Shear Lip/Plastic Zone Finite Element Model Development.

摘要

This study focused on the development of shear-lip in DT specimens under quasi-static loading rate. The objective of the study was to demonstrate the feasibility of a numerical simulation of shear-lips for a 25mm base metal DT specimen in three-point bend test. Three real stress-real strain curves representing three different materials with varying degrees of plastic behaviour were considered. These material curves are designated as Curves 1, 2 and 3. Curve 1 represents the actual real stress- real-strain curve of the 350WT steel material. On the other hand, Curve 2 represents the same curve, but with the fracture strain reduced to half that of Curve 1; while Curve 3 represents a similar curve as Curve 1, but with the yield stress reduced to half the Curve 1 value. Crack advance and element or node release was based on two possible criteria, namely (a) when the average strain in the crack tip elements that occupy a physical surface of 1.25 mm (0.050 inches) exceeds the strain at fracture on the supplied data; and (b) when the strain energy density in elements occupying a volume defined by 1.25 mm (0.050 inches) of free surface at the crack tip and 1.25 mm (0.050 inches) of material depth exceeds the strain energy density calculated from the supplied real stress real strain curves. It was shown that the plastic strain contour patterns obtained from the finite element analyses could be used to estimate the shear-lip sizes. At any given crack size (a/W level), the shear-lip size is smallest for Curve 2 material and largest for Curve 3. This trend is reasonable as the Curve 2 material is the least plastic (100% strain to failure as opposed to 200% strain for Curves 1 and 3); and the Curve 3 material is the most plastic (has lower yield stress of 197MPa compared to 395MPa for Curves 1 and 2, and high failure strain of 200%). For a given material, the shear-lip size tends to reduce with increasing crack size. For instance, for the Curve 1 material, the shear-lip sizes for a/W = 0.4, 0.45 and 0.5 are 10.95mm, 10.30mm and 9.70mm, respectively. The same trends of shear-lip sizes were observed, regardless of whether the plastic strain criterion of strain energy density criterion was used for crack advance. However, for any given material and crack size, the shear-lip size predicted based on the strain energy density criterion was greater than that predicted based on the plastic strain criterion.