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• Effects of hard/soft Al 2 RE phases on damage behaviors of Mg alloys have been uncovered by using a CPFEM model. • Microscale damage mechanisms have been found by DIC tests and Al 2 RE quantifications using TEM and 3D XCT. • Crystal plasticity model based on dislocation density proves crack initiation at Al 2 RE phases. • CPFEM predicts stiffer Al 2 RE having better damage resistance than soft ones matching SEM fracture analysis. The influence of hard Al 2 RE phases (Sc , Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) on the overall and local deformation as well as damage mechanism of Mg alloys has been studied by using a crystal plasticity model based on dislocation density with a brittle damage criterion. Microcracks that lead to swift damage initiation and propagation throughout the matrix have been predicted. It has been found that the hard Al 2 RE with higher elastic modulus enhances the damage resistance of the Mg matrix, which was confirmed by fracture SEM/EDS characterizations and phase-field damage simulation. This discovery provides valuable insights for designing Mg alloys with both high stiffness and enhanced damage resistance. [Display omitted] [ABSTRACT FROM AUTHOR]

• Evident tension axis direction—[100] axis within single crystal superalloys along different crystallographic axes during EA tension. • Decreased strength anisotropy along the non-tensile axis direction with higher current density. • Increased stress drop and anisotropy under the current direction increasing from 0° to 45°. The electrically assisted (EA) deformation process has received considerable attention in recent years, accompanied by research on current-induced deformation mechanisms. However, there are still challenges in eliminating thermal effects, which have prevented a comprehensive understanding of the underlying current-induced mechanisms. Opting for a single crystal (SC) in research provides advantages in decoupling the nonthermal effect of electric current at smaller scales and eliminating the complex interactions that exist in polycrystalline materials. Therefore, the innovation of this work lies in decoupling the nonthermal effect of electric current and conducting a comprehensive analysis of anisotropic deformation and mechanisms within a Ni-based SC with different crystallographic axes and various current directions during electrically assisted tensile simulation. A significant tension axis direction in the SC during EA tension was induced by the combination of a higher current direction factor (| cos θ |) and a dimensionless factor for the current density (| J α / J 0 α |) along the [100] axis. The stress drop within the SC due to the nonthermal effect of electric current generally increased with increasing current direction. This was attributed to the increased dislocation density differences and decreased temperature. The increased stress anisotropy of the SC at a current direction of 45° was attributed to fewer activated (111) slip systems and the pinning effect of more dislocations within these systems. This study advances our understanding of the thermal and nonthermal effects of electric current and offers valuable insights for the informed application of EA deformations in industrial and aerospace settings with SC superalloys. [Display omitted] [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this study is to develop a new numerical algorithm to simulate the phase-field model. Design/methodology/approach: First, the derivative of the temporal direction is discretized by a second-order linearized finite difference scheme where it conserves the energy stability of the mathematical model. Then, the isogeometric collocation (IGC) method is used to approximate the derivative of spacial direction. The IGC procedure can be applied on irregular physical domains. The IGC method is constructed based upon the nonuniform rational B-splines (NURBS). Each curve and surface can be approximated by the NURBS. Also, a map will be defined to project the physical domain to a simple computational domain. In this procedure, the partial derivatives will be transformed to the new domain by the Jacobian and Hessian matrices. According to the mentioned procedure, the first- and second-order differential matrices are built. Furthermore, the pseudo-spectral algorithm is used to derive the first- and second-order nodal differential matrices. In the end, the Greville Abscissae points are used to the collocation method. Findings: In the numerical experiments, the efficiency and accuracy of the proposed method are assessed through two examples, demonstrating its performance on both rectangular and nonrectangular domains. Originality/value: This research work introduces the IGC method as a simulation technique for the phase-field crystal model. [ABSTRACT FROM AUTHOR]

For the two-mode phase field crystal models, the evolutions of the solutions and energy vary fast at certain time. To resolve varying time scales efficiently and reduce the computational cost, a variable-step BDF2 Fourier pseudo-spectral method is proposed. It is shown that the fully-discrete scheme is volume-conserving and unconditional energy-stable. Moreover, a robust error estimate is established by using the discrete orthogonal convolution kernels and the corresponding convolution inequalities. Numerical experiments by using the random and adaptive time-stepping strategies are presented to confirm the effectiveness of the scheme. [ABSTRACT FROM AUTHOR]

Refractory high-entropy alloys (RHEAs) are considered as potential candidates for high-temperature applications, with the glide resistance of edge dislocations being a crucial factor in determining the high-temperature strength. However, the solid-solution strengthening mechanism of edge dislocations in RHEAs is not fully understood. The existing Labusch-type models mainly focus on the long-range interaction of solute atoms with the dislocation stress field, while there is little attention paid to the short-range interaction in the dislocation core region. Here, we conduct carefully designed atomic simulations to decouple the long-range and short-range interactions in a typical RHEA, NbMoTaW. Furthermore, the total change in solute-dislocation interaction energy is decomposed, and a hierarchical energy landscape is revealed, demonstrating that the short-range interaction at the core region gains more importance in the solid-solution strengthening of edge dislocations in NbMoTaW. Then, we determine the Larkin length, which signifies the transition from size-dependent to size-independent dislocation behavior. The activation barrier extracted from the simulation with the dislocation length above the Larkin length is incorporated into the crystal plasticity model, and the high-temperature yield strength is well predicted by the strengthening from edge dislocations. Our work provides deep insight into the solid-solution strengthening mechanism in random solution solids, elucidating the importance of the local atomic configuration around the dislocation core. [ABSTRACT FROM AUTHOR]

Creep poses a significant threat to the integrity and longevity of structural components at high-temperature. The most current understanding of creep mainly focuses on the coupled dynamics of point defects and dislocation, which may well describe the first and second stage of creep. However, the behavior of the three stages of creep is jointly controlled by point defect (vacancy) diffusion, dislocation glide, dislocation climb, grain boundary (GB) sliding, and void evolution. A critical knowledge gap still exists regarding how these different creep mechanisms are simultaneously coupled during the three stages of creep. In this work, a multi-physical mechanisms-based crystal plasticity model is proposed to consider the concurrent evolution of point defect, dislocation, GB, and void based on a unified thermodynamic framework. In-situ scanning electron microscope creep experiments and macroscopic creep experiments of Ti-6Al-4V were conducted to validate our model. The in-situ creep experiment directly revealed the GB sliding creep failure behavior of Ti-6Al-4V for the first time. The proposed model well predicts both the microscopic and macroscopic experimental behavior of creep. The contribution of different microstructure evolutions is discussed, and a phase diagram of the dominated creep mechanism is obtained. An in-depth analysis was conducted on the coupling effects and microstructure characteristics of different creep mechanisms. This work not only deepens our understanding of the micro creep mechanism but also offers valuable insights for designing materials with specific microstructures to enhance their creep resistance. [ABSTRACT FROM AUTHOR]

In this paper, we consider the generalized Allen–Cahn-type phase-field crystal model with face-centered-cubic ordering structure (PFC-FCC). Due to the combined complexity of the eighth-order spatial derivative and inherent nonlinearity, it poses a significant challenge to design a numerical scheme of high accuracy, stability, and efficiency to solve the PFC-FCC model. Endeavoring towards this objective, we adopt operator splitting method to address the PFC-FCC model. Based on Fourier spectral method for spatial discretization and SSP-RK method for temporal discretization, we propose an effective and easy-to-implement second-order scheme. We are also able to proffer an analytical proof for discrete mass conservation, and engage a discussion on an optimal error estimate for the second-order scheme. In addition, the energy stability of the numerical scheme is derived. Ultimately, a series of numerical experiments specifically designed to substantiate its accuracy, efficiency, and capability for phase transition are performed. • We propose and analyze a second-order scheme for the PFC-FCC model. • We demonstrate the mass conservation, convergence and the energy stability. • Various numerical experiments are performed. [ABSTRACT FROM AUTHOR]

• The cold dwell behaviour of Ti6Al is analysed by a combination of digital image correlation, electron backscatter diffraction and dislocation based crystal plasticity simulations • Experiments and simulations are carried out between room temperature and 230°C to understand the worst case scenario for cold dwell and understand its physical origin • A data set of pairs of grains is analysed: some pairs of grains show the "rogue" and "non-rogue" behaviour respectively, while a novel behaviour called "non-typical rogue" is observed, in which a moderate load shedding takes place during cold dwell • The correlation between stress discontinuity at the grain boundary in "rogue" grain pairs and the distribution of geometrically necessary dislocations is analysed • The worst case scenario at 120°C is explained by the temperature dependence of the strain rate sensitivity of basal and prismatic slip systems, and the temperature dependence of the spread of geometrically necessary dislocations around the grain boundary Digital image correlation (DIC) and dislocation based crystal plasticity simulation were utilised to study cold dwell behaviour in a coarse grain Ti-6Al alloy at 3 different temperatures up to 230 °C. Strains extracted from large volume grains were measured during creep by DIC and were used to calibrate the crystal plasticity model. The values of critical resolved shear stresses (CRSS) of the two main slip systems (basal and prismatic) were determined as a function of temperature. Stress along paths across the boundaries of four grain pairs, three "rogue" grain pairs and one "non-rogue" grain pair, were determined at different temperatures. Large load shedding was observed in one of the "rogue" grain pairs, where a stress increment during the creep period was found in the "hard" grain. A minor load shedding mechanism was observed in two non-typical "rogue" grain pairs, in which the plastic deformation is nonuniform inside the grains and geometrically necessary dislocations accumulate in the centre of the grains. At elevated temperatures, 120 °C was found to be the worst case scenario as the stress difference at the grain boundaries of these four grain pairs was found to be the largest among the three temperatures analysed. The origin of this critical temperature is debated in the literature and it is investigated for the first time in the present work by analysing the simultaneous effects of the geometrically necessary dislocations (GND) and the strain rate sensitivity (SRS) of the slip systems. The analysis shows that the combined effects of the peak SRS of both prismatic and basal slip systems at 80 °C and of the increase of the spread of the GND distribution around the grain boundary at higher temperatures are the origin of the observed worst case scenario. [Display omitted] [ABSTRACT FROM AUTHOR]

The article discusses the work of Nobel laureate Frank Wilczek on time crystal, space-time crystal, or four-dimensional crystal, which is a periodic structure that repeats in time and space. Normal three-dimensional crystals have a repeating pattern in space but remain unchanged with respect to time; time crystals repeat themselves in time and space leading the crystal to change from moment to moment

Active materials hold substantial potential for self-sustaining motion, however, the dependency on movable light or extensive area illumination in current structures often restricts the design and practical deployment of such active machines. In this study, we report a novel zero-energy-mode, self-rolling unicycle equipped with a liquid crystal elastomer rod engine, which fueled by a fixed, small-area light source. By employing an elaborate dynamic model for liquid crystal elastomer, we derive the lateral curvature of the liquid crystal elastomer rod and the driving moment necessary for the unicycle's self-rolling. The study results demonstrate that the self-rolling of the unicycle is driven by a moment induced by the shift in the center of gravity of the curved liquid crystal elastomer rod. Our numerical simulations indicate the presence of a supercritical Hopf bifurcation point delineating the transition between the self-rolling mode and the static mode within the unicycle system. Additionally, the rolling velocity of the unicycle relies on a handful of key system parameters, notably including light intensity, light penetration depth, length of the liquid crystal elastomer rod, rolling friction coefficient, total mass of the unicycle, and wheel radius of the unicycle. The experimental validation of a self-rolling unicycle with zero-energy-mode has been conducted. The self-rolling unicycle constructed in this paper has excellent characteristics of simple structure, zero-energy-mode, horizontal constant light source, and small area light source, providing valuable insights for the utilization of photoresponsive liquid crystal elastomer rods in soft robotics, medical devices, energy harvesting systems, and actuators. • A light-fueled self-rolling unicycle with a liquid crystal elastomer rod engine is proposed. • The experiment confirmed the functionality of the light-powered self-rolling unicycle with an LCE rod engine. • The steady state solution of a self-rolling unicycle with zero energy mode is obtained. • The system parameters can affect the motion patterns and self-rolling velocity. [ABSTRACT FROM AUTHOR]

Self-sustained chaotic system based on active materials, where energy is absorbed directly from the environment to maintain one's own motion, furnishes an extensive scope of applications in energy harvesters, encrypted communication, bionic heart devices and other fields. This paper seeks to put forward a self-sustained chaotic pendulum system consisting of a liquid crystal elastomer fiber and a mass sphere under steady illumination. To investigate the self-sustained chaotic behavior of the pendulum system, we combine the dynamic liquid crystal elastomer model with principles of dynamics to establish the corresponding theoretical model of the system. Numerical results suggest that three typical motion modes, namely, static mode, self-sustained oscillation mode and self-sustained chaotic motion mode, are involved in the liquid crystal elastomer pendulum. The self-sustained motion is maintained by the work done by the contraction of the liquid crystal elastomer fiber with a light-blocking coating, which compensates for the energy dissipated by the damping. Furthermore, this study also explores the influences of five system parameters on the motion behavior of the LCE pendulum, and determines the key parameter values for the three distinct motion modes through detailed calculations and bifurcation diagrams. The present research findings demonstrate that introducing a new degree of freedom into the self-sustained periodic vibration system, it is possible to achieve self-sustained chaotic motion, providing significant insights into the development of self-sustained chaotic systems derived from active materials. [ABSTRACT FROM AUTHOR]

We have developed a parallel implementation of an Elasto-Viscoplastic Fast Fourier Transform-based (EVPFFT) micromechanical solver to enable computationally efficient crystal plasticity modeling for polycrystalline materials. Our primary focus lies in achieving performance portability, allowing a single EVPFFT implementation to run optimally on various homogeneous architectures, including multi-core Central Processing Units (CPUs), as well as on heterogeneous computer architectures comprising multi-core CPUs and Graphics Processing Units (GPUs) from different vendors. To accomplish this goal, we have leveraged MATAR, a C++ software library that simplifies the creation and utilization of multidimensional dense or sparse matrix and array data structures. These data structures are designed to be portable across diverse architectures through the use of Kokkos, a performance-portable library. Additionally, we have employed the Message Passing Interface (MPI) to efficiently distribute the computational workload among processors. The heFFTe (Highly Efficient FFT for Exascale) library is used to facilitate the performance portability of the fast Fourier transforms (FFTs) computation. The computational performance of EVPFFT is evaluated and presented in terms of parallel scalability and simulation runtime on different high-performance computing (HPC) architectures. The utility of the developed framework to efficiently simulate the micro-mechanical fields in polycrystalline microstructures in engineering applications is discussed. Program Title: EVPFFT CPC Library link to program files: https://doi.org/10.17632/2k8579fyyv.1 Developer's repository link: https://github.com/lanl/Fierro Licensing provisions: BSD 3-Clause License Programming language: C++ External routines/libraries: MPI, Kokkos, MATAR, HeFFTe, HDF5 Nature of problem: EVPFFT is a crystal plasticity code designed to compute micro-mechanical fields within a polycrystalline representative volume element (RVE) and predict the macroscale response of the RVE. Solution method: EVPFFT uses the periodic Green's function method in Fourier space to solve the field equations of static stress equilibrium in a periodic spatial domain. • MPI+X (where X can be CUDA, HIP, SYCL, OpenMP, or Pthreads) implementation of the EVPFFT model is developed. • Achieved performance portability on diverse computing architectures, including CPUs and GPUs. • Demonstrated parallel scalability across different representative volume element sizes using both multi-CPUs and multi-GPUs. • Future-proofed the EVPFFT program for evolving high-performance computing platforms. [ABSTRACT FROM AUTHOR]

• The double minimum creep is studied using the phase-field method coupled to a crystal plasticity model. • The deformation mechanism is explored from the point of evolutions of γ/γʹ microstructure and dislocation. • The changes of stress and strain at the slip system level are analyzed. • The dislocation annihilation in the intersections of γ channels plays a key role in local softening stage. The double minimum creep, characterized by two creep rate minima, in Co-based superalloy is investigated using a phase-field model coupled with a crystal plasticity model. The constitutive modeling, based on the dislocation slip theory considering dislocation interaction, is applied to simulate microstructural evolution and deformation behavior. Rafting process commences at the beginning of creep until the global minimum of creep rate is reached, demonstrating a strengthening effect from N-type rafts under compressive creep. The high shear strain rate of (111) [ 0 1 ¯ 1 ] slip system in the intersections of horizontal and vertical γ channels leads to a slight increase of creep rate after the first local minimum. The evolution of stress field shows that the softening effect is the combined effect of the increase of resolved shear stress and the decrease of hardening stress in the intersections. Further, these changes in stress are primarily caused by the dislocation annihilation and the inhomogeneous plastic deformation. This study indicates that the intermediate local softening stage during creep may be eliminated if the initial inter-distance between γʹ precipitates is decreased. [ABSTRACT FROM AUTHOR]

[Display omitted] • Highly deformable Mg-Zn-Ca alloy is synthesized via permanent casting and one-step hot extrusion. • Prismatic slip is promoted due to the significantly reduced ratio of slip resistances between prismatic and basal slip systems. • Zn and Ca solutes are found to strongly segregate at grain boundaries. • Co-segregation of Zn and Ca makes grain boundaries stronger. • Co-segregation of Zn and Ca makes grain boundaries tougher by mediating plasticity at grain boundaries during deformation. Low ductility and strength are major bottlenecks against Mg alloys' wide applications. In this work, we systematically design the composition and fabrication process for a low-alloyed Mg-Zn-Ca alloy, showing that it can be extruded at low temperatures (∼250 ℃) and high speeds (∼2 mm/s). After the extrusion, this alloy exhibits a substantially weakened basal texture, relatively small grain size, very high tensile elongation (∼30%), and good strength. The origin of the considerably improved ductility was studied using a combination of three-dimensional atom probe tomography (3D-APT), transmission electron microscopy (TEM), electron backscattered diffraction (EBSD) in conjunction with surface slip trace analysis, in-situ synchrotron X-ray diffraction, and elasto-plastic self-consistent (EPSC) modeling. Co-segregation of Zn and Ca atoms at a grain boundary is observed and associated with texture weakening and grain boundary mediated plasticity, both improving the ductility. While basal slip and prismatic slip are identified as the dominant deformation systems in the alloy, the ratio between their slip resistances is substantially reduced relative to pure Mg and most other Mg alloys, significantly contributing to the improved ductility of the alloy. This Mg-Zn-Ca alloy exhibiting excellent mechanical properties and low fabrication cost is a promising candidate for industrial productions. [ABSTRACT FROM AUTHOR]

A research study conducted at the Harbin Institute of Technology in China has developed a nucleation kinetics model for crystal growth in supercooled water. The model aims to design ice-templating soft matter scaffolds with programmable structure-property relationships. The study investigated the effects of diffusion coefficient and density of supercooled water on ice nucleation kinetics and crystal growth. The results showed excellent agreement with experimental data and provided a new methodology for understanding the nucleation kinetics and growth of ice crystals in supercooled water. The study has implications for designing ice-templating soft matter scaffolds. [Extracted from the article]

The article discusses the increasing popularity and affordability of large TVs, specifically 85-inch and 98-inch models. Sales of these TVs have skyrocketed, with companies like Hisense and Samsung struggling to meet the demand. The article suggests that these large TVs are now a viable alternative to projection-based systems, offering superior picture quality and catering to a broader range of interests. However, it also acknowledges that high-end projectors still have their place for movie enthusiasts. The article concludes by stating that the choice between a TV and a projector ultimately depends on individual preferences and the desired viewing experience. [Extracted from the article]

Refractory high entropy alloys (RHEAs) have drawn growing attention due to their remarkable strength retention at high temperatures. Understanding dislocation mobility is vital for optimizing high-temperature properties and ambient temperature ductility of RHEAs. Nevertheless, fundamental questions persist regarding the variability of dislocation motion in the rugged energy landscape and the effective activation barrier for specific mechanisms, such as kink-pair nucleation and kink migration. Here we perform systematic atomistic simulations and conduct statistical analysis to obtain the effective activation barriers for the mechanisms underlying various types of dislocation motion in a typical RHEA, NbMoTaW. Moreover, a stochastic line tension model is developed to calculate the activation barrier with substantially reduced computational costs. By incorporating the effective activation barriers into the crystal plasticity model, a multiscale simulation framework for predicting the mechanical properties of RHEAs is established. The ambient temperature yield strength of NbMoTaW is well-predicted by the kink-pair nucleation mechanism of screw dislocations, while the strengthening originating from screw dislocations does not predominate at high temperatures. Our work provides a robust foundation for atomistic studies of effective dislocation behaviors in random solution solids, elucidating the intricate relationship between microscopic mechanisms and macroscopic properties. [ABSTRACT FROM AUTHOR]

• An optimization procedure for the compaction of crystallographic texture data is developed. • The procedure is based on the spectral representation of orientation distributions using generalized spherical harmonics basis. • Gradient vector and Hessian matrix are derived analytically and implemented to facilitate a rapid convergence of the procedure in Matlab. • Case studies involving metals with cubic, hexagonal, and orthorhombic crystal structures demonstrated utility of the procedure. • The procedure is an essential tool for compacting input texture data in metal forming process simulations with crystal plasticity. An orientation distribution is a necessary input in any crystal plasticity simulation. The computational time involved in crystal plasticity simulations scales linearly with the number of crystal orientations in the input distributions. Reducing the number of crystal orientations in representing the input orientation distributions quantitatively is a critical and necessary requirement for performing computationally efficient crystal plasticity simulations of deformation processes. A procedure for the compaction of orientation distribution functions (ODFs) relying on a spectral representation using series of generalized spherical harmonics (GSH) basis functions was recently developed. Linear fitting of the spectral representation of an ODF containing a compact set of weighted orientations towards a full-size ODF containing many crystal orientations was in the core of the procedure. This paper advances the compaction procedure by replacing the linear with a nonlinear optimization in Matlab for which a suitably defined error, gradient, and Hessian matrix are derived to allow for more efficient, accurate, and greater compactions. The utility of the new procedure is to allow for not only fitting the weights of a compacted set of orientations but to allow for optimizing weighted orientations or a combination of optimizing weights and orientations. The new compaction procedure has been successfully applied to compactions of large ODFs of cubic, hexagonal, and orthorhombic polycrystalline metals. In doing so, the evolution of texture, twinning, and stress-strain are predicted at large plastic strains with compact ODFs to agree with the corresponding full size ODFs using crystal plasticity models. In closing, guidance for effective texture compaction trading off the accuracy and computational gains are provided. [ABSTRACT FROM AUTHOR]

We examine a reduced membrane model of liquid crystal polymer networks (LCNs) via asymptotics and computation. This model requires solving a minimization problem for a non-convex stretching energy. We show a formal asymptotic derivation of the 2 D membrane model from 3 D rubber elasticity. We construct approximate solutions with point defects. We design a finite element method with regularization, and propose a nonlinear gradient flow with Newton inner iteration to solve the non-convex discrete minimization problem. We present numerical simulations of practical interests to illustrate the ability of the model and our method to capture rich physical phenomena. [ABSTRACT FROM AUTHOR]

Former model Crystal McKinney alleges Combs drugged and sexually assaulted her at his New York studio in 2003. [ABSTRACT FROM AUTHOR]

Thermally-induced cracking typically occurs during the cooling stage of various manufacturing processes, and is commonly seen in multiphase or the joints of dissimilar materials due to mismatch in their thermo-mechanical properties, such as thermal expansion, elastic-plastic deformation and, in some cases, phase transformation. However, the underlying cracking mechanism associated with local microstructure is still elusive. To improve the mechanistic understanding of thermal cracking, this work uses the diffusion-bonded 9Cr-1Mo steel as an example to study the key microstructural variables, such as interfacial phases, voids, grain boundary migration and crystallographic orientations. Meanwhile, a temperature-dependent crystal plasticity model coupled with a cohesive zone model is developed to provide more insights into the thermal-induced stress distribution at the grain scale. It is found that the stress at the void-free boundary of martensite and ferrite is dominated by shear, and its magnitude is insufficient to nucleate cracks. Whereas voids at phase boundaries can induce significant tensile stress, resulting in cracking at the phase boundaries as well as diffusion-bonded interfaces. Also, the occurrence of interfacial grain boundary migration plays an important role in local stress distribution. These microstructure features and their evolution are experimentally observed and used to verify the developed crystal plasticity models. These findings enhance the understanding of the influence of microstructure features on thermal cracking and provide a guide to designing and fabricating the microstructure with improved thermal crack resistance in various manufacturing processes. [ABSTRACT FROM AUTHOR]

In this paper, we propose and analyze an efficient numerical method for the anisotropic phase field dendritic crystal growth model, which is challenging because we are facing the nonlinear coupling and anisotropic coefficient in the model. The proposed method is a two-step scheme. In the first step, an intermediate solution is computed by using BDF schemes of order up to three for both the phase-field and heat equations. In the second step the intermediate solution is stabilized by multiplying an auxiliary variable. The key of the second step is to stabilize the overall scheme while maintaining the convergence order of the stabilized solution. In order to overcome the difficulty caused by the gradient-dependent anisotropic coefficient and the nonlinear terms, some stabilization terms are added to the BDF schemes in the first step. The second step makes use of a generalized auxiliary variable approach with relaxation. The Fourier spectral method is applied for the spatial discretization. Our analysis shows that the proposed scheme is unconditionally stable and has accuracy in time up to third order. We also provide a sophisticated implementation showing that the computational complexity of our schemes is equivalent to solving two linear equations and some algebraic equations. To the best of our knowledge, this is the cheapest unconditionally stable schemes reported in the literature. Some numerical examples are given to verify the efficiency of the proposed method. [ABSTRACT FROM AUTHOR]

In this study, we present an efficient, fast, and fully explicit adaptive numerical scheme for solving a recently developed novel phase-field model of crystal growth in both two-dimensional (2D) and three-dimensional (3D) spaces. The novel phase-field model employed in this research incorporates a term specifically designed to eliminate the artificial curvature effect, thereby facilitating accelerated evolution when compared to traditional models. This enhancement significantly enhances the efficiency and speed of the simulation, leading to more expedited results. The crystal growth model employed in this study incorporates a phase-field equation to accurately represent the crystal interface, in addition to a heat equation that effectively models the distribution of temperature. To effectively solve the phase-field equation, we employ an adaptive numerical algorithm that optimizes the computational process. Our numerical scheme, specifically tailored for simulating dendritic growth, incorporates an adaptive narrow-band domain approach to accurately resolve the interfacial transition layer of the phase field. Furthermore, we enhance computational efficiency by implementing a double-sized grid for the temperature distribution, further improving the overall efficiency of the model. By combining these strategies, we achieve accurate and efficient solutions for the dendritic growth model. To validate the accuracy and efficiency of our proposed adaptive numerical method for solving the phase-field equation of dendritic growth, we conduct a series of numerical experiments in both 2D and 3D spaces. In these experiments, we assess the performance of our algorithm, analyzing its ability to accurately capture the intricate dynamics of dendritic growth while maintaining computational efficiency. By thoroughly evaluating the results obtained from these experiments, we provide strong evidence supporting the reliability and effectiveness of our adaptive numerical algorithm. • A fast adaptive numerical method for a novel phase-field model of crystal growth. • We apply a crystal growth model without artificial curvature term. • We propose a buffer parameter based on the interfacial thickness. [ABSTRACT FROM AUTHOR]

Density change is ubiquitous in phase transformation, and it can induce melt convection which strongly influences the crystal growth. Here, an anisotropic lattice Boltzmann-phase-field method was extended to predict the dendritic growth under the shrinkage or expansion melt convection by density change induced. A novel LB equation with an anisotropic coefficient was constructed to model the advancement of ordering parameter, coupling with the passive scalar LB equation for convective and diffusive heat transfer during phase transition. We studied dendritic growth and shape selection with melt convection induced by density change in crystal growth. Results show that the melt convection induced by density change affects strongly the dendritic growth. The shrinkage flow results in a higher tip velocity while the expansion flow leads to a slower one. Predicted Péclet number with respect to the relative density change was compared with an analytical solution. Moreover, the modified selection parameter has been verified by numerical simulations. [ABSTRACT FROM AUTHOR]

The low-cost nature of NB-IoT modems encourages them to deploy uncompensated crystal oscillators (XOs) as frequency references. The frequency offset of an uncompensated XO, however, makes network acquisition inefficient under low network coverage. In the worst case, the bulk of an NB-IoT modem’s power is consumed in network acquisition. This work demonstrates a discrete frequency synthesizer prototype that employs its phase-locked loop to compensate for the frequency offset of its reference XO. We propose an accurate crystal model and a compensation logic that are suitable for 32-bit microprocessors, commonly available in NB-IoT modems. Alternatively, when synthesized in a commercial 65-nm process in 24-bit precision, the proposed compensation logic is simulated to require a total area of 0.029 mm2 and power of 290 nW at a refresh rate of 1.4 kHz. Moreover, the XO model requires only 0.16 kB of RAM. The prototype achieves a compensation error level of down to 27 ppb ($3\sigma $) over the temperature range from −40 to 85 °C. The dominant error sources of the prototype are discussed in detail. In addition, we show that an NB-IoT modem can use the information acquired from sequential network acquisitions to compose and update its XO model in the field. This support for field calibration removes the need for XO characterization in production and ensures the validity of the model over the NB-IoT modem’s lifespan. The prototype achieves a compensation error level of down to 50 ppb ($3\sigma $) in an emulated in-field calibration test, sufficient to ensure energy-efficient low-latency network acquisition under low network coverage. [ABSTRACT FROM AUTHOR]

A crystal plasticity model is developed to predict the cyclic plasticity during the low-cycle fatigue of GH4169 superalloy. Accumulated plastic slip and energy dissipation as fatigue indicator parameters (FIPs) are used to predict fatigue crack initiation and the fatigue life until failure. Results show that fatigue damage is most likely to initiate at triple points and grain boundaries where severe plastic slip and energy dissipation are present. The predicted fatigue life until failure is within the scatter band of factor 2 when compared with experimental data for the total strain amplitudes ranging from 0.8% to 2.4%. Microscopically, the adjacent grain arrangements and their interactions account for the stress concentration. In addition, different sets of grain orientations with the same total grain numbers of 150 were generated using the present model. Results show that different sets have significant influence on the distribution of stresses between each individual grain at the meso-scale, although little effect is found on the macroscopic length-scale. [ABSTRACT FROM AUTHOR]

A recent study from the Chinese Academy of Sciences in Shenzhen, People's Republic of China, explores the challenges of preparing large-sized and high-quality single crystals for various technological applications. The researchers emphasize the importance of theoretical models in crystal growth research and propose future research directions to overcome the difficulties in crystal preparation. They suggest that utilizing artificial intelligence technology, establishing cross-scale simulation methods, and accurately calculating interface positions may be key factors in promoting the development of large-sized crystal preparation. The study concludes that an accurate cross-scale model is crucial for effective information transmission. [Extracted from the article]

RHEED_DIFF_2D is an open-source software capable of performing qualitative numerical simulations of changes to the intensity of RHEED oscillations in the function of the layer deposited, employing various models of scattering crystal potential for heteroepitaxial structures of bcc (001) films nucleated on a fcc (001) surface, including the possible existence of various diffuse scattering models through the layer parallel to the surface. This model can be used for interpreting data weakly dependent on the azimuth of the incident electron beam direction and for 2D monolayer-by-monolayer growth modes. The program does not use any external data sources. Program title: RHEED_DIFF_2D CPC Library link to program files: https://doi.org/10.17632/83ht2kc8xt.1 Licensing provisions: GNU General Public License 3 Programming language used: C++ Journal reference of previous version: Computer Physics Communications 185 (2014) 3001–3009 Does the new version supersede the previous version?: No. It is a supplement to the previous version. [ABSTRACT FROM AUTHOR]

In this paper, we derive a new phase field crystal model based on the L 2 -gradient flow approach, where the total mass of atoms is conserved through a nonlocal Lagrange multiplier. We develop a second-order, unconditionally energy stable scheme by combining the IEQ approach with the stabilization technique, where two extra stabilization terms are added to enhance the stability and keep the required accuracy while using large time steps. The unconditional energy stability of the algorithm is proved rigorously. Through the comparisons with the classical H − 1 -gradient flow based phase field crystal model and several other type numerical schemes for simulating some benchmark numerical examples in 2D and 3D, we demonstrate the robustness of the new model, as well as the stability and the accuracy of the developed scheme, numerically. [ABSTRACT FROM AUTHOR]

The paper explores plastic deformation mechanisms in metal–graphene nanocomposites, illustrating their material strengthening effects through a crystal plasticity finite element (CPFE) model. This model is compared with published experimental results, which have previously shown that the two-dimensional shape of graphene effectively controls dislocation motion and significantly enhances the strength of metals. Simulated nanopillar compression tests, using a physics-based CP model that incorporates surface nucleation and single-arm source dislocation mechanisms, help us understand dislocation motions at submicron length scales. The crystal plasticity models are applied to nanolayered composites with copper grain layers and monolayer graphene, featuring repeat layer spacings of 200 nm, 125 nm, and 70 nm, respectively. This study quantifies the accumulation of dislocations at the graphene interfaces, contributing to the ultra-high strength of copper–graphene composites. Moreover, a Hall–Petch-like correlation is established between yield strength and the number of embedded graphene layers. [Display omitted] • Integrating crystal plasticity with submicron dislocation mechanisms. • Establishing a Hall–Petch-like correlation with Gr layer count and yield strength. • Analyzing dislocation density evolution in Cu–Gr composites and Cu polycrystals. • Investigating the interfacial mechanical behavior of Cu–graphene composites. • Linking graphene's nonlinear elasticity to dislocation patterns in Cu grains. [ABSTRACT FROM AUTHOR]

In the simulation of microstructural evolutions, detailed priori knowledge for the model parameters and initial states is difficult to be observed by experiments. For an improved simulation, we present a data assimilation framework for the phase field crystal model with the effect of stochastic noise. A sequential data assimilation method based on the ensemble Kalman filter is applied to integrate phase field simulation and observational data from experiments. Furthermore, we couple the present framework with a second-order accurate unconditional-energy stable scheme, and thus the issue of stability restriction can be avoided. A series of twin experiments are performed to demonstrate the performance of our present framework. The results reveal that our framework can successfully improve the simulation accuracy, even when some parameters are uncertain and the initial value significantly deviates from the observed situation. • We establish a novel data assimilation framework for the phase field crystal model. • We propose a second-order accurate unconditional-energy stable scheme. • The method improve the simulation with uncertain parameters and initial condition. [ABSTRACT FROM AUTHOR]

Our news reporters obtained a quote from the research from Ufa State Petroleum Technological University: "The paper considers nematic liquid crystals of the class of two ringed ethers with different terminal groups. Keywords: Biosensors; Biotechnology; Nanotechnology EN Biosensors Biotechnology Nanotechnology 274 274 1 10/09/23 20231012 NES 231012 2023 OCT 12 (NewsRx) -- By a News Reporter-Staff News Editor at Blood Weekly -- New study results on biosensors have been published. [Extracted from the article]

Jiangsu, People's Republic of China, Asia, Chemicals and Chemistry, Crystal Growth, Health and Medicine, Phosphorus Keywords: Jiangsu; People's Republic of China; Asia; Chemicals and Chemistry; Crystal Growth; Health and Medicine; Phosphorus EN Jiangsu People's Republic of China Asia Chemicals and Chemistry Crystal Growth Health and Medicine Phosphorus 4616 4616 1 08/21/23 20230825 NES 230825 2023 AUG 25 (NewsRx) -- By a News Reporter-Staff News Editor at Health & Medicine Week -- Research findings on Chemicals and Chemistry are discussed in a new report. [Extracted from the article]

Keywords: Nanjing; People's Republic of China; Asia; Crystal Growth; Health and Medicine; Mathematics; Numerical Modeling EN Nanjing People's Republic of China Asia Crystal Growth Health and Medicine Mathematics Numerical Modeling 6336 6336 1 08/07/23 20230811 NES 230811 2023 AUG 11 (NewsRx) -- By a News Reporter-Staff News Editor at Health & Medicine Week -- Fresh data on Mathematics are presented in a new report. In this model, a flow field solver and a concentration field solver are coupled with the phase field equation to study faceted crystal growth with fluid convection and solute transfer.". [Extracted from the article]

Victorinox watches are designed, developed, tested and manufactured by Victorinox in its own factory, making the brand unique and soon will pursuing the integration further with upcoming lines. It's scratch-resistant and has anti-reflective sapphire crystal, is water-resistant to 200m and has a uni-directional rotating bezel with inlay in aluminium on quartz models and ceramic on automatic models. [Extracted from the article]

Liquid crystal elastomers (LCEs) are a class of active polymers of increasing interest, because of their excellent actuation performances. To quantify the actuation performances and understand the thermomechanical behavior, many theoretical models were developed, mainly based on the free energy framework with uniaxial order tensor, which, however, cannot well capture the biaxial liquid crystal alignment under biaxial stretching or shearing. The LCE with the shape memory cycle effect exhibits an evident loading-history dependence of the thermomechanical process, which cannot be described without introducing the evolution condition of the alignment. In this work, a constitutive model of LCE is established by introducing a triaxial order tensor to describe the complex alignment under uniaxial/biaxial loading conditions. Inspired by the classical theory of plasticity, an equivalent order parameter is proposed to characterize the order degree of the alignment, and its evolution condition is introduced to specify the condition of the alignment evolution. Experiments of LCE under a variety of thermomechanical loading conditions were carried out to validate the developed model, showing the capability of the model in capturing complex thermomechanical responses of the polydomain LCE with shape memory cycle effect under uniaxial/biaxial stretching. Furthermore, the constitutive model can be extended to predict nonlinear stress-strain curves and actuation performances of LCE lattices, which hold promising potential for applications in soft actuators and flexible robots. [ABSTRACT FROM AUTHOR]

In this paper, a generalized Allen–Cahn-type phase-field crystal model with face-centered-cubic ordering structure is presented. By introducing a space-time dependent Lagrange multiplier, the mass conservation is enforced and the local effect can be reflected. Moreover, the proposed model is lower-order in space and will be more efficient for numerical computation. For the simulation of crystallization, the main challenge is to design practical and stable algorithm which meanwhile guarantees the high-order accuracy. To resolve this problem, we propose a temporally high-order (up to third-order) accurate and linear multi-stage scheme based on implicit-explicit Runge–Kutta approach. The nonlinear term is explicitly treated and the appropriate stabilizer is added to balance the stiffness. By utilizing the Fourier spectral method in space, the numerical calculation is easy to implement. We analytically proved the discrete mass conservation property based on the fully discrete scheme. Extensive numerical experiments are performed to validate the accuracy, efficiency, and capability for phase transition. The effects of parameters and local interaction are investigated in detail. To facilitate the interested readers, we provide MATLAB codes of our proposed method in Appendix A. • Generalized AC-type PFC model with FCC ordering is proposed. • High-order time-accurate linear algorithm is developed. • The discrete mass conservation law is strictly satisfied. • Effects of parameter and local multiplier are investigated. [ABSTRACT FROM AUTHOR]

The motion of dislocations governs the plastic deformation of crystalline materials, which in turn determines the mechanical properties. The complex thermal history, large temperature gradients and high cooling rates during the process of additive manufacturing (AM) can induce high dislocation density and unique dislocation structures in the material. The origin of these dislocation structures and their stability during mechanical loading are debated. A novel temperature dependent continuum dislocation dynamics (CDD) model is developed, in which four state variables are used for each slip system representing the total dislocation density, edge and screw geometrically necessary dislocation densities and dislocation curvature. The CDD model is fully coupled with a crystal plasticity solver, which captures the plastic deformation induced by the dislocation motion. A hybrid continuous and discontinuous Galerkin formulation is developed to accurately reproduce the dynamics of highly discontinuous dislocation density fields that are typical of dislocation structures. A multiscale modeling approach is used, in which the thermally induced deformation in specific grains of a polycrystal is extracted from larger scale crystal plasticity simulations of the laser powder-bed fusion process, and is then used for single crystal scale dislocation dynamics simulations. Simulation results reveal the dynamics of dislocation structure formation in grains at different positions during laser scanning and cooling stages. The effect of the cyclic thermal stress during multi-layer AM fabrication is also investigated. The simulations provide a new perspective on the specific conditions that should be satisfied during AM process for the formation of stable dislocation structures. [Display omitted] • A CDD model is developed and coupled with a crystal plasticity framework. • A multiscale approach is proposed to simulate the dislocation evolution in AM process. • Thermal stress effect on dislocation structure formation in AM process is revealed. • Significant effect of annihilation on dislocation structure is presented. • Factors affecting dislocation evolution in cyclic thermal loading of AM are reported. [ABSTRACT FROM AUTHOR]

Chemistry, Drug Development, Drug Molecules, Drugs and Therapies, Health and Medicine, Physics, Thermodynamics, University of Utah Keywords: Chemistry; Drug Development; Drug Molecules; Drugs and Therapies; Health and Medicine; Physics; Thermodynamics; University of Utah EN Chemistry Drug Development Drug Molecules Drugs and Therapies Health and Medicine Physics Thermodynamics University of Utah 118 118 1 03/24/23 20230217 NES 230217 2023 FEB 17 (NewsRx) -- By a News Reporter-Staff News Editor at Drug Week -- Michael Grunwald, Ryan Looper and Rodrigo Noriega, of the University of Utah Department of Chemistry, received a $1 million grant from the W.M. Keck Foundation funding studies of currently unpredictable aspects of the process of crystallization. "With our research on how drug molecules crystallize, we hope to really speed things up, so that new antibiotics or antivirals drugs can reach patients more quickly and cheaply.". [Extracted from the article]

A fast, accurate, and stable numerical algorithm is proposed to solve the anisotropic phase-field dendritic crystal growth model. The algorithm combines the first-order direction splitting method and the linear stabilization technique, which preserve the energy stability while ensuring fast computing. The related stability analysis is shown. To obtain high accurate solution, the solution of first-order direction splitting method is extrapolated to be fourth-order, and the fourth-order difference method is applied to spatial discretization. To further improve the stability and prevent the blow-up of numerical solution, two post-processing methods, the bound preserving least-distance modification and the cut-off approach, are developed to control the boundedness of numerical solution, and their theoretical proofs are given. The proposed novel algorithm can be performed in parallel in each time step, significantly improving computing efficiency. Several numerical examples demonstrate the effectiveness of the proposed algorithm, including convergence and stability tests, the effectiveness of two post-processing techniques, and a series of 2D and 3D dendritic crystal growth simulations. • Direction splitting method for simulating anisotropic dendritic crystal growth. • Stabilizing and post-processing for the boundedness control of numerical solution. • The method has the advantages of accuracy, stability, and speed. • Theoretical analyses and numerical simulations are carried out. [ABSTRACT FROM AUTHOR]

Plastic deformation of metals involves the complex evolution of dislocations forming strongly connected dislocation networks. These dislocation networks are based on dislocation reactions, which can form junctions during the interactions of different slip systems. Extracting the fundamentals of the network behaviour during plastic deformation by adequate physically based theories is essential for crystal plasticity models. In this work, we demonstrate how knowledge from discrete dislocation dynamics simulations to continuum-based formulations can be transferred by applying a physically based dislocation network evolution theory. By using data-driven methods, we validate a slip system dependent rate formulation of network evolution. We analyse different discrete dislocation dynamics simulation data sets of face-centred cubic single-crystals in high symmetric and non-high symmetric orientations under uniaxial tensile loading. Here, we focus on the reaction evolution during stage II plastic deformation. Our physically based model for network evolution depends on the plastic shear rate and the dislocation travel distance described by the dislocation density. We reveal a dependence of the reaction kinetics on the crystal orientation and the activity of the interacting slip systems, which can be described by the Schmid factor. It has been found, that the generation of new reaction density is mainly driven by active slip systems. However, the deposition of generated reaction density is not necessarily dependent on the slip system activity of the considered slip system, i.e. we observe a deposition of reaction density on inactive slip systems especially for glissile and coplanar reactions. [ABSTRACT FROM AUTHOR]

The low-cycle fatigue of strongly-textured Mg alloys is dominated mainly by an alternation of twinning-detwinning process, which poses a great challenge to conventional constitutive models. As a result, a good reproduction of both mechanical response and deformation behavior often fails in previous simulations, in particular for high strain amplitudes. In the present study, the numerical simulations of low-cycle fatigue behavior of an Mg AZ31 plate with a ± 2% axial strain amplitude along the rolling direction were conducted, using a modified crystal-plasticity based on the finite strain elastic-viscoplastic self-consistent model containing twinning and detwinning mechanisms (EVPSC-TDT), and the results were compared with the mechanical response and deformation behavior determined by a real-time in-situ neutron diffraction. The simulations well predict the hysteresis loops and cyclic-hardening responses throughout the whole fatigue life (80 cycles), along with the evolution of the maximum twin volume fraction and residual twins. For the first time, the evolution of lattice strain throughout the whole fatigue life was calculated, and the results are in good accordance with that determined by neutron diffraction. The present study strongly demonstrates that the EVPSC-TDT model is very effective for modeling the low-cycle fatigue behavior of Mg alloys. More details about the evolution of the maximum twin volume fraction with fatigue cycles are found, an increase from 1st to 2nd cycle, followed by a decrease from 2nd to 20th cycle and a secondary increase after 20th cycle. This finding corrects the previous opinion that the maximum twin volume fraction increases at the initial stage and tends to be saturated at the late stage. Combining the results of simulations and neutron diffractions, the corresponding reasons are explained. Afterward, the mechanisms of the cyclic-hardening behavior at tension stage and compression stage are revisited, and some new insights are provided. [Display omitted] [ABSTRACT FROM AUTHOR]

• Generalized constitutive relations that incorporate the thermally activated and drag mechanisms. • Continuum description of crystal plasticity framework combined with the geometrically necessary dislocation densities and the mobile/immobile statistically stored dislocation densities. • Computation of the geometrically necessary dislocation densities based on the L 1 -norm minimization scheme to provide physical interpretation of the lower bound on overall GND population. • Dislocation mechanisms depending on generation, annihilation, interactions, trapping, and recovery. • Evolution laws of dislocation densities with mechanism-based material parameters. A new nonlocal crystal plasticity model is developed to study the mechanical behavior of face-centered cubic single crystals under heterogeneous inelastic deformation through a crystal plasticity finite element method. The main feature of this work is generalized constitutive relations that incorporate the thermally activated and drag mechanisms to cover different kinetics of viscoplastic flow in metals at a variety of ranges of stresses and strain rates. The constitutive laws are founded upon integrating continuum description of crystal plasticity framework with dislocation densities which is relevant to the geometrically necessary dislocation densities and the statistically stored dislocation densities. The model describes the plastic flow and the yielding of face-centered cubic single-crystal employing evolution laws of dislocation densities with mechanism-based material parameters passed from experiments or small-scale computational models. The geometrically necessary dislocation densities evolve on account of the curl of the plastic deformation gradient where its associated closure failure of the Burgers circuit exists. A minimization scheme termed L 1 -norm is utilized to secure the physical values of the geometrically necessary dislocation densities on slip systems. The evolution equations of statistically stored dislocation densities describe the complex interactions between two distinct dislocation populations, mobile, and immobile statistically stored dislocation dislocations, relying on generation, annihilation, interactions, trapping, and recovery. The experiments of a micropillar compression for the copper single crystal are compared to the computational results obtained using the formulation. The physics-based model clarifies the complex microstructural evolution of dislocation densities in metals and alloys, allowing for more accurate prediction. [Display omitted]. [ABSTRACT FROM AUTHOR]

We introduce a dislocation density tensor and derive its kinematic evolution law from a phase field description of crystal deformations in three dimensions. The phase field crystal (PFC) model is used to define the lattice distortion, including topological singularities, and the associated configurational stresses. We derive an exact expression for the velocity of dislocation line determined by the phase field evolution, and show that dislocation motion in the PFC is driven by a Peach–Koehler force. As is well known from earlier PFC model studies, the configurational stress is not divergence free for a general field configuration. Therefore, we also present a method (PFCMEq) to constrain the diffusive dynamics to mechanical equilibrium by adding an independent and integrable distortion so that the total resulting stress is divergence free. In the PFCMEq model, the far-field stress agrees very well with the predictions from continuum elasticity, while the near-field stress around the dislocation core is regularized by the smooth nature of the phase-field. We apply this framework to study the rate of shrinkage of an dislocation loop seeded in its glide plane. [ABSTRACT FROM AUTHOR]

Upon increasing strain rate a switch operates in tantalum response from a plasticity dominated regime to a twinning dominated regime. This transition is investigated by means of a polyphase crystal plasticity model which combines a Phase Field-Reaction Pathway formalism and a dislocation-based crystal plasticity model. The proposed formalism for twinning considers an unbounded number of variants which permits the observation of twinning, detwinning and retwinning phenomena. The crystal plasticity model takes into account slip systems interactions and includes two glide regimes to deal with high strain rates. A model for dislocation inheritance during twinning is proposed. Simulations highlight a dual role of plasticity: strain hardening inside the matrix may, under certain conditions, hinder the formation of twin variants whereas plasticity inside the variants further relaxes the residual stress due to twins interaction and contributes to shape the variant. [ABSTRACT FROM AUTHOR]

The purpose of the current work is the formulation of finite-deformation phase-field microelasticity (FDPFM) and its application to the modeling of (i) the dislocation core and (ii) dislocation interaction/reaction on intersecting glide planes in fcc crystals. The corresponding model formulation is carried out in the context of continuum thermodynamics; for simplicity, isothermal, quasi-static conditions are assumed. The resulting model rests in particular on generalized Ginzburg–Landau relations for dislocation slip-line phase field evolution depending on the Peach-Koehler (PK) force. Restricting attention to (periodic) bulk single crystal behavior, the algorithmic formulation and numerical implementation of FDPFM employs Green function, spectral, and Fourier methods generalized to geometric non-linearity. More specifically, algorithms for control of either the mean deformation gradient, or the mean Cauchy stress (i.e., PK force control) are developed. As in "standard" linear PFM, the free energy model in FDPFM is based on elastic, crystal and gradient contributions. In order to model dislocation interaction and reactions on multiple intersecting glide planes, the "standard" 2D stacking-fault-energy-based PFM crystal energy is generalized here to 3D crystallographic form for dissociation, partial fcc dislocations and stacking fault formation. Comparison of FDPFM and atomistic (MS) simulation results for higher-order local continuous and discrete deformation measures (e.g., dislocation tensor) in the core of a dissociated edge dislocation in Au show generally good agreement. In addition, results from FDPFM and MS are compared for dislocation reactions in Al on two intersecting glide planes. In the case of collinear reaction, for example, good qualitative agreement with MS results is obtained only when the dislocation slip on multiple glide planes is energetically coupled in the crystal energy. [ABSTRACT FROM AUTHOR]

A new finite strain thermomechanical model for the high-rate deformation of the β-polymorph of cyclotetramethylene tetranitramine (β-HMX) has been developed and applied to simulations of plate impact experiments. The crystal plasticity model is based on a model developed previously for RDX (Luscher et al. 2017), which is extended to incorporate deformation twinning. Twinning during normal plate impacts is simulated with a phase-field twin model. First, material parameters governing the kinetics of dislocation slip are calibrated on the subset of simulations which had negative Schmid factors for the twin system. Second, a parametric study of the twin material parameters was performed to find suitable values. The results of the simulations with the phase-field twinning model are reported for impacts on several crystal orientations. We find that the twin growth decreases with increasing distance from the impact surface because of dissipation of the shock front via dislocation-mediated plasticity, and that the simulated interface velocity with and without phase-field twinning do not show appreciable differences. These modeling results suggest that the significance of twinning in β-HMX cannot be determined with traditional loading configurations and diagnostics. [ABSTRACT FROM AUTHOR]

• A pseudoinverse coordinate matrix uniquely extends the gradient operator to discrete variables. • The related divergence enables expression of a truly discrete stress balance equation. • Elastic non-linearity is treated in terms of the theoretical crystal strength. • The dislocation core is simulated while avoiding consumptive first principles. To facilitate the modeling of crystal defects on their core scales, the present paper introduces a discrete stress balance equation that admits non-linear elasticity of the defected crystal cell and its arbitrary boundary conditions. Thus, the cell may be free or embedded into continuum. In the latter case, when considering a sufficiently large domain tractable by the proposed method, boundary forces can be related to long-range stresses of the defect. For a case study, an edge dislocation in the primitive cubic lattice is simulated to assess influence of the crystal dimensions and elastic properties on the microscopic discrete core. [ABSTRACT FROM AUTHOR]