Computer-Aided Interpretation of Stress-Strain Curves

Abstract A computer scheme for interpreting stress-strain curves has been developed using two basic algorithms. The first locates the initial linear portion of the curve by comparing the fit of linear and quadratic curves to the data. The second determines the intersection of the offset line with the data. The scheme was tested by comparing computer results with manual results obtained by skilled observers. Results were good: tensile strength and 0.2 percent offset yield strength showed small differences, less than 2 percent. For the modulus and yield strength at 0.01 percent offset, the differences between the various observers were more significant than the differences between the computer results and the observers. For 32 samples (95 specimens) the computer results for the modulus were generally within ±2 percent of the average of the results from four observers and within ±10 percent for the 0.01 percent yield strength. Based on these results, a standard computer program has been developed which generates graphical summaries of the mechanical properties in a form suitable for permanent records.