Institute Of Mechanics,Chinese Academy of Sciences
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一种用于大型土槽实验的砂质土体制备装置和制备方法
No full text本发明实施例公开了一种用于大型土槽实验的砂质土体制备装置和制备方法， 包括：实验槽， 形成有用于容纳实验土体的容纳腔；渗流单元， 与所述容纳腔连通， 能够自所述容纳腔的上方自上而下， 或， 自所述容纳腔的下方自下而上作为渗流方向向实验土体中渗流液体， 且渗流方向可切换；砂雨单元， 包括供砂机构， 以及与所述供砂机构相连且能够向所述容纳腔中提供砂土的分散撒砂机构， 且所述分散撒砂机构通过沿所述实验槽的延伸方向往复移动实现均匀地提供砂土。通过上述方案， 克服了现有技术中在土槽中的砂土的制备， 尤其是大型土槽中的砂土制备过程中存在的铺料不均、耗时长、效率低， 以及砂土参数较难控制的问题
多场辅助金属熔丝增材熔体定向转移装置及方法
No full text本发明提供多场辅助金属熔丝增材熔体定向转移装置及方法， 装置包括激光能量源系统、金属送丝系统、恒定磁场系统、电场系统、同轴保护气系统、超声发生器、多轴运动平台和成形基板；成形基板固定安装在多轴运动平台的上方， 通过多轴运动平台实现成形基板在空间多自由度的运动；激光能量源系统固定在成形基板的上方， 使激光能量源系统发射的激光照射到成形基板的上表面；金属送丝系统固定在激光能量源系统的侧面， 将金属丝材输送到激光光斑的尺寸范围内；恒定磁场系统、电场系统和超声发生器分别固定在金属送丝系统上；所述多轴运动平台包括X、Y、Z轴运动和平台转动四个自由度。本发明通过分配辅助场的安装位置实现在金属丝材端部施加特定的场
The influence of horizontal borehole spacing on the interaction of two dynamic cracks propagating towards each other under unequal biaxial confining pressure
No full textAs resource extraction depth increases, deep rock engineering often encounters geostress environments where horizontal stress significantly exceeds vertical stress, sometimes by factors up to three. This distinctive stress state critically impacts the propagation paths and interaction mechanisms of blasting cracks. This study establishes an experimental system for blasting photoelasticity under unequal biaxial confining pressure (9 MPa horizontal, 3 MPa vertical). It investigates the propagation behavior of opposing cracks and the effects of explosive stress waves and crack-tip stress fields on nearby cracks at various horizontal spacings (8-14 cm). Results indicate that under unequal biaxial confining pressure, the shaped charge shows a marked directional effect, with the optimal horizontal spacing between boreholes being 11 cm. At this spacing, the main cracks between the two boreholes have longer propagation lengths and better connectivity. As horizontal spacing increases, both wave-crack and crack-crack interactions weaken, with crack-crack interactions attenuating faster than wave-crack interactions. When the spacing exceeds 11 cm, the influence of crack-crack interactions on the mode II stress intensity factor at the crack tip rapidly diminishes. Under dynamic-static loading, predictions of crack deflection angle prediction using the Maximum Tangential Stress (MTS) and Generalized Maximum Tangential Stress (GMTS) criteria align closely with experimental trends, particularly regarding the timing of inflection points. However, predictions are consistently larger than actual values, and T-stress has minimal effect on crack deflection. Thus, the simpler MTS criterion is preferable for practical applications. These findings provide key insights into the interaction of opposing dynamic cracks at varying horizontal spacings and strengthen the theoretical foundation for optimizing perimeter-hole blasting parameters in horizontal stress-dominated environments
Image of a time-dependent rotating regular black hole
No full textIn this study, we develop a modeling framework based on spatio-temporal generalized random fields to simulate the time-evolving accretion flows and their associated imaging signatures around rotating regular black holes. We extend the Mat & eacute;rn field formalism to the spatio-temporal domain and introduce a locally anisotropic tensor structure Lambda(x), which encodes direction-dependent correlation scales motivated by Keplerian velocity fields, thereby generating physically informed perturbation structures. Coupled with a computationally efficient light ray-tracing scheme, this framework produces a sequence of time-resolved images of regular black hole shadows and accretion structures. By incorporating light-travel time effects, we identify significant temporal smearing of features within strongly lensed regions and rapidly varying sources, thus enhancing the physical realism of the modeling. Comparison with existing general relativistic magnetohydrodynamic simulations demonstrates that our stochastic generative model maintains statistical consistency while offering substantial computational efficiency. Moreover, the simulated results reproduce the dynamic positional shift of the bright ring structure observed in M87*, providing theoretical support for interpreting its time-variable images
Wavelength-dependent strain gradient modeling of two-dimensional lattice metamaterials
No full textA robust generalized continuum model called the wavelength-dependent strain gradient continuum model (WDSGM) has been proposed to predict dispersion properties of two-dimensional (2D) periodic lattice metamaterials. The key idea lies in replacing the classical Taylor expansion of displacement fields with a wavelength-dependent one, naturally leading to new equations of motion and therefore a significantly improved capability of predicting dispersion characteristics. For different 2D lattices, dispersion results derived from the proposed WDSGM are verified by comparing with those obtained from the discrete model and the existing strain gradient continuum model (SGM) in the irreducible Brillouin zone. Based on the proposed model, the effects of SG orders have been investigated. Results suggest that considering the wavelength-dependent Taylor expansion and increasing the SG order are beneficial to improving the predictive performance of continuum models. The proposed model is free of any instability issue which is challenging for many existing SG methods. Under given parameters, the proposed WDSGM with eighth-order truncation is enough to predict the dispersion relation of three lattices, i.e., the square, triangular and hexagonal lattices throughout the irreducible Brillouin zone
Effects of laser beam oscillation on molten pool formation and solidification characteristic in directed energy deposition of Inconel 718 alloy
No full textDirected energy deposition with laser beam oscillation (DED-LBO) is a promising technology to modify the solidification structure and improve the deposition quality by introducing an oscillating laser. In this study, a multiphase computational fluid dynamics (CFD) model incorporating a ray-tracing algorithm was developed to simulate the DED-LBO process of Inconel 718 powder on a 316 L stainless steel substrate, based on several reasonable assumptions. The results show that the average interaction angle between the molten pool surface and the laser beam, as well as the laser absorptivity, fluctuates periodically over time due to the oscillating laser. The larger the oscillation amplitude, the larger the surface area of the molten pool, resulting in more Inconel 718 powder being melted and a reduction in laser absorptivity. The periodic heat input induced by the oscillating laser beam causes fluctuations in temperature, fluid velocity, solute distribution uniformity, and molten pool volume, all of which decrease with increasing oscillation amplitude, ultimately leading to the formation of distinct solidification textures. The cooling rate decreases with an increase in oscillation amplitude, which results in finer grain size at lower oscillation amplitudes. Furthermore, the oscillating laser beam demonstrates potential in modifying the direction of columnar grain growth. The columnar crystals grow at an angle with the build direction at a smaller oscillation amplitude (0.4 mm), whereas at a larger amplitude (1.2 mm), they are aligned nearly parallel. This study enhances the understanding of laser-material interaction and thermal-fluid-solute transport behavior, as well as their role in molten pool formation and solidification during the DED-LBO process
Study of the Stagnation-Point Boundary Layer in Hypersonic Magnetohydrodynamic Flows
No full textTo investigate the effect of a magnetic field on the stagnation-point boundary layer in hypersonic flows, this study developed a magnetohydrodynamic boundary-layer model that incorporates real gas effects. Variations in the boundary layer, including stagnation-point heat flux, heat transfer function, and skin friction function, were examined to elucidate the mechanisms associated with different boundary-layer-edge conditions. Parameters at the boundary-layer edge were obtained using the quasi-one-dimensional stagnation streamline method. The results indicate that the nonequilibrium state at the boundary-layer edge has minimal impact on the inner boundary layer. In contrast, the magnetic strength reduces convective heat transfer primarily by decreasing the velocity gradient at the boundary-layer edge. The enhancement of the heat transfer function is mainly driven by the "acceleration effect" on the flow within the boundary layer, resulting from decreased velocity gradients and increased Lorentz force. This interaction ultimately leads to a saturation effect in the reduction of heat transfer. Additionally, the increase in the skin friction function is primarily due to velocity overshoot within the boundary layer induced by the magnetic field. The Lorentz force induced by the magnetic field expands the inviscid shock layer while simultaneously reducing the boundary-layer thickness. Overall, the stagnation-point boundary-layer model developed in this study not only facilitates rapid assessment of stagnation parameters, but also deepens our understanding of the magnetic field's role within the stagnation-point boundary layer
An overbend strategy to manyfold enhance the designed elastic bendability of flexible electronics
No full textElastic bendability is crucial for flexible electronics to achieve conformal contact and enable widespread applications. However, reducing the thickness of the structure is almost the only strategy to enhance the elastic bendability of inorganic flexible electronics. This study proposes an overbend strategy, whose operation is beyond the designed elasticity of the fabricated structure. Mechanical theories, finite element analysis, and experiments verified that, with multilayer stacks and interconnects with various geometric designs as examples, the overbend strategy can enhance the designed elastic bendability to twice for the material of the ideal elastoplastic/kinematic hardening constitutive relationship and to more than twice for the mixed hardening/isotropic hardening constitutive relationship. The mechanism is extending the elastic strain range at the critical section to twice or more times the original value by the evolution of the elastoplastic constitutive relationship. Notably, the overbend strategy is virtually costless, combinative with other strategies and widely applicable for inorganic flexible electronics
Extraordinary specimen-size effect on long-life fatigue of additively manufactured AlSi10Mg
No full textIt is well known that the mechanical properties of materials are strongly influenced by the size of the testing specimens, especially for the defect-induced high-cycle fatigue (HCF) and very-high-cycle fatigue (VHCF) of high-strength alloys with failure cycles beyond 107. Typically, this phenomenon of specimen-size effect becomes more pronounced as the fatigue life extends, and the fatal fatigue-crack initiates within a risk domain of control volume V90 where the applied stress is equal or larger than 90 % of the nominal one. Here, for the first time, we report a newly observed specimen-size effect on fatigue behavior of an additively manufactured aluminium alloy (AlSi10Mg) produced by powder bed fusion - laser beam. Fatigue tests were precisely conducted by ultrasonic cycling at a resonant frequency of 20 +/- 0.5 kHz under a stress ratio R = -1 at room temperature and in ambient air. Five types of specimens with minimal diameters of 3.5, 5.3, 8.1, 12.25 and 18.6 mm were tested. As specimen size increases, the HCF resistance drops sharply and exhibits a large scatter, whereas the VHCF limit degrades only slightly. For small-sized types, fatal crack initiates at specimen surface, subsurface or interior with the increasing failure cycles. But for large-sized types, fatal crack nucleates frequently in specimen interior even with "fish eye" morphology in HCF regime. Furthermore, the crack initiation site gradually tends to shift beyond the control volume part with the increase of specimen size, making the concept of V90 challenging for large-sized specimens, regardless of fatigue lives
A framework of crystal plasticity finite element incorporating multiple fatigue cracking mechanisms in titanium alloys
No full textFatigue failure is the result of competition of multiple crack initiation mechanisms in most cases. Crystal plasticity finite element method is a powerful tool for understanding the microscopic process of fatigue crack initiation and evolution. However, existing researches generally concern the single crack initiation mechanism, which cannot elucidate the essence of fatigue mechanisms. This paper develops a framework of crystal plasticity coupling slip and twinning and incorporating the competition of different fatigue cracking mechanisms in titanium alloys, i.e., crack initiation due to slip bands, grain refinement, cleavage on slip planes, and cleavage on non-slip planes. Particularly, a strategy is presented for simulating the refining grains, and a criterion is proposed for crack initiation due to grain refinement. The effect of grain size is also considered in the framework. Then, the fatigue cracks of TC17 titanium alloy due to different crack initiation mechanisms under very high cycle fatigue loading are simulated. The results of fatigue initiation and microstructural evolution accord well with the experiments. The present work provides a method not only to deal with the competition of fatigue cracking mechanisms in titanium alloys but also to simulate the microscopic process of crack initiation and early growth accompanied by microstructure evolution