Determining Crack Initiation Fracture Toughness and Crack Initiation Length Using Ae and Dic Approach for Hdpe Materials
28 Pages Posted: 6 Jan 2025
Abstract
Fracture toughness JIC is a crucial indicator for characterizing the ability of materials to prevent crack propagation. For high density polyethylene (HDPE), multi-specimen method is generally adopted to construct crack resistance (J-R) curve following ASTM D6068. The polymer community has suggested J0.2 at 0.2 mm of crack growth from J-R curve as crack-initiation toughness, while the dilemma is still faced in experimentally observing crack initiation. This paper attempts to develop a single-specimen method to measure JIC, as well as crack initiation length. The method requires acoustic emission (AE) technique to determine crack initiation, and digital image correlation (DIC) technique to provide displacement and strain information for J-integral calculation. The accuracy of JIC was validated by comparison of J0.2 and FE simulation. Average crack initiation length was evaluated by inverting JIC on J-R curve. Research results show that, within loading rate from 0.1 mm/min to 3.0 mm/min, crack initiation length decreases from 0.1965 mm to 0.1932 mm, and JIC shows slightly decreasing tendency while J0.2 varies oppositely, therefore, using 0.2 mm extension as crack initiation will overestimate fracture toughness at higher loading speed. When the variation of loading rate is not significant, JIC can be approximated as constant as 19.9 kJ/m2.
Keywords: Fracture toughness, crack initiation length, J-integral, acoustic emission, Digital image correlation, J-R curve
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