Research On Fretting Fatigue Of Sandwich Structure Clinch-bonded Hybrid Joints

As a light weight and high strength material,aluminum alloy has been widely used in the automotive field in recent years.As a mechanical cold forming connection technology,clinching technology which has the advantages of simple process,green environmental protection,and can connect multi-layer,dissimilar,and plating materials,has more and more applications in the field of sheets connection.Clinch-bonded hybrid joining technology,which combining bonding technology and clinching technology,avoid the drawbacks of the two joining techniques when used alone.Foam metal is a new functional material with pores inside.It has the characteristics of light weight and the ability of shock absorption,sound absorption,buffering and shielding electromagnetic.In recent years,it has been widely used as an energy absorbing member in automobiles.Considering the low strength of foam metal materials,it is currently used.With other metal sheets as sandwich structure to improve the impact resistance of the structure and to reduce mechanical vibration.In this paper,foam metal is used as the interlayer of the clinch-bonded hybrid joint.The influence of foam metal on the fatigue performance of the clinch-bonded hybrid joint and the fretting wear mechanism can be studied.It can provide strong theoretical guidance for the promotion and application of metal form and clinch-bonded hybrid technology.(1)The research on the connection process,the sandwich structure hybrid joint is prepared by the clinch-bonded hybrid joining technology.Since the failure mode of the clinched joint is mainly the neck fracture and button separation,the interlocking force and the strength of the neck material can be used to measure the joining quality of the joints.After analysis,the joint quality can be measured by the easy-to-measure bottom thickness.The foamed nickel,foamed copper and foamed iron-nickel were used as the interlayer material for the single-lap joints and the cross-lap joints.After measuring the bottom thickness of the joints,it was found that under the same test conditions,the density of the interlayer was larger,and the bottom thickness of the joint was larger.(2)The research on the static performance of the joints.The tensile-shear tests were adopted to obtain the static strength of different joints,it is found that the foam metal interlayer does not change the failure mode of the clinch-bonded hybrid joint,but the maximum load will be reduced while the maximum displacement will be increased of the single-lap joint.The maximum load will be increased while the maximum displacement will be reduced of the cross-lap joint.The influence of the load and displacement will affect the energy absorption value of the joints.In practical applications,the interlayer with small surface density will make the clinch-bonded hybrid joint have better energy absorption capacity.(3)The research on the fatigue performance of the joints,in order to acquire the fatigue data at different load levels,the fatigue tests were carried out on each groups of the joints.And the test data was fitted by straight line fitting method and curve fitting method.It was found that the curve fitting method can better fit the sub-fatigue zone data.By comparing and analyzing the fatigue life curve,it is found that the foam metal interlayer can significantly improve the fatigue strength of the clinch-bonded hybrid joint,and the foamed iron-nickel interlayer has the best effect.By comparing and analyzing the fatigue failure modes of the four groups of joints,it is found that the joint fatigue failure position is mainly at the neck of the joint when the loading level is high,and the failure position is transferred to the sheets when the loading level is increased.(4)The research on the fretting wear of the joints,by scanning the fretting wear position under different failure modes and performing elemental analysis on the fretting wear debris,it is concluded that when the loading level is high,the fretting wear debris is mainly concentrated at the indentation – surrounding area of the contact point of the two sheets.As the loading load decreases,the position of the fretting wear is located between the interlock part of the upper sheet and the lower plate.