Abstract
The use of composite materials continuously extends design capabilities in all branches of engineering. Composite materials offer flexibility in design due to the fact that they can be manufactured to a wide set of custom requirements. For this reason, composite materials enable better application of their virtues while minimising deficiencies. Applications of Carbon Fibre Reinforced Composites (CFRCs) has been on the rise, with research focused on the advantages of CFRCs over conventional engineering materials. CFRCs are suitable for light weight applications and have a high resistance to fracture. These characteristics make them suitable for structural applications in automobiles, satellites and in the aerospace industry. CFRCs have a reputation for good fatigue behaviour and because of this, fatigue phenomenon is often ignored in composite material design, yet it is still an important problem from an engineering design perspective. This document presents an investigation on the performance of CFRCs exposed to cyclic loading. A thorough literature review on fatigue of CFRCs is presented. The different factors that affect fatigue of composite materials are discussed, including the damage mechanics, life prediction and a review of testing standards. Biaxial CFRC with a stacking sequence of [±45°]7 was used to make a composite of 30% fibre volume fraction in an Ampreg 21 epoxy resin. The composite specimens were manufactured using a hand layup moulding technique which was found to be the optimum process. A CNC cutting process was used for machining static and fatigue specimens. Static tests were conducted on the epoxy resin and CFRC to get the mechanical properties and to also determine the load levels to be used in the fatigue testing. Specimens were tested under a flexural fatigue load at three load levels which were selected as 25%, 50% and 75% of the proportionality limit. Damage development was monitored by the use of Electrical Strain Gages (ESGs). A post-test analysis was conducted by the use of an optical microscope, to clearly visualise the damage developed. The obtained results show that insignificant damage is observed at 25% load level with matrix cracking as the only damage mode, whilst mixed damage is observed at 50% and 75% load levels.
M.Ing. (Mechanical Engineering)