Experimental study on fracture behavior of rubber-toughened epoxy in bulk and laminated composite specimens

To study the toughening mechanisms of liquid rubber (LR) in bulk epoxy and laminated composite, experimental investigations were carried out on single-edge notched bending (SENB), double-cantilever-beam (DCB) and end notch flexure (ENF) specimens under mode-I and II loading. The matrix materials were pure epoxy (bisphenol A) and LR (ATBN, CTBN, VTBN) modified epoxies. The results showed that using rubber particles would improve fracture toughness of neat epoxy resin and laminated composites. The behavior of the composite was affected by the pattern that the particles are spread in resin or the final laminated composite. Inappropriate spread of the particles would decrease the fracture toughness in some cases. However, if they are spreaded perfectly, they will improve the composite resistance against fracture. The modulus, E, of the epoxy polymer decreases with the addition of the LR. Of course, these relatively minor changes in these properties of the rubber-toughened epoxy polymer are more than compensated for by the significant increases in the fracture toghness value. The poor toughness behavior of CTBN in the glass fiber laminate was thought to be caused by the concentration of LR particles in the resin-fiber bonding surface. Morphographs of the fracture surfaces also testified this prospect.