Surface damage accumulation in Sn–Ag solder joints under large reversed strains
During service, solder joints may encounter repeated reversed stress states. Since realistic solder joint specimen geometry employed for creep/stress relaxation studies does not facilitate stress reversal, shear test specimens consisting of 3/8″×3/8″×1″ copper blocks joined with eutectic Sn–Ag solder of realistic thickness of about 400 μm were used for this study. The mechanical behavior and microstructural features of the solder joint subjected to repeated reversed straining were investigated by imposing large shear strains. Damage accumulation on the surface of the solder joints due to a few such large shear strain reversals is very similar to that observed on the surface of thermomechanically fatigued joints made with the same solder.
Abstract A layer of random defects in the simple cubic Ising model with nearest neighbor ferromagnetic interactions of strength J is considered. Using the real space renormalization group method we calculate defect free energy in the whole temperature range. Specifically, we analyze: the layer of diluted defects, the layer of spin-glass type defects, and the layer of mixed defects. The free energy is strongly dependent on the value of couplings between the defect and the bulk.