13:50   Session 18: Airworthiness considerations II Chair: Laurent Touzet 13:50 20 mins Design and experimental validation of a MDAF bonded structure fail safe damage arrest concept David Bardenstein, Iddo Kressel, Alex Lukatsky, Zvi Deutch, Noam Shemesh, Stephen Clay, Brian Smyers, Philip Knoth Abstract: The need for light-weight and cost-effective fibre reinforced airborne primary structures, drives the industry towards more integral design concepts. Adhesive bonding is increasingly employed as an attractive alternative to mechanical fastening. Aside from the weight reduction due to elimination of fasteners, the high stiffness of bonded joints and the smooth load transfer they provide, are major advantages of this concept. However, the lack of reliable bonded-joint damage-growth analysis combined with the inadequacy of commercially available non-destructive inspection methods to evaluate the strength of bonded joints – has inhibited full adaptation of such joining concepts. This work presents an innovative fail-safe MDAF (Mushroom Damage Arresting Feature) fail-safe crack arrest concept for bonded joints in order to ensure predictable slow damage growth. It was proved both by numerical CZM analysis and mechanical Pull test that by implementing a series of unique geometrical mushrooms and recesses along a stiffened panel's stringer foot, damage arresting capability may be achieved and once an initially dis-bond crack reaches the first mushroom front, after an expected loading event, it will be stopped there and a significantly additional energy will be required to overcome the mushrooms bond-line and to further propagate the dis-bond crack. Subsequently, the load will drop and a rapid unstable crack propagation will take place until the next mushroom is reached, where additional energy will be required again to propagate the crack and so forth. On the other hand, it was shown that for the standard baseline specimen with straight stringer foot, an unstable catastrophically damage propagation is expected once the critical load is reached. 14:10 20 mins Characterization of MSD in emerging metallic structures in fuselage lap joints Kevin Stonaker, Terry Zhang, John Bakuckas, Mike Kulak, Kimberly Maciejewski, Walt Sippel, Fabricio Fanton, Carlos Chaves, Paul Jonas Abstract: In partnership with Arconic and Embraer, the Federal Aviation Administration (FAA) is evaluating the behavior of multi-site damage (MSD) for emerging aluminum alloys in a generic fuselage lap joint configuration. This program is a comparative study of the initiation and growth characteristics of MSD for two aerospace aluminum alloys, namely: 2524-T3 aluminum-copper alloy (baseline) and 2060-T8 aluminum-lithium alloy (new generation). This behavior is being studied by conducting fatigue testing on a common lap joint design at three different specimens sizes, namely: (1) single rivet column coupons, (2) wide flat panel specimens, and (3) curved sub-scale panel specimens. Data from this study will be used to assess the relevance of existing regulations and to inform whether additional safety standards and regulatory guidance should be developed to provide improved safety beyond that afforded by the existing airworthiness standards. Additionally, results will be used to support potential improved weight and structural safety performance expectations of the EMST and to evaluate the effect of specimen scale on fatigue performance. As part of this program a subset of the 2524-T3 wide flat panels and curved sub-scaled panels were manufactured with an initial MSD scenario. The purpose of the MSD scenario was to establish a common starting point for the crack growth and residual strength portions of the tests in order to facilitate better posttest comparisons. Additionally, using finite element modeling it was anticipated that the wide flat panels would experience higher secondary bending of the joint compared to the curved sub-scaled panels. Therefore, a subset of the MSD wide flat panels were also tested with an anti-bend device that was designed to constrain the bending and bring it closer to the predicted curved panel behavior. This paper will provide a brief overview of this program with focus on the test and analysis of the wide flat panel with the initial MSD scenario. 14:30 20 mins Bonded repair size limit studies of representation composite wing panel Reewanshu Chadha, John Bakuckas, John Lin, Tim Labik, Michael Fleming, Erick Espinar-Mick Abstract: The Federal Aviation Administration and The Boeing Company have been investigating the safety and structural integrity issues of bonded repair technology. Under a Cooperative Research and Development Agreement (CRDA), efforts are focused on testing and analyzing bonded repairs to representative composite wing panels using the Aircraft Beam Structural Test (ABST) fixture, an innovative structural test capability at the FAA William J. Hughes Technical Center. The program objectives are to characterize the fatigue and damage tolerance performance of bonded repairs subjected to simulated service load and to evaluate the limit load capability of a typical composite wing panel of transport category aircraft with a failed repair patch. Emphasis has been placed on investigating methods and tools used to conduct analysis and performance predictions of bonded repairs as well as those used to monitor and evaluate repair quality over the life of the part. The initial phases of the program supported ABST fixture development, verified analysis models, and provided an initial reference point for inspection and monitoring systems used to detect and track damage formation. Current efforts support bonded repair size limit (BRSL) studies, which includes a redundant strength check with the repair patch removed, and methods used to predict the limit load residual strength for a variety of composite systems including solid laminate, honeycomb and thermoplastic panels. This paper/presentation will provide the ICAF community an overview and update of this multi-phase collaborative program. 14:50 20 mins Machine learning requirements for the airworthiness of structural health monitoring systems in aircraft Haroun El Mir, Stephen King, Martin Skote, Suresh Perinpanayagam Abstract: In the evolving realm of airworthiness and aircraft maintenance task scheduling, the introduction of data-driven Predictive Maintenance (PdM) and Structural Health Monitoring (SHM) has prompted a paradigm shift, which underscores the profound implications of innovative sensing techniques within damage and operational monitoring. Concurrently, the role of avionics in data acquisition and processing has drawn renewed focus, with machine learning (ML) algorithms facilitating pattern recognition, trend analysis, and anomaly detection. This paper discusses the diagnostic sequence in SHM systems, the necessity for damage information, and delves into active and passive sensing techniques within damage and operational monitoring. The role of avionics is also emphasized, especially in data acquisition and processing for operational monitoring. The utilization of ML algorithms for efficient use within SHM is explored, alongside supervised and unsupervised learning methods. The paper underlines how integrating ML in aircraft systems applications can optimize maintenance schedules and lay a solid foundation for SHM integration in aircraft health systems. The study also covers the application of ML techniques for detection, localization, and assessment of structural damage. It reviews research implementations using ML, statistical, and hybrid approaches in monitoring and predicting aircraft damage. The incorporation of non- exclusive ML in SHM to minimize environmental feature uncertainty and enable trackable model behaviour is illustrated. Lastly, the paper discusses evolving regulatory requirements and standards for ML application in aviation SHM, provided by authorities and workgroups like EASA and the SAE G-34 AI in Aviation Committee, respectively, and concludes with an overview of the future trends and standards in this dynamic domain. The aim is to spotlight the transformative potential of PdM and SHM, and their critical roles in boosting the operational efficiency of the aviation industry.

end %-->