Effect of Tensile Ratcheting Deformation on Creep-Fatigue Life of Sn-37Pb Solder Material

摘要

The effects of ratcheting strain on creep-fatigue life of Sn-37Pb solder material were studied by conducting isothermal constant amplitude strain controlled creep-fatigue tests under four kinds of triangular strain waveform accompanying a small tensile ratcheting strain at room temperature. Four kinds of strain waveform used are so called fast-fast, fast-slow, slow-fast and slow-slow ones, and their applied inelastic deformations can be partitioned into Δε{sub}(pp)+δ{sub}p, Δε{sub}(pp)+ Δε{sub}(pc)+δ{sub}p, Δε{sub}(pp)+ Δε{sub}(cp)+δ{sub}c, Δε{sub}(pp)+ Δε{sub}(cc)+δ{sub}c, respectively, based on the strainrange partitioning concept, where Δε{sub}(ij)(ij=pp, pc, cp and cc ), δ{sub}p andδ{sub}c are partitioned inelastic strain ranges, fast-strain-rate ratchet strain and slowstrain-rate ratchet strain, respectively. The test results were analyzed by usingΔε{sub}(ij)-N{sub}(ij) relationships (ij=pp, pc, cp, cc ) and tensile properties of the material. As the results, the creep-fatigue lives in constant amplitude creep-fatigue tests accompanying a tensile ratcheting strain could be evaluated within an accuracy of a factor of 2 by the following equation of life prediction: 1/N{sub}f=1/N{sub}(pp) + 1/N{sub}(ij) + δ{sub}i/D{sub}i (ij=pc, cp, cc), where D{sub}p and D{sub}c are values of material ductility obtained by fast and slow straining tensile tests, respectively. It should be noted, however, that this equation tends to evaluate, PC-ratchet test life with conservatism, while CP-ratchet test life with nonconservatism.