Deformation Propagation Research Articles

A coupled 3D thermo-mechanical peridynamic model for cracking analysis of homogeneous and heterogeneous materials

This paper proposes a variable timestep-strategy that can speed up the peridynamic modeling of thermomechanical cracking in both homogeneous and heterogeneous materials. A piecewise continuous time-step variation function is incorporated into the peridynamic framework that dynamically adjusts the time-step size, which ranges from a small value to a maximum value that remains below the critical stable time-step. The advantages of this variable timestep strategy are threefold: (1) The exceptional computational efficiency of this approach is mainly manifested in enabling peridynamic simulation that is 20 times faster compared to that employing a constant time step; (2) Taking advantage of the proposed method, both two- and three-dimensional peridynamic modeling of thermomechanical deformation and crack propagation has been demonstrated to be of great accuracy and robustness; (3) Facilitated with this variable timestep strategy, we achieve a remarkable advancement in peridynamics to capture intricate 3D crack patterns with complex topological structures in homogeneous specimens subjected to water quenching. Furthermore, the effects of the temperature difference, specimen geometrical configurations and the initial water entry velocity on the crack patterns of the specimens under water quenching are systematically explored.

Mesozoic-Cenozoic Exhumation Processes of the Harlik Mountain (East Tianshan), NW China: Evidence from Apatite (U-Th)/He Thermochronology

Abstract The Tianshan Mountains, which formed through the prolonged and complex subduction-accretion of the paleo-Asian ocean, experienced multiple widespread erosions and reactivations during the Mesozoic-Cenozoic period. Thus, the Tianshan has become a crucial area to explore the process and mechanism of intracontinental orogeny. The Harlik Mountain located in the easternmost part of Tianshan has special significance in revealing crustal deformation and far-field stress propagation. In this study, we use the apatite (U-Th)/He method to investigate the near-surface exhumation process of Harlik Mountain, which is the result of tectonic events and erosion. The apatite (U-Th)/He data and thermal history modeling reveal three enhanced exhumation events in the Harlik Mountain, i.e., the early Cretaceous, the late Cretaceous-Paleocene, and the middle Eocene. These events are consistent with the exhumation patterns observed throughout the entire Tianshan. Notably, the exhumation rate and amplitude in the early Cenozoic period were significantly higher in the Harlik Mountain compared with the Mesozoic period. Our findings reveal that the exhumation of the Harlik Mountain and the entire Tianshan displayed pronounced spatial-temporal variations throughout the Mesozoic-Cenozoic period. These variations can be attributed to the combined effect of uneven northward compression of the southern Asian margin, the heterogeneous rheological properties of the lithosphere, and the complex structure of the Tianshan.

Betholletia excelsa Fruit: Unveiling Toughening Mechanisms and Biomimetic Potential for Advanced Materials.

Dry fruits and nutshells are biological capsules of outstanding toughness and strength with biomimetic potential to boost fiber-reinforced composites and protective structures. The strategies behind the Betholletia excelsa fruit mechanical performance were investigated with C-ring and compression tests. This last test was monitored with shearography and simulated with a finite element model. Microtomography and digital and scanning electron microscopy evaluated crack development. The fruit geometry, the preferential orientation of fibers involved in foam-like sclereid cells, promoted anisotropic properties but efficient energy dissipating mechanisms in different directions. For instance, the mesocarp cut parallel to its latitudinal section sustained higher forces (26.0 ± 2.8 kN) and showed higher deformation and slower crack propagation. The main toughening mechanisms are fiber deflection and fiber bridging and pullout, observed when fiber bundles are orthogonal to the crack path. Additionally, the debonding of fiber bundles oriented parallel to the crack path and intercellular cracks through sclereid and fiber cells created a tortuous path.

Analogue modelling of the Ainsa oblique zone in the Southern Central Pyrenees, Spain

The Pyrenees are a collisional orogen striking WNW-ESE. However, in the Ainsa oblique zone in the south-central part of the Pyrenees, faults and folds rotate to ∼N–S over a westward thinning evaporitic layer. The influence of lateral change in basal friction due to declining evaporitic layer thickness in a fold-and-thrust belt is studied by analogue modelling simulating the Ainsa oblique zone. In the experiments the transition zone is simulated by a viscous silicone mixture sheet that laterally changes in thickness adjacent to frictional-plastic quartz-sand. The models confirm that a transition between weak and strong basal friction causes oblique structures to develop. Weak detachment zones are prone to fault propagation whereas strong detachment zones are prone to imbrication. At the transition zone those structural styles are combined, resulting in a complex domain. The differences in deformation style cause dextral shear and clockwise rotation in the transition zone and larger horizontal deformation propagation in the weak basal friction zone. Structures produced in the analogue models are compared to structures in the Ainsa oblique zone and found to be representative. Therefore, this study shows that transition between weak and strong detachment layers can explain the regional structural deformation style in the Ainsa oblique zone.

Numerical modeling and simulation of underwater explosions interacting with discrete rigid bodies

The smoothed particle hydrodynamics (SPH) method is widely used to simulate underwater explosion phenomena. However, previous studies have focused on the interaction between the underwater explosion and continuous structures (e.g., steel plates and dams), while studies on the interaction between the explosion and discrete objects (e.g., debris) have not been reported. In this study, a multi-media coupled model containing water, explosion gas, discrete objects, and steel plates is developed based on the SPH method. The discrete object is modeled as a rigid body with a certain shape, which is discretized by SPH particles. The interaction between the discrete object and the adjacent fluid particles is realized by the kernel approximation, while the collision between different objects is realized by the contact algorithm. To improve the numerical stability, an artificial viscous term containing a threshold switch is added to the SPH momentum equation, while a density dissipation term is introduced into the continuity equation to reduce the noise of the pressure field. Subsequently, the established SPH model is used to simulate the underwater explosion process containing discrete rigid bodies, and the effects of the distribution, stacking form, and number of rigid bodies on the propagation of shock waves, bubble expansion, and deformation of steel plates and the effect of damage are analyzed. The results show that the rigid body will hinder the propagation of shock waves, help reduce the peak pressure of the shock wave behind, and then affect the direction of the diffusion of the explosion energy. Shock waves would produce diffraction, reflection, and transmission when passing through the rigid bodies, and the superposition of various waves would make the pressure distribution near the liquid–gas interface irregular. The rigid bodies stacked above the explosives would enhance the damage effect of the explosion on the steel plates below, and the damage effect is affected by the stacking form. The established model can simulate the multi-medium coupling process in a unified framework without coupling other methods and can effectively restore the complex interaction process between underwater explosion, discrete object, and structure.

Effects of Stress State, Crack—γ/γ′ Phase Interface Relative Locations and Orientations on the Deformation and Crack Propagation Behaviors of the Ni-Based Superalloy—A Molecular Dynamics Study

In this study, we systematically investigate the influence of stress states, relative locations, and orientations of crack—γ/γ′ phase interfaces on the deformation and crack propagation behaviors of the Ni-based superalloy through molecular dynamics simulations. The stress state with high stress triaxiality will impede the plastic deformation process of the system, thereby promoting brittle crack propagation within the system. But the stress state of low stress triaxiality results in obvious plastic deformation and plastic crack propagation behaviors of the system. The deformation system with cracks located in both the γ and γ′ phase exhibits the slowest growth rate, regardless of applied stress states. Additionally, the deformation process demonstrates prominent plastic behavior. For the deformation system with cracks perpendicular to the γ/γ′ phase interface, the γ/γ′ phase interface will hinder the crack propagation. Our research provides interesting observations on deformation and crack propagation behaviors at an atomic level and at a nano-scale which are important for understanding deformation and fracture behaviors at a macroscopic scale for the Ni-based superalloy.

Evolution from gas outburst to coal outburst: An analysis from the perspective of asynchronous transfer difference of gas mass and coal deformation

Considering that coal and gas outburst is a highly complex nonlinear process, the synchronous energy criterion based on the gas expansion energy and the coal deformation potential energy is often adopted to evaluate the hazard. However, the synchronous energy criterion without considering the transfer difference of gas mass and coal deformation has defects in describing the evolution characteristics of coal-rock gas dynamic disasters. Hence, it is necessary to investigate the asynchronous characteristics of the gas expansion energy and the coal deformation potential energy. In this study, the deformation characteristics of coal injected with He and CH4 were measured respectively with the aid of a self-developed device for observing the asynchronous characteristics of effective stress and adsorption-induced deformation. Besides, the differentiated propagation characteristics of gas pressure and adsorption-induced deformation were obtained, and the asynchronous propagation starting point and propagation rate difference between them were analyzed and determined. Furthermore, based on the calculation formula of gas expansion energy and coal deformation potential energy, the values and propagation differences of the two types of energy at different times were revealed. Finally, the typical outburst phenomena were explained using the energy asynchronous theory. The following research findings were yielded. The adsorption-induced expansion process lasts longer than the gas pressure reduction process, which is the reason for asynchronous propagation of gas expansion energy and coal deformation potential energy. The coal deformation potential energy can be further divided into mechanical compression strain energy and desorption shrinkage strain energy. In the initial stage of outburst, the main sources of energy are free gas expansion energy and mechanical compression strain energy. As time progresses, the effect of desorption gas expansion energy and desorption shrinkage strain energy gradually strengthens. From the perspective of energy asynchrony, outburst occurrence at a low gas concentration in deep regions and delayed outburst in cross-cut coal uncovering can be explained as the result of dynamic load instability in surrounding stopes brought about by lagging superimposed deformation disturbances after gas desorption, or the result of self-induced lagging shrinkage deformation formed under special boundary conditions. The findings of this study are helpful to guide the design and connection of the prevention and control methods of deep coal-rock gas dynamic disasters.

The mechanism for Li-addition induced homogeneous deformation in Mg-4.5wt.% Li alloy

The mechanism by which Li additions induce a more homogeneous deformation was systematically investigated in this study by comparing the deformation behavior of pure Mg and Mg-4.5 wt.% Li using experiments, crystal plasticity simulations, and theoretical calculations. The results of the digital image correlation measurements showed that under tension along the transverse direction (TD), strong localized deformation bands with an angle of approximately 20° with respect to the TD were observed in pure Mg, but were absent in Mg-4.5 wt.% Li. Slip trace analyses indicated that basal slip was the predominant deformation mode for pure Mg, whereas that for Mg-4.5 wt.% Li was prismatic slip. A high relative activity of pyramidal 〈c+a〉 slip, approximately 17 %, was observed in Mg-4.5 wt.% Li at a high strain of 10 %. Contraction or double twins were hardly detected during the entire tension process. Crystal plasticity simulations revealed that the 4.5 wt.% Li addition dramatically reduced the critical resolved shear stress (CRSS) ratio of pyramidal 〈c+a〉 slip: prismatic slip: basal slip, which was 31.5:21:1 for pure Mg and 4.3:1.3:1 for Mg-4.5 wt.% Li. Theoretical calculations using the CRSS ratios determined by simulations revealed that easy and uniform deformation propagation induced by a dramatically reduced CRSS ratio of prismatic slip to basal slip played a more important role in improving the deformation homogeneity, in addition to the enhanced activity of pyramidal 〈c+a〉 slip. The mechanisms for how Li additions improve the ductility of Mg are also revisited in this paper.

Numerical modelling and field observations on the failure mechanisms of deep tunnels in layered surrounding rock

Tunnelling through layered rock mass with high geo-stress often leads to large deformation disasters, including rock collapses and structural failures. This study investigates the asymmetrical deformation and failure behaviors of deep tunnels in layered phyllite strata in Chengdu-Lanzhou railway (China). It has been observed that the mechanical behavior of these tunnels exhibits evident correlations with the orientations between geo-stress conditions and bedding plane. For in-depth analysis, a modeling method was first proposed considering the difference between interlayer bedding planes and intralayer joints. The excavation disturbance behaviors of unsupported tunnels with various bedding angles, such as deformation characteristics, crack generation and propagation, and stress distribution, were simulated and compared with on-site phenomena. Afterward, the crack distributions were classified into four typical types based on simulation results, and their causes, differences, characteristics, and evolutionary process mechanisms were also systematically analyzed. Additionally, the asymmetric failure caused by the weak plane effect was investigated and discussed. The results revealed that the bedding angle, the direction of principal stress and the effect of layer thickness primarily influenced the failure patterns of layered surrounding rock, which resulted in variations in both the direction and depth of failure. Engineering practice demonstrated that the classification method, based on the proposed numerical modeling approach, can serve as a valuable reference for tunnel support design.

Development of a new type sprayed high ductility concrete (SHDC) and uniaxial compression test of rock-SHDC combined body

The application prospect of sprayed high ductility concrete (SHDC) as a tunnel and coal mine roadway supporting material is extensive. In this paper, modified desulfurization gypsum, manufactured sand, PVA-PP hybrid fiber, expansion agent, and shrinkage reducer were used as the primary raw materials to solve the environmental and cost problems caused by traditional SHDC, and an orthogonal experiment with four factors and three-level designs was conducted. The SHDC mix proportion in the orthogonal experiment was optimized on the basis of entropy weight method to optimize the grey correlation analysis. Then, the specimens were prepared by spraying to verify their performance. Finally, a low-cost, high-performance, and green SHDC was designed. The rebound rate of the vault was 17%, and the full face was 11%. The 28d compressive strength was 32.18 MPa, the ultimate tensile strain was 1.19%, and the autogenous shrinkage was 518.79με. In addition, the microstructure of SHDC and the synergistic mechanism of hybrid fibers were analyzed by optical microscopy, SEM, XRD, and TGA. On the basis of the engineering background of sprayed concrete, the rock-SHDC combined body was processed and manufactured, and uniaxial compression test was carried out. The DIC technology and surface-bonded strain gauge were used to explore the deformation and crack propagation characteristics of the composite, the energy evolution, and the impact tendency. When multiple cracks in the rock mass propagated to SHDC, convergence occurred, and 2–3 cracks converged into 1 crack. The rock monomer showed weak impact tendency, whereas the combined body and SHDC monomer showed non-impact tendency. So, SHDC can effectively limit rock deformation and maintain good integrity.

The weaving art of mechanically and electronically robust hydrogel realizes multi-dimensional response of stretchable sensors

In recent years, hydrogel-based soft electronics have been developed for the application of human motion, flexible robots and foldable displays. However, most existing conductive hydrogels have low toughness, single electron conduction or ionic conduction and poor adaptability towards complex applications. In this work, we obtained the toughness fiber-like hydrogel in three steps by doping nanofillers, directional extrusion freezing, and salting out. The proposed tough fiber-like hydrogel has a rich porous structure, which is achieved by doping the hydrophilic graphene nanosheets (HGNs) into a physically cross-linking polyvinyl alcohol (PVA) gel matrix. Directional extrusion freezing and salting out effect endow fiber-like hydrogel with better orientation ultimate nominal stress (∼9.5 MPa) and nominal strain (∼2200%). Meanwhile, the abundant porous structure facilitates ion migration and greatly enhances the ionic conductivity (up to 2.8 S m −1, at f = 1 MHz) of the hydrogel. The presence of HGNs endows the fiber-like hydrogel with excellent electronic conduction properties. Moreover, the weaving strategy is proposed to fabricate fiber-like hydrogel into hydrogel fabric film, which is effective for increased safety of stress-induced deformation and crack propagation. The woven hydrogel mesh bag can lift 6 kg of watermelon and the woven hydrogel net can bear a top-down weight impact of 1 kg. We also develop a novel type of woven hydrogel glove that can monitor complex hand movement. This work will provide new insight into the design of multifunctional materials with applications on electronic skin, wearable devices, and health monitoring.

The link between Somalian Plate rotation and the East African Rift System: an analogue modelling study

Abstract. The East African Rift System (EARS) represents a major tectonic feature that splits the African continent between the Nubian Plate situated to the west and the Somalian Plate to the east. The EARS comprises various rift segments and microplates and represents a key location for studying rift evolution. Researchers have proposed various scenarios for the evolution of the EARS, but the impact of continent-scale rotational rifting, linked to the rotation of the Somalian Plate, has received only limited attention. In this study we apply analogue models to explore the dynamic evolution of the EARS within its broader rotational-rifting framework. Our models show that rotational rifting leads to the lateral propagation of deformation towards the rotation axis, which reflects the general southward propagation of the EARS. However, we must distinguish between the propagation of distributed deformation, which can move very rapidly, and localized deformation, which can significantly lag behind the former. The various structural-weakness arrangements in our models (simulating the pre-existing lithospheric heterogeneities that localize rifting along the EARS) lead to a variety of structures. Laterally overlapping weaknesses are required for localizing parallel rift basins to create rift pass structures, leading to the rotation and segregation of microplates such as the Victoria Plate in the EARS, as well as to the simultaneous north- and southward propagation of the adjacent Western Rift. Additional model observations concern the development of early pairs of rift-bounding faults flanking the rift basins, followed by the localization of deformation along the axes of the most developed rift basins. Furthermore, the orientation of rift segments with respect to the regional (rotational) plate divergence affects deformation along these segments: oblique rift segments are less wide due to a strike-slip deformation component. Overall, our model results generally fit the large-scale present-day features of the EARS, with implications for general rift development and for the segregation and rotation of the Victoria Plate.

Localization of Deformation in a Non‐Collisional Subduction Orogen: The Roles of Dip Geometry and Plate Strength on the Evolution of the Broken Andean Foreland, Sierras Pampeanas, Argentina

AbstractThe southern Central Andes (SCA, 27°–40°S) exhibit a complex deformation pattern that is influenced by multiple factors, including the present‐day dip angle of the subducting oceanic Nazca plate and the influence of inherited heterogeneities in the continental South American plate. This study employs a data‐driven geodynamic workflow to assess the role of various forcing factors in determining upper‐plate strain localization, both above the flat slab and the steeper segment to the south. These include the dip angle of the Nazca plate, the mechanically weak sedimentary basins, the thickness and composition of the continental crust, the strength of the subduction interface, and the plate velocities. Our modeling results predict two main deformation modes: (a) pure‐shear shortening in the broken foreland above the flat‐slab segment and eastward propagation of deformation, and (b) simple‐shear shortening restricted to the eastern margin of the Andean fold‐and‐thrust belt above the steep‐slab segment. While the convergence velocity and the frictional strength of the subduction interface primarily control the intensity of the deformation, inherited heterogeneities tend to localize deformation, and weak sediments leads to intensified surface deformation. Thicker crust and surface topography also influences strain localization by transferring stress to the eastern orogenic front. Above the flat‐slab segment deformation migrates eastward, which is facilitated by enhanced interface coupling. The transition between the steep and sub‐horizontal subduction segments is characterized by a diffuse transpressional shear zone, likely controlled by the change in dip geometry of the Nazca plate, and the presence of inherited faults and weak sedimentary basins.

Convergence study of stabilized non-ordinary state-based peridynamics for elastic and fracture problems

Non-ordinary state-based peridynamics simulates crack propagation while avoiding the imposition of additional criteria to describe the responses at discontinuities. However, an incomplete coverage by the sphere of a horizon near the boundaries and crack surfaces could cause the boundary effect. In this study, the boundary effects occurring in the stress concentration region are investigated in δ- and m-convergence tests for elastic deformation and crack propagation. Three types of boundary imposition methods are investigated in m-convergence and the method showing the fastest convergence is applied to fracture problems. The weighted average stress estimation is proposed for the damage criterion to reduce the variation in the crack paths in the convergence test, and the weight function is defined as a parameter that can change the shape of the function into three different forms: linear, bilinear, and constant. The fracture simulation is performed in an L-shaped panel with varying geometrical parameters. As a result, the bilinear weighted average stress estimation reduces the variation in the crack path compared to the conventional arithmetic average estimation method. Therefore, the proposed weighted average stress estimation method increases the accuracy of the crack path prediction and will enlarge the application area for fracture simulation using peridynamics.

Dynamic responses of aluminum alloy plates coated with polyurea elastomer subjected to repeated blast loads: Experimental and numerical investigation

As one of the commonly used component units of engineering structures, aluminum alloy plates will likely suffer from multiple blast loads in terrorist bombing attacks and industrial explosion accidents. Given such structures, the research of technical measures to resist extreme blast disasters is an important topic. Polyurea, is a potential excellent strategy for improving the blast resistance of aluminum alloy plates, with a promising application prospect. This study experimentally investigated the dynamic response and damage characteristics of polyurea-coated aluminum alloy plates under repeated blast loads, and the microscopic characteristics of polyurea material and Vickers hardness properties of aluminum material after loading were analyzed. Based on the developed numerical model, the plastic deformation and energy propagation laws of composite plates were analyzed. Finally, a parametric study on the coating position of polyurea, blast scaled distance, and number of blasts was conducted. The damage regularity of the aluminum plate was obtained, and the damage assessment was performed. The results revealed that polyurea coated on the back or double sides of the aluminum plate could exhibit improved blast resistance. Under repeated blasts, compared with that of the Category A plate (uncoated polyurea), the Category B plate (coated with polyurea on the back side) exhibited improvements of 33.9% and 31.3% in the local and overall deformation resistances, respectively. The Category C plate (coated with polyurea on both sides) exhibited improvements of 19.3% and 22.5%, respectively. Polyurea significantly alleviated the damage of the aluminum plates after two explosive loads.

Propagation of crust deformation anomalies related to the Menyuan MS 6.9 earthquake

Decoding the variation laws of the deformation field before strong earthquakes has long been recognized as an essential issue in earthquake prediction research. In this paper, the temporal and spatial distribution characteristics of deformation anomalies in the northeastern margin of the Qinghai-Tibetan Plateau before and after the Menyuan MS 6.9 earthquake were studied by using the Fisher statistical test method. By analyzing the characteristics of these anomalies, we found that: 1) The deformation anomalies are mainly distributed in the marginal front area of the Qinghai-Tibetan Plateau, where short-term deformation anomalies are prone to occur due to a high gradient of gravity; 2) The deformation anomalies along the northeastern margin of the Qinghai-Tibetan Plateau are characterized by spatial propagation, and the migration rate is about 2.4 ​km/d. The propagation pattern is counterclockwise, consistent with the migration direction of MS ​≥ ​6.0 earthquakes; 3) The time and location of the Menyuan earthquake are related to the group migration of earthquakes with MS ​≥ ​6.0. Finally, based on the results of gravity field variation and the theory of crust stress wave, the law of deformation anomaly distribution was discussed. We suggest that both the deformation propagation along the northeastern margin of the Qinghai-Tibetan Plateau and the earthquake migration are possibly associated with the variation of the stress field caused by subsurface mass flow.

High strain-rate deformation analysis of open-cell aluminium foam

This study investigated the high-strain rate mechanical properties of open-cell aluminium foam M-pore®. While previous research has examined the response of this type of foam under quasi-static and transitional dynamic loading conditions, there is a lack of knowledge about its behaviour under higher strain rates (transitional and shock loading regimes). To address this gap in understanding, cylindrical open-cell foam specimens were tested using a modified Direct Impact Hopkinson Bar (DIHB) apparatus over a wide range of strain rates, up to 93 m/s. The results showed a strong dependency of the foam's behaviour on the loading rate, with increased plateau stress and changes in deformation front formation and propagation at higher strain rates. The internal structure of the specimens was examined using X-ray micro-computed tomography (mCT). The mCT images were used to build simplified 3D numerical models of analysed aluminium foam specimens that were used in computational simulations of their behaviour under all experimentally tested loading regimes using LS-DYNA software. The overall agreement between the experimental and computational results was good enough to validate the built numerical models capable of correctly simulating the mechanical response of analysed aluminium foam at different loading rates.

Probing plastic mechanisms in gradient dual-phase high-entropy alloys under nanoindentation

The plastic deformation mechanisms of gradient nanostructured high entropy alloys (HEAs) subjected to nanoindentation tests have been examined. First, we have constructed gradient glass/crystal (GGC) dual-phase HEAs by embedding crystalline CoCrFeNi HEA grains into CoCrFeNiAlx (x = 0.5, 1, and 2) metallic glass (MG) matrix in a gradient manner, leading to a gradient change in both the grain size and MG matrix shell thickness. Then, nanoindentation tests on the specimens under proper boundary and loading conditions are simulated by molecular dynamics software. It is found that the gradient-distributed MG shell effectively reduces the degree of strain localization within the region around the indenter, which results in a considerable hardening effect, thanks to the coexistence of both dislocation motion in the grain phase and plastic flow activated simultaneously in the MG phase. The results also show that the damage tolerance of GGC specimens is higher than that of the polycrystalline specimen because gradient-distributed MG phases can effectively prevent FCC to HCP transformation. Besides, the Al addition in the gradient-distributed MG shell can reduce its deformation propagation capability, weakening the hardening effect. The proposed method of constructing GGC can be promisingly helpful, for example, in the surface engineering of high-entropy alloys.

In-situ TEM investigation on deformation mechanisms of a fine-grained 316L stainless steel

The present study explores the deformation behavior of fine-grained 316L stainless steel through in-situ tensile transmission electron microscopy (TEM), with a focus on both intergranular and intragranular deformation. The results demonstrate that grain boundaries are a critical factor in accommodating plastic deformation and serve as the primary dislocation sources (DS) for dislocation emission into the grain interior. The propagation of plastic deformation within grains occurs through the successive activation of grain boundary DSs. In addition, the fine-grained sample exhibits active deformation twin and cross-slip of extended dislocations due to its proper apparent stacking fault energy (SFE) of 27 mJ/m2 and high internal stress, which significantly enhances its strain hardening ability. These findings shed light on the underlying mechanisms of plastic deformation in fine-grained 316L stainless steel and have important implications for the design of metallic materials with superior mechanical properties.

Synthetically non-Hermitian nonlinear wave-like behavior in a topological mechanical metamaterial

Topological mechanical metamaterials have enabled new ways to control stress and deformation propagation. Exemplified by Maxwell lattices, they have been studied extensively using a linearized formalism. Herein, we study a two-dimensional topological Maxwell lattice by exploring its large deformation quasi-static response using geometric numerical simulations and experiments. We observe spatial nonlinear wave-like phenomena such as harmonic generation, localized domain switching, amplification-enhanced frequency conversion, and solitary waves. We further map our linearized, homogenized system to a non-Hermitian, nonreciprocal, one-dimensional wave equation, revealing an equivalence between the deformation fields of two-dimensional topological Maxwell lattices and nonlinear dynamical phenomena in one-dimensional active systems. Our study opens a regime for topological mechanical metamaterials and expands their application potential in areas including adaptive and smart materials and mechanical logic, wherein concepts from nonlinear dynamics may be used to create intricate, tailored spatial deformation and stress fields greatly transcending conventional elasticity.