Overview of EASICS Weldment Assessment Route Development Through Inelastic Analysis

Structural integrity assessment of weldments within metal structures is key to substantiate any nuclear reactor design. The assessment of weldments should consider the localised strain enhancement due to weldment geometry and material mismatch. For high temperature plant designs (operating within the creep regime), R5 Volume 2/3 Appendix A4 provides a procedure for the assessment of creep-fatigue initiation in austenitic and ferritic steel weldments, which accounts for the associated strain enhancement using a Weld Strain Enhancement Factor (WSEF). The current austenitic Type 1 WSEFs in R5 Volume 2/3 have been defined by data attained primarily for plate butt weldments under applied bending loads, and this factor is used for all butt weldments. It has been proposed that the weld strain enhancement may be dependent on loading, geometric and material mismatch conditions, and that adopting a single factor in an assessment may introduce varying levels of conservatism, which are unquantified. This work has included reviewing the current R5 Type 1 WSEF against existing validation data, previous inelastic Finite Element Analysis (FEA) studies and the use of inelastic material models in the FEA of weldments subject to cyclic loading.

Mismatch Effect on the Mode II Type Crack Tip Field in Power-Law Creeping Materials

The mismatch effect in weldments are widely to be seen in engineering practices. In this paper, the material mismatch effect on the mode II creep crack tip field is investigated and discussed. The effects of material mismatch and heat affected zone (HAZ) width on the C(t)-integral are presented. Both the local mismatch effect and the general mismatch effect are found to play important roles in the variations of C(t)-integral. The mismatch effect on the stress field of the mode II creep crack is also studied. The two-order term solutions are presented to characterize the material mismatch constraint effect on the mode II type creep crack. Some typical cases by considering general mismatch effect and local mismatch effect are given so as to make comparisons between the HRR field, FE solutions and the two-order term solutions. It can be seen that the two-order term solutions can coincide with the FE solutions quite reasonably regardless of creep extent, creep exponent, mismatch factor and HAZ width. This research also reveals the significant effect of the material mismatch on the high order term solutions under various conditions for mode II creep crack.

Numerical simulation of the interaction between a crack and an inclusion

Purpose The purpose of this paper is to propose the interaction integral method combing with a XFEM-based local mesh replacement method to evaluate both the stress intensity factors (SIFs) and T-stress at the crack tip near a circular inclusion. Design/methodology/approach Special attention is pay to the effect of T-stress on crack initiation angle in 2D composite medium. The generalized maximum tangential stress criterion is employed during the simulation which simultaneously involves the effects of the mixed-mode SIFs, the T-stress and a physical length scale rc (the size of the fracture process zone). Findings It is shown that T-stress could affect the crack initiation angle significantly for mixed-mode conditions. Varies types of material mismatch are also considered and their influences on T-stress are given quantitatively. Originality/value The proposed numerical method allows a considerable flexibility for such problems and provides a basic framework for quasi-static crack growth in materials containing complex interfaces.

Mismatch Constraint Effect for Bimaterial Interfacial Creep Crack

Mismatch effect of weldments is important for the assessment of structural integrity at elevated temperature. The interfacial creep crack is a common model which can be found in lots of engineering practices. Recently, the constraint effect is also considered to be significant for the evaluation of creep crack growth under high temperature. In this paper, a model for bimaterial interfacial creep crack is introduced to study the mismatch constraint effect. The stress field for bimaterial interfacial creep crack is investigated. An M*-parameter is proposed to characterize the constraint effect caused by material mismatch for bimaterial creep crack. A comparison is made between the geometry constraint caused by specimen loading and mismatch constraint caused by inhomogeneous material.

Mismatch Constraint Effect of Creep Crack With Modified Boundary Layer Model

Mismatch effect plays a crucial role in weldments, and an independent mismatch constraint parameter M* is proposed to characterize the material mismatch constraint effect in this paper. A mismatched modified boundary layer (MBL) model for creeping solids is developed to simulate the stress field of creep cracks in mismatched weldments. It can be found that there still exists the similarity between creep crack tip stress fields under different mismatch factors. Numerical results show that M* obtains the minimum value on the under match condition and the maximum value on the over match condition. Comparisons between M* and other geometric constraint parameters (A2(t) and Q22) are carried out and the applicability of M* is verified. A modified assessment formula for creep crack growth rate ratio is proposed based on the parameter M*. It is found that M* is a reasonable and remarkable parameter to characterize the mismatch constraint effect of creeping cracks.