Influence of printing direction on mechanical behavior of additively manufactured high strength low alloy steel

• Main Author: Hardi Pardi
• Other Authors: Liu Erjia
• Format: Final Year Project
• Language: English
• Published: Nanyang Technological University 2020
• Subjects: Engineering::Materials::Mechanical strength of materials
• Online Access: https://hdl.handle.net/10356/145537
• Institution: Nanyang Technological University

Additive manufacturing (AM) has been rapidly adopted by various industries to optimize their design and manufacturing processes. This includes the aerospace and medical industries. The marine and offshore industry, however, is relatively slower in accepting the AM technology. This is due to the reasons such as a lack of research on the quality and reliability of the products that are AMed using materials that are commonly used in the industry. This has caused a lack of confidence in the safety of the AMed products, leading to a reluctance in using them. This Final Year Project (FYP) seeks to investigate the effects of build orientation on the mechanical properties of the AMed products of ASTM A131 EH36 and API 5L X65 structural steels. The specimens used in this project were printed using a Laser Engineered Net Shaping (LENS) method with build orientations of XY0°, XY45°, XZ45°, and XZ90°. They were then put through a series of mechanical testing, namely, Charpy V-notched impact, tensile and fatigue tests. The impact toughness, ductility, fatigue life, yield, and tensile strength of the specimens were evaluated. It was discovered that the build orientation can critically affect the mechanical properties of the products. Generally, for both materials, printing with the build orientation of XY45° would produce products with the best overall mechanical properties while printing with the build orientation of XZ90° would consistently produce the worst overall mechanical properties. Through fractography analysis of the fatigue specimens, defects such as inclusions, porosities and lack of fusion were uncovered. The presence of such defects can greatly affect the fatigue life and other mechanical properties of the AMed products. It highlighted the need to improve the printing quality by having more research on optimizing the LENS process parameters for the printing of EH36 and X65 materials. Through this, the products can have fewer defects and improved mechanical properties that can meet the relevant standards. This would directly increase the safety and confidence in applying the AMed products for marine and offshore use.