Mode III critical distance determination with optimized V-notched specimen under torsional fatigue and size effects on the inverse search probability distribution

An optimized V-notched specimen is proposed for the determination of mode III, or torsional, critical distance. Numerical procedures are provided for the inverse determination of this length, and then for a statistical analysis of the resulting skew-normal distribution, as obtained from (symmetric) normal distributions of the plain and notched specimen strengths. An experimental example is shown on steel 42CrMo4 + QT, with clear evidence of a significantly larger mode III critical distance than mode I. A parametric analysis is then presented to evaluate the effects of size of the specimen on the standard deviation of the inverse search critical distance probability distribution.