Thermal cycle response of a lead-free solder reinforced with adaptive shape memory alloy

Shape memory alloy (SMA) discontinuous reinforcements in a solder matrix have the potential to reduce inelastic strains and improve thermo-mechanical fatigue (TMF) life of solder joints. In this work, concept viability was tested on a simpler configuration consisting of a single NiTi wire embedded in a cylindrical Sn–3.5Ag solder matrix. The composite samples were thermally cycled at a constant shear stress under double shear loading perpendicular to the fiber axis, and the local shear displacement was monitored. The local displacement plots indicate significant reduction in creep rate of the SMA reinforced composite versus a control Cu-wire reinforced composite, suggesting that SMA particulate reinforcements may be a feasible option. In order to understand and model the composite response, tests were also conducted on the bare NiTi wire. A preliminary model based on Eshelbyʹs transformation strains provided reasonable agreement with the displacement response of the composites.