Derivation of elastic fracture toughness for ductile metal pipes with circumferential external cracks under combined tension and bending

Abstract

Linear elastic fracture mechanics has been widely employed for fracture analysis of cracked pipes. For ductile metal pipes, the existence of plasticity eases the stress concentration at the crack front, which increases the fracture toughness of the pipe. Therefore, when using linear elastic fracture mechanics to predict the fracture failure of ductile pipes, the plastic portion of the fracture toughness should be excluded. This paper intends to derive an analytical model of elastic fracture toughness for ductile metal pipes with circumferential external surface cracks under combined axial tension and bending. The derived elastic fracture toughness is a function of crack geometry, material properties and loading conditions of the cracked pipe. The significance of the derived model is that the well established linear elastic fracture mechanics can be used for ductile materials in predicting the fracture failure. It is found in the paper that, the elastic fracture toughness increases with the increase of the internal pressure of the pipe and that an increase in fracture toughness and yield strength of the pipe materials will result in a more ductile and brittle pipe failure respectively. The derived analytical model enables more accurate prediction of fracture failure of ductile metal pipes with circumferential external cracks.

Deformation Behavior of C15E + C Steel under Different Uniaxial Stress Tests

“…The same types of specimens in experimental investigations of fracture toughness parameter may be used in both cases of testing K Ic and J Ic as critical value of J. Linear elastic fracture mechanics has been widely used in analysis of cracked structure [29]. To avoid problems with material procurement and test specimens manufacturing technology, an approximate but sufficiently correct method is available.…”

J-Integral Solution for Elastic Fracture Toughness for Plates with Inclined Cracks under Biaxial Loading

“…Consequently, fracture toughness increases and consists of elastic and plastic portions. In order to extract elastic fracture toughness from total fracture toughness, a failure assessment diagram was employed by Yang et al (2016Yang et al ( , 2017 and Li et al (2017). The adopted failure assessment curve (Milne et al 1988) is independent of both geometry and material properties and may be used for any structure.…”