Ultrasonic characterisation of Laminar Damage in composites

Abstract

Non-Destructive Testing (NDT) is a method for determining the integrity of a component without performing a destructive stress test. Ultrasonic Testing (UT) is a NDT technique that uses high frequency sound waves to detect damage in structures.This Thesis has systematically evaluated the damage detection capability of the Olympus Omniscan MX2 Phased Array (PA). The MX2 is a state of the art Phased Array UT machine.The effect of changing various machine settings, PA probes designs, and material samples on the MX2’s capability for effective damage detection has been investigated.The MX2 has been shown to be very effective at detecting artificial delaminations that simulate low velocity barely visible impact damage in thin monolithic structures (0-10mm).The MX2 currently has three PA probes. It was found that the 5L60 probe was the most robust of the three, it was the least sensitive to setting changes, and was the easiest probe to detect damage with. The 5L32 probe with its novel wedge material/design provided great near surface detection capabilities. Its lower number of elements but with a similar scanning width to the 5L60 results in a comparatively less detailed scan. The 10L32 was the most difficult probe to use, requiring a lot of time to setup, and not always guaranteeing efficient damage detection. It was recommended that this probe not be used during initial damage detection if the other probes are available. Although it requires more user experience to effective setup, the 10L32 has shown great potential for producing high quality scans of thin composites due to its high frequency and large number of elements relative to its small width.A brief comparison was made to the detection capabilities of Conventional UT. It was shown that Conventional UT was able to effectively locate known damages. It was shown that its ability to perform a broad area search for hidden damages was inferior to PA UT, due to the small size of the single element transducer compared to the larger PA probes.Finally, this Thesis has provided UQ Composites with a set of Standard Operating Procedures (SOP) that can be referred to when performing damage detection in thin composite structures. These were developed from the experience gained when learning how to operate the MX2 and perform scans during the course of the project.