Notch root biaxial cyclic strain behavior of type 304 stainless steel at elevated temperature using laser speckle strain/displacement gauge

A laser speckle biaxial strain gauge was developed to measure local strains , epsilon (y), epsilon (z), at notch roots. Measurements were made on singl e edge-notched type 304 stainless specimens under fully reversed cyclic loa ding at both 673 K and room temperature. The strain ranges, Delta epsilon ( y), Delta epsilon (z), and a ratio of those, phi=Delta epsilon (z)/Delta ep silon (y), were discussed in terms of a proposed notch root deformation con straint parameter which consisted of a notch root radius, a thickness of th e plate and a nominal stress level. It was found that the biaxial strain ra tio, phi, was uniquely correlated with the proposed parameter for all the t ested notches. It was also found that no change in the notch root strain ra nge during the whole fatigue life was observed for the limited condition in which the constraint parameter took a sufficiently large value. Furthermor e, the verification of Neuber's rule in terms of the measured strain was di scussed.