Evaluation and fabrication of damaged composite material using non-destructive testing

• Main Author: Lai, Abigail Jang Wai
• Other Authors: Wong, Brian Stephen
• Format: Final Year Project
• Language: English
• Published: 2019
• Subjects: DRNTU::Engineering::Mechanical engineering
• Online Access: http://hdl.handle.net/10356/78455
• Institution: Nanyang Technological University

Composite materials are being used widely in many industries today, for example, in automotive, aviation, research and development, as well as in sports. Since composites are extensively employed in many areas, it is important to determine the existence of surface and sub-surface defects before production and during regular maintenance checks. As time goes on, wear and tear occur to a material. After some usage, a component might experience mechanical damage, resulting in cracks or irregularities in the material. The presence of these flaws may result in reduced strength and stiffness of a structure, fatigue failure and eventually leading to disastrous consequences. Non-destructive testing methods such as ultrasonic testing is used to determine sub-surface flaws in fibre reinforced composite materials without impairing the test object’s structure. Visual inspection will only be able to determine macroscopic surface flaws. Internal damages cannot be determined with the human eye, it is essential that non-destructive testing methods are employed to ascertain the possibility of existence of sub-surface defects. More often than not, occurrences of these internal damages come with an external visual damage. This paper will discuss the experimental equipment, procedures and observations of ultrasonic testing on fibre reinforced composite materials, mainly carbon fibre and fibre glass composites, that have been damaged by heat or mechanically damaged. The experimental results will then be recorded and analysed to determine the size and location (in terms of depth below testing surface) of damaged areas. Finally, the sub-surface damages will be compared with the external visual damages to establish if there are relations between the two. The carbon fibre and fibre glass composites in this experiment are fabricated in a profession laboratory in Nanyang Technological University using wet lay-up technique and then cured in an Autoclave pressure chamber. An undamaged specimen will also be used in this study, to ensure that all heat and mechanical damages observed and recorded are a result of the heat and mechanical damages applied. Heat damages will be induced on the test specimen using an oven to ensure even heat distribution over the entire specimen surface. The temperatures applied will range from 120°C to 200°C for 3 cycles of 10 minutes each. Mechanical damages will be induced on the test specimen creating delamination in the composite materials.