Rigid and Flexible Double Shear Lap Adhesive Joint at Elevated Temperature-An Experimental Study

Area of Science:

• Materials Science
• Structural Engineering
• Adhesive Technology

Background:

• Adhesive joints are critical in various engineering applications.
• Understanding the performance of adhesives under different environmental conditions, such as elevated temperatures, is essential for reliable structural design.
• This study focuses on double lap adhesive connections, comparing flexible polyurethane and rigid epoxy adhesives.

Purpose of the Study:

• To investigate the impact of elevated temperatures (20 °C and 80 °C) on the shear load capacity of double lap adhesive joints.
• To comparatively analyze the performance of a flexible polyurethane adhesive (Sika® PS) and a rigid epoxy adhesive (Monolit EP 2579-1).
• To assess the influence of adhesive layer thickness (1, 2, and 4 mm) on joint behavior at different temperatures.

Main Methods:

• Experimental shear tests were conducted on double lap adhesive joints under quasi-static loading.
• Tests were performed at two distinct temperatures: 20 °C (room temperature) and 80 °C (elevated temperature).
• Adhesive layer thickness was varied (1, 2, and 4 mm), and joint failure modes were visually assessed.

Main Results:

• At 20 °C, epoxy joints exhibited significantly higher ultimate loads than polyurethane joints across all tested thicknesses.
• Increasing temperature to 80 °C reduced the mean destructive force for both adhesive types.
• The greatest load capacity reduction was observed for the 2 mm thick Sika® PS joint (55%) and the 4 mm thick epoxy joint (89%).

Conclusions:

• Elevated temperatures substantially decrease the load capacity of both polyurethane and epoxy adhesive joints.
• Flexible polyurethane joints demonstrated the ability to retain partial load capacity post-failure, unlike rigid epoxy joints.
• Adhesive type and layer thickness significantly influence joint performance under thermal stress.