Low-velocity Impact Response Of CFRP/6061 Aluminium Alloy Glued-riveted Joints

In recent years,automobile lightweight has always been an important way of energy conservation and emission reduction in the automobile field.The introduction of CFRP into automobile body has become an effective means to reduce vehicle weight.As the main connection method of automobile body sheet parts,glue riveting composite connection process can effectively connect CFRP and metal.In order to study the impact damage types of joints and the influence of low-speed impact damage on the static properties and fatigue life of glue riveted composite joints,the drop weight impact test,static tensile test and high cycle fatigue test of CFRP / 6061 aluminum alloy glue riveted joints with different adhesive layer thickness were carried out to explore the low-speed impact response of CFRP / 6061 aluminum alloy glue riveted joints.In this paper,the glue riveted composite joints with three glue layer thicknesses of 0.2mm,0.35 mm and 0.5 mm were prepared.The drop hammer impact tests of 5 J,10 J,20 J and30 J were carried out respectively.The impact damage types of the joints were analyzed by section method and SEM.The analysis shows that the adhesive riveted joint with the thickness of 0.35 mm adhesive layer has good static strength and shock absorption capacity.The shear failure forms are the initial failure of adhesive layer fracture and the de riveting failure of rivet and upper plate separation.The three kinds of glue riveted joints have good impact resistance to impact energy of 10 J and below.The joint with 0.2 mm glue layer thickness has the possibility of penetration under high-energy impact.After 20 J and 30 J energy impact,the joint with 0.5 mm glue layer thickness is more prone to load failure earlier.The comprehensive analysis shows that the glue riveted joints with the thickness of 0.35 mm and 0.5 mm glue layer can better withstand the high-energy impact load.There are four main types of low-speed impact damage: 1.Matrix cracking and internal fiber fracture of CFRP plate;2.Plastic deformation of aluminum alloy lower plate;3.The adhesive layer in the bonding area is cracked;4.The interlock performance decreases due to rivet movement.The static tensile test of the glue riveted composite joint before and after impact is carried out,and the microstructure and energy absorption value of the joint failure are analyzed.The results show that the joint with the thickness of 0.2 mm adhesive layer has good shear resistance and good residual strength after impact.The energy absorption value of the glue riveted joint with a thickness of 0.35 mm decreases significantly after 10 J energy impact.The impact damage doesn’t change the shear failure mode of the joint,and the influence of the static performance of the butt joint is reflected in the reduction of the maximum shear load and shear failure displacement of the joint.The failure mode of adhesive layer is the mixed failure of interface failure and adhesive layer shear fracture.There are two failure modes of carbon fiber bundle in CFRP plate: separation and radial fracture.Select the joint with the thickness of 0.35 mm adhesive layer as the test object,carry out high cycle fatigue test and SEM analysis on the joint before and after the impact of 10 J energy,and then carry out static tensile test on the joint with adhesive layer failure to analyze the residual strength of the joint after adhesive layer fatigue failure.The results show that the low-speed impact damage reduces the fatigue life of the adhesive layer of the glue riveted joint.Under small loading load,the fatigue life of the adhesive layer of the joint decreases greatly.After impact,the fatigue life of the adhesive layer of the joint is more sensitive to the change of fatigue load.The small cracks caused by impact damage extend under the action of fatigue load,which leads to the shear failure at the edge of the adhesive layer.The riveting part still has good riveting performance,and the adhesive layer near the rivet has fatigue failure.After the failure of the joint adhesive layer,the damage to the riveted part caused by low-speed impact makes the connection performance of the riveted part of the impact joint lower than that of the non impact joint.