24 research outputs found
Proportional/non-proportional constant/variable amplitude multiaxial notch fatigue: cyclic plasticity, non-zero mean stresses, and critical distance/plane
This paper deals with the formulation and experimental validation of a novel fatigue lifetime estimation technique suitable for assessing the extent of damage in notched metallic materials subjected to inâservice proportional/nonproportional constant/variable amplitude multiaxial load histories. The methodology being formulated makes use of the Modified MansonâCoffin Curve Method, the Shear StrainâMaximum Variance Method, and the elastoâplastic Theory of Critical Distances, with the latter theory being applied in the form of the Point Method. The accuracy and reliability of our novel fatigue lifetime estimation technique were checked against a large number of experimental results we generated by testing, under proportional/nonproportional constant/variable amplitude axialâtorsional loading, Vânotched cylindrical specimens made of unalloyed mediumâcarbon steel En8 (080M40). Specific experimental trials were run to investigate also the effect of nonâzero mean stresses as well as of different frequencies between the axial and torsional stress/strain components. This systematic validation exercise allowed us to demonstrate that our novel multiaxial fatigue assessment methodology is remarkably accurate, with the estimates falling within an error factor of 2. By modelling the cyclic elastoâplastic behaviour of metals explicitly, the design methodology being formulated and validated in the present paper offers a complete solution to the problem of estimating multiaxial fatigue lifetime of notched metallic materials, with this holding true independently of sharpness of the stress/strain raiser and complexity of the load history