Dynamic Mechanical Deformation Research Articles

Constructing Long and Stable Ag‐Al2O3 Core–Shell Nanowires for Humidity Sensing and Triboelectric Energy Generation

Silver nanowires (AgNWs) are a promising alternative material to indium tin oxide as flexible transparent electrodes owing to their excellent optoelectrical properties and mechanical performance. However, the main challenge is the poor stability under diverse environments, ranging from high humidity, chemical exposure, and dynamic mechanical deformation. Herein, ultralong AgNWs (≈100 μm) have been synthesized via controlling growth kinetics by a facile acetic acid‐assisted solvothermal method, further decorated with a thin Al2O3 layer by electrodeposition to form a core–shell architecture. The resultant films based on Ag‐Al2O3 core–shell nanowires (NWs) possess a higher conductivity while preserving the optical transparency due to the enhanced NWs contact. More importantly, the constructed films exhibit strong resistance to various conditions, such as exposure to high temperature/humidity and immersion in NaCl, HCl, and Na2S solutions. The laser‐etched interdigital electrodes based on the chemically stable AgNWs are further integrated with graphene oxide layer for humidity sensing and respiration monitoring. Furthermore, the developed NWs with superior mechanical stability are constructed as triboelectric nanogenerators for electricity generation, and reliable output performance has been demonstrated. This work provides a convenient, scalable, and cost‐effective solution that offers great potential for designing robust, transparent electrodes for next‐generation flexible electronics.

Microstructure and dynamic deformation mechanism of laser powder bed fusion of 316L-containing Ti–6Al–4V with dual-phase heterostructure

In this paper, 316L-containing Ti–6Al–4V alloy was fabricated by laser powder bed fusion (LPBF) through mixing Ti–6Al–4V and 4.5 wt% 316L powders, and the dynamic compressive mechanical properties and deformation mechanism at different strain rates were studied. The results show that the volume fraction of β phase sharply increases from 1.8% (in TC4) to 61.4% (in HST), and micro- and submicron-sized grains coexist in the HST alloy, producing heterostructure in the form of bimodal grain size distribution. The presence of the heterostructure led to superior heterogeneous deformation induced stress, thus facilitating the additional strain hardening and deformation coordinating ability, thus made the HST alloy achieved ultimate compressive stress of ∼1750 MPa and fracture strain of ∼17%, showing excellent comprehensive mechanical properties. Under quasi-static load, the deformation mode of HST alloy is mainly attributed to progressive deformation-induced martensitic transformation. However, at high strain rates, the impact loading inhibited the activation of progressive DIMT, and thus the deformation mode changed to combination of dislocation slipping and deformation twinning.

Deformation mechanism of dislocation slip and kinking behaviour in dynamic compression response of TiZrHfNb alloy fabricated by laser directed energy deposition

ABSTRACT In this study, the dynamic response and deformation mechanism of TiZrHfNb RHEA fabricated by laser directed energy deposition (L-DED) were researched under a dynamic compression test at a nominal strain rate of 3500 s−1. The L-DED TiZrHfNb alloy with columnar grains exhibits exceptional mechanical properties with a uniform dynamic flow stress of 1670 ± 10 MPa and a maximum plastic strain of 0.28 ± 0.03. The dislocation slipping and kinking behaviour dominate uniform plastic deformation. First, the dislocations are primarily confined within dislocation channels due to coplanar slip, and the evolution of them in dynamic compressive deformation process has undergone spacing refinement and crossing. Furthermore, the kinking behaviour induced by the lattice rotation with the T = <011> axis denotes the work hardening effect. Particularly, the second kinking behaviour effectively relieves local stress concentration and delays fracture before the formation of adiabatic shear band (ASB).

Study on the room temperature compression deformation mechanism and microstructural evolution of Mg-Gd-Y-Zr alloy

This study explores the dynamic impact deformation mechanisms of Mg-Gd-Y-Zr alloys, specifically focusing on the influence of varying Gd content. Using metallographic observation, SEM, EDS, XRD, EBSD, and TEM, along with hardness and room-temperature compression tests, the research investigates the effects of Gd content on the microstructure, mechanical properties, and deformation behaviors of as-cast Mg-(x)Gd-3Y-0.5Zr (x = 6.5/7.5/8.5) alloys.The results show that increasing Gd content reduces grain size and increases the volume fraction of the non-equilibrium eutectic phase Mg24(Gd,Y)5, though with smaller phase dimensions. These alloys exhibit excellent compressive properties at room temperature, with the highest compression deformation rate of 27.8 % observed at 6.5 % Gd and the maximum compressive strength of 401 MPa recorded at 8.5 % Gd, surpassing some high-Gd-content cast and extruded alloys.At lower Gd content, basal slip and tensile twinning are the primary deformation mechanisms. As Gd content increases, these mechanisms evolve to include prismatic slip and compressive twinning. The fracture mode transitions from predominantly ductile to a combination of ductile and brittle features, with an increase in brittle cleavage at higher Gd levels.

Laser powder bed fusion of Fex(CoCrMnNi)100-x medium-entropy ferrous alloys: Processability, microstructure and dynamic deformation mechanism

In this work, Fex(CoCrMnNi)100-x (x = 40, 60 and 80 at.%) medium-entropy ferrous alloys (MEFAs) were fabricated through laser powder bed fusion (LPBF) of mixed powders composed of FeCoCrNiMn and Fe powders, and the dynamic compressive properties and deformation mechanisms were studied with combination of experiment and molecular dynamics simulation. The results demonstrate that all MEFAs exhibit good processability.The Fe40 and Fe60 samples were predominantly composed of FCC phase with coarse grains, while the Fe80 mainly consisted of BCC phase with a smaller grain size. When subjected to quasi-static and dynamic compression at 3000/s, the yield strengths of Fe40, Fe60 and Fe80 increases by 131, 220 and 256 MPa, respectively, illustrating the positive strain rate sensitivity and influence of Fe on the mechanical properties of MEFAs. Further, both the single-crystal and the polycrystalline models suggested that the incompatibility between the BCC and FCC phases is responsible for the enhancement of strength. Therefore, it is more likely to produce deformation twins, dislocations and thus stress concentration around the BCC phase, which is consistent with the TEM observations.

Integrating dynamic relaxation with inelastic deformation in metallic glasses: Theoretical insights and experimental validation

Metallic glasses (MGs), a metastable material far from equilibrium, exhibit intricate dynamic relaxation behaviors. The challenge lies in developing a model that accurately describes the dynamics and deformation mechanisms of MG. This paper introduces a model integrating dynamic relaxation with deformation behavior. Validation through dynamic mechanical analysis, stress relaxation, creep, and strain recovery tests confirm the existence of four deformation modes: elasticity, anelasticity from β relaxation, anelasticity from α relaxation at low temperatures, and viscoplasticity from α relaxation at high temperatures. The model captures all of these deformation modes. The dynamical mechanical spectrum and stress relaxation spectrum unveil dynamic features during glass to liquid transition, and a simple and effective experimental method was developed for identifying ultra-low-frequency dynamic relaxation. This work provides new perspectives on the study of relaxation dynamics in glassy states and establishes important connections between dynamic relaxation behavior and deformation mechanisms. These findings lay a theoretical and experimental foundation for the broad application of MGs.

In vivo imaging and computational modeling of nonlinear shear waves in living skeletal muscles

How the state of living muscles modulates the features of nonlinear elastic waves generated by external dynamic loads remains unclear because of the challenge of directly observing and modeling nonlinear elastic waves in skeletal muscles in vivo, considering their active deformation behavior. Here, this important issue is addressed by combining experiments performed with an ultrafast ultrasound imaging system to track nonlinear shear waves (shear shock waves) in muscles in vivo and finite element analysis relying on a physically motivated constitutive model to study the effect of muscle activation level. Skeletal muscle was loaded with a deep muscle stimulator to generate shear shock waves (SSWs). The particle velocities, second and third harmonics, and group velocities of the SSWs in living muscles under both passive and active states were measured in vivo. Our experimental results reveal, for the first time, that muscle states have a pronounced effect on wave features; a low level of activation may facilitate the occurrence of both the second and third harmonics, whereas a high level of activation may inhibit the third harmonic. Finite element analysis was further carried out to quantitatively explore the effect of active muscle deformation behavior on the generation and propagation of SSWs. The simulation results at different muscle activation levels confirmed the experimental findings. The ability to reveal the effects of muscle state on the features of SSWs may be helpful in elucidating the unique dynamic deformation mechanism of living skeletal muscles, quantitatively characterizing diverse shock wave-based therapy instruments, and guiding the design of muscle-mimicking soft materials.

Dynamic mechanical properties and constitutive model of oil-immersed and thermally-treated red sandstone

To thoroughly investigate the stability of reservoir rock mass in heavy oil thermal recovery projects, this study explored the dynamic mechanical properties and deformation behaviors of thermally-treated red sandstone from the oil-immersed reservoir, taking the dry and water-saturated reservoirs as the comparison. The results show that the dynamic compression strength and energy transmission rate of oil-immersed and thermally-treated red sandstone are enhanced. With the help of scanning electron microscopy (SEM) tests, we observed the grain-coating on the surface of the mineral particles of oil-immersed rock. The grain-coating enhances the rock matrix integrity and leads to the mechanical strengthening effect of oil-immersed rock. The fractal dimension of oil-immersed samples is smaller than that of dry and water-saturated samples. In addition, the theoretical values of the damage constitutive model are consistent with the experimental data, which verifies the validity of the damage model. Our new findings support that the oil weakens the deformation resistance ability of the micro-crack part but strengthens that of the rock matrix.

Experimental study on dynamic deformation and breaking mechanism of high-temperature hard rock cutting by abrasive water jet

The development of deep geothermal resources encounters challenges related to high temperatures and hard reservoir rocks. Abrasive water jets (AWJ) offer a potential solution to enhance the efficiency of breaking high-temperature hard rocks in deep ground. This mainly originated from their combined characteristics of jet cooling impact and high-speed abrasive grinding. In order to investigate the dynamic deformation process and rock-breaking mechanism of high-temperature hard rocks cut by AWJ, laboratory tests were conducted on high-pressure abrasive water jets cutting granite, sandstone, and marble. Rock strains were monitored using dynamic strain gauges and the digital image correlation (DIC) technique. The results indicate that in the process of abrasive jet cutting high-temperature hard rock, the rock strain is divided into three stages: compression deformation, deformation release, and stable deformation. The strain response zone can be divided into strain concentration zone, strain transition zone, and strain weak response zone. The high strain region and heat exchange region of high-temperature hard rock during AWJ cutting process are almost consistent. Jet vaporization weakens the water cushion effect during the water hammer stage, leading to high strain concentration at the stagnation point of the jet. During the stagnation stage, the fluid weakens the binding of particles, the abrasive becomes more divergent, and the range of high strain response region expands. Unlike the dynamic strain generated by jet erosion of hard rock, when jet cutting rocks, the strain in the vertical jet direction is generally greater than that along the jet direction. The cutting effect increases with the increase of rock temperature. When the rock temperature is 300 °C, the cutting depth of sandstone, granite, and marble increases by 50 %, 120 %, and 180 %, respectively. Under the combined effects of high-frequency jet impact, high-speed abrasive grinding, and thermal stress, hard rock undergoes varying degrees of damage and failure.

Preliminary study on the dynamic deformation mechanism of CoCrFeNi high-entropy alloy and its application in the shaped charge liner

High-entropy alloys (HEAs) with a face-centered cubic structure offer numerous advantages, including high plasticity, good processability, and high-temperature resistance. They are also suitable for use as materials in shaped-charge liners, which can cause significant damage. In this study, CoCrFeNi HEAs were prepared, and their mechanical characteristics were examined. The results indicated that the alloy exhibited good plasticity and processability. After dynamic compression, the samples were analyzed using electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). It was found that dislocation was the primary deformation mechanism at low strain rates. However, as the strain rate increased, the deformation mechanism shifted from dislocations to a combination of dislocations and twinning. The damage performance of the CoCrFeNi HEA was verified through a static penetration experiment using a conical charge. The results were then compared with simulation results obtained using the AUTODYN software. This study demonstrated that the CoCrFeNi HEA could form a condensed, stable-shaped charge jet, leading to efficient damage after penetrating the steel target plate. Therefore, after uniform treatment, the CoCrFeNi HEA can be utilized as a high-energy structural material to design shaped charge structures that achieve highly efficient damage.

Phenomenological Model for the Dynamic Superplastic Deformation Mechanism in a Zn-Al Eutectoid Alloy Modified with 2 wt% Cu

Phenomenological Model for the Dynamic Superplastic Deformation Mechanism in a Zn-Al Eutectoid Alloy Modified with 2 wt% Cu

Shock compression of single-crystal stainless steel

We studied the orientation-dependent dynamic properties and plastic deformation mechanisms in single-crystal austenitic FeCr18Ni12.5 stainless steel shocked to peak stresses ranging 3.8-12.0 GPa. The 〈110〉 and 〈111〉 principal Hugoniots generally match that of polycrystalline 304L stainless steel, but the 〈100〉 Hugoniot exhibits lower shock velocities and comprises two distinct regions. The Hugoniot elastic limits (HELs) and spallation strengths range 0.5-1.2 GPa and 2.2-3.8 GPa, respectively, and exhibit trends previously observed in polycrystalline steels. We generally observed the largest HELs along 〈100〉 and the largest spallation strengths along 〈111〉. Microscopy revealed larger twin and martensite fractions in the 〈100〉 samples, correlations in twinning and martensite prevalence with dynamic response, and orientation-dependent differences in dislocation behavior near the spallation plane.

Orientation-dependent deformation mechanisms of alpha-uranium single crystals under shock compression

Large-scale non-equilibrium molecular dynamics (NEMD) simulations were employed to investigate the dynamic deformations of alpha-uranium (α-U) single crystals subjected to varying shock strengths along low-index crystallographic orientations. The pronounced anisotropy of α-U gives rise to a complex microstructural evolution under shock loading. In-depth microstructural analysis of post-shock specimens reveals the identification of multiple dynamic deformation mechanisms. Notably, when the shock loading direction aligns with the a-axis, dynamic deformation of the α-U single crystals is primarily dominated by lattice instability, which attributes to a crystalline-to-amorphous transition serving as the dominant shear stress relaxation pathway. On the other hand, shock loading along the b-axis results in an abundance of deformation twins, with twinning planes identified as (130) and (13¯0). During the twinning event, the α-U matrix undergoes a transition to a metastable intermediate phase, subsequently decomposing into a composite structure comprising α-U twins and matrix. This unconventional twinning mechanism significantly deviates from classical theories. Furthermore, upon loading along the c-axis, twinning and a phase transition from α-U to body-centered tetragonal phase (bct-U) occur in α-U single crystal samples. Given that the pressure threshold of this phase transition predicted by ab initio calculations is as high as ∼270 GPa, the phase transition from α-U to bct-U might be implausible. An alternative interatomic potential of uranium with the higher pressure threshold was employed to reinvestigate the shock response of α-U single crystals along the c-axis. The phase transition of α-U to bct-U disappears, and twinning dominates the plastic deformation, with the twinning orientation conforming to the {112} twinning. The strong anisotropy of the α-U lattice triggers a wealth of orientation-dependent dynamic deformation mechanisms. The activation of the twinning system is evidently associated with the loading direction, constituting the potential cause for the discovery of multiple twinning variants during the deformation in polycrystalline uranium.

Dynamic deformation mechanism for distinct flow behaviors in FGH4113A superalloy with high γ′ content during isothermal compression at sub-/near-/super-solvus temperatures

This study examines the flow behavior and deformation mechanism of a FGH4113A superalloy with high γ′ content for different strain rates (0.01–1 s−1) at sub-solvus (1030, 1080 °C), near-solvus (1130 °C), and sup-solvus temperatures (1180 °C). The results indicated that the alloy exhibits four different flow behaviors: rapid softening after reaching peak stress (at 1030–1080 °C), slow softening after reaching peak stress (at 1130–1180 °C/0.1–1 s−1), steady state flow (at 1130 °C/0.01 s−1), and continuous hardening (at 1180 °C/0.01 s−1). The strain rate sensitivity exponent decreases as the flow behavior transforms from dynamic softening to continuous hardening. Moreover, the dynamic recrystallization (DRX) fraction decreases with increasing strain rate at sub-solvus temperatures, where an inverse trend was observed at near- or sup-solvus temperatures. These observations are influenced by the interplay of continuous original grain boundary migration (COBM), DRX, and grain growth. Meanwhile, the primary γ′ phase has different roles under distinct deformation conditions. At sub-solvus temperature, the primary γ′ phase facilitates DRX, grain refinement, and coordinated plastic deformation. At near-solve temperature, the primary γ′ phase predominantly contributes to coordinated plastic deformation. At the sup-solvus temperature, the γ′ phase entirely dissolves, with the grains coarsened by COBM continuously undergoing compressed, exhibiting continuous hardening.

Dynamic mechanical response and deformation mechanism of poly (ε-caprolactone) (PCL) / epoxy resin(EP) shape memory polymer composites

The dynamic mechanical response and deformation mechanism of poly (ε-caprolactone) (PCL) and epoxy resins shape memory polymer (SMP) composites were investigated in this paper. The SMP composites were a blend of PCL and epoxy resins by using the facile melt-mixing method. The distribution of PCL in the composites was observed by SEM, which was in from microparticle morphology to continuous morphology with the increasing PCL content. And the dynamic mechanical analyzer (DMA) tests were performed to demonstrate the viscoelastic properties and shape memory effect of the PCL/EP composites. Based on the above characterization of PCL/EP composites, the split Hopkinson pressure bar (SHPB) tests were performed to study the dynamic mechanical properties at the strain rates of 4000/s to 7000/s. The results showed that the flow stress increased with the increasing strain rate, which exhibited an obvious sensitivity to strain rate. However, the flow stress of PCL/EP decreases with the increasing PCL content due to the low strength of PCL. And PCL/EP composites failed in a typical ductile failure mode under quasi-static loading, whereas an excellent plastic deformation ability was observed at high strain rates, which was attributed to the heat generated by the plastic work during the adiabatic compression. Combining with the experimental results, the corresponding deformation mechanism was also discussed.

A structural-thermal coupled modeling approach on the formation of adiabatic shear bands in steel sheet blanking process

Adiabatic shear banding reflects an unstable and dynamic plastic deformation mechanism occurring at high strain and strain rates which is strongly conjugated to fracture. Current work carries out a numerical study on the initiation and development of adiabatic shear bands (ASBs) in blanking process of AISI 4340 steel sheet. A structural-thermal coupled finite element analysis is developed in LS-DYNA software by implementing a thermo-viscoplastic flow rule for material plasticity and a damage criterion considering dynamic failure. The numerical simulations are focused on capturing ASB genesis through intense shear localization by evincing strain instability. Also, the evolution of ASB mechanism is investigated, aiming to contribute a stage-by-stage propagation and highlight its connection to dynamic failure. Further, the effect of ASB temperature and strain field on fracture is analysed, while the influence of strain/strain rate hardening and thermal softening on strain instability, peak force and the blanked surface is studied. The results revealed an S-shaped ASB due to severe shear localization and significant temperature increase, leading to dynamic recrystallization around punch-die corners and reacting to strain instability and dynamic. Finally, high magnitude thermal softening during ASB development resulted in earlier ASB generation and reduction of the peak blanking force, while further it decreased shear zone expansion and increased fractured length in the blanked surface.

Dynamic Constitutive Model and Deformation Mechanism of 2219 Aluminum Alloy Based on the Dynamic Interruption Recovery

Dynamic compression and interruption‐recovery experiments are carried out to investigate the dynamic adiabatic and isothermal deformation behavior of the 2219 aluminum alloy at various strain rates (0.001–5000 s−1). The results of the experiments show that adiabatic temperature increase and strain rates have an impact on the compression behavior of 2219 aluminum alloy. The yield strength is strongly associated with strain rates, demonstrating an evident strain rate hardening effect. The increase in adiabatic temperature is the key factor contributing to the decline in adiabatic strain hardening rate. According to microstructural analysis, the adiabatic shear band is first detected with strain rate of 3200 s−1 along the loading direction. At a strain of 30.3%, cracks begin to appear, and shearing fractures occur with a strain rate of 5000 s−1 in the direction of 45°. Finally, the Johnson–Cook constitutive model is modified with the strain rate reinforcement terms corrected and an adiabatic softening term added to reflect the isothermal and adiabatic compression behaviors. The improved model is better at describing the strain rates affect the behavior of isothermal and adiabatic deformation.

Study on dynamic characteristics and non-constant fractional dynamic creep model for frozen silty clay

The long-term dynamic characteristics of frozen soil are important theoretical basis for the dynamic stability evaluation of geoengineering in cold regions. Compared to unfrozen soil, the dynamic creep behaviour is more complicated owing to its rheological property. In this study, triaxial tests under cyclic loads with different constant stress amplitudes and confining pressures for frozen silty clay (FSC) are carried out. The long-term dynamic creep process and deformation mechanism under different dynamic stress amplitudes were investigated. The test results show that with the cyclic numbers increasing, the dynamic elastic modulus and the hysteretic loop area decrease because of the damage accumulation in the samples. Also the dynamic strength decreases with an increase in failure cyclic numbers under different confining pressures. Based on the fractional calculus theory, replacing the Newton's dashpot in the traditional Maxwell model with fractional Abel's dashpot, a fractional dynamic creep model is established. Considering the melting and crushing of the ice inclusion, the slip effect in frozen soil is increasingly significant, the viscosity coefficient of dashpot element is decreasing with an increase in loading time. In the proposed model, a non-constant dashpot element is introduced to clarify the constitutive relation of the FSC in the accelerated creep stage. The comparison results confirm that the proposed constitutive model is valid and suitable for reflecting the long-term dynamic creep behaviours of the FSC.

Dynamic mechanical properties and microstructural evolutions of nanocrystalline Ni at 77 K and 298 K

Dynamic mechanical responses and microstructural evolutions of nanocrystalline Ni with an average grain size of 14 nm at both 77 K and 298 K were investigated by using Split-Hopkinson pressure bar in this work. Nanocrystalline Ni deformed at 77 K exhibited better dynamic compression strength and plasticity. Microstructural characterizations suggested that the deformation processes of Ni were jointly regulated by dislocation activities (such as full dislocations, stacking faults, twinning, and phase transitions) and grain boundary-dominant mechanisms (grain rotation) in the uniformly deformed regions, while dynamic recrystallization was the main feature in shear bands. The cryogenic temperature was conducive to suppressing grain coarsening and obtaining better dynamic mechanical properties. The work is beneficial to understanding dynamic deformation mechanisms and the service of nanocrystalline materials in extreme conditions, in addition to the development of high-performance nanocrystalline metallic materials.

Dynamic deformation behaviors and mechanisms of CoCrFeNi high-entropy alloys

Due to their unique microstructures and chemical compositions, high-entropy alloys (HEAs) exhibit remarkable mechanical properties, such as high strength, excellent ductility and good thermal stability. However, to date, there have been limited studies on the dynamic behaviors of HEAs. Here, we systemically investigated the mechanical behaviors and deformation mechanisms of CoCrFeNi HEAs and their connections under dynamic loading by combining mechanical tests and molecular dynamics simulations. Compressive testing on polycrystalline CoCrFeNi HEA samples at different strain rates showed that both yield and flow stresses increase with strain rate and exhibit a significant strain rate sensitivity due to solid solution strengthening and lattice distortion of the HEA. The strain rate sensitivity of the CoCrFeNi HEA transitions from 0.010 at low strain rates (5.0×10−5–2.5×103 s−1) to 0.333 at high strain rates (2.5×103–6.5×103 s−1). Large-scale molecular dynamics simulations further revealed that this transition is related to the plastic deformation mechanism transition from dislocation nucleation and slip at low strain rates to massive dislocation nucleation and drag at high strain rates. Furthermore, the CoCrFeNi HEA exhibited a remarkable strain-hardening capability at high strain rates, which originated from the formation of primary and secondary nanoscale twins and twin-twin and twin-dislocation interactions. Our current study sheds light on the plastic deformation mechanisms of HEAs under dynamic loading, providing guidance for the design and fabrication of HEAs with excellent dynamic mechanical properties.