塑性変形の程度に依存しない破壊靱性の評価

概要

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The experimentally observed fracture toughness K^*_<IC> is proportional to the true fracture stress σ_T and the root of Charpy impact value I_<CP> as K^*_<IC>=Kσ_T √<I_<CP>/E> where E is the Young's modulus and k a nondimensional constant. This formula is important to estimate the fracture toughness by easily observed values. The crack energy density (CED) Ε proposed by Watanabe as the strain energy per unit area at the edge of a crack, is the key concept in this discussion. If K^*_<IC> is redefined as the energy per unit area to break the edge of crack as Ε=((1- ν^2)/E)(K^*_<IC>)^2 where Ε_C is the critical value of Ε for breaking and ν the Poisson's ratio, the equation K^*_<IC>=K_<IC>√<Φ_C> is derived, where Φ_C the ratio of the observed energy to break the elastic-plastic solid and the one to break the perfectly deformed same solid with the fracture toughness K_<IC>. The above-mentioned estimation formula is derived from this equation which is meaningful in all states of metallic materials such as elastic, small scale yielding, large scale yielding and general yielding.
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