INVESTIGATIONS ON THE INFLUENCE OF DESIGN PARAMETERS ON THE STRENGTH OF CFRP REPAIRS
Topic(s) : Special Sessions
Co-authors :
Philip ROSE (GERMANY), Koerwien THOMAS (GERMANY)Abstract :
The percentage of carbon fiber reinforced plastic (CFRP) in the primary structural components of aircraft has steadily increased over recent decades. Consequently, CFRP components are experiencing more frequent instances of damage. In numerous cases, the economic feasibility of repair outweighs the option of replacing the damaged component. To address the increasing demand for CFRP repairs, several studies on CFRP component repairs have been conducted.
Owing to the internal composition of CFRP, which consists of reinforcing fibers and matrix material, localized damage such as holes that disrupt the reinforcing fibers poses a significant drawback for CFRP. Traditional repair methods involving riveted joints necessitate the creation of numerous holes in still-intact material, thereby compromising the structural integrity of the area. Load transmission between the joined components occurs within this weakened zone. This disadvantage can be avoided through adhesive-based repairs.
Presently, aviation authorities only certify the use of bonded repairs for very small areas of damage. The development of repair methods commonly involves destructive testing of representative repairs. For the experimental investigation of bonded repairs, a standardized specimen at the coupon level, the prEn6066 specimen, is available. However, this specimen represents a considerable simplification compared to actual repairs. This means that effects that have a significant influence may no longer occur, or only to a small extent, when they are analysed on more realistic specimens.
In this study, "Cupped" and "Straight" repair configurations, differing in the arrangement of repair plies, were experimentally tested at both coupon and element levels under quasi-static loading. Significant variations were observed between the levels of the test-pyramid, strength differences between Cupped and Straight at the coupon level varies by about 27%, whereas the configurations exhibited only a 2% strength difference when tested at the element level. These disparities primarily stem from the distinct detailing of the represented repair geometry, illustrating the challenges associated with designing specimens for investigating repair methods. Additionally, the study presents insights into optimizing specimens representing CFRP repairs to systematically evaluate the influences of different repair methods.
This research was carried out by Airbus® Defence and Space GmbH as part of the joint research project ” FACTOR – Future Advanced Composite Bonding and Bonded Repair”, funded by the German Federal Ministry for Economics and Climate Action
Owing to the internal composition of CFRP, which consists of reinforcing fibers and matrix material, localized damage such as holes that disrupt the reinforcing fibers poses a significant drawback for CFRP. Traditional repair methods involving riveted joints necessitate the creation of numerous holes in still-intact material, thereby compromising the structural integrity of the area. Load transmission between the joined components occurs within this weakened zone. This disadvantage can be avoided through adhesive-based repairs.
Presently, aviation authorities only certify the use of bonded repairs for very small areas of damage. The development of repair methods commonly involves destructive testing of representative repairs. For the experimental investigation of bonded repairs, a standardized specimen at the coupon level, the prEn6066 specimen, is available. However, this specimen represents a considerable simplification compared to actual repairs. This means that effects that have a significant influence may no longer occur, or only to a small extent, when they are analysed on more realistic specimens.
In this study, "Cupped" and "Straight" repair configurations, differing in the arrangement of repair plies, were experimentally tested at both coupon and element levels under quasi-static loading. Significant variations were observed between the levels of the test-pyramid, strength differences between Cupped and Straight at the coupon level varies by about 27%, whereas the configurations exhibited only a 2% strength difference when tested at the element level. These disparities primarily stem from the distinct detailing of the represented repair geometry, illustrating the challenges associated with designing specimens for investigating repair methods. Additionally, the study presents insights into optimizing specimens representing CFRP repairs to systematically evaluate the influences of different repair methods.
This research was carried out by Airbus® Defence and Space GmbH as part of the joint research project ” FACTOR – Future Advanced Composite Bonding and Bonded Repair”, funded by the German Federal Ministry for Economics and Climate Action