point to study deformation states exhibiting more complex strain fields. Graphic abstract
8
Shen, Yang, Thilo F. Morgeneyer, Jérôme Garnier, Lucien Allais, Lukas Helfen e Jérôme Crépin. "Quantitative Anisotropic Damage Mechanism in a Forged Aluminum Alloy Studied by Synchrotron Tomography and Finite Element Simulations". Advances in Materials Science and Engineering 2019 (25 de julho de 2019): 1–12. http://dx.doi.org/10.1155/2019/8739419.
Resumo:
A highly anisotropic toughness behavior has been revealed on a forged AA6061 aluminum alloy by toughness tests with CT specimens. The toughness values with specimens loaded on the longitudinal direction are larger than that loaded on the transverse direction due to the anisotropic shape and distribution of coarse precipitates induced by the morphological anisotropy of grains during forging process. Synchrotron radiation computed tomography analysis on as-received material and arrested cracks revealed different fracture modes for the two loading configurations. The damage mechanism has been validated by finite element simulations based on the Gurson–Tvergaard–Needleman micromechanical damage model with different sets of damage parameters for the two loading configurations obtained from quantitative void volume fraction analysis on SRCT data, in situ SEM experiments, and SRCT microstructural analysis.
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Roscioli, Gianluca, Seyedeh Mohadeseh Taheri-Mousavi e Cemal Cem Tasan. "How hair deforms steel". Science 369, n.º 6504 (6 de agosto de 2020): 689–94. http://dx.doi.org/10.1126/science.aba9490.
Resumo:
Steels for sharp edges or tools typically have martensitic microstructures, high carbide contents, and various coatings to exhibit high hardness and wear resistance. Yet they become practically unusable upon cutting much softer materials such as human hair, cheese, or potatoes. Despite this being an everyday observation, the underlying physical micromechanisms are poorly understood because of the structural complexity of the interacting materials and the complex boundary conditions of their co-deformation. To unravel this complexity, we carried out interrupted tests and in situ electron microscopy cutting experiments with two micromechanical testing setups. We investigated the findings analytically and numerically, revealing that the spatial variation of lath martensite structure plays the key role leading to a mixed-mode II-III cracking phenomenon before appreciable wear.
10
Fiedler, Bodo, Stefan Holst, Thomas Hobbiebrunken, Masaki Hojo e Karl Schulte. "Modelling of the Initial Failure of Cfrp Structures by Partial Discretisation: Amicro / Macro-Mechanical Approach of First Ply Failure". Advanced Composites Letters 13, n.º 5 (setembro de 2004): 096369350401300. http://dx.doi.org/10.1177/096369350401300501.
Resumo:
The formation of transverse matrix cracks is the early failure in carbon fibre reinforced composites (CFRP). Unidirectional laminates with 90° fibre orientation were tested by transverse tensile tests and in situ under 3 point bending load in the scanning electron microscope (SEM). Finite element analysis were carried on the microscopic level hexagonal unit cell of fibre and matrix, as on the macroscopic level based on homogenized fibre and matrix properties as well. To link the micromechanical approach with the homogenized description of composite structures was done by transferring boundary conditions from one model to the other. The influence of the temperature on the Young's modulus, the non-linear stress-strain behaviour and the strength of the matrix on the micro residual stresses and matrix failure was taken into account has been investigated in detail. Process induced thermal residual stresses and matrix failure of unidirectional carbon fibre reinforced composites (CFRP).
11
Li, D. S., e M. R. Wisnom. "Non-linear stress-strain behaviour of unidirectional silicon carbide fibre reinforced aluminium alloy". Journal of Strain Analysis for Engineering Design 27, n.º 3 (1 de julho de 1992): 137–44. http://dx.doi.org/10.1243/03093247v273137.
Resumo:
Longitudinal tensile tests have been conducted on unidirectional SiC fibre reinforced 6061 aluminium matrix composites in the annealed and as-manufactured conditions. The results are presented in terms of stress-strain curves and tangent modulus-strain relations, which show considerable non-linearity. Corresponding micromechanical finite element modelling is performed including the effects of the manufacturing process on the matrix in-situ properties. The analysis shows that the non-linear behaviour of the composite is caused by the elastic-plastic deformation of the matrix alloy. The matrix fully yields during the cooldown from manufacturing. Residual stress relaxation plays an important role in the stress-strain characteristics of the annealed aluminium matrix composite by introducing some initial elastic deformation. The amount of elastic deformation for the as-manufactured condition is greater because of subsequent age hardening. However, more linear elastic deformation was observed than predicted in the as-manufactured specimens, which is believed to be due to higher precipitation hardening caused by metallurgical effects induced in the manufacturing process.
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Li, Qiong, Jürgen Gluch, Zhongquan Liao, Juliane Posseckardt, André Clausner, Magdalena Łępicka, Małgorzata Grądzka-Dahlke e Ehrenfried Zschech. "Morphology and Mechanical Properties of Fossil Diatom Frustules from Genera of Ellerbeckia and Melosira". Nanomaterials 11, n.º 6 (20 de junho de 2021): 1615. http://dx.doi.org/10.3390/nano11061615.
Resumo:
Fossil frustules of Ellerbeckia and Melosira were studied using laboratory-based nano X-ray tomography (nano-XCT), transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS). Three-dimensional (3D) morphology characterization using nondestructive nano-XCT reveals the continuous connection of fultoportulae, tube processes and protrusions. The study confirms that Ellerbeckia is different from Melosira. Both genera reveal heavily silicified frustules with valve faces linking together and forming cylindrical chains. For this cylindrical architecture of both genera, valve face thickness, mantle wall thickness and copulae thickness change with the cylindrical diameter. Furthermore, EDS reveals that these fossil frustules contain Si and O only, with no other elements in the percentage concentration range. Nanopores with a diameter of approximately 15 nm were detected inside the biosilica of both genera using TEM. In situ micromechanical experiments with uniaxial loading were carried out within the nano-XCT on these fossil frustules to determine the maximal loading force under compression and to describe the fracture behavior. The fracture force of both genera is correlated to the dimension of the fossil frustules. The results from in situ mechanical tests show that the crack initiation starts either at very thin features or at linking structures of the frustules.
13
Charara, Mohammad, Mohammad Abshirini, Mrinal C. Saha, M. Cengiz Altan e Yingtao Liu. "Highly sensitive compression sensors using three-dimensional printed polydimethylsiloxane/carbon nanotube nanocomposites". Journal of Intelligent Material Systems and Structures 30, n.º 8 (18 de março de 2019): 1216–24. http://dx.doi.org/10.1177/1045389x19835953.
Resumo:
This article presents three-dimensional printed and highly sensitive polydimethylsiloxane/multi-walled carbon nanotube sensors for compressive strain and pressure measurements. An electrically conductive polydimethylsiloxane/multi-walled carbon nanotube nanocomposite is developed to three-dimensional print compression sensors in a freestanding and layer-by-layer manner. The dispersion of multi-walled carbon nanotubes in polydimethylsiloxane allows the uncured nanocomposite to stand freely without any support throughout the printing process. The cross section of the compression sensors is examined under scanning electron microscope to identify the microstructure of nanocomposites, revealing good dispersion of multi-walled carbon nanotubes within the polydimethylsiloxane matrix. The sensor’s sensitivity was characterized under cyclic compression loading at various max strains, showing an especially high sensitivity at lower strains. The sensing capability of the three-dimensional printed nanocomposites shows minimum variation at various applied strain rates, indicating its versatile potential in a wide range of applications. Cyclic tests under compressive loading for over 8 h demonstrate that the long-term sensing performance is consistent. Finally, in situ micromechanical compressive tests under scanning electron microscope validated the sensor’s piezoresistive mechanism, showing the rearrangement, reorientation, and bending of the multi-walled carbon nanotubes under compressive loads, were the main reasons that lead to the piezoresistive sensing capabilities in the three-dimensional printed nanocomposites.
14
Neag, Adriana, Véronique Favier, Régis Bigot e Helen V. Atkinson. "Analysis by Micromechanical Modeling on Material Flow under Rapid Compression in the Semi-Solid State". Solid State Phenomena 217-218 (setembro de 2014): 182–87. http://dx.doi.org/10.4028/www.scientific.net/ssp.217-218.182.
Resumo:
Different types of semi-solid processing are used to produce a variety of components. In this context, the use of FE simulations to obtain the filling of the dies and to optimize the semi-solid processing is clearly of a great interest. To carry it out properly in an isothermal case, the semi-solid flow into the die and friction phenomena have to be correctly described. In addition, comparisons between experiments and simulations are needed to assess the reliability of the modeling and to improve the understanding of the processing. In situ visualization of the semi-solid flow during processing is complex since the dies are closed and opaque. One of the main recent work with transparent glass sided dies to film die filling is that by Atkinson and Ward (2006). The purpose of this work is to compare numerical simulations to these experiments. Numerical simulations were performed with the solid mechanics-based software FORGE©. A micromechanical model accounting for the liquid and solid behaviour and their spatial distribution within the material (Favier et al, 2009) was used. The model parameters were identified using rapid compression tests on the A357 aluminium alloy (Favier and Atkinson, 2011). The slurry temperature corresponds to 0.5 solid fraction. Comparisons were focused on the flow behaviour. The impact of the presence of an obstacle and of the shape of the obstacle was investigated. The numerical simulations reproduced quite well the flow behaviour for the case with and without central obstacle. However, the change in flow due to an increase of the ram speed from 250 mm/s to 1000 mm/s is not captured.
15
Altstädt, V., L. Lucca de Freitas e D. W. Schubert. "Rheological and mechanical properties of poly(α-methylstyrene-co-acrylonitrile)/ poly[(methyl acrylate-co-methyl methacrylate)] blends in miscible and phase separated regimes of various morphologies. Part IV: Influence of the morphology on the mechanical properties (IUPAC Technical Report)". Pure and Applied Chemistry 76, n.º 2 (1 de janeiro de 2004): 389–413. http://dx.doi.org/10.1351/pac200476020389.
Resumo:
Influences of the morphology on the thermal and mechanical properties of poly(α-methylstyrene-co-acrylonitrile)/poly[(methyl acrylate-co-methyl methacrylate)] (PαMSAN/PMMA) blends have been investigated. DSC measurements confirm that all blends were phase-separated due to the temperature at which they have been extruded and squeeze-molded. Based on the cloudpoints of 17 blends and TEM micrographs, the interaction parameters as a function of temperature and composition were calculated for the lower critical solution temperature (LCST) system. Varying the morphology by annealing without changing the composition of the system resulted in a finer morphology for the 85/15 blends, while the 40/60 blend showed an increase in the domain size with annealing time. Tensile strength and fracture toughness indicate that the PαMSAN domains in the tougher PMMA matrix cause a deterioration in the mechanical properties of the blends, while the PMMA domains in the PαMSAN matrix improve the mechanical properties. No clear conclusions on the influence of morphology on fracture toughness could be drawn because in one case (40/60 blend) the fracture toughness decreases slightly by annealing and in the other case (85/15 blend) fracture toughness values increase slightly with decreasing phase separation by annealing. In situ strained thin sections in the TEM indicated no effect of annealing on the micromechanical behavior. Shear deformation was observed as the prevailing deformation mechanism in the PαMSAN and fibrillized crazing in the PMMA-rich blends. From fatigue crack growth experiments it was concluded that the fatigue crack propagation threshold is higher for PMMA than for PαMSAN. Tests on the annealed samples of PαMSAN/PMMA 85/15 and 40/60 showed that the differences in morphology did not affect the fatigue crack growth resistance significantly. From the features of the fracture surface investigated by SEM, the conclusion can be drawn that the fatigue crack propagates faster in the more brittle PαMSAN phase, but the overall advance of the crack front is controlled at the interphases, resulting in a crack propagation gradient along the interphase.
16
Du, Hui, Kristen Carpenter, David Hui e Mileva Radonjic. "MICROSTRUCTURE AND MICROMECHANICS OF SHALE ROCKS: CASE STUDY OF MARCELLUS SHALE". Facta Universitatis, Series: Mechanical Engineering 15, n.º 2 (2 de agosto de 2017): 331. http://dx.doi.org/10.22190/fume170602016d.
Resumo:
Shale rocks play an essential role in petroleum exploration and production because they can occur either as source rocks or caprocks depending on their mineralogical composition and microstructures. More than 60% of effective seals for geologic hydrocarbon bearing formations as natural hydraulic barriers constitute of shale caprocks. The effectiveness of caprock depends on its ability to immobilize fluids, which include a low permeability and resilience to the in-situ formation of fractures as a result of pressurized injection. The alteration in sealing properties of shale rocks is directly related to the differences in their mineralogical composition and microstructure.Failure of the shale starts with deterioration at micro/nanoscale, the structural features and properties at the micro/nanoscale can significantly impact the durability performance of these materials at the macroscale, therefore, study at micro/nanoscale becomes necessary to get better understanding of the hydraulic barriers materials to prevent failure and enhance long-term geologic storage of fluids.Indentation tests were conducted at both micro and nanometer level on Marcellus shale samples to get the mechanical properties of bulk and individual phase of the multiphase materials. The mechanical properties map were created based on the nano indentation results and the properties of each individual phase can be correlated with bulk response in the multiphase composite; the effect of each component on the microstructure and bulk mechanical properties can be better understood.
17
Rojas-Ulloa, Carlos, Marian Valenzuela, Víctor Tuninetti e Anne-Marie Habraken. "Identification and validation of an extended Stewart-Cazacu micromechanics damage model applied to Ti–6Al–4V specimens exhibiting positive stress triaxialities". Proceedings of the Institution of Mechanical Engineers, Part L: Journal of Materials: Design and Applications 235, n.º 6 (6 de maio de 2021): 1248–61. http://dx.doi.org/10.1177/14644207211009933.
Resumo:
In this research, the Stewart-Cazacu micromechanics coupled damage model is extended and validated adding nucleation and coalescence models as new damage mechanisms. The Ti–6Al–4V titanium alloy is chosen as a suitable hcp ductile material to be modeled using this extended damage law. The characterization of the damage evolution in this alloy is addressed throughout a quasi-static experimental campaign. Damage characterization relies on in situ X-ray tomography data and scanning electron microscopy imaging technique. The validation procedure consists in the implementation into the finite element research software Lagamine of ULiège and in the comparison of numerical predictions and experimental results. Load–displacement curves and damage-related state variables at fracture configuration from smooth and notched bar specimens submitted to tensile tests are analyzed. The nucleation and coalescence model extensions as well as an accurate elastoplastic and damage material parameter identification for Ti–6Al–4V samples are essential features to reach a validated model. The prediction capabilities exhibited for large strains are in good agreement with experimental results, while the near-fracture strains can still be improved.
18
Ignat, Michel T., Sabine Lay, Francine Roussel d'Herbey, Cedric Seguineau, Christophe Malhaire, Xavier Lafontan, Jean Michel Desmarres e Sebastiano Brida. "Micro Tensile Tests on Aluminium Thin Films: Tensile Device and In Situ Observations". MRS Proceedings 1139 (2008). http://dx.doi.org/10.1557/proc-1139-gg04-04.
Resumo:
AbstractThe results of micromechanical tensile experiments performed on thin aluminum samples are presented and discussed. The micro tensile test system and the design of the samples, based on finite element modeling (FEM), and their production by micromachining are briefly described. Some examples of the stress strain curves are presented. The Young's modulus and critical parameters (flow and rupture stress and strains) are reported. The micro structural changes induced by the tensile experiment were observed during and after the testing by scanning electron microscopy (SEM) and transmission electron microscopy (TEM).The results of micromechanical tensile experiments performed on thin aluminum samples are presented and discussed. The micro tensile test system and the design of the samples, based on finite element modeling (FEM), and their production by micromachining are briefly described. Some examples of the stress strain curves are presented. The Young's modulus and critical parameters (flow and rupture stress and strains) are reported. The micro structural changes induced by the tensile experiment were observed during and after the testing by scanning electron microscopy (SEM) and transmission electron microscopy (TEM).
19
Greek, S., F. Ericson, S. Johansson e J. Å. Schweitz. "Micromechanical Tensile Testing". MRS Proceedings 436 (1996). http://dx.doi.org/10.1557/proc-436-227.
Resumo:
AbstractA method is described where tensile tests can be performed in situ on micromachined structures. The testing equipment consists of a testing unit mounted on a micromanipulator in a Scanning Electron Microscope (SEM). The fracture loads of micromachined beam structures made from thick and thin film polysilicon as well as from electrodeposited nickel and nickeliron alloy were measured, and the fracture strengths then calculated via measurements of the test structures’ initial cross-sectional areas. The statistical scatter of the polysilicon fracture strength values were evaluated by Weibull statistics. The mean fracture strength and the Weibull modulus, a measure of the scatter, were obtained
20
Zagrebelnya, Andrey V., John C. Nelson, Erica T. Lilleodden, Sundar Ramamurthy e C. Barry Carter. "Alumina-Silicate Glass Interfacial Properties Probed by Micromechanical Testing Techniques". MRS Proceedings 401 (1995). http://dx.doi.org/10.1557/proc-401-103.
Resumo:
AbstractMicromechanical properties of the interfaces between alumina and calcium-aluminosilicate (CAS) glasses were tested using various micro/nanoindentation techniques. The interfaces were produced by depositing continuous films of anorhtite (CaAl2Si2O8) onto single-crstal α-Al2O3 of two crystallographic orientations by pulsed-laser deposition (PLD).The mechanical behavior of the interfaces was examined using two different depthsensing indentation instruments. Three types of tests, namely indentation, microscratch, and in-situ indentation combined with atomic force microscopy (AFM) imaging were conducted using different operating modes. The deformation behavior observed for the indentations and microscratches has been correlated with irregularities observed in the load-displacement curves. In the first two cases, scanning electron microscopy (SEM) has been used to characterize the deformation structures associated with the deformed regions. The in-situ experiments allow force-displacement measurements and AFM imaging immediately before and after indentation. The preindent and postindent morphology of the surface could then be characterized.
21
Meindlhumer, M., T. Ziegelwanger, J. Grau, H. Sternschulte, M. Sztucki, D. Steinmüller-Nethl e J. Keckes. "Micromechanical properties of micro- and nanocrystalline CVD diamond thin films with gradient microstructures and stresses". Journal of Vacuum Science & Technology A 42, n.º 2 (12 de janeiro de 2024). http://dx.doi.org/10.1116/6.0003235.
Resumo:
Chemical vapor deposition produced diamonds attract considerable scientific and industrial interest due to their exceptional mechanical and functional properties. Here, hot filament (HF) chemical vapor deposition was used to synthesize two diamond thin films with different cross-sectional microstructure and residual stresses. Structural characterization by scanning electron microscopy, Raman spectroscopy, and cross-sectional synchrotron x-ray nanodiffraction revealed different diamond morphologies. While the microcrystalline diamond film exhibits pronounced microstructural gradients expressed by gradually increasing (i) intensities of the 111 Debye-Scherrer rings, (ii) ⟨110⟩ fiber texture sharpness, (iii) grain size, and (iv) slightly oscillating residual stress at the level of −0.5 GPa, the nanocrystalline diamond film showed no pronounced cross-sectional variation of microstructure above the nucleation zone of ∼0.5 μm and a steady stress level of 0.25 GPa. In situ micromechanical cantilever bending tests revealed highly different mechanical properties of the two films. In detail, Young's modulus of 830 ± 53 and 459 ± 53 GPa, fracture stress of 12.4 ± 0.8 and 7.8 ± 1.0 GPa, and fracture toughness values of 6.9 ± 0.4 and 3.6 ± 0.3 MPa⋅m½ were evaluated for the micro- and nanocrystalline diamond films, respectively. In summary, this study provides valuable insights into the microstructure-residual stress correlation in micro- and nanocrystalline diamond films, especially illuminating their influence on micromechanical properties.
22
Kalchev, Y., R. Zehl, T. Piotrowiak, A. Kostka, D. Naujoks, J. Pfetzing-Micklich e A. Ludwig. "Microstructure and Mechanical Properties of a Ni-Based Superalloy Thin Film Investigated by Micropillar Compression". Metallurgical and Materials Transactions A, 23 de março de 2023. http://dx.doi.org/10.1007/s11661-023-07017-9.
Resumo:
AbstractThe microstructure and local micromechanical properties of a Ni-based superalloy thin film produced by magnetron sputtering using ERBO/1 sputter targets were investigated. The thin film consists of columnar nanograins (an average size of ~ 45 nm) with mostly < 111 > orientation. Inside the nanograins, very fine nanotwins with an average thickness of ~ 3 nm are present. In-situ micropillar compression tests, complemented by nanoindentation, were conducted to evaluate the mechanical characteristics. The microhardness and Young’s modulus of the thin film correspond to ~ 11 and 255 GPa, respectively, the critical strength to ~ 4 GPa. The plastic deformation of the micropillars occurs through the formation of a shear band initiating at the top of the pillar. Inside the shear band, globular grains with random orientation form during the deformation process, while the regions near to the shear band remained unaffected.
23
Zagrebelny, Andrey V., Erica T. Lilleodden e C. Barry Carter. "Effect of Glass Composition on Mechanical Properties of Interfaces Between Alumina and Silicate Glass". MRS Proceedings 458 (1996). http://dx.doi.org/10.1557/proc-458-179.
Resumo:
ABSTRACTInterfaces between glass and crystalline grains have been examined using a thin-film geometry which allows the use of newly developed experimental methods for micromechanical testing of interfaces. In this approach, continuous films of thicknesses ranging 100–200 nm of anorthite (CaAl2Si2O8), celsian (BaAl2Si2O8), and monticellite (CaMgSiO4) are deposited onto single-crystal Al2O3 (α-structure) surfaces of different crystallographic orientations by pulsed-laser deposition (PLD).Mechanical properties such as hardness, stiffness, and reduced Young's modulus were probed with a newly developed high-resolution depth-sensing indentation instrument. Emphasis has been placed on examining how changes in the glass composition will affect the mechanical properties of the single-crystal Al2O3/silicate-glass interfaces. The indentation data obtained from these experiments correlate directly to the morphology of the deformed regions imaged with atomic force microscopy (AFM). Nanomechanical tests combined with AFM imaging of the deformed regions allow force-displacement measurements and in-situ imaging of the same regions of the specimen before and immediately after indentation. This new technique eliminates the uncertainty of locating the indenter after unloading.
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Sayers, Colin M., W. Scott Leaney e Tom R. Bratton. "Stress‐induced anisotropy in Gulf of Mexico sandstones and the prediction of in situ stress". Geophysical Prospecting, 29 de fevereiro de 2024. http://dx.doi.org/10.1111/1365-2478.13497.
Resumo:
AbstractThe strong sensitivity of velocity to stress observed in many sandstones originates from the response of stress‐sensitive discontinuities such as grain contacts and microcracks to a change in effective stress. If the change in stress is anisotropic, then the change in elastic wave velocities will also be anisotropic. Characterization of stress‐induced elastic anisotropy in sandstones may enable estimation of the in situ three dimensional stress tensor with important application in solving problems occurring during drilling, such as borehole instability, and during production, such as sanding and reservoir compaction. Other applications include designing hydraulic fracture stimulations and quantifying production‐induced stresses which may lead to rock failure. Current methods for estimating stress anisotropy from acoustic anisotropy rely on third‐order elasticity, which ignores rock microstructure and gives elastic moduli that vary linearly with strain. Elastic stiffnesses in sandstones vary non‐linearly with stress. Using P‐ and S‐wave velocities measured on Gulf of Mexico sandstones, this non‐linearity is found to be consistent with a micromechanical model in which the discontinuities are represented by stress‐dependent normal and shear compliances. Stress‐induced anisotropy increases with increasing stress anisotropy at small stress but then decreases at larger stresses as the discontinuities close and their compliance decreases. When the ratio of normal‐to‐shear compliance of the discontinuities is unity, the stress‐induced anisotropy is elliptical, but for values different from unity, the stress‐induced anisotropy becomes anelliptic. Although vertical stress can be obtained by integrating the formation's bulk density from the surface to the depth of interest, and minimum horizontal stress can be estimated using leak‐off tests or hydraulic fracture data, maximum horizontal stress is more difficult to estimate. Maximum horizontal stress is overpredicted based on third‐order elasticity using measured shear moduli, with estimates of pore pressure, vertical stress and minimum horizontal stress as input. The non‐linear response of grain contacts and microcracks to stress must be considered to improve such estimates.
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Pu, Chao, e Yanfei Gao. "Crystal Plasticity Analysis of Stress Partitioning Mechanisms and Their Microstructural Dependence in Advanced Steels". Journal of Applied Mechanics 82, n.º 3 (1 de março de 2015). http://dx.doi.org/10.1115/1.4029552.
Resumo:
Two-phase advanced steels have an optimized combination of high yield strength and large elongation strain at failure, as a result of stress partitioning between a hard phase (martensite) and a ductile phase (ferrite or austenite). Provided with strong interfaces between the constituent phases, the failure in the brittle martensite phase will be delayed by the surrounding geometric constraints, while the rule of mixture will dictate a large strength of the composite. To this end, the microstructural design of these composites is imperative especially in terms of the stress partitioning mechanisms among the constituent phases. Based on the characteristic microstructures of dual phase and multilayered steels, two polycrystalline aggregate models are constructed to simulate the microscopic lattice strain evolution of these materials during uniaxial tensile tests. By comparing the lattice strain evolution from crystal plasticity finite element simulations with advanced in situ diffraction measurements in literature, this study investigates the correlations between the material microstructure and the micromechanical interactions on the intergranular and interphase levels. It is found that although the applied stress will be ultimately accommodated by the hard phase and hard grain families, the sequence of the stress partitioning on grain and phase levels can be altered by microstructural designs. Implications of these findings on delaying localized failure are also discussed.
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Busch, Andreas, Suzanne Hangx, Stephanie Vialle, Roberto Emanuele Rizzo e Niko Kampman. "Mechanical weakening of a mudrock seal by reaction with CO2-charged fluids". Geology, 25 de abril de 2023. http://dx.doi.org/10.1130/g51250.1.
Resumo:
The long-term interaction of CO2-charged fluids with low permeability cap rocks is important for seal integrity assessment. To address this potential risk, we studied long-term geomechanical changes in a reservoir seal due to fluid-rock interactions with CO2-charged fluids, focusing on a natural CO2 analogue near Green River, Utah, USA. The observed chemo-mechanical changes are on the millimeter scale, which required small-scale petrophysical, mineralogical, and micromechanical analyses. Results showed that over the 7 cm thick reaction front, the low permeability cap rock underwent mechanical weakening, as indicated by indentation tests. This weakening is inferred to be due to dissolution of dolomite and hematite, with the former leading to porosity increase, as shown by small-angle neutron scattering, while the latter likely led to loss of electrostatic forces between the clay particles. This resulted in loss of cohesion, compaction, and formation of bedding-parallel fractures. Microfracturing occurred in situ, as evidenced by fractures infilled with pyrite and gypsum. This study demonstrates that mechanical weakening of cap rocks might occur, but only over time scales of ∼100,000 yr and over small distances. Considering the thickness of cap rocks above CO2 storage reservoirs, we do not anticipate a considerable threat of losing containment integrity over time scales of hundreds to thousands of years as a result of these small-scale fluid-rock interactions.
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Hurley, Ryan C., Ghassan Shahin, Brett S. Kuwik e Kwangmin Lee. "Assessing continuum plasticity postulates with grain stress and local strain measurements in triaxially compressed sand". Proceedings of the National Academy of Sciences 120, n.º 32 (31 de julho de 2023). http://dx.doi.org/10.1073/pnas.2301607120.
Resumo:
Critical state and continuum plasticity theories have been used in research and engineering practice in soil and rock mechanics for decades. These theories rely on postulated relationships between material stresses and strains. Some classical postulates include coaxiality between stress and strain rates, stress–dilatancy relationships, and kinematic assumptions in shear bands. Although numerical and experimental data have quantified the strains and grain kinematics in such experiments, little data quantifying grain stresses are available. Here, we report the first-known grain stress and local strain measurements in triaxial compression tests on synthetic quartz sands using synchrotron X-ray tomography and 3D X-ray diffraction. We use these data to examine the micromechanics of shear banding, with a focus on coaxiality, stress-dilatancy, and kinematics within bands. Our results indicate the following: 1) elevated deviatoric stress, strain, and stress ratios in shear bands throughout experiments; 2) coaxial principal compressive stresses and strains throughout samples; 3) significant contraction along shear bands; 4) vanishing volumetric strain but nonvanishing stress fluctuations throughout samples at all stages of deformation. Our results provide some of the first-known in situ stress and strain measurements able to aid in critically evaluating postulates employed in continuum plasticity and strain localization theories for sands.