Improvement of impact strength of friction-welded joints by weld interface shape optimisation.

摘要

This paper describes an analytical investigation and experimental verification of an attempt to improve the impact strength properties of Cu/Al friction-welded joints through the stress concentration at the interface of welded joints produced from dissimilar materials being reduced through control of the weld interface edge shape by edge bevelling. The results obtained may be summarised as follows.The free-edge stress singularities at the Cu/Al weld interface edge in a plane strain state disappear within the apex angle ranges (the apex angle being the angle subtended between the free edge and weld interface) #theta#_1<= 58 deg, 98 deg<= #theta#_1 <= 126 deg, the free edge stress singularities are found to disappear. For normal joints, stress singularities of around p = 0.03 are found at #theta#_1 = 90 deg. The stress singularity exponents of the intersection also have a finite value at all angles excluding #theta#_1 = 90 deg.The results of the FEM analyses suggest that, near the intersection, the stress component in the tensile axis direction #sigma#_a gives tensile stress concentration in joints with #theta#_1 = 45 deg and compressive stress concentration in joints with #theta#_1 = ll0 deg and #theta#_1 = 135 deg. Near the weld interface edge, however, free-edge stress singularities are found in joints with #theta#_1 = 90 deg and #theta#_1 = 135 deg. In joints with #theta#_1 = 45 deg, stress component #sigma#_a imposed on the weld interface edge tends to decrease. In joints with #theta#_1 = 110 deg, stress component #theta#_a has a virtually constant value.The results of static tensile strength tests of joints with #theta#_1 = 40 deg, #theta#_1 = 45 deg, #theta#_1 = 90 deg, #theta#_1 = 110 deg, and #theta#_1=135 deg indicate that the fracture position is always in the Al raw material and that the strength of the weld interface in Cu/Al friction-welded joints is better than the tensile strength of the Al raw material. high absorbed energies, and low scatter of data. The results of the FEM analyses and corresponding experimental results further indicate that, within the experimental range adopted in the present study, the intersection of the weld interface strongly affects the impact fracture behaviour.