728 Sn-37Pb はんだ材のクリープ疲労寿命におよぼすラチェット変形の影響

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

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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 teir applied inelastic deformations can be partitioned into (Δε)_<pp>+δ_p, (Δε)_<pp>+(Δε)_<pc>+δ_p, (Δε)_<pp>+(Δε)_<cp>+δ_c, (Δε)_<pp>+(Δε)_<cc>+δ_c, respectively, based on the strainrange partitioning concept, where (Δε)_<jj> (ij=pp, pc, cp and cc), δ_p and δ_c are partitioned inelastic strain ranges, fast-strain-rate ratchet strain and slow-strain-rate ratchet strain, respectively. The test results were analyzed by using (Δε)_<ij>-N_<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 a accuracy of a factor of 2 by the following equation of life prediction : 1/N_f=1/N_<pp>+1/N_<ij>+δ_i/D_i (ij=pc, cp, cc), where D_p and D_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 CP-ratchet test life with conservatism, while CP-ratchet test life with nonconservatism.

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