Investigation of high-cycle fatigue properties of 3D-printed steel parts

Manufacturing technology has made significant improvement over the years and additive manufacturing (AM) technology, also known as three-dimension (3D) printing, specifically Laser Engineered Net Shaping (LENS), is becoming more popular in many industries. In the marine industry, High Strength Low Alloy (HSLA) ASTM A131 steel is one of the most widely used materials in the marine structures due to its excellent mechanical properties. Although LENS processes can optimize the usage of materials and has the ability to produce complex parts, the inherent process-related defects such as pores and voids will cause mechanical inferiorities. Therefore, this project aims to investigate the fatigue behaviour of A131 steel specimens fabricated by a LENS process. As-built A131 steel samples in four different orientations (XY-0°, XY-45°, XZ-45° and XZ-90°) were subjected to tensile and fatigue tests. In the tensile tests, most of the specimens passed the ASTM standard except XZ-45° specimens. In the fatigue testing, all the specimens were subjected to a constant amplitude uniaxial fully reversed fatigue loading. The fatigue results were plotted in the S-N curve. Fractographic analyses also conducted using Scanning Electron Microscope (SEM). In general, the fatigue life of the as-built LENS A131 steel specimens of different orientations was in the high-cycle regime. The fatigue failure was mainly attributed to the LENS process induced defects such as pores and lack of fusion. Most of the specimens showed the obvious stages of crack initiation, propagation and final failure.Bachelor of Engineering (Mechanical Engineering