Propagation Of Shear Bands Research Articles

Catastrophic failure of submarine slopes with elastic shearing zones

Submarine landslides can be devastating to offshore facilities and coastal areas. This study explores the triggering mechanisms of catastrophic failure of an infinite planar slope in sensitive soil deposits under undrained conditions. The strain-softening behaviour of sensitive soils can cause rapid growth of the shear band along a thin layer of weak materials and ultimately lead to a large landslide. A new analytical criterion for catastrophic shear band propagation taking into account elastic shear deformation in the shear band was derived using a process zone approach. A mechanical analysis was conducted on the fully softened zone, end zone and elastic shearing zone, among which the evolution of the shear band and the development of key mechanical variables were presented to illustrate the formation mechanism of the large submarine planar landslides. The influences of the elastic properties of soils on the initiation of catastrophic failure were investigated for both clay and sand slopes, demonstrating that the consideration of the elastic properties result in a more conservative failure criterion compared with that presented in the previous study.

Computational investigation of deformation mechanisms at the atomistic scale of metallic glass-graphene composites (MGGCs)

While metallic glasses exhibit exceptionally high strength, their relatively low ductility, accompanied by catastrophic failure caused by the formation of shear bands, is the major obstacle to using these materials in practical applications. Despite discovering some methodologies for improving the near-zero ductility of metallic glasses, overcoming this deficiency is still the most active field of research in designing and fabricating bulk metallic glasses. This work utilizes computational studies at the atomistic scale to demonstrate that adding graphene to metallic glasses is a superior method to improve their ductility. Our results show that the graphene layers in metallic glass-graphene composites will enhance the ductility by activation of three deformation mechanisms, including (i) confining the space for shear band formation, (ii) retarding the propagation of embryonic shear bands, and (iii) increasing the resistance of the metallic glass matrix against shearing during the nucleation and propagation of shear bands.

Kinematic and thermal characteristic of discontinuous plastic flow in metastable austenitic stainless steels

The strain induced martensitic phase stabilizes the propagation of macroscopic shear band during displacement-controlled uniaxial tensile test of metastable austenitic stainless steels (316 L, 304) at liquid helium temperature (4.2 K). It leads to huge Lüders-type deformation, high hardening and large ductility of the specimen. In Lüders range, shear band develops across the specimen in discontinuous and sequential way, which is reflected by stress oscillation on stress-strain curve and comb-like profile of temperature recorded during tests (so called discontinuous plastic flow - DPF). Based on the time responses of temperature and elongation transducers, a full picture of the localized deformation behaviour of specimen at 4.2 K was obtained, including its both spatial and temporal features. Moreover, the experimental results clarified that DPF has mechanical origin and it is accompanied by thermal effects. The model of temperature distribution during DPF was proposed. The model involves temperature effects driven by the elastocaloric phenomenon (experimentally identified at 4.2 K) and the plastic power dissipation. Based on the model, kinematic and thermal limits of DPF in the austenitic stainless steels were determined.

Enhancing strength-ductility synergy in an ex situ Zr-based metallic glass composite via nanocrystal formation within high-entropy alloy particles

In this work, we prepared equiatomic AlCoCrFeNi high-entropy alloy (HEA)-particle-toughened, Zr-based metallic glass composites by spark plasma sintering. By adding HEA particles as the second phase, the strength and plasticity of the Zr-based metallic glass composites improved concomitantly. After fracture, high-density dislocations and nanocrystals were formed in the HEA particles due to local severe plastic deformation, which consumed massive strain energy to enable the resistance to crack formation. Substantial lattice distortion imparted a remarkable work-hardening capacity to the HEAs and enhanced crack-tip dislocation trapping, and thus led to an extreme refinement of the grain size. Finite-element analyses indicated that the strain hardening behavior of HEA particles reduced the magnitude of strain localization, promoted generation of multiple shear bands, and stabilized shear band propagation. We attribute the enhanced strength-ductility synergy in the current composites to high-density dislocations and nanocrystal formation in the HEA particles, and stable propagation of multiple shear bands.

Upslope Failure Mechanisms and Criteria in Submarine Landslides: Shear Band Propagation, Slab Failure and Retrogression

AbstractThe volume of a submarine landslide is likely to be amplified by shear band propagation along a basal surface or spreading failure extension in the sliding layer. Although the mechanism of translational submarine landslides has been understood using the interpretation of shear band propagation, assessment of the limits of failure extension, either through shear band propagation or retrogressive spreading, remains a challenge due to the diversity of post failure mechanisms. The paper aims to explore all post failure possibilities and quantify failure initiation and extension accordingly, focusing on the upslope conditions. The different failure mechanisms are explored with the aid of the large deformation finite element modeling. Original criteria for scarp position, shear band length at slab failure, retrogression conditions and ultimate spreading limits are proposed, following the process zone approach considering force equilibrium of the sliding mass. Simplified analytical predictions are shown to agree well with the numerical observations. The findings and criteria presented in the study are expected to help assess the ultimate scale of upslope failure in submarine landslides, which is important in determining geohazard zonation of submarine landslides.

Stability analyses of submarine slopes based on shear band propagation method

Stability analyses of submarine slopes based on shear band propagation method

Interfacial deformation and failure mechanisms at the single-splat length scale revealed in-situ by indentation of cold sprayed aluminum microparticles

Cold spray deposition exploits the phenomenon of impact bonding for solid-state consolidation of metallic microparticles. However, the particle interfaces in the deposits are susceptible to crack propagation under mechanical stresses, which results in inferior ductility. In this work, we seek to develop insights into splat-substrate interface bonding by in-situ micromechanical investigations. A miniaturized mechanical testing approach is reported here, which relies on micromachining, targeted indentation, and real-time scanning electron microscopy to probe deformation and failure at buried interfaces. Investigations at the “single splat length scale” enabled us to distinguish deformation mechanisms associated with 6061Al splats with globular and pancake-shaped morphologies. We observed a transition from mechanical interlocking to metallurgical bonding with an increase in the degree of particle flattening during deposition. The mechanically interlocked splats debond from the substrate via crack propagation and splat sliding. On the other hand, metallurgically bonded splats do not fail under indentation stresses exceeding 380 MPa; instead, displaying shear band propagation and pile-up mechanisms. A four-fold enhancement in the critical stress for crack propagation in mechanically-interlocked splats is achieved after a two-step annealing-aging heat-treatment cycle. We demonstrate that interface bonding plays a more dominant role than the inherent plasticity of splats in influencing bulk deposits' ductility, underscoring the importance of interface engineering in cold sprayed materials.

Development of Zr-based metallic glass matrix composites with hybrid reinforcing structures

The hybrid reinforcing structures, which contain Ta-rich particles, B2–CuZr and B19′-CuZr phases, have been successfully introduced into a Zr-based metallic glass matrix by doping with Ta. Due to the high melting temperature of Ta, the Ta-rich particles precipitate firstly, and contribute to the homogeneous distribution of B2 and B19′-CuZr phases by acting as their nuclei to form a core-shell reinforcing structure. The plasticity of the present hybrid structures reinforced metallic glass matrix composites have been improved a lot when compared with the monolithic counterparts. The rapid propagation of main shear bands in the matrix is considered to be hindered by the presence of the hybrid reinforcing structures. The martensitic transformation of B2–CuZr phases and the deformation of the Ta-rich particles cooperatively contribute to the plasticity and work-hardening behavior of the composites. The simulation results suggest that the core phase (Ta-rich particle) bears the highest strain and triggers the initiation of shear bands.

Mechanical characteristics and deformation mechanism of functionally graded triply periodic minimal surface structures fabricated using stereolithography

Triply periodic minimal surface (TPMS) structures have gained widespread applications because they offer a smooth surface and pore interconnectivity that meet biological and mechanical requirements and mimic native tissues. A novel design approach for functionally graded TPMS structures was proposed based on the log-sigmoid function, and these structures were successfully fabricated using stereolithography. The mechanical properties and deformation mechanism of three kinds of functionally graded TPMS structures were discussed. I-Wrapped Package (I-WP) type with low porosity exhibited a superior elastic modulus and yield stress than other structures. Compared with the Schwarz-P (P) and Gyroid (G) types, the Diamond (D) and I-WP types influenced the behaviors indicated by the stress-strain curves. A combination of stretching- and bending-dominated failure deformations was observed in functionally graded TPMS structures. I-WP type hindered dislocation slips and controlled the propagation of shear bands, whereas G and D types occupied a dominated status where shear bands spread to the unit cells in functionally graded TPMS structures. The mechanical properties were modified to the appropriate range in a specific region based on the functionally graded design, and this study exhibited tremendous potential for dental and other orthopedic implants.

Synergetic toughening mechanism of spherical α-La phases and micron-sized AlLa3 intermetallic in La-based bulk metallic glass composite

A La74Al14Cu6Ni6 bulk metallic glass matrix composite (BMGMC) with in situ spherical α-La phases and micron-sized AlLa3 intermetallic compounds is prepared by adjusting the processing parameters and presents a good combination of high strength and plasticity. Compared with conventional single α-La dendrite-reinforced La74Al14Cu6Ni6 BMGMCs that have a low fracture strength and plasticity, the obtained composite shows a significant plastic strain of 17% and a high fracture strength of 566 MPa. The results show that the formation of ductile bulky spherical α-La phases and hard AlLa3 intermetallic compounds can effectively hinder the rapid propagation of single shear band, and the synergistic effect of the two phases accounts for the significant increase in plasticity. Furthermore, in situ formed AlLa3 intermetallic compounds with a hardness of 238 HV, which has strong interaction with multiple shear bands, dramatically improve the fracture strength of the composite.

Improving the glass-forming ability and plasticity of a TiCu-based bulk metallic glass composite by minor Ta doping

The effects of Ta doping on the glass-forming ability and the mechanical behavior of a B2 phase formable Ti-Cu-Ni-Zr bulk metallic glass composite have been investigated. The doped Ta causes the morphology change of in-situ precipitated B2 phase, from patch-like shapes to homogeneously distributed spherical shapes. The solid-dissolved Ta in the matrix improves the glass-forming ability, suppressing the precipitation of unexpected brittle Ti2Cu phase. Doping Ta with 2 at% generates a homogeneously distributed spherical B2 phase without other crystalline phases, and shows the best mechanical property, including a fracture strength of 1804 MPa and plastic strain of 3.2%. The precipitated B2 phase could hinder the rapid propagation of the main shear band, causing branching, stopping and multiplication of it. The multiplied shear bands accommodate the improved plasticity. The present study provides an important insight into tailoring the phase formation and plasticity of in-situ bulk metallic glass composites via minor alloying.

Shear Band Evolution under Cyclic Loading and Fatigue Property in Metallic Glasses: A Brief Review

The fatigue damage and fracture of metallic glasses (MGs) were reported to be dominated by shear band. While there exist several reviews about the fatigue behavior of MGs, an overview that mainly focuses on shear bands under cyclic loading is urgent, and is of great importance for the understanding of fatigue mechanisms and properties. In this review paper, based on the previous research results, the shear band evolution under cyclic loading including shear band formation, propagation and cracking, was summarized and elucidated. Furthermore, one strategy of enhancing the fatigue property through manipulating the microstructure to suppress the shear band formation was proposed. Additionally, the applications of the effect of annealing treatment and processing condition on fatigue behaviors were utilized to verify the strategy. Finally, several future directions of fatigue research in MG were presented.

Mechanical properties of Cu50Zr50 amorphous/B2-CuZr crystalline composites studied by molecular dynamic method

The effects of uniformly distributed spherical B2-CuZr crystal particles on the mechanical properties of Cu50Zr50 amorphous alloy were studied. With the increasing of the radius of B2-CuZr particles, the yield strength of nanocomposites decreases first and then increases. In this study, the material shows the best comprehensive mechanical properties when the radius of B2-CuZr particle is 2.3 nm, corresponding volume fraction is 29.1%. Compared with the Cu50Zr50 amorphous alloy, multiple shear bands were formed in the Cu50Zr50 amorphous/B2 crystalline composites during compression. Analysis of the deformation mechanism show that the amorphous-crystalline interfaces play the key role in this process. B2-CuZr particles retard the rapid expansion and propagation of the single shear band, and it makes the nanocomposites have the better plasticity than the Cu50Zr50 amorphous alloy.

Depth integrated modelling of submarine landslide evolution

Submarine landslides are a major geohazard among worldwide continental slopes, posing significant threats to offshore infrastructure, marine animal habitats and coastal urban centres. This study establishes an original numerical package for time-efficient modelling of the entire submarine landslide evolution covering the pre-failure shear band propagation, slab failure and post-failure dynamics. The numerical scheme is based on the conservation of mass and the conservation of momentum and combines the shear band propagation theory and the depth-integrated method, with the consideration of the drag force from the ambient water. Shear band propagation in the weak layer and slab failure in the sliding layer are controlled by the strain softening and rate dependency of the corresponding undrained strength parameters. The post-failure behaviour in the sliding layer, such as retrogression upslope and frontally confined and frontally emergent mechanisms downslope, is also simulated. The numerical results from the proposed method are comparable to the analytical solutions and the large deformation finite element analysis. Application of this method to a back analysis of the St. Niklausen slide in Lake Lucerne reproduced the observed shape of the mass transport deposits, the position of the main scar and the travel distance. Because of its easy implementation and efficiency, the proposed numerical method for modelling of submarine landslides seems promising for practical applications.

Experimental and numerical investigation of the effects of preheating temperature on cutting force, chip shape and surface roughness in hot turning of AISI630 hardened stainless steel

Hot machining is a type of cutting operation that an external heat source is used to pre-heat and consequently reduce the yield strength of the workpiece material. In this study, the conventional and hot turning of AISI630 hardened stainless steel, which is widely used in energy equipment, aerospace, and petrochemical industries, have been evaluated in both numerical and experimental methods. Simulation of the turning process is carried out by finite elements method (FEM) using AdvantEdge software. To predict chip morphology and cutting forces, the 2D and 3D FEM analyses have been used, respectively. The numerical analysis showed that hot turning in 300°C causes a reduction of 28% in cutting forces and consequently decreases stressed on the cutting tool. It is found that the main factor affecting the fluctuations of the cutting forces in turning of hardened AISI630 is the saw-tooth formation phenomenon (chip segmentation) as well as the shear band generation due to thermal softening of the workpiece material. Furthermore, the relation between cutting force fluctuation and the machined surface roughness has been investigated applying numerical analysis and experimental data. The results of roughness measurement revealed that hot turning in 300°C reduces the machined surface roughness up to 23%. In addition, it has been observed that hot turning technique decreases side flow and surface damages in comparison to conventional turning.

Tuning of mechanical properties of Tantalum-based metallic glasses

Metallic glasses (MGs) are materials characterized by high performance in terms of their mechanical properties such as excellent elastic behavior and high strength. These famous properties are directly linked to the amorphous structure which is the principal feature behind the absence of atomic order at long range. Nonetheless, MGs usually fail catastrophically by shear localization without showing any synonyms of important plastic deformation under mechanical solicitations and therefore are notoriously brittle, so the reinforcement of MG matrix to form MG-based composite materials is demanded. Molecular dynamics (MD) simulations are of great importance in designing such materials allowing atomic scale insights into the structural-mechanical properties relationship. In this work, we study the effect of adding Ta and W monocrystalline fibers in Ta-MG matrix using MD simulations with the embedded atom method (EAM) to describe the interatomic interactions. In addition, mechanical solicitations have been performed using a tensile test under a strain rate of 107s−1, the evolutions of stress-strain curves have been compared between four samples (Ta-MG, nanoporous Ta-MG, monocrystalline Ta-reinforced Ta-MG and monocrystalline W-reinforced Ta-MG). Tensile tests have shown that plastic deformations are characterized by the localization of shear bands (SBs) in amorphous zones and the addition of Ta monocrystalline fibers increases the ductility and the toughness of the material and decreases its ultimate tensile stress (UTS); this ductility was found to be a result of the crystal growth inside the glassy matrix triggered by the crystal phase of the fiber. In contrast, the addition of W reinforces the MG matrix and increases the maximum strength and the toughness of the material, this improvement of the mechanical properties was explained by the presence of the heterogeneous interface which behaves as an obstacle to the propagation of SBs.

In-situ synthesis of Mg-based bulk metallic glass matrix composites with primary α-Mg phases

Herein, we systematically investigate the in-situ synthesis and mechanical properties of Mg-based bulk metallic glass matrix composites (BMGMCs). From a well-known Mg65Cu25Gd10 bulk glass former, a series of Mg65+xCu20–2x/3Zn5Gd10−x/3 (x = 0–18 at%) alloys are systematically designed and Mg-rich (>77 at% Mg) glassy/crystalline matrix composites containing primary α-Mg phases are successfully developed. Mg77Cu12Zn5Gd6 BMGMC (x = 12 at%) exhibits over two times higher compressive fracture strength (773 ± 20.6 MPa) and specific strength (2.6 × 105 N m kg−1) than commercial Mg alloys such as AZ31 or AZ91. In particular, compared with monolithic Mg-based BMGs, the BMGMC displays obvious yielding, serrated plastic flow and plastic strain of 0.22 ± 0.02%. This result is attributed to the dispersed primary α-Mg phases which prevent the rapid propagation of shear bands and promote the formation of multiple shear bands. The Mg-rich crystalline matrix composites (x = 14-18 at%) containing primary α-Mg phases exhibit an enhancement in the plastic strain (from 0% to 1.51%) and pronounced work hardening at the expense of yield strength (<500 MPa) due to the absence of the amorphous phase. These results would give us a promising strategy to fabricate Mg-based BMGMCs with high specific strength and enhanced plasticity for lightweight structural applications.

Microstructure and Mechanical Properties of Cu-Ni-Zr-Ti Bulk Metallic Glass Composites by Spark Plasma Sintering

In the present study, Cu54Ni6Zr22Ti18 bulk metallic glass composites were developed by spark plasma sintering(SPS) using gas atomized Cu54Ni6Zr22Ti18 metallic glass powders and Ta powders. Metallic glass composites with Ta phase were fabricated by SPS. The successful consolidation of Cu54Ni6Zr22Ti18 metallic glass matrix composites with the Ta phase was achieved through the strong bonding due to the plastic deformation of the Ta powder and the super-plastic behavior of the metallic glass powder in the supercooled liquid state during SPS. The deformed Ta phases were well distributed in the Cu54Ni6Zr22Ti18 metallic glass matrix. The compressive fracture strength and total strain were 1770 Mpa and 10.2%, respectively, for the Cu54Ni6Zr22Ti18 bulk metallic glass composite with 40 wt% Ta phases. The uniformly dispersed deformed Ta phase in the Cu54Ni6Zr22Ti18 metallic glass matrix effectively impedes the propagation of the first shear band and generates a second shear band, causing a crossing of the shear bands, resulting in an improvement in plastic strain. This increase in plastic deformation is related to the fact that the deformed Ta phase, uniformly distributed in the Cu54Ni6Zr22Ti18 metallic glass matrix, acts as a source of shear bands and at the same time effectively suppresses the movement of the shear bands, dispersing the stress and causing wide plastic deformation.

Preparation and mechanical properties of tungsten-particle-reinforced Zr-based bulk-metallic-glass composites

Abstract Tungsten-particle (Wp)-reinforced bulk-metallic-glass composites (Wp/BMGCs) with a Wp volume fraction of 0%–50% were prepared by spark plasma sintering (SPS). The sintering process parameters were optimized through an orthogonal experiment. With increasing volume fraction of Wp, the compressive yield strength of the Wp/BMGCs decreased, while their ultimate strength and plastic strain increased. Nanoindentation experiments revealed that the elastic modulus and hardness of the composites increased with increasing volume fraction of Wp. The elastic modulus mismatch between the tungsten particles and metallic glass matrix resulted in a stress concentration at the interface of the two phases, promoting the initiation and propagation of shear bands in the metallic glass matrix. Fracture morphology analysis of the composites showed that the failure mode of the composites was shear fracture mode, which is beneficial to the self-sharpening of the composites. With increasing volume fraction of Wp, the plastic deformation of Wp became more obvious, and the deformation was most obvious near the shear fracture surface. The degree of plastic deformation of Wp in the region far away from the shear fracture surface gradually decreased. In addition, the reliability of the mechanical properties of Wp/BMGCs sintered in the same preparation parameters was verified by three-parameter Weibull statistical analysis. These results help deepen our understanding of the preparation and mechanical properties of Wp/BMGCs and further promote their application.

Effect of sample geometry on the macroscopic shear deformation of the titanium alloy Ti-10V-2Fe-3Al subjected to quasi-static and dynamic compression-shear loading

We investigate the evolution of shear bands in a Ti-10V-3Fe-2Al alloy with three different initial microstructures: solution-annealed β-titanium, β-titanium with primary α-phase precipitates as well as a condition with primary and secondary α-phase precipitates. Quasi-static and dynamic testing of compression-shear specimens with strain rates of 10-3 s-1 and 102 s-1 is performed at room temperature. The influence of two different sample geometries on the macroscopic shearing tendency is investigated: samples with a cylindrical cross section and samples with a square cross section. The results of digital image correlation and the nominal stress-strain behavior under quasi-static and dynamic loading indicate a stronger localization tendency of the aged conditions with additional α-phase precipitates compared to the solution-annealed pure β-condition. Our results also demonstrate that compression-shear testing with samples with a square cross-section reduces facet loss, increases the resolution even at high strain rates and therefore allows to analyze strain distributions during shear band formation and propagation with higher accuracy.