PSI - Issue 14

Ashok Saxena / Procedia Structural Integrity 14 (2019) 774–781 Author name / Structural Integrity Procedia 00 (2018) 000 – 000

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crystallographic orientations on the creep deformation at the crack tip as the crack transitions from one grain to the next.  Some progress has been made in the assessment of crack growth in the presence of microstructural gradients such as with performance of welds under creep-fatigue. Future studies must consider microstructural gradients and transition layers between the weld metal and the base metal. Plastic and creep deformation zones and their evolution in the presence of microstructural gradients including their interaction with the transition layer must be studied in detail. Crack growth studies performed should model cracks that meander from one region of the weld to another.  Fundamental studies are needed to better understand creep-fatigue-environment interactions.  Field validation of creep-fatigue model predictions should be conducted where possible.

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Fig. 5- Creep-fatigue crack growth rates in specimens with cracks nominally located at the fusion line (left) in weldments of 2.25 Cr- 1 Mo steel for over-matched and under-matched weldments and (right) photomicrograph of the crack path relative to the fusion line [Saxena, 2007].

Fig. 6- (left) Evolution of the crack tip creep zone in a C(T) specimen of GTD-111 alloy with the crack lying at the interface of two grains with different orientation [Gardner, Saxena, and Qu, 2001]; and (right) creep crack growth in specimens of directionally solidified GTD-111 at twp temperatures correlated with the C t parameter [Ibanez, Saxena, and Kang, 2006]