Influence of humidity on the durability of adhesively bonded aluminium composite structures

Abstract

The manufacture of an adhesively bonded structure which involves the joining of a carbon-fibre-reinforced plastic (CFRP) composite panel and an aluminium sheet is described. The thermal characteristics of CFRP composites and aluminium structures are very dissimilar. Hence careful design of the joint is required in order to achieve a bond which has the potential of durability when exposed to a high-humidity environment, such as is met in aircraft structures. The design of such a set of joint structures and their ageing in a high-humidity environment are described. The durability of the joints was assessed using high-frequency dielectric measurements as a non-destructive method and, in a parallel investigation, destructive shear strength and fracture toughness measurements were undertaken. Changes in the mechanical properties of the joints are correlated with the effects of moisture ingress into the joint structures. The joints obtained were surprisingly durable and this study implies that the design of aluminium-CFRP composite joints are a practical proposition.

Dielectric and mechanical studies of the durability of adhesively bonded aluminium structures subjected to temperature cycling. Part 1: examination of moisture absorption

“…The test was designed around ASTM D 3433-93 [14] and ASTM D 3807-93 [15] and has been discussed previously [10][11][12]. The load was applied using the Zwick 1445 tensile testing machine, with a constant crosshead separation rate of 3 mm/min.…”

“…The details of the measurements have been discussed previously [10][11][12]. Prior to each test the surface of the joint was abraded to maximize the electrical contact between the joint and connector.…”

“…An investigation by Li et al [9] of etched only, phosphoric and chromic acid anodized joints indicated that the changes in the dielectric profile with time reflected possible differences in the mechanism of ageing. These preliminary studies [10][11][12] were performed in an attempt to establish whether the dielectric measurements could detect changes in the bond line. In this paper, a systematic study is reported of the dielectric and mechanical studies of ageing of a series of adhesively bonded joints, aged both at constant temperatures and cycled between two temperatures.…”

Dielectric and mechanical studies of the durability of adhesively bonded aluminium structures subjected to temperature cycling. Part 1: Examination of moisture absorption

“…The details of the measurements have been discussed previously [10][11][12]. Prior to each test the surface of the joint was abraded to maximize the electrical contact between the joint and connector.…”

“…Data were recorded in both the time and frequency domains. The method using time domain reflectometry (TDR) has also been described previously [10][11][12]. The joints were scanned between 1 and 9 ns and the first three reflections were recorded.…”