Inelastic Strain Analysis of Solder Joint in NASA Fatigue Specimen

摘要

The solder fatigue specimen designed by NASA-Goddard/UNISYS is analyzed in orderto obtain the inelastic strain history during two different representative temperature cycles specified by UNISYS. Results are summarized from viscoplastic finite element analysis of the solder fatigue specimen for delta(T) = 113 C cycle. Large deformation continuum formulations in conjunction with a standard linear solid model is used for modeling the solder constitutive creep plasticity behavior. Relevant material properties are obtained from the literature. Strain amplitudes, mean strains, and residual strains (as well as stresses) accumulated due to a representative complete temperature cycle are obtained as a result of this analysis. The partitioning between elastic strains, time independent inelastic (plastic) strains, and time dependent (creep) strains is also explicitly obtained for two representative cycles. Detailed plots are presented for two representative temperature cycles. This information forms an important input for fatigue damage models, when predicting the fatigue life of solder joints under thermal cycling.