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Belt grinding is gradually considered to be an effective method for precision machining those aeronautical parts with weak rigidity and complex surface. However, the characteristic of flexible grinding makes it difficult to precisely control the machining process and hinders its further development. In this paper, a series of detailed numerical studies are conducted to study the effect of complex contact deformation on the flexible precision grinding operation of titanium alloy. The flexible process of belt grinding was simulated numerically, and the spatial trajectory equation of abrasive grains in nonlinear time-varying contact state was obtained. Subsequently, the finite element simulation modelling and analysis of a single abrasive grain cutting titanium alloy workpiece under three different boundary conditions (no contact deformation, sinusoidal transformation contact deformation, nonlinear time-varying contact deformation) were performed. The characteristics of grinding morphology and the variation trends of grinding force obtained by simulation were almost consistent with the results of scratch experiments. On this basis, a series of orthogonal simulation studies were conducted to obtain the optimal processing parameters of belt grinding, in consideration of the changes in the spatial positions of abrasive grains caused by the time-varying contact deformation. The above research provides a theoretical framework for investigating the effect of nonlinear time-varying contact deformation, which is of great significance to reveal the mechanism of belt flexible grinding and expand its application in precision machining of aviation parts. [ABSTRACT FROM AUTHOR]

Accurate flow stress data are essential for the design and optimization of thermo-mechanical processes for a wide range of metallic materials. Hot compression testing is generally used to establish the dependence of flow stress on temperature, strain and strain rate. Flow stress measurements have mostly used cylindrical specimens of different sizes. While the data has been corrected for friction and adiabatic heating, the measurements assume idealized uniform deformation in the test specimen when obtaining the flow stress data from the measured load and displacement. In this paper, it is shown that there is significant non-uniform deformation in the test specimen under practical testing conditions, and a methodology is developed to correct the flow stress data. This correction is generally more significant than the correction due to friction or adiabatic heating and is necessary to obtain more accurate flow stress data. The effect of specimen geometry is also investigated, and a geometry which results in more uniform strain distribution than a cylindrical specimen is used. Measurements are conducted for a prototype powder metallurgy nickel-base superalloy at a low strain rate over a deformation temperature range. Constitutive equations are constructed with the measured flow stress data. Finite element modeling of the tests using the corrected data provides a better agreement with the measured loads. The grain microstructures vary with the test parameters and are used to correlate the flow behavior. [ABSTRACT FROM AUTHOR]

Silicon (Si) is extensively used as an electrode in lithium (Li) ion batteries for its superiority in the charging capacity. However, the lithiation of Si would induce large deformation and significant stress jump across a two-phase interface in Si electrodes and might eventually lead to structure failure of batteries. To improve the performance and life of Li ion batteries, it is of great importance to exactly model the lithiation process. In the past decade, although many models have been developed for the lithiation, most of them just relate the deformation with the diffusion, without considering the effect of electrochemical reactions, so that they cannot simulate the formation of the two-phase interface. In this paper, we aim to develop a fully coupling diffusion–reaction–deformation model for large deformation cases and apply it to simulate the lithiation process, where a reaction barrier effect is proposed to describe the formation of the two-phase interface due to fast reaction and the mechanical behaviors of Si electrodes such as large plastic flow during lithiation process are predicted. [ABSTRACT FROM AUTHOR]

The fatigue characteristics of rock materials are usually studied by cyclic load–unload tests, and the deformation and damage development reflect their weakening characteristics. In this paper, according to the mechanical characteristics of rock materials during load/unload cycles, the total strain can be separated into three types, that is, elastic strain, viscoelastic strain, and viscoplastic strain. The elastic strain is linear with stress, and viscoelastic strain exhibits a special behavior after unloading, the viscoplastic strain also displays its own unique features and reflects the damage in rocks. Based on their unique characteristics, we establish elastic, viscoelastic, and viscoplastic submodels, then an elastic-visco-plastic model can be obtained by connecting three submodels in series, which can reflect the development of the law of different strains. In order to verify the reliability of the model, red sandstone samples are selected for cyclic load/unload tests. The results show that the collected strain–time data are well fitted by the model. In addition, the characteristics of strain–time curves imply the deformation and damage development of rocks during load/unload cycles. [ABSTRACT FROM AUTHOR]

Silicon carbide is desirable for many nuclear applications, making it necessary to understand how it deforms after irradiation. Ion implantation combined with nanoindentation is commonly used to measure radiation-induced changes to mechanical properties; hardness and modulus can be calculated from load–displacement curves, and fracture toughness can be estimated from surface crack lengths. Further insight into indentation deformation and fracture is required to understand the observed changes to mechanical properties caused by irradiation. This paper investigates indentation deformation using high-resolution electron backscatter diffraction (HR-EBSD) and Raman spectroscopy. Significant differences exist after irradiation: fracture is suppressed by swelling-induced compressive residual stresses, and the plastically deformed region extends further from the indentation. During focused ion beam cross-sectioning, indentation cracks grow, and residual stresses are modified. The results clarify the mechanisms responsible for the modification of apparent hardness and apparent indentation toughness values caused by the compressive residual stresses in ion-implanted specimens. [ABSTRACT FROM AUTHOR]

In the paper, the deformation features of the propagation of cleavage cracks in low-alloy low-carbon steel with a ferritic-pearlite microstructure by example of steel 09G2S after hot rolling are investigated. The studied cleavage cracks were obtained in impact bending tests at temperatures in the ductile to brittle transition interval. The study was carried out by transmission electron microscopy, transmission Kikuchi diffraction, and electron backscattered diffraction. It is shown that the deformation accompanying the growth of the cleavage crack in the ferritic-pearlite microstructure is formed when the joints between the cracks propagating in parallel planes break. The crack growth within a single plane occurs without any recorded deformation. The joints are broken by a ductile mechanism according to the scheme of mixed loading by opening and shear. Overlapping of the cleavage cracks determines the relationship between the shear mode and the opening mode during joint deformation, which controls the shape and depth of the plastic deformation zones. [ABSTRACT FROM AUTHOR]

Ultrasonic-assisted forming technology has great potential in micro-coining. In this paper, ultrasonic-assisted micro-coining experiments comparing different ultrasonic frequencies, amplitudes, action times and other parameters were conducted. The experimental results were analyzed by numerical simulation. It was shown that ultrasonic duration was the main factor determining micro-cylinder height. The micro-cylinder height increased rapidly when ultrasonic duration time was less than 10 s, but longer ultrasonic treatment provided little extra gain micro-cylinder growth. The ultrasonic frequency and amplitude also played an important role in micro-coining. Ultrasonic frequency closest to natural frequency of tools and larger ultrasonic amplitude could provide more ultrasonic energy to specimens, thus leading to higher micro-cylinders. When the ultrasonic frequency and amplitude were 20 kHz and 8.6 μm, respectively, the micro-cylinder height increased the most, nearly five times higher than that achieved without ultrasound. Numerical simulation showed that the surface effect of ultrasonic played a major role in micro-coining by effectively reducing the friction coefficient between tools and specimens, contributing >90% of the increase of micro-cylinder height. Conversely, the contribution of ultrasonic volume effect was <10%. Finally, ultrasonic vibration assistance was applied to the fabrication of micro-cylinder arrays, and effectively improved their height and surface quality, demonstrating that ultrasonic-assisted micro-coining has broad applicability in practical production. [ABSTRACT FROM AUTHOR]

The present paper aims at analytically evaluating the natural frequencies of cracked slender masonry elements. The problem is dealt with in the framework of linear perturbation, and the small oscillations of the structure are studied under loaded conditions, after the equilibrium for permanent loads has been achieved. A masonry beam element made of no-tension (masonry-like) material is considered, and some explicit expressions of the beam's fundamental frequency as a function of the external loads and the amplitude of imposed deformations are derived. The analytical results are validated via finite-element analysis. [ABSTRACT FROM AUTHOR]

The in-plane thermoelastic response of curved beams made of porous materials with different types of functionally graded (FG) porosity is studied in this research contribution. Nonlinear governing equations are derived based on the first-order shear deformation theory along with the nonlinear Green strains. The nonlinear governing equations are solved by the aid of the Rayleigh–Ritz method along with the Newton–Raphson method. The modified rule-of-mixture is employed to derive the material properties of imperfect FG porous curved beams. Comprehensive parametric studies are conducted to explore the effects of volume fraction and various dispersion patterns of porosities, temperature field, and arch geometry as well as boundary conditions on the nonlinear equilibrium path and stability behavior of the FG porous curved beams. Results reveal that dispersion and volume fraction of porosities have a significant effect on the thermal stability path, maximum stress, and bending moment at the crown of the curved beams. Moreover, the influence of porosity dispersion and structural geometry on the central radial and in-plane displacement of the curved beams is evaluated. Results show that various boundary conditions make a considerable difference in the central radial displacements of the curved beams with the same porosity dispersion. Due to the absence of similar results in the specialized literature, this paper is likely to provide pertinent results that are instrumental toward a reliable design of FG porous curved beams in thermal environment. [ABSTRACT FROM AUTHOR]

The paper presents basic approaches to assessment of strength, service life, and survivability of structural components of technical systems subjected to various types of operating loading regimes. These include: (i) thermo-mechanical loading regimes of normal operation inducing the states of stress and strain that can be considered using traditional stress-based methods and criteria; (ii) extreme design basis loading regimes related to design basis emergency situations that require a transition to design according to strain-based fracture criteria with accounting for temperature, force and frequency factors, and (iii) loading regimes induced by beyond design basis (accident and catastrophic) situations that should be analyzed using equations and criteria of nonlinear deformation mechanics in its most complex thermally coupled formulation. [ABSTRACT FROM AUTHOR]

The performance of the flexibility and stretchability of flexible electronics depends on the mechanical structure design, for which a great progress has been made in past years. The use of prestrain in the substrate, causing the compression of the transferred interconnects, can provide high elastic stretchability. Recently, the nonbuckling interconnects have been designed, where thick bar replaces thin ribbon layout to yield scissor-like in-plane deformation instead of in- or out-of-plane buckling modes. The nonbuckling interconnect design achieves significantly enhanced stretchability. However, combined use of prestrain and nonbuckling interconnects has not been explored. This paper aims to study the mechanical behavior of nonbuckling interconnects bonded to the prestrained substrate analytically and numerically. It is found that larger prestrain, longer straight segment, and smaller arc radius yield smaller strain in the interconnects. On the other hand, larger prestrain can also cause larger strain in the interconnects after releasing the prestrain. Therefore, the optimization of the prestrain needs to be found to achieve favorable stretchability. [ABSTRACT FROM AUTHOR]

The paper deals with the numerical investigation of the possibilities to control convective flows in the liquid bridge in zero gravity conditions applying axial vibrations. The surface tension is assumed to be dependent both on the temperature and on the solute concentration. The free surface deformations and the curvature of the phase change surfaces are neglected but pulsational deformations of the free surface are accounted for. The first part of the paper concerns axisymmetric steady flows. The calculations show that the evolution of convective flow with the variation of thermal Marangoni number at a fixed value of the solutal Marangoni number is accompanied by the hysteresis phenomenon, which is related to the existence of two stable steady regimes in a certain parameter range. One of these regimes is thermocapillary dominated, it corresponds to the two-vortex flow, and the other is solutocapillary dominated, it corresponds to the single-vortex flow. Under vibrations, the range of the Marangoni numbers where hysteresis is observed becomes narrower and is shifted to the area of larger values. The second part of the paper concerns the stability of axisymmetric thermo-and solutocapillary flows and the transition to three-dimensional regimes. Significant mutual influence of flows generated by each process on the stability of the other is discovered. Stability maps in the parametric plane for the thermal Marangoni number, the solutal Marangoni number, are obtained for different values of vibration parameters. It is shown, that vibrations exert a stabilizing effect, increasing critical Marangoni numbers for all modes of instability. However, this effect is different for different modes and at high vibration intensity destabilization is possible. Consequently, vibrations can modify the scenario of the transition to the three-dimensional mode. [ABSTRACT FROM AUTHOR]

Dynamic recrystallization (DRX) plays an important role in microstructure evolution during hot deformation. In this paper, the hot deformation behavior and DRX mechanism of 7075 aluminum alloy were investigated by hot compression tests at a temperature of 250-450 °C and strain rate of 0.01-10 s−1. The experimental results show that the DRX is the main softening mechanism of the AA7075, and the relationships among temperature, strain rate and Z parameter were established. Besides that, the recrystallization fraction and grain size increase with the rising of temperature (250-450 °C) due to the accelerating of the grain boundary migration and movement. As the values of Z parameters increase, three typical softening mechanisms occur, ranging from discontinuous dynamic recrystallization (DDRX) to continuous dynamic recrystallization (CDRX). The characteristic of DDRX is mainly grain boundary (GB) bulging relying on GB migration. With regard to the situation of CDRX, the transformation of low angle grain boundary to high angle grain boundary due to the rearrangement of dislocation could be observed based on the electron backscatter diffraction analysis. The mechanism of CDRX and DDRX existed simultaneously in condition of moderate Z parameter. [ABSTRACT FROM AUTHOR]

Research on micro/nano-electro-mechanical system (MEMS/NEMS) reliability is of crucial importance, due to the fact that we are facing an era in which MEMS and emerging NEMS are expected to have a major impact on our lives. Over the last decade, significant efforts have gone into the reliability study of MEMS/NEMS. Failure roots in micro- and nano-scales can be addressed by mechanical, electrical, chemical, thermal factors, or combinations of them, which can occur during different manufacturing and post-manufacturing phases. This paper reviews and integrates the reliability issues of MEMS and NEMS in different phases of their life cycles including design, manufacturing, logistics, and operation. This paper surveys the common failure modes and mechanisms (i.e., wear, degradation, adhesion, stiction, deformation, packaging, contamination, and electrical failure modes), the reliability aspects of design and manufacturing, as well as reliability evaluation and testing techniques for MEMS/NEMS. An extensive collection of papers were selected and integrated to cover various studies in this area, in order to provide an intuition and insight for researchers who are interested in reliability research of MEMS/NEMS. Systematic literature search shows the lack of research in system-level and probabilistic reliability analysis for MEMS/NEMS. [ABSTRACT FROM AUTHOR]

In this paper, the spreading process of two XPP model droplets impacting on a plate in sequence at low Reynolds number is numerically simulated by using an improved smoothed particle hydrodynamics (I-SPH) method. The I-SPH method is a coupled approach which uses the traditional SPH (TSPH) method near the boundary domain and uses a kernel-gradient-corrected SPH method in the interior of fluid flow for the reason of remedying the accuracy and stability of TSPH. Meanwhile, an artificial stress term and a periodic density re-initialization technique are presented to eliminate the tensile instability and restrain pressure oscillation, respectively. A new boundary treatment is also adopted. The ability and merit of proposed I-SPH method combined with other techniques are first illustrated by simulating three typical examples. Subsequently, the deformation phenomena of two viscoelastic droplets impacting and spreading on a plate in sequence are numerically investigated. Particularly, the influences of the falling time interval, Weissenberg number and other rheological parameters on the deformation process are studied respectively. All numerical results agree well with the available data. [ABSTRACT FROM AUTHOR]

The vestibular receptor of cupula acts an important role in maintaining body balance. However, the cupula buried in the semicircular canals (SCCs) will be destroyed if it is detached from the relevant environment. The mechanical properties of human cupula still remain ambiguous. In this paper, we explored the cupula responses changing with temperature by experiments and numerical simulation of SCCs model. We obtained 3 volunteers' nystagmus induced by constant angular acceleration when the temperature of volunteers' SCCs was 36 °C and 37 °C respectively. The slow-phase velocity of 3 volunteers decreased by approximately 3°/s when the temperature of SCCs reduced by 1 °C, which corresponded to the reduction of cupula deformation by 0.3–0.8 μm in the numerical model. Furthermore, we investigated the effects of the variation of endolymphatic properties induced by temperature reduction on cupula deformation through numerical simulation. We found that the decrease of cupula deformation was not caused by the change of endolymphatic properties, but probably by the increase of cupula's elastic modulus. With the temperature reducing by 1 °C, the cupula's elastic modulus may increase by 6–20%, suggesting that the stiffness of cupula is enhanced. This exploration of temperature characteristic of human cupula promotes the research of alleviating vestibular diseases. [ABSTRACT FROM AUTHOR]

Ultrasonic shot peen forming (USPF) is a promising and widely used forming technique for thin metallic parts. In this paper, detailed deformation behavior of the aluminum alloy ring caused by USPF was studied, which is of a great significance to industrial applications for roundness correction and reshaping of the ring parts, such as wheel hub, petrochemical containers, pressure vessels, and spacecraft shells. Firstly, the motion of the single pin during USPF was recorded by a high-speed camera. Then, by combining the recorded results and the stress wave theory, the firing pin motion was approximately described as an effective impact of 100 times per second and the average impact velocity of 5 m/s. By considering the firing pin movement, the 3D USPF FE model of a cell AA6061-T6 sheet was developed successfully for obtaining the accurate plastic strain field. Subsequently, a 2D USPF FE model of the ring part was developed, which is able to obtain similar residual stress profiles with the 3D cell's FE model by inputting the plastic strain profiles induced by the firing pin impact. Based on the results of experimental and numerical simulation, it was observed that the convex deformation of the ring part increases as the wall thickness decreases and the central angle of the treatment area increases. In addition, a wave contour and a local deformation with a little influence on the other area of the ring part can be achieved by three USPF treatment areas distributed in one-sided surface and two-sided surface, respectively. [ABSTRACT FROM AUTHOR]

Longwall extraction of coal seam disturbs the whole overburden strata, from the coal seam to the surface, and forms a subsidence basin. This paper investigated the mechanism of the overburden strata bending deformation, the alluvium mechanical parameters, and their effect on surface subsidence by the theoretical analysis and numerical simulation analysis. The dynamic processes of overburden failure and surface subsidence due to longwall mining was analyzed by a novel two-dimensional trapezoidal-area method. A "π-shaped" model was first developed to reveal that surface subsidence consists of the overburden strata bending deformation and the subsidence of the alluvium. The process and mechanism of the overburden strata bending transfer were analyzed, and two mechanical models of the strata bending deformation were established, i.e., the strata suspended bending model and the strata overhanging bending model. The maximum subsidence equation of the overburden strata bending basin was derived based on the theoretical analysis. Also, the effect of the alluvium mechanical parameters on the surface subsidence was investigated by numerical simulation analysis. The rationalities of the numerical simulation were validated by the field measurements. The results show that surface subsidence increases logarithmically during increased alluvium thickness and decreases exponentially and logarithmically during increased internal friction angles and increased cohesions, respectively. [ABSTRACT FROM AUTHOR]

The investigation on the mechanical mechanism of the retaining and protection structure of superdeep excavations is an important subject, and its deformation control research is particularly important. Taking the deepest foundation pit with full-section overall excavation in Beijing as an example, this paper studies the stress and deformation characteristics of composite soil nailing wall and anchored soldier pile wall combined retaining system under complex geological conditions of multi-layer groundwater during the process of excavating 31.4 m deep. The Midas simulation software and monitoring data are used to analyze the construction process of foundation excavation. The simulated results and monitored values of anchor force, ground settlement, and soil deformation during foundation excavation are analyzed and discussed to verify the reliability of the model. The spatial effect of internal force and deformation of composite retaining and protection structure for superdeep foundation excavation is discussed, and the parameters affecting the retaining structure are analyzed and investigated. The research shows that with the increase of excavation depth, both the extremum of the bending moment and the extremum of lateral displacement of retaining piles are increasing, and the position of the extremum of bending moment is located near the excavation face; then, the bending moment reaches the maximum when the foundation pit is excavated to the bottom. Within a certain range, increasing the rigidity or the embedded depth of the retaining pile or the prestress of the anchor can effectively control the lateral displacement of the excavation. However, when the rigidity of retaining pile is too large, its lateral displacement does not change significantly. Similarly, when the embedded depth is too long or the prestress of the anchor is too powerful, the effect of controlling deformation is also not obvious. The research results will provide theoretical basis and practical experience for the design and construction of superdeep excavations. [ABSTRACT FROM AUTHOR]

During automatic electromagnetic riveting, the positioning deviation between punch and rivet is easy to occur. This leads to the asymmetric deformation of rivet tail and affects the performance of riveted joint. In this paper, the riveted specimens under various angle deflections (0°, 2°, 4°, 6°) were prepared to investigate the effect of angle deflection on deformation characteristic and mechanical property of electromagnetic riveted joint. The microstructure observation, interference analysis, hardness measurement, and shear and pull-out test were performed to evaluate the performance of riveted joints. Results showed that the angle deflection had significant effects on the deformation characteristics and mechanical properties of riveted joints. Compared to the riveted joint with 0° angle deflection, the rivet shaft of riveted joints with 2°, 4°, and 6° angle deflection would tilt. The tilt of the rivet shaft caused relative displacement between riveted sheets and generated a clearance between the rivet shaft and riveted sheets, affecting the interference of riveted joints. The mechanical property of riveted joint decreased with the increase of angle deflection. For shear tests, the failure modes were all rivet failure, and the rupture positions were all in the middle portion of the rivet shaft. For the pull-out test, there were three failure modes. In addition, the reliability of automatic electromagnetic riveted joint could be preliminarily judged by this work, which provided scientific guidance for the engineering application of automatic electromagnetic riveting technology. [ABSTRACT FROM AUTHOR]

Three-dimensional ion and particle concentrations under hydrodynamic focusing in a Y-shaped square microchannel are numerically simulated to clarify the decrease of the ion concentration along the flow direction within the focused particle stream. The simulation model is theoretically governed by the laminar flow and advection–diffusion equations. The governing equations are solved by the finite volume method. The ion and particle concentration distributions at five cross sections after the confluence of the branch channels are analyzed in 30 cases in which the sheath to sample flow rate ratio Qsh/Qsam and the Reynolds number Re are varied as parameters. The results show that the decrease of the cross-sectional average ion concentration along the flow direction within the particle stream c ¯ i is described by the diffusion length during the residence time with a characteristic velocity scale. In addition, the deformation of the particle stream due to inertial effects is described by a scaled Reynolds number that is a function of the flow rate ratio. The simulated particle stream thicknesses are validated by theory and a simple experiment. This paper reveals the relationship between the ion and particle concentrations and the dimensionless parameters for hydrodynamic focusing in the Y-shaped square microchannel under typical conditions. [ABSTRACT FROM AUTHOR]

This paper reviews the basic understanding of Mg-based thermoelectric materials and various approaches for increasing their thermoelectric efficiency. Recent developments in terms of enhancement of electrical properties and reduction of thermal conductivity of Mg2(Si,Sn) materials through experimental investigation and applying modeling approaches are discussed in detail. Further, the role of deformation and heat treatment analysis for achieving optimum thermoelectric properties in this material system and its prospects for further developments as a commercially viable solution is enumerated. The solid solutions of Mg2X (X = Si,Ge,Sn) thermoelectric material are identified as the most favorable alloy class of thermoelectric materials for application in the intermediate temperature range (400–800 K). The reason for Mg2X alloys becoming the preferred choice over others is because they are cheap, abundant and non-toxic. Improving the efficiency of magnesium-based thermoelectric materials through various advancements in experimental methods has appeared as a matter of great commercial importance. However, theoretical understanding of the phenomenological issues confronting the attainment of desirably high thermoelectric properties has not been widely touched upon; this leads to enormous opportunities for optimizing the figure of merit of thermoelectric materials through numerical modeling and simulation techniques. Also, deforming the alloys has been proved to be favorable for the thermoelectric performance of the material; a lot of work has been carried out for other classes of thermoelectric materials, but there is a disparity in interpreting the deformation behavior of Mg2Si1−xSnx alloys and its impact on thermoelectric properties due to lack of adequate efforts to conduct systematic investigations in the area of concern. [ABSTRACT FROM AUTHOR]

This paper presents a new joining by forming process capable of attaching a sheet to the end of a tube without the need of accessories and extra materials. The process is named as 'self-pierce riveting of tubes to sheets' and is an extension to sheet-tube connections of the working principle of double-sided self-pierce riveting utilized for connecting two overlapped sheets. The process requires tubes with chamfered ends to be pushed against the sheets and its ends to flare (curl) in order to create an interlocking that holds the sheets and tubes tightly together. The resulting joints are invisible because the interlockings are hidden inside the sheets. The presentation draws from deformation mechanics and identification of the major parameters to characterization of the interlocking and evaluation of the pull-out destructive strength that the new joints are capable to withstand without failure. Aluminium sheets and carbon steel tubes are utilized to demonstrate the effectiveness of the new joining by forming process and to demonstrate its ability to connect sheets and tubes made from dissimilar materials at room temperature. Finite element modelling using an in-house computer program gives support to the presentation. [ABSTRACT FROM AUTHOR]

Mechanical behavior and deformation characteristics of rock under unloading conditions are of particular significance for analyzing excavation-induced instability problems of underground rock masses. In this paper, triaxial compression tests with progressive unloading of confining pressure were conducted upon sandstone specimens under different combinations of initial confining pressures and pore pressures. It is shown from the tests that the magnitude of initial confining pressure and pore pressure influences significantly the rock strength, energy conversion, crack propagation, and dilatancy during unloading process. The strength under unloading conditions is in compliance with the linear Mogi-Coulomb criterion. The energy conversion method can be employed to determine the crack damage thresholds during the unloading process. The analysis on cracking process suggests that crack damage thresholds increase linearly with initial confining pressure, but decrease with pore pressure. Under unloading conditions, material yield and brittle failure occur more easily with the increase in pore pressure. Furthermore, given the initial confining pressure, a higher level of pore pressure can accelerate volumetric expansion in the specimens. [ABSTRACT FROM AUTHOR]

In this paper, we continue the study of T T ¯ deformation in d = 1 quantum mechanical systems and propose possible analogues of J T ¯ deformation and deformation by a general linear combination of T T ¯ and J T ¯ in quantum mechanics. We construct flow equations for the partition functions of the deformed theory, the solutions to which yields the deformed partition functions as integral of the undeformed partition function weighted by some kernels. The kernel formula turns out to be very useful in studying the deformed two-point functions and analyzing the thermodynamics of the deformed theory. Finally, we show that a non-perturbative UV completion of the deformed theory is given by minimally coupling the undeformed theory to worldline gravity and U(1) gauge theory. [ABSTRACT FROM AUTHOR]

The sidewalls of thin-walled deep cavity components can easily deform during the milling process because of their low rigidity, which seriously affects the machining accuracy. To resolve this problem, this paper proposes a novel method to predict milling errors based on the finite element method (FEM). A dynamic model of the tool is first established, and the motion state of an arbitrary point on the tool during the continuous milling process is obtained by solving for the key parameters. In addition, both the deflection of the workpiece/tool system and the springback deformation of the workpiece are considered. The material is then removed based on a Boolean operation and a hexahedral mapping algorithm for the points; finally, the continuous tooling process and the milling error of the arbitrary point on the finished surface are obtained. This study uses a typical waveguide cover as the simulation object and verifies the veracity of the simulation method through experiments. [ABSTRACT FROM AUTHOR]

Stacking fault energy (SFE) is an intrinsic material property whose value is crucial in determining different secondary deformation mechanisms in austenitic (face-centered cubic, fcc) steels. Considerable experimental and computational work suggests that the SFE itself is highly dependent-in a complex manner-on chemical composition and temperature. Over the past decades, there have been a large number of efforts focused on determining the composition dependence of SFE in austenitic steel alloys by means of experimental, theoretical or computational methods. Unfortunately, experimental methods suffer from the indirect nature of the methodologies used to estimate the value of SFE, while computational and/or theoretical approaches are either limited by the physics that they can incorporate into the predictions or have more practical limitations associated, for example, to the size of the systems that can be modeled or the assumptions that must be made. In this paper, we review the major experimental and computational approaches to determine SFE in austenitic steel alloys, and we discuss their limitations. We then demonstrate a data-driven machine learning technique to mine the literature of experimental SFE data in steels, while algorithms at the fore-front of machine learning have been used to visualize the SFE data and then construct a three-class classifier. The classifier is used then to predict likely secondary deformation mechanisms of untested compositions, while the classifier itself is presented as a valuable tool for the further development of austenitic steel alloys in which the specific secondary plastic deformation mechanisms are a feature to design for. The data as well as the entire analysis workflow are made available to the wider community through a public github repository. [ABSTRACT FROM AUTHOR]

A new type of displacement pile, the X-section cast-in-place concrete (XCC) pile, has recently been developed in China. Extensive field tests and laboratory experiments are undertaken to evaluate its performance and quantify the non-uniform deformation effect (NUDE) of the X-shaped cross section during installation. This paper develops a simplified theoretical model that attempts to capture the NUDE. Based on the theory of complex variable plane elasticity, closed-form solutions of the stress and displacement for the X-shaped cavity boundary value problem are given. Subsequently, the analytical solution is used to evaluate the NUDE, the concrete filling index (CFI), and the perimeter reduction coefficient of the XCC pile cross section. The computed results are compared with field test results, showing reasonable agreement. The present simplified theoretical model reveals the deformation mechanism of the X-shaped cavity and facilitates application of the newly developed XCC pile technique in geotechnical engineering. [ABSTRACT FROM AUTHOR]

The formation of rabbit ears during the gear rolling process, caused by the generating motion between the gear roller and the blank, is a common and undesirable phenomenon encountered in gear rolling. It generally leads to fold defects, waste of material, and decline in mechanical properties after removal, seriously affecting the quality of the gear to be formed. In this paper, a finite element model of gear rolling is first established, the gear rolling process are simulated, and the rabbit ear formation mechanism and its morphology change are studied. The phenomenon and the morphology of the rabbit ear are then verified experimentally. The formation mechanism of the rabbit ear was analyzed by means of the stress state, the deformation distribution, and the material flow. The results show the following: (1) the continuous localized contact between the gear roller and the blank induces the material on the surface area of the tooth sequential plastic deformation, while at the same time, the material is squeezed by the tooth flank of the gear roller and flows towards the direction of the smaller resistance, that is, the flank of the tooth. The difference in the material flow velocity between the flank of the tooth and the center of the tooth leads to the formation of the rabbit ear; (2) the asymmetric shape of the ears appears to be related to the different direction of friction exerted on two sides of the tooth depending on the rotational direction of the gear roller. These findings provide a scientific basis to further explore measures to control the rabbit ear defect and improve the forming quality in gear rolling. [ABSTRACT FROM AUTHOR]

Significance of application of metal matrix composites (MMCs) in various industries has already been demonstrated. In order to address the challenges faced during machining MMCs, development of novel modeling techniques for understanding the mechanics of the process is crucial. This paper presents a new approach towards finite element modeling of MMC machining process to facilitate the analysis of plastic deformations. Transient Lagrangian modeling is used with adaptive remeshing control in order to reduce the effects of mesh distortions on accurate estimation of plastic deformation during machining. The thorough understanding of MMC plastic deformations, which is achieved using the developed model, is an asset in analysis of MMC behavior during the process. [ABSTRACT FROM AUTHOR]

In this paper, a simulation model for two-roll cross wedge rolling (CWR) was presented to investigate the deformation mechanism for forming shafts without concavity by using the finite element method. Based on the simulation results, the reason for concavity in both sides of the rolled piece in the CWR process was analyzed in detail, and a method to implement the CWR process without loss of material was brought forward by billet compensation. In addition, the influence of the main process parameters on the concavity depth of the workpiece with a tapered or circular-arc end was compared and ascertained. The study results show that the concavity depth is in direct proportion to the cone angle, but in inverse proportion to the central angle, and the concavity can be improved with larger area reduction and mill length under the two profiled ends. Subsequently, the feasibility of using profiled billets to effectively control the concavity was verified via the rolling experiments. [ABSTRACT FROM AUTHOR]

Stereo digital image correlation (stereo-DIC) is in wide-spread use for full-field shape, motion and deformation-measurements. However there are very few papers investigating the influence of the setup on the measurement uncertainty. This is mainly due to the highly non-linear measurement chain involving both optical and numerical aspects, making it difficult to investigate how error sources are propagated through the stereo-DIC chain. Indeed, it is impossible to separate all the error sources that are present during a physical measurement. This paper tries to investigate a selection of error sources that are present during experiments. This is based on a simulator introduced in a previous article (Balcaen et al., Exp Mech, 1-16 2017) and briefly reviewed here. Based on these simulations we suggest some 'best-practices' guidelines of optimal stereo-DIC setups. [ABSTRACT FROM AUTHOR]

In this paper, T-joint of 316L steel is obtained by subsection laser welding method without jig, while a thermal elastic-plastic finite element model considering multi-linear yield stress curves and multi-point constraint equations is developed to estimate welding deformation and residual stress. A simplified heat source model with the actual bead geometry is proposed to reduce the number of finite element meshes. Prediction errors between the simulation and experimental measurement results of angular distortions of three reference lines are −11.0, 0.9, and 7.9 % respectively, and the maximum residual stress is 396 MPa. Meanwhile by microstructure analysis, austenite and ferrite are consisted in weld, segregation and dendritic structures are also observed, while the heat-affected zone is very narrow. In a word, weld line with large travel can be welded by subsection laser welding method without jig, while the finite element method proposed in this paper is effective to predict welding deformation and residual stress. [ABSTRACT FROM AUTHOR]

The selection of machining parameters in milling thin-walled plates affects deformation, quality, and productivity of the machined parts. This paper presents an optimization procedure to determine and validate the optimum machining parameters in milling thin-walled plates. The regression models for cutting force and surface roughness are developed as objective functions according to experimental results. Besides, the influences of machining parameters on cutting force and surface roughness are also investigated. The objectives under investigation in this study are cutting force, surface roughness, and material removal rate subjected to constraints conditions. As the effects of milling parameters on optimization objectives are conflicting in nature, the multi-objective optimization problem in thin-walled plates milling is proposed. A non-dominated sorting genetic algorithm (NSGA-II) is then adopted to solve this multi-objective optimization problem. The optimized combinations of machining parameters are achieved by the Pareto optimal solutions, and these solutions are verified by the chatter stability. [ABSTRACT FROM AUTHOR]

Nowadays, the modeling and simulation of grinding have become powerful tools in predicting the process performance and work results. However, common simulations focus on material removal process of abrasive grains and neglect deformations of machine structure. The grinding quality can be influenced by various factors, of which the process-machine interaction results in often unpredictable effects, especially in the processing of hard-to-cut material. This paper proposes a simulation approach based on integrated process-machine model in plunge face grinding of cemented carbide. The approach synthesizes the interactive influence between machine dynamics and physical factors in grinding process. A virtual wheel model is built considering the stochastic nature of abrasive grains on the wheel surface, and the simulated forces and surface roughness are further predicted. The spindle-wheel structure is also modeled based on the finite element method. In order to implement the process-machine interaction, a coupled simulation by using self-developed interface is applied to accomplish data exchanges between different simulation environments. The simulation results are verified and found to be in good agreement with experimental results. [ABSTRACT FROM AUTHOR]

The paper describes an investigation into the use of mechanical clinching in cold-formed steel trusses. One of new joining methods is hybrid joining; the thin sheets were joined using different materials. The material behaviour law used is elasto-plastic. Due to the incremental nature of the plastic law, the updated Lagrangian formulation is utilized to describe the large elasto-plastic deformation process. The contact and friction described by the Coulomb law are considered by the penalty method. In the present work, we have used the dynamic explicit approach based on finite element method to get the hybrid joining and the effect of geometrical and mechanical parameters of the clinching process. Furthermore, we have numerically evaluated the pure tensile test to get the mechanical strength of the assembly. [ABSTRACT FROM AUTHOR]

In a previous paper, a simple model was developed to extend the application of the traditional flower pattern diagram as a design tool for roll forming. The position of a point on the strip as it passes through each set of rolls can be identified as a series of points in the two-dimensional flower pattern diagram. In three dimensions, these points will lie on a non-circular cylindrical surface having its axis parallel to the machine axis. Assuming that these points are joined by a smooth curve, the forming path of a point on the strip as it passes through the roll forming process can be obtained as a plane curve on the plane development of this surface. It was shown in previous work that the longitudinal membrane strain and, in certain cases, local curvature of the sheet are functions of the slope of this plane curve. In this work, the strains on both surfaces at the edge of a strip in the forming of a simple V-channel are measured using strain gauges. It is shown that near the point of contact with the rolls, the strains differ by nearly an order of magnitude from those determined from the simple model which assumes that the trajectory is a smooth curve. A modification of the forming path is obtained from the measured bending strains. Although the changes in displacement are small, the peak values of strain near the point of roll contact are large and a consequence of highly localised changes in the forming path as the strip passes over each roll. Measurement of this perturbation in the forming path is difficult as the region is obscured by the forming rolls. The technique described here permits the reconstruction of this path and identifies a new area of investigation of longitudinal strains in roll forming. These are often associated with shape defects such as bow, warping and end flare. [ABSTRACT FROM AUTHOR]

In this paper, a mixed Lagrangian multiplier formulation is developed for consistent size-dependent couple stress elastodynamic response. This extends previous work on quasistatic couple stress response that also requires the rotation to be one half of the curl of displacement. A Lagrange multiplier, which turns out to be related to the skew-symmetric part of the force stress, is used to constrain the relation between rotation and displacement, so that rotation becomes an independent variable and $$\hbox {C}^{1}$$ continuity is avoided in the weak form. The finite element method is applied first to obtain the matrix form of the Lagrangian formulation in space, and then, discrete variational time integration is introduced to produce the discrete action. Afterward, the variation of discrete action is applied to derive the governing equations in algebraic form, which are used, along with the initial condition relations, to obtain the solutions at finite time steps. Finally, the problems of uniaxial deformation of a square plate, transverse deformation of a cantilever, and uniform traction on a square plate with a hole are investigated under this formulation, and the results are compared to existing methods where possible. [ABSTRACT FROM AUTHOR]

For the case of metals with large viscoplastic strains, it is necessary to define appropriate constitutive models in order to obtain reliable results from the simulations. In this paper, two large strain viscoplastic Perzyna type models are considered. The first constitutive model has been proposed by Ponthot, and the elastic response is based on hypoelasticity. In this case, the kinematics of the constitutive model is based on the additive decomposition of the rate deformation tensor. The second constitutive model has been proposed by García Garino et al., and the elastic response is based on hyperelasticity. In this case, the kinematics of the constitutive model is based on the multiplicative decomposition of the deformation gradient tensor. In both cases, the resultant numerical models have been implemented in updated Lagrangian formulation. In this work, global and local numerical results of the mechanical response of both constitutive models are analyzed and discussed. To this end, numerical experiments are performed and different parameters of the constitutive models are tested in order to study the sensitivity of the resultant algorithms. In particular, the evolution of the reaction forces, the effective plastic strain, the deformed shapes and the sensitivity of the numerical results to the finite element mesh discretization have been compared and analyzed. The obtained results show that both models have a very good agreement and represent very well the characteristic of the viscoplastic constitutive model. [ABSTRACT FROM AUTHOR]

The numerical simulation of contact problems is nowadays a standard procedure in many engineering applications. The contact constraints are usually formulated using either the Lagrange multiplier, the penalty approach or variants of both methodologies. The aim of this paper is to introduce a new scheme that is based on a space filling mesh in which the contacting bodies can move and interact. To be able to account for the contact constraints, the property of the medium, that imbeds the bodies coming into contact, has to change with respect to the movements of the bodies. Within this approach the medium will be formulated as an isotropic/anisotropic material with changing characteristics and directions. In this paper we will derive a new finite element formulation that is based on the above mentioned ideas. The formulation is presented for large deformation analysis and frictionless contact. [ABSTRACT FROM AUTHOR]

The fixture determines the workpiece position in a machining process; therefore, an increasing amount of attention has been given to fixture layout design. While machining, the workpiece position is affected by two major sources: (a) the locator displacement and (b) the force-deformation of the workpiece-fixture system. In the beginning of this paper, a geometric model considering the shape of a locator is developed to analyze the location performance, followed by the presentation of a simplified solving method and a location layout performance index. Second, to complete the force-deformation analysis, a finite element method-based force-deformation model is built and accelerated by a new method with a lower computer memory cost. Based on these two models, multiple objects of fixture layout optimization problems are proposed, and a multi-objective genetic algorithm-based optimization method is constructed. Finally, testing examples are approved to examine the validity of the method represented in this paper. These methods can provide a more accurate prediction of the locating performance in more widely used cases, and they have faster calculating speeds with lower computer memory costs. [ABSTRACT FROM AUTHOR]

The characteristics of temperature change on die and billet are very complex during the deformation process because of the interaction between them and some unstable external factors. In this paper, the numerical simulation model for the crank shaft die forging was established by means of the rigid-plastic FEM method. The model was validated by optical non-contact 3D measurement-ATOS. Based on available research results, this paper explored the effect of temperature conditions on material deformation and die wear. Three parameters, press velocity and initial temperature of billet and die, were chosen to illustrate the effects. From the experimental results, the effect of process parameters on deformation ability of the material is simple, while the effect on die wear is relatively complicated. The press velocity plays an important role on die wear when the initial temperature of the billet has larger influence on material deformation. A conclusion can be drawn that when the initial temperature of the billet is 1100 °C, the initial temperature of the die is 250 °C, and the velocity is kept in the range of 200-300 mm/s, the optimum solution for deformation ability of the material and die wear can be obtained. It is possible for the conclusion to be extended further for the control of temperature condition to optimize die life and material deformation. [ABSTRACT FROM AUTHOR]

In the present paper, a nonlinear analysis is presented for response prediction of a low-velocity eccentric impact between a functionally graded rectangular plate and a rigid sphere or a projectile with a spherical nose. Some of the novelties of the present paper are (i) considering the more general case of eccentric impact, (ii) investigating effects of the initial in-plane loads on the impact responses of the functionally graded plates, especially for compressive loads that are comparable but not equal to the buckling loads, (iii) using a contact law that incorporates influences of the transverse variations of the material properties of the substrate layers and the plate thickness, and (iv) using nonlinear strain-displacement relations instead of using the traditional infinitesimal deformations assumption for assessment of influences of the initial preloads. Due to using von Karman strain-displacement relations and a nonlinear contact law, the governing equations are highly nonlinear. For this reason, an iterative solution scheme is employed. A sensitivity analysis is performed to investigate influences of the specifications of the plate and the indenter, the eccentric value, and the in-plane preloads on the indentation and force time histories. Results reveal that due to the resulting increase in the contact force, slightly higher damages may be expected for impacted FGM plates subjected to initial compressive in-plane loads. [ABSTRACT FROM AUTHOR]

In this paper, a series of hot compression tests were carried out by using a Thermecamastor-Z thermomechanical simulator in the temperature range of 1020 ~ 1140 °C and a strain rate range of 0.01 ~ 1 s−1. The microstructure evolution mechanism for the GH4742 nickel-based superalloy during hot compression was studied using electron backscatter diffraction (EBSD) and scanning electron microscopy (SEM) techniques. Constitutive models for the γ + γ' double-phase and γ single-phase regions are established. The hot deformation activation energies for γ + γ' double-phase and γ single-phase microstructures are determined to be 828.996 kJ/mol and 230.707 kJ/mol, respectively. Furthermore, the internal relationship between the flow stress, hot processing map, and dynamic recrystallization (DRX) mechanism is analyzed. The results show that the high Z value is mainly located in the instability region, and the DRX mechanism is dominated by discontinuous dynamic recrystallization (DDRX), supplemented by continuous dynamic recrystallization (CDRX), particle-stimulated nucleation (PSN), and the strong pinning of γ' precipitates, which delays the development of DRX. At moderate Z values, the DRX mechanism involves the combined effect of DDRX and weak CDRX, PSN, and γ' precipitate pinning, while at low Z values, the DRX mechanism mainly involves DDRX. The transition for the DRX mechanism is extremely sensitive to the Z value. [ABSTRACT FROM AUTHOR]

Thin-walled parts are widely used in the aerospace industry, where the milling deformation of the parts caused by their thin-walled draping and extremely large size ratio characteristics as well as high material removal rate has been the most common quality issue that greatly affects the assembly performance and operation safety of aerospace equipment. Hence, effective management of milling deformation for a thin-walled part will significantly improve its quality, which, however, is still made difficult by the lack of a real-time deformation perception, optimization, and control method. To bridge this gap, a novel online optimal control method of milling deformation for thin-walled parts is proposed by incorporating digital twins into the milling process of thin-walled parts. To this end, a reference framework of the milling process digital twin (MPDT) for thin-walled parts are designed, where the autonomous operation logic of MPDT for online optimal control of milling deformation is further clarified. On that basis, three key enabling technologies of MPDT are introduced from the perspective of multidimensional high-fidelity MPDT modeling, knowledge-driven low-latency milling deformation simulation, and online optimal control of milling deformation, which provide an insight into the industrial implementation of MPDT. Eventually, a MPDT prototype system is implemented, where its application and evaluation results demonstrate the feasibility and effectiveness of the proposed approach. [ABSTRACT FROM AUTHOR]

Novel numerical methods, known as Meshless Methods or Meshfree Methods and, in a wider perspective, Partition of Unity Methods, promise to overcome most of disadvantages of the traditional finite element techniques. The absence of a mesh makes meshfree methods very attractive for those problems involving large deformations, moving boundaries and crack propagation. However, meshfree methods still have significant limitations that prevent their acceptance among researchers and engineers, namely the computational costs. This paper presents an in-depth analysis of computational techniques to speed-up the computation of the shape functions in the Reproducing Kernel Particle Method and Moving Least Squares, with particular focus on their bottlenecks, like the neighbour search, the inversion of the moment matrix and the assembly of the stiffness matrix. The paper presents numerous computational solutions aimed at a considerable reduction of the computational times: the use of kd-trees for the neighbour search, sparse indexing of the nodes-points connectivity and, most importantly, the explicit and vectorized inversion of the moment matrix without using loops and numerical routines. [ABSTRACT FROM AUTHOR]

In spite of the development of automated tolerance inspection systems for manufactured parts over the years, there are still processes that inevitably require manual intervention making full automation impossible in most cases; in particular when dealing with deformable parts. In most current industrial inspection systems, a deformable part under inspection must first be mechanically constrained on a rigid support or jig so as to be able to compare it with its nominal shape. This paper presents a new system to perform real-time surface inspection of deformable parts that does not require fixturing. Instead, the proposed system applies virtual forces to the part's CAD model as if the part was installed in the fixturing device. Normally, a precise finite element method (FEM) simulation should be used to approximate the deformation that appends when the part is installed in the device. Even with a fast parallel computer, FEM is far from being real-time and cannot be used for on-line inspection. In the proposed system, a radial basis function approximation of the FEM simulation is trained off-line and used to speed-up the simulation by an order of magnitude. Experimental evaluation of the proposed system is presented for three plastic parts. Using the proposed scheme, an approximation of 0.25 mm compared with the real deformation was obtained. In this paper, statistical results are presented such as the average deviation, standard deviation, and processing time between the approximations obtained with the proposed method and with the finite element method applied to the full CAD model. [ABSTRACT FROM AUTHOR]

The traditional contour method maps a single component of residual stress by cutting a body carefully in two and measuring the contour of the cut surface. The cut also exposes previously inaccessible regions of the body to residual stress measurement using a variety of other techniques, but the stresses have been changed by the relaxation after cutting. In this paper, it is shown that superposition of stresses measured post-cutting with results from the contour method analysis can determine the original (pre-cut) residual stresses. The general superposition theory using Bueckner's principle is developed and limitations are discussed. The procedure is experimentally demonstrated by determining the triaxial residual stress state on a cross section plane. The 2024-T351 aluminum alloy test specimen was a disk plastically indented to produce multiaxial residual stresses. After cutting the disk in half, the stresses on the cut surface of one half were determined with X-ray diffraction and with hole drilling on the other half. To determine the original residual stresses, the measured surface stresses were superimposed with the change stress calculated by the contour method. Within uncertainty, the results agreed with neutron diffraction measurements taken on an uncut disk. [ABSTRACT FROM AUTHOR]

A cavity optimization method based on the principle of reverse deformation was prompted in this paper. In the reverse deformation method, the displacement which represents the nonlinear shrinkage was superposed on the initial profile of cavity and compensated the shrinkage of wax and alloy solidification. Moreover, an estimation algorithm was prompted to calculate the displacement based on reverse engineering, and its key technologies such as blade measurement, model registration, and statistical analysis of the displacement were investigated. Finally, a sample application was presented for demonstration in this paper. [ABSTRACT FROM AUTHOR]

In order to simulate the magnesium alloy-forming processes accurately, it is necessary to consider the plastic anisotropy. In this paper, a new rate-independent constitutive model for polycrystalline plastic deformation by slip and twinning has been formulated, and then introduced into a FEM program. Metal flow is assumed to occur by crystallographic slip on given slip and twinning systems within each crystal. Each integration point represents a single crystal. Then uniaxial compression and cup drawing of Mg alloy are studied by using a rate-independent polycrystalline plasticity finite element analysis. In this paper, the ear distributions of the polycrystal are predicted for different typical initial orientation cases. The values of the twinning factors associated with slip system deformation are deduced. It is found that the twinning factors vary with the value of the stress. The basal slip and twinning system plays the dominant role in the deformation of magnesium alloy, which might be the most important contribution to strain hardening. [ABSTRACT FROM AUTHOR]