A method of fracture toughness JIC measurement based on digital image correlation and acoustic emission technique

Abstract

The accurate measurement of fracture toughness depends on the accurate determination of crack initiation. Our previous study demonstrates a relationship between the acoustic features and microstructure transition of polyethylene pipe material using acoustic emission (AE) technique. In this study, acoustic criterion for crack initiation of single-edge notched specimen is proposed, with digital image correlation (DIC) observation, crack initiation time is determined. A combination method of DIC and AE technique is proposed to measure the fracture toughness JIC of polyethylene pipe material. DIC technique is used to obtain the deformation on specimen surface to calculate J-integral according to the rigorous definition, and AE technique is used to monitor the internal damage and capture the moment of crack initiation synchronously. Numerical simulation by ABAQUS as well as literature comparisons is conducted to verify the testing results. It's shown that fracture toughness is independent of tensile speed within range of 0.01 mm/min ~ 1.00 mm/min, JIC obtained by DIC measurement and numerical simulation is about 19.88 kJ/m2 and 19.58 kJ/m2 respectively, the average relative error is about 5.70%. The research results prove the validity and accuracy of the proposed method and can provide a reference for the fracture toughness measurement for other engineering materials.

Keywords

• Fracture toughness
• J-integral
• Crack propagation
• Acoustic emission
• Digital image correlation
• Polyethylene pipe material