A basic principle for damage-tolerant structural bonding in aerospace applications
Topic(s) : Special Sessions
Co-authors :
Martin BLACHA (GERMANY), Büsing SEBASTIAN (GERMANY), Thomas JOACHIMAbstract :
Besides bonding quality, reliability and reproducibility, the biggest challenge in structural bonding for aerospace applications is the behavior of the bond line related to damage tolerance. This aspect is the key question for a certification of structural bondings. In the German funded R&T project “JoinDT”, several industrial and research partners are examining the damage tolerant structural CFRP and hybrid bondings with respect to with respect to different aspects including repairs, typical damages, and manufacturing parameters.
Within this research project, a novel design principle for damage tolerant structural bondings in aerospace applications has been developed at Airbus Helicopters. This will be presented in this publication. The general approach of this new concept is to establish the principle of damage tolerance by a structure-mechanical modification of the well-known lap-shear splices: Instead of a continuous lap-shear joint the bonded parts are modified with a special shaped end. This forms an intermeshing pattern along the bond line. In combination with the splice-plate, this intermeshing pattern creates a bond-line which is sub-divided into a plurality of separated sub-bondings. All these separated sub-bondings form the load transferring structural bonding.
The advantage of splitting up into multiple sub-bondings is that imperfections or damages on the bonding (manufacturing imperfections, impact damages, etc.) which might lead to cracks in the adhesive cannot propagate from one sub-bonding to the next: The complete geometric separation of the sub-bondings creates an effective crack-stopping feature.
In the context of the research project different aspects of the new concept were considered and examined in detail. FEM-based simulations were carried out on different detail levels, including parameter studies, crack-growth and residual strength analyses.
In addition, a test campaign was performed on element level and on structural detail level. The structural detail test represents the typical use case of joining two sandwich panels with a splice plate. All tests are intended to validate the basic concept and to calibrate analyses as well as to demonstrate structural strength and damage tolerance capability.
The outcome of the tests proves the validity of the novel design principle in terms of increased strength, insensitivity to impact damages and general damage tolerance. With this, the basis for a certification approach for structural bondings in aerospace applications is given.
Within this research project, a novel design principle for damage tolerant structural bondings in aerospace applications has been developed at Airbus Helicopters. This will be presented in this publication. The general approach of this new concept is to establish the principle of damage tolerance by a structure-mechanical modification of the well-known lap-shear splices: Instead of a continuous lap-shear joint the bonded parts are modified with a special shaped end. This forms an intermeshing pattern along the bond line. In combination with the splice-plate, this intermeshing pattern creates a bond-line which is sub-divided into a plurality of separated sub-bondings. All these separated sub-bondings form the load transferring structural bonding.
The advantage of splitting up into multiple sub-bondings is that imperfections or damages on the bonding (manufacturing imperfections, impact damages, etc.) which might lead to cracks in the adhesive cannot propagate from one sub-bonding to the next: The complete geometric separation of the sub-bondings creates an effective crack-stopping feature.
In the context of the research project different aspects of the new concept were considered and examined in detail. FEM-based simulations were carried out on different detail levels, including parameter studies, crack-growth and residual strength analyses.
In addition, a test campaign was performed on element level and on structural detail level. The structural detail test represents the typical use case of joining two sandwich panels with a splice plate. All tests are intended to validate the basic concept and to calibrate analyses as well as to demonstrate structural strength and damage tolerance capability.
The outcome of the tests proves the validity of the novel design principle in terms of increased strength, insensitivity to impact damages and general damage tolerance. With this, the basis for a certification approach for structural bondings in aerospace applications is given.