A round-robin testing exercise on the application of the load separation criterion in J-testing of ductile polymers

The most used approach for determining the fracture resistance of ductile polymers at low loading rates is based on the construction of the material crack growth resistance curve (J vs crack extension, Δa), usually constructed by the application of a multi-specimen methodology (ESIS TC4 procedure). ESIS TC4 round-robin, RR, tests have pointed out that often this methodology does not provide reliable data due to the uncertainties associated with the measurement of Δa; further, in many cases, an initiation fracture resistance parameter, JIc, cannot be properly evaluated. With the aim to strengthen this multi-specimen methodology, the ESIS TC4 attention has been recently focused on the analysis of a single-specimen testing scheme based on the load separation criterion, that does not require the measurement of Δa, and would allow to: i. determine a material pseudo-initiation fracture resistance parameter; ii. provide a rough measure of Δa produced during the fracture test, in the plastic region. To employ this new approach into a standardized procedure, the degree of reproducibility of the results obtainable with the application of this testing scheme has to be assessed and, with this in mind, a specific multi-laboratory RR testing exercise has started in September 2011. Nine different laboratories participate in this ESIS TC4 RR, and a reference draft protocol has been prepared by the coordinating laboratory (Università degli Studi di Brescia, Italy). In the present work, this RR activity is shown; more specifically, the testing procedure is described and the main results obtained by the working group discussed