Periodic Reporting for period 2 - SealedwithoUTaKiss (Non-destructive testing (NDT) of bonded assemblies)
Periodo di rendicontazione: 2020-10-01 al 2022-03-31
A kissing bond is a defect where two surfaces are partially bonded or de-bonded, but still, touch or are in very close proximity. A defect of this kind can’t be observed/detected macroscopically, and because of their intimate contact, its detection using NDT techniques is more limited than that of conventional defects. The presence of these defects in bonded joints leads to catastrophic failure due to the nature of the defects. SealedwithoUTaKiss presents NDT inspection techniques including a TRL6 demonstrator of laser shock and ultrasonic guided waves for the reliable detection of structural defects in bonded assemblies (e.g. kissing bonds) with a high level of accuracy. The project implemented mechanical adherence testing and comparative experimental analysis of different NDT techniques, in order to identify defects in various bonded assemblies. To create the kissing bonds, white grease has been used to induce kissing bond defects in the bonded joints. The bonded joints were then tested with ultrasonic probes to check if the bonded joints with defects can be identified. Upon confirming that ultrasonic scanning cannot detect the defects, the samples are subjected to mechanical testing (destructive testing). Defective-samples failed at a load less than 20% of the load at which reference-samples failed in the mechanical testing. Thus, it is concluded that the creation of bonded joints with kissing bond defects is successful. A protocol has been documented on the procedure of inducing kissing bond defects in bonded joints. Later, advanced NDT methods namely (i) Guided waves NDT (ii) Laser shock have been explored and optimised for the detection of kissing bonds. Time signals of the test sample are obtained in both the experiments. Power spectrum analysis is used to analyse the time signals. Power spectrum of the time signal is identified as the feature indicative of kissing bonds. It has been found that both UGW and laser shock are effective at detecting kissing bonds in bonded joints. Results obtained using both methods show a specific trend of frequency shift of the highest peak which differentiates reference-samples from defective-samples.
The main WP1 objective was to review micro/macro scale models of adherence and cohesion for use cases covering main types of bonded assemblies, including adherence models and mechanical constraints. WP2 provided use cases composed of a representative set of coupons and few assembled parts and proposed innovative surface preparation and control. Among methods tested, the use of “White Grease” as contamination could better meet the defined "kissing bond" criteria and a special kissing bond creation protocol has been issued. WP3 studied and evaluated the NDT techniques for bonded structures, including laser shock and guided waves and a report on evaluation of all the NDT methods has been prepared. Different NDT methods were analyzed and evaluated for different bonded structure cases and manufacturing processes, in order to identify the most suitable to be further validated. Design and development of laser shock and guided wave NDT system and testing of manufactured representative use cases and samples provided by the TM was performed. WP4 involved the identification of mechanical testing criteria to be used for evaluating the mechanical performance of different adhesively bonded structures. There-in mechanical testing was conducted following procedures/protocols developed for each adhesively bonded structure. Two complex assemblies have been selected as demonstrators, i.e. a stiffened panel and a repaired panel, which were provided by the TM and treated by project Partners. In WP5 a TRL6 demonstration of selected NDT techniques has been enabled for representative cases of bonding, while mechanical testing and evaluation of bonded structures samples and demonstrators has followed. WP6 included the dissemination and exploitation activities of the project. Despite the COVID-19 obstacles and related travel restrictions, the SealedwithoUTaKiss Consortium, with the continuous support of the TM, managed to timely conclude the project, performing all related activities.
Smart answers to market demand: systems and equipment must increase their intrinsic performance to meet new aircraft needs without a corresponding increase in weight and volume: kW/kg, flux/dm3 are key indicators of systems innovation: The SealedwithoUTaKiss solution will directly answer market needs, as adhesively bonded structures allowing high reliability will offer an alternative to bolts and rivets in aircraft structures thus, will significantly reduce weight and ultimately fuel of aircraft resulting in meeting future needs of economical and efficient aircraft operations. Reduction of weight due to use of fewer rivets and bolts and more adhesively bonded material will allow improvement in flight operation due to a lightweight structure, higher performance, better maintenance and high efficiency. For sales development a fundamental parameter is that the MROs will have to address this growing market challenge through enlarging their capability in repair of composite materials. Composite repair has developed during last twenty years on aircraft having up to 20 % of composite structure only and not on primary structural parts. Today, the B787 is already fully operational while the A350 will be soon in the hangars of customers. These aircraft have more than 55 % of composite structures, considering that even their fuselage is in composites, which means that a much greater number of composite repair requirements will be expected. But the B787 and the A350 are not the only ones. A new era opens for Advanced Composite Structure Repair in Workshop as well as in Flight Line (repairs on the aircraft itself between two flights), that will necessitate new technologies and training services, so that the technical services will be in position to face the new challenges dealing with the damages in complex structures, potentially including “kissing bonds”. Engineers and technicians responsible for such operations are conscious that up to now their teams have been practicing on simple secondary structures. How to reliably and efficiently detect “kissing bonds” and then repair complex structures like a panel of a fuselage, a new radome, very large areas on an engine internal part appear challenging. Reviewing the above mentioned data, it can be confirmed that the innovative technology and methodology developed within SealedwithoUTaKiss are absolutely relevant from a commercial point of view and present a much better cost vs. performance ratio (value for money) compared to state-of-the-art and competitive approaches/products. This gives to SealedwithoUTaKiss Partners a 2-3 years advance compared to competition, should any similar products be developed. Manufacturers and repair centres using innovative GMI solutions will be provided with a very important advantage compared to competition, in terms of range of available solutions, cost efficiency and performance. In a similar manner, TWI and BRU will be able to innovative NDT propose services mainly to the aeronautical industry concerning the detection of kissing bonds. Such services would not only include performance of tests for third parties, but also training and consulting activities, thus maximizing the impact of the project for both entities.