Core shell rubber crack#
Impact strength by providing crack pinning and stress distribution mechanisms. The addition of the second phase significantly improves fracture toughness and Flexibilized adhesives are molecular blends of polymers in a single-phase system, whereas toughened structural adhesives have discrete particles (sizes on the order of 10 -6 to 10 -9 meters, minor phase) embedded in the resin (larger phase) matrix of the adhesive. Modern structural adhesive formulations benefit from tougheners, which operate on a completely different mechanism than flexibilizers. The minor phase consists of small (micro- and nano-sized) distributed entitiesĪ variety of toughening agents have been used to modify structural adhesives without significantly affecting other properties of the base resin, as flexibilizers or reactive liquid elastomers do.Major toughening mechanism, responsible for 80–90% of the increase in fracture energy, was the plastic void growth.Toughened structural adhesives generally have two distinct phases: approach (J Mater Sci 45:1193–1210).Įxcellent agreement between the experimental and the predicted fracture energies was found. Mechanisms of shear band yielding and plastic void growth were modelled using the Hsieh et al. Of the CSR particles from the shells was observed, accompanied by plastic void growth of the epoxy and shell. The toughening mechanisms were identified using scanning electron microscopy of the fracture surfaces. The CTBN particles provided a larger tougheningĮffect when compared to CSR particles, but reduced the glass transition temperature of the epoxy. Similar amount of carboxyl-terminated butadiene-acrylonitrile (CTBN) rubber. The measured fracture energies were compared to those using a The fracture energy increased from 77 J/m2 for the unmodified epoxy to 840 J/m2 for the epoxy with 15 wt% of 100-nm diameter CSR particles.
The Young’s modulus and tensile strength were reduced, and the glass transition temperature of the epoxy was unchanged by Microscopy showed that the CSR particles were well dispersed through the epoxy matrix. Particles which were approximately 100 or 300 nm in diameter. All rights reserved.Īn epoxy resin, cured using an anhydride hardener, has been modified by the addition of preformed core–shell rubber (CSR) G(c) of the nanoparticle-filled polymers. The modelling studies have emphasised the important roles of the stress versus strain behaviour of the epoxy polymer and the silica nanoparticle/epoxy-polymer interfacial adhesion in influencing the extent of the two toughening mechanisms, and hence the overall fracture energy. Finally, the toughening mechanisms have been quantitatively modelled and there was good agreement between the experimentally-measured values and the predicted values of the fracture energy, G(c), for all the epoxy polymers modified by the presence of silica nanoparticles. Thirdly, the two toughening mechanisms which were operative in all the epoxy polymers containing silica nanoparticles were identified to be (a) localised shear bands initiated by the stress concentrations around the periphery of the silica nanoparticles, and (b) debonding of the silica nanoparticles followed by subsequent plastic void growth of the epoxy polymer. However, to what extent a given epoxy polymer could be so toughened was related to structure/property relationships which were governed by (a) the values of glass transition temperature, T(g), and molecular weight, M(c) between cross-links of the epoxy polymer, and (b) the adhesion acting at the silica nanoparticle/epoxy-polymer interface. Secondly, the presence of silica nanoparticles always led to an increase in the toughness of the epoxy polymer. Modelling studies showed that the measured moduli of the different silica-nanoparticle filled epoxy polymers lay between upper-bound values set by the Halpin-Tsai and the Nielsen 'no-slip' models, and lower-bound values set by the Nielsen 'slip' model with the last model being the more accurate at relatively high values of v(f).
Firstly, it was found that, for any given epoxy polymer, their Young's modulus steadily increased as the volume fraction, v(f), of the silica nanoparticles was increased. The present paper considers the mechanical and fracture properties of four different epoxy polymers containing 0,10 and 20 wt.% of well-dispersed silica nanoparticles.
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