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Active metamaterials are a type of metamaterial with tunable properties enabled by structural reconfigurations. Existing active metamaterials often achieve only a limited number of structural reconfigurations upon the application of an external load across the entire structure. Here, a selective actuation strategy is proposed for inhomogeneous deformations of magneto‐mechanical metamaterials, which allows for the integration of multiple elastic wave‐tuning functionalities into a single metamaterial design. Central to this actuation strategy is that a magnetic field is applied to specific unit cells instead of the entire metamaterial, and the unit cell can transform between two geometrically distinct shapes, which exhibit very different mechanical responses to elastic wave excitations. The numerical simulations and experiments demonstrate that the tunable response of the unit cell, coupled with inhomogeneous deformation achieved through selective actuation, unlocks multifunctional capabilities of magneto‐mechanical metamaterials such as tunable elastic wave transmittance, elastic waveguide, and vibration isolation. The proposed selective actuation strategy offers a simple but effective way to control the tunable properties and thus enhances the programmability of magneto‐mechanical metamaterials, which also expands the application space of magneto‐mechanical metamaterials in elastic wave manipulation. [ABSTRACT FROM AUTHOR]

Icing is ubiquitous in nature and engineering applications, and imposes threats to road and air transportations, wind energy infrastructures, etc. However, current active de‐icing solutions, especially the most popular one, i.e., heating, suffer from high energy consumption whilst passive methods are often ineffective at high‐speed, long‐term, or large‐particle conditions. Herein, a promising strategy adopting magnetic‐responsive microfins (MRS) featuring reversible deformations is developed for de‐icing. A novel micro‐scale ice shoveling effect induced by the localized destruction of the ice adhesion interface owing to the inhomogeneous deformation is demonstrated, and its dependence on the ice particle size and temperature is investigated. An analytical model is proposed to describe the mechanism of this effect, showing a linear relation between the position of the magnet and the induced force agreeing well with experiments, leading to a system straightforward to predict and control. Specifically, the de‐icing capacity of the surface becomes prominent when small‐scale ice particles merge to large ones, providing a promising solution for applications on aircraft, wind turbines, etc., as the first of its kind to remove large particles under high‐speed conditions effectively. [ABSTRACT FROM AUTHOR]

Abstract The feasibility of microwave heating-assisted rock breakage technology in geotechnical engineering has been widely explored. However, the limited knowledge of the impact of the contrast properties between different bedding planes and outer formation stresses limits its application at the field scale. In this work, the mechanics of mineral processing, rock breakage, and unconventional gas and oil exploitation were first characterized. A coupled model is subsequently proposed to govern the coupling process of microwave heating and induce inhomogeneous deformation and stress in various bedding planes. Three stress forms are considered in this approach: horizontal stress, normal stress, and shear stress. With the assistance of the finite element method, the stress conditions of bedding planes composed of rock under free swelling, constant stress, and constant volume were addressed. A bedding plane characterized by high microwave adsorption ability is usually compressed by a bedding plane characterized by low microwave adsorption ability. The bedding ore is under the condition of free swelling during mineral processing, whereas in the remaining two scenarios, the bedding rock is stress controlled. The tensile and compressive stresses can reach their maximum values under the condition of free swelling. The outer formation stress reduces the values of tensile and compressive stresses but has little impact on the shearing stresses. Additionally, this work provides criteria for defining an a priori evaluation of the effectiveness of microwave treatment of bedded ore and rock for different geotechnical engineering applications.

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Fractures are commonly found throughout rock masses. The propagation and coalescence of these fractures can significantly weaken the surrounding rock strength during underground excavations. In order to investigate the cracking behavior of pre-existing fractures affected by excavation unloading, this study proposed an innovative laboratory excavation test to simulate excavation unloading in deep rock masses. Corresponding numerical stepped excavation tests were also conducted using RFPA (Realistic Failure Process Analysis). The excavation area in specimen was pre-filled with polylactic acid (PLA), and stepped excavation under constant normal stress was performed using an electric cutter. The results reveal that the stress-strain curves of the specimens during stepped excavation can be categorized into four stages based on deformation behavior and the crack process. There are four different patterns of crack coalescence, ultimately leading to specimen failure. Numerical results indicate that the inhomogeneous deformation caused by stepped excavation is responsible for crack initiation, propagation, and eventual specimen failure. The rock bridges between fissures and excavation areas break in three modes: shear sliding, segregation due to tensile cracks, and the formation of ubiquitous fractures. Furthermore, the inclination of the fissure and the initial normal load applied to the specimens have a significant impact on the crack coalescence modes and initiation. These findings can contribute to a better understanding of crack evolution behaviors, including initiation, propagation, coalescence, and transfixion, during excavation unloading in underground engineering projects. [ABSTRACT FROM AUTHOR]

Rock masses have complex block-hierarchical structures involving various scale levels, which should be considered in dynamic and static conditions. Because the interlayer has weak mechanical properties, the deformation of rock masses is primarily concentrated at the interlayers, which provides the possibility of translation and rotation for rock blocks. In situ experimental data have shown that the blocky rock masses undergo significant angular deformation under a dynamic impact, and the rotation of blocks can significantly affect the wave propagation and dynamic behavior of rock masses. Consequently, to investigate the rotation of blocks, a two-dimensional dynamic model of blocky rock masses was established based on the accurate consideration of the rotation effect. This research revealed the mechanism of the rotation of blocks and determined the characteristics of energy transfer and the influence of block rotation on the inhomogeneous deformation of interlayers. The findings showed that the rotation of blocks is caused by the nonequilibrium shear between the interfaces in the absence of external torques, resulting in inhomogeneous deformation of interlayers. The blocky rock masses can produce additional tension and compression deformation caused by the rotation of blocks at local positions in addition to the deformation caused by the translation. The energy transfer and influence of the rotation of blocks under an external torque are inconsistent with those under a horizontal impact load. This study theoretically solves the problems of wave propagation in block media under arbitrary loads and torques and is helpful for the research of seismic wave propagation in block media with inhomogeneous complex structures. [ABSTRACT FROM AUTHOR]

In this paper, the inhomogeneous deformation in the radial direction of the cold radial forged 30SiMn2MoVA steel tube was studied by finite element method, analyzing the microstructure and mechanical tests. The simulated result shows that the inhomogeneous deformation mainly distributed from the inner layer to the middle layer. In this region, the equivalent plastic strain rapidly decreases. The change from the middle to the outer is not significant. The distribution of microstructure and the results of mechanical properties also follow this pattern. The inner layer has the most refined grain size and the highest dislocation density. The strongest {110}<110> texture component has also been formed in the inner layer. The strength value of the inner layer is the highest, and the elongation is the lowest. There is not much difference in these indicators between the middle and outer regions. By calculating the strengthening contributions of solid solutions, dislocation density, and grain boundaries to yield strength, it was found that dislocation density is the main contributor. The calculated yield strength value is consistent with the experimental value. • The inhomogeneous deformation in the radial direction of the cold radial forged 30SiMn2MoVA steel tube was observed. • The inner layer has the highest degree of grain refinement, strength and forms the strongest {110}<110> texture component. • The contribution of dislocation density to the strengthening of yield strength is the most significant. [ABSTRACT FROM AUTHOR]

Gradient nano-grained (GNG) metals have shown high synergetic strength and good ductility due to their unique gradient microstructure. In this study, the mechanical behavior of gradient nano-grained metals was investigated by three-dimensional discrete dislocation dynamics. The simulation results show a trend that the successive yielding and gradual "transmission" of dislocations along the gradient direction result in a gradient distribution of stress and plastic strain. The distribution of geometrically necessary dislocations is more inhomogeneous in the gradient nano-grained (GNG) sample compared with those homogenous counterparts. The non-uniform deformation response of component layers induces the synergetic-deformation-induced (SDI) strengthening in the GNG sample. The back stress originates from geometrically necessary dislocations that pile up near the interface of gradient layers and leads to a significant hardening while there is a slight softening in different gradient layers in the GNG sample. This study provides a deeper insight into the SDI strengthening in gradient structure from the submicron scale. [ABSTRACT FROM AUTHOR]

As a typical and complex failure type of rock slopes, flexural toppling failure has increasingly received attention, mainly focused on its failure mechanism and introducing a proper numerical method to reproduce the failure phenomena. However, there are few studies related to the supporting mechanism against flexural toppling failure. This study attempted to make a preliminary analysis on the research gap. For this purpose, an anti-dip layered rock slope supported with anchor cables that failed owning to flexural toppling was taken as an example, and the numerical method discontinuous deformation analysis (DDA) was taken as the major analytical tool. Firstly, the rationality of DDA was verified by correctly simulating the failure state of the anti-layered rock slope and the underlying failure mechanism was studied. The results indicated that the lack of the support from slope toe is the crucial factor inducing the flexural toppling failure, which posed a great obstacle to the further excavation of the open-pit mine. Secondly, by introducing the anchor cable support to the slope toe in the DDA model, the interaction mechanism between the anchor cables and the rock slope was investigated. the results indicated that the supporting system of the ordinary anchor cables is very sensitive to the inhomogeneous flexural toppling deformation. The tension values of the anchor cables are very inhomogeneous, and once some of anchor cables beyond their tension limit, the anchor cables failed, which will greatly threaten the safety of the adjacent anchor cables and even the stability of the whole slope. Meanwhile, a novel anchor cable called constant-resistance-large-deformation (CRLD) anchor cable was introduced for a comparative study using DDA. just replacing the anchor cables of the original slope with the CRLD anchor cables, the slope can reach stable state eventually even without the slope toe being enhanced. In addition, the CRLD anchor cables were able to support the slope well against the inhomogeneous deformation, because they can provide high constant resistances and withstand large deformations. This study can provide a deeper insight into the support mechanism for the snit-layered rock slope against flexural toppling failure and introduce a novel supporting method for such slopes. [ABSTRACT FROM AUTHOR]

In a roadway affected by the superposition of in situ stress and mining-induced stress, inhomogeneous deformation and even roof accidents may occur. The stability control of rock surrounding a mining roadway is the key to realizing safe and efficient mining. A track roadway of the No. 152106 working face in Changling No. 1 Coal Mine was severely deformed under the influence of mining. In view of this, deformation characteristics of rock surrounding a plastic zone in the mining roadway were investigated by field monitoring, theoretical analysis, and numerical simulation. The results demonstrate that deformation of rock surrounding the roadway is inhomogeneous under the influence of mining. The deformation of rock surrounding the roadway in rear of the working face is greater than that in front of the working face and deformation of a coal pillar in the roadway is larger than that of solid coal. Furthermore, bed separation occurs on the roof and the floor heave near the coal pillar is greater. The maximum principal stress, ratio of the maximum principal stress to the minimum principal stress (hereinafter referred to as principal stress ratio), and range of the plastic zone in front of the working face are smaller than those to rear of the working face, and the displacement and range of the plastic zone in rock surrounding the roadway are consistent in terms of trend. Affected by secondary mining, the plastic zone changes from an elliptical to a butterfly shape. On this basis, reinforcement support schemes for the mining roadway were proposed, namely adding anchor cables to the roof, applying thru-anchor cables to coal pillars, and setting single hydraulic props in a roadway affected by primary mining. The field test results show that deformation of rock surrounding the track roadway decreases significantly. [ABSTRACT FROM AUTHOR]

This work addresses the long-standing debate over fractal models of packing structure in metallic glasses (MGs). Through detailed fractal and percolation analyses of MG structures, derived from simulations spanning a range of compositions and quenching rates, we conclude that there is no fractal atomic-level structure associated with the packing of all atoms or solute-centered clusters. The results are in contradiction with conclusions derived from previous studies based on analyses of shifts in radial distribution function and structure factor peaks associated with volume changes induced by pressure and compositional variations. The interpretation of such shifts is shown to be challenged by the heterogeneous nature of MG structure and deformation at the atomic scale. Moreover, our analysis in the present work illustrates clearly the percolation theory applied to MGs, for example, the percolation threshold and characteristics of percolation clusters formed by subsets of atoms, which can have important consequences for structure-property relationships in these amorphous materials.

In this study, we present a distinctive phenomenon of strain localization observed in pre-strained AZ31 alloy during tensile deformation. The strain localization behavior involves the repetitive formation, propagation, and subsequent annihilation of localized deformation bands within the gage section of the specimen. Although this strain localization behavior bears resemblance to the Portevin–Le Chatelier (PLC) effect commonly observed in steels and Al-Mg alloys, it is driven by a fundamentally different mechanism. Through detailed microstructural analysis, we reveal that this unique strain localization is closely associated with the process of de-twinning. Our findings contribute to a deeper understanding of the deformation behavior in magnesium alloys and offer new insights for the strain localization in metals. [Display omitted] [ABSTRACT FROM AUTHOR]

Laser powder bed fusion (L-PBF) is an additive manufacturing technology widely applied to the manufacture of metallic parts. The L-PBF processed aluminum-silicon (Al–Si) cast-type alloy components exhibit an anisotropic tensile ductility. In this study, we investigated the influence of heat treatments on the microstructural features of an Al–12%Si binary alloy fabricated via L-PBF and the associated inhomogeneous deformation of its melt-pool structure, which contributes to the resulting anisotropic tensile ductility. The mechanical inhomogeneity of the melt-pool structure and the change induced by annealing at various temperatures (300 and 530 °C) were characterized using microscale digital-image correlation analyses of scanning electron microscopy images obtained in situ during tensile deformation and nanoindentation hardness mapping. In the specimen fabricated via L-PBF, the high strain was concentrated at the locally coarsened microstructure (the soft region) along the boundaries of the melt pools rather than at the refined solidification microstructure (the hard region) within the melt pools. The localized strain varied depending on the geometrical relation between the orientation of the melt-pool boundary and the tensile direction, thus contributing to the anisotropic tensile ductility. This tendency appeared less pronounced in the specimen annealed at 300 °C, which exhibited a slightly homogenized melt-pool structure. The reduced strain localization is associated with a reduced difference in local strength between the melt-pool boundary (soft region) and the melt-pool interior (hard region). The slight homogenization of the melt-pool structure emphasized the effect of grain morphologies in the α-Al matrix on the inhomogeneous deformation within melt pools. In the specimen annealed at 530 °C, which exhibited a homogenized α-Al/Si two-phase microstructure, the uniformly distributed Si phase would be responsible for the homogenous deformation, resulting in an isotropic tensile ductility. This study advances our understanding of the correlation between the melt-pool structure and the deformation behavior of Al–Si alloys processed using L-PBF, which provides new insights for controlling the ductility by post-processing. [Display omitted] • Microstructures of L-PBF Al–12Si alloy after annealing at 300/500 °C were studied. • Nanoindentation revealed that melt-pool boundary was locally softer than interior. • Micro-DIC analysis captured inhomogeneous deformation on the melt-pool structure. • Strain localization behavior at melt-pool boundary depended on tensile direction. • Strain distribution in melt-pool interior can be affected by α-Al grain structure. [ABSTRACT FROM AUTHOR]

Herein, the effects of Si content on the microstructure evolution of Al-Mg-Si alloys during twin-roll casting (TRC) and subsequent heat treatment were characterized using scanning electron microscopy, emission electron probe micro analysis, electron backscatter diffraction, and transmission electron microscopy. The effects of insoluble Si particles, solute gradient, and recrystallization on the mechanical properties of the alloy in the T4P state were analyzed. An inhomogeneous deformation in the thickness direction of the TRC strip was observed during the pre-strain test. A premature local deformation at the element barren region (EBR) in the middle of the strip was considered to be the origin of the limited mechanical properties. By increasing the Si from 0.7 wt% to 1.1 wt%, the content and uniformity of the solute in the EBR can be effectively improved. The stronger work-hardening ability weakens the inhomogeneous deformation. Si addition significantly increased the number of insoluble Si particles during the heat treatment. The structure with a hard shell and soft core in the TRC strip significantly reduced the negative effect of insoluble Si particles on the mechanical properties. The tensile strength and uniform elongation of the strip increased from 159.44 MPa and 18.36% to 209.96 MPa and 29.791%, respectively. [ABSTRACT FROM AUTHOR]

Gradient nano-grained (GNG) metals have shown high synergetic strength and good ductility due to their unique gradient microstructure. In this study, the mechanical behavior of gradient nano-grained metals was investigated by three-dimensional discrete dislocation dynamics. The simulation results show a trend that the successive yielding and gradual “transmission” of dislocations along the gradient direction result in a gradient distribution of stress and plastic strain. The distribution of geometrically necessary dislocations is more inhomogeneous in the gradient nano-grained (GNG) sample compared with those homogenous counterparts. The non-uniform deformation response of component layers induces the synergetic-deformation-induced (SDI) strengthening in the GNG sample. The back stress originates from geometrically necessary dislocations that pile up near the interface of gradient layers and leads to a significant hardening while there is a slight softening in different gradient layers in the GNG sample. This study provides a deeper insight into the SDI strengthening in gradient structure from the submicron scale.

Pseudoelastic NiTi structural components have been shown to exhibit tension/compression asymmetry. Under tension, phase transformation induces localized strains of nearly 7% that spread under nearly constant stress, while under compression the transformation leads to hardening at significantly higher stress, the strain is smaller and grows homogeneously. Bending of tubes ovalizes their cross-section, a nonlinearity that reduces the bending rigidity and precipitates instabilities that can lead to collapse. This paper uses experiment and analysis to examine the interaction of these geometric nonlinearities with the complex material behavior of pseudoelastic NiTi tubes of moderate diameter-to-thickness ratios under bending. An experiment on a tube with a diameter-to-thickness ratio of 18.7 shows that transformation causes the nucleation of several dispersed high strain banded patterns of martensite on the tensioned side. The zone where the bands coalesce into intersecting diamonds undergoes excessive local ovalization causing buckling and collapse at a relatively low overall tube curvature. The bending experiment is simulated with a finite element model coupled with a custom constitutive model of pseudoelastic NiTi that allows for plastic deformation of the martensitic phase. The analysis reproduces the moment-end rotation response, and the nucleation and evolution of the high strain diamond shaped patterns. Zones that develop such patterns exhibit accelerated growth of ovalization that degrades the local bending rigidity. In the presence of small geometric imperfections this degradation evolves into a buckle in the form of diffuse local ovalization that precipitates collapse that can negate the recoverable property of NiTi. Parametric studies show that as the tube D/t increases, the interaction between the material and geometric nonlinearities becomes stronger making buckling more imperfection sensitive. [ABSTRACT FROM AUTHOR]

Herein, the effects of Si content on the microstructure evolution of Al-Mg-Si alloys during twin-roll casting (TRC) and subsequent heat treatment were characterized using scanning electron microscopy, emission electron probe micro analysis, electron backscatter diffraction, and transmission electron microscopy. The effects of insoluble Si particles, solute gradient, and recrystallization on the mechanical properties of the alloy in the T4P state were analyzed. An inhomogeneous deformation in the thickness direction of the TRC strip was observed during the pre-strain test. A premature local deformation at the element barren region (EBR) in the middle of the strip was considered to be the origin of the limited mechanical properties. By increasing the Si from 0.7 wt% to 1.1 wt%, the content and uniformity of the solute in the EBR can be effectively improved. The stronger work-hardening ability weakens the inhomogeneous deformation. Si addition significantly increased the number of insoluble Si particles during the heat treatment. The structure with a hard shell and soft core in the TRC strip significantly reduced the negative effect of insoluble Si particles on the mechanical properties. The tensile strength and uniform elongation of the strip increased from 159.44 MPa and 18.36% to 209.96 MPa and 29.791%, respectively.

Based on the three-dimensional digital image correlation (3D-DIC) technique, the stereovision system has been applied to the improved triaxial apparatus to obtain 3D full-field deformation of the specimen during triaxial testing. Through the calibration process, the 3D-DIC technique can obtain the accurate specimen's spatial displacement deformation. Meanwhile, a subpixel edge detection algorithm has been combined with 3D-DIC technique to calculate the radial strain and the volume strain of the specimen directly. Furthermore, a series of consolidated drained and undrained triaxial tests were carried out on Hainan (China) sand specimens and measured by the conventional and the image measurement methods. Compared to the results measured by the conventional method, the image measurement technique can obtain the more experimental data, such as the 3D displacement field of the whole specimen, the local strain distribution, and so on. The measurement results also show the conventional method would be disturbed by the end constraints in triaxial tests so that the strength of the soil would be overestimated. Meanwhile, the middle of the specimen would be selected to calculate the stress–strain relationship without the influence of the end constraints in the proposed method. Based on the image measurement results, the proposed method has the potential to be used in geotechnical tests for exploring the soil's progressive failure behaviors, inhomogeneous deformation and mechanical characteristics. [ABSTRACT FROM AUTHOR]

The initial blank employed to form aluminum alloy thin-walled special head was cut in metal strip, which has the unavoidable fluctuation of blank thickness, i.e., blank flatness (BF) because of the rolling technology. The BF increases the uncertainty of forming process and causes difference in the forming quality. In this paper, to research the influence of BF on forming quality, different BF types are defined as edge-down, edge-up, edge-w, and ideal blank flatness, and the different BF values are ± 0.5 mm and ± 1.0 mm got by experimental measurement. And three-dimensional finite element (FE) spinning models considering BF were established. Different BF types are achieved by assigning discrete ordinates to nodes using Latin hypercube sampling. Models are verified by theoretical methods. Further, influence of BF on spinning force (F), degree of inhomogeneous deformation (φ), and thickness of head (T) is investigated. The results show that the BF has different influence on F in the earlier, middle, and later stage of spinning. φ of BF of edge-down is largest; φ caused by BF = ± 0.5 mm is less than that caused by BF = ± 1.0 mm. BF type and value of the metal blank have no significant influence on T. In conclusion, the BF of the circular blank required by the spinning head should be typed in edge-w, and the value should be less than ± 1.0 mm. The research offers an in-depth understanding of the effects of BF on the forming quality in the head spinning process and thus lays a basis for choosing the initial blank. [ABSTRACT FROM AUTHOR]

• Crushing of closed-cell foam under combined axial compression and external pressure. • Stress response rises to a maximum and drops to an extended stress plateau. • Deformation localizes in a band of crushed cells that propagates with stress unchanged. • Maximum stress and plateau stress decrease as pressure increases. • Custom testing facility that allows visualization of the evolution of deformation. The crushing behavior of a polymeric closed-cell foam with a relative density of 0.077 under combined axial compression and external pressure is investigated experimentally. The foam has a nearly monodisperse polyhedral microstructure with mean cell size and wall thickness of 0.50 mm and 0.0348 mm respectively. A custom triaxial apparatus is used to compress cylindrical specimens at different levels of external pressure. A typical axial stress-displacement response exhibits a stiff elastic branch that terminates into a maximum beyond which deformation localizes into a horizontal axisymmetric band of crushed cells. The band then propagates axially with the stress remaining essentially constant. Both the initial stress maximum and the plateau stress decrease linearly as the pressure increases. Micro-computed tomography imaging of the microstructure of a specimen crushed axially at zero pressure confirmed that during the stress plateau, a highly crushed zone of cells with an average strain of about 50 % coexists with zones of essentially undeformed cells. Above a critical pressure, the mode of instability switches to predominantly lateral contraction that evolves into a neck. This is also the mechanism of failure under pure pressure. The localized crushing behavior observed is similar to that of low-density open-cell foams and the results should inform and guide further development of homogenized models for this class of materials. [ABSTRACT FROM AUTHOR]

In some temperature regimes NiTi can be deformed to strain of 5–7% that recovers fully on unloading. Under tensile loading it traces a closed hysteresis with two stress plateaus associated with the reversible solid-state phase transformation between the austenitic (A) and the martensitic (M) phases, during which the deformation localizes and propagates through the specimen. Hallai and Kyriakides (2013) extracted the underlying softening response associated with A-M transformation from a tensile test on a NiTi strip laminated between two hardening steel face-strips that ensured that it deformed uniformly. The test finishes with the laminate permanently deformed to a strain of 6%. Extraction of the softening response of the M-A transformation requires compressing the thin laminate back to zero strain. The present paper presents a new experimental set-up that enables completion of the load/reverse load test on such a laminate by laterally supporting the specimen during compression to prevent buckling. The extracted response of NiTi exhibits softening branches with up-down-up trajectories for both the A-M and M-A transformations, and Maxwell stresses that match those of the stress plateaus of the tensile hysteresis of a NiTi strip. The extracted response is used to calibrate a custom SMA constitutive model, which when incorporated in a finite element analysis reproduces the measured hysteresis of NiTi nearly perfectly for the first time. Extraction of the complete underlying partially unstable response of SMAs enables modeling of the unstable behavior of SMA structures with the confidence provided by measured data. • SMA phase transformation causes propagation of localized deformation. • Phase transformation is modeled as partial softening in the constitutive model. • Experimental method for extracting the underlying up-down-up transformation response. • Calibration of constitutive model to the extracted up-down-up responses. [ABSTRACT FROM AUTHOR]

In this paper, exact solutions with a linear velocity field are sought for the gas dynamics equations in the case of the special state equation and the state equation of a monatomic gas. These state equations extend the transformation group admitted by the system to 12 and 14 parameters, respectively. Invariant submodels of rank one are constructed from two three-dimensional subalgebras of the corresponding Lie algebras, and exact solutions with a linear velocity field with inhomogeneous deformation are obtained. On the one hand of the special state equation, the submodel describes an isochoric vortex motion of particles, isobaric along each world line and restricted by a moving plane. The motions of particles occur along parabolas and along rays in parallel planes. The spherical volume of particles turns into an ellipsoid at finite moments of time, and as time tends to infinity, the particles end up on an infinite strip of finite width. On the other hand of the state equation of a monatomic gas, the submodel describes vortex compaction to the origin and the subsequent expansion of gas particles in half-spaces. The motion of any allocated volume of gas retains a spherical shape. It is shown that for any positive moment of time, it is possible to choose the radius of a spherical volume such that the characteristic conoid beginning from its center never reaches particles outside this volume. As a result of the generalization of the solutions with a linear velocity field, exact solutions of a wider class are obtained without conditions of invariance of density and pressure with respect to the selected three-dimensional subalgebras.

Abstract In the present work, the characteristics of α texture transformed from the strong <100> β fiber texture and their effect on the tensile deformation behavior of Ti–6Al–4V alloy fabricated using electron beam rapid manufacturing (EBRM) have been investigated. The results show a concentrated distribution of transformed α texture along the transverse direction (TD) while a relatively random distribution along the longitudinal direction (LD). This different orientation distribution of α phase leads to anisotropy in tensile strength. Moreover, inhomogeneous deformation is found in the longitudinal sample, which is not observed in the transverse sample. This can also be attributed to the relatively discrete α orientation distribution in the LD. The relationship between the deformation ability of each columnar prior β grain and its corresponding crystallographic orientation was investigated. Both the calculated and experimental results indicate that a relatively low deformation resistance is found when the angle of the [001] β direction of a columnar grain to the LD is relatively small and a higher deformation resistance is found when the angle is about 45°. During the loading process in the LD, deformation may concentrate in some "weak" columnar grains with relatively low deformation resistance, resulting in decreased integral ductility compared to the transverse sample. [ABSTRACT FROM AUTHOR]

The problem of the influence of deformation properties of elastic elements on specific electric resistance of isotropic electrically conductive materials is considered. It is shown that when in isotropic elastic elements inhomogeneity of elastic deformation is taken into account the electric current density is changed, which in its turn leads to anisotropy of electrical conductivity of material. The anisotropic properties of electrical conductivity σi along material anisotropy principal axes are characterized by both of deformation influence and new physical constants αi. [ABSTRACT FROM AUTHOR]

Room-temperature rolling experiments were performed on Pd 40 Ni 40 P 20 bulk metallic glass at two different strain rates. It is found that at each strain rate the shear band density increases with increasing strain for the deformed samples. However, for samples endured the same deformation strain, more amounts of shear bands (i.e., a higher shear band density) was introduced into the sample deformed at the higher strain rate. In addition, the higher strain rate also leads to the generation of more amount of free volume for samples endured a same deformation strain. The hardness change behavior investigation result suggests that the introduction of multiple intersected shear bands leads to hardening of Pd 40 Ni 40 P 20 bulk metallic glass. [ABSTRACT FROM AUTHOR]

Taking a typical multi-cavity part, AISI-5140 tee valve, as object, the complicated inhomogeneous deformation law and related forming defect generation in multi-direction loading process were explored under four representative loading paths. It is found that four deformation modes, i.e., forward extrusion, forward-lateral combined extrusion, backward-lateral combined extrusion and backward extrusion, occur in different orders and times according to loading path. The cavum and folding defects are caused by metal's rapid flow to the vertical cavity in severe lateral extrusion when horizontal punch loads and subsequent loading of vertical punch. Vertical punch loading before the end of horizontal punch is beneficial to weakening backward-lateral combined extrusion and avoiding cavum and folding defects, but the vertical punch should not finish loading before the horizontal when load and offset load considered. By synthetically considering the deformation uniformity, metal flow, avoiding folding defect, forming load and offset load, the reasonable loading path is proposed. [ABSTRACT FROM AUTHOR]

A physical model method allows the estimation of the strain inhomogeneity in a material subjected to equal channel angular pressing. Copper samples which deformed with ECAP with a standard die-set showed significant inhomogeneity. The sample section was split into two sections, which have significantly different values of accumulated strain and, as a consequence in the microstructure. Application of a die-set with a special geometry modification allows uniform strain across the sample. A comparative analysis of physical modeling results, changes of microstructure and properties showed complete correlation. Known theoretical models of the ECAP process with deformation modes close to simple shear are analyzed.

The inhomogeneous deformation which appears in hot rough rolling of aluminum alloy plate, reduces rolling output and negatively affects the rolling process. To study the formation mechanism of the inhomogeneous deformation, a finite element model for the five-pass hot rough rolling process of aluminum alloy plate is built. Results show that inhomogeneous deformation distribution in thickness direction causes two bulges at head and tail ends, as indicated by the analysis of the equivalent plastic strain distribution and deformation. However, formation mechanism of the inhomogeneous deformation at head end differs from that at tail end. Changing the end shape and angular rolling are adopted for decreasing the length and width of the crocodile mouth. It can be found that the crocodile mouth can be improved effectively by increasing the central bump length and the rotation angles through simulation and experiments. Then, the combination effect of two methods is simulated and results show that the combination effect is better than respectively using of each method. In addition, combination of two methods can avoid the restricted conditions for respectively using of each method. [ABSTRACT FROM AUTHOR]

A polycrystalline Voronoi aggregation with a free surface is applied as the representative volume element (RVE) of the nickel-based GH4169 superalloy. Considering the plastic deformation mechanism at the grain level and the Bauschinger effect, a crystal plasticity model reflecting the nonlinear kinematic hardening of crystal slipping system is applied. The microscopic inhomogeneous deformation during cyclic loading is calculated through numerical simulation of crystal plasticity. The deformation inhomogeneity on the free surface of the RVE under cyclic loading is described respectively by using the following parameters: standard deviation of the longitudinal strain in macro tensile direction, statistical average of first principal strains, and standard deviation of longitudinal displacement. The relationship between the fatigue cycle number and the evolution of inhomogeneous deformation of the material's free surface is investigated. This research finds that: (1) The inhomogeneous deformation of the material free surface is significantly higher than that of the RVE inside; (2) the increases of the characterization parameters of inhomogeneous deformation on the free surface with cycles reflect the local maximum deformation of the RVE growing during cyclic loading; (3) these parameters can be used as criteria to assess and predict the low-cycle fatigue life rationally. [ABSTRACT FROM AUTHOR]

In this study, reflective coherent gradient sensing (CGS) method is introduced to measure large deformations of Ni–Cr alloy in instrumented indentation. The effects of grating distance, collimation property of incident beam, camera lens focal length, screen and specimen location are analyzed. The presence or absence of screen and the camera lens focal length are found out to be the most important factors when measuring large deformations with CGS method. Moreover, we develop a method to obtain the ‘true’ interferograms by Fourier and inverse Fourier transformation algorithms. The measuring scale of reflective CGS method for large deformation is obtained. A criterion is developed to distinguish the boundaries between small and large deformations in measuring inhomogeneous deformations with reflective CGS method. [ABSTRACT FROM AUTHOR]

Tension induced phase transformation in pseudoelastic NiTi leads to inhomogeneous deformation with the austenitic and martensitic phases coexisting. Deformation of nearly 7% is recovered on unloading during which the deformation is again inhomogeneous. By contrast, under compression the transformation stress is significantly higher, the strain is lower and is essentially homogeneous. In pure bending experiments on pseudoelastic NiTi tubes, this asymmetry manifests as coexistence of two curvature regimes with diamond-shaped patterns of martensite developing on the tensioned side. Two curvatures exist also on unloading accompanied by progressive erasure of the diamond patterns. A recently developed constitutive model for the pseudoelastic behavior of NiTi is implemented in a finite element analysis used to simulate the tube bending experiments. The model captures the tension/compression asymmetry by incorporating both the tensile and compressive responses of the material, and includes softening over the extents of the unstable branches of the tensile response. The analysis reproduces the major features of the experimental results and provides insight into how the nonlinearities of the NiTi material interact with geometric nonlinearities to produce: the hysteretic moment-end rotation response with an upper and a lower plateau, the values of the two curvature regimes during loading and unloading, and the progressive initiation of higher strain diamond patterns on the tensioned side and the nearly homogeneous deformation on the compressive side. The sensitivity of the solution to the mesh and the softening moduli is discussed. [ABSTRACT FROM AUTHOR]

This work addresses the long-standing debate over fractal models of packing structure in metallic glasses (MGs). Through detailed fractal and percolation analyses of MG structures, derived from simulations spanning a range of compositions and quenching rates, we conclude that there is no fractal atomic-level structure associated with the packing of all atoms or solute-centered clusters. The results are in contradiction with conclusions derived from previous studies based on analyses of shifts in radial distribution function and structure factor peaks associated with volume changes induced by pressure and compositional variations. The interpretation of such shifts is shown to be challenged by the heterogeneous nature of MG structure and deformation at the atomic scale.Moreover, our analysis in the present work illustrates clearly the percolation theory applied to MGs, for example, the percolation threshold and characteristics of percolation clusters formed by subsets of atoms, which can have important consequences for structure-property relationships in these amorphous materials. [ABSTRACT FROM AUTHOR]

Tension induced solid-state transformation in a nearly equiatomic NiTi results in inhomogeneous deformation with transformed and untransformed material coexisting. Strains of the order of 7% are recovered on unloading with the material reverting to its original phase. In a thin strip the two coexisting phases and deformation regimes are separated by inclined fronts monitored with digital image correlation. The fronts propagate along the strip until the transformation is completed with the stress remaining nearly unchanged. A recently developed constitutive model for the pseudoelastic behavior of NiTi is implemented in a finite element analysis used to simulate the strip experiment. The model is capable of addressing the tension/compression asymmetry by incorporating both the tensile and compressive responses of the material. Softening moduli are introduced over the extents of the plateaus of the tensile response at approximately the Maxwell stress levels. The numerical solution reproduced the closed hysteresis with the correct stress plateau levels and extents. Localized deformation initiates in a single narrow band of higher strain inclined to the axis of the strip. The high strain zone propagates initially with inclined fronts and subsequently with a crisscross pattern with the stress remaining essentially unchanged. The details of the front propagation are influenced by in-plane moment caused by secondary kinking of the strip. The strip unloads by tracing a lower stress plateau developing a similar propagation of localization patterns. Overall, the numerical simulation captures the main features of the response and the associated localization configurations. The sensitivity of the solution to the mesh, the boundary conditions, and the softening moduli are discussed. [ABSTRACT FROM AUTHOR]

Bulk metallic glass composites (BMGCs) consisting of soft crystalline phases (commonly referred to as dendrites) in a metallic glass matrix have shown enhanced tensile ductility compared to conventional bulk metallic glasses (BMGs). Experiments and atomistic simulations suggest that a large number of geometrical parameters such as aspect ratio, spacing and orientation of dendrites as well as their spatial distribution can affect the mechanical response of BMGCs. However, the precise mechanism by which these parameters influence shear band initiation and propagation is not well understood. Therefore, continuum simulations of tensile loading on BMGCs with different morphologies are performed in this work. The results show that aspect ratio of dendrites has weak effect on the mechanical response up to the peak stress stage. However, it influences ductility considerably, albeit in a different manner for BMGCs with high and low hardening dendrites. The present analysis suggests that a BMGC capable of displaying mildly strain hardening response with large strain to failure can be designed by using closely spaced dendrites of high aspect ratio, and aligning them parallel to the maximum tensile stress direction. [ABSTRACT FROM AUTHOR]

This work focuses on the influence of cryo-rolling on subsequent recrystallization of hexagonal Zr-4 alloy. With initial recrystallized microstructure, the as-received Zr-4 sheets were rolled at liquid nitrogen temperature (LNT) and room temperature (RT). For each rolling temperature, two levels of strain, 20% and 40%, were applied. Then, samples, including as-received and rolled sheets, were annealed at 700 °C for 3 min–5 min. Microstructures of the deformed and annealed Zr-4 samples were characterized in detail by electron backscatter diffraction (EBSD) method. After rolling, no twin lamella is observed in Zr-4 sample. It is found that the intensity of the heterogeneous deformation in cryo-rolling is more severe than that in RT-rolling. After annealing, the recrystallized average grain size of Zr-4 decreases with the increases of the applied strain at both deformation temperatures. For a given rolling reduction, the recrystallized average grain size increases with decreasing deformation temperature. The texture orientation of Zr-4 was not remarkably changed during the rolling deformation and annealing process. [ABSTRACT FROM AUTHOR]

The coupling effects of low asymmetry of HCP structure and transient non-uniform stress/strain states during multi-pass deformation processing cause a great variation in crystallographic orientation of titanium tubes, which may induce anisotropic/asymmetrical behaviors and affect the formability and service performance of the materials. The unique plastic deformation and mechanisms under 3D stress need to be accurately and fully understood for integrated design of fabrication and forming of titanium tubular products achieving shape forming and property tailoring simultaneously. How to address this eluded and tantalized issue, however, is still a bottleneck issue. In tandem with this, taking high strength titanium tube (HSTT) as a case, by using macro/meso scaled hybrid methodology, a correlation among loading condition, distorted plasticity and texture evolution of the material is established and articulated: 1) Via Knoop indentation, tension/compression and EBSD, the distorted plasticity of HSTT is identified, and the coupling of three slip and two twinning modes are found to dominate the inhomogeneous deformation, which must be introduced in viscoplastic self-consistent (VPSC) crystal plasticity; 2) A compression-based orthogonal inverse method is used to calibrate the crystal plasticity parameters and validated from various aspects, and the VPSC-based computation is conducted for tubular materials with six typical initial textures under six fundamental loadings; 3) The remarkable distorted plasticity and evolution in strain hardening, strain flow and yield loci are observed for most cases; The interactions among slipping/slipping, slipping/twinning and twinning/twinning coordinate the anisotropic/asymmetrical behaviors and hence induce the distorted evolution of plasticity; The relationship between deformation modes (strain vectors) and texture evolution is constructed, and the tubes with the desired textures and bespoke properties can be tailored in cold rolling by allocating spatial plastic flow. [ABSTRACT FROM AUTHOR]

The mechanical properties of novel alloys with two-phase γ-TiAl + σ-Nb 2 Al microstructures were evaluated under compression at room temperature. Microstructures of varying scales were developed through solutionizing and aging heat treatments and the volume fraction of phases were varied with changes in composition. Ultra-fine, aged γ+σ microstructures were achieved for the alloys which effectively retained high volume fractions of the parent β-phase upon quenching from the solutionizing temperature. The yield strength and compressive strain to failure of these alloys show a strong dependence on the relative scale and volume fraction of phases. Surprisingly, the hard brittle σ-phase particles were not found to control fracture in the refined microstructures. [ABSTRACT FROM AUTHOR]

• Thermomechanical behavior of shape memory alloys. • Thermal cycling under constant stress of NiTi tubes. • Single surface fully coupled thermomechanical constitutive model. • Custom testing facility for precise control of temperature and load. A novel experimental setup is presented that allows for precise control of thermal and mechanical loads, and simultaneous monitoring of the temperature and the full-field deformation of small SMA structures that undergo phase transformations. The facility is used to conduct two experiments in which NiTi tubes are taken through a temperature cycle under constant load that leads to phase transformations in the form of helical localization bands that propagate along the specimen. The latent heat of transformation causes a complex interaction with the prescribed load and thermal environment. By changing the rate of the airflow through the environmental chamber it is revealed that the velocities of the transformation fronts depend on the rate at which heat is removed/added by the controlled environment. The experiments are simulated using a new fully coupled thermomechanical extension of the constitutive framework developed by this research group. Key features of the framework include the modeling of the reversible A ⇄ M transformation through a single surface in the deviatoric stress-temperature space that obeys kinematic hardening; with the transformation strain and entropy as the internal variables governed by an associative flow rule; and the inhomogeneous deformation exhibited in tension being modeled as softening. The tube is analyzed in a finite element coupled static displacement transient temperature analysis, and taken through the cool/heat cycle of the experiment. The temperature-strain response is accurately reproduced with the two transformations initiating at essentially the same temperatures as in the experiment and propagating in similar localized banded manners at similar speeds. Reproduction of the complex behavior observed in the experiments requires the calibration of the constitutive model, its discretization, and the modeling of the structure and its boundary conditions to work together to near perfection. The simulation also demonstrated that the heat exchange between the structure and the environment, in the present analysis governed by only by convection, requires further enhancement. [ABSTRACT FROM AUTHOR]

Preceding experiments and analyses revealed that bending of tubes whose material exhibits Lüders banding leads to the progressive nucleation of inclined bands of higher strain organized into periodic diamond clusters. The diamonds cover both the tensioned and compressed sides of the tube with the affected length developing a higher curvature than the unaffected section. Between the diamond patterns are elastic zones required for each periodic domain to conform to the curvature of the tube (Hallai and Kyriakides, 2011a ,b). The present work examines how this inhomogeneously deformed structure behaves on unloading, reverse bending, and curvature symmetric cycling. The inelastic behavior of the material is modeled through a combined isotropic/kinematic hardening constitutive model. The model incorporates partial softening over the extent of the Lüders strain and uses nonlinear kinematic hardening for reverse loading. A tube of virgin material is bent until the whole length is Lüders deformed and is in uniform curvature. The curvature remains uniform during unloading with the strain in the diamonds gradually being erased, but simultaneously a secondary set of local higher strain patterns emerge in the hitherto elastic zones between the original diamonds. During reverse bending to the symmetric negative curvature, the secondary patterns continue to grow in intensity. The tube is unloaded again and bent back to positive curvature completing the cycle. In the course of the second half cycle, localized strain patterns evolve in the reverse order to that of the first half cycle. The secondary patterns are gradually erased, and the diamond patterns reappear now concurrently reaching the same intensity as that acquired progressively during the bending of the virgin material. The same appearance, erasure, and reappearance of localized deformation take place in subsequent cycles. Once past the initial bending, the structure bends uniformly. [ABSTRACT FROM AUTHOR]

• An in-situ measurement system for global deformation field is developed. • A 3D intercalation-induced expansion model of a 100-Ah prismatic battery is proposed. • The mechanisms of the uneven deformation at the cell-level are revealed. • The displacement variance is reduced by 63.7% with a equal-stiffness spacer. Inhomogeneous deformation is one of the most critical reasons for performance degradation in lithium-ion battery cells integrated into a complete battery system. However, the mechanism of inhomogeneous deformation at the cell-level remains poorly understood owing to the limited experimental and simulation studies on the subject. In this study, an in-situ measurement platform and a three-dimensional intercalation-induced expansion model are proposed for the heterogeneity analysis of a 100-Ah prismatic battery. The platform can precisely acquire the surface topography and multi-points strain distribution in three directions. Furthermore, the expansion model can accurately predict the electrochemical and mechanical responses of the battery by introducing an equivalent coefficient of intercalation-induced expansion. We obtained three typical characteristics of non-uniform deformation, which can be attributed to a warped shell with variable stiffness. Accordingly, a lattice composite sandwich spacer based on equal-stiffness theory is presented, with the maximum deformation and displacement variance reduced by 40.3% and 63.7%, respectively. Our proposed approach is beneficial for mitigating the inhomogeneous deformation and also conducive to a more uniform temperature field, as it allows refrigerant flow through the voids of spacers. [ABSTRACT FROM AUTHOR]