Acta Mechanica Solida Sinica最新文献

This paper presents a theoretical model of dislocation penetration through grain boundaries (GBs) in micro-crystalline materials, taking into account the interactions between dislocations and GBs in a hydrogen environment. It describes the pile-up and penetration of dislocations at GBs in poly-crystalline materials, and discusses the effects of grain size and GB disorientation angle on dislocation distribution within grains. The results reveal that decreasing grain size or increasing GB disorientation angle reduces the dislocation distribution region in grains. Moreover, the presence of hydrogen further decreases this distribution area, suggesting a reduction in dislocations emitted in a hydrogen environment. Consequently, this diminishes the shielding effect of slip band dislocations on crack growth and weakens the passivation ability of the crack, promoting increased crack propagation. The maximum reduction in the critical stress intensity factor for poly-crystalline materials in a hydrogen environment is approximately 16%. These results are significant for understanding the fracture behavior of poly-crystalline materials exposed to hydrogen.

In this paper, the mutual influence of plastic behaviors between kinked macro-crack and kinked micro-crack is analyzed based on the distributed dislocation technique and the dislocation-free zone model. A novel theoretical model for the size of the plastic zone is proposed, where the length of the dislocation array calculated in a specific direction is utilized to characterize the size of the plastic zone at the crack tip. The results demonstrate that, compared with the length of the dislocation array distributed along the crack direction, the length of the dislocation array distributed at a certain specific angle can more accurately characterize the plastic zone at the crack tip. When compared with the results of finite element analysis, the relative error is within 0.2%. Within the theoretical framework of this paper, it is considered that when the dislocation array is set at the crack tip and forms an angle of approximately 25° with respect to the horizontal direction, the calculated length of the dislocation array can effectively characterize the size of the plastic zone. The dislocation density increases with the decrease of the kinking angle of the crack. These results are conducive to predicting the plastic and fracture behaviors of materials containing kinked cracks.

This study investigates the effects of loading rates on the stick–slip behavior of polymethyl methacrylate material. A series of friction experiments were conducted using a direct shear apparatus to systematically assess how loading rates influences stick–slip behavior. Three loading rates were adopted: 0.1, 1, and 5 mm/min, all under a constant normal stress of 2.5 MPa. The experimental results indicate that loading rates significantly influence the mechanical behavior of stick–slip. The recurrence intervals, shear force drops, and fracture energy decrease as loading rates increase. By monitoring changes in the interface contact area using the total internal reflection method, we observed that the reduction in interface contact area diminishes with increasing loading rates. At lower loading rates, micro-asperities have sufficient time to reform, resulting in stronger interaction forces and fracture dissipated energy; conversely, at higher loading rates, limited recovery of contact area results in reduced fracture dissipated energy. These findings highlight the close relationship between loading rates and interface contact behavior, providing new experimental data and insights for analyzing and understanding fault slip and rupture processes.

Combining the continuously distributed dislocation technique (DDT) and the von Mises yield criterion, new double-crack and multi-crack models were established. The influences of multi-segment kinked micro-cracks and groups of kinked micro-cracks on the plastic behavior of the macro-crack were investigated. The results show that a smaller kinking angle of the micro-crack enhances its influence on the plastic deformation of the macro-crack, potentially leading to plastic zone fusion. Meanwhile, micro-cracks with smaller kinking angles exert a stronger attracting force on macro-crack growth, facilitating convergence between them. Furthermore, annularly distributed micro-crack groups demonstrate a more pronounced attraction on macro-crack propagation compared to linearly distributed micro-crack groups. The double-crack and multi-crack models established in this paper offer a theoretical framework for analyzing the plastic fracture behavior of metallic materials containing complex kinked cracks.

Through-silicon via (TSV) is an important technique in three-dimension integration. The mechanical performance of TSV-Cu is critical to the electrical performance and signal transmission. In this work, the deformation of single-crystalline TSV-Cu during annealing process was studied using molecular dynamics method. The protrusion morphology and protrusion height of Cu column were revealed. The protrusion height curves can be divided into four stages: slow increase, fast increase, fast decrease, and saturation. During the deformation process, the main deformation mode is temporary amorphous region followed by residual dislocations. The influences of annealing temperatures, heating rates, and column sizes on protrusion height were studied. Results show that the residual protrusion height increases with increasing annealing temperatures and decreasing heating rates. The residual protrusion height increases with increasing column sizes in terms of column diameter and length. This work provides new insights into understanding the mechanical performance of nano-TSV-Cu.

In this paper, enhanced near-field shock wave propagation in underwater explosion is achieved by introducing a fragile air-tube under the explosive. Firstly, based on the ALE algorithm in the ANSYS/LS-DYNA software, a numerical model integrating the water, the air, the explosive, and the air-tube is developed. Comparative discussion for explosion with air-tube in the air, as well as explosion in the water without air-tube, is made to highlight the distinct energy attenuation mechanism due to the introduction of the air-tube. Then, the influence of the tube geometry, as well as evolving structural boundaries, on the explosive process is discussed exhaustively. The results indicate that the air-tube acts as a shock focusing apparatus, significantly altering explosion flow dynamics. Tube damage mode relies on tube geometrical size. Time-refreshed structural boundary affects the position the fluid flowing into the air-tube, which in turn plays an impact on the bubble pattern and energy distribution near the tube outlet. Enhanced outlet pressure is strengthened along with the decrease of the outlet radius, cross-section height ratio and tube thickness. These insights offer valuable guidance for optimizing underwater explosion and possess prospectively scientific and practical significance.

Electric vehicles, powered by electricity stored in a battery pack, are developing rapidly due to the rapid development of energy storage and the related motor systems being environmentally friendly. However, thermal runaway is the key scientific problem in battery safety research, which can cause fire and even lead to battery explosion under impact loading. In this work, a detailed computational model simulating the mechanical deformation and predicting the short-circuit onset of the 18,650 cylindrical battery is established. The detailed computational model, including the anode, cathode, separator, winding, and battery casing, is then developed under the indentation condition. The failure criteria are subsequently established based on the force–displacement curve and the separator failure. Two methods for improving the anti-short circuit ability are proposed. Results show the three causes of the short circuit and the failure sequence of components and reveal the reason why the fire is more serious under dynamic loading than under quasi-static loading.

A novel hollow optimized simple cubic (SC) lattice structure based on the triply periodic minimal surface (TPMS) geometry was proposed, inspired by bamboo geometry, aiming at enhancing both load bearing and energy absorption properties. Conventional SC lattice structures, despite their high load bearing capability and ease of fabrication, suffer from poor energy absorption performance due to their high stress concentration at the nodes and the induced deformation instability under compressive loads. By integrating the hollow and tapered features of TPMS geometry into the SC lattice, the proposed structure design effectively mitigates these issues, improving energy absorption simultaneously. The effectiveness of this design is demonstrated by finite element (FE) simulations and experimental tests, showcasing significant improvements in energy absorption capacity and strength, particularly after properly adjusting the shape parameters (e.g., C = 0.6). This research provides a promising pathway for developing lightweight, high-performance lattice structures for engineering applications with complex and volatile loading conditions.

Atomic-scale strain mapping has become increasingly vital for investigating deformation mechanisms and the governing principles of solid materials. This is due to the significant impact of atomic-scale strain on the physical, chemical, and mechanical properties of nanomaterials that comprise functional devices such as nanoelectronics, communication devices, electromechanical systems, and sensors. The advent of advanced electron microscopes has enabled the acquisition of high-magnification images with atomic resolution, providing an exceptional platform for measuring the atomic-scale strain of solid materials. However, accurate and unified strain mapping methods and standards for evaluating atomic-scale strain distribution remain scarce. Consequently, a unified strain mapping framework is proposed for atomic-scale strain measurement. Utilizing finite deformation analysis and the least-squares mathematical method, two types of atomic-scale strain field mapping methods have been developed, including the phase analysis-based methods (PAD and PAS) and the peak matching-based strain mapping method (PMS) for high-resolution scanning transmission electron microscope images. The prototypical 2D materials, graphene and molybdenum disulfide, serve as the subjects for the strain field mapping research, conducted through both simulation and experimentation. Upon comparing the theoretical strain mapping results of single-layer graphene and molybdenum disulfide with and without defects, it is demonstrated that the proposed strain mapping methods, particularly the PMS method, can accurately describe the large deformation surrounding a significant strain gradient.