Seismic and vibration control of segmented isolation layer in underground structure-diaphragm wall system

In this paper,a seismic and vibration reduction measure of subway station is developed by setting a segmented isolation layer between the sidewall of structure and the diaphragm wall.The segmented isolation layer consists of a rigid layer and a flexible layer.The rigid layer is installed at the joint section between the structural sidewall and slab,and the flexible layer is installed at the remaining sections.A diaphragm wall-segmented isolation layer-subway station structure system is constructed.Seismic and vibration control performance of the diaphragm wall-segmented isolation layer-subway station structure system is evaluated by the detailed numerical analysis.Firstly,a three-dimensional nonlinear time-history analysis is carried out to study the seismic response of the station structure by considering the effect of different earthquake motions and stiffness of segmented isolation layer.Subsequently,the vibration response of site under training loading is also studied by considering the influence of different train velocities and stiffness of the segmented isolation layer.Numerical results demonstrate that the diaphragm wall-segmented isolation layer-subway station structure system can not only effectively reduce the lateral deformation of station structure,but also reduce the tensile damage of the roof slab.On the other hand,the developed reduction measure can also significantly reduce the vertical peak displacements of site under training loading.

Adiabatic shear fracture prediction in high-speed cuttingat various negative rake angles and feeds

The critical characteristics of adiabatic shearfracture （ASF） that induce the formation of isolated seg-ment chip in high-speed machining was further investi-gated. Based on the saturation limit theory, combining withthe stress and deformation conditions and the modifiedJohnson-Cook constitutive relation, the theoretical predic-tion model of ASF was established. The predicted criticalcutting speeds of ASF in high-speed machining ofa hardened carbon steel and a stainless steel were verifiedthrough the chip morphology observations at various neg-ative rake angles and feeds. The influences of the cuttingparameters and thermal-mechanical variables on theoccurrence of ASF were discussed. It was concluded thatthe critical cutting speed of ASF in the hardened carbonsteel was higher than that in the stainless steel under alarger feed and a lower negative rake angle. The proposedprediction model of ASF could predict reasonable results ina wide cutting speed range, facilitating the engineeringapplications in high-speed cutting operations.