09:00   Session 16; Digital engineering III Chair: David Hallam 09:00 20 mins Meso-scale models to analyse the interactions of damage modes in composites laminates Sara Ghiasvand, Alessandro Airoldi, Giuseppe Sala, Pietro Aceti, Pietro Ballarin, Andrea Baldi, Emanuele Mesiani Abstract: The response of complex composite parts for primary aeronautical structures, such as rotorcraft rotors, is influenced by the evolution of different damage modes. The numerical analysis of such phenomena has been undertaken within a joint project of Politecnico di Milano and Leonardo Helicopter. The approach consists of a ply-wise bi-phasic FE model of the laminate that makes possible a representation of both delamination and intralaminar matrix damage within the elements representing an idealized matrix phase [1]. Accordingly, the coupling between intralaminar cracks and delamination can be introduced in the matrix constitutive law, without requiring meshes refined at the sub-ply level. The theoretical aspects of the approach are summarized and attention is focused on a series of application cases, to illustrate the effectiveness of the technique. The modelling of inter-intralaminar damage interactions in glass-reinforced specimens is applied to represent the saturation of transverse cracking evolution in cross-ply tensile coupons as well as to predict the failures influenced by delamination in angle-ply laminates. The interaction between transverse cracking and delamination is analysed in detail for relatively thick L-shaped carbon-reinforced laminates, also considering the role of thermal residual stress and applying different coupling methods, such as coupled damage evolution and combined criteria for damage threshold. Finally, more cases referred to hybrid glass- and carbon-reinforced laminates are considered. The results indicates the potential of the approach for the prediction of the loads required to nucleate and propagate damages in real-world structural elements with complex geometry and lay-ups. [1] Airoldi A., Mirani C., Principito L. (2020). A bi-phasic modelling approach for interlaminar and intralaminar damage in the matrix of composite laminates. Composite Structures 234; 1-19 [2] Ghiasvand S., Airoldi A., Bettini P., Mirani C. (2022). Analysis of residual stresses and interface damage propagation in hybrid composite/metallic elements monitored through optical fiber sensors. Aerospace Science and Technology,129 09:20 20 mins A holistic digital twin for service life extension programs Javier Gomez-Escalonilla, Fernando Sanchez, Oscar Valencia, Manuel J Rebollo Abstract: Aircraft are affected by their continuous exposure to the conditions under which they operate. The well-known combination of fatigue, environmental and accidental damages in the airframe leads to a progressive reduction of the capability to carry load. Although the maintenance strategies promoted by the civil and military regulatory frameworks ensure that the degraded structure will withstand limit load at any moment, thus solving the safety implications of ageing, there are still significant economic considerations to be addressed in terms of the growing maintenance costs needed to meet these requirements, including inspections, repairs and replacements. This scenario is particularly demanding in the case of some of the products developed by Airbus Defence & Space, such as CN-235/C-295 tactical aircraft for maritime patrolling missions, in which a strong interaction between fatigue and corrosion appears, combined with a severe usage pattern that evolves throughout the service life depending on the operational needs. Among the options available to implement a Service Life Extension Program (SLEP) for these aircraft, the use of a digital twin (called Fatigue Digital Equivalent, FDE) has been selected in order to determine the condition of the structure by simulating the occurrence, growth and eventual interaction of the different degradation sources. At its core, the FDE is a collection of deterministic and probabilistic models representing all the aspects involved in the airframe's safety including design, manufacturing, maintenance, repair, configuration management and flight operations. The models are then incorporated into a set of holistic analyses used to estimate the remaining useful life of the relevant elements. One of the main challenges of the construction of the FDE is the integration into a single repository of heterogeneous sources of data, including design information created in many cases years ago by multiple teams working in silos, maintenance records generated over the years following different formats and standards, and external in-service inputs provided by the operators. Another relevant activity is the combination of conventional analysis tools with state-of-the-art procedures, such as Machine Learning (ML), in a harmonized process aimed to obtain an accurate assessment of the potential for extension of the structure. 09:40 20 mins Model based engineering approach in aeronautical fatigue and structural integrity testing Shawn You, Shawn Gao Abstract: In order to reduce the huge research cost and shorten the lengthy development cycle caused by design iterations, the Model-Based System Engineering (MBSE) method is introduced across the industry. Researchers are trying to use advanced testing and simulation methods, such as virtual testing and model assisted testing to accelerate the development process. Before physical testing, virtual testing can be conducted to simulate the physical test. Virtual model of the full testing system including controller, actuators, test article, and fixtures can be constructed and validated. Virtual testing can provide valuable insight of the real test system such as test system capability, desired PID tuning values, and system controllability. The virtual testing models can be implemented in MBSE models so that the system models can be more accurate. During tests, analysis models can be run in parallel with the test predicting the specimen behavior and guide physical tests in real-time. This approach is called model assisted testing. Model Assisted Compensator (MAC) was developed in this principal and was proven to be effective in compensating the cross coupling effect and achieving accurate control and speeding up the fatigue tests. In this study, a 4-channel test system was used to show the virtual testing process and the effectiveness of MAC. A virtual test model mimicking the physical test system was created and validated. This high-fidelity virtual test system not only could predict the test results, but also, in some instances, help identifying the root-cause of system instabilities. Based upon this model, MAC was created and utilized in a fatigue test. It had been demonstrated that MAC allowed the test to run fast enough that the test article inertia became the limiting factor. Even under complex load control, the transition from one loading stiffness to another can be applied with ease. This model-based approach is scalable to accommodate large scale testing with tens or even hundreds of actuators and complicated dynamic cross coupling.

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