Mixed-mode crack growth in bonded composite joints under standard and impact-fatigue loading

• Published in: Journal of materials science 2008-10, Vol.43 (20), p.6704-6713
• Main Authors: Ashcroft, Ian A., Casas-Rodriguez, Juan Pablo, Silberschmidt, Vadim V.
• Format: Article
• Language: English
• Subjects: Adhesive bonding; Adhesive joints; Application fields; Applied sciences; Bonded joints; Carbon fiber reinforced plastics; Characterization and Evaluation of Materials; Chemistry and Materials Science; Classical Mechanics; Crack propagation; Crystallography and Scattering Methods; Exact sciences and technology; Failure modes; Fatigue failure; Fiber composites; Fiber reinforced polymers; Fracture mechanics; Materials Science; Polymer industry, paints, wood; Polymer Sciences; Solid Mechanics; Strain gauges; Strap joints; Stretching the Endurance Boundary of Composite Materials: Pushing the Performance Limit of Composite Structures; Technology of polymers
• ISSN: 0022-2461; 1573-4803
• DOI: 10.1007/s10853-008-2646-6

Carbon fibre reinforced polymers (CFRPs) are now well established in many high-performance applications and look set to see increased usage in the future, especially if lower cost manufacturing and solutions to certain technical issues, such as poor out-of-plane strength, can be achieved. A significant question when manufacturing with CFRP is the best joining technique to use, with adhesive bonding and mechanical fastening currently the two most popular methods. It is a common view that mechanical fastening is preferred for thicker sections and adhesive bonding for thinner ones; however, advances in the technology and better understanding of ways to design joints have lead to increasing consideration of adhesive bonding for traditionally mechanically fastened joints. In high-performance applications fatigue loading is likely and in some cases repetitive low-energy impacts, or impact fatigue, can appear in the load spectrum. This article looks at mixed-mode crack growth in epoxy bonded CFRP joints in standard and impact fatigue. It is shown that the back-face strain technique can be used to monitor cracking in lap-strap joints (LSJs) and piezo strain gauges can be used to measure the strain response of impacted samples. It is seen that there is significant variation in the failure modes seen in the samples and that the crack propagation rate is highly dependent on the fracture mode. Furthermore, it is found that the crack propagation rate is higher in impact fatigue than in standard fatigue even when the maximum load is significantly lower.