Thomas Koerwien

Structure Technologies and Challenges for Military Aircraft

Abstract:

The evolution of military aircraft design, encompassing both manned and unmanned platforms, has been profoundly influenced by advancements in structural technologies aimed at enhancing performance, durability, and operational efficiency. This contribution explores the development and use of structural bonding technologies and the associated challenges in modern military aircraft, with a focus on the emerging drone platforms. The technology offers significant cost savings as well as a reduction of the signature of an aircraft.

Using structural bonding, in particular with the use of carbon composites (CFRP) is linked to a number of fundamental technology bricks. Among them are the development of adhesives as well as the understanding of the process or what makes adhesion work. Furthermore, the design for bonding, manufacturing for bonding, quality control and last but not least certification are essential enablers. In this paper the certification aspect as well as quality control will be explored further.

Nowadays, certification of bonded joints requires the limitation of crack growth of possible local damages through design features in order to maintain limit load capability, or a repeatable measurement of strength, or proof load testing up to the limit load of each bonded joint. The determination of the actual bondline strength is not within reach. Proof load testing is applicable for prototyping. The way to certify a bonded joint is to use design features for damage containment of local damages. In order to leverage the potential of bonding technology a design and sizing methodology is required to design for damage tolerance. This involves the modelling of e.g. impact damages, virtual fatiguing and approximation of the residual strength. The presentation will strive on the strategy to comply to certification requirements with insights concerning test methodologies.

The assessment of bonded joints and its integrity is also paramount for this technology. As the direct measurement of bonding strength is not possible, indirect way to determine it are becoming more important. Airbus has developed a non-destructive method to determine whether a surface is ready to bond or whether it requires further cleaning.

An important element to enable cost savings is the design and its manufacturability. Key in here is the reduction of part count, leading to larger parts in combination with the reduction seams the require of rivets. At the same time the design of the joints shall be shear driven. In terms of manufacturing gap management is important. This will be addressed in the EDF project MaJoR, where an outlook is given.

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