cranfield university mahadi abd murad an integrated structural ...

first is to calculate the shear angle using the theoretical equation based on the kinematic
analysis of the bias-extension test. The second is to draw straight lines along the yarns
for various images from the bias test. The third method is to use a series of images
obtained from the test along with soft image correlation software. However, all these
approaches carried out by the above researchers cannot be used for the woven
composite that is wrapped round the pipe. The only way to measure the shear angle,
strain and others due to thermal expansion is to apply Mohr‘s Circle theory using a
strain gauge and surface temperature detector.
5.6 Summary and Conclusions
From the above results, from this experimental approach of using the surface
temperature detector, it is possible to measure the CTE of the test material on site
provided the measurement is carried out at proper locations; it also provides an
alternative method to the bonded temperature sensor which may involve extra cost and
time. For unreachable locations, for example, between layers of the composite repair,
the temperature sensor has to be bonded next to the bonded strain gauge so that more
accurate readings can be obtained. From these experimental results also, it can be
concluded that the CTE measurement using this simple approach produced is acceptable
and practical in this composite based pipeline repair. However, this approach produces
better and accurate result in the isotropic material (i.e. steel) than in the anisotropic
material (i.e. composite).
The results of maximum thermal strain at both layers (fourth and eight layers)
show that the thermal strain is directly proportional to the temperature increase. In the
investigation of shear strain in the thermal expansion experiment, the shear strain is
found to be higher at the eighth layer (i.e. 172 microstrain) compared to the fourth layer
of composite (i.e. 73.3 microstrain). However, at the eighth layer, the shear strain was
nearly constant as temperatures increased. Therefore, the CTE readings at C3 and C4
(both at the eighth layer) as illustrated in Figure 5.12, were much closer to each other if
compared to C1 and C2 (at the fourth layer) which were less apparent. This shows that
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