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Aerospace Composite Components - Ultrasonic Robot Assisted Testing (ACCURATE)

Periodic Reporting for period 3 - ACCURATE (Aerospace Composite Components - Ultrasonic Robot Assisted Testing (ACCURATE))

Reporting period: 2020-02-01 to 2022-01-31

The aim of the ACCURATe project is to develop a prototype system based on Laser Ultrasonic Testing (LUT) technology to be used for Non-Destructive Inspection (NDI) of hybrid composite structures, including thick laminates and highly attenuating materials which are used increasingly throughout the aerospace industry.

The project partners combine complementary world leading expertise in Laser R&D and manufacture (Innolas) robotics R&D and manufacture (KUKA systems UK Ltd), laser ultrasonic technology and its applications (RECENDT GmbH) and signal processing for defect characterisation as well as adaptation of robotic systems through software and hardware development for complex aerospace NDI solutions (TWI).

The project is part of a wider framework of research which aims to support the introduction of complex composite structures such as carbon fibre reinforced polymers and hybrid polymer-metal multilayer sandwich structures (laminates) which in turn will offer much strength to weight ratios than metals currently used and therefore provide a pathway to reducing fuel costs and emissions.

Although the benefits of these materials are well understood, there are two key barriers to overcome; they are more expensive that traditional aluminium alloy structures and the risks of the development of both internal defects and impact damage leading to structural failure are higher. Improved Non-Destructive Inspection processes and equipment such as the prototype system being developed here, will provide a significant step forward towards overcoming these barriers.
The project commenced with the detailed definition of the composite panels to be inspected, the prototype system requirements and a full analysis of the inspection requirements. A test book detailing all of the inspection processes required was then outlined and a concept design for the LUT prototype system was formed.

Reference samples using representative materials have been manufactured, including artificial defects. These will be used to develop and optimise the prototype system and test its performance.

The concept comprises a high speed scanning system for the fiberized laser beams, an indexing platform to support the panels during inspection, a high power, short-pulsed laser for ultrasound generation, along-pulsed detection laser for detecting surface displacements and an interferometer and optical system. The scanning system is based on a six-axis robotic arm mounted on a linear track. The arm allows the laser head unit (connected via fibre optic cables) to access the entire panel surface.

A digital data acquisition module has been developed to interpret the output of the laser system, including bespoke post-processing software for visualisation of inspection results.

The laser system has been assembled and bench testing is currently progressing well. All major components of the scanning system such as the robotic arm, linear track and robotic controls have been ordered. The next stage will be to assemble these components and undertake further testing, development and optimisation of the system.

The system was assembled and integrated in a partner's facilities for initial tests and optimization trials. The system integration was flawless, with the robotic inspection system being pre-validated using a bespoke reference panel. The system was then dissembled and shipped to the topic manager's facilities ready for installation, commissioning and final acceptance tests.

The project results have been disseminated via scientific papers and attendance to conferences, as well as the project website, which is regularly updated and will be maintained for another four years. In addition, all partners distributed marketing material and made social media announcements to share key milestones. Moreover, the consortium disseminated the ACCURATe system capabilities directly to its members/clients/stakeholders via direct meeting and other company events.
The prototype system delivered a number of improvements beyond the current state of the art. These include the following:

• Significant reduction in platform weight and therefore cost. Modularity of the system and fiber coupling of lasers to the optical head lead to great weight and cost savings on the robotic platform required to carry the LUT system.
• Significant reduction in end-effector payload, reducing cost and size of robotic arm. The end effector footprint is reduced by more than 6 time and has a weight of a few kilograms compared to 1300kg of the state of the art.
• Reduced pulsed laser energy, allowing repetition rates to be increased by a factor of up to 5, able to achieve scanning speeds of 8m2 per hour.
• Signal to Noise Ratio improvements
• Improved defect detection sensitivity resulting from the use of the specific laser systems
• Reduced system footprint- use of fibre coupled lasers allows for the robotic system footprint to be greatly reduced

This project will directly support the European aeronautics industry in realising the Clean Sky 2 objectives of developing the technologies required to deliver the next generation aircraft by 2025. A key target of the programme is the reduction of aircraft weight by 30% to produce to produce corresponding cuts in raw material usage, energy consumption and emissions during all manufacturing stages, fuel reduction and emissions during aircraft surface and energy use and emissions during decommissioning.

To meet the ambitious aims of the programme, the industry will need to fully embrace the potential for composite materials in aircraft design and manufacture. To do this, it will be essential to develop innovative new inspection technologies to ensure the safety and reliability of these new structures. These structures require total area/volume inspection and LUT deployed by robots shows promise of becoming the major global monitoring technique for the structural integrity of aerospace composites and hence a key enabling technology for all -composite aircraft. ACCURATe will deliver the new LUT inspection technologies required for reliable inspection and assessment of complex integrated composite structures.
Photograph of LUT system bench testing
Photograph of LUT system bench testing
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