Fatigue Strength And Behaviour Of Notched Steel Specimens

Yeck, Wai Hoong (2011) Fatigue Strength And Behaviour Of Notched Steel Specimens. Project Report. UTeM, Melaka, Malaysia. (Submitted)

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Abstract

Fatigue is refers to the behaviour of materials under the action of repeated stresses or strain as distinguished from their behaviour under monotonic or static stresses or strains. Fatigue is the leading causes of failure in mechanical components and structures since they have been manmade structures or components. Fatigue has become progressively more prevalent as industries have developed various types of equipments that subjected to repeated loading and vibration. Fatigue failure is particularly insidious because it happened without any obvious warning. In this thesis, the material used is AISI 1020. A total of 24 specimens are prepared according to the specified design in ASTM standard for unnotched and notched specimens to compare their fatigue strength and behaviours. Certain machining process need to be done in order to prepare the specimen to the required dimension for the test specimens. The stress concentration factors applied to the notched specimen is defined and U-notch is chosen in this study. The fatigue test is conducted by using the INSTRON 8802 servohydraulic machine with its software and the test is run at low stress ratio (R = 0.1) and high stress ratio (R = 0.5). The data obtained from this study are plotted in the S-N curves and FDM of the materials. Based on the overall results, the fatigue strength for the unnotched specimens is higher than the notched specimens for both low and high stress ratio. Besides, the specimens conducted at high stress ratio also have higher fatigue strength and fatigue life. However, there are differences between the experimental and theoretical fatigue limits for the test specimens due to few factors which include effect of stress concentration, surface condition, stress parameters and etc. Finally, the faceted fracture surface is analysed as well as its relationship with the stress ratio and three different stages of crack propagation.

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