Showing papers on "Shear band published in 2011"
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09 Oct 2011
TL;DR: In this paper, the authors describe the transformation of shocks in Laminated and Porous materials under dynamic loading and shear localization and band patterning in Heterogeneous Materials.
Abstract: 1. Nonlinear Impulses in Particulate Materials. 2. Mesomechanics of Porous Materials Under Intense Dynamic Loading. 3. Transformation of Shocks in Laminated and Porous Materials. 4. Shear Localization and Shear Band Patterning in Heterogeneous Materials. 5. Non-Equilibrium Heating of Powders Under Shock Loading. 6. Advanced Materials Treatment by Shock Waves.
706 citations
TL;DR: In this paper, the authors focused on understanding the mechanisms for ductility improvement by microstructure analysis, texture analysis and slip trace analysis based on electron backscatter diffraction and transmission electron microscopy.
662 citations
TL;DR: In this paper, several criteria under the categories of uncoupled damage and coupled damage were investigated to determine their reliability in ductile failure prediction in metal plastic deformation, including the continuum damage mechanics (CDM)-based Lemaitre model and the Gurson-Tvergaard-Needleman (GTN) model, and the two categories of criteria were coded into finite element models based on the unconditional stress integration algorithm in the VUMAT/ABAQUS platform.
432 citations
TL;DR: In this paper, a dual-phase bulk metallic glass matrix composite (BMGMC) with a homogeneous distribution of dendrites and the composition of Ti 46 Zr 20 V 12 Cu 5 Be 17 is characterized by a high tensile strength of ∼1640 MPa and a large tensile strain of ∼15.5% at room temperature.
262 citations
TL;DR: In this article, the authors used a digital image processing (DIP) method to obtain the proportion and distribution of the rock blocks in soil-rock mixtures (S-RM) samples.
217 citations
TL;DR: In this article, the authors conducted a controlled experiment to form a single shear band in the specimen, which enabled them to probe shearinduced softening and dilatation directly on the shear bands itself.
183 citations
TL;DR: In this article, it was shown that the transition from serrated to non-serrated flow can be directly linked to the shear-band propagation velocity, such that a transition occurs at the temperature for which the crosshead velocity equals that of the cross-head velocity applied during the test.
176 citations
TL;DR: This work systematically study how the creep velocity V(creep) of the rod varies with F(c) - F and with the distance to the shear band, and shows that the behavior can be described by an Eyring-like activated process.
Abstract: We study how a shear band in a granular medium dramatically changes the mechanical behavior of the material further in the non sheared region. To this end, we carry out a microrheology experiment, where a constant force $F$ is applied to a small rod immersed outside the shear band. In the absence of a shear band, a critical force ${F}_{c}$ is necessary to move the intruder. When a shear band exists, the intruder moves even for a force $F$ less than the critical force ${F}_{c}$. We systematically study how the creep velocity ${V}_{\mathrm{creep}}$ of the rod varies with ${F}_{c}\ensuremath{-}F$ and with the distance to the shear band, and show that the behavior can be described by an Eyring-like activated process.
140 citations
TL;DR: By employing a quantitative approach, the critical volume change associated with shear-band initiation in a metallic glass is estimated to be a few percent only, which agrees with typical values of excess free volume found in the supercooled liquid regime near the glass transition temperature.
Abstract: In situ acoustic emission monitoring is shown to capture the initiation of shear bands in metallic glasses. A model picture is inferred from stick-slip flow in granular media such that the origin of acoustic emission is attributed to a mechanism of structural dilatation. By employing a quantitative approach, the critical volume change associated with shear-band initiation in a metallic glass is estimated to be a few percent only. This result agrees with typical values of excess free volume found in the supercooled liquid regime near the glass transition temperature.
139 citations
TL;DR: In this article, the authors characterize the mechanical properties of Cu64Zr36 nanoglasses under tensile load by means of large-scale molecular dynamics simulations and compare the deformation behavior to the case of a homogeneous bulk glass.
Abstract: In this study, we characterize the mechanical properties of Cu64Zr36 nanoglasses under tensile load by means of large-scale molecular dynamics simulations and compare the deformation behavior to the case of a homogeneous bulk glass. The simulations reveal that interfaces act as precursors for the formation of multiple shear bands. In contrast, a bulk metallic glass under uniaxial tension shows inhomogeneous plastic flow confined in one dominant shear band. The results suggest that controlling the microstructure of a nanoglass can pave the way for tuning the mechanical properties of glassy materials.
134 citations
TL;DR: In this paper, the hot deformation behavior of Stir cast 7075 alloy was studied using processing map technique and the map has been interpreted in terms of the microstructural processes occurring in situ with deformation, based on the values of a dimensionless parameter η which is an efficiency index of energy dissipation through micro-structural process.
TL;DR: In this paper, the authors discuss the relation between wall slip and internal cohesive breakdown and summarize all available findings in terms of a phase diagram, which specifies the conditions under which shear homogeneity, interfacial slip, and bulk shear inhomogeneity would prevail.
Abstract: The recent particle-tracking velocimetric (PTV) observations revealed that well-entangled polymer solutions and melts tend to either exhibit wall slip or assume an inhomogeneous state of deformation and flow during nonlinear rheological measurements in simple-shear rheometric setups. Many material parameters and external conditions have been explored since 2006, and a new phenomenological picture has emerged. In this Perspective, we not only point out the challenges to perform reliable rheometric measurements but also discuss the relation between wall slip and internal (bulk) cohesive breakdown and summarize all available findings in terms of a phase diagram. This map specifies the conditions under which shear homogeneity, interfacial slip, and bulk shear inhomogeneity would prevail. The paper is closed by enumerating a number of unresolved questions for future studies.
TL;DR: In this paper, high-pressure torsion was applied to nanocrystalline tantalum by high-resolution transmission electron microscopy to reveal non-equilibrium grain boundaries and grains decorated with high-density dislocations, implying a shift in the deformation mechanism from the screw dislocation dominated regime.
TL;DR: In this paper, internal interfaces in a Cu64Zr36 glass were generated by joining two planar surfaces and studied with respect to their structure and stability by means of molecular dynamics simulations.
TL;DR: In this paper, the authors combine computer simulations and the cooperative shear model to find that the yield strain of metallic glass can be as high as ∼10% in pure shear, and the corresponding ideal shear strength is G /10 (where G is the shear modulus), at which shear bands nucleate homogeneously in the metallic glass.
TL;DR: In this article, the inclination angle of the bedding plane with respect to the shear plane was used as a reference geometrical descriptor of inherent fabric anisotropy.
Abstract: This paper investigates shear strength of granular materials with inherent fabric anisotropy. Most previous studies have described strength of these materials in the principal stress space, and the orientation of the bedding plane with respect to the principal stress directions was used as the reference geometrical descriptor of inherent fabric. The present study has found that it is theoretically more convenient and practically more useful to use instead the inclination angle of the bedding plane with respect to the shear plane for the same purpose. Direct shear tests and biaxial compression tests with different loading directions with respect to the bedding planes were simulated with discrete element method (DEM) models consisting of ellipse-shaped particles. Key mechanical behaviors of natural sands reported in the literature were successfully captured in the numerical simulation. A shear failure criterion was determined as a function of the inclination angle based on the direct shear simulation results, and was used to successfully predict the results of the biaxial compression simulations. Microstructural inspection of deformation and strain localization of the biaxial compression simulations found that the proposed shear failure criterion can reasonably predict the orientations of the initial failure planes. It was also discovered that shear bands in directions conjugate to the initial failure plane orientations can develop and dominate specimen deformation at larger strain levels. Considering the availability of biaxial compression test equipment and historical data, two methods for back-calculating inclination angle-dependent shear strength from biaxial compression results were proposed, and validated using DEM simulation results. Copyright © 2010 John Wiley & Sons, Ltd.
TL;DR: In this paper, the structural evolution of an Au-based bulk metallic glass (BMG) after severe plastic deformation (SPD) was investigated, and it was shown that SPD modifies the atomic structure of BMGs by localized shear band formation, thus producing so-called nanoglasses.
TL;DR: In this paper, the authors investigated the fracture behavior of the aluminium alloy AA7075-T651 for quasi-static and dynamic loading conditions and different stress states, and the fracture surfaces obtained in tensile tests on smooth and notched axisymmetric specimens and compression tests on cylindrical specimens are compared to the fracture surface that occur when a projectile, having either a blunt or an ogival nose shape, strikes a 20 mm thick plate of the aluminum alloy.
TL;DR: In this paper, the effect of sample size on the shear deformation and compressive plasticity of different metallic glasses was investigated, and it was shown that sample size can significantly influence the density of elastic energy dissipated in the Shear band.
15 Mar 2011-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the microstructure and the phase transformation within the adiabatic shear band (ASB) were investigated by means of TEM, and it was shown that the elongated subgrains with the width of 0.2-0.4μm have been observed in the ASB boundary.
Abstract: The adiabatic shear band (ASB) was obtained by split Hopkinson pressure bar (SHPB) technique in the hat-shaped specimen of a near beta-Ti alloy. The microstructure and the phase transformation within the ASB were investigated by means of TEM. The results show that the elongated subgrains with the width of 0.2–0.4 μm have been observed in the shear band boundary, while the microstructure inside the ASB consists of fine equiaxed subgrains that are three orders of magnitude smaller than the grains in the matrix. The β → ω(althermal) phase transformation has been observed in the ASB, and further analysis indicates that the shear band offers thermodynamic and kinetic conditions for the ω(althermal) phase formation and the high alloying of this alloy is another essential factor for this transformation to take place. The thermo-mechanical history during the shear localization is calculated. The rotational dynamic recrystallization (RDR) mechanism is used to explain the microstructure evolution mechanism in the shear band. Kinetic calculations indicate that the recrystallized fine subgrains are formed during the deformation and do not undergo significant growth by grain boundary migration after deformation.
TL;DR: In this article, tripleaxial tests on gypsum polycrystal samples are performed at confining pressure (Pc) ranging from 2 to 95 MPa and temperatures up to 70°C.
Abstract: [1] Triaxial tests on gypsum polycrystal samples are performed at confining pressure (Pc) ranging from 2 to 95 MPa and temperatures up to 70°C. During the tests, stress, strain, elastic wave velocities, and acoustic emissions are recorded. At Pc ≤ 10 MPa, the macroscopic behavior is brittle, and above 20 MPa the macroscopic behavior becomes ductile. Ductile deformation is cataclastic, as shown by the continuous decrease of elastic wave velocities interpreted in terms of microcrack accumulation. Surprisingly, ductile deformation and strain hardening are also accompanied by small stress drops from 0.5 to 6 MPa in amplitude. Microstructural observations of the deformed samples suggest that each stress drop corresponds to the generation of a single shear band, formed by microcracks and kinked grains. At room temperature, the stress drops are not correlated to acoustic emssions (AEs). At 70°C, the stress drops are larger and systematically associated with a low-frequency AE (LFAE). Rupture velocities can be inferred from the LFAE high-frequency content and range from 50 to 200 m s−1. The LFAE amplitude also increases with increasing rupture speed and is not correlated with the amplitude of the macroscopic stress drops. LFAEs are thus attributed to dynamic propagation of shear bands. In Volterra gypsum, the result of the competition between microcracking and plasticity is counterintuitive: Dynamic instalibilities at 70°C may arise from the thermal activation of mineral kinking.
TL;DR: In this paper, a series of experimental efforts have been made in an attempt to gain understanding of shear band propagation in metallic glasses, and it was found that plastic flow serration observed in compression was actually caused by successive (intermittent) shear along a single shear plane, not random shear bands emission.
TL;DR: In this article, a ductilization strategy based on the creation of alternating soft and hard regions via imprinting at room temperature was proposed to limit shear bands from propagating catastrophically.
TL;DR: In this article, a comparative study on mechanical properties and microstructure of 316L austenitic stainless steel between solution treated specimen and hot rolled specimen was conducted, which revealed that the solution treated sample has an excellent combination of strength and elongation, and that this steel is easy to work-hardening during deformation.
Abstract: A comparative study on mechanical properties and microstructure of 316L austenitic stainless steel between solution treated specimen and hot rolled specimen was conducted. After a specimen was subjected to solution treatment at 1050 °C for 6 min, its mechanical properties were determined through tensile and hardness tests. Based on the true stress vs true strain and engineering stress vs engineering strain flow curves, the work hardening rate has been explored. The results show that the solution treated specimen has an excellent combination of strength and elongation, and that this steel is easy to work-hardening during deformation. Optical microscope, scanning electron microscope, transmission electron microscope and X-ray diffraction examinations were conducted, these reveal that twins in 316L austenitic stainless steel can be divided into suspended twin and transgranular twin which have different formation mechanisms in growth, and that the deformation induced martensite nucleated and grown in the shear band intersections can be observed, and that the fracture surfaces are mainly composed of dimples and exhibit a tough fracture character.
TL;DR: In this paper, a diffusive Rolie-Poly model is used to model the steady state shear banding in a Newtonian solvent, whose steady state constitutive behavior can be monotonic or non-monotonic depending on the degree of convective constraint release.
Abstract: Spatially inhomogeneous shear flow occurs in entangled polymer solutions, both as steady state shear banding and transiently after a large step strain or during startup to a steady uniform shear rate. Theoretically, steady state shear banding is a hallmark of models with a nonmonotonic constitutive relation between total shear stress and applied shear rate, but transient banding is sometimes seen in fluids that do not shear band at steady state. We model this behavior using the diffusive Rolie-Poly model in a Newtonian solvent, whose steady state constitutive behavior can be monotonic or nonmonotonic depending on the degree of convective constraint release. We study monotonic steady state constitutive behavior. Linear stability analysis of the startup to a sufficiently high shear rate shows that spatial fluctuations are unstable at early times. There is a strong correlation between this instability and the negative slope of the (time dependent) constitutive curve. If the time integral of the most unstable...
TL;DR: In this article, the authors review atomistic simulation studies of deformation processes in metallic glasses, i.e., local shear transformation (LST), structural characterization of the Local Shear Transformation Zones (STZs), deformation-induced softening, shear band formation and its development, by use of elemental and metal-metal alloy models.
TL;DR: In this paper, the effects of cutting parameters on character of the serrated chip were studied through observing chip metallographic graph and conditions under which a crack appeared and adiabatic shear that occurred were also analyzed.
Abstract: During the process of high-speed machining nickel-based alloy the material presents serrated chips. An experiment involving quick-stop device was conducted. The chip root obtained in the experiment was presented in a metallographic graph. Through the analysis of metallographic graph, the physical features showed that shear angle is reduced and shear plane is converted into shear body when serrated chips formed were analyzed. Conditions under which a crack appeared and adiabatic shear that occurred were also analyzed. Based on the research, shear strain, shear strain rate and shear stress model in the adiabatic shear band were established. The effects of cutting parameters on character of the serrated chip were studied through observing chip metallographic graph.
TL;DR: In this article, a ratchetting model based on the non-linear kinematic-isotropic hardening law of Leimatre and Chaboche was proposed to predict the shear strain accumulation during rolling contact loading and including wear as a competitive phenomenon.
TL;DR: In-situ x-ray tomography has been used to follow deformation processes in 3D during two triaxial compression tests, one on a specimen of bio-cemented Ottawa 50-70 sand and the other on a sample of noncemented sand as mentioned in this paper.
Abstract: In-situ x-ray tomography has been used to follow deformation processes in 3D during two triaxial compression tests, one on a specimen of bio-cemented Ottawa 50–70 sand and the other on a specimen of the non-cemented sand. The global stress-strain responses show that the bio-cementation process increases the shear strength (peak deviator stress is approximately doubled), and causes the material to exhibit a linear behaviour up until peak, as well as increasing the dilatancy angle. The residual strength of the two samples is very close at large strain. Quantitative 3D digital image analysis (porosity, cement-density and strain field measurements), reveals that a dilatant shear band gradually develops pre-peak in the reference material. The cemented sample however undergoes an abrupt change of deformation mechanism at peak stress: from homogeneous deformation to localised dilatant shearing, which is associated with a local loss of cementation.
TL;DR: In this article, the capability of a discrete element method (DEM) to simulate a pattern of quasi-static shear zones in initially dense sand was checked with a rigid and very rough retaining wall.