Investigation On Low-velocity Impact And Interlaminar Enhanced Mechanism Of Metal/Carbon Fiber Reinforced Composites

Fiber reinforced polymer composites are widely used in aerospace,automobile,construction and other fields because of their excellent properties such as high strength,high stiffness,light weight and fatigue resistance.However,it will inevitably be subjected to external loads such as low-velocity impact during the service process,resulting in invisible internal damage such as interlaminar delamination,fiber broken and matrix crush.In order to prolong the service life and improve the safety of fiber reinforced composite structures,it is of great significance to enhance their low-velocity impact resistance,impact damage tolerance and interlaminar fracture toughness.Four kinds of metal hybrid carbon fiber reinforced composite laminates with different ply structures,C14,C14 SS,C14AL and C16,were prepared by hot pressing technology with thermosetting epoxy resin,twill woven prepreg T300-30 K carbon fiber cloth,rhombic stainless steel wire mesh and aluminum alloy wire mesh.In order to investigate the low-velocity impact damage behavior,damage tolerance after impact and interlaminar strengthening mechanism of metal mesh hybrid composite laminates,low-velocity impact test,compression after impact test,double cantilever beam(DCB)tensile test and end notch flexure(ENF)test were carried out.The specific research contents and conclusions are as follows:(1)The low-velocity impact tests of composite laminates with four different ply structures were carried out.Four kinds of impact energies(10 J,15 J,20 J and 25 J)were used to carry out impact tests on the specimens,and the damage morphology of the laminates under impact load was recorded.The internal damage differences of the specimens were detected and analyzed by immersion ultrasonic scanning.And the damage behavior and low-velocity impact response of different laminated under low-velocity impact were obtained.The test results show that the greater the impact load on composite specimens,the larger the internal damage area caused by impact.Adding metal mesh improves the plasticity of composite laminates and thus improves the ability of specimens to absorb impact energy.(2)The compression after impact(CAI)test of metal hybrid carbon fiber reinforced composite laminates after impact was carried out.In the CAI experiment,the changes of strain and displacement field of the specimen during compression were measured by using2D-VIC instrument,and the changes of CAI strength of composite laminates with different structures were analyzed.By analyzing the damage evolution and the change of impact damage tolerance during the compression process,the failure mechanism and mode of specimens with different laminated structures in post-impact compression test are obtained.The experimental results show that the smaller the thickness of composite laminates,the smaller their bending stiffness,which may lead to buckling failure during the compression process.With the increase of impact energy,the damage inside the specimen is more serious,and the stress concentration caused by the damage leads to the decrease of CAI strength.The addition of metal mesh can effectively improve the impact resistance of laminates and reduce the impact damage of specimens,thus making the composite structure have higher CAI strength.(3)Two kinds of specimens,carbon fiber-reinforced polymer(CFRP)and metal/carbon fiber-reinforced polymer(CFMRP)with prefabricated cracks,were made by hot compression molding technology,and the DCB tensile test and ENF test were carried out.The crack propagation during the test was recorded by camera.Based on the collected test data,the model I and II interlaminar fracture toughness were calculated,and the damage morphology of the specimen after disconnection was analyzed.The influence of hybrid composite structure with aluminum alloy mesh on the interlaminar fracture toughness of the composite and the interface damage mechanism were studied.The test results show that,compared with CFRP specimens,the interlaminar fracture toughness of CFMRP specimens is increased by10.2% and that of model II cracks by 96.8%.By observing the fiber-metal mesh bending interface of CFMRP specimens,it is found that in the process of fiber-metal mesh bending and shearing,the destruction of the interface is not only the destruction of the matrix,but also the shear fracture of the fiber.