STUDY ON MECHANISM OF STRESS-STRAIN REDISTRIBUTION BY ELASTIC-PLASTIC-CREEP DEFORMATION

摘要

Design of structures subjected to elevated temperature is substantial, especially at structural discontinuities where strain concentration induced by stress-strain redistribution causes a reduction of creep fatigue strength. In the design of those structures, it is needed to consider elastic-plastic-creep deformation. Methods to estimate elastic-plastic-creep deformation are categorized into inelastic FEM analyses and simple methods based on elastic FEM analyses. The latter methods provide the advantages of shorter calculation time and uniqueness of results. Stress Redistribution Locus (SRL) was proposed as one of the simplified methods. Previous analyses indicate that SRL depends on neither constitutive equations nor magnitude of loads. By clarifying the mechanism of stress-strain redistribution, and determining a condition where the SRL coincide, this method can be utilized as a rational analysis for inelastic structural design. The objective of this study is to clarify the mechanism which determines SRL in elastic-plastic-creep deformation. Firstly, elastic-plastic analyses were achieved in a pipe model. Considering an analogy based on the theoretical solution of a two bars model, the pipe model with fixed elastic core ratio was analyzed. In consequence, it was clarified that stress-strain redistribution by elastic-plastic deformation depends on the area of the elastic cores. Secondly, elastic-creep analyses and elastic-plastic-creep analyses were performed in the same model, and it was revealed that the elastic core is the main factor on stress-strain redistribution induced by elastic-plastic-creep deformation.