Abstract:In order to study the machining distortion of aluminum monolithic structures in the aerospace industry, the internal residual stresses in monolithic die forging beam of aluminum alloy 7050-T74 were measured by using contour method. Electrical discharge machining was performed to cut the cross section of the specimen and the cut surfaces were measured by using laser scanner. The measured contours were fitted by using a 3D cubic spline based algorithm and then applied as an initial displacement boundary condition normal to the cut plane in the FE model but in the opposite direction. A linear elastic finite element analysis was then undertaken to calculate the corresponding distribution of residual stress normal to the cut face. In addition, the hole drilling method was employed to measure the surface residual stress of specimen, and its results were compared with those by the contour method at the same locations. The results indicate that the residual stresses in the specimen can be attributed to the stretch bending craft. The T-shaped cross section residual stress distribution shows a typical bending distribution of compression near the convex zone balanced by tension in the concave zone. Contour method efficiently provides accurate residual stress distribution in the test material. The test error at the edge area can be modified in compliance with surface residual stress measurement techniques.

Key words: 7050 aluminum alloy; die forging; residual stress; contour method