Essential work of fracture compared to fracture mechanics—towards a thickness independent plane stress toughness |
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Authors: | T PardoenF Delannay |
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Affiliation: | Département des Sciences des Matériaux et des Procédés, Université catholique de Louvain, PCIM, 2 Place Sainte Barbe, B-1348 Louvain-la-Neuve, Belgium |
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Abstract: | The essential work of fracture (EWF) and the J-integral methods were applied in a study of the effect of the thickness on the cracking resistance of thin plates. The paper discusses two themes: (1) the relationships between the two methods or concepts is elucidated, and (2) a new, thickness independent plane stress toughness parameter is proposed. For that purpose, cracked aluminium 6082O thin plates of 1-6 mm thickness were tested in tension until final separation. The EWF, we, and the J-integral at cracking initiation, Ji, increase identically with thickness except at larger thickness for which the increase of Ji levels off. Ji reaches a maximum for 5-6 mm thickness whereas we keeps increasing linearly with thickness. This difference is related to the more progressive development of the necking zone in front of the crack tip when thickness increases: at large thickness, cracking initiates well before the neck has developed to its stationary value during propagation. A linear regression on the fracture toughness/thickness curve allows partitioning the two contributions of the work of fracture: the plastic work per unit area for crack tip necking and a plane stress work per unit area for material separation. The pertinence of this new measure of the pure plane stress cracking resistance is critically discussed based on a micromechanical model for ductile fracture. The micromechanical void growth model incorporates void shape effects, which is essential in the low stress triaxiality regime. |
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