Novel Integrated Imaging Approaches for Damage Characterisation of Composite Materials and Structures

Lead Research Organisation: University of Southampton
Department Name: Faculty of Engineering & the Environment


Fibre reinforced polymer (FRP) composite materials are widely used for aero, marine, transportation and energy structure applications. They exhibit high stiffness and strength relative to their weight, and excellent performance when subjected to fatigue loads. A significant drawback is understanding how damage evolves in the materials and the ability to assess if a component should be repaired or continue in service. The outcome is conservative design and unnecessary scrap at the manufacturing stage. Efforts have been made to better assess composite structures using a variety of non-destructive evaluation (NDE) techniques. However the industrially desired 'one stop shop' for inspection has remained elusive. The current industrially preferred technique in the aerospace and wind turbine sectors is ultrasound, and in the shipping sector simple tap tests are often used. The limitation of current techniques (such as ultrasound (UT)) is they cannot provide details on how damage or defects evolve and affect the service life of a component.
The PhD project aims at developing an idea known as 'Strain-based NDE'. Here full field imaging techniques are used to capture data that is directly related to the strain caused by the damage to provide prognostic information on the effect of damage. The system will enable decisions to be made on scrap/repair/continue in service. A focus is reducing the cost of such a system by replacing expensive IR detectors with low cost bolometers. A major challenge is the integration of the images collected by white light and infrared imaging.
It is well known that composite materials behave differently when they are constructed into a large structure of complex shape and subjected to multi-axial loading. The strain based NDE technique has been demonstrated on simple components so the purpose of this project is to examine actual structural components of complex geometry and characterise the material damage state in-situ.

Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/N509747/1 01/10/2016 30/09/2021
1941831 Studentship EP/N509747/1 01/06/2017 30/11/2020 Irene Jiménez Fortunato
Description 1) Better understand how a non-common infrared (IR) camera, i.e. microbolometer, works in comparison with the most used system (photon detector) for the application of Thermoelastic Stress Analysis (TSA) technique to inspect a sample or structure to obtain the stress-field. TSA is a well-known full-field stress analysis technique that is based on the measurement of a component surface temperature using an infra-red (IR) camera. A sinusoidal cyclic load is required so that the peak-to-peak temperature change can be extracted from a temperature signal obtained from an infrared (IR) detector. The temperature change is related to the sum of the principal stresses. There are different factors that can vary on TSA i.e. loading amplitude, loading frequency, IR camera frame rate, noise reduction feature of the camera, and material inspected. Hence, a parametric study *(experiments and simulations) for different loading amplitudes, loading frequencies, noise reduction feature, different waveforms, camera frame rates and materials was performed. Therefore, the main outcome is the development of a calibration procedure that needs to be done for each type of microbolometer to use TSA that depends on the loading frequency. The use of microbolometers will reduce the cost of using TSA as the cost is one order of magnitude lower than a photon detector.
2) Understand the thermoelastic response measured with TSA from orthotropic laminated composite materials as the thermoelastic response can be driven by different variables i.e. the temperature change in the resin-rich surface layer, the fibre reinforced substrate layers or a combination of both. It uses Digital Image Correlation (DIC) to obtain an independent measurement of the strain without the influence of heat transfer. Hence, it is possible to calculate the thermoelastic response from DIC measured strains based on different approaches to compare with the measured thermoelastic response measured with TSA to identify the source of the thermoelastic response.
3) Integration of microbolometer based TSA with Digital Image Correlation technique as they provide the stress and strain fields, respectively. It is proposed that the combination of these 2 techniques can provide a damage parameter (based on stiffness) that will inform on the structure's state and how the damage can progress.
Exploitation Route The outcomes will be taken forward by other researchers in the group at the University of Bristol where the main supervisors are based. It will also be used by the industry and universities involved in the Structures 2025 Grant that will provide what can be termed high-fidelity data-rich testing of structural components, to integrate with multi-scale computational modelling to provide better predictive models of structural failure and create safer and more efficient structures.
Sectors Aerospace, Defence and Marine,Construction,Manufacturing, including Industrial Biotechology,Transport

Description It is currently contributing to the Structures 2025, which will provide what can be termed high-fidelity data-rich testing of structural components, to integrate with multi-scale computational modelling to provide better predictive models of structural failure and create safer and more efficient structures. In this project, different industries, such as Airbus, Siemens Gamesa, Lloyd's, Arup, BAE systems among others are working in conjunction with universities, such as the University of Southampton, the University of Bristol and the University of Bath.
Sector Aerospace, Defence and Marine,Construction,Energy,Manufacturing, including Industrial Biotechology,Transport
Impact Types Societal,Economic