Effect of surface defect on specimen and insertion distance of striker bar in tensile split Hopkinson pressure bar test

• Main Author: Lim, Zhi Hong
• Other Authors: Shu Dong Wei
• Format: Final Year Project
• Language: English
• Published: Nanyang Technological University 2022
• Subjects: Engineering::Materials::Mechanical strength of materials; Engineering::Materials::Material testing and characterization
• Online Access: https://hdl.handle.net/10356/157263
• Institution: Nanyang Technological University

Available in the materials laboratory of Nanyang Technological University (NTU) Singapore, are three variations of Split Hopkinson Pressure Bar (SHPB). The SHPBs are used to evaluate the mechanical characteristics of materials under high strain rates, at various dynamic loading situations through compression, tension and torsion. The dynamic tension SHPB will be the sole focus for this report. The tensile SHPB is used to assess dynamic stress and strain response under tension at high strain rates ranging from 102 to 104 S-1. Its theory is based on longitudinal stress waves propagating along elastic bars. Strain gauges are installed on the input and output bars, raw data is collected by using an oscilloscope to transfer voltage signal from the strain gauges. Stress vs strain, strain rate vs time, and strain vs time curves are generated after data collection and compared to existing literature articles. The goal of this project is to verify that the SHPB experimental setup at NTU is accurate, reliable, and repeatable. Multiple tests such as empty runs and calibration runs were conducted. The results from each of these tests should preferably differ by less than 5% but a percentage error of less than 10% is acceptable. The results are also compared to past year papers to ensure repeatability. Once calibration is done, the project will investigate the effects of varying insertion distance of the striker bar into the barrel of the gas chamber, on the mechanical properties of sheet metal Al6061-T6 test piece. The velocity of the striker bar will also be measured. In addition, the effects of a surface defect on the mechanical properties of test piece will also be looked into. Conclusion of the project will be included at the end of the report. Problems faced during this project will also be discussed, followed by recommendations to improve on this project.