Dynamic indentation response of porous SiC/Ti-based metallic glass composite

Porous SiC/Ti-based metallic glass composite (Ti-BMGC), a new kind of composite, has significant application prospectin the field of light armor. To evaluate the dynamic mechanical response of the composite, dynamic Vickers hardness andindentation-induced deformation behavior were investigated by comparison with that under static indentation. The dynamic hardnesswas measured by a modified split Hopkinson pressure bar (SHPB). The dynamic hardness is obviously greater than the statichardness. The brittleness parameter under dynamic indentation is also greater than that under static indentation. Although thedynamic indentation induced more severe deformation behavior than the static indentation, the deformation and fracturecharacteristics in the two loading cases are nearly the same, both exhibiting extensive cracks in the SiC phase and severe plasticdeformation in the metallic glass phase.

Characterization of transient groundwater flow through a high arch dam foundation during reservoir impounding

Numerous deep underground projects have been designed and constructed in China, which are beyond the current specifications in terms of scale and construction difficulty. The severe failure problems induced by high in situ stress, such as rockburst, spalling, damage of deep surrounding rocks, and timedependent damage, were observed during construction of these projects. To address these problems, the dynamic design method for deep hard rock tunnels is proposed based on the disintegration process of surrounding rocks using associated dynamic control theories and technologies. Seven steps are basically employed：（i） determination of design objective,（ii） characteristics of site, rock mass and project, and identification of constraint conditions,（iii） selection or development of global design strategy,（iv）determination of modeling method and software,（v） preliminary design,（vi） comprehensive integrated method and dynamic feedback analysis, and（vii） final design. This dynamic method was applied to the construction of the headrace tunnels at Jinping II hydropower station. The key technical issues encountered during the construction of deep hard rock tunnels, such as in situ stress distribution along the tunnels, mechanical properties and constitutive model of deep hard rocks, determination of mechanical parameters of surrounding rocks, stability evaluation of surrounding rocks, and optimization design of rock support and lining, have been adequately addressed. The proposed method and its application can provide guidance for deep underground projects characterized with similar geological conditions.

Influence of wall motion on particle sedimentation using hybrid LB-IBM scheme

We integrate the lattice Boltzmann method(LBM) and immersed boundary method(IBM) to capture the coupling between a rigid boundary surface and the hydrodynamic response of an enclosed particle laden fluid. We focus on a rigid box filled with a Newtonian fluid where the drag force based on the slip velocity at the wall and settling particles induces the interaction. We impose an external harmonic oscillation on the system boundary and found interesting results in the sedimentation behavior. Our results reveal that the sedimentation and particle locations are sensitive to the boundary walls oscillation amplitude and the subsequent changes on the enclosed flow field. Two different particle distribution analyses were performed and showed the presence of an agglomerate structure of particles. Despite the increase in the amplitude of wall motion, the turbulence level of the flow field and distribution of particles are found to be less in quantity compared to the stationary walls. The integrated LBM-IBM methodology promised the prospect of an efficient and accurate dynamic coupling between a non-compliant bounding surface and flow field in a wide-range of systems. Understanding the dynamics of the fluid-filled box can be particularly important in a simulation of particle deposition within biological systems and other engineering applications.