Two-parameter characterization of the near-tip stress fields for a bi-material elastic-plastic interface crack

Abstract

A particular case of interface cracks is considered. The materials at each side of the interface are assumed to have different yield strength and plastic strain hardening exponent, while elastic properties are identical. The problem is considered to be a relevant idealization of a crack at the fusion line in a weldment. A systematic investigation of the mismatch effect in this bi-material plane strain mode I dominating interface crack has been performed by finite strain finite element analyses. Results for loading causing small scale yielding at the crack tip are described. It is concluded that the near-tip stress field in the forward sector can be separated, at least approximately, into two parts. The first part is characterized by the homogeneous small scale yielding field controlled by J for one of the interface materials, the reference material. The second part which influences the absolute value of stresses at the crack tip and measures the deviation of the fields from the first part can be characterized by a mismatch constraint parameter M. Results have indicated that the second part is a very weak function of distance from the crack tip in the forward sector, and the angular distribution of the second part is only a function of the plastic hardening property of the reference material.

Interfacial crack-tip constraints and J-integral for bi-materials with plastic hardening mismatch

“…The explicit dependence of the T-stress on interfacial crack tip constraint, however, was found not to be the same as that for homogeneous materials, but to depend on the strength mismatch (Shih 1991;Ganti et al 1997;Lee and Kim 2001). For more general cases of mismatch in both yield strength and strain hardening, Zhang et al (1996) proposed the J-Q-M theory where the parameter M reflects the constraint due to the mismatch in plastic properties, in contrast to the Q-parameter simply reflecting the constraint effect due to the geometry and the mode of the loading (O'Dowd and Shih 1991a, b). The M-parameter was determined in the similar fashion to the Q-parameter, namely from detailed elastic-plastic finite element (FE) analyses.…”

Effect of residual stresses on the crack-tip constraint in a modified boundary layer model

“…In the present context we prefer to understand the level of constraint as an indicator of the near-tip stress state, and the constraint is regarded as the factors or conditions which influence the transferability and invalidate the one-to-one relation between the crack driving force and near-tip stress field. The geometry constraint is caused by crack size, specimen dimensions and loading mode; inhomogeneous material properties can induce the mismatch constraint at the crack tip (Zhang et al, 1996;Betegón and Peñuelas, 2006;Burstow et al, 1998); both the prestrain history (Eikrem et al, 2007) and the welding residual stresses influence the crack-tip constraint as well. In recent decades, a series of studies has been carried out to characterize the different crack-tip constraints.…”

“…Because of the nature of welding, there is often a mismatch between the weld metal and the base metal. By considering the interface crack as a bi-material system, Zhang et al (1996) carried out a numerical investigation on the near-tip stress field and found that the near-tip field in the forward sector can be separated into two parts. The first is characterized by the J-integral for a reference material; the second part which influences the absolute levels of stresses at the crack tip and measures the deviation of the field from the first part can be described by a mismatch constraint parameter, M (Zhang et al, 1997b):…”

Effects of crack depth and specimen size on ductile crack growth of SENT and SENB specimens for fracture mechanics evaluation of pipeline steels

“…It is now well understood that crack tip constraints due to specimen geometries, loading modes and yield strength mismatches as well as residual stresses [1][2][3][4][5][6][7][8][9][10] affect the stress distribution around a crack and consequently preclude the use of a single parameter characterization of the crack tip stress field. A second parameter based on the elastic T-stress has been proposed by Betegon and Hancock [11] to describe the crack tip stress field.…”