Assessment of Fatigue Behaviour under Different Loading Sequences Using Signal Analysis Approaches

Constant amplitude data obtained from smooth specimens have been used for many years to evaluate the fatigue life of components. However, most of the loadings used in real applications are variable or random. In this research, three types of loading were applied – constant, low–high (LH), and high–low (HL) loading sequences. This paper presents an assessment of the fatigue behaviour under these three types of loading, and the effects of each loading on the fatigue behaviour as well as on life are highlighted. Fatigue tests were performed according to ASTM E466-96 standard with a strain gauge attached to the specimen being tested. AISI 1045 carbon steel was used as material for this tests due to its wide applications in the automotive industry. Fatigue tests were carried out at a constant, LH, and HL loading stresses at a sampling frequency of 8 Hz. A set of data acquisition system was used to collect the fatigue strain signals. All signals obtained were analyzed using two signal-processing approaches – the power spectral density (PSD) method and the integrated Kurtosis-based algorithm for Z-filter (I-kaz) technique. Fatigue behaviour was observed from the initial until the last stage of the fatigue test. The PSD peak values and I-kaz coefficients were determined to explain and describe the behaviour of fatigue damage. Both results are comparable in the fatigue damage assessment.