Whilst the basic advantages of composite laminates, such as carbon fibre-reinforced plastic, are well proven, they are often compromised by high cost, long development time and poor quality due to multiple defects, particularly in complex parts such as those found in aerospace applications. Within the aerospace industry, where safety is paramount, design changes require expensive programmes of empirical testing over a variety of length scales, the so-called "test pyramid". An important objective of this complex engineering system is to minimize the probability of failing the certification test. Modelling technologies and testing at various stages of development are all orchestrated toward this objective, which has been heuristically developed over the last decades without a clear understanding of how each player contributes to uncertainty reduction. This project will engage a multidisciplinary team of engineers and mathematicians to develop novel mathematical modelling tools to address this issue. An embedded university-industry partnership will focus effort on creation of new capability with underlying fundamental research to reduce design-to-manufacture time and increase quality in airframe and aero-engine manufacture, critically important to the international standing of the UK aerospace sector. We will systematically develop stochastic models that integrate uncertainties from simulations and empirical testing (at different stages of the test pyramid) and quantify their propagation through the system to provide effective and reliable quality control for high-quality carbon fibre manufacture. New and fully-validated, laminate designs will be developed that challenge the inherent conservatism and the expensive industry standard which predominantly uses empirical testing for structural integrity certification. A central theme to the project is the complex interaction of multiple scales within the structural hierarchy of an aircraft component. Interaction over all the scales strongly influences each of the three research areas addressed within this programme. Recently gained expertise in the modelling of folding in layered geological structures will be exploited to study the physically analogous formation of defects during automated manufacture of laminated parts. Multiscale structural performance models will draw upon novel numerical upscaling techniques to predict the strength of large aerospace components containing microscale internal defects. Novel probabilistic uncertainty quantification tools, such as multilevel Monte Carlo and multilevel Monte Carlo Markov Chain, will be brought to bear in performance analyses of entire sub-components. The data for these models will be inferred directly from images obtained using Computational X-ray Tomography (CT). Manufacturing practices will be informed by seconding team members to GKN Aerospace, located at the National Composites Centre, to explore the interaction between the technical and business objectives of the industry, assisting researchers in the use of the new modelling tools, and in the selection of optimal manufacturing solutions. Target components will be wing spars, skin-stringer panels, and engine fan blades. The development and application of the novel stochastic methods for failure prediction will be undertaken with expert guidance of visiting researchers from the University of Florida and Lawrence Livermore National Laboratory, CA. Our vision is to enable a greater than 50% reduction in design-to-manufacture time whilst ensuring predictable product improvement, amounting to significant (>10%) component weight saving.

Commercial aviation contributes 2-3 % to global carbon emissions and the International Energy Agency has predicted that this will triple within the next three decades if no action is taken. In the UK the current contribution is 10% due to high levels of international traffic, and this could reach 40% by 2050 without action. The UK government has therefore set out an ambitious target to demonstrate a zero-carbon emission aircraft by 2030 within the UK Hydrogen and Net Zero Strategies. The design and manufacture of aircraft has previously focused on incrementally improving structural efficiency and productivity of the semi-monocoque parts which make up the wing, fuselage and tail, with a degree of linkage between fuel tank boundaries and structural function. However, next-generation aircraft will require energy storage using fully integrated structures and materials whilst accounting for environmental impact. GKN is the leading global Tier-one supplier of parts for most of the world's aircraft manufacturers. The University of Bath has world-leading expertise in the analysis, design and manufacture of composite parts, as well as in the creation of functional materials and their use for sustainable hydrogen energy. GKN and Bath have a track record of collaboration via a Royal Academy of Engineering Research Chair, eighteen joint PhDs and as formal partner in four EPSRC projects including an ongoing Programme Grant (CerTest, EP/S017038/1). Previous research has focussed in the areas of structural composites and manufacture, with most collaboration within Bath's Materials and Structures (MAST) Centre. The ZENITH Prosperity Partnership arises from GKN's ambition to realise zero-emission aircraft in the 2030-40 timeframe and the University of Bath identifying sustainability as a priority research theme. It addresses fundamental challenges within the two major research themes of Hydrogen Storage and Sustainable Structures. It brings together a highly skilled, multidisciplinary team of scientists and engineers from MAST, the Departments of Chemical Engineering (hydrogen storage, heat transfer), Chemistry (sustainable polymers, porous materials) and Mathematical Sciences (statistical modelling). It will exploit links with leading research institutes and centres at Bath, including the Centre for Sustainable and Circular Technologies (CSCT), the Institute for Advanced Propulsion Systems (IAAPS) and the planned UKRI Centre of Excellence for Hydrogen Research. ZENITH will establish GKN and UK academia as world leaders in manufacture of parts for zero emission aircraft, positioning the UK at the forefront of this rapidly developing market.

Ultrasonic waves in thin plates have a number of interesting properties, such as velocities that vary with frequency and multiple possible modes of vibration at a given frequency. This project will use one particular group of modes, which follow the edges of thin plates, to create a method of monitoring the edges of carbon fibre reinforced polymer (CFRP) aircraft components for damage. Structural health monitoring, whereby engineering structures are continually tested for damage, allows significant improvements in the way that the useful lifetime of engineering structures is managed. Methods based on designing structures to be viable long beyond their planned working life are being replaced by approaches that rely on monitoring for the first signs of deterioration and then repairing or replacing appropriately. This allows lighter structures to be used safely resulting in significant savings in construction materials and, for structures such as aircraft, ships and automobiles, improved efficiency throughout their working life. Ultrasonic waves have been successfully applied to structural health monitoring of plate-like structures and pipes, but structures with complicated geometries and physical properties that vary with direction (anisotropic materials) present particular challenges for ultrasonic structural health monitoring. This work will generate understanding of edge guided waves in anisotropic materials as a method of testing important sections of complicated structures. Ultrasonic waves in thin, plate-like, structures have more complicated behaviour than waves travelling through bulk materials due to the effect of the surfaces of the restricting the possible shapes (or modes) through the thickness of the structure as the wave propagates. These guided waves can travel large distances (up to tens of metres) and are scattered by defects, allowing them to be used to detect damage. They can also have multiple modes at any given frequency, each with a different frequency-dependent velocity and this complicates their use. Substantial work has been done to find methods of applying them to damage detection. The behaviour of ultrasonic waves at the edges of thin structures is further complicated by the edge also acting as a guide to the wave. This leads to modes that propagate along the plate edges, but decay rapidly away from the edge. In addition to representing an interesting physical problem, these modes, collectively referred to as edge waves, are a candidate solution to the problem of inspecting important parts of complicated geometry structures. In particularly they are ideally suited to inspecting for damage on the edges of thin structures such as: the stiffeners of wing panels or control surfaces of aircraft, turbine blades or exposed steel girders. The inspection of wing-panel stiffeners (small plates perpendicular to the panel to prevent it bending) is of interest as they are particularly susceptible to damage and carry significant loads. The following objectives will need to be achieved for this application to be realized: creating numerical models of edge waves in anisotropic materials, designing methods of generating and measuring edge waves, and performing experiments on damaged structures to determine the effect of defects on edge waves. A method of inspecting a specific structure (wing panel stiffeners) will be created and techniques generated to allow application to inspecting the edges of any thin structure for damage. A demonstrator system will be produced that showcases this technique.

The proposed project will create new capability to improve the structural efficiency of laminated carbon fibre composites. It will reduce weight and production cost by at least 10% (and possibly up to 30%) compared with existing stiffened panels made from pre-impregnated material. The new methods will facilitate the development of game-changing technology. The key innovation of the project will be to exploit state-of-the-art manufacturing, Variable Angle Tow (VAT) placement (where stiff carbon fibres are steered along curves to maximize structural performance). Ongoing studies suggest that such savings are achievable for standard test specimens (coupons) but new understanding is required to fully characterise structural and material behaviour from the full component level down to individual lamina and their interfaces. The entire structural system including material, geometrical and manufacturing parameters will be optimised. The extra design freedoms, created by curved fibre trajectories, provide scope for pushing back the envelope of structural efficiency. The academic team provide a unique capability to fulfil this vision. They have a proven track record in manufacture, modelling and design of composite materials and structures and have clear routes to exploitation via a pivotal industrial base. Their novel damage tolerance modelling techniques indicate that large improvements in material efficiency can be achieved if critical positions of delamination damage are tailored via through-thickness laminate optimisation. The team's preliminary VAT results indicate the prospect of developing buckle-free structures, reducing the need for stiffeners, with associated substantial cost and weight savings. Moreover, the specific manufacturing capability to produce variable angle fibres is unique to the UK, having been modified from an embroidery machine, using dry fibres rather than pre-impregnated material. Airbus and GKN will support the project with 290k of direct funding.

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