Analysis Round Robin Results on the Linearity of Fracture Toughness Test Data

All ASTM standards require precision and bias statements that address the typical variability observed when performing the standard. It is useful to determine the different sources of variability in a given standard so that future efforts can be undertaken to minimize error in the resulting material properties measured by that standard. This analysis round robin was undertaken with nine participants using fifteen different previously measured load-displacement datasets from linear-elastic, K-IC fracture toughness tests fabricated from aluminum, titanium, and steel material. Each round robin participant analyzed the data using their own previously proven methods. A bi-modal trend in PQ variation was noted with +/- 1 % variability capturing 40 % of the datasets and +/- 4 % generally capturing the remaining 60 % of the datasets, although there were outliers observed. In summary, the method used to analyze the load-displacement response in a linear-elastic fracture toughness test contributes to between a minimum of one-tenth and on average one-third of the overall uncertainty quoted in the K-IC precision and bias statement. Although the analysis methodology is likely not a primary contributor to the overall variability observed in a fracture toughness test, it is a significant contributor. In two of the nine datasets, linearity analysis methodology accounted for in excess of 10 % error. The observed variability did not definitively appear to be material related although some systematic trends were noted as a function of participant.