Chevron-notched specimens in a number of configurations have been recently used to determine plane-strain fracture toughness. Most researchers have employed tensile short-rod and short-bar specimens, while the three-point bend configuration has been used only to a limited extent despite its convenience for testing at ambient and high temperatures.

In the present study, both experimental and analytical K-calibrations for three-point bend chevron-notched specimens were carried out. Fracture toughness tests were performed in accordance with ASTM Standard of Test Method for Plane-Strain Fracture Toughness of Metallic Materials (E 399-81) to determine plane-strain fracture toughness, K_Ic, for polymethyl methacrylate (PMMA), 60/40 brass, 7075-T651 aluminum, and quenched and tempered 4140 steel. In parallel, three-point bend chevron-notched specimens of these materials were loaded to failure. The ratio (K_Ic/P_max) B · √W is the dimensionless quantity Y*. This quantity was found to be 11.6 for the specimen geometry employed in the present study.

Three analytical models, which have been used successfully for the short-bar and shor t-rod configurations were used to calculate the stress-intensity coefficient and the critical crack length for the three-point bend configuration. The predicted stress intensity coefficients are 20 to 60% higher than the experimental value, and the predicted critical crack length is at least 20% lower than the directly measured critical crack length.