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CONTINUOUS SEM OBSERVATIONS OF CREEP‐FATIGUE DAMAGE PROCESSES
Author(s) -
Tetsuya Ogata,
Arai
Publication year - 1998
Publication title -
fatigue and fracture of engineering materials and structures
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.887
H-Index - 84
eISSN - 1460-2695
pISSN - 8756-758X
DOI - 10.1046/j.1460-2695.1998.00072.x
Subject(s) - creep , materials science , coalescence (physics) , microstructure , scanning electron microscope , grain boundary , composite material , dislocation , fracture mechanics , grain size , metallurgy , optical microscope , physics , astrobiology
In order to examine the relation between damage evolution and changes in microstructure, e.g. from creep cavities, surface micro‐cracks and dislocation structures at high temperature, strain controlled creep‐fatigue tests were performed and interrupted at several damage levels on Types 304 and 316 stainless steels. The creep‐fatigue tests on Type 304 stainless steel at a low strain level were conducted in a high‐temperature fatigue testing machine combined with a scanning electron microscope, and the micro‐crack initiation and growth behaviour were continuously observed to clarify the damage extension mechanism. It was found that even though many cavities were initiated and grew on the internal grain boundaries of the specimens during the strain‐controlled tests, the failure life was governed by the propagation of surface cracks. On the other hand, micro‐cracks of about the order of one grain size were initiated mainly along grain boundaries normal to the loading axis under low stress creep‐fatigue, and the crack propagation rate of the micro‐cracks was slow and random due to the nature of the microstructures. The micro‐cracks gradually opened in the loading direction with increasing number of cycles and coalescence contributed to growth.