High-performance epoxy-based adhesives reinforced with alumina and silica for carbon fiber composite/steel bonded joints

Epoxy-based adhesives reinforced with silica and alumina fillers (20, 40, and 60 phr) were prepared and successfully applied for lap-joint bonding of carbon fiber composite with steel. The mechanical properties of adhesives were assessed as different cure temperatures to find optimum cure temperature. Morphology of the reinforced epoxy adhesives was observed by optical microscopy to disclose the interplay between composite properties and distribution fashion of the silica and alumina fillers within the epoxy matrix. Thermal stability and interfacial interaction situation were explored by thermogravimetric and Fourier transform infrared spectroscopy analyses, respectively. Rheological behavior of the composite samples was also studied. Lap shear test was an indication for a considerable improvement of about 12% and 20%, compared to unfilled epoxy/hardener systems, for composites containing 60 phr of alumina and silica, respectively. However, the presence and population of voids in case of samples cured at elevated temperature deteriorated lap shear strength. Of note, the storage and loss modulus of the latter adhesive have been increased by 797% and 472%, respectively. Thermal stability on the basis of initial degradation temperature and char yield (> 500℃) of the assigned adhesive under N 2 and air have also been enhanced. Higher performance of silica-based adhesives was mechanistically and morphologically discussed on the bedrock of formation of a 3D inter-connected network of filler particles.