New Formulae for Determining Fracture Toughness of a Wide Range of Different Materials with Chevron-Notched Short-Rod and Short-Bar Specimens

New formulae are presented to re-evaluate plain strain fracture toughness of brittle and ductile materials from previous works on chevron-notched specimens. The fracture toughness K_Im from the new formulae agree with values of K_IC from ASTM specimens. The K_Im measurements are successful in tests of tough aluminum when the fracture toughness exceeds 40 MPa · m^{1 2} and steel 20G with the plasticity factor p approach 1. It is found that the valid specimen size could be smaller than 1.25(K_IC/σ_S)² for aluminum alloys, and even less than 0.1(K_IC/σ_S) for steel 20G when the K_Im formulae are used.