PSI - Issue 39

Abhishek Tiwari / Procedia Structural Integrity 39 (2022) 290–300 Author name / Structural Integrity Procedia 00 (2019) 000–000

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The rate of change J nlel and C t integrals obtained from Abaqus are compared in Fig. 3(b), where it is shown that in comparison to d J /dt values C t values show significant path dependence. It has been confirmed that for a homogeneous material d J /dt values are path independent for small scale creep conditions (Kolednik et al. 2021).

5.1 Influence of Creep inhomogeneity on CDF The effect on the crack driving force in the form of J tip / J far ratio is plotted for different crack tip location in Fig. 4(a). This ratio achieves a constant value w.r.t. to time as long as the creep zone remains smaller and does not turn into a general creeping condition. The creep zone developing in material post-interlayer and the back face creep zones are shown in Fig. 4(b). It is important to understand that the back face creep zone would cause the J far integral value to decrease. The reason for such behavior in explained by Kolednik et al. (2019). The influence of transition from Material 1 to Material 2 is similar to a stiff/compliant transition of crack in an elastic plastic material (Tiwari et al. 2020). The crack driving force increases as the crack tip comes closed to the interface. This is due to the fact that for the creep exponent of the Material 2 which is on the right hand side of the interface is larger than that of Material 1. This makes Material 2 creep more for the same amount of load applied and for the same value of creeping time. Hence, the crack at any value of time undergoes a stiff to compliant transition. 5.2 Influence of Plastic to Creep transition on CDF The situation of crack transition from a time independent permanent deformation material to a time dependent creep deformation is simulated at a constant load of 40kN and the configurational force based J nlel values are plotted for the first stage where the load reaches to a value of 40kN in Fig. 5(a). For the next step where the creep deformation starts and only Material 2 deforms with change in time, the J nlel values for 2mm (representing tip values) and far contour are plotted in Fig. 5(b) for a L / b o of -0.2 (i.e. away from the interface). The results show that the J -integral is path independent as the deformed zone is small and the creep has not developed post interlayer due to small values of stresses.

(a) (b) Fig. 4. (a) Schematic material inhomogeneity in a heterogeneous half symmetric compact tension specimen where a sharp transition from a material with lower creep exponent to another material with higher creep exponent takes place along an interface and (b) its effect on the crack driving force as the crack tip approaches the interface.