繰返し荷重下の船体用構造材料の変形挙動と強度特性に関する研究(その3)

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In the previous paper, a method for determining the fatigue limit of mild steel SM 41 B under variable-amplitude loading condition has been proposed. It is shown that the fatigue limit coincidences with the stress level where the deformation mechanism of the material changes from visco-elastic to visco-plastic-elastic behavior. The transition point is detected by measuring hysteresis energy of cyclic stress-strain response when cyclic hardening disappears (stress-strain behavior keeps constant). A visco-plastic-elastic constitutive equation is proposed in order to analyze the above behavior. For arbitrary loading history, the transition stress level, that is the same as the fatigue limit, can be calculated by formalizing the developing equations of the coefficients of the constitutive equation. In this report, the relationship between macroscopic stress-strain response and strength characteristics of Aluminum alloy A 5083 P-O is investigated. However, the above method can not be applied to A 5083 P-O, because this material yields no plastic strain when cyclic hardening disappears. That is, plastic strain increases just after applied stress amplitude increases, then plastic strain decreases gradually and stress-strain behavior keeps completely elastic stress-strain state. This stress-strain behavior is called "strain burst". This plastic strain is mainly investigated as a parameter instead of stable stress-strain behavior. Main points are as follows : 1)Plastic strain measured during transition term depends on loading history, such as load sequence, increment of applied stress and number of loading cycle, etc. 2)It Is possible to estimate the density of dislocations which is released when strain burst occurs. The density of released dislocation would be related to the possibility that PSB (persistent slip band) is developed.
社団法人日本船舶海洋工学会の論文

繰返し荷重下の船体用構造材料の変形挙動と強度特性に関する研究(その3)

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