Investigating the constraint role in J-CTOD relationship for compact tension (CT) specimen

Abstract

The Crack Tip Opening Displacement (CTOD or δ) estimation from J-integral (J) defined by ASTM 1820 considers the CTOD dependency on material properties, and the constraint factor (m). The m in Compact Tension (CT) specimen is based on yield to tensile strength ratio (σys/σut) without taking into account of in-plane dimensions as in Single Edge Notch Bending (SENB). Hence, an attempt is made to understand the effect of crack length to specimen width (a/W), specimen thickness to specimen width (B/W) for different σys/σut on CTOD using CT specimen. A new method of estimating the CTOD from FE analysis is demonstrated and validated with 450-intercept method. It has been found that the ASTM 1820 based CTOD (δASTM) assessed values under-estimate the actual CTOD present in the CT specimen. The variation in a/W and B/W doesn’t affect the J-CTOD relationship as stated by ASTM 1820. However, the CTOD measured by FE analysis (δFE) are consistently higher than the δASTM. Therefore, an effort is made to correct the constraint factor, m based on present FE analysis by considering the effect of σys/σut. The proposed corrected constraint factor, mFE, can be employed in fracture applications that generally need both the J-integral and the CTOD.