Kink Bands Research Articles

Geometry, kinematics and mechanism of growth unconformities in the Biertuokuoyi piggy-back basin: implications for episodic growth of the Pamir frontal thrust

Piggy-back basins are characterized by growth stratigraphic sequences bounded by growth unconformities and record the complete deformational history of the related structures. The Biertuokuoyi piggy-back basin, located in the hanging wall of the Pamir frontal thrust (PFT), provides a remarkable example documenting the geometry, kinematics and mechanism of growth unconformities. High-resolution seismic data reveal that multiple growth sequences were folded with constant-dip kink band migration and their dips are equal to the change in the fault-bend angle of the PFT, indicating their kinematic coupling. Divided by a basal Cenozoic detachment, the PFT system contains five lower thrust ramps that cut Paleozoic–Mesozoic strata and an upper thrust ramp that cuts Cenozoic strata. The growth strata and unconformities record c. 4425 m of dip-slip and six stages of episodic thrusting for the PFT. We propose a coeval thrusting style for the five lower thrust ramps. The present seismic section reveals at least 31.1 km of total shortening at the northeastern Pamir front. In particular, the latest shortening of c. 8.0 km is recorded by the Biertuokuoyi Basin and the Mushi anticline. Our results show that multiple growth sequences bounded by growth unconformities are powerful resources for documenting the evolution of deformation. Supplementary material: Supporting figures and data, including seismic profiles and kinematic simulation results, are available at https://doi.org/10.17605/OSF.IO/DNQBS . Thematic collection: This article is part of the Fold-and-thrust belts collection available at: https://www.lyellcollection.org/cc/fold-and-thrust-belts

Tectonic evolution of the Indio Hills segment of the San Andreas fault in southern California, southwestern USA

Abstract. Transpressional uplift domains of inverted Pliocene–Pleistocene basin fill along the San Andreas fault zone in Coachella Valley, southern California (USA), are characterized by fault linkage and segmentation and deformation partitioning. The Indio Hills wedge-shaped uplift block is located in between two boundary fault strands, the Indio Hills fault to the northeast and the main San Andreas fault to the southwest, which merge to the southeast. Uplift commenced about or later than 0.76 million years ago and involved progressive fold and faulting stages caused by a change from distributed strain to partly partitioned right-slip and reverse/thrust displacement on the bounding faults when approaching the fault junction. Major fold structures in the study area include oblique, right-stepping, partly overturned en echelon macro-folds that tighten and bend into parallelism with the Indio Hills fault to the east and become more open towards the main San Andreas fault to the west, indicating an early and close relationship of the macro-folds with the Indio Hills fault and a late initiation of the main San Andreas fault. Sets of strike-slip to reverse step-over and right- and left-lateral cross faults and conjugate kink bands affect the entire uplifted area, and locally offset the en echelon macro-folds. Comparison with the Mecca Hills and Durmid Hills uplifts farther southeast along strike in Coachella Valley reveals notable similarities, but also differences in fault architectures, spatial and temporal evolution, and deformation mechanisms. The present work contributes to better understand the structure and tectonic history of a major fault system along a transform plate boundary.

Reduced order multiscale model for compression kink-band failure in composites

A multiscale model for compression kink band failure in fibrous composites is presented. The computational model predicts the progression of damage associated with the formation of kink bands, which experiments demonstrate to involve excessive shear straining of the matrix material and fiber fracture. The uniqueness of the study is establishing the concurrent treatment of nonlinear deformation and failure of the composite constituents at the scale of the material microstructure, and the formation of kink bands at the mesoscopic scale. The model incorporates computational homogenization of the material response, a nonlocal gradient regularization scheme, and a curvature-based criterion for macroscopic fiber break to predict kink band formation. The multiscale approach resolves mesoscale mechanisms associated with kink banding while offering computational benefits compared to direct mesomechanical approaches. An accessible implementation within finite element analysis software is presented and the model is verified with analysis of a mesoscale domain incorporating initial fiber waviness. In quasi-static simulations, the kink band initiates due to matrix softening that results in the onset of buckling and is completely formed when fibers break as a result of localized curvature. Results from parametric studies confirm that compression strength is not directly related to measures of the kink band morphology, but it is strongly correlated with the shear strength and initial fiber misalignment angle. The predicted effects of material properties representing various carbon fiber reinforced polymers and a range of fiber misalignment angles on kink band width and failure strength corroborate analytical and experimental results presented in the literature.

Simultaneously Improving Ductility and Stretch Formability of Mg-3Y Sheet via High Temperature Cross-Rolling and Subsequent Short-Term Annealing.

In this work, Mg-3Y sheet was prepared by high temperature cross-rolling and subsequent short-term annealing. The effect of annealing on microstructure, texture, mechanical properties, and stretch formability of Mg-3Y sheet was primarily investigated. Micro-nano size coexistence of β-Mg24Y5 phases can be well deformed with matrix. The as-rolled Mg-3Y sheet exhibited a homogeneous deformation microstructure consisting of deformed grains with extensive kink bands and dispersed β-Mg24Y5 phases. A double peak texture character appeared in as-rolled Mg-3Y sheet with a split of the texture peaks of about ±20° tilted to rolling direction. After annealing, the as-annealed Mg-3Y sheet presented complete static recrystallized (SRXed) microstructure consisting of uniform equiaxed grains. The texture orientation distribution was more dispersed and a weakened multiple-peak texture orientation distribution appeared. In addition, the maximum intensity of basal plane decreased from 5.2 to 3.1. The change of texture character was attributed to static recrystallization (SRX) induced by kink bands and grain boundaries. The as-annealed Mg-3Y sheet with high Schmid factor (SF) for basal <a> slip, prismatic <a> slip, pyramidal <a> slip, and pyramidal <c+a> slip exhibited high ductility (~25.6%). Simultaneously, enhanced activity of basal <a> slip and randomized grain orientation played a significant role in decreasing anisotropy for the as-annealed Mg-3Y sheet, which contributed to the formation of high stretch formability (~6.2 mm) at room temperature.

Kink mechanism in Cu/Nb nanolaminates explored by in situ pillar compression

Nano metallic laminates (NMLs) exhibit different failure modes depending on the loading conditions due to their mechanical anisotropies. Kinking is a typical failure mode in many NMLs compressed along a layer-parallel direction. However, a detailed description of the microstructure evolution during kink band (KB) formation and an in-depth understanding of the formation mechanisms are lacking. In this work, the KB process is investigated in Cu/Nb NMLs by in situ micro pillar compression in the scanning electron microscope (SEM) along a layer-parallel direction. Post-mortem S/TEM and transmission Kikuchi diffraction (TKD) analyses show that kink banding leads to significant microstructure changes characterized by an accumulation of geometrically necessary dislocations (GNDs) and of tilt geometrically necessary boundaries (GNBs) near KB boundaries (KBBs). The distinct microstructure evolution implies that KB formation is facilitated by the inhomogeneous microstructures resulting in constrained deformation modes. Specifically, dislocations active on slip planes nearly parallel to the interfaces make a major contribution to kink evolution after the onset of kinking. Once layer-parallel slip systems are activated, preexisting lattice dislocations and dislocations nucleating from interfaces will accumulate as GNDs near KBBs via the stochastic storage of lattice dislocations that have certain Burgers vectors. GNDs can further transform into GNBs via cross-slip and climb driven processes near the KBB. Furthermore, GNBs near KBBs can grow by incorporating more GNDs or by coalescence to accommodate the KB evolution. We further hypothesize that microstructural perturbations and their ensuing stresses can initiate KB formation in Cu/Nb NMLs.

Potential kink band formation on [formula omitted] two-phase Ti-10Cr alloy under compressive condition

The plastic deformation of an α/β two-phase Ti-10Cr alloy with fine lamella microstructure was investigated under uniaxial compression. The material was composed of coarse equiaxed β grains with {332}〈113〉 twins introduced by cold rolling and α precipitates after aging. The crystallographic relationship between the matrix, the twin, and the precipitates was analyzed. A combination of optical microscopy, scanning electron microscopy, and electron backscatter diffraction with energy-dispersive X-ray spectroscopy analyses was carried out to investigate the microstructure and plastic deformation behavior of the Ti-10Cr alloy. During uniaxial compression tests, {110}β - rotation-type kinks were located in the Ti-10Cr alloy. The crystallographic and kinematical relationships among the formed deformation bands were clarified with the rank-1 connection theory.

Kink Formation through Creep Deformation and Possibility of Kink Strengthening in Ti&lt;sub&gt;3&lt;/sub&gt;SiC&lt;sub&gt;2&lt;/sub&gt; MAX Phase

Kink formation and kink strengthening mechanisms were examined in the polycrystalline Ti3SiC2 MAX phase prepared by a reaction sintering process using a spark-plasma-sintering machine. The creep behavior tested by compression at 1200°C showed two deformation regions depending on the applied stresses; at stresses lower than 120 MPa, the stress exponent n exhibited ≈1.8, whereas at higher stresses, it exhibited n ≥ 6. The creep behavior can be ascribed to grain boundary sliding mechanisms for the lower stresses with n ≈ 1.8 and to dislocation-related creep mechanisms for the higher stresses with n ≥ 6. The kink bands were frequently observed to form in the grains deformed only at the higher stresses when its basal plane was inclined by about 10–20° against the compressive axis. This suggests that the kink bands might be formed only when two factors of the high stresses acting on the basal plane and the resultant dislocation activities were satisfied. Nanoindentation tests conducted around the formed kink bands showed that the nanohardness linearly changed with the distance from the kink bands and showed higher values around the kink bands. Since the kink bands blocked the slip line caused by the nanoindentation, those become obstacles against the dislocation motion caused by the indentation deformation. This suggests that the kink bands would contribute to improving the mechanical properties of the Ti3SiC2 MAX phase.

Mechanical properties of unidirectional nanoporous gold under compression

Dealloyed nanoporous (NP) metals are expected to be stronger by more than one order of magnitude than conventional porous metals of same porosity. However, the strengths of random-structured NP metals in practice are limited by the low mechanical efficiency of their network structure. In this paper, we report that an anisotropic nanoporous gold (NPG) with unidirectional pore channels can also be self-organized in dealloying. This material combines a mechanically efficient topology structure with ultra-strong nanoscale solid skeleton. In consequence, its out-of-plane mean strength (461 ± 52 MPa) is more than twice that of the strongest NPGs reported in previous studies. Because of the structural anisotropy, unidirectional NPGs deform by the formation and expansion of kink bands under compression, unlike the uniform densification of most previous NPGs. The pore-channel misalignment and other defects such as the voids in pore walls may have reduced macroscopic strength, which accounts for a large scatter in the measured strength and a gap between theoretical and experimental data. We anticipate that the structure and mechanical properties of unidirectional NPGs will be further improved in the future by optimizing dealloying parameters. A combination of high strength, unidirectional pore channels, and excellent thermal and electrical conductivity of metallic pore-wall phase might enable novel applications of this material in many areas.

On the micromechanics of voids in nanotwinned materials

This work investigates internal damage by void growth in NT microstructures via crystal plasticity. The framework incorporates length-scale effects and explicitly models twin boundary migration. Using finite-deformation, plane strain finite element calculations of porous unit cells, we analyze the roles of twin size, plastic anisotropy and twin boundary migration on void evolution over a range of controlled biaxial stress states. The simulations provide insights into crystallographic aspects of porosity growth in NT microstructures. Emphasis is placed on correlating the micromechanics of failure by internal necking. Irrespective of the level of crystallographic plastic anisotropy, twin boundary migration effectively shields the void growth process, delaying the porosity evolution compared to non-twinned microstructures. It is found that crystallographic plastic anisotropy causes kink band instability that can affect void growth. Coupled with twin boundary mobility, twin size and crystallographic plastic anisotropy create a rich landscape of failure characteristics as a function of the stress state.

Distinct impacts of growth band on the mechanical properties of abalone nacre under compressive and tensile stresses

In abalone nacre, growth bands occur periodically with the change of living environments. To explore the specific role of growth bands playing in the mechanical properties of nacre, the compressive and three-point bending behaviors of composites with growth bands in green abalone shell and pure nacre without growth bands in whitened ear abalone shell were comparatively investigated. It is found that the mechanical effects of growth bands under different stress states are significantly distinct, mainly attributing to the different responses of organic matrix interlayer in growth bands. Specifically, due to the remarkable ductility of thicker organic matrix interlayer under the action of compressive stress, the growth bands could be bent without fracturing in the region of kink band. However, the existence of growth bands leads to a lower interfacial strength, finally causing the fact that the composites with growth bands exhibit a lower strength but a higher toughness than pure nacre under uniaxial compression tests. Contrastively, both the strength and toughness of the composites are lower than those of pure nacre under three-point bending tests, since micro-cracks will be first initiated in growth bands on account of the weaker organic matrix interlayer under tensile stress. Therefore, the growth bands actually play different roles in the mechanical performances of nacre under compressive and tensile stresses.

Ultrafast severe plastic deformation in high-entropy alloy [formula omitted] via dynamic equal channel angular pressing

An extensively investigated high-entropy alloy (HEA), Al0.1CoCrFeNi, is processed by dynamic equal channel angular pressing (D-ECAP) and subsequent annealing. Severe shear deformation and ultrahigh strain rate give rise to simultaneous activation of the {111}〈112〉 macro deformation twins and kink bands with the 〈110〉 or 〈112〉 rotation axes. Secondary kink bands are also observed in primary kink bands. With increasing annealing temperature, the deformation twins and kink bands both become less or disappear. The yield strength is increased by ∼255% solely by D-ECAP compared to the as-cast HEA. A reasonable combination of high strength and good ductility is achieved through annealing twins in recrystallized grains via annealing the D-ECAP-processed alloy at 900 °C. It is the first observation on kink bands within a face-centered cubic HEA under various loading conditions. The strengthening in these D-ECAP-processed samples before and after annealing is discussed in terms of grain boundary strengthening and dislocation strengthening.

Dislocation glide and mechanical twinning in a ductile VNbTi medium entropy alloy

• {112}<111> mechanical twinning was activated in an equiatomic refractory VNbTi medium entropy alloy at room temperature. • Twinning nucleation mostly occurred at the beginning of plastic deformation, and a twinning-kinking mixed microstructure was formed. • Dislocation glide dominates the subsequent deformation, and kinking was helpful to relax the stress concentration. • The synergistic activation dislocation glide, twinning and kinking provide a new path to design ductile refractory medium-/high-entropy alloys. An equiatomic VNbTi medium-entropy alloy with outstanding tensile properties and unique deformation behavior is reported. The screw dislocation glide, deformation twinning, and dislocation accumulation induced kink bands are identified as three deformation mechanisms that contribute to a large elongation above 20%. The {112}<111> twins are activated at the beginning of the yield stage accompanied by sudden stress-drop and pronounced acoustic emission. Dislocations dominate subsequent tensile deformation, and the prevalent multiplanar dislocation slip promotes the formation of complex dislocation configurations (e.g., debris, dipoles, and loops) and dense dislocation networks. The twin bands and kink bands can further impede the dislocation motion meanwhile effectively alleviate stress concentration. The synergistic activation of these deformation mechanisms provides new opportunities to design ductile refractory medium- and high-entropy alloys.

Cylindrical microplane model for compressive kink band failures and combined friction/inelasticity in fiber composites II: Analyses

This two-part paper presents a novel 3D cylindrical microplane model for the longitudinal compressive failure of fiber reinforced composites by kink band formation. The model formulation was described in part I, and here in part II, its implementation and numerical analyses are described. Through both material point and structure level analyses, the model is shown to predict well the geometric features of the failure, including damage localization, in-plane and out of plane kink band formation, and local fiber rotation. Further, the model is able to capture the entire load displacement curve including the peak load, the prolonged post-peak load plateau, and most importantly, the quasi-brittle fracture mechanics-based strength size effect, in agreement with experiments. The model is also able to capture the effect of the misalignment angle on the peak and post-peak loads. The validated model is used to investigate and quantify the effect of friction on the failure behavior. Results suggest that friction is a major effect, contributing to a higher peak load and post-peak load plateau. Additionally, a simpler and efficient alternative for the combined friction/damage is proposed, which involves a simple modification of the microplane level damage law.

Core structure and Peierls barrier of basal edge dislocations in Ti[formula omitted]AlC[formula omitted] MAX phase

In the MAX phase, the nucleation and motion of basal dislocations dominate the plastic deformation at room temperature. Therefore, information on the dislocation core properties and energy barrier for dislocation glide is essential to understand their plasticity. Dislocations in MAX phases are mainly 〈a〉-type basal edge dislocations (b=a/3[112̄0]) and can glide in the basal plane (typical slip) or form kink bands depending on the load direction and crystal orientation owing to the strong plastic anisotropy. In this study, we determined the core structure, Peierls barrier, and corresponding stress of a/3(0001)[112̄0] edge dislocations in Ti3AlC2 MAX phase by multiple computational approaches using the semidiscrete variational Peierls–Nabarro method, density functional theory, and classical bond-order-potential-based molecular statics calculations. The a/3[112̄0] basal edge dislocation was dissociated into two Shockley partial dislocations with a 2–2.5b-wide stacking fault in between. These partial dislocations glide between the Ti(4f) and Al atomic layer. For straight dislocation motion, the Peierls barrier was single-humped and the corresponding Peierls stress was estimated to be approximately 182 MPa.

Effects of various porosities on the damage evolution behavior of carbon fiber/epoxy composites using acoustic emission and micro-CT

Void defects can reduce the mechanical properties of composites and increase the potential danger of composite components in service. The effects of various porosities on damage evolution behaviors of carbon fiber/epoxy composites are deeply investigated by combining the damage visualization and acoustic emission response. The results showed that the increased porosity accelerates the damage evolution from micro-scale to macro-damage. Acoustic signals in composites are captured in advance when the porosity is high, and the voids below the kink band accelerate matrix cracking and delamination, while specimens with low porosity easily cause fiber damage and fiber/matrix debonding. Additionally, applying extra pressure during the resin transfer molding process can decrease the porosity, but excessive extra pressure may result in an inverse result. The method combining acoustic emission and micro-CT can provide a reference for improving quality and the health monitoring of composites.

Compressive stress and shear stress on the deformation mechanism of Mg-13Gd-4Y–2Zn-0.5Zr alloy at different deformation temperatures

At present, alloys are affected by various stress states during their deformation process. Various stresses can facilitate alloy deformation at the same time, and the influence of these stresses on material deformation is difficult to clarify. It is essential to clarify the difference in the deformation mechanism of an alloy in a single stress state In this work, the internal deformation mechanism of the Mg-13Gd-4Y–2Zn-0.5Zr alloy under two stress states at different deformation temperatures was studied by compression and torsion experiments. The results show that the grain is slightly deformed under shear stress deformation, and the long period stacking ordered (LPSO) phases of different forms show smaller kink angles, fewer kink times, and larger relative width ratios of the kink bands. Under compressive stress deformation, the grain is obviously compressed along the CD direction and presents a streamline, and the LPSO phase is severely kinked. Different stress states have a great influence on dislocation slip, and the shear stress state can easily provoke the initiation of non-basal slip. Non-basal slip has difficulty starting under compressive stress, which leads to dislocation packing. The dynamic recrystallization (DRX) fraction of compressive stress deformation is higher than that of shear stress deformation. Shear and compressive stress deformation alloys activate different kinds of twinning. In shear stress deformed alloys, tensile twins usually occur in grains with a small basal slip Schmid factor (SF). However, compression twins are activated in the compressive stress deformation alloy and occur in grains with larger SF values. When the slip is not fully coordinated with the deformation, kinking and twining occur to coordinate the deformation.

Mechanical behavior and damage kinetics of a unidirectional carbon/epoxy laminated composite under dynamic compressive loading

AbstractIn this work, mechanical behavior and damage kinetics of a unidirectional carbon/epoxy laminated composite (CFRP) under dynamic compressive loading were investigated. An Instron testing machine and a pulse‐shaped split Hopkinson pressure bar (SHPB) apparatus were employed to test the quasi‐static and dynamic mechanical properties of the material, respectively. Digital image correlation (DIC) combined with ultra high‐speed photography was used to study the deformation and failure process of the specimen under dynamic loading. The results show that the failure modes of the material along the main direction were strain‐rate sensitive. The failure mode along the fiber direction was observed to change from crushing followed by fiber kink banding to predominantly interlaminar delamination, longitudinal cracking and fiber buckling delamination as the strain rate increases from quasi‐static to high strain rates. Furthermore, an empirical formula for dynamic compression strength was established based on the test data. Model predictions and experimental data are in very good agreement. Finally, a simplified Zhu‐Wang‐Tang (ZWT) nonlinear visco‐hyperelastic constitutive model ZWT nonlinear viscoelastic model was developed to predict the mechanical behaviors of CFRP under dynamic impact loading. The predicted values are observed to essentially match the trends of the experimental results. This research will further improve the design of CFRP composites subjected to high‐speed impact loads during service.

Unidirectional CFRP kinking under uniaxial compression modeled using synchrotron radiation computed tomography imaging

The kinking mechanism in unidirectional carbon fiber-reinforced polymers (CFRPs) needs be characterized to improve structural design. Thus, we performed a uniaxial compression test on a CFRP under synchrotron radiation computed tomography to experimentally obtain its load–displacement relationship. The specimen was observed to be fractured with a kink band during postmortem analysis. The shape and size of the kink band coincided with previously reported data. In addition, the fiber locations on the tomographic images prior to loading were identified via image processing, and three-dimensional unidirectional CFRP models were constructed using the geometric information. Subsequently, finite element models were developed to simulate the compressive failure conditions. The numerical analysis revealed that the kink formation was caused by expanded matrix yielding and fiber breakage.

Cylindrical microplane model for compressive kink band failures and combined friction/inelasticity in fiber composites I: Formulation

This two-part paper presents a novel 3D cylindrical microplane model for the longitudinal compressive failure of fiber reinforced composites by kink band formation. The formulation details are presented in part-I, while the implementation, calibration, and validation, in part-II. The primary novelty is the first adaptation of the semi-multiscale microplane modeling approach to compressive kink band failures in composites. The salient novel feature of this adaptation is a cylindrical system of microplanes, introduced to capture the transversely isotropic behavior of the unidirectional lamina. The model implicitly resolves the macro–micro compatibility to calculate the local fiber rotation in the kink band, thus defining the orientation of the cylindrical microplane system. This allows an intuitive formulation of the kink band triggering mechanism involving axial inter-fiber microcracks at the microplane level. As another new advance, the internal friction is formulated at the microplane level, via a thermodynamically consistent combined damage/friction scheme, which is integral to compressive failures. The model formulation is general enough to allow application to both brittle and ductile matrix materials, and to in-plane and out-of-plane kinking. The macro–micro elastic correlations are established via strain energy density equivalence, and the calculation of the stiffness tensor of one microplane system is demonstrated.

Rolling reduction-dependent deformation mechanisms and tensile properties in a β titanium alloy

• When the reduction is 10%-60%, the dislocation, martensite, {332}<113> deformation twins, kink band are activated in the matrix. • Secondary kink band and {331}<113>deformation twins are triggered in the primary kink band. • As the level of deformation gradually increases, the tensile and yield strength of the alloy increase significantly, while elongation exhibits a wavy trend. • The work hardening effect of the alloy is affected by the dynamic Hall-Petch effect and the multi-scale structure strengthening effect. This work investigated the dependence of deformation mechanisms and mechanical properties on cold rolling reductions of the metastable TB8 titanium alloy. Results shown that the crystal orientation of the matrix changes with the increasing level of reduction, leading to the activation of complex deformation mechanisms in the matrix. When the rolling reduction is 10%, the deformation mechanisms are dominated by dislocations and {332}<113> deformation twins. As the reductions increase to 20%-50%, the secondary deformation twinning (SDT) is triggered in primary deformation twins besides the primary kink band is activated. Meanwhile, the secondary kink bands and {332}<113> twins have be observed in the primary kink bands. When the reduction reaches to 60%, the deformation mechanisms are dominated by dislocations and deformation twins. Furthermore, the matrix refined by crisscrossing among the twins, kink bands and other deformation mechanisms during cold rolling, which shortens the dislocation mean free path and then affects the strength and shape of the alloy. The dynamic Hall-Petch effect and the interaction between multi-scale deformed structures control the work hardening behavior of the alloy.