DWELL SENSITIVITY .1. BEHAVIOR AND MODELING

This paper examines the dwell sensitive behavior of materials subjecte d to creep-fatigue deformation. A study of published creep-fatigue dat a on seventeen materials was conducted to investigate the dwell sensit ivity for different materials under different hold times applied in te nsion and compression. The seventeen materials selected were such that their melting temperatures varied from 250 to 1700 degrees C, and the test temperatures ranged from 0.4 to 0.75 of the homologous temperatu re, where creep and fatigue interact. The dwell sensitivity was found to depend upon the test temperature, period of hold time, and hardenin g and softening phenomena of the materials subjected to a particular c yclic waveform. Since no previous model exists for the prediction of d well sensitivity, it is conceptualized in a cycle in terms of hardenin g (H) and softening (S) and their combinations in tension (T) and comp ression (C) directions. Thus, for a cycle (TC), there are four possibl e combinations namely HS, HH, SH and SS. A demonstration of such combi nations with H and S was made for a tensile dwell sensitive material w here cycles produced tensile hardening and compressive hardening or HH were found to cause dwell sensitivity. However, for a compressive dwe ll sensitive material, the combinations were tensile hardening and com pressive softening or HS. This study on dwell sensitivity attempts to address an important material behavior which is not very well understo od and may initiate further research interests.