Degradation of single lap adhesively bonded composite joints due to hot water ageing

ABSTRACT

Joints, which are the most critical part of fibre-reinforced epoxy plastic structures, can be exposed to continuous hydrothermal action. In order to estimate their long-term performance, an accelerated ageing process was performed on adhesively bonded joints of glass-fibre-reinforced epoxy plastics with [0/90/45/−45]_s fibre orientations. Changes in the static tensile properties of single lap shear samples due to hot-wet exposure were investigated for one- and two-week immersion periods and at three different water temperatures (50°C, 70°C, and 90°C). Both the ageing temperature and immersion time were found to be influential on load–displacement characteristics, maximum failure loads, and apparent failure modes of joints bonded with Loctite Hysol-9466 epoxy type adhesive. Due to the hydrothermal exposure, maximum failure loads, distance to failure values, and stiffness of joints decreased by a certain amount in proportion to the immersion time and temperature. While unaged samples and those aged at 50°C and 70°C exhibited mainly light fibre-tear (LFT) failures, the samples treated at 90°C ruptured through the material cross section in stock-break (SB) failure mode.

KEYWORDS:

• Aerospace
• ageing
• composites
• destructive testing
• epoxy/epoxides

Acknowledgement

The author gratefully acknowledges the use of facilities and instrumentation supported by Department of Mechanical Engineering, Dokuz Eylul University, İzmir, Turkey.