Research On Fretting And Fatigue Mechanism Of Self-piercing Riveting In Aerial Light Alloy Sheets

Recenty,the technology of self-piercing riveting(SPR)has been widely applied in all walks of life gradually,because of its distinctive features,such as:simple process,convenient operation,easy to implement mass production.And to date,it has become the most promising connection technology of green and safe,which is most possible to displace the resistance spot welding.In order to make a preliminary exploration on the application prospect of self-piercing riveting technology in aerospace manufacturing industry,the riveting feasibilities of aerial light alloy sheets,such as:titanium alloys and aluminium lithium alloys,and the static and fatigue performances of SPR joints were investigated in this paper,based on the technology of self-piercing riveting.And the failure and fretting mechanisms of the joints were also analysed emphatically in this paper.The research works are mainly summarized as below:1.The research on the self-piercing riveting process.Self-piercing riveting tests were carried out to connect similar and dissimilar sheets in TA1 titanium alloys and AL1420 aluminium lithium alloys.And the sheet combination in TA1-AL1420 was conducted in the same specifications of the rivets with different hardnesses of H4 and H6.The optimal riveting process parameters of five kinds of SPR joints were obtained through the contrast tests.And the forming quality evaluations of corresponding joints were executed later.Results show that similar or dissimilar sheet combinations in aerial light alloys can be connected availably using the technology of self-piercing riveting,and the forming qualities of the joints are qualified.2.The research on the static performances of SPR joints.The static tensile-shear tests were adopted to obtain the static strength of different joints.And the detailed mathematical analyses and validation tests were carried out on the static test data of each group of SPR joints.The mean of relevant data of different joints were calculated based on MATLAB 2014b,and the comparative analyses were conducted for the static failure loads and energy absorption abilities of different groups of the joints.At last,the macro failure modes and static failure mechanisms of the joints were analysed in detail.Tests show that substrate performances and overlap forms of dissimilar sheets have a significantly influence on the static performances of the joints,and the hardnesses of the rivets also have a certain effect on the static performances.3.The research on the fatigue properties of SPR joints.In order to acquire the fatigue data at different load levels,the fatigue tests with single tensile-tensile mode were executed on each groups of the joints.The straight line fitting and curve fitting were conducted based on MATLAB 2014b for plotting the fatigue curves of different joints.And the comparative analyses about these two fitting methods were made in detail.At last,the macro fatigue failure modes and microstructures of different groups of the joints were analysed particularly.Researches indicate that the fatigue strengths of the joints in similar sheets are much better than that of the joints in dissimilar sheets.The fatigue strength of the joints in dissimilar sheets with AL1420 as the upper sheets is superior to that of the joints in dissimilar sheets with TA1 as the upper sheets.And the fatigue property of the joints in TA1-AL1420 with the rivet H6 is significantly better than that of the joints in TA1-AL1420 with the rivet H4.4.The research on the fretting mechanisms of SPR joints.On the basis of the analyses about the macro fatigue failure modes and microstructures,the black fretting debrises existed in the failure spcimens were studied further.And qualitative investigations were carried out on these fretting debrises in order to obtain the elementary compositions.The generation mechanisms of the fretting debrises and the initiation mechanisms of the fatigue cracks were discussed deeply based on the failure features of the joints and the distribution areas of the fretting debris.Analyses demonstrate that the fretting wear has a direct influence on the fatigue strength and failure modes of the joints and the initiation areas and expanding paths of fatigue cracks.