TY - BOOK

T1 - Structural Integrity and Durability of Adhesively Bonded Joints for Composite Repair in Aircraft Applications

AU - Röper, Florian

N1 - no embargo

PY - 2020

Y1 - 2020

N2 - Polymer matrix composites are nowadays well established construction materials in all types of structures of modern military as well as civil aircraft, ranging from tertiary to primary structures. However, with the composite content in modern aircraft exceeding 50 % by weight combined with the increasing demand for new aircraft in the future, the risk of damage by e. g. loading and environmental conditions, collisions as well as manufacture induced defects to composite components is increasing as well. Hence, the demand for appropriate repair technologies is continuously rising. For more extensive damage, mechanically fastened or bonded repairs, which are either flush (i. e. tapered) or externally patched, can be conducted. When compared to mechanically fastened repairs, bonded tapered repairs offer advantages. However, structural adhesive bonding in general is still seen as an unreliable technology. Hence, certain aspects have to be investigated, which is the reason for addressing adhesively bonded repairs. Within this thesis, the influence of an alternative surface preparation method by a combination of corona and wet chemical treatment by an organosilane on the bond strength and failure behavior of single-lap specimens and of repair specimens was compared to the conventional sanding technique. For the repair specimens, which were repaired by a soft patch repair approach, the influence of the repair design was characterized by investigating scarfed and stepped tapered repairs as well as by varying the taper ratio from 1:9 to 1:50. Additionally, two types of adhesive, a supported and an unsupported film adhesive, were used for the production of the repair specimens. In order to characterize the bond strength and failure behavior under aircraft relevant environmental conditions, the single-lap specimens and the repair specimens were conditioned in selected media. Quasi-static tensile tests were performed at room temperature and 70 ◦C to investigate the influence of the increase in test temperature. In addition, the bond constituents were conditioned and tested under the same conditions as the bonded specimens, which ensured that the material behavior of the neat adhesive as well as of the adherents could be assessed under aircraft relevant environmental conditions. It has to be noted, that studies addressing certain aspects of these topics exist in literature. However, within this thesis, the influence of surface preparation as well as of environmental conditions on one set of bond constituents as well as of two different types of bonds manufactured from exactly these constituents on the mechanical behavior is investigated. This is of high importance, as the mechanical behavior of bonds is, besides other factors, influenced by the combination of adherent and adhesive.

AB - Polymer matrix composites are nowadays well established construction materials in all types of structures of modern military as well as civil aircraft, ranging from tertiary to primary structures. However, with the composite content in modern aircraft exceeding 50 % by weight combined with the increasing demand for new aircraft in the future, the risk of damage by e. g. loading and environmental conditions, collisions as well as manufacture induced defects to composite components is increasing as well. Hence, the demand for appropriate repair technologies is continuously rising. For more extensive damage, mechanically fastened or bonded repairs, which are either flush (i. e. tapered) or externally patched, can be conducted. When compared to mechanically fastened repairs, bonded tapered repairs offer advantages. However, structural adhesive bonding in general is still seen as an unreliable technology. Hence, certain aspects have to be investigated, which is the reason for addressing adhesively bonded repairs. Within this thesis, the influence of an alternative surface preparation method by a combination of corona and wet chemical treatment by an organosilane on the bond strength and failure behavior of single-lap specimens and of repair specimens was compared to the conventional sanding technique. For the repair specimens, which were repaired by a soft patch repair approach, the influence of the repair design was characterized by investigating scarfed and stepped tapered repairs as well as by varying the taper ratio from 1:9 to 1:50. Additionally, two types of adhesive, a supported and an unsupported film adhesive, were used for the production of the repair specimens. In order to characterize the bond strength and failure behavior under aircraft relevant environmental conditions, the single-lap specimens and the repair specimens were conditioned in selected media. Quasi-static tensile tests were performed at room temperature and 70 ◦C to investigate the influence of the increase in test temperature. In addition, the bond constituents were conditioned and tested under the same conditions as the bonded specimens, which ensured that the material behavior of the neat adhesive as well as of the adherents could be assessed under aircraft relevant environmental conditions. It has to be noted, that studies addressing certain aspects of these topics exist in literature. However, within this thesis, the influence of surface preparation as well as of environmental conditions on one set of bond constituents as well as of two different types of bonds manufactured from exactly these constituents on the mechanical behavior is investigated. This is of high importance, as the mechanical behavior of bonds is, besides other factors, influenced by the combination of adherent and adhesive.

KW - Faserverbundwerkstoffe

KW - Reparaturen

KW - Kleben

KW - Umgebungsbedingungen

KW - Composites

KW - Repair

KW - Adhesive bonding

KW - Environmental conditions

M3 - Doctoral Thesis

ER -