Fracture toughness testing at the micro-scale − The effect of the unloading compliance method

Abstract

Fracture mechanical testing of micro-sized cantilevers was conducted in order to quantify the fracture toughness and behaviour of the (1 0 0)[0 1¯ 1] crack system in α-iron at 37.5 K, 133 K and room temperature. The cantilevers are outside the range of validity for linear-elastic fracture mechanics due to the small sample size, rendering the cantilevers out of bounds in relation to linear-elastic fracture mechanics and classical fracture mechanics. Elastic-plastic fracture mechanics has therefore been applied to determine the conditional fracture parameters KQC and JQC. A comparison between cantilevers continuously loaded with corrected dynamic stiffness measurements and another data set of cantilevers tested with the unloading compliance method has been made. A distinct difference in determined fracture toughness and crack behaviour was identified, indicating potential concerns when applying the unloading compliance method at the micro-scale on ductile materials.