Use this URL to cite or link to this record in EThOS:
Title: The effect of voids on the flexural fatigue properties of carbon/epoxy composites
Author: Suhot, Mohamed Azlan
ISNI:       0000 0004 2693 3511
Awarding Body: University of Southampton
Current Institution: University of Southampton
Date of Award: 2010
Availability of Full Text:
Access from EThOS:
Full text unavailable from EThOS. Please try the link below.
Access from Institution:
The role of voids in composite failures has not been well understood or been characterized. This study presents the result of an investigation aimed at examining the mechanical behaviour of unidirectional carbon fibre-reinforced polymer matrix materials as used by the wind turbine industry. The experimental program investigates the effect of the void content, different manufacturing methods, type of loading (the three-point bending vs. the four-point bending) on the static strength and fatigue life under a flexural load. The four ply unidirectional carbon/epoxy composites were manufactured using the SPRINT and prepreg manufacturing methods. Manufacturing by these methods has successfully produced the composite materials with varied void contents and the voids are found to concentrate primarily in the area where the adjacent plies meet. The SPRINT materials contain voids in the range of 1.63- 2.89% while the prepreg laminates have an average void content of 3.6% for the debaulked laminates and 6.8% for the non-debaulked laminates. The voids in the SPRINT laminate are small and they are distributed inhomogeneously. The majority of the voids are less than 0.04 mm2 in size with a shape between a circle and an ellipse. The three point bending tests show that the flexural strength exponentially decrease as much as 6.4% for the SPRINT and 6% for the prepreg for every 1% increase of the void content. The similar void effect for both materials may be due to their similar microstructures. There is a similar effect on the increase in the void content for the flexural strength and the flexural fatigue sensitivity for both the three and four point bending tests. This means that the voids do not play any large role in the three-point bending as compared to the four point bending. The mechanism of failure is observed using the optical microscopy and the X-ray tomography of the polished edge and cross section of the area near the failure. The voids are found to interact with the cracks in both the static and fatigue failures. The image of the cross section near the failure area of the static test samples seem to suggest that the voids coalesce to each other under loading. By using the acoustic emission, it can be confirmed that a major failure occurs due to the fibre breakage. In addition, the acoustic emission results also show that the failure behaviour of the low and high void content specimens is significantly different.
Supervisor: Chambers, Alan Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: TS Manufactures ; TD Environmental technology. Sanitary engineering