This work consists of an investigation into the microstructure
and mechanical behaviour of glass fibre reinforced polyester
resin beams. The volume fraction occupied by glass fibres
was 20-30%, which is that typically used in boat building.
The beams tested were all unidirectional, with fibres oriented
parallel or perpendicular to the long axis of the beam.
Various techniques have been developed which may be applicable
to other composite materials.
The microstructure of the beams was investigated by observation
of cross-sections using a Quantimet 720 Image Analysing
Computer. Volume fractions and the distribution. of fibre
cross-sectional areas were measured. Methods have been
developed for the quantitative definition of the microstructure,
in terms of the fibre arrangement.
Cracks were grown in four-point flexural loading while
monitoring acoustic emission. The acoustic emission circuit
was built in the laboratory, and designed to monitor fibre
failures only, one count being associated with one fibre
failure. The processes of crack growth were further
investigated by observation of fracture surfaces using a scanning
electron microscope and measurement of crack profiles. The
factors controlling the processes of crack growth have been
elucidated.
The material condition was monitored by specific damping
capacity measurements. A free-free rig with excitation at
the ends of the beam was developed. In addition measurements
were made using a cantilever rig. Simple analyses involving
the solution of the classical wave equation were carried out;
a receptance analysis was also developed which allows the
undamaged and cracked portions of the beam to be separated
in the analysis. Invisible cracks, which had been indicated
by acoustic emission, were successfully detected in both rigs.
The correlation between recorded acoustic emissions and
specific damping capacity measurements supports the validity
of both techniques. Some correlation between properties and
measured microstructures has been obtained here. These
quantitative methods for the measurement of the microstructure
of composite materials should prove very useful in a wide
range of applications.
Date of Award | 1978 |
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Original language | English |
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Awarding Institution | |
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PROPERTY-MICROSTRUCTURAL RELATIONSHIPS IN GFRP
Guild, F. J. (Author). 1978
Student thesis: PhD