Mechanical behaviour of carbon fibre reinforced composites in three-point bending test

• Main Author: Tan, Hui Yi.
• Other Authors: Chai Gin Boay
• Format: Final Year Project
• Language: English
• Published: 2013
• Subjects: DRNTU::Engineering::Aeronautical engineering::Materials of construction
• Online Access: http://hdl.handle.net/10356/53944
• Institution: Nanyang Technological University

This paper serves to investigate the effect of varying porosity content on the flexural properties of the fabricated unidirectional carbon fibre reinforced composite (CFRC). Porosity content of the CFRC was varied with different suction pressures (00cmHg, 16cmHg, 26cmHg, 36cmHg, 46cmHg and 56cmHg suction pressure) to the resin-hardener mixture before applying it to the carbon fibre cloth. Optical microscopy was performed on the fabricated CFRC to characterize the porosity content of the specimens. Obvious trend relating the amount of suction pressure to the porosity content was not observed but CFRC specimens fabricated with a 36cmHg suction pressure revealed the highest porosity content while specimens created under atmospheric condition showed the lowest. This finding was in contrast to initial belief that the application of suction actually draws any inherent porosity out of the resin-hardener mixture resulting in lower porosity content. This prompted the author to investigate further into the changes in the porosity content of the resin-hardener mixture at varying suction pressure using the stereomicroscope. A six fold increase in the radius of the air bubbles were found when the cure pressure was decreased from 101kPa to 40KPa. The number of bubbles on the other hand shows an irregular trend. In the analysis of the overall porosity content, highest porosity content was found to be produced at 36cmHg and the lowest at atmospheric condition. The flexural strength and the flexural modulus of the CFRC specimens were experimentally determined using the Instron 5569 universal testing machine in accordance to ASTMD790. The experimental results show that the flexural strength and flexural modulus are inversely proportional to the porosity content of the specimen with a least square regression R2 value of 0.854 and 0.9207 respectively. In addition, the tensile modulus of the resin-hardener specimen was also determined. In this test, Instron 5569 universal testing machine was also used as closely as possible in accordance to ASTM3039 subjected to equipment constraints. The experiment results also show a negative correlation between the tensile properties of the specimen and its porosity content. With a least square regression value of 0.7693, the tensile modulus showed a 12.8% decrease when the porosity content increases by 1%.