Testing and characterisation

Surface properties such as roughness and contamination are a critical aspect of composite materials during adhesive bonding, co-curing or even welding of different components. UQ Composites has acquired extensive experience in film surface characterisation through the use of stereo microscopy and Atomic Force Microscopy (AFM) for physical properties; Scanning Electron Microscopy with Energy Dispersive X-rays (SEM-EDX) and X-ray Photoelectron Spectroscopy (XPS) for chemical composition and surface contamination analysis. The combination of these high-precision techniques allows to detect key differences in the chemical composition of the first few atomic layers, which are found to affect the performance of the bonded joints.

Interface Analysis

The extent of interdiffusion at the interface between two dissimilar materials typically occurs on a micro or sub-micrometre scale and is often difficult to characterise. However, the morphology of these interfaces provide valuable information on the compatibility of the two polymers and consequently of the mechanical performance of the interface. Interface characterization is part of UQ Composites’ expertise. The mechanical properties of the interface can be obtained via phase imaging of Atomic Force Microscopy (AFM) in tapping mode, and combined with a chemical composition analysis across the interface using Scanning Electron Microscopy with Energy Dispersive X-rays (SEM-EDX). These provide the necessary information for predicting interface behaviours.

3D Digital image correlation (DIC) is an optical non-contact technique to measure strains on deforming bodies. In this technique, a speckled spray pattern is painted on the surface of the specimen to be tested and a two-camera system captures images of the deformation event. The images are latter processed by a software to create a map in three dimensions of the deformation field in the body. This technique is the ideal solution for the study of the inhomogeneous strain fields developed in complex geometries such as automotive or aircraft components when subjected to a specific loading situation. DIC is also suitable for the verification of Finite Element Analysis predictions

SHM systems aim at assessing the state of a structure periodically or during service using fully integrated monitoring devices. For plate-like structures, ultrasonic guided waves propagate over long distances and enable to inspect large areas from a set of permanently bonded sensors. UQ-Composites has historically contributed in the field of guided waves for SHM. Fundamental research has been carried out theoretically, numerically and experimentally to investigate guided wave generation and propagation in composite material, interaction of wave with defect as hole or delamination, detection and imaging of defects, effect of environmental parameters. Theses efforts make the use of ultrasonic SHM more efficient for real applications.

Non-linear acoustics

Classical ultrasonic methods suffer from limitations when it comes to small fatigue cracks or delaminations. However, it is possible to activate nonlinear phenomena such as contact dynamics in these defects. The nonlinear behaviours result in spectral enrichment that differs according to the employed method. These new frequencies are then attributed to the presence of a defect. Nonlinear acoustics are promising methods but substantial development has to be done for practical implementation. Research has been done to apply the Nonlinear Wave Modulation Spectroscopy to a delaminated beam. Moreover, in-house electronic hardware equipment has been developed to improve the quality of nonlinear acoustic experiments.

Transducer design and characterisation

The service life of many civil and military aircrafts are extended well beyond their original design limits. Hence aircraft corrosion becomes one of the main cost drivers for aircraft maintenance, and aircraft coating systems serve as the first line of defence against corrosion.

A special purpose finite element simulation program has been developed to investigate damage evolution in aircraft coatings. Cohesive cracks within the polymer matrix material are modelled as well as adhesive cracks along the interphase between filler particles and the polymer matrix.

Guided wave beamforming and diffraction tomography