Intrinsic ductility for structural materials as a function of stress and temperature

Abstract

In recent years, a method has been developed to measure current creep strength at nearly constant structure in a high precision stress relaxation test (SRT), covering at least five decades in creep rate in a one day test. Results have been reported on a wide range of metallic alloys, polymers, composites and ceramics. In the present paper it is shown that these same data can be used to determine a measure of intrinsic ductility over the same range of stress, using results on a low alloy Cr–Mo–V steel. This is based on an experimental and theoretical correlation between elongation at failure and strain rate sensitivity, m. This refined SRT test can now be used to evaluate both the intrinsic creep strength and the intrinsic ductility as a function of stress in a single short-time test. The test can detect embrittling phenomena at very low creep rates as a function of temperature. This measure of ductility may be used directly in engineering design and remaining life assessment.

Keywords:

• Ductility
• creep
• stress relaxation
• strain rate sensitivity
• plastic instability
• low alloy steel

Acknowledgement

The experimental work was supported by Hitachi America Ltd. through Dr. Katsumi Iijima. Testing was conducted at Metcut Research Inc.

Disclosure statement

No potential conflict of interest was reported by the author.