Extrapolation of tearing resistance curves

Due to the measuring capacity limitation in normal test specimens, it is often necessary to extrapolate the tearing resistance curves beyond the measuring limit of the specimen. There are theoretically two possible limits for extrapolation. A conservative estimate, sometimes used in e.g. the British R6 failure assessment method is to assume crack growth at a constant J, equal to the limiting value. A more realistic, but possibly un-conservative estimate of the tearing resistance is based on the assumption that crack growth will continue with the same slope at the limiting value. The true behavior is likely to lie somewhere between these two extremes. Conservative extrapolation beyond a limiting crack growth can be performed by considering the change in tearing resistance with crack growth. Two possible methods are in this presentation highlighted through a simple hypothetic example. The realism of the two methods is then tested on actual tearing resistance data going to large crack growths.