Improved Analysis of Miniature Impact Toughness Tests

A series of miniature impact tests was conducted. The analysis of instrumented impact curves was studied, and explicit procedures were sought to increase the consistency and reproducibility of results, as well as a decrease human influence on the analysis. These procedures are suggested for future considerations. In order to smoothen noise and oscillations in the force-displacement curve, low-pass filtering of data is considered the most promising alternative. The method results in the most consistent elastic slopes and forces at onset of general yielding Fgy. A suitable cutoff frequency can be found by spectral analysis of the signal since it varies between test setups, but a phase shift in the resulting data needs to be addressed. In the analysis, different characteristic points are identified on the force-displacement curve. When determining these points, the curve is sectioned into parts. Fitting Hooke’s line in the elastic region follows previously suggested methods. A polynomial of varying degree is fitted to the region following the elastic limit. Points of discontinuity reveal unstable fracture initiation and arrest locations, and a model consisting of linear and exponential terms is fitted to data beyond arrest. Once finalized, the points of interest in the instrumented impact curve are determined in accordance with ASTM and ISO standard guidance by searching the intersections of the fitted curves. Identification of the characteristic points in a consistent manner increases the confidence on material assessment from the data.