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 cyclic strains are measured over short gage lengths (150 or 200 micrometers) with a laser-based strain measuring system. Then, cyclic stresses are computed from those measured strains by using an elastoplastic constitutive model. The material selected for this study is HY-80 steel which has a fine grain size and is isotropic. Double-notched specimens were prepared with two different notch geometries: a U-shaped notch with a 4.76 mm radius and a V-shaped notch with a 1.0 mm radius. Two thicknesses, 2.54 and 12.7 mm, were tested for each notch geometry to produce four different amounts of notch constraint. The results of cyclic biaxial strain measurements show good reproducibility. Stress computations based on two different constitutive models were used to compute stresses for the first cycle and a stable cycle. One of the constitutive models is the classical J₂flow theory and the other is a two-surface cyclic plasticity model. The results computed using these two models show good agreement with each other. The measured stresses show the effect of constraint on the elastoplastic behavior at notch roots under cyclic loading conditions.