MEASUREMENT OF CYCLIC BIAXIAL ELASTOPLASTIC STRESSES AT NOTCH ROOTS

A straightforward procedure is demonstrated for measuring local cyclic elastoplastic biaxial stresses at notch roots. First, the biaxial cyc lic strains are measured over short gage lengths (150 or 200 micromete rs) with a laser-based strain measuring system. Then, cyclic stresses are computed from those measured strains by using an elastoplastic con stitutive model. The material selected for this study is HY-80 steel w hich has a fine grain size and is isotropic. Double-notched specimens were prepared with two different notch geometries: a U-shaped notch wi th a 4.76 mm radius and a V-shaped notch with a 1.0 mm radius, Two thi cknesses, 2.54 and 12.7 mm, were tested for each notch geometry to pro duce four different amounts of notch constraint. The results of cyclic biaxial strain measurements show good reproducibility. Stress computa tions based on two different constitutive models were used to compute stresses for the first cycle and a stable cycle. One of the constituti ve models is the classical J(2) flow theory and the other is a two-sur face cyclic plasticity model. The results computed using these two mod els show good agreement with each other, The measured stresses show th e effect of constraint on the elastoplastic behavior at notch roots un der cyclic loading conditions.