REVIEW OF NONLINEAR REPRESENTATION OF THE LOAD FREQUENCY CHARACTERISTICS OF FRACTURE LIFE FOR NOTCHED SPECIMENS UNDER CREEP-FATIGUE CONDITIONS FOR HEAT RESISTANT METALS BASED ON CHAOS THEORY

摘要

The load frequency characteristics of fracture life for notched specimens under high temperature creep-fatigue conditions for various heat resistant metals were found to show various features such as linear or nonlinear load frequency characteristics. The effect of temperature, stress holding time and multi axial stress on the load frequency characteristics of fracture life were described using our proposed catastrophic curved surface theory (chaos theory) for creep brittle and ductile materials. Furthermore, on the basis of chaos theory, the relationships between fracture life and load frequency were formulated as a function of our proposed time dependent promoting factor, P which quantifies the occurrence degree of time dependent mechanism. From these results, decrease in temperature (environmental condition) and stress holding time (loading condition) and increase in multi-axial stress (structural brittleness) were found to suppress time dependent mechanism of fracture life and cyclic dependent mechanism becomes dominant in fracture life. These were also quantified by P.