Characterization of Pre-bond Contamination and Aging Effects for CFRP Bonded Joints Using Reference Laboratory Methods, Mechanical Tests, and Numerical Simulation

Abstract

In this chapter, the pre-bond contamination and ageing effects on carbon fiber reinforced plastic (CFRP) adherends and CFRP bonded joints are characterized by means of reference laboratory non-destructive testing (NDT) methods, mechanical tests, and numerical simulation. Contaminations from two fields of application are considered, namely in aircraft manufacturing (i.e. production) and for in-service bonded repair. The production-related scenarios comprise release agent, moisture, and fingerprint, while the repair-related scenarios comprise fingerprint, thermal degradation, de-icing fluid, and a faulty curing of the adhesive. For each scenario, three different levels of contamination were pre-set and applied, namely low, medium and high level. Furthermore, two types of samples were tested, namely coupons and pilot samples (a stiffened panel and scarf repairs). The CFRP adherends were contaminated prior to bonding and the obtained surfaces were characterized using X-ray photoelectron spectroscopy. After bonding, the joints were tested by ultrasonic testing. To characterize the effects of each contamination on the strength of the bonded joints, mode-I and mode-II fracture toughness tests, and novel centrifuge tests were conducted on the coupons, while tensile tests were performed on the scarfed samples. Additionally, numerical simulation was performed on CFRP stiffened panels under compression using the LS-DYNA finite element (FE) platform.

Extended non-destructive testing for inline quality control of cleaning and pre-treatment processes in adhesive bonding of polymer blends

“…On the one hand, such evidence related to the benefits of surface cleaning before bonding is not wondrous in adhesive bonding technology but was reported in numerous contributions [12,[22][23][24][25]. As on the other hand only after climatic ageing of the manufactured joints mechanical effects of fingerprints are revealed in -furthermore -destructive tests, post-process quality assurance appears to result challenging in the presented application.…”

“…Until this day artificial fingerprint contamination or fingerprinted deposits from technical liquids are in the focus of establishing quality assurance procedures for adhesive bonding assembly, e.g. in the European joint research projects FP7-JTI-CleanSky-ICARO, FP7-ENCOMB and Horizon2020-COMBONDT [7,[10][11][12]. Beyond that, greasy or sebaceous [13] natural and latent, i.e.…”

“…In this contribution, selected findings related to one of these demonstrator joints are highlighted and a focus is on greasy fingerprints as potentially relevant, unconsciously applied surface contaminations. They may be latently present on adherends which are introduced into the adhesive bonding process during production or repair or inexpertly handling during these processes [12]. An exemplary and nominally qualified adhesive bonding process with ABS adherends is considered which comprises surface cleaning and a pre-treatment of the adherends prior to the application of the adhesive system.…”