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Epoxy resins are classically toughened by rubber additives, but the effectiveness of rubber toughening tends to diminish with increasing strain rate, decreasing temperature, and decreasing matrix ductility. In this study, we demonstrate that low loadings of 100–200-nm core–shell rubber (CSR) particulate additives can improve high strain rate (104–105 s−1) impact resistance by nearly 200 % for epoxy resins with glass transition temperatures T g in a range between 60 and 110 °C, without large reductions in T g or stiffness. In addition, CSR additives improve low-temperature impact resistance of the epoxies down to 0 °C. Size and surface chemistry of the CSR particles influence the ballistic response, with 200-nm diameter, weakly bound, and poorly dispersed CSR particles providing the greatest toughening performance at low filler loadings and high rates. Impact resistance for a systematic series of CSR-modified epoxies covers a transition from brittle to tough behavior, where the failure mechanism changes with effective fracture resistance. For brittle resins, failure is dominated by initiation of Hertzian cone fracture which depends strongly on fracture toughness K IC, while for tough resins, failure is dominated by plastic yield at the impact site and is independent of fracture toughness above a minimum K IC value of approximately 1.2–1.5 MPa m1/2. Interestingly, quasistatic mechanical properties are reasonably effective qualitative predictors of high-rate impact resistance, suggesting that the toughening mechanisms of CSR particles are similar over the rates studied here. The insights gained from this study are valuable for design of next generation adhesives, polymers, and polymer composite matrices for lightweight protective applications.

When researching the effect of rubber toughening in acrylonitrile-butadiene-styrene (ABS) copolymer and high-impact polystyrene (HIPS) and also toughening methods used in other materials, then, often comparisons are needed between materials with and without the toughening agents over the full crack velocity range. This is from the threshold stress to just maintain crack propagation up to the limiting crack velocity conditions. However, the toughening of materials can change other material properties including, for example, the onset of yield in the material under static stress. The result can be that a crack velocity versus stress curve cannot be obtained by experiment over the full crack velocity range for some toughened materials. However, as used in this study, combined experimental and computer simulations can provide for a meaningful and informative comparison between crack velocity versus stress curves for materials with and without toughening agents over the full crack velocity range.

The toughening behavior of short glass fiber reinforced toughened polymers was studied using fracture mechanics and microscopic techniques. The essential work of fracture (EWF) analysis shows that the inclusion of short glass fibers not only provided a stiffening effect but also a toughening influence. It was observed that rubber-related toughening and fiber-related toughening were competitive in nature for the reinforced, toughened nylon 6,6. When the matrix stress was substantially reduced by the presence of short fibers via the load-shedding mechanism, rubber toughening was severely curtailed. At higher fiber volume fractions, fiber pull-out work contributed significantly to the enhancement of the specific essential fracture work. Fiber-end plasticity was evident under microscopic examination.

Tensile tests were carried out at both constant stress and constant extension rate on polyamide 6.6 blends containing 0–20 wt% of maleinated ethylene-propylene rubber (EPR-g-ma), using specimens conditioned at 50% RH. Longitudinal and lateral strain measurements on creep specimens showed that blends containing EPR-g-ma exhibited dilatation at tensile stresses above 27 MPa. This observation is consistent with the predictions of the particle cavitation model proposed in an earlier paper (A. Lazzeri and C. B. Bucknall, J. Mater. Sci. 28 (1993) 6799). In standard tensile tests on PA6.6/EPR-g-ma blends, cavitation preceded yielding (defined by the 1% offset strain). Creep and yield data obtained over a range of temperatures and strain rates were correlated using the Eyring equation. The onset of dilatation in these PA6.6/EPR blends was marked by a change in deformation kinetics, which is analysed using a modified version of Gurson's equation.

The aim of this study was to research fracture surface features for polymers of different toughness and type. The materials chosen provided for an interesting comparison of fracture surfaces. Two brittle amorphous thermoplastics (SAN & PMMA) of the same toughness had very different fracture surfaces. An amorphous thermoplastic (PC) exhibited similar features as both SAN and PMMA but had a higher toughness. Two semi-crystalline thermoplastics (PE1 & PE2) had similar fracture surface features but one was twice the toughness of the other. A rubber toughened polymer (ABS) showed a very different fracture surface to SAN (the host material) and all the other polymers studied. A particular interest was to use the comparison of the fracture surfaces of the above materials to investigate the toughening effects of rubber particles in ABS.

The role of rubber particle type, location and morphology on toughening in blends of nylon 6,6 with styrene acrylonitrile (SAN), with and without fibre reinforcements was examined in this study. The rubber used was ethylene propylene diene monomer (EPDM) rubber and the results were compared to a previous study that used butadiene rubber. The compositions of the blends ranged from pure nylon 6,6 to pure SAN. EPDM rubber was chemically compatibilized with one of the matrix phases rather than grafted, as in the ABS. In order to study the effect of rubber location on fracture behaviour, the approach was to compatibilize EPDM with either the minor phase or the major phase component of the blend. Attention was focused on fracture initiation toughness and fracture propagation toughness, measured through the parameters J IC and J SS, respectively. J SS refers to the steady-state, or plateau value of the material R-curve and was therefore a measure of total toughness which included the additional component derived from crack extension. The results indicated that EPDM rubber was not as effective a toughening agent as was butadiene in the Acrylonitrile Butadiene Styrene (ABS) system, primarily due to the morphology of EPDM and its interface character with the nylon 6,6 or SAN matrix. It was demonstrated that the embrittlement effects of a second rigid polymer phase can be mitigated by selectively adding rubber to that phase in the alloy or blend. With regard to the role of fibre reinforcement, a strong fibre matrix interface was found to be essential for toughening. Further, the extent of rubber toughening was larger when fibres were present than when fibres were absent, provided the fibre matrix interface was strong. Fibres also, like rubber, enhanced local matrix plasticity as well as reduced the embrittlement effects associated with a second polymer phase.

New formulations of rubber toughening agents for difunctional and tetrafunctional commercial epoxies are attempted, on the basis of their increased thermal stability compared with classical unsaturated elastomers. Quite satisfactory results are obtained where a block copolymer of polydimethylsiloxane and polyoxyethylene elastomer or a functionalized poly (1 -butene) in difunctional epoxy are used. On the other hand, poor results are obtained when the same elastomers are employed in tetrafunctional epoxies. A tentative explanation is given on the basis of the different networks obtained in the two matrix systems.

Crack propagation in epoxy resins filled with alumina trihydrate has been observed by dynamic in situ scanning electron microscopy. Double torsion specimens were fractured inside a scanning electron microscope (SEM) connected to a video recorder. Characteristic features of the crack propagation process were observed. The fracture mode was mainly intergranular at low crack velocities, (ca. 10 μm/s) with evidence of filler particle cracking (transgranular fracture) at higher velocities or after acid-washing the particles. Extensive shear yielding of the epoxy matrix occurred between closely spaced filler particles within the crack tip damage zone. Post-mortem static observations of the fracture surfaces were also carried out. The addition of rubber toughening agents modified the crack propagation process. In some cases the rubber was present as fine, evenly distributed particles while in others there were coarser precipitates and/or what appeared to be rubber-rich epoxy phases. Ligamentary bridges across crack faces in the crack wake necked to fracture at low crack velocities but failed by cavitation under rapid loading. Energy dissipation by local shear yielding of the matrix was still prominent. Vinyl terminated rubber addition induced especially widespread yielding. Out-of-SEM determinations of tensile and fracture parameters were consistent with dynamic SEM observations.

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

The fatigue crack propagation behaviour of rubber toughened blends of poly(2,6-dimethyl-1,4-phenylene oxide) (PXE) and polystyrene (PS) were studied. The nature of the fatigue crack tip damage zone development and the subsequent crack tip advance mechanism through this damage zone were also examined. In the control blend with no rubber particles, several long crazes preceded the crack tip and provided an easy path for crack propagation. The addition of rubber particles, however, led to massive microcrazing over a considerably enlarged zone about the crack tip. This proved to be an effective energy dissipation mechanism which resulted in reduced fatigue crack growth rates. When PS was substituted for PXE in the polymer matrix, although microcrazing still occurred over an enlarged crack tip damage zone, many of the microcrazes grew to macroscopic size, thus reducing the fatigue toughness.

Mesures de la repartition des tailles des particules, de la fraction en volume, du module d'elasticite, de la resistance a la rupture et aux chocs de 14 polystyrenes chocs

Etude comparative du comportement en traction de polyamide 66 renforcee ou non par 20% d'elastomere