ASTM E561-10 Standard test for K-R curve determination

Scope:

ASTM E561-10 keeps track of the toughness of a fracture as it is stably driven under increasing applied stress intensity factor K. The K-R curve can be matched with the crack driving curves for an untested shape to predict the degree of stable crack extension and the conditions required for unstable crack propagation.

Procedure:

The growing crack extension resistance KR is equal to the applied stress intensity factor K during slow stable fracturing. Continuously or progressively increased force or displacement drives the crack ahead. The approach includes two methods for determining effective crack size: direct measurement of crack size and compliance measuring technique. 

Specimen size:

The specimen should be conditioned at ±0.5% of thickness.

Data:

Secant slope can be calculated by using the following formula:

 (Δv/ΔP)_{I =} (v_i –v_o)/P_i