2003 Volume 21 Issue 1 Pages 68-72
Residual stress in a bonded dissimilar material induced by the mismatch of material properties significantly reduces its bonding strength. For the purpose of the reduction of bonding residual stress, low yield strength materials have been widely used as an insert layer. However, introducing such a low yield strength material layer usually increases the mismatch of thermal expansion. There are two ways to reduce the bonding residual stress ; one is the decrease in the mismatch, which reduces the residual stress induced during the bonding process, and the other is the relaxation of bonding residual stress after bonding process. The later method seems to be more effective and economic. This paper proposed a simple method to relax the bonding residual stress by employing the properties of cyclic plastic deformation. Both the effects of cyclic pre-loading on the static and the fatigue strengths of the bonded dissimilar material were investigated experimentally by using bonded W/Cu joints. It is found that only the first few cycles of the pre-loading corresponds to the relaxation of the residual stress, and the relaxation effect depends on the amplitude of the cyclic pre-loading. Numerical analysis by finite element method was also carried out to explain the relaxation mechanism of the residual stress. It is also found that it is possible to raise the static and fatigue strength of the bonded material up to the level of monotonic Cu strength, if proper pre-loading condition is selected.
