Experimental Uncertainties affecting the Accuracy of Stress-Strain Equations by the Example of a Hensel-Spittel Approach

摘要

The accuracy of numerical simulations in metal forming highly depends on the description of the plastic flow behavior. Due to experimental uncertainties flow curves recorded at equal testing conditions (combinations of temperature and strain rate) show scatter. This scatter influences the fit of material models and the resulting fit parameters. In this paper, factors causing uncertainties and systematic errors as well as ways to statistically describe uncertainties in the flow stress are analyzed by means of finite element simulations and experimental analyses of compression tests. To this end, compression tests were conducted for a 25MoCr4 steel to record flow curves for various temperatures and strain rates. To grasp experimental uncertainties, each experiment was repeated five times. The well known Bootstrap method was applied to characterize the uncertainties in fitting a Hensel-Spittel flow curve model to the experimental data. This method is compared with an alternative strategy of resampling the experimental data regarding the confidence intervals of the predictions made with the model.