Abstract
A vast amount of research has been carried out towards the goal of quantifying changes related to the fatigue damaging process in materials throughout the fatigue life. However, no recommended practice has been developed for the experimental measurement of fatigue damage before a macroscopic crack has been initiated. Therefore, this paper reviews the existing fatigue damage detection and measurement techniques on the basis of both momentum within the research field and their being considered non-destructive. The techniques are separated into two categories, namely, fatigue crack monitoring and fatigue damage monitoring. The parameters of these techniques, which quantify the physical and mechanical changes of the materials during the fatigue life, were critically reviewed in regard to the mechanism behind the change, limitations, shortcomings, etc. The acoustic emission, hardness, ultrasonic, magnetic and potential drop methods are applicable for in-situ measurements while positron annihilation and X-ray diffraction are more suitable for laboratory assessments. Even though all the revived methods are applicable for metals, acoustic emissions, X-ray diffraction, ultrasonic, strain-based and thermometric methods are also suitable for composites. The reliability, advantages, weaknesses, case/material dependency and applicability of each method are compared and tabulated for making a framework for choosing suitable technique for fatigue crack or damage detection of material or components.
Highlights
The iterative deterioration caused by the cyclic loading of a component or material, which eventually leads to crack initiation and, shortly after, final fracture, is generally known as “fatigue” by practising engineers
Similar work was performed by Yu et al in [26], where Acoustic emission (AE) data below 80% of the peak load was removed from the dataset, and crack extension and fatigue life prediction were performed on the basis of count rate and absolute energy rate
The results show that the change is certainly more prominent at the surface, as indentation depths of 2, 4 and 6 μm were measured, with the most significant change in hardness being observed for the 2 μm measurements
Summary
The iterative deterioration caused by the cyclic loading of a component or material, which eventually leads to crack initiation and, shortly after, final fracture, is generally known as “fatigue” by practising engineers. The current methodology to prevent this catastrophic failure is commonly based upon statistical analysis, with the addition of a damage accumulation rule, which is known to introduce further scatter It can be seen in DNVGL-RP [1] and in a paper by Keprate and Ratnayake [2] that the common methodology for life extension involves estimating crack growth through statistical analysis and initi ating an inspection program. The issue comes down to the fact that the crack propagation phase is commonly short, compared to the total fa tigue life [3] This results in a frequent and costly inspection program being initiated, from the time that conservative estimations of the fa tigue life have been surpassed, until the point of decommissioning or, alternatively, retrofitting. The mechanisms before crack initiation will for example increase the surface hardness, generate heat, and nonuniformly deform the surface crystals, resulting in the hardness-based, thermometric and X-ray diffraction methods which will be reviewed
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