Influence of Hole Surface Finish, Cyclic Frequency and Spectrum Severity on the Fatigue Behaviour of Thick Section Aluminium Alloy Pin Joints.

摘要

An extensive series of tests has been carried out on thick (29 mm) clearance-fit pin joints of 2L.65 aluminium alloy to investigate the effects of lug hole surface finish, frequency of cycling, spectrum severity, loading sequence and maximum load truncation on fatigue behavior. It was found that lug holes having a fine surface finish (1.9 micrometers) did not have fatigue lives greater than those with a coarse finish (27 micrometers), under either constant-amplitude or multi-load-level fatigue loading sequences. Thus, unless needed for other functional reasons, it may not be necessary to specify fine circumferential surface finishes in situations where fretting fatigue is likely to be a problem. Within the range 1 Hz to 16 Hz frequency of cycling had no significant effect on the lives to failure under constant-amplitude and multi-load-level sequences. For each of two severities of spectrum adopted (consisting of 1049 cycles per block) there were essentially no significant differences in fatigue lives under program and pseudo-random loading sequences. Truncation of the once-per-block peak load resulted in significant reductions in life under both spectra. Detailed fractographic studies suggested that the size of the plastic zone caused by the peak load was greater than the extent of fatigue crack propagations within a block. Fractographic examination of small fatigue cracks initiated either at intermetallics or by fretting showed no evidence of early rapid crack growth associated with the 'short-crack' effect. Keywords: Joints; Crack propagation. (kt)