Constant-Amplitude and Program-Load Fatigue Tests at Low Cyclic Frequencies on Thick Aluminum Alloy Pin Joints.
AERONAUTICAL RESEARCH LABS MELBOURNE (AUSTRALIA)
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An investigation has been made of the fatigue behaviour of 32 mm thick 2L.65 aluminum alloy lugs loaded through 19 mm diameter steel pins. It involved constant-amplitude and program-load tests at cyclic frequencies of approximately 1 Hz. At high alternating stresses, the constant-amplitude test results fall within the relevant data band in ESDU Data Sheet 72020. However, additional data are needed to clarify the fatigue performance of thick lugs for lives exceeding about 5 x ten to the 5th power cycles. Under program-loading, the cycles actually applied at two of the intermediate stress levels exceeded the maximum experimental endurances obtained under constant-amplitude at the same stress levels. In addition, the actual lives of specimens under program-loading were about 10 times those predicted from the constant-amplitude data using the simple Palmgren-Miner hypothesis. Static tests on about 20 of the fatigued pin-lug joints indicated that fatigue crack geometry may have an important influence on the residual strength of such a connection. A satisfactory theoretical treatment of this problem is thus of practical importance. Author
- Metallurgy and Metallography