1986 Volume 27 Issue 6 Pages 416-424
The influence of notch shape on the elongation has been investigated for a Sn-38.1 mass%Pb superplastic alloy using specimens with a couple of various V-type notches or a small hole type notch.
The elongation of the notched specimen seemed to have a correspondence with the ratio of the cross-sectional area of the specimen, An⁄As, where An was the minimum area appearing at the bottom of notch and As the original area in the smooth part. However, since the concept based on the ratio itself had no consideration on the significant difference due to the shape of notch, the analysis could not explain the variation in the elongation of specimens with different shapes of notch. Therefore, a simple model of superplastic deformation has been proposed in order to express the difference in notch shape more properly. The model is taking account for distributions of both the strain rate and the m-value (σ=K\dotεm, σ: flow stress, \dotε: strain rate and K: constant) over the gage length on the specimen, which correspond to the change in cross-sectional area in the gage section including the notch. Using the model, the elongation of the notched specimen has been calculated by the numerical analysis on the basis of the relation between the true stress and the true strain rate for the smooth specimen; a comparison between the experimental and the calculated values of the elongation has been carried out systematically. As a result, it is revealed that the two values are in a fairly good agreement. It is also considered that the flow stress during superplastic deformation is almost directly related to the true strain rate.
