Deformation Mechanisms Research Articles

Failure Behavior and Mechanism of Vat Photopolymerization Additively Manufactured Al2O3 Ceramic Lattice Structures

Vat photopolymerization additive manufacturing produces lightweight load-bearing ceramic lattice structures that have flexibility, time-efficiency, and high precision, compared to conventional technology. However, understanding the compression behavior and failure mechanism of such structures under loading remains a challenge. In this study, considering the correlation between the strut angle and bearing capacity, body-centered tetragonal (BCT) lattice structures with varying angles are designed based on a body-centered cubic (BCC) structure. BCT Al2O3 ceramic lattice structures with varying angles are fabricated by vat photopolymerization. The mechanical properties, deformation process, and failure mechanism of the Al2O3 ceramic lattice structures are characterized through a combination of ex- and in-situ X-ray computed tomography (X-CT) compression testing and analyzed using a finite element method (FEM) at macro- and micro-levels. The results demonstrate that as the angle increases, the stress concentration gradually expands from the node to the strut, resulting in an increased load-bearing capacity. Additionally, the failure mode of the Al2O3 ceramic lattice structures is identified as diagonal slip shear failure. These findings provide a greater understanding of ceramic lattice structure failures and design optimization approaches.

Effect of bell annealing on the interface microstructure and mechanical properties of titanium/steel composite plates prepared by hot rolling

This study investigates the effect of bell annealing (600°C-750°C/3 h-15 h) on the interfacial microstructure and mechanical characteristics of hot-rolled titanium/steel (Ti/steel) bi-metallic plates, aiming to improve their mechanical performance and deformation compatibility. The interfacial bonding mechanism and growth process of the interfacial TiC layer were studied using multi-scale characterization. The microstructural evolution during annealing and the effect of the TiC layer on element interdiffusion were considered. Results show that the TiC interlayer inhibits Ti and Fe diffusion, preventing undesirable Ti-Fe phases, and the TiC layer thickens towards the Ti side. Higher annealing temperatures and longer times worsened the grain size difference between the Ti and steel layers and produced a thick TiC layer, severely degrading deformation compatibility. Microcracks, caused by severe lattice mismatch, are mostly initial at the α-Fe/TiC interface during plastic deformation. Thin to moderate TiC layers resulted in a combination of ductile and brittle fractures, while thick layers led to brittle fractures. In terms of mechanical properties, the ultimate tensile strength (UTS), yield strength (YS), shear strength, and elongation (EL) of the hot-rolled composite plate were measured at 337 MPa, 232 MPa, 238 MPa, and 29%, respectively. All annealed samples exhibited a reduction in UTS, YS, and shear strength compared to the hot-rolled state; however, they demonstrated improved elongation and deformation compatibility, with the elongation achieving its optimal value at 650°C-3 h. The annealing, at 650°C for 3 h, was identified as the optimal condition for post-rolling heat treatment, resulting in a composite plate with a comprehensive mechanical performance characterized by UTS, YS, shear strength, and EL values of 267 MPa, 127 MPa, 171 MPa, and 46%, respectively.

Microstructure evolution by thermomechanical processing and high-temperature mechanical properties of HCP-high entropy alloys (HEAs)

The solid solution strengthening and deformation mechanisms of the hcp-high entropy alloys (HEAs) have not been elucidated yet because of the complexity introduced by the martensite structure, particularly in alloys undergoing phase transformation from bcc to hcp structures. This study attempted to fabricate an equiaxed hcp microstructure for TiZrHf, TiZrHfAl, and TiZrHfAlSc using the hot rolling process and subsequent heat treatment. The equiaxed hcp phase was successfully formed in TiZrHfAl, but the martensite structure remained in TiZrHf and TiZrHfAlSc. The 0.2 % proof stress at 400 and 600°C increased with the increase of the average atomic size misfit δ and the mixing entropy . The low activation volume and high-stress exponent of TiZrHfAl with equiaxed hcp phase at room temperature suggest minor obstacles such as cluster or short-range order inhibit the movement of dislocation and leading to the significant solid-solution strengthening. However, the effect diminished at 600 °C.

Molecular dynamics study on the deformation mechanism of Cu–Zr/Al laminated composites

In this paper, molecular dynamics simulation was used to investigate the micromechanical behavior of the Cu–Zr/Al composite interface after rapid solidification. The effects of different Zr contents and different strain rates on the tensile strength of the Cu–Zr/Al composite interface were investigated. The results show that the tensile strength of the composite plate increased and then decreased with the increase of Zr content, and the tensile strength is the highest when the Zr content is 0.33 wt%. It was found that the plastic deformation process of the composite model at different strain rates is similar, which is divided into three stages: the expansion of stacking faults in the Cu–Zr/Al solid solution, the expansion of stacking faults successively in the Al and Cu–Zr alloy layers, and the spreading of cross - stacking faults. But the greater the strain rate is, the slower the stacking faults fracture is. So the composite model with different strain rates had different fracture modes during the tensile fracture process. When the strain rate is 0.01 ps−1 and 0.001 ps−1, it is a ductile fracture, while when the strain rate is 0.0001 ps−1, it is a brittle fracture.

A comparative study of hot tensile deformation behavior of 6016 aluminum alloy under LSTM neural network and Arrhenius model

Abstract The isothermal tensile test of 6016-T6 aluminum alloy was carried out on Gleeble-3500 at the temperature range of 400 °C–550 °C and the strain rate range of 0.01–10 s−1. The results show that the thermal deformation mechanism of 6016-T6 is dynamic recovery and dynamic recrystallization. In this paper, the phenomenological Arrhenius constitutive model and the data-driven WOA-LSTM constitutive model for predicting the hot tensile deformation behavior of 6016-T6 aluminum alloy were studied in contrast. The whale optimization algorithm was used to optimize the hyperparameters of LSTM neural network to improve the prediction accuracy of flow stress. The optimization results show that the optimal hidden layer node, maximum training period, initial learning rate and mini batch size of WOA-LSTM are 46, 260, 0.0248 and 16, respectively. In addition, the influence of the number of hidden layers on the results of the network was discussed. The appropriate hidden layer of the network was determined to be 2. The result show that the prediction accuracy of WOA-LSTM constitutive model is better than the Arrhenius constitutive model. The mean absolute error and correlation coefficient are 0.9348% and 0.99952, respectively. Among them, in this study, the Arrhenius constitutive model has low precision and only has high precision within a single temperature range.

Molecular dynamics study on the effect of crystal orientation on the plasticity and fracture behavior of α-Fe crack tip

Abstract In this paper, the molecular dynamics technique is utilized to simulate crack propagation within the localized vicinity of the crack tip, aiming to investigate the plastic deformation behavior of the α-Fe crack tip under different crystal orientations. The influences of crystal orientation on the mechanical properties of the models were obtained, and the weakest crystal orientation associated with fracture was determined. Meanwhile, the plastic deformation mechanism of the α-Fe model under different crystal orientations was obtained by analyzing the microscopic atomic evolution process of the four models.

An investigation of rapid surface melting in nanowires

The investigation into virtual melting phenomena in nanowires holds significant relevance owing to its profound impact on material durability under extreme loading conditions. Thus, the exploration of this pivotal plastic deformation mechanism is undertaken utilizing the phase-field methodology. Employing a monolithic solver, we solve the coupled highly nonlinear time-dependent Ginzburg–Landau equation and dynamic elasticity equation. Our analysis encompasses the consideration of surface tension stress in conjunction with a coherent solid–liquid interface subjected to uniaxial transformation strain, thereby unveiling intriguing facets of melting phenomena. The investigation delves into the influence of transformation strain, kinetic coefficient, and temperature on the thickness of the solid–liquid interface and its corresponding velocity. This analysis is conducted through meticulous comparison with existing experimental data and analytical solutions. Moreover, employing the phase-field method yields precise descriptions of the system kinetics, capturing virtual melting phenomena in both pristine and flawed nanowire configurations.

Effects of hot isostatic pressing on the micron-scale residual stress of nickel-based single-crystal superalloys

Quantifying the residual stress at micron-scale is crucial for comprehending the trans- and inter-granular deformation mechanisms and the influence of heat treatment, but remains technically challenging. This study utilized focused ion beam and digital image correlation (FIB-DIC) techniques to assess residual stress within the dendrite stem and arm of nickel-based single-crystal superalloys. The influence of hot isostatic pressing (HIP) on the microstructure and residual stress was also elucidated. Our results revealed that the residual stresses in the dendrite stem and arm regions manifest as tensile stress along the x-axis and compressive stress along the y-axis, with a range of -720 MPa to 680 MPa. HIP treatment effectively improved microstructure and regulated residual stress in nickel-based single-crystal superalloys, leading to a rapid reduction in residual stress levels. The present study lays a solid theoretical groundwork for optimizing processing strategies to regulate residual stress and enhance mechanical properties in next-generation single-crystal superalloys.

Research on the ultra-low temperature tensile deformation mechanism of Al-Mg-Si alloys in different heat treatment states

The susceptibility of Al-Mg-Si alloy to cracking during room temperature large plastic deformation poses a significant obstacle to its widespread application. Cryogenic temperature forming of aluminum alloys has emerged as a prominent research topic. However, the precise mechanisms underlying the enhancement of aluminum alloy plasticity in different states remain elusive. In order to elucidate this matter, a series of uniaxial tensile experiments were conducted on Al-Mg-Si alloy featuring diverse initial states, under varying temperature conditions. The results show that when the deformation temperature is reduced from 25℃ to -196℃, the tensile strength and elongation of the wrought material are increased by 48MPa and 5.42%, and the tensile strength and elongation of the annealed material are increased by 118MPa and 5.65%. In contrast, while the T4 state sample exhibited a significant improvement in tensile strength (103MPa), no substantial enhancement in elongation was observed. This disparity can be primarily attributed to the absence of second-phase precipitation in the as-forged and annealed states. As the temperature decreased, the critical shear stress increased, resulting in increased resistance to deformation. Consequently, an increased degree of lattice rotation and activation of dislocations in various slip systems ensued, thereby improving the deformation uniformity. The formation of initial microvoids predominantly occurred close to grain boundaries. Therefore, compared with room temperature deformation, low temperature deformation caused by the accumulation of dislocations and hole sprouting concentrated at a single location was less likely. As a result, the dislocation distribution was more uniform and fracture was less likely to occur. Conversely, in the T4 state, the aging process resulted in the precipitation of a substantial amount of the soluble second phase (Mg5Si6). Consequently, microvoid nucleation transpired at the phase boundaries, leading to an elevated tensile strength. However, because of the increased dislocation hindrance when the deformation temperature was lowered, no significant enhancement in plasticity was observed.

Pursuing ultrahigh strength–ductility CoCrNi-based medium-entropy alloy by low-temperature pre-aging

Developing high-performance alloys with gigapascal strength and excellent ductility is crucial for modern engineering applications. The concept of multi-component high/medium entropy alloys (H/MEAs) provides an innovative approach to designing such alloys. In this work, we developed the Co1.5CrNi1.5Al0.2Ti0.2 MEA, which exhibits outstanding mechanical properties at room temperature through low-temperature pre-aging followed by annealing treatment. Tensile testing reveals that the MEA possesses an ultrahigh yield strength of 20±0785 MPa, an ultimate tensile strength of 2365 ± 70 MPa, and exceptional ductility of 15.8% ±1.7%. The superior tensile properties are attributed to the formation of fully recrystallized heterogeneous structures (HGS) composed of ultrafine grain (UFG) and fine grain (FG) regions, along with discontinuous precipitation of coherent nano-size lamellar L12 precipitates. The mechanical incompatibility between the UFG region and the FG regions during deformation induces the accumulation of a large number of geometrically necessary dislocations at the interface, resulting in strain distribution and hetero-deformation-induced (HDI) stress accumulation, contributing significantly to HDI strengthening. HDI strengthening, precipitation strengthening, and grain boundary strengthening are the primary mechanisms responsible for the ultra-high yield strength of the MEA. During deformation, the dominant deformation mechanisms include dislocation slip, deformation-induced stacking faults, and Lomer–Cottrell locks, with minor deformation twinning. The synergistic interaction of these multiple deformation modes provides the MEA with excellent work hardening capability, delaying plastic instability and achieving an excellent combination of strength and ductility. This study provides an effective strategy for synergistically strengthening MEAs by combining HDI strengthening with traditional strengthening mechanisms. These findings pave the way for the development of advanced structural materials with high performance tailored for demanding applications in engineering.

Study on the tensile behaviour and nano deformation mechanism of Nickel-based single crystal superalloys with γ/γ' structure at atomic scale

To study the deformation mechanism of nickel-based single crystal superalloys (NBSC) during tensile process, tensile experiments on NBSC are carried out by molecular dynamics to systematically analyze stress-strain, shear strain, atomic migration and defect evolution. The effects of the structure of the two phases and the strengthening elements on the tensile behavior are analyzed by comparing the pure Ni phase, the pure Ni3Al phase and the Ni phase containing the strengthening elements Cr and Co from a microscopic view. The results show that the interaction between the two-phase structural dislocations during tensile process balances the stress concentration and reduces the degree of plastic deformation that occurs within the matrix. The γ/γ' interface separates the strain morphology and inhibits the slip of the shear band between the two phases, resulting in enhanced deformation resistance of the matrix. By comparing the three single-phase structures, the γ/γ' structure has the highest yield point. From the shear strain distribution pattern, the portion of the two-phase structure with a larger degree of shear strain mainly occurs at the interface as well as at the edge of the matrix.

Investigation on the energy absorption characteristics of novel graded auxetic re-entrant honeycombs

In this work, innovative graded auxetic re-entrant honeycombs constructed by adjusting the geometric parameters of a core unit cell are proposed, and their deformation modes and energy absorption characteristics with different impact speeds are systematically investigated. The novel graded design utilizes structural hierarchy on the meso-scale and functional gradient on the macro-scale. The numerical simulation models are verified by comparing the experimental results. The results show that compared with the ungraded honeycomb (URH), one of the graded honeycombs (GRHs), named GRH1, can greatly improve the specific energy absorption by 36.4%, 10.8%, and 6.00% for the quasi-static, low, and high-speed impact at a strain of 0.6. At the same time, the initial peak stress of GRH1 is decreased by 43.2% and 27.1% compared with that of URH for low and high-speed impact, respectively. It could be indicated that the GRH1 was an ideal energy-absorbing structure. This work provides a new route for designing graded auxetic honeycombs with enough insight to understand the deformation mechanism of the structures, which could be used in lightweight buffer protective systems.

On the influence of heat-induced evaporation over interfacial atomization driven by surface acoustic waves

In this work, the influence of evaporative flux over the atomization driven by surface acoustic waves (SAWs) of a Newtonian water drop is studied. The drop is placed on a heated substrate at constant temperature, higher than the saturation temperature at a given vapor pressure. In this manner, an interfacial temperature distribution arises along the drop free surface in terms evaporative mass flux and vapor recoil, which repercussion over aerosol size is studied by determining the asymptotic evolution equation governing the acoustically driven free surface. At such scenario, the connection between surface tension and temperature is also considered; thus, thermocapillary flow is incorporated into our drop model, described in terms of fundamental parameters, like the evaporation number, Marangoni number, and acoustic capillary number. Numerical solution of the evolution equation led us to obtain a simplified representation of the drop interfacial deformation mechanism, capable of predicting atomization and portraying the influence of evaporation over atomization. Subsequent analysis shows that the incorporation of evaporation at SAW atomization traduces in normal stresses counteracting the acoustic and thermocapillary effect, leading to the development of smaller drop aspect ratios with respect to the no-evaporative case. Being aware that the aerosol size is deeply related to the aspect ratio, we propose an analytical expression to estimate aerosol diameter under evaporative conditions. The results show that aspect ratio reduction leads to a decrement on aerosol size, up to two orders of magnitude, with respect to the no-evaporative case. Our study is a first approach providing insight about the importance of evaporation on aerosol regulation at SAW atomization.

Structural Analysis for Qazzaz Metamorphic Core Complex, Northwestern Arabian Shield, Saudi Arabia

AbstractIdentifying deformational mechanisms and associated structures at various scales, ranging from regional‐scale structures to microscopic fabric, is crucial for the assessment of tectonic development. Thirty‐three samples were taken from the Qazzaz metamorphic core complex to estimate the finite strain for felsic and mafic minerals. These samples included gneisses rocks, monzogranite, and metavolcano–sedimentary rocks for both the Thalbah and Bayda groups. Using the Rf/j and Fry methods, the axial ratios (XZ) range about 2.20 to 7.10 and 1.90 to 9.10, respectively. For various rock units, the strain measurements show moderate to highly deformation. Most of the observed samples show shallow WNW dipping along a N to WNW trend of finite strain (X). The short axes (Z) based to be subvertical foliation related with a subhorizontal foliation. The results demonstrate that contacts generated at semi‐brittle to ductile deformation and that the strain of magnitude has the same value for different lithologic units. It concluded that nappe generation in orogens results from pure shear deformation.

Directionally solidified NiCoCrFeAlW eutectic high-entropy alloy: Microstructure and mechanical properties

The NiCoCrFeAlW eutectic high-entropy alloy exhibits a balanced combination of ductility and strength. This study examines the microstructure evolution and mechanical properties of the Ni30Co30Cr10Fe10Al18W2 alloy at varying growth velocities (10, 20, 50, 100, and 200 μm/s), which in its as-cast state, features a microstructure that includes both coarse dendrites and lamellar eutectic. The structure of the coarse dendrites is characterized by an ordered body-centered cubic (B2) phase, while the lamellar eutectic, features a combination of face-centered cubic (FCC) and ordered B2 phases. The microstructure, characterized by lamellar and dendritic structures that are parallel to the growth direction after directional solidification, undergoes a morphological transition at the solid-liquid interface from a planar to a dendritic form as growth velocity increases. The tensile fracture strength initially increases with the growth velocity, reaching a peak of 1286 MPa at a velocity of 50 μm/s, and then subsequently decreases as the growth velocity continues to increase. Directional solidification results in an increase in sample elongation with increasing growth velocity, achieving an elongation of 22.5% at 200 μm/s. An examination of the deformation mechanism reveals that the lamellar structure, composed of the more ductile FCC phase and the harder B2 phase, effectively harmonizes the plasticity and strength of the alloy. Therefore, directional solidification significantly adjusts the eutectic microstructure's orientation, thereby enhancing the mechanical properties along the direction of solidification.

Evolution of microstructure and properties of nanocrystalline NiCo alloy under high-energy laser shock

In this study, nanocrystalline NiCo alloy was prepared through electrodeposition and subjected to high-energy laser shock (HELS) treatment to investigate the influence of laser shock on the microstructures and properties. An analysis of phase composition, microstructural evolution, texture evolution, and hardness was conducted. The results indicated that under HELS, there was no change in phase composition, while there was a slight reduction in grain size, as well as in the quantities of Low-angle grain boundaries (LAGBs) and twin boundaries (TBs). The texture evolution revealed that HELS led to a more uniform overall texture due to grain boundary (GB) mediate deformation mechanisms, along with the generation of a significant amount of 9R phases, causing a shift in texture orientation from (110) to (100). The internal structure of nanocrystalline NiCo showed an accumulation of numerous dislocations post-laser shock, with randomly oriented dislocations interacting to form Lomer-Cottrell Locks (L-C Locks) and 9R phases. Additionally, interactions with large stacking faults (SFs) also resulted in their dissociation into multiple 9R phases. The hardness enhancement was mainly attributed to the accumulation of dislocations within the grain and the generation of a significant quantity of 9R phases.

Visualized analysis of microscale rock mechanism research: A bibliometric data mining approach

Rock mechanics is an indispensable discipline in diverse sectors, from resource retrieval to disaster mitigation. Diving deeper into this field, particularly into microscale rock mechanics, offers strategic insights and potential advancements for rock engineering practice. The objective of this research is to map the scientific production tied to microscale rock mechanics to date. In doing so, we perform a bibliometric analysis to look over and discuss the performance of the related literature. The conceptual fabric of microscale rock mechanics research, constituted by four central themes, was revealed and visualized through a text mining analysis. These areas include (1) modeling and simulation of fluid flow and transport within porous media, (2) characterizing fracture and failure in rocks, (3) understanding the deformation mechanism in response to geological processes, and (4) studying the mechanical properties of rocks subjected to extreme conditions. Lastly, an upcoming research agenda for microscale rock mechanics was proposed, centered on addressing three identified research gaps: (I) the integration of geological processes to characterize mineral properties, (II) the augmentation of fracture predictions achieved through multiscale modeling of rock heterogeneity, and (III) the exploitation of Artificial Intelligence technologies for anticipating complex fracturing scenarios. This comprehensive approach promises to enrich our understanding of rock mechanics and its applications.

Microstructure and compressive behaviour of PLA/PHA-wood lattice structures processed using additive manufacturing

This study investigates the microstructure and compressive behaviour of PLA/PHA-wood lattice structures manufactured using fused filament fabrication (FFF). The primary objective is to evaluate the effects of defects, such as porosity and surface roughness, on the mechanical properties of these lattice structures. X-ray micro-tomography (XRT) and finite element analysis are employed to compare CAD models with real lattice structures, offering insights into defect-induced performance deviations. The novel approach integrates experimental and numerical methods to better understand damage accumulation in porous structures. The methodology includes uniaxial compression testing and image processing for microstructural characterization. Results reveal significant differences in relative density and stress concentration due to manufacturing defects. In particular, 3D printed lattice structures display typical cellular material behaviour with a primary bending deformation mechanism. X-ray tomography reveals that process-induced porosity generate stress heterogeneity, which is not captured from CAD-based model resulting in an overestimation of the stiffness. The study concludes that accounting for these defects can be quantified by shifting the target relative density to compensate lack of performance in 3D-printed lattice materials.

Dynamic Strength and Fragmentation of Highly Oriented Ti3SiC2 under Multiaxial Compression

MAX phases are distinguished by their unique kink band formation, a distinct deformation mechanism in layered materials. This study explores the influence of global grain orientation c-axis, strain rate, and stress state on the compressive response of highly oriented Ti3SiC2 through experimental methods. A Kolsky (or split-Hopkinson) bar is employed to evaluate the dynamic compressive response under uniaxial and biaxial (planar confinement) conditions under 102s-1 strain rate. Macroscopic ultra-high-speed visualization during loading and microscopic post-mortem fractography reveal that confinement states significantly impact both macroscopic failure patterns and microscopic fracture mechanisms. Notably, biaxial loading with dynamic load edge-on to the grains and 80MPa planar confinement along the layers resulted in the highest dynamic compressive strength observed (1636±136MPa), a 66% increase compared to the unconfined uniaxial dynamic condition. The planar confinement appears to delay crack propagation and enhance inelastic deformation.

Microstructural evolution and deformation mechanisms of superplastic aluminium alloys: A review

Microstructural evolution and deformation mechanisms of superplastic aluminium alloys: A review