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 single edge-notched type 304 stainless specimens under fully reversed cyclic loading 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 epsilon (y), were discussed in terms of a proposed notch root deformation constraint parameter which consisted of a notch root radius, a thickness of the plate and a nominal stress level. It was found that the biaxial strain ratio, phi, was uniquely correlated with the proposed parameter for all the tested notches. It was also found that no change in the notch root strain range during the whole fatigue life was observed for the limited condition in which the constraint parameter took a sufficiently large value. Furthermore, the verification of Neuber's rule in terms of the measured strain was discussed.