PSI - Issue 71

Sudarshan Solanki et al. / Procedia Structural Integrity 71 (2025) 95–102

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Kumar et al. (2017) examined the tensile and fracture toughness characteristics of DMW, formed by joining the parent metals SA508 and SS304LN with various weld or filler materials such as Inconel-82, Inconel-182 and SS309L. Kuwabara et al. (1992) carried out fatigue tests on DMW and brought out that the primary cause of reduced fatigue strength is the strain non-uniformity, which arises due to variations in cyclic plastic deformation across different regions of the weld. Cheng et al. (1995) finds that the base metal has the longest fatigue life, but the HAZ has the shortest due to its lower ductility. As HAZ is weaker than weld metal, fatigue life of the weld joint is governed by HAZ. Further, to investigate the effect of strain gradient on fatigue life, Jena et al. (2022) conducted systematic experiments on the parent metal of C-Mn steel with different notches. In the numerical investigation of fatigue damage, constraints and loading conditions are critical. They have brought out that the fatigue life is dependent on strain gradient for a given peak equivalent strain amplitude Jena et al. (2022) . However, limited work has been carried out DMW of SA508-SS304LN parent material combination to understand the effect of strain gradient on fatigue life. In view of this, the current study involves a numerical analysis of cyclic plastic deformation and strain gradients on SA508-SS304LN DMW. Finite element analyses were performed to quantify the strain gradients under remotely applied pure axial and pure torsion conditions. 2. Scope of Work The present study aims to bring out the effect of material discontinuity on fatigue life. Axisymmetric Finite Element (FE) modelling has been carried out under pure axial and pure torsion cyclic loading conditions. Three distinct materials have been utilized in the present case (two base materials: SA 508 Gr. 3 Cl.1 and SS 304LN and one weld material: SS308L).

Fig.1. Scope of present study specifying materials, loadings details for fatigue life assessment. The cyclic plasticity calculations have been performed using three decomposed Chaboche model. A total of four different peak equivalent strain amplitudes have been considered to quantify the strain gradients along axial and radial directions and across various material regions. Subsequently, fatigue life assessment has been carried out using corresponding fatigue life curves and Basquin & Coffin-Manson equations Dieter et al. (1996) based on peak strain amplitudes across various material regions . The figure above indicates the scope of present work. 3. Material Details The tensile properties of base (SA-508 Gr. 3 Cl.1 Kumar’s (201 7) and SS304LN Goyal’s (2011)) and weld material (SS308L Chaturvedi et al. (2013)) are given in table 1 at room temperature in air environment. The typical comparisons between tensile and cyclic stress-strain curves for all three materials is shown in Fig. 2. This figure clearly shows that SA-508 base is having higher yield & ultimate tensile strengths (Table 1) than that of SS308L (weld) and SS304LN (base). Similarly, the cyclic stress-strain curves also follow similar variations amongst these materials. For simulating the stress-strain behaviour ahead of material discontinuity, Chaboche et al. (1991) non linear kinematic hardening material model has been used (as described in Appendix). The Chaboche model