Effect of Size on Elastic-Plastic Fracture Toughness Parameters

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Abstract
An investigation has been carried out to determine the influence of thickness and width on the elastic-plastic fracture toughness parameters: J value obtained from area under load/displacement curve JR, tearing modulus, and stress intensity factor corrected for plasticity KR. Compact tension specimens prepared from aircraft quality American Iran and Steel Institute (AISI) 4340 (Unified Numbering System [UNS] G43400) steel heat treated to a yield strength of 1000 MPa were used. All specimens satisfied the ASTM Test for JIc, a measure of Fracture Toughness (E 813) standard size requirements.This investigation demonstrates that when the specimens satisfy all ASTM standard size requirements, ductile fracture toughness JIc is independent of size. JIc values were found to vary a maximum of ±16% of mean value even in the present of some shear lips. Conversely, the tearing modulus was found to decrease as specimen thickness increased. A one to one relationship was found to exist between JR and JK, where JR is the J value calculated from the area under the load/displacement curve and JK is the J value computed from KR using the linear elastic fracture mechanics (LEFM) relationship.

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