The role Of matrix ductility on the toughenability and toughening mechanism of elastomer-modified, diglycidyl ether of bisphenol A (DGEBA)-based epoxies is investigated Matrix ductility is varied by using epoxide resins of varying epoxide monomer molecular weights These epoxide resins are cured using 4,4′ diaminodiphenyl sulphone (DDS) and, in some cases, modified with 10 vol% carboxyl-terminated copolymer of butadiene and acrylonitrile (CTBN) Fracture toughness values for the neat epoxies are found to be almost independent of the monomer molecular weight of the epoxide resin used However, the fracture toughness of the elastomer-modified epoxies is found to be very dependent upon the epoxide monomer molecular weight Tensile dilatometry indicates that the toughening mechanism, when present, is similar to the mechanism found for piperidine cured, elastomer-modified epoxies studied previously Scanning electron microscopy and optical microscopy techniques corroborate this finding

/pdf/toughening-mechanisms-in-elastomer-modified-epoxies-5775eqdi9l.pdf

Toughening mechanisms in elastomer-modified epoxies

The incorporation of nanomaterials in the polymer matrix is considered to be a highly effective technique to improve the mechanical properties of resins. In this paper the effects of the addition of different nanoparticles such as single-walled CNT (SWCNT), double-walled CNT (DWCNT), multi-walled CNT (MWCNT), graphene, nanoclay and nanosilica on fracture toughness, strength and stiffness of the epoxy matrix have been reviewed. The Young's modulus (E), ultimate tensile strength (UTS), mode I (GIC) and mode II (GIIC) fracture toughness of the various nanocomposites at different nanoparticle loadings are compared. The review shows that, depending on the type of nanoparticles, the integration of the nanoparticles has a substantial effect on mode I and mode II fracture toughness, strength and stiffness. The critical factors such as maintaining a homogeneous dispersion and good adhesion between the matrix and the nanoparticles are highlighted. The effect of surface functionalization, its relevancy and toughening mechanism are also scrutinized and discussed. A large variety of data comprised of the mechanical properties of nanomaterial toughened composites reported to date has thus been compiled to facilitate the evolution of this emerging field, and the results are presented in maps showing the effect of nanoparticle loading on mode I fracture toughness, stiffness and strength.

/pdf/improving-the-fracture-toughness-and-the-strength-of-epoxy-2wqzw19lab.pdf

Improving the fracture toughness and the strength of epoxy using nanomaterials – a review of the current status

The principal toughening mechanism of a substantially toughened, rubber-modified epoxy has again been shown to involve internal cavitation of the rubber particles and the subsequent formation of shear bands. Additional evidence supporting this sequence of events which provides a significant amount of toughness enhancement, is presented. However, in addition to this well-known mechanism, more subtle toughening mechanisms have been found in this work. Evidence for such mechanisms as crack deflection and particle bridging is shown under certain circumstances in rubber-modified epoxies. The occurrence of these toughening mechanisms appears to have a particle size dependence. Relatively large particles provide only a modest increase in fracture toughness by a particle bridging/crack deflection mechanism. In contrast, smaller particles provide a significant increase in toughness by cavitation-induced shear banding. A critical, minimum diameter for particles which act as bridging particles exists and this critical diameter appears to scale with the properties of the neat epoxy. Bimodal mixtures of epoxies containing small and large particles are also examined and no synergistic effects are observed.

/pdf/influence-of-particle-size-and-particle-size-distribution-on-2othozgvms.pdf

Influence of particle size and particle size distribution on toughening mechanisms in rubber-modified epoxies

Fracture toughness and failure mechanism of graphene based epoxy composites

Failure mechanisms in toughened epoxy resins—A review

Proprietes mecaniques de melange resines epoxyde-caoutchoucs liquides (copolymeres d'acrylonitrile et de carboxybutadiene). Mecanisme etudie par dilatometrie en etirage uniaxial

/pdf/toughening-mechanisms-in-elastomer-modified-epoxies-part-1-2cagbbaheh.pdf

A. F. Yee

Papers

Toughening mechanisms in elastomer-modified epoxies Part 1 Mechanical studies