A study of creep damage using microradiography and continuum damage mechanics
The development of intergranular creep damage was investigated in several alloys using the synchrotron x ray microradiography, an x ray imaging technique utilizing the transmitted beam. The technique of synchrotron microradiography was developed and refined. A 100-fold improvement in the resolution of the technique was realized, and features on the order of microns can now be routinely observed. The resolution which can be achieved as well as the factors influencing resolution and sensitivity were determined. The technique was then applied to the study of the development of creep damage around notches in three metals. Notched tensile samples of copper, iron, and a low alloy steel were subjected to slow strain rate tensile testing at 500 or 700 C. The tests were interrupted at various fractions of the creep life. The density and distribution of creep damage was measured from the microradiographs with an image analysis system; and the results from the image analysis were compared to damage predictions from a continuum damage mechanics model of the damage process. Creep damage in the copper alloy was concentrated in a fairly narrow band around the plane of minimum cross-section in the samples. This is in stark contrast to the results from iron and the low alloy steel. The creep damage in these materials developed at fairly sharp angles to the notch or crack plane. The results show that the damage processes in iron and this steel are controlled by the equivalent stress, consistent with a plasticity mechanism of cavity growth. The formation of damage in copper is controlled by the maximum principal or hydrostatic stress, confirming a diffusive creep damage growth process.
- Research Organization:
- Pennsylvania Univ., Philadelphia, PA (USA)
- OSTI ID:
- 7075213
- Resource Relation:
- Other Information: Ph.D. Thesis
- Country of Publication:
- United States
- Language:
- English
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