Dwell Time Effects on Fatigue Life and Damage Mechanisms

An overview of dwell sensitivity fatigue behavior of high temperature materialssubjected to various creep-fatigue cycles is summarized. Published data from the literature werepresented in terms of strain range and normalized cycle ratio and dwell sensitivity behaviormapped for various alloy groups. A summary of dwell sensitivity behavior has been presentedsummarizing alloy group in terms of dwell sensitivity. It is elucidated that mechanisms controlingdwell sensitivity were due to mixed transgranular and intergranular cracking, creep damage bytriple point cracking, cavity formation, and oxidation striated surface damage. The transition fromtransgranular to intergranular damage was from resulting deterioration in tensile properties andother test parameters. It is speculated that dwell cycles evolved mean stresses in tension andcompression directions. Mean stress in tension was more deleterious and caused more dwellsensitivity than compressive mean stresses. However, compressive mean stress in steel alloyscaused also accelerated cracking and dwell sensitivity. The observations for different materials aresummarized.