Research On Residual Strength Of CFRP Single-Lap Adhesive Joint With Low Velocity Impact Damage

With the continuous tightening of national policies on saving energy and reducing emission,lightweight technology has received more and more attentions.Carbon Fiber Reinforced Plastic(CFRP)has broad application prospect in the design of vehicles and aircrafts due to its excellent performance such as light weight,high strength and good designability.The adhesive joint is one of the core components in CFRP automobile structure,and it is inevitably subjected to low velocity impact in the process of manufacture,usage and maintenance.Under low velocity impact,multiple impact damages are prone to occur,thus considerably reducing the residual strength and service life of CFRP adhesive joints.Therefore,the research on low velocity impact response and impact damage,and further research on residual strength of CFRP adhesive joints are of great significance to damage tolerance design for CFRP bonding structure.In this dissertation,CFRP single-lap adhesive joint was taken as the research object and the low velocity impact response and residual strength were studied by using simulation and experimental methods.The main contents are as follows:The cumulative damage models of CFRP single-lap adhesive joint for low velocity impact and residual strength were introduced respectively based on mechanics of composite materials and damage mechanics.Meanwhile,the failure criterion and material properties degradation scheme for CFRP laminate and adhesive were chosen correspondingly.A whole-process analysis method of low velocity impact and residual strength of CFRP single-lap adhesive joint after impact was established.The simulation model of CFRP single-lap adhesive joint was established in ABAQUS to study the effect of impact energy on impact response parameters and impact damage parameters.The results show that the first damage threshold energy is 0.17 J for CFRP single-lap adhesive joint with 20 mm overlap length.Delamination area and depression depth both increase with the increase of impact energy.For CFRP single-lap adhesive joint with 20 mm overlap length,some area of the adhesive fails completely and the growth of delamination area of the adherend slows down while the growth of depression depth accelerates when impact energy exceeds 4J.Low velocity impact damage was imported to undamaged model by means of Results Transfer Bracket in ABAQUS and the residual strength of damaged CFRP single-lap adhesive joint was predicted.The effects of impact energy and overlap length on residual strength of CFRP single-lap adhesive joint were studied respectively and the results show there is little effect of overlap length on the strength of undamaged CFRP single-lap adhesive joint when the overlap length exceeds 20 mm.Only when the impact energy exceeds 4J will the residual strength of CFRP single-lap adhesive joint with low velocity impact damage decrease significantly.The damage tolerance behavior of CFRP single-lap adhesive joint will not improve when the overlap length exceeds 30 mm.The specimens with different overlap length were made and the strength tests for undamaged CFRP single-lap adhesive joints,low velocity impact tests and the residual strength tests for CFRP single-lap adhesive joints with low velocity impact damage were carried on sequentially.The test results agree well with the simulation results,thus proving that the effects of impact energy and overlap length on residual strength of damaged CFRP single-lap adhesive joint obtained from simulation are reasonable and reliable.