Rationale

In the late 1970s, Paris, Tada, Zahoor, and Ernst proposed a new fracture parameter to characterize a material’s resistance to ductile crack propagation, which they called the tearing modulus (T) of the material. At the time, the portion of the J-R curve following the onset of ductile crack propagation, which was termed “stable tearing”, was represented by a straight line with constant slope dJ/da . The tearing modulus was therefore a temperature-dependent constant, calculated from a fracture toughness test by normalizing dJ/da . A linear fit was also used for data points beyond initiation in the first version of the precursor standard to ASTM E1820, E813-81. By the time E813 was replaced by E1820 in 1996, a power law fit was prescribed instead of a linear fit, and therefore a constant slope could not be assumed anymore in the stable tearing regime. With a non-linear regression curve, the tearing modulus should be defined at a specific value of crack extension, Da. Neither E813 not E1820 have ever included tearing modulus as a fracture parameter, despite a quantitative indication of crack growth resistance (via the slope of the regression curve) could be an important piece of information in a material’s fracture characterization. This ballot proposes the introduction in E1820 of a J integral-based tearing modulus TM, obtained by normalizing the power law fit slope in DaQ (onset of ductile crack propagation) by the ratio between the Young’s modulus and the effective yield strength, in accordance with Paris’ original proposal. Alternative values of tearing modulus can be optionally established, using the slope corresponding to other values of Da (0.5 mm, 1 mm, etc.). Proposed changes and additions are highlighted using “Track Changes”.