Bonded aerospace repairs under tensile loading: Wet chemical surface treatment and selected environmental conditions

Abstract

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.

Elevated temperature mechanical behavior of nano Al2O3 embedded interpenetrating polymer network/glass fiber composites

“…In recent years, owing to the fiber-reinforced polymer (FRP) composites' superior performance, they are increasingly being used in numerous industries, namely automotive, aerospace/aircraft, railways, shipbuilding, and space vehicles. [1][2][3][4][5] In general, FRP composites exhibit low density, good fatigue performance, excellent corrosion resistance, and most importantly, high specific strength and specific modulus. [6][7][8][9] However, FRP composites possess poor out-of-plane properties.…”

XCT inspection in bonded aircraft repairs for composites

“…A detailed depiction of the delamination found in the specimen in dried and wet condition as well as after cyclic conditioning can be found in figure 2. It was not possible to detect significant growth of preexisting delamination after the cyclic conditioning with the current specimen dimensions using the high-resolution XCT in AC mode [6]. Only the contrast and sharpness of the delamination after cyclic conditioning seems to be slightly higher, which can be an indication of a slightly increased crack width or of marginally better XCT-measurement conditions during the scan time of 175 min (e.g.…”

“…All information on the experimental procedures were given in detail in the previous publication [6]. Consequently, the procedures will be described briefly in this section.…”

“…As a consequence of the need to repair composites via bonding, selected XCT techniques have been used in this study to inspect repaired specimens and to investigate the influence of cyclic conditioning between -30 °C and 70 °C / 85 % r. h. In addition to previous work performed by Röper et al [6], where high resolution XCT images were obtained from specimens in dried condition and after cyclic conditioning, a scan on a sample with reduced dimensions was performed in the present study to enhance the resolution of the obtained images. This additional work was performed because, despite the fact that it was possible to identify the tracer yarns as well as the adhesive and the knit carrier within the adhesive in specimens with a size of (14 x 14 x 2.5) mm 3 , it was not possible to distinguish the CF from the epoxy matrix in the parent as well as the repair laminate [6]. Furthermore, TLGI-XCT images using AC, DPC as well as DFC mode were additionally taken to extract information about the laminate layup as well as on resin rich areas.…”

Current state-of-the-art of carbonaceous nanofiller coated carbon fiber in polymeric nanocomposites

“…For better interface formation between the carbon fiber and polymer, various dry and wet chemical treatments approaches have been used for the filler surface modification. 10 The important carbon fiber modification methods involve the acid treatment, chemical modification, electrochemical and other techniques. Consequently, the carbon fibers have been modified with the nanocarbons and reinforced in the polymeric matrices.…”