Research On Crack Control Of CFRP In Ultrasound Vibration Grinding

Carbon Fiber Reinforced Plastic(CFRP)are more and more widely used in aerospace due to their excellent properties and light weight.This application field of high precision requirements makes it very high requirement for the processing quality of CFRP.The special material structure of CFRP makes it easy to produce various defects during the secondary processing,and ultimately makes the material fail ahead of time.In the process of traditional CFRP processing,there are many defects such as delamination,burr and crack.In order to improve the surface quality and reduce the occurrence of delamination defects,ultrasonic vibration assisted grinding has been widely used in the secondary processing of CFRP.Ultrasound vibration assisted grinding can effectively reduce the surface roughness and grinding force,thus reducing the occurrence of delamination.However,in the ply,cracks will also occur within the matrix and between the fiber and the matrix interface due to various factors during grinding.When the components are in service,the micro-cracks will continue to expand under the loads,and eventually spread between the layers,forming a delamination defect.Moreover,the cracks in the surface layer gradually extend to the interior of the material,which makes the bending strength of the material decrease.Therefore,the formation and propagation of cracks in the process of ultrasonic vibration assisted grinding are studied by means of finite element simulation and grinding test,so as to reduce the generation of cracks.The main research results are as follows:(1)The form of crack was observed and characterized,and the severity of crack was evaluated by crack density and start-stop depth.The effect of crack on material strength was studied from both micro and macro aspects.(2)The three-dimensional multi-phase micro-simulation of CFRP is carried out by commercial finite element software ABAQUS.The elastic-brittle constitutive model of fibers,the elastic-plastic constitutive model of matrix and the separation model of bonding elements are defined respectively.The finite element model of single abrasive grinding of CFRP is established,and the material removal mechanism of four typical fibers with cutting angles of 0,45,90 and 135 degrees is analyzed.A critical grinding force model for crack propagation was established to deal with the serious crack defect in 90 degree fiber cutting angle.The crack propagation caused by ultrasonic vibration impact in ultrasonic vibration assisted grinding is analyzed.A single factor experiment on the amplitude is carried out and the appropriate vibration parameters are obtained.(3)Based on the influence of each parameter on crack density in the established critical grinding force model,the spindle speed,feed speed and radial shear depth were optimized in the range of common processing parameters in ultrasonic vibration grinding.The empirical prediction formula of surface crack density of CFRP is obtained by three factors and four levels test,and the control of surface crack is realized.