Abstract:
This thesis focuses on the application of high frequency ultrasound as a
tool for performing non-destructive testing for pultruded fibre reinforced
composite (FRC) rods. These composite rods are popular in the manufacturing,
construction and electrical industries due to their chemical,
electrical and strength properties. Such FRCs are manufactured on automated
production lines that operate day and night. Non-destructive testing
techniques are desired to quickly and accurately detectmanufacturing
flaws such as coating thickness irregularities and surface cracks. Layers
and cracks can present as large changes in acoustic impedance and will
strongly reflect ultrasonic waves. Combined with their low cost, east of
use and absense of potentially harmful radiation, ultrasound has proven
popular worldwide for Non-Destructive Testing.
Finite Element Analysis (FEA) was employed to investigate the propagation
of ultrasonic waves through layers of material to simulate a thickness
measurement and the ability of ultrasound to measure thicknesses
was proven. Experimental work was conducted on two fibre reinforced
composite samples with varying thickness coatings of plastic and paint.
The thickness was measured accurately using immersion transducers at
50MHz and a resolution of 20μm was attained through the use of matched
filtering techniques.
Surface acoustic waves, particularly Rayleigh waves were investigated using
FEA techniques so that the generation, scattering and detection of such
waves was understood. This lead to the development of methods for detecting
surface cracks in glass using Rayleigh waves and these methods were successfully used in experimental work. Wave propagation in fibre
reinforced composites was modelled and experimentally investigated
with the results confirming theoretical expectations. Finally a Rayleigh
wave was launched onto a fibre reinforced composite sample however the
amount of energy leakage into the water was so great, due to the acoustic
impedance of water, the detection of the wave was prevented. The
conclusion reached was that an immersion setup was not appropriate for
launching a travelling Rayleigh wave.
