Non-destructive evaluation of composite structures in aircrafts

• Main Author: Tan, Zhi Long
• Other Authors: School of Mechanical and Aerospace Engineering
• Format: Final Year Project
• Language: English
• Published: 2014
• Subjects: DRNTU::Engineering
• Online Access: http://hdl.handle.net/10356/60952
• Institution: Nanyang Technological University

The use of Carbon Fibre Reinforced Composites (CFRP) has permeated many industries, from bicycle and car components, to aerospace grade applications, and even for Dyson vacuum Cleaners. In the past 30 years researchers have been working hard to improve composite materials to its current level. Now that it is widely used in the industry due to its high strength to weight ratio, anticorrosive properties and easy application, it becomes more imperative than ever to be able to characterise defects in CFRP. In this report, defects of CFRP specimens which underwent a three point bending test at three different temperatures are characterised with beautiful 3D Computed Tomographic images, which showcase the defects of compressive failure, tensile failure and the hard to detect delamination that occurs in composites which would not be detectable by visual inspection. The 3D images produced have a 14 micron resolution, and would thus deepen the reader’s understanding of how the CFRP fails under different temperature conditions. As the matrix Tg is 120 degrees Celsius, at temperatures over that when the three point bending tests are conducted the CFRP specimens show lesser tensile and compressive failure, which suggests increased flexibility due to the transition of the matrix to a rubber-like state. However, there was increased delamination observed, which suggested increased thermal stresses between the plies which are laid out in different orientations. In addition, this report contains information about Computed Tomography, the process of how the author has chosen optimised parameters for using a high energy commercial grade CT system to scan low density CFRP. Reverse Engineering techniques were also explored, using three different methods and a multitude of software such as VG studio, Avizo, ImageJ, meshlab, Netfabb, Rhino 5, Solidworks, Ansys workbench and ABAQUS. The author has methodised this process, and the steps in this report would enable the reader to export CT data for 3D printing and Finite Element Analysis of complex structures. This would enable the reader to analyse hard to model structures and predict the failure mechanisms and stress concentrations without destructive testing. The closeness of the mesh to the real structure would depend on the computational power available.