Repair of composite structures and the impact of demanding environmental conditions is a crucial issue for the aircraft industry because of the increasing use of composites in modern aircraft. Consequently, the impact of environmental conditions common for aircraft applications on repair specimens in comparison to nonrepaired specimens is studied. All specimens are produced from a woven carbon fiber‐reinforced epoxy‐based prepreg. For the repair‐specimens, an epoxy‐based film adhesive is used for the soft patch repair approach. During the repair process, the surface of the precured prepreg is prepared by a mechanical method (sanding) and an additional chemical functionalization, respectively. Moisture absorption of the repair specimens is independent of the surface preparation method and higher for the repaired than for the nonrepaired specimens. The key influencing environmental conditions for the tensile strength and the failure mode of the repair specimens are elevated temperature testing as well as hot/wet conditioning and conditioning in deionized water. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47506.

No abstract

As bonded composite repairs are gaining importance for modern civil aircraft, it is necessary to investigate such repairs in detail under relevant environmental conditions. In this work, X-ray computed tomography (XCT) was performed on bonded repairs for carbon fiber (CF) reinforced epoxy matrix composites before and after cyclic conditioning between dry/cold and hot/wet conditions. In detail, high resolution XCT scans in absorption contrast (AC) mode as well as Talbot-Lau grating interferometer (TLGI)-XCT scans to obtain additional differential phase contrast (DPC) and dark-field contrast (DFC) modalities were performed. The repair bonds' constituents could be identified by the high resolution XCT scans. Additional information about fiber alignment, at least of the fiber bundles, could be extracted from the TLGI-XCT scans. In order to gain detailed information on certain specimen features, specimen dimensions were reduced for additional high resolution XCT scans.