Research On Strengthening Performance Of The Hole After Cold Expansion Of Split Sleeve

Cold expansion strengthening technology of split sleeve is widely used in aviation field,and it is one of the most effective technologies for strengthening structural holes of aircraft at present.In this paper,combined with the theoretical basis of cold expansion and finite element simulation software,taking 7050 aluminum alloy perforated plate as the research object,the technological effect and fatigue life of cold expansion strengthened hole of split sleeve are studied.Firstly,the advantages of cold expansion strengthening of split sleeve compared with other holes are analyzed.Starting with the preparation method of split sleeve,the influence of preparation method on the strengthening effect of split sleeve is expounded.Based on the theory of elastic-plastic deformation,the stress and strain of sleeve and test plate during expansion and the springback of test plate after expansion are quantitatively analyzed.Based on ABAQUS simulation software,the finite element model of cold expansion strengthening process of split sleeve was established.The stress and strain distribution of metal sheet,hole deformation and mandrel tension were analyzed,and the finite element model was verified.The results show that a certain range of residual compressive stress layer is produced around the strengthened hole,and the hole wall metal flows out toward both ends along the axial direction of the hole.The change of hole diameter and the tension of mandrel are consistent with the actual situation.Based on the correct simulation model,the effects of different expansion parameters,such as expansion amount,split width of sleeve and working section length of mandrel,on cold expansion strengthening effect of split sleeve were studied.The results show that the residual compressive stress increases with the increase of expansion amount,and the maximum value of residual compressive stress remains unchanged when the expansion amount reaches 4.5%.Under the same expansion amount,the best expansion process is that the slit width is about 0.1mm and the working section length of mandrel is about2 mm.The fatigue life is preliminarily predicted by fatigue theoretical calculation and fatigue simulation.The fatigue test was carried out to verify the cold expansion strengthening effect of split sleeve and the accuracy of prediction,and the appearance of fracture was analyzed.The results show that both theoretical calculation method and simulation method can prove that expansion strengthening of split sleeve can improve the fatigue life of hole.Through the fatigue test,the fatigue life of the extruded and reamed plate is 10 times longer than that of the un-extruded and strengthened plate.According to the analysis of fracture appearance,the fatigue crack first originates on the side of the hole wall near the expansion surface,which is consistent with the simulation analysis.