Effect of temperature and loading rate on the mode I fracture energy of structural acrylic adhesives

Abstract

Understanding the changes in the adhesive properties with the temperature and loading rate is important, particularly for designing adhesively bonded joints in structural applications. The viscoelastic behavior of adhesives is widely known to be based on the time–temperature superposition principle. In the case of the elastoplastic behavior, the stress–strain relationship is significantly affected by the external conditions, particularly for ductile adhesives. Similarly, the fracture behavior is expected to exhibit a temperature–loading rate dependence; however, few studies have focused on them, especially for structural acrylic adhesives.In this study, the impact of the temperature and test speed on the fracture energy of structural acrylic adhesives was investigated. Bulk tensile tests and double cantilever beam (DCB) tests were performed at different temperatures and test speeds. Bulk behavior showed an increase in the maximum stress and a decrease in the elongation at lower temperatures and higher loading rates. Conversely, the fracture toughness increased with a combination of higher temperatures and loading rates when the crack stably propagated. The mode I fracture energies of the test speed of 500 mm/min at 60°C increased by approximately 1.5–2 times that of 0.05 mm/min at room temperature. In addition, stick-slip crack propagation was observed at lower temperatures or higher loading rates.

Keywords

• Ductile adhesive
• Fracture mechanics
• Time–temperature dependence
• Stable–unstable transition