An Introduction to Digital Performance Qualification with
CAELESTIS’ core aim to enable future aircraft to be built from composites materials relies on the key advantages composites could hold over older, and primarily metal, aircraft. First and foremost, composites are lighter, improving fuel-efficiency and overall performance. Also, composites don’t rust or corrode like metals, potentially increasing their lifespan and reducing maintenance efforts, while also offering increased design flexibility around complex shapes for better aerodynamic performance. Composites may even reduce aircraft noise, much to the comfort of tomorrow’s passengers!
Unfortunately for us though, it’s not quite as straight forward as simply switching material. That’s where the third Work Package in CAELESTIS comes in – Digital product and structural performance qualification – led by the AMADE research group from the University of Girona in Catalonia, Spain. As Post-Doc Researcher with AMADE, Aravind Sasikumar, explains, the idea behind the Work Package is to define the methodology used to “simulate the mechanical performance” of prototype composite components. If CAELESTIS’ objectives are met, then using high-powered computing to simulate the mechanical performance of lightweight components could speed up their adoption.
We posed a few questions to Aravind from AMADE, to find out more about this incredible research group and their contribution to CAELESTIS.
Maybe you could start by giving us a very quick summary of what AMADE is, and what the group’s experience is like with projects similar to CAELESTIS in the past?
AMADE (Analysis and Advanced Materials for Structural Design) is a research and technology transfer group of the University of Girona devoted to the mechanics of materials and structures with a specific focus on fibre-reinforced composite materials. AMADE has more than two decades of experience in the study, characterization and analysis of the mechanical behaviour of advanced composite materials. The composite group of AMADE is dedicated to the understanding of the mechanical behaviour and fracture of fibre-reinforced polymer materials and developing robust and reliable numerical models for an improved structural design.
What are some of the challenges working with composite materials? Fibres ‘inside’ the body of a component can start to fail over time – but it’s very difficult to know what is going on inside a material. Is that relevant to this project?
Yes, this is the key topic, to understand how damage is initiating and propagating within the composite material. Compared to conventional materials like metals, composites are made of fibres and resin, to say it in a simple way. These composite materials provide excellent material properties compared to metals, and they are lightweight too – in technical terms we call that high specific strength (strength to weight ratio). The disadvantage when dealing with composites is that they are no longer isotropic like the metals, meaning, composites are made out of different plies (more like a sandwich), and unlike metals, there are numerous ways for the damage to initiate. It can be through matrix cracks, that could grow during aircraft lifecycles and can reach an interface of a composite ply to grow into a delamination, etc. The fibres could break at a certain point critical to the structural integrity of the component. In a nutshell, there are various damage mechanisms that can happen depending on the loading case, and the interaction of these different damages needs to be understood. In order to correctly predict the failure of a part, simulations need to be able to capture all this damage morphology.
Maybe you can tell us a bit about the manufacturing defects mentioned in WP3’s description. What sort of defects are we talking about? How can they affect a plane mid-flight? How can you ‘predict’ them happening during future manufacture?
Manufacturing defects are quite normal to happen during the different processes. Defects such as tape overlaps, gaps, wrinkles are commonly reported. During an automated fibre placement (AFP), the fibre tape is placed side to side by a robot. There are possibilities that while laying one tape next to the other, there can be gaps between tapes or on the contrary, overlaps (where one tape overlaps the other, see the image below). The objective of CAELESTIS is to have these tools put together in a High-Performance Computing system, where if we input an overlap during the AFP process, it should be able to propagate this effect through all the different models and give a prediction on the effect on the mechanical performance.
With regard to carbon emissions from fuel burn, do you take this into account and model this at all already at the material stage? Do you have an understanding or way of predicting how weight affects ultimate emissions?
The simulations we perform are mainly dedicated to the prediction of the strengths (mechanical performance of a part) and we don’t take this into account at the material characterization or at the virtual testing stage. This should be a different stream like the life cycle analysis (LCA), where emissions must be calculated rooting back the whole process since it’s not just the weight of the part but also its whole life cycle (what material was used, how was it manufactured, all this can sum to the total carbon footprint.)
What is your involvement in other WPs?
In fact, AMADE-UDG is the only partner in CAELESTIS that is involved in all the WPs. Apart from being the work package leader in WP3, our main involvement is in WP5 and WP6. In WP5, we need to define a methodology to estimate the design allowables, that includes global sensitivity analysis approach and UQ&M (uncertainty quantification and management). AMADE has been involved in this topic in different projects in the recent years, and recently being able to join CONCERTO, a Clean Aviation project, that aims to provide a new certification framework to shorten the certification time of future aircrafts.
In WP6, AMADE is responsible for the material characterization and demonstrator coupons testing. In this WP, AMADE also plays a key role which is to perform X-ray tomography on specimens with defects to understand the defect topology and model these defects into FEM software.
In the context of CAELESTIS, the groundbreaking work of AMADE group represents perhaps the key research to facilitate our vision for the future of aeronautical engineering. The dynamic group’s two decades of experience, and their close work with the Barcelona Supercomputing Centre, are real show of strength for the European or, more specifically the Spanish, research community, and wield the unique ability to confidently prove composites’ viable usage in flight. AMADE’s holistic view of how composite components function, how they are built, and most importantly how they can fail, is central to proving they can help make tomorrow’s aircraft lighter – and safer – than ever.