Fatigue Life Properties Of Alloy Steel At Different Stress Ratio

Elmahi, Saad Ali Eltigani (2016) Fatigue Life Properties Of Alloy Steel At Different Stress Ratio. Project Report. UTeM, Melaka, Malaysia. (Submitted)

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Abstract

Fatigue failures are common problem that will affect any moving mechanical items and it is the main cause of mechanical service failures. Due to the nature that fatigue cycles are accumulative and it receives different loading, the problem on the mechanical items will not be identified till the last minute. Usually by the time detection is made, the failure occurred is already at the last stage of cracking. So it is pertinent to conduct a study on fatigue life behavior. In this study, a fatigue life behavior test was conducted on a specific type of alloy steel. The three main aims of the study were to first identify the type of alloy steel used in automobile steering knuckle which was used as the case study in this study; to investigate the fatigue life properties under constant amplitude loading of the selected alloy steel; to compare the fatigue life behavior under different stress ratio of the selected alloy steel. Three different tests were conducted in order to answer the three objectives. The alloy steel taken from the steering knuckle underwent a SEM test in order to identify the chemical composition and determine the type of the alloy steel. The same sample was ordered from the supplier and tensile test and fatigue test were conducted using the universal testing machine. The SEM test revealed that the alloy steel consists of carbon (c) 7.95% silicon (Si) 2.26% and iron (Fe) 89.80% of ASTM A536 grade 65-45-12 ductile iron. The findings from tensile test show that the ultimate strength of the iron was 470.7 MPa and the yield strength was 300.3 MPa and it is within the average grade of 65-4512 ductile iron of the SEM results. The fatigue tests which were done based on R=-1, R=0 and R=0.5 revealed that R=-1 had the lowest cracking timing as the stress amplitude is equal to the maximum amplitude and the mean is equal to 0, R=0 had minimum stress of 0 while R=0.5 recorded the lowest amplitude and mean stress.

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