Our research focuses on structural health monitoring using guided waves and non-linear acoustics, as well as mechanical testing and high resolution surface/interface characterisation.

Surface and interface analysis

Surface Analysis

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.

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Mechanical and Environmental Characterisation

Mechanical testing

The non-isotropic mechanical response of composite materials requires specific testing procedures, specimen preparation and data processing in order to address their unique properties. The UQ Composites group has the capability of carrying out composite testing in accordance to ASTM Standard Test Methods as well as specific custom specifications. Some of the standard composite testing procedure conducted at the UQ Composites lab include: tensile and compressive testing using CLC fixture (ASTM D3039 and ASTM D 3410), in-plane shear response (ASTM D3518), three and four point bending (ASTM D790 and ASTM D6272). Testing can be conducted in an environmental chamber at a temperature ranging from -150 °C to 350 °C.

Optical 3D Deformation Analysis using Digital Image Correlation (DIC)

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


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Non-destructive testing and Structural health management

Guided wave ultrasonics

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

Piezoceramic transducers are the commonly used active and passive sensor elements in structural health management applications. During service they are frequently subjected to dynamic, high strain loading, which may result in damage to the piezoceramic element or the attaching bondline. We developed a novel method of attaching piezoceramic transducers to specially prepared thermoset composite surfaces using thermoplastic as the bondline media with the aim to improve the protection of the transducer from the damaging effects of high strain structural loading.


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Success stories

Paint degradation analysis

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

Plate wave based SHM methodologies have been widely reported to be convenient and efficient in detecting fatigue cracks in metallic structures, disbonds and delaminations in composite structures and for the assessment of structural repairs.

A plate wave beam forming methodology has been developed and its imaging performance characterised to locate damage in thin plates based on numerical simulation and experimental studies. In addition the issue of optimal transducer network design has been addressed using probabilistic system optimisation concepts.

Moisture detection in helicopter honeycomb sandwich panels

The effect of moisture on the performance of honeycomb sandwich structures is an important issue. No experimental NDE method currently exists that can detect and quantify the moisture absorbed in a composite sandwich structure exposed to a humid environment.  We have developed a thickness-resonance sonotronic NDE technique, which is able to determine the level of humidity in the core of carbon-fibre/ Nomex composite sandwich panels.

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