Fracture Toughness

The fracture toughness test is performed to determine the value of the critical stress-intensity value, or plane-strain fracture toughness, K_IC. This material property is used in the design of structural members made of high-strength materials. These materials are often susceptible to rapid fracture in loading regimes in which lower-strength materials yield without fracture. Specifically, K_IC expresses a relationship between the applied stress and the length of a surface crack.

Fracture toughness is determined using an MTS servo-hydraulic test frame. A compact tension specimen that has been precracked in fatigue is loaded by the test frame. A crack opening displacement (COD) gage is attached. A data acquisition system records and plots the applied load versus COD. K_IC is calculated from these results.