Temperature Effects on the Fatigue Life and Tensile Strength of Structural Adhesives

Abstract

In recent decades, structural adhesives have become widely used in the field of construction for the purpose of retrofitting existing structures using composite materials such as fibre reinforced polymers (FRP). The available standards for strengthening structures utilise the adhesive properties as listed in manufacturer's technical sheets. However, members with adhesively bonded CFRPs are sometimes exposed to loadings or conditions that may differ to the scenarios used to measure these material properties. Steel and concrete bridges are usually exposed to cyclic loading associated with elevated temperatures, for example, while the manufacturer's technical sheets provide material properties under quasi static loading and ambient temperatures. There is thus a lack of understanding of the properties of adhesives under more difficult conditions that may lead to issues in predicting the design strength of composite elements. This paper presents a series of experimental tests to investigate the adhesive properties under both medium temperature (25 and 40°C) and cyclic loading, with adhesives cured under two curing temperatures. All specimens and tests were developed according to ASTM-D638. The results showed significant effects of temperature on the tensile strength and fatigue life of adhesives, as measured by monitoring the number of cycles until failure; the number of cycles was increased by 8 times for two types of structural adhesives cured under high temperature and tested under normal temperatures of 25°C.