A part with an unchanging cross-sectional area under the load has uniform and homogeneous stress and strain distribution. Any type of notch existence or sudden changes in cross-section causes inhomogeneous distribution of stress and strain. Typically, fatigue failure of an element arises where the stress level rises due to the stress concentration effect such as a notch on a surface. Notch is usually defined as a geometric discontinuity. Notch may be introduced either by design or by the manufacturing process. A hole in a component is an example of a design notch. Material and fabrication defects such as weld defects, inclusions, casting defects, or machining marks are notches which are introduced due to the manufacturing process. The present paper investigates the effect of notch on the fatigue life of the HSLA100 steel which is widely applicable in the marine industry. HSLA is a type of alloy steel that provides better mechanical properties or greater resistance to corrosion compared to carbon steel . HSLA steels are not made to meet a specific chemical composition but rather to specific mechanical properties and as a result, they are different from other kinds of steels. The main goal of this research is to compare different methods of predicting fatigue life of notched HSLA100 specimens and find which ones yield better results. Experimental were conducted on the smooth and notched specimen and mechanical properties and S-N curve were obtained. Rotating bending fatigue tests were conducted on cylindrical specimens according to ASTM E 466. A constant load is applied perpendicular to the specimens which is rotated at 50 Hz. Fourteen smooth specimens and twelve notched specimens were tested. The finite-element software used in the present investigation was not capable of directly modelling the stress amplitude distribution in an axisymmetric specimen under rotating bending. However, by superimposing suitably weighted FEA stress distributions from bending about the y- and z-axes, the stress amplitude distribution in rotating bending can be readily obtained. Based on the obtained experimental S-N curve for smooth specimens and modelling the stress amplitude distribution of rotating cylindrical notched specimen, S-N curves for notched specimens were predicted by Weibull's weakest-link, Peterson, Neuber, stress gradient and critical distance methods. The S-N curves and fatigue stress concentration factor were obtained of all methods and compared with experimental result and weakest-link theory was selected best method in terms of the availability of the required materials data, the predictive capability, and the compatibility with FEA stresses. Key words Fatigue life, Weakes t-link theory, Notch, Steel HSLA100, Modelling, Predictive capability
