A new upper bound solution for highly undermatched welded DE(T) specimens is proposed. A distinguished feature of this solution is that it accounts for the thickness of the specimen. Even though this ...case is more general than plane-strain and plane-stress solutions, the final result is given in terms of ordinary and double integrals. Comparison with a plane strain solution shows that the thickness of the specimen has a great effect of the limit load.
In two previous papers, mis-match yield load solutions for middle crack tension and single edge cracked bars in pure bending were derived. These specimens contained cracks which were located in the ...centre of the weld metal as well as in the interface between weld metal and base plate, and in positions in between. The present paper investigates additional three specimen types, namely double edge crack tension, single edge cracked bend and compact specimens, with cracks in the centre of the weld metal and in the interface between weld metal and base plate. As in the previous investigations, the conditions of plane strain and plane stress are considered. The results are presented as closed form solutions and diagrams.
The present work provides mis-match limit loads for welded pipes with constant-depth, circumferential part-through surface cracks in the centre of the weld metal. As limiting cases, circumferential ...through-wall and fully circumferential cracks are also considered. Based on systematic finite element limit analyses, mis-match limit loads are quantified by the strength mis-match ratio and only one geometry-related slenderness parameter, not requiring additional geometry-related parameters. This implies that mis-match limit loads for surface cracked pipes can be found from those for idealized axi-symmetric problems, which offers significant benefit in assessment of surface cracks in welds of pipes.
This study investigated ductile crack initiation limit of pipeline girth welded joints with different strength mis-match. The ductile crack initiation limit for the girth welded joints was evaluated ...by conducting three point bending fracture toughness tests and wide plate tensile tests with a surface notch. In addition, effect of heat input on the ductile crack initiation limit of weld metal was evaluated on the assumption that a welding condition would be varied in the field in the actual pipeline construction. As the results, the equivalent plastic strain at the notch tip for the ductile crack initiation of the three point bending tests was consistent with those of the wide plate tests, and the heat input hardly affected the ductile crack initiation limit within the range of this study. This meant that the ductile crack initiation limit of the pipeline girth welded joints with strength mis-match was able to be estimated using the equivalent plastic strain obtained from the three point bending tests. Based on these results, we proposed a procedure to determine the rational fracture toughness requirements which took into account the difference in the plastic constraint between standard fracture toughness test and pipeline girth welded joints. This procedure was also possible to determine the required strength matching level for a strain-based design for girth welded joint containing surface notch in the center of the weld metal in terms of preventing the ductile crack initiation.
Fracture behavior of a hot-rolled bi-material plate consisting of a substrate (low carbon ferritic–pearlitic steel) and a clad layer (austenitic stainless steel), has been investigated. ...Micro-hardness and tensile properties measured from the clad down to the substrate showed an abrupt change adjacent to the interface, due to a coarse grained soft ferritic band near the interface. Flat bi-material tensile specimens were tested and two formulae were established to correlate the relative thickness of the bi-material components to the tensile properties of the bi-material system. Crack tip opening displacement (
δ
5) based
R-curves of thick bi-material SENB specimens with a deep crack (
a
0/
W=0.50), located in both the substrate and the clad, are found to be similar to the curve of the homogeneous substrate. Thinner SENB specimens with a shallow crack (
a
0/
W≤0.20) located in the clad material, showed higher fracture toughness than homogeneous clad CT specimens, because of the lower strength substrate and shallower crack size. Studying cross-sections machined out from SENB specimens revealed crack deviation into the underclad soft coarse grained region band due to the strength mis-matching nature of the bi-material system.
It has been well known that ductile fracture of steels is accelerated by triaxial stresses. The characteristics of ductile crack initiation in steels are evaluated quantitatively using a ...two-parameter criterion based on equivalent plastic strain and stress triaxiality.
The present study focuses on the effects of geometrical discontinuity, strength mis-match, which can elevate plastic constraint due to heterogeneous plastic straining, and loading rate on the critical condition for ductile fracture initiation using a two-parameter criterion. Fracture initiation testing has been conducted under static and dynamic loading using circumferentially notched round-bar specimens. In order to evaluate the stress/strain state in the specimens, especially under dynamic loading, a thermal elastic–plastic dynamic finite element (FE) analysis considering the temperature rise due to plastic deformation has been carried out.
The tensile tests on specimens with an undermatching interlayer showed that the relationship between the critical equivalent plastic strain to initiate ductile fracture and stress triaxiality was equivalent to that obtained on homogeneous specimens under static loading. Moreover, the two-parameter criterion for ductile fracture initiation is shown to be independent of the loading rate. It was demonstrated that the critical global strain to initiate ductile fracture in specimens with strength mis-match under various loading rate can be estimated based on the local criterion, that is two-parameter criterion obtained on homogeneous specimens under static tension, by mean of FE-analysis taken into account accurately both strength mis-match and dynamic loading effects on stress/strain behaviors.
Plane strain and plane stress slip-line solutions for single notched bending specimens with a central mismatched welded joint have been derived. The crack has been located on the fusion line ...(interface) and at the middle of the weld metal. 2D and 3D finite element analysis has been performed to verify the theoretical results and to investigate the effect of specimen thickness. From these solutions, the stress distribution and deformation field in the weld metal, the expressions for the yield load as well as the constraint state at the crack tip are determined. The resulting relations for estimating 3D effects coincide with the test results.
This paper presents a simple method to estimate fully plastic crack tip stresses based on the equilibrium condition of the least upper bounds for plane strain deformation fields consisting of ...rigid-body rotation across a circular arc extending from a crack tip across the remaining ligament. The method is applied to deep, single-edge-cracked specimens under combined bending and tension. For various bending-to-tension ratios, the limit loads and crack tip stresses are estimated from the present method and compared with results from finite element limit analyses. The present method gives impressive results.
This paper investigates the stress fields for a crack located at the fusion line of a weldment. The strength mis-matching and the size of the HAZ were varied, and the corresponding distribution of ...the maximum principal stress was examined. The weld metal strength was globally overmatched with respect to the base material, but locally over- and undermatched with respect to the heat affected zone. Three cases of mis-match were compared, and it was found that reducing the strength of the HAZ lowered the maximum principal stresses.
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