Institute Of Mechanics,Chinese Academy of Sciences
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Material frame formulation of the FE-based virtual fields method and applications to hyperelastic composites
No full textAs typical heterogeneous composites, traditional material parameter identification of the biological tissues has recently been challenged by the popularization of full-field measurements during experimental tests. The Finite Element Model Updating (FEMU) method, which is known for its robustness, has to face prohibitive computational costs with the massive data offered by full-field measurements. A promising alternative is the Virtual Fields Method (VFM) which is notably more efficient computationally when these full-field measurements are available. We recently proposed a general and robust VFM framework for identifying the material parameters of nonlinear elasticity. However, the framework was formulated with the spatial form of the principle of virtual power. In the current paper, we introduce a more concise formulation with the material form of the principle of virtual power, expanding the application to multiple measurement cases. Verification with analytical and numerical examples demonstrates its significant efficiency compared to the FEMU method as well as generality and robustness across various applications, including the noise sensitivity analysis and heterogeneous biological tissue cases. The accurate identification results highlight the significant potential of this method in nonlinear biological composites
An improved particle neighbor search algorithm with multi-level cache optimization strategy for discrete element method using GPU
No full textThis paper proposes an improved particle neighbor search algorithm, focusing on optimizing computational efficiency and memory usage in large-scale particle system simulations. By partitioning the simulation space into grids and combining it with Morton encoding, it ensures that adjacent grids are stored contiguously in memory, thereby enhancing the locality of data access and reducing the probability of cache misses. In the particle sorting phase, Morton encoding is used to rearrange the particles, further enhancing memory continuity and leveraging the hardware cache's prefetching mechanism to reduce data read latency. The algorithm also incorporates the idea of the Verlet table method by setting a sorting threshold to optimize the sorting process, avoiding redundant calculations and unnecessary sorting operations. Through the above optimization methods, a multi-level cache optimization strategy is achieved, significantly improving the algorithm's performance and memory utilization efficiency. Experimental results show that the algorithm proposed in this paper has significant advantages in largescale particle simulations. (c) 2025 Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences. Published by Elsevier B.V. All rights are reserved, including those for text and data mining, AI training, and similar technologies
Noise suppression mechanism of flow in annular cavity using annular groove at subsonic speeds
No full textTo investigate the mechanism of noise reduction of landing gear hubs, the noise suppression effect and mechanism of an annular groove (simplification of an annular wheel hub rim) on an annular cavity (simplification of an annular wheel hub) have been studied computationally using the Detached Eddy Simulation method combined with the Ffowcs Williams-Hawkings acoustic analogy in this paper. The Mach number of the freestream is from 0.13 to 0.21. The results demonstrated that the annular groove alters the boundary layer profile in the vicinity of the annular cavity. This causes the kinetic energy within the boundary layer to move towards the upper boundary layer, the boundary layer displacement thickness to increase, and the flow mass loss to increase. Concurrently, the annular groove results in a reduction in shear layer flow velocity, thereby weakening the interaction of the flow with the center cylinder (simplification of a wheel axle), the rear-edge and the internal wall of the annular cavity, reducing the velocity fluctuation and the turbulent kinetic energy near the annular cavity walls. This suppresses the intensity of flow-acoustic feedback noise, while simultaneously suppresses the intensity of both the acoustic feedback noise and the turbulent broadband noise
Bioinspired Strategy for Controlling Crack Network Morphology on Curved Films
No full textFragmentation of films is not only a widely observed failure mode in engineering but can also be harnessed to modulate the performance of functional devices such as flexible sensors, nanofluidic channels, and lithographic templates. Both the sizes and geometry of fragments may influence the performance of these devices. However, existing strategies are limited to overall adjustments of fragment sizes and geometry in net-like fragmentation across the entire films, while programming these characteristics in localized areas remains a challenge. Inspired by cracking patterns observed in animal skins, a curvature-mediated strategy is proposed to regulate the crack network morphology on curved films. Peridynamic simulations and experiments reveal that cracks hierarchically form in thin films as substrate expansion increases, a process explained by a hierarchical shear-lag model. Furthermore, a unified scaling law demonstrates that increasing curvature radius reduces the fragment size while increasing the number of fragment edges. This bionic strategy offers a promising method to regulate conductive pathways in thin films, providing a potential approach for the fabrication of programmable functional electronic devices
Microstructure evolution, hardening mechanism and penetration behavior of copper-based jet modified with Nd
No full textIn this study, the formation, evolution, hardening and penetration behaviors of the copper-based jets were investigated based on SEM, EBSD, XRD, TEM techniques and finite element simulation methods. The results show that, compared with the penetration depth and hardness of the pure copper jets, the penetration depth of the Cu-Nd alloy jets has increased by approximately 22.2 %, and the hardness has increased by approximately 25.5 %. The increase in the jet penetration depth of the Cu-Nd alloy is mainly related to the fact that the addition of rare earth Nd element can simultaneously enhance the plasticity and strength of the alloy, and Nd element may react with O and S elements to release chemical energy. The hardening mechanisms of the Cu-Nd alloy jets mainly include: dispersion strengthening, grain refinement strengthening, dislocation strengthening and twinning strengthening
Experimental study of the rotation characteristics of magnetically driven vacuum-arc cathode spots
No full textAchieving uniform, stable, and reliable erosion of electrode materials is crucial for enhancing the performance and lifespan of vacuum-arc devices. This study investigates the rotation and erosion characteristics of cathode spots on Cu and Ti cathodes with various applied magnetic fields. The results indicate that with the discharge current changes, cathode spots evolve from a single spot to multiple spots and then back to a single spot. Without an applied magnetic field, Ti cathode spots exhibit a large-scale random walk, while Cu cathode spots show a concentrated distribution. With an applied magnetic field, cathode spots of both materials undergo directional rotation. The velocity of the Ti cathode spots is higher than that of Cu, and spot velocity increases with the increase of magnetic flux density. When the radial magnetic field is enhanced to 70 mT, the rotational velocity of the cathode spots actually decreases with the increase of the peak current. The increase of applied magnetic field leads to a significant decrease in the total erosion rate and macroparticle loss, accompanied by an increase in the average ion charge state. The application of an applied magnetic field can effectively regulate the rotation of cathode spots, allowing both Cu and Ti cathode spots to rotate for more than one full circle. Scanning electron microscopy observations indicate that the dimensions of the erosion craters on the cathode surfaces are significantly reduced, leading to a substantial improvement in the uniformity of erosion
Near-Injector Hydrodynamic Perturbation and Its Interplay With Inflow Boundary Conditions in Combustion Simulations
No full textCombustion simulation has become integral to the industrial design of energy and propulsion systems, serving as an efficient computational tool. Due to the complexity of real engines and thermal power devices, combustors are usually modeled solely with proper boundary conditions to describe inflow and outflow behaviors. In this work, we found that near-injector flow perturbations, often arising from peculiar geometric configurations, can interact with the prescribed inflow boundary conditions, leading to great influence on the predicted flame dynamics, thermoacoustic oscillations, and even statistical results of combustion fields. The objective of this study is to elucidate such an interplay between near-injector hydrodynamic perturbation (NIHP) and the prescribed inflow conditions with the consideration of several commonly used inflow boundary conditions. The receptivity of inflow conditions to NIHP is first examined in a one-dimensional Rijke-tube-like configuration and then demonstrated in the combustion large-eddy simulation of a realistic combustor configuration (thermoacoustically stable). Our findings reveal that inflow conditions exhibiting similar behaviors without NIHP can differ markedly under its influence. This underscores the necessity for careful selection of inflow boundary conditions in combustion simulations when NIHP is present
Synergistic enhancement of mechanical strength, friction coefficient and wear resistance of C/C-ZrC-HfC-SiC carbon-ceramic composites through matrix-interface modification
No full textCarbon fiber-reinforced ceramic materials are promising candidates for braking and transmission systems due to their lightweight structure, high strength, excellent high-temperature performance, and superior tribological characteristics. In this study, C/C-ZrC-HfC-SiC carbon-ceramic composites with varying ceramic contents were fabricated using a combined chemical vapor infiltration and precursor impregnation and pyrolysis process. The microstructure, mechanical properties, and tribological behavior of these composites were systematically investigated. Compared to C/C-SiC composites, the C/C-ZrC-HfC-SiC composites exhibit a synergistic enhancement in mechanical strength, friction coefficient and wear resistance. This enhancement is attributed to the reduced stress concentration arising from the interface modulus gradient effect induced by the introduction of ZrC and HfC into the matrix and their segregation near the carbon fibers. Moreover, the tribological performance of the composites is influenced by both the ceramic content and applied load, and the underlying mechanisms are elucidated. These findings provide valuable insights for the application and further optimization of carbon-ceramic composites
Experimental observation and theoretical modeling of multi-stage power-law creep in metallic glass
No full textPower-law creep, where the creep strain rate follows a power-law relationship with time, is ubiquitous in crystalline materials. However, this behavior typically exhibits multi-stage characteristics in amorphous materials due to the intrinsic structural and dynamic heterogeneity. In this study, we systematically performed high-temperature creep experiments on a Pd20Pt20Cu20Ni20P20 metallic glass. It is found each stage in multi-stage creep is governed by different deformation mechanisms, influenced by factors such as temperature, stress, and structural relaxation. Experimental results indicate that increasing temperature causes the power-law creep behavior to change from two stages to three stages, while increasing stress does not alter this behavior. After cyclic creep, the power-law creep behavior reverts from three stages to two stages. Based on the quasi-point defect theory, we propose a creep constitutive model that includes the contribution of structural relaxation to creep behavior in the generic metastable materials. Theoretical modelings show creep response is primarily driven by two deformation mechanisms: the activation of inherent deformation units (shear microdomains), which dominate the early stage of creep; and the mechanism related to structural relaxation, with atomic correlations significantly influenced by temperature and aging conditions. The constitutive model reveals the factors influencing the power-law creep and clarifies the intrinsic mechanism underlying the transition from two stages to three stages. These mechanisms align with the thermal and mechanical effects observed in the experiments
Thermoplastic polyimide with high glass transition temperature enabled by<i><i> N</i>-butyl-N</i>-phenylaniline groups
No full textThermoplastic polyimides (TPIs) exhibit favorable processing capabilities, and meanwhile preserve most of the superior properties of PIs, such as excellent heat resistance, insulation performance, chemical stability and so on. TPI can be obtained by incorporating flexible linkages and side groups. However, it would lead to either flexible polymer chains or weakened intermolecular interaction, causing the decline in thermal stability. Herein, we develop TPIs with good thermal stability through the introduction of an N-butyl-N-phenylaniline group. Its flexible linkage-N-and the twisted structure are conducive to achieving flexible polymer chains and increasing free volume, respectively, leading to good thermoplasticity. Simultaneously, the N-butyl-N-phenylaniline group, as electron-rich aromatic moiety in the diamine monomer, is able to maintain strong charge transfer complex (CTC) effect, beneficial for preserving high thermal stability. As a result, the as-prepared TPI exhibits good thermoplasticity as well as a high Tg of 357 degrees C