The standardisation of the EWF test

A description of the background to the essential work of fracture (EWF) test method is given and its relation to J tests. The scheme used in the proposed standard is outlined including the various constraints which have evolved during the round-robin testing exercise. Also given are criteria for excluding data points based on stresses and deviations from linear fits. Two sets of data from eight groups are then reported and the problem of significant variations in the extrapolated values of the essential work we is explored. Apparently satisfactory data gave values outside ±S, the standard error of the average. It is suggested that a notch sharpness criteria (20 μm) and either an S value (3 kJ/m2) or a correlation coefficient R2 value (0.98) needs to be imposed to give a satisfactory procedure.