Study on the Residual Stress and Fatigue Performance of Cold Expansion Hole on 7050-T7451

Cold expansion was employed on 7050-T7451 aluminum. Residual stresses were measured, fatigue tests were carried out for joints with different expansion, and the fracture surfaces of specimens were observed by scanning electron microscope (SEM). The results show that residual compressive stresses generate by cold expansion process. The maximum values of radial residual compressive stresses locate the middle of the inner wall of the hole and residual compressive stresses extend radially up to one diameter from the edge of the hole. Axial residual compressive stresses distribute near the exit. The fatigue lives N50 and N95,95 for specimen with strengthened hole with 5% expansion are respectively 3.54 and 3.68 times compared with non-strengthened hole. Fatigue fracture morphology shows the characteristics of mixed transgranular fracture and the propagation speed of the crack along horizontal direction is larger than vertical direction.

Effect of Thinckness on Residual Stress Fields of Cold Expansion Hole

In this paper, four axisymmetrical finite element models have been established to study effect of thinckness on residual stress fields of cold expansion hole, experiments were carried out to measure the residual stress of cold expansion hole and verify simulation results. The experiment results also show that cold expansion processing can decrease surface roughness of holes and improve surface quality. The FEM results show, at the top(bottom) surface, the volue of the radial residual stress varies with the plate’s thickness, and the regularities of distribution of the radial residual stress are identical. The volue and the regularities of distribution of the circumferential residual stress vary with the plate’s thickness. At the mid-thickness surface, the volue and the regularities of distribution of radial residual stress vary with the plate’s thickness. The volue of the circumferential residual stress varies with the plate’s thickness, and the regularities of distribution of the radial residual stress are identical.

Experiment and FEM Simulation on Residual Stress of Cold Expansion Hole

A 2D cylindrical plate model has been established to study the distribution of residual stress of cold expansion hole under different interference values. In addition, the effects of material models on residual stress fields are considered also. Experiments are carried out to measure the residual stress of cold expansion hole and verify simulation results. FEM results show, with interference values increasing, the higher residual radial and circumferential stresses are obtained. At same interference value, the residual stress of Hardening Material( HM ) model is much larger than that of Elastic Perfectly Plastic Material( EPPM ) model.

FEM Simulation and Experimental Test on Residual Stress of Cold Expansion Hole of Rectangular Plate

A 2D rectangular plate model has been established to study the residual stress fields of cold expansion hole. Experiments were carried out to measure the residual stress of cold expansion hole and verify simulation results. The FEM results show, with interference values developing, the maximum values of circumferential residual compressive/tensile stress increase and higher positive stress values are obtained at the boundary of the rectangular plate. However, higher positive stresses at the boundary of plate are harmful to the capacity of fatigue resistance, the determinations of best interference value to a certain wide plate were proposed. Finally, the effect of the plate width on the residual stress distribution was analyzed.