| The mechanical structure is connected by a large number of rivets,bolts and other fasteners.These connection methods cause a large number of connection holes in the structure,causing material discontinuity and stress concentration,increasing the probability of fatigue failure in the process of using,and affecting structural safety.At present,in the fastening hole strengthening technology,the split-sleeve cold extrusion strengthening process is the most advanced,but the research about residual stress and fatigue life after strengthening is not comprehensive enough.In addition,Aluminum alloy is widely used in ship and aerospace,vehicle manufacturing,biological implantation,nuclear industry and other fields due to its high thermal stability,ratio of strength and corrosion resistance.In this paper,the split-sleeve cold extrusion strengthening and hole-reaming of 7050 and 7075 aluminum alloy substrate holes are numerically simulated,and cold extrusion test,fatigue test and full life simulation are carried out to study the effect of these process on residual stress distribution and fatigue gain effect.A three-dimensional model of the split-sleeve cold extrusion strengthening process was established and numerically simulated.The error of the extrusion amount between the simulation results and the test results was within 5%.The distribution law of the residual stress field after strengthening was obtained,and the tangential residual stress distribution law of the hole after cold extrusion strengthening under different relative extrusion amounts and different hole depths was analyzed.A three-dimensional model of the hole-reaming process was established.The distribution law of the residual stress field after the reaming was obtained after numerical simulation.The orthogonal test design of three factors and three levels was carried out on the relative extrusion amount,hole depth and reaming amount.The influence of the three factors on the tangential residual stress distribution of the extrusion surface was analyzed.The fatigue test is designed and completed.The results show that the fatigue life of 7050 and 7075 aluminum alloy perforated plates with relative extrusion amount of 3% is increased by 3 ～ 4 times.It is also found that after the split-sleeve cold extrusion strengthening process,different reaming amounts have slightly different results on the final fatigue life.Based on the residual stress field after cold extrusion strengthening and reaming,the fatigue life simulation is carried out and the fatigue life and fatigue failure position of the unstrengthened and strengthened perforated plate are obtained.The fatigue life results are compared with the fatigue test results,and the errors are within 20%.The fatigue life simulation was carried out for different relative extrusion amount,hole depth and stress ratio,and the influence of the three on the fatigue life of split-sleeve cold extrusion strengthening was obtained. |
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