A discussion on two alternative approaches to CT coupon based K1C determination providing results comparable with ASTM E 399

Abstract

The value of Plane Strain Fracture Toughness of a material calculated in accordance with the ASTM E 399 has been noted to be a specimen size-dependent value. The size-dependency of the same with respect to ductile materials has been an area of debate both for quality testing in production and the best applicable value for new structural design of components. While in case of production quality assessment the primary challenge is the repeatability of complying results for ductile materials, for new design – it is of a representative value for the material. Crack Mouth Opening Displacement (CMOD) and the applied load are traditionally used to calculate K_1C from CT specimen by ASTM (2023). A discussion on the comparison of two K_1C equivalents is presented here based upon observations with respect to specific Aluminium alloys and their relationship with this established material indicator is explored. Equivalents considered are K_1si and round tensile specimen inspired by Sarchamy et al (1996) and Wilson (1997). While K_1si is based upon CMOD estimation by assuming a fixed amount of crack extension of 0.5 mm irrespective of tested specimen size, round specimen may be applicable when dimensionally constrained.