The use of thermally expandable microcapsules for increasing the toughness and heal structural adhesives

Abstract

In this research, the effect of thermally expandable microcapsules (TEMs) on mode I fracturetoughness of structural adhesives were investigated. The single-edge-notch bending (SENB) test was used.Firstly, a standard toughness test was performed on adhesives with microcapsules. Secondly, since TEMs starttheir expansion at approximately 60�C, the next specimens were fatigue tested expecting a local heating in thenotch leading to the desired expansion before being statically loaded for fracture toughness determination.Thirdly, a manual local heating at 90�C was applied in the notch before the fracture static test. The experimentalresults were successfully cross-checked through a numerical analysis using the virtual crack closure technique(VCCT) based on linear elastic fracture mechanics (LEFM). The major conclusion is that fracture toughness ofthe modified adhesives increased as the mass fraction of the TEMs increased.