Relationship between crack growth resistance curves and critical CTOA

The relationship between K-R curves and critical CTOA is investigated in this paper. A novel CTOA calculation method is proposed, where the load and physical crack extension size are the only data required to be measured. The critical CTOA values are then determined from corresponding K-R curves. The calculated CTOA values are within 5% of ones from corresponding literatures. The relationship between K-R curves and critical CTOA values has also been discussed. It is sufficient to calculate critical CTOA values just from K-R curves. Unloading compliance does consider the effects of tunneling, and physical crack extension data measured from unloading compliance may give a better assessment of CTOA values. For certain material, a steeper K-R curve will lead to a larger CTOA, and there exist upper and lower limit values for critical CTOA that correspond to plane stress and plane strain state respectively.