Shear Banding Behavior Research Articles

Fabrication of Inconel 718 composites reinforced with TiCN via laser powder bed fusion: Integration of triply periodic minimal surface lattice structures

The integration of TiCN particles into superalloy composites for laser powder bed fusion (LPBF) and the construction of Triply Periodic Minimal Surface (TPMS) lattice structures have been understudied. This research systematically examines the microstructure and mechanical properties of LPBF-processed 10 vol% micron sized TiCN particle reinforced Inconel 718 (IN718) composites. The compressive behavior of the resultant TPMS lattice structures, derived from the TiCN-IN718 composite, was scrutinized through a combination of experimental testing and Finite Element (FE) simulation. The micro-sized TiCN reinforcement is demonstrated to notably augment the hardness, tensile strength, and wear resistance of the LPBFed TiCN-IN718 composite. Furthermore, the application of homogenization-solution-aging (HSA) heat treatment is shown to provide additional enhancements to the composite's mechanical behavior. Both the TiCN reinforcement and the HSA heat treatment are identified as pivotal factors influencing the compressive response of the TPMS lattice structures. Experimental findings indicate that the HSA-treated D-structure attains the highest compressive strength, reaching 122 MPa, outperforming both the G- and P-structures. During quasi-static compression testing, the D- and G-structures undergo a layer-by-layer collapse, while the P-structure exhibits tilt shear band behavior. The congruence between FE simulation results and experimental data substantiates the simulation's reliability and its capacity to accurately evaluate the mechanical behavior of TPMS lattice structures.

Analysis on shear band development under large strain torsion of amorphous glassy polymers

Unlike the shear band development of metals generally regarded as the precursor to failure, the shear banding process in amorphous glassy polymers is known to influence both the strengthening and fracturing behaviors. Complementary to the previous experimental work in the literature on the shear band development under torsion under limited cases, the finite element (FE) analysis has been conducted to investigate the general shear banding behaviors in terms of the initiation and propagation in more detail. The FE model has been established by incorporating the Boyce-Parks-Argon (BPA) constitutive model with the full-network modification via a user material subroutine in ABAQUS. A series of nondimensional quantities were used to discuss the mesh sensitivity and the effects of predefined imperfections, specimen geometry, and torsion mode. Besides, by altering the extents of the intrinsic material softening and the strain hardening, the shear banding behaviors of typical materials under typical temperature and strain rate conditions are equivalently investigated. The validity of the simulation has been qualitatively validated by directly comparing with the experimental results from the literature.

Dynamic mechanical response and constitutive model of (Ti37.31Zr22.75Be26.39Al4.55Cu9)94Co6 high-entropy bulk metallic glass

In this work, the mechanical response and fracture characteristics of (Ti37.31Zr22.75Be26.39Al4.55Cu9)94Co6 high-entropy bulk metallic glass (HE-BMG) were investigated in detail over a wide range of strain rates (10−4–105 s−1). The HE-BMG exhibited a negative strain rate sensitivity under uniaxial compression, with the strength showing more significant rate dependence under dynamic conditions. The shear band behavior translated from the dominance of multiple shear bands propagations under quasi-static compression to the rapid propagation of a single shear band to form cracks under dynamic compression. Under dynamic loading, the shearing velocity increased along an arc-shaped displacement path, and the local stress state on the shear fracture surface shifted from compressive-shear to tensile-shear, accompanied by changes in fracture morphologies. The spall strength of HE-BMG decreased as flyer impact speed increased, while the long-term dependence of spall strength on strain rate may be positive. With the increase of impact speed, the main microstructural features of the spalling surface translated from flat regions accompanied by dimples to cup-cone structures. Furthermore, the complete parameters of the Johnson–Holmquist II (JH-2) model for HE-BMG were obtained based on experimental data. Numerical simulations of planar impact, penetration, and hypervelocity impact are in good agreement with experimental results, demonstrating the validity of the JH-2 model parameters. The current work has important guiding value for the application of HE-BMG in space debris protection.

Evolution Behavior of Shear Band in Al‐0.5Mg‐0.4Si‐0.1Cu Alloy during Hot Compression Process

To clarify the evolution behavior of shear bands in Al‐0.5Mg‐0.4Si‐0.1Cu alloy under high‐temperature conditions, isothermal compression tests are carried out under 400, 450, and 500 °C with 50% compression at a strain rate of 1 s−1. Through electron backscattered diffraction (EBSD), Schmid factors are mainly distributed between 0.395 and 0.495, making lattices easy to rotate and shear bands formed. The shear band, a local plastic deformation structure, has a significant impact on the dynamic recrystallization and preferred orientation of grains. Through the recrystallization distribution maps, subgrains absorb a large amount of dislocations, which increases the grains’ orientation difference, resulting in the formation of recrystallized grains with high‐angle grain boundaries. In addition, bulging grain boundaries promote the formation of new nuclei. The newly formed nuclei will generate and grow by absorption of dislocations, which is the feature of discontinuous dynamic recrystallization. These two phenomena are further confirmed by transmission electron microscope tests. Finally, R‐Cube textures mainly form in shear bands at 400 °C, while in the matrix, E‐textures mainly form at 400 and 450 °C, and R‐Goss textures are rotated to form at 500 °C, which is confirmed by EBSD test results.

Quantifying the Size-Dependent Shear Banding Behavior in High-Entropy Alloy-Based Nanolayered Glass.

Extensive research has shown that nanolayered structures are capable of suppressing the shear banding in metallic glass in nanoindentation experiments. However, the specific mode and mechanism of the shear banding underneath the indenter remains unknown. Also, the quantification of shear banding-induced strain localization is still a challenge. Herein, the size-dependent shear banding behavior of a CuTiZrNb high-entropy alloy-based nanolayered glass with individual layer thicknesses (h) ranging from 5 to 80 nm was systematically investigated by nanoindentation tests. It was found that the hardness of the designed structure was almost size-independent. Yet, a clear transition in the deformation modes from the cutting-like shear bands to the kinking-like ones was discovered as h decreased to 10 nm. Moreover, multiple secondary shear bands also appeared, in addition to the primary ones, in the sample with h = 10 nm. The transition leads to an obvious strain delocalization, as clearly illustrated by the proposed theoretical model, which is based on the assumption of a pure shear stress state to quantify the shear banding-induced strain localization. The strain delocalization results from the higher density of amorphous/amorphous interfaces that exhibit the change in morphology with a refined layered glass structure.

Shear banding suppression in Cu/TiZrNb nanolayered composites through dual crystalline/amorphous interfaces

Medium/high entropy alloys (M/HEAs)-based nanolayered composites have attracted intense scientific interest due to the improved mechanical properties. However, the shear banding (or shear instability) behavior of the M/HEAs-based nanolayered composites is rarely studied due to the lack of theoretical model to quantify the shear banding-induced strain localization. Herein, the size-dependent strengthening and shear instability behavior of Cu/amorphous TiZrNb nanolayered composites with individual layer thickness (h) of 2–100 nm was systematically investigated by using a combination of nano/microindentations and a detailed theoretical analysis. The results show that the strength of the Cu/TiZrNb composites obeys the trend of “smaller is stronger”. The size-dependent strengthening behavior of the samples with h in the range of 10–100 nm can be well described by the confined layer slip model, while the continuous increase in strength of those with h = 2 and 5 nm is related to the gradually amorphization of the Cu layers. It is intriguingly found that the shear instability of the Cu/TiZrNb composites shows a first-decrease-and-then-increase size dependence, which is apparently different from that of existing face-centered cubic/amorphous nanolayered composites that exhibits a monotonic size dependence. The non-monotonic trend leads to a significantly suppressed shear instability in the sample with h = 50 nm, in which only slight kinks are observed in microindentation. The enhanced resistance to shear banding is attributed to the dual crystalline/amorphous interfaces generated by the layered structure and the amorphous TiZrNb constituent layers that contains crystalline phase at h > 10 nm.

Nanomechanical properties of Al-Tb marginal metallic glass

Al-Rare Earth (RE) metallic glasses provide an effective model system to study the effect of nanocrystallites in an amorphous matrix on nanomechanical behavior. In this work, we achieved a series of Al-Tb metallic glass-crystalline composites with systematically varying crystalline content through annealing. The nanomechanical properties were characterized using micropillar compression tests and nanoindentation for as-quenched amorphous and annealed amorphous/nanocrystalline composite specimens. The promising hardness increases after annealing from 3.0 GPa to 4.6 GPa and elastic modulus increment from 68 GPa to 92 GPa were discussed in detail, considering the structural features of Al-RE marginal metallic glass formers. The increase in elastic modulus is associated with the nucleated fcc-Al nanocrystals that divide the amorphous matrix, leading to the branching of the shear bands. The correlation between the fcc-Al nanocrystals and the behavior of shear bands was discussed in detail.

Effect of geometry of crystalline dendrite on the uniaxial tension behavior of metallic glass matrix composites based on molecular dynamics simulations

Introducing crystalline dendrites can effectively enhance the plasticity of metallic glass matrix composites. The geometry (e.g., shape and orientation) of the crystalline dendrites can significantly influence the mechanical properties of the material. In this study, we create numerical Cu-Zr glassy samples containing crystalline dendrites of realistic geometries and study their mechanical behaviors under uniaxial tension loading through large-scale molecular dynamics simulations. The results indicate that shear band formation is sensitive to the shape and orientation of the dendrites. The geometry of the dendrites significantly affects the behavior of shear bands in the materials and ultimately leads to different tensile plasticity. This work is aimed at providing guidelines for the design of metallic glass matrix composites with complex second phase dendritic structures.

A generalized elastoplastic load-transfer model for axially loaded piles in clay: Incorporation of modulus degradation and skin friction softening

The softening behavior of skin friction is commonly observed from load-displacement responses of axially loaded piles in stiff clay, sensitive clay, and dense sands at a large loading level. This paper presents a generalized and novel elastoplastic load-transfer model to predict the load-displacement response of axially loaded piles in clay considering the degradation of skin friction. In this model, the soil around piles is divided into the shear band immediately adjacent to piles and the soil outside shear bands. An elastoplastic model in terms of the critical state theory-based modified Cam-clay model is developed to describe the mechanical behavior of shear bands. The elastoplastic model can explicitly consider both hardening and softening behaviors of skin friction. The elastic behavior of the soil outside shear bands is represented by a modulus degradation model, which captures the shear modulus degradation with the shear strain. Subsequently, an elastoplastic load-transfer model possessing generalized ability to describe both hardening and softening behaviors is developed by combining these two theoretical models. Predictions of the load-settlement curves are compared with the measured values from three well-documented cases to verify the proposed model. Good agreements demonstrate that the proposed load-transfer model provides reasonable and effective prediction for bearing performance of piles.

Research progress on the shear band of metallic glasses

Metallic glasses have received considerable attention in the fields of materials science and condensed matter physics. The disordered structure of metallic glasses gives rise to unique mechanical properties, such as high strength, large elasticity and a distinct deformation mechanism in contrast to conventional crystalline alloys. The plastic deformation of metallic glasses at temperatures well below the glass transition is generally carried out through the formation of highly localized shear bands. Therefore, a thorough understanding of shear banding behavior is vital for improving the mechanical properties of metallic glasses and tailoring the properties of post-deformed metallic glasses. This review article aims to provide an up-to-date overview of the atomic mechanisms underlying shear band nucleation, propagation and interaction. Additionally, the dynamics of shear bands and their correlation with plasticity are also presented. This article also focuses on the progress in the fundamental structure and properties of mature shear bands, such as density fluctuation, medium-range order, shear-band affected zone, and diffusivity. Furthermore, the fracture mechanism based on the development of cavities is elaborated. Finally, we identify a number of key unsolved issues on this subject.

Micro-scaled plastic yielding and shear-banding dynamics in metallic glasses

Shear-banding behavior in metallic glasses plays a key role in the operation of plastic deformation, which is associated with yield strength. In a micro-scale, the shear-banding behavior must be affected by many factors from the test machine and the substrate. Therefore, in this study, comprehensively considering a machine compliance, a geometry imperfection of micro-pillar, and a substrate sink- in the machine-sample-substrate system, we developed a plastic-strength model at a micrometer scale in this study, which is evidenced by the microscale compressive properties of 18 kinds of metallic glasses. The theoretical model provides a guidance for the elastic limits and shear-banding dynamics of metallic glasses at the micro-scale, which can be applicable to characterize the microscale deformation behavior of other amorphous materials.

Recrystallization Behavior of Warm Rolling and Cold Rolling Cr-Ti-B Steel during Annealing

To study the nucleation and recrystallization behavior of deformation bands, shear bands and grain boundaries during the recrystallization process, a heat treatment test was carried out on Cr-Ti-B low-carbon steel after warm rolling and cold rolling. The results show that recrystallization occurs preferentially in shear bands and grain boundaries. The γ deformation texture can be enhanced and the Goss texture can be weakened during the warm rolling and subsequent cold rolling process. Recrystallization of the deformation bands was observed, but the nucleation time of recrystallization in the deformation band is much slower than that in the shear band and grain boundary.

Shear banding and serrated flow behaviors of high toughness Zr61Ti2Cu25Al12 bulk metallic glass under bending

By interrupted three-point bending experiments, the detailed evolutions of shear-banding and serrated flow as well as their correlation of high toughness Z61Ti2Cu25Al12 bulk metallic glass (BMG) under bending were systematically studied. Three stages can be classified during plastic bending of Z61Ti2Cu25Al12 BMG based on the different characteristics of shear-banding and serrated flow behaviors. Moreover, there has a strong correlation between shear-banding and serrated flow at different stages of plastic bending. It is noteworthy that the driving force for shear bands propagation of BMG beam under bending depends on the bending moment, instead of the applied load. Thus, remarkable positive correlations among bending moment, shear band zone height and average load drop of serrations were found during plastic bending. During the progressive propagation of multiple shear bands, intense interactions and competitions among these shear bands have occurred, which manifested by the self-organized criticality behavior from serrated flow dynamics, as well as the very finer irregular striation patterns and uneven fluctuant morphologies which presented on the shear offset surface. The sizeable plastic zone of Z61Ti2Cu25Al12 BMG is very favorable to achieve the greater macroscopic plasticity and lower the risk of fast catastrophic fracture. Thus, Z61Ti2Cu25Al12 BMG is a promising engineering material for structure elements which are naturally subjected to bending load, such as compliant mechanisms and microelectromechanical systems.

The formation and propagation mechanism of shear band in bulk metallic glasses under dynamic compression

Shear banding behavior plays a significant role in the deformation and failure mechanisms of metallic glasses (MGs). However, due to the limits of dynamic loading and associated characterization methodologies, relevant studies of shear band in dynamic loading remain hazy. Using digital image correlation technologies, the spatial–temporal evolutions of shear bands such as formation, propagation, effective thickness, and instability are in-situ revealed and discussed during the SHPB test. Specific determinism exists for the nucleated locations and orientations of the primary shear band, which is responsible for final failure. The progressive propagation front of the shear band is found to be strongly correlated to the primary shear stress profile, suggesting that the importance of the principal shear stress in driving shear-band propagation. Additionally, a long-range stress zone of the shear band on the order of hundreds of microns is found, which exhibits uniform shear viscosity. The findings of this article shed light on the viability of artificially created shear bands in metallic glasses.

A constitutive model for metallic glasses based on two-temperature nonequilibrium thermodynamics

We develop a new finite deformation constitutive model for metallic glass within the framework of irreversible nonequilibrium thermodynamics. To consider the intrinsically out-of-equilibrium characteristics of metallic glass, its total internal energy is divided into two weakly coupled configurational and kinetic subsystems, and configurational temperature coupling with configurational degrees of freedom is introduced as a thermodynamic state variable to characterize the evolution of the disordered structure. Furthermore, the classical shear transformation zone theory is extended by reasonably considering the reverse shear transformation as a form of the relaxation of the strain field, which is stored in the elastic matrix and produced by the constraint of the matrix on shear transformation. With the help of the finite element implementation for the new model, the effectiveness of the proposed model is validated by comparing the modeling stress–strain responses of the macroscopic deformations under different temperatures and strain rates with the experimental results, and the utility of the model for predicting the shear banding behavior of metallic glasses is examined as well. The results therefore show that the constructed constitutive model can not only effectively predict the deformations of metallic glass under different ambient temperatures and applied strain rates, but also reasonably explain the mechanisms of deformation mode evolution and shear band formation.

Structural design of additively manufactured porous Zr‐based bulk metallic glass

AbstractRecently, designing light‐weight BMGs with high‐strength has attracted much attention. Additive manufacturing (3D‐printing) using selective laser melting (SLM) enables the production of porous bulk metallic glasses (BMGs), which is difficult to achieve by applying traditional manufacturing techniques. In this study, different porous structural prototypes of 3D‐printed Zr‐based BMGs are comparatively studied. Main focus is put on the strength optimization by varying pore arrangement and pore morphology. A constitutive model based on Mohr‐Coulomb theory with multi‐slips system is applied to describe the shear banding behaviors of 3D‐printed amorphous BMGs.

High-pressure homogenized citrus fiber cellulose dispersions: Structural characterization and flow behavior

Functionalized biomass waste sources of cellulose have drawn attention due to their high availability and sustainability properties. In this work we characterize the structural and flow properties of high-pressure homogenized citrus fiber cellulose dispersions, employing SAXS, rheology and rheo-MRI techniques. The high-pressure treatment disrupts the microfibrillar network within the citrus fibers, but leaves the individual microfibrils intact. Under moderate shear (0.1-100 s-1) in a confined (<1 mm) geometry, these functionalized citrus fiber cellulose dispersions exhibit thixotropic shear-banding behavior accompanied by cooperative flow of microfibril flocs with correlation lengths ξ~ 100 μm. The presented findings form a basis towards understanding and manipulating the structural and rheological properties of non-wood biomass cellulose microfibrils under industrially-relevant conditions.

An Insight into Amorphous Shear Band in Magnetorheological Solid by Atomic Force Microscope.

Micro mechanism consideration is critical for gaining a thorough understanding of amorphous shear band behavior in magnetorheological (MR) solids, particularly those with viscoelastic matrices. Heretofore, the characteristics of shear bands in terms of formation, physical evolution, and response to stress distribution at the localized region have gone largely unnoticed and unexplored. Notwithstanding these limitations, atomic force microscopy (AFM) has been used to explore the nature of shear band deformation in MR materials during stress relaxation. Stress relaxation at a constant low strain of 0.01% and an oscillatory shear of defined test duration played a major role in the creation of the shear band. In this analysis, the localized area of the study defined shear bands as varying in size and dominantly deformed in the matrix with no evidence of inhibition by embedded carbonyl iron particles (CIPs). The association between the shear band and the adjacent zone was further studied using in-phase imaging of AFM tapping mode and demonstrated the presence of localized affected zone around the shear band. Taken together, the results provide important insights into the proposed shear band deformation zone (SBDZ). This study sheds a contemporary light on the contentious issue of amorphous shear band deformation behavior and makes several contributions to the current literature.

High fatigue endurance limit of a metastable Ti-based metallic glass composite with martensitic transformation

Introducing the dendrite phase is an effective solution to overcome the low fatigue resistance of metallic glass (MG). In present study, we examined the four-point bending fatigue behavior of a new Ti50.32Zr33.92Cu4.56Ni2.12Be9.08 metallic glass composite (MGC) containing metastable dendrites. The stress-life (S–N) test and various characterization techniques including X-ray diffractometer (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM) were carried out. The fatigue endurance limit, defined as the maximum stress amplitude to which the sample is subjected for 107 cycles without failure, was measured to be ~360 MPa in current MGC. Just compared to the four-point bending fatigue data in previously reported MGCs, the fatigue limit of current MGC is highest. Such excellent fatigue property results from the coupled effect of two aspects on the shear banding and fatigue damage behaviors, i.e., one is the fine separation between the dendrite phases and the other is the martensitic transformation of the metastable dendrites. These findings may improve the understanding on the fatigue mechanisms and provide a promising way for designing the MGs or MGCs with better fatigue performance.

Effect of Fabric Anisotropy on Bifurcation and Shear Band Evolution in Granular Geomaterials

Strain localization, usually manifesting as shear bands, is frequently observed in geomaterials and is of the essential reason inducing the failure of geostructures. Anisotropic characteristics of soils has an important effect on the shear band behavior. This paper is devoted to study the effect of the fabric anisotropy on the initiation and evolution of the shear bands. In particular, the anisotropy is introduced to the strength parameter of the yield criterion by incorporating the material principal direction and the joint invariant of the stress tensor and the microstructure tensor. Furtherly, an elasto-plastic constitutive model considering the fabric anisotropy is established in the micropolar theory framework, and is then applied to simulate the shear bands in transversely geomaterials via three numerical examples, including the plane strain compression test, slope stability and the shallow foundation problems. Moreover, the mesh independency of the proposed model is discussed. Results show that the bifurcation, the shear bands pattern, and the bearing capacity highly depend on the material principal orientation and the anisotropic degree. Comparison with existing study indicates that the proposed model has a good performance in simulating the typical pre and post strain localization behaviors of transversely isotropic geomaterials.