Analysis and optimization of ultrasonic imaging methods for inhomogeneous structures

Linas Svilainis *
Doctoral thesis abstract


Ultrasonic non-destructive testing automation and digital control ensures reliability, increases the speed of testing, and allows 2- and 3-dimensional images to be acquired. However, the wide range of ultrasonic signal amplitudes and the frequency are increasing the requirements for equipment used for inspection. The common instrumentation used for NDT usually cannot satisfy this. Although ultrasonic NDT is popular for inspection of composite materials, application to certain types of composites produces unsatisfactory results if conventional methods are used. Reinforced aluminum matrix composite is a very high attenuation material. High resolution imaging, using high frequency signals and sharply focused transducers is therefore not possible. If lower frequencies are used, there will be problems with both poor axial and lateral resolutions and structural noise still remains.

Multilayered composite plates are widely used in many advanced industries for their properties. One of the pivotal problems still remains efficient detection and characterisation of delaminations occurring in multilayered thin composite plates, the thickness of which is less than the spatial length of the ultrasonic pulse. Limited bandwidth of a commonly used ultrasonic testing equipment distorts the information about delaminations so these are not easily detectable. Two different techniques have been developed for detection and characterisation of the delaminations in thin multilayered composite materials using band-limited ultrasonic signals acquired by commercially available instrumentation.


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