Nondisruptive Measurement of Fatigue Damage in Materials
S. Rosinski, EPRI NDE Centre, Charlotte, USA; C. Fukuoka, Y. Nakagawa, IHI, Tokyo, Japan
ABSTRACT
An effective nondisruptive method for measuring the fatigue damage accumulation state in a structural material was identified and applied. The method, Selected area Diffraction (SAD). Identifies small cell-to-cell angular misorientations in the crystal lattice of a material. It was observed that this misorientation can be correlated quantitatively to fatigue damage level. Fatigue damage was induced in SA508 samples by various loading histories in order to examine the influence of prior cyclic loading below and above the fatigue limit. Specimens were subjected to high-to-low and low-to-high amplitude cyclic strain including both below (total strain range of 0. 40%) and above (total strain range of 0. 62%) the fatigue limit. High-to-low loadings initially included 10 and 100 cycles of high strain range loadings. These small numbers of cycles were less than 1% of the total lifetime when the specimens were subjected to the constant amplitude fatigue test. Transmission electron microscopy was utilised to obtain microstructural characteristic of the samples, and cell-to-cell angular misorientation differences were measured by the SAD method. The SAD measurements were then correlated with the total fatigue damage in the samples. Those samples that failed through fatigue all exhibited a consistent angular misorientation value. This suggests the feasibility of establishing a critical misorientation value for use in a future screening methodology for assessment of plant component fatigue.
Publication Source: First International Conference on NDE in Relation to Structural Integrity for Nuclear and Pressurised Components , 20 - 22 October 1998, Amsterdam, Netherlands. Held by the Joint Research Centre of the European Commission. Publisher:Woodhead Publishing Limited
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