Showing papers on "Shear band published in 2020"
TL;DR: Relative density grading, cell size grading, and multi-morphology (lattice type grading) are mechanically investigated for sheet-based lattices with topologies based on triply periodic minimal surfaces, and FE analysis revealed that sheet-networks multi- morphology lattices exhibit higher elastic properties as compared to solid-network multi- Morphology lattice.
Abstract: Functionally graded and multi-morphology lattices are gaining increased attention recently in the tissue engineering research community because of the ability to control their physical, mechanical and geometrical properties spatially. In this work, relative density grading, cell size grading, and multi-morphology (lattice type grading) are mechanically investigated for sheet-based lattices with topologies based on triply periodic minimal surfaces (TPMS), namely; the Schoen Gyroid, and Schwarz Diamond minimal surfaces. To investigate the role of loading direction on the exhibited deformation mechanism, tests were performed parallel and perpendicular to the grading direction. For relative density grading, testing parallel to grading direction exhibited a layer-by-layer deformation mechanism with a lower Young's Modulus as compared to samples tested perpendicular to grading direction which exhibited a shear band deformation. Moreover, multi-morphology lattices exhibited a shift in deformation mechanism from layer-by-layer to the formation of a shear band at the interface between the different TPMS morphologies when tested parallel and perpendicular to hybridization direction, respectively. FE analysis revealed that sheet-networks multi-morphology lattices exhibit higher elastic properties as compared to solid-networks multi-morphology lattices.
166 citations
TL;DR: In this paper, a study was conducted on the microstructures and mechanical properties of nickel samples with two distinct types of heterostructures, including coarse-grained lamellae embedded in a matrix consisting of a very high density of dislocation structures.
129 citations
TL;DR: In this paper, a series of triaxial compression tests equipped with permeability measurement on sandstone specimens to examine their mechanical properties and permeability evolution during the failure of weakly anisotropic rock is examined.
112 citations
TL;DR: In this article, a split Hopkinson pressure bar (SHPB) modified with axial and radial confining systems was used to characterize the failure behaviors of hydrostatically confined rocks under combined compression-shear loading.
101 citations
TL;DR: In this article, a high density of shear bands that are homogeneously dispersed in the nanostructured (NS) layer of a gradient Ni sample was observed, and these bands were nucleated at early elastic/plastic strain stage, reached number saturation at ∼3% strain, and remained arrested by the central coarse-grained matrix during the entire plastic deformation, resulting in a uniform tensile plasticity comparable to that of CG matrix.
71 citations
TL;DR: In this article, a series of indentation tests were conducted on lithium-ion cells with different capacities up to the occurrence of internal short circuit (ISC) and the external response and internal configuration of these cells were investigated.
70 citations
TL;DR: In this article, the authors provide an atomistic description of the shear band multiplication mechanisms in a heterogeneous metallic glass consisting of two distinct amorphous regions with different amounts of free volume and degrees of short-range order.
69 citations
TL;DR: In this article, the authors investigated the effect of plasticity on dynamic fracture propagation and observed the increment of the instantaneous dynamic stress intensity factor during the acceleration stage of the crack without introducing a rate dependent critical fracture energy.
60 citations
TL;DR: In this article, the authors investigated the mechanical response of 3D interfaces for nanocomposites containing three-dimensional (3D) Cu/Nb interfaces consisting of a chemical/structural gradient separating pure Cu and Nb layers, through which the lattice mismatch between facecentered cubic Cu and body-centered cubic Nb is accommodated over a distance of several nanometers.
55 citations
TL;DR: In this article, two different observation windows in the specimen were chosen for the contact fabric analysis: one inside and another one outside a shear band, and individual contact orientations were measured using advanced image analysis approaches within these windows.
Abstract: Numerous studies have shown that the fabric of granular materials plays a fundamental role in its macroscopic behaviour. Due to technical limitations, this fabric remained inaccessible in real experiments until recently when X-ray tomography became accessible. However, determining the fabric from tomographic images is relatively challenging, due to various inherent imaging properties. Triaxial experiments on natural sands are chosen to investigate the contact fabric evolution. Two different observation windows in the specimen are chosen for the contact fabric analysis: one inside and another one outside a shear band. Individual contact orientations are measured using advanced image analysis approaches within these windows. The fabric is then statistically captured using a second-order tensor, and the evolution of its anisotropy is related to the macroscopic behaviour.
49 citations
TL;DR: In this paper, the authors report deformation bands ahead of the crack tip in a CrCoNi alloy under impact loading, and analyze the effects of deformation twinning on strain localization in the form of shear banding.
TL;DR: In this article, the constitutive behavior and workability of ZE20 (Mg-2Zn-0.2Ce) alloy was investigated and a new general approach at application of the extended Ludwik equation was demonstrated and was found to be more accurate than the hyperbolic sine Arrhenius model with a similar number of model constants.
05 Aug 2020-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the hot working behavior of additively manufactured Ti-6Al-4V pre-forms by Electron Beam Melting (EBM) has been studied at temperatures of 1000-1200°C and strain rates of 0.001-1 s−1.
Abstract: The hot working behaviour of additively manufactured Ti–6Al–4V pre-forms by Electron Beam Melting (EBM) has been studied at temperatures of 1000–1200 °C and strain rates of 0.001–1 s−1. As a reference, a wrought Ti–6Al–4V alloy was also analyzed as same as the EBM one. In order to investigate the hot working behaviour of these samples, all the data evaluations were carried out step by step, and the stepwise procedure was discussed. No localized strain as a consequence of shear band formation was found in the samples after the hot compression. The flow stress curves of all the samples showed peak stress at low strains, followed by a regime of flow softening with a near-steady-state flow at large strains. Interestingly, it is found that the initial microstructure and porosity content as well as the chemistry of material (e.g. oxygen content) as being possible contributors to the lower level of flow stress that could be beneficial from the industrial point of view. The flow softening mechanism(s) were discussed in detail using the microstructure of the specimens before and after the hot deformation. Dynamic Recrystalization (DRX) could also explain the gentle oscillation in the appearance of the flow softening curves of the EBM samples. Moreover, the hot working analysis indicated that the activation energy for hot deformation of as-built EBM Ti–6Al–4V alloy was calculated as ~193.25 kJ/mol, which was much lower than the wrought alloy (229.34 kJ/mol). These findings can shed lights on a new integration of metal Additive Manufacturing (AM) and thermomechanical processing. It is very interesting to highlight that through this new integration, it would be possible to reduce the forging steps and save more energy and materials with respect to the conventional routes.
TL;DR: In this paper, the mesoscopically-based framework was proposed to interpret both hardening and softening mechanisms of dense granular assemblies. But the authors focused on mesoscopic evolutions of the densities of granular assembly during a typical drained biaxial test conducted by DEM.
TL;DR: In this paper, a set of isotropic thermal-conductivity degradation functions is derived based on a micro-mechanics void extension model of Laplace's equation, which can be obtained by minimization of the flux differences at the outer surfaces of the two problems.
Abstract: Dynamic loading of polycrystalline metallic materials can result in brittle or ductile fracture depending on the loading rates, geometry and material type. At high strain rates, mechanical energy due to plastic deformation may lead to significant temperature rise and shear localization due to thermal softening. These shear bands reduce the stress bearing capacity of the material and act as a precursor to ductile fracture (e.g. cracks that develop rapidly on top of a shear band). Understanding the heat transfer physics in thermo-mechanical problems when cracks are developed, is a fundamental science that has not been rigorously addressed. In particular, reliable damage models, that degrade the thermal-conductivity in continuum crack descriptions, are necessary to capture the correct heat transfer physics across fracture surfaces but are currently absent. In this paper, a novel set of isotropic thermal-conductivity degradation functions is derived based on a micro-mechanics void extension model of Laplace’s equation. The key idea is to employ an analytical homogenization process to find the effective thermal-conductivity of an equivalent sphere with expanding spherical void. The closed form solution is obtained by minimization of the flux differences at the outer surfaces of the two problems, which can be achieved using the analytical solution of Laplace’s equations, so called spherical-harmonics. A unified model, which has been developed in McAuliffe and Waisman (2015) to account for the simultaneous formation of shear bands and cracks is used herein as a numerical tool to investigate the behavior of the aforementioned thermal-conductivity model. In this unified model, the phase-field method is used to model crack initiation and propagation and is coupled to a temperature dependent visco-plastic model that captures shear bands. Two benchmark problems are presented to show the necessity of such physics-based degradation function in dynamic fracture problems.
TL;DR: In this article, the effects of the particle shape on soil arching by simulating the trapdoor problem using the discrete element method (DEM) is presented. But, the results indicate that the effect of particle shape has a limited effect on the ultimate soil arcing behavior.
TL;DR: In this paper, the authors used an original transparent shear box to conduct direct shear tests on tunneling rock spoils of sandstone and shale and found that particles with strong mineralogy were more likely to produce an arching effect as compared to angular particles with weaker minerals.
TL;DR: In this paper, a Breakage Mechanics model formulated in the framework of Cosserat continuum theory is introduced to account for the interaction of grain size evolution with shear band formation in a physically motivated and thermodynamically consistent way.
Abstract: This paper introduces a Breakage Mechanics model formulated in the framework of Cosserat continuum theory. This formulation allows us to account for the interaction of grain size evolution with shear band formation in a physically motivated and thermodynamically consistent way. We provide an upscaling procedure that introduces material parameters accounting for the contribution of the Cosserat rotations, as well as the micro-inertia of the entire grain size distribution. A particular highlight of the new formulation is the capacity to describe an evolving internal Cosserat length that takes account of the complete grain size distribution and its evolution. In addition, we specify a particular model that requires no additional calibration relative to the same model in the classical continuum. We apply this model to the study of a layer sheared under constant volume which simulates the fast undrained deformation observed in seismogenic faults. Through linear stability analysis we use the model to examine the effect of grain size polydispersity on the thickness of shear bands. By implementing the model using the finite element method we provide an explanation for the geological formation of double cataclastic shear bands.
TL;DR: In this article, the authors numerically study how finite deformation rates influence ductile and brittle yielding behaviors using model glasses in two and three spatial dimensions, and they find that a finite shear rate systematically enhances the stress overshoot of poorly-annealed systems, without necessarily producing shear bands.
Abstract: Amorphous solids display a ductile to brittle transition as the kinetic stability of the quiescent glass is increased, which leads to a material failure controlled by the sudden emergence of a macroscopic shear band in quasi-static protocols. We numerically study how finite deformation rates influence ductile and brittle yielding behaviors using model glasses in two and three spatial dimensions. We find that a finite shear rate systematically enhances the stress overshoot of poorly-annealed systems, without necessarily producing shear bands. For well-annealed systems, the non-equilibrium discontinuous yielding transition is smeared out by finite shear rates and it is accompanied by the emergence of multiple shear bands that have been also reported in metallic glass experiments. We show that the typical size of the bands and the distance between them increases algebraically with the inverse shear rate. We provide a dynamic scaling argument for the corresponding lengthscale, based on the competition between the deformation rate and the propagation time of the shear bands.
TL;DR: In this paper, an atomic-level investigation of the correlation between elastic and structural heterogeneities and the mechanisms of shear banding in CuZr metallic glass is conducted using molecular dynamics simulations.
TL;DR: In this paper, the fracture-induced initiation characteristics of aluminum particle filled polytetrafluoroethylene (PTFE/Al) reactive material were studied in two experimental configurations: (a) thin disks for compression and (b) hat-shaped specimens with predesigned shear bands of different widths for compression-shear, at elevated strain rates and temperatures.
TL;DR: In this article, the macro-and micro-mechanical shear behaviors of railway ballast are investigated by using Discrete Element Method (DEM) to simulate real particle shapes for the direct shear test.
Abstract: Ballast layer is a part of railway foundation that its behavior is affected by the properties of constituent particles. The shape of the particles, which affects ballast behavior, is an important characteristic that is represented by angularity and sphericity indexes. In this study, the macro- and micro-mechanical shear behaviors of railway ballast are investigated by using Discrete Element Method (DEM). For this purpose, a three-dimensional (3D) program based on DEM has been modified and verified with the experimental results to simulate different real particle shapes for the direct shear test. Eight assemblies with different particle shape indexes were prepared. The results showed that the shear strength of ballast layer increased significantly with an increase in the angularity index; however, the strength initially increased with increasing sphericity and then dropped in as the sphericity decreased in the assembly of particles. Also, micro-mechanical responses showed that particle shape affected the formation of shear band.
TL;DR: In this article, the results of an experimental study on the dynamic fracture behavior of 3D printed rock-like disc specimens with various pre-existing flaw configurations under high strain rate loading were presented.
Abstract: This paper presents the results of an experimental study on the dynamic fracture behaviour of 3D printed rock-like disc specimens with various pre-existing flaw configurations under high strain rate loading. The 3D printing technology is utilized to prepare disc specimens containing a single or a pair of unfilled or filled flaws. A split Hopkinson pressure bar is employed to generate high rate loading on the specimens, while the digital image correlation (DIC) technique is adopted to determine the type of new cracks, and their initiation, propagation paths and coalescence types. The results show that the dynamic strengths of the 3D printed specimens are higher than the quasi-static ones. When under high strain rate loading, not only can the specimens with filled flaws carry more load than the corresponding specimens with an unfilled flaw, but also their cracking pattern is different as compared to the unfilled flaw counterpart. It is interesting to note that the dynamic peak loads are not dependent on the flaw inclination angle, while the quasi-static peak loads show obvious flaw inclination angle dependence. Moreover, DIC results reveal that under some specific flaw configurations, the filling material undergoes shear strain concentration and a shear band develops inside the filled flaws. Overall this study confirms the strong effects of the flaw configurations and filling material on the deformation and crack patterns of the 3D printed rock-like materials under impact loading.
TL;DR: An ultra-large fracture resistance in a Ti-12Mo alloy (wt.%), that results from a high resistance to damage nucleation, with an unexpected fracture phenomenology under quasi-static loading is reported, opening alternative avenues toward Ti alloys toughening.
Abstract: Extensive use of titanium alloys is partly hindered by a lack of ductility, strain hardening, and fracture toughness. Recently, several β-metastable titanium alloys were designed to simultaneously activate both transformation-induced plasticity and twinning-induced plasticity effects, resulting in significant improvements to their strain hardening capacity and resistance to plastic localization. Here, we report an ultra-large fracture resistance in a Ti-12Mo alloy (wt.%), that results from a high resistance to damage nucleation, with an unexpected fracture phenomenology under quasi-static loading. Necking develops at a large uniform true strain of 0.3 while fracture initiates at a true fracture strain of 1.0 by intense through-thickness shear within a thin localized shear band. Transmission electron microscopy reveals that dynamic recrystallization occurs in this band, while local partial melting is observed on the fracture surface. Shear band temperatures of 1250–2450 °C are estimated by the fusible coating method. The reported high ductility combined to the unconventional fracture process opens alternative avenues toward Ti alloys toughening. Specific titanium alloys combine transformation-induced plasticity and twinning-induced plasticity for improved work hardening. Here, the authors show that these alloys also have an ultra-large fracture resistance and an unexpected fracture mechanism via dynamic recrystallization and local melting in a deformation band.
TL;DR: In this paper, the multiaxial large deformation and ductile fracture behavior of laser powder bed fusion (L-PBF) additively manufactured austenitic 316L stainless steel was experimentally measured.
TL;DR: In this article, molecular dynamics simulations are used to investigate the plastic deformation behavior of Cu50Zr50/Cu amorphous/crystalline (A/C) multilayered nanofilms with different interface directions, number of layers and temperatures under the imprinting process.
TL;DR: In this article, a visco-elasto-viscoplastic (V•E•VP) model was proposed to model shear banding at crustal-scale.
Abstract: Strain localization is a fundamental characteristic of plate tectonics. The resulting deformation structures shape the margins of continents and the internal structure of tectonic plates. To model the occurrence of faulting, geodynamic models generally rely on frictional plasticity. Frictional plasticity is normally embedded in visco‐plastic (V‐P) or visco‐elasto‐plastic (V‐E‐P) rheologies. This poses some fundamental issues, such as the difficulty, or often inability, to obtain a converged equilibrium state and a severe grid sensitivity. Here, we study shear banding at crustal‐scale using a visco‐elasto‐viscoplastic (V‐E‐VP) model. We show that this rheology allows to accurately satisfy equilibrium, leads to shear band patterns that converge upon mesh refinement, and preserves characteristic shear band angles. Moreover, a comparison with analytic models and laboratory data reveals that V‐E‐VP rheology captures first‐order characteristics of frictional plasticity. V‐E‐VP models thus overcomes limitations of V‐P and V‐E‐P models and appears as an attractive alternative for geodynamic modeling.
TL;DR: In this article, a tensile loading molecular dynamics simulation on the gradient nanoglasses (GNGs) was performed to characterize their mechanical behavior and the results demonstrate the synergistic effects generated by heterogeneous gradient designs in the mechanical behavior of MGs.
TL;DR: In this article, a comprehensive experimental program is carried out to rigorously examine the significant influence of inclined bedding plane and deposition angle on the mechanical behavior of sands over a wide range of strains, from very small to large levels.