Plastic stress-strain history at notch roots in tensile strips under monotonic loading

Various authors have proposed analytic relations for predicting the plastic behavior at the root of a notch. Among these are relations by Neuber and by Hardrath and Ohman, the latter having generalized on earlier work by Stowell. These methods have had limited experimental confirmation and it was the objective of the investigation reported herein to assess the predictive value of each of the two theories by comparison with test data on externally notched tensile specimens, monotonically loaded to large strains. Since maximum notch-root strain and net-section stress are the only parameters which can be directly measured in a test, theoretical predictions of these same parameters were developed. This was done using a piece-wise analytical representation of the stress-strain curve. Computer programs were developed for analyzing the stress-strain data and for computing the theoretical results. A comparison of theory with tests on flat, notched specimens of AISI 4340 steel, heat treated, with initial elastic concentration factors of 1.5 to 2.0 showed a systematic discrepancy which is attributed in part to notch strengthening due to triaxial stress. The discrepancy is of the order of 5 percent for the Neuber theory and larger for the Hardrath-Ohman theory for notch strains less than of 0.015 in./in. and becomes progressively larger for both theories at notch strains in excess of 0.015 in./in. For the mild notches studied here, the Neuber theory has better predictive value.