16:20   Session 9: Airworthiness considerations I Chair: Marcel Bos 16:20 20 mins Compression after impact fatigue damage growth in CFRP - What does no-growth really mean? Davide Biagini, John-Alan Pascoe, René C. Alderliesten Abstract: Impacts on carbon fiber reinforced composites (CFRP) can produce internal damage comprising of matrix cracks, multiple delaminations and possibly fiber fracture, which is hard to detect from simple surface inspection. This situation is known as barely visible impact damage (BVID). Considering that every airplane faces impacts of various severities during its operational life and that the majority of exposed surfaces in new-generation aircraft are made of CFRP, there is a high chance that aircraft will be flying with unnoticed impact damage. For this reason, BVID fatigue propagation must be taken into account in design. The EASA and the FAA dictate a no-growth design philosophy for BVID. This is usually verified by tracking the projected delaminated area using ultrasound inspections. However ultrasound inspection can only detect delamination and suffers from a well-known shadowing phenomenon. Up to what extend does a no-growth in the detected damage (using ultrasound inspection) correspond to a no-growth in the real damage? To investigate this question, fatigue compression after impact (CAI) tests were conducted on a quasi-isotropic layup of CFRP. The following fatigue damage propagation was monitored by combining through thickness attenuation scan, echo-pulse C-scan and acoustic emission. The delamination growth was precisely reconstructed and combined with acoustic emission data leading to the following critical considerations: - Projected delaminated area is not sufficient to describe the fatigue damage propagation of BVID. Through thickness attenuation scan showed growth inside the impact cone, while echo pulse scan showed the outward growth of short delamination falling inside the projected area of larger ones (see figure). Both types of growth are not captured if only the overall projected area is considered. - Mechanisms of damage accumulation different from delamination cannot be excluded a priori. Acoustic activity was detected also when no delamination propagation was observed using ultrasound. The conclusion is that current damage descriptions are insufficient, and that a no-growth in the detected damage (using the current procedure) does not necessarily correspond to a no-growth in the real damage. 16:40 20 mins How the holistic approach for GLARE development still brings benefits Rik-Jan Lemmen, Derk Daverschot, Paul Mattheij, Thomas Beumler Abstract: This paper presents the approach for the FAR26.21 Widespread Fatigue Damage (WFD) compliance demonstration for GLARE® skin panels of the A380-800. In 1997, Airbus decided to apply this Fibre Metal Laminate (FML) as a novel structural material for the fuselage skin panels of the A380-800. GLARE® is developed with the vision to combine the high-strength properties of glass fibres with the advantages offered by metals, i.e. stability, ductility, isotropy, etc. As a result, a structural material is developed, which exhibits excellent damage tolerance and residual strength capabilities. A holistic development approach ensures that all requirements for certification, manufacturing and operation are considered from the start. Consequently, the FAR26.21 WFD requirement is anticipated at type certification. Moreover, the full-scale fatigue test was exploited to fully support the F&DT and WFD certification by ensuring significant coverage. Following completion of the full-scale fatigue test, a tear-down campaign is performed, which provided information on the health of the structure at the end of the test. The tear-down included an extensive inspection campaign of the tested structure with dismantling and detailed inspection of all areas relevant for F&DT and WFD compliance. In addition to the inspections on the tested structure, test coupons are extracted from areas representing specific design solutions, which exhibited most fatigue damage in order to conduct residual strength tests. The test results confirmed that the residual strength capability exceeds limit loads and exhibits even significant margin beyond ultimate load. For the WFD compliance exercise, the list of WFD candidates from the FAA are evaluated as a minimum. Additionally, GLARE® design specific areas such as the Splices®, the internal doubler run-outs are evaluated. It became apparent during the A380-800 WFD compliance exercise that the holistic development approach of GLARE® resulted in a structural material concept with outstanding damage tolerance properties; i.e. no crack-tip interaction, ultimate load capability, etc. These properties, together with the design principles and margins applied at design, significantly simplified the WFD compliance exercise for the A380-800 GLARE® structure. 17:00 20 mins Will the metaverse transcend the status quo?: Challenges to overcome for relying on multiphysics smarter testing and simulation in aerospace Linden Harris Abstract: Smarter testing and simulation of aerospace structures can allow development lead-time and costs to be decreased when compared to the current methods, which rely almost solely on physical testing. By combining outputs from computer simulations with physical approaches, an optimised process of hybrid testing, based on the concept of a digital twin, can be applied throughout the lifecycle of a product from development to certification. But now our challenge is to integrate cryogenic LH2 fuel storage and distribution systems into our airframes which will require our thinking to transcend into a multiphysics world, with a high level of credibility.

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