Abstract
An experimental campaign was developed to study fatigue crack growth in Haynes 230, a Ni-based superalloy. The effects of crack closure were investigated with digital image correlation, by applying two different approaches. Initially, full field regression algorithms were applied to extract the effective stress intensity factor ranges from the singular displacement field measured at crack tips. Local closure measurements were then performed by considering crack flanks relative displacements. Two points virtual extensometers were applied in this phase. Experimental results were then compared to the reference da/dN –?Keff curve: it was found that the correct estimation of crack opening levels shifts all the experimental points on the reference curve, showing that DIC can be successfully applied to measure crack closure effects.
Highlights
The continuously increasing demand of electrical power, together with the necessity to provide energy in a more sustainable way, has led to a renewed interest in nickel-based superalloys
The results provided by full field regression algorithms are initially presented and compared to the crack closure measurements provided by local methods based on virtual extensometers
Fatigue crack growth in Haynes 230 was investigated at room temperature
Summary
The continuously increasing demand of electrical power, together with the necessity to provide energy in a more sustainable way, has led to a renewed interest in nickel-based superalloys. In 1970, Elber[1] discovered the phenomenon of plasticity induced crack closure and proposed to modify the Paris equation, by replacing ∆K with the effective stress intensity factor range, ∆Keff, computed considering only the portion of the load cycle where the crack stays open. This modification removed the dependency of crack growth rates on R, demonstrating that crack closure plays an important role in fatigue and that only a parameter can be used to describe Mode I propagation. In a study of fatigue crack growth in Haynes 230 single crystals[9], DIC was employed to extract effective stress intensity factor ranges during mixed mode propagation in an anisotropic body.
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