Research On Mechanical Properties Of Single-lap Joint

For aircraft assembly,the lap joint is the key part,about 85%of the damage occurred in the mechanical joints of rivet connection and bolt connection.The pin-load ratio of each rivet is different in the multi row rivet structure of the lap joint.Systematic study was carried out from the respect of interference to do the research of pin-load distribution homogenization of single,lap joint on which the risk area’s stress concentration optimization and load-bearing capability improvement of the lap joint was based.The following research work was carried out in this paper to optimize the mechanical properties of the lap joint.Firstly,Riveting process was analyzed and simplified calculation formula of residual stress around the hole after riveting was studied to offer contrast to simulation results.Further study of different holes expansion in the inner and outer side of joint was carried out.Secondly,the type force and transfer mode in the process of the load transfer from one plate to another through the rivet was analyzed.The pin-load distribution research of multi-riveted lap joint was carried out by means of the theory of rivet flexibility and the risk areas of the lap joint was predicted while it was loaded.Thirdly,three different optimization schemes were designed:a)different vertical offset of the pusher;b)same aperture,different rivet diameter;c)same rivet diameter,different aperture.Lap joint model was built and the riveting and tensile process simulation of three different schemes was carried out with ABAQUS.Last but not least,the mechanical properties of the lap joints of different groups were tested and verified.The main research results of this paper include:(a)Finite element model of the lap joint was established and simulation of the riveting and tensile process of different schemes was carried out.The simulation results of different vertical offset and fit clearances were analyzed and the regular pattern distribution of residual stress around rivet hole was summarized.Analysis of the ratio of pin-load and the distribution of stress was carried out basing on the simulation results of different vertical offset and fit clearances.Good and bad points of different optimization schemes were compared.(b)The mechanical properties of the scheme of different vertical offset were tested,and the real-time strain monitoring was carried out on the risk points and the critical sections.The stress and strain of the risk points and the trend of load transfer of the critical sections were analyzed,the results show that the simulation model was correct and effective.(c)Both of the simulation and experiment show:First,from the aspect rivet,reasonable control of the vertical offset of three rivets can uniform pin-load of single-lap joint and reduce the stress concentration of the rivet at both ends so as to improve the rivets’ bearing capacity of lap joint.Second,from the aspect sheet,reasonable control of the vertical offset of three rivets can reduce the risk areas’ stress concentration and uniform the stress distribution of inner and outer sheet at most so as to improve the sheets’ bearing capacity of lap joint.(d)For the countersunk head three-riveted single-lap joint,the optimal combination of the vertical offset is the vertical offset of the middle rivet larger than that of the two sides and the vertical offset of the rivet on the fixed side larger than the other side.