Validity limits of the one-parameter elastic-plastic fracture mechanics (J-integral) considering SE(B), C(T) and clamped SE(T) specimens

Abstract

The increasing severity of current structural applications (stresses, strains, displacements and aggressive environments), combined to the use of high toughness materials and low constraint geometries, strongly affects the validity of fracture mechanics methods to predict the mechanical behavior and final fracture of such structures using data obtained from laboratory tests, motivating further research in the field. However, the most important aspect of the one-parameter fracture mechanics framework is to ensure that the stress-fields in a reduced laboratory specimen are comparable to those found in real structures to whose design the properties taken from the specimen will be employed. This is the similitude concept, in which a single-parameter can describe the stress-fields ahead of a specimen’s or structure’s crack tip. To establish objective criteria for assessing similitude, this work compared the stress-fields obtained from high-constraint reference models (MBL) with those obtained from laboratory scale fracture mechanics specimens. The extensive analysis matrix, considering computational simulations under plane-strain, complemented by 3-D analyses, allowed the determination of the deformation limits M for C(T), SE(B) and clamped SE(T) geometries considering a wide range of geometrical features and material properties characteristic of structural steels applicable to pressure vessels and pipelines. The results confirmed the low constraint response for short-cracked SE(B) and SE(T) specimens and clarified the effects of crack depth and thickness on M values. In addition, some unexpected behaviors were evidenced and explained, as the case in which (for some particular crack depths and loading modes) thin specimens seem to be more constrained than thick ones. Thus, this work provides insights and quantitative results that enable the development of an objective basis to guarantee similitude in structural integrity assessments based on elastic-plastic fracture mechanics supported by the J-integral either with its critical values (Jc) or J-R curves.