This paper presents the results of several DSTO research programmes which investigated the effectiveness of the fatigue life enhancement method used on RAAF F/A‐18 aircraft – glass bead peening. The research identified ways in which process improvement could enhance this effectiveness, and developed a procedure for mid‐life reworking of critical airframe parts to effectively restore the original fatigue life. The procedure included removing a very thin layer of material (and with it, any undesirable manufacturing features and accumulated fatigue cracking) from the surface. Further life recovery can be achieved, if required, by applying an optimized peening procedure. This process has been developed to allow restoration of fatigue life to critical airframe components which are thought to be accumulating fatigue crack damage faster than desired.
This paper presents a closure model for predicting the growth behavior of short cracks in the presence of large-scale yielding and residual compressive stresses, representative of structures that have been shot-peened. The plasticity-induced crack closure model developed by Newman is first extended by using the cyclic crack-tip opening displacement as the correlating parameter for fatigue crack growth rates. This new approach also enables a better characterization of the effect of large-scale yielding on short crack growth. The effect of residual stress on crack closure is then analyzed by adding to the loading spectrum an equivalent stress, which varies with the applied load level and the crack size. It is shown that predictions of the extended closure model are within a factor of two of the experimental results of etched specimens tested under spectrum loading, highlighting the capability of the predictive model along with some important issues for future research in this area.
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