Molecular fracture in polymers

Andrews, E. H.; Reed, P. E.

doi:10.1007/3-540-08829-6_1

Cited by 65 publications

(22 citation statements)

References 49 publications

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“…Such a fracture surface is typical of a brittle thermoset [48]. No observable differences in the appearance of the fracture surfaces were detected between the two test temperatures.…”

Section: Fractographic Studies: Bulk Polymersmentioning

confidence: 75%

Toughened carbon fibre-reinforced polymer composites with nanoparticle-modified epoxy matrices

et al. 2016

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In the current work, the microstructure and fracture performance of carbon fibre-reinforced polymer (CFRP) composites based upon matrices of an anhydride-cured epoxy resin (formulated with a reactive diluent), and containing silica nanoparticles and/or polysiloxane core-shell rubber (CSR) nanoparticles, were investigated. Double cantilever beam tests were performed in order to determine the interlaminar fracture energy of the CFRP composites, while the single-edge-notched bend specimen was employed to evaluate the fracture energy of the bulk polymers. The fracture energy of the bulk epoxy polymers increased from 173 J/m 2 for the unmodified polymer to a maximum of 1237 J/ m 2 with the addition of 16 wt% of CSR nanoparticles. The toughening mechanisms were identified as (a) localised plastic shear yielding and (b) cavitation of the CSR particles followed by plastic void growth of the matrix. The steady-state propagation value of the interlaminar fracture energy of the CFRP composites increased with increasing nanoparticle concentration, from 1246 J/m 2 for the unmodified epoxy matrix to a maximum of 1851 J/m 2 with 4 wt% of silica nanoparticles and 8 wt% of CSR nanoparticles. Crack growth in the CFRP composites was dominated by fibre-bridging toughening mechanisms. The efficiency of the transfer of toughness from the bulk polymers to the carbon fibre composites was considered. The measured fracture energy of both bulk and composite materials decreased at a test temperature of -80°C, compared with room temperature, i.e. 20°C. Nevertheless, the toughening effects of both the silica and CSR nanoparticles on the bulk epoxy polymers and the CFRP composites, compared with the unmodified epoxy polymers, were still evident even at the lower temperature. Indeed, the toughening effect of the silica nanoparticles was greater at -80°C than at room temperature.

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“…Such a fracture surface is typical of a brittle thermoset [48]. No observable differences in the appearance of the fracture surfaces were detected between the two test temperatures.…”

Section: Fractographic Studies: Bulk Polymersmentioning

confidence: 75%

Toughened carbon fibre-reinforced polymer composites with nanoparticle-modified epoxy matrices

et al. 2016

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“…The fracture surfaces of the unmodified epoxy appear smooth, and feature only riverlines that represent step changes in height as the crack propagates. Crack forking and the multi-planar nature of the surface observed here are the main mechanisms to absorb excess energy in such brittle materials [38].…”

Section: Toughening Mechanismsmentioning

confidence: 80%

Graphene nanoplatelet-modified epoxy: effect of aspect ratio and surface functionality on mechanical properties and toughening mechanisms

2016

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Graphene has the potential to act as a high-performance reinforcement for adhesives or fibre composites when combined with epoxy polymer. However, it is currently mostly available not as single high aspect ratio sheets but as graphene nanoplatelets (GNPs), comprised of stacks of graphene sheets.Graphene nanoplatelets of a range of lateral size, thickness, aspect ratio and surface functionality were used to modify an anhydride cured epoxy polymer.The morphology, mechanical properties and toughening mechanisms of these modified epoxies were investigated. The GNPs were sonicated in tetrahydrofuran (THF) or n-methyl-pyrrolidone (NMP) to facilitate dispersion in the epoxy. The use of THF resulted in large agglomerates, whereas more finely dispersed stacks of GNPs were observed for NMP. The maximum values of modulus (3.6 GPa at 1 wt%) and fracture energy (343 J/m 2 at 2 wt%) were * Corresponding author, Tel.: +44 20 7594 7149Email address: a.c.taylor@imperial.ac.uk (A. C. Taylor) April 11, 2016 measured for the epoxy modified with an intermediate platelet size of approximately 4 µm, compared to 2.9 GPa and 96 J/m 2 respectively for the unmodified epoxy. The Young's modulus was highly dependent on the dispersion quality, whereas the fracture energy was independent of the degree of GNP dispersion. The larger agglomerates of the GNPs which were dispersed in THF toughened the epoxy by crack deflection, whereas the GNPs dispersed in NMP showed platelet debonding, pull-out and plastic void growth of the epoxy. This work indicates that reinforcement and toughening can be achieved at much lower contents than for conventional modifiers. Further, achieving a good dispersion is crucial to the engineering application of these materials, and intermediate-sized graphene achieves the best balance of properties. Preprint submitted to Journal of Materials Science

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“…These features are feather markings, which are caused by the crack forking due to the excess of energy associated with the relatively fast crack growth. This repeated forking and the multi-planar nature of the surface are ways of absorbing this excess energy in a very brittle material [43].…”

Section: Fracture Surfacesmentioning

confidence: 99%

Toughening mechanisms of nanoparticle-modified epoxy polymers

Johnsen

Kinloch

Mohammed

et al. 2007

Polymer

852

576

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An epoxy resin, cured with an anhydride, has been modified by the addition of silica nanoparticles.The particles were introduced via a sol-gel technique which gave a very well dispersed phase of nanosilica particles which were about 20 nm in diameter. Atomic force and electron microscopy showed that the nanoparticles were well dispersed throughout the epoxy matrix. The glass transition temperature was unchanged by the addition of the nanoparticles, but both the modulus and toughness were increased. The measured modulus was compared to theoretical models, and good agreement was found. The fracture energy increased from 100 J/m 2 for the unmodified epoxy to 460 J/m 2 for the epoxy with 13 vol% of nanosilica. The fracture surfaces were inspected using scanning electron and atomic force microscopy, and the results were compared to various toughening mechanisms proposed in the literature. The toughening mechanisms of crack pinning, crack deflection and immobilised polymer were discounted. The microscopy showed evidence of debonding of the nanoparticles and subsequent plastic void growth. A theoretical model of plastic void growth was used to confirm that this mechanism was indeed most likely to be responsible for the increased toughness that was observed due to the addition of the nanoparticles. IntroductionEpoxy polymers are widely used for the matrices of fibre-reinforced composite materials and as adhesives. When cured, epoxies are amorphous and highly-crosslinked (i.e. thermosetting)polymers. This microstructure results in many useful properties for structural engineering applications, such as a high modulus and failure strength, low creep, and good performance at elevated temperatures.However, the structure of such thermosetting polymers also leads to a highly undesirable property in that they are relatively brittle materials, with a poor resistance to crack initiation and growth.Nevertheless, it has been well established for many years that the incorporation of a second microphase of a dispersed rubber, e.g. Hence rigid, inorganic particles have also been used, as these can increase the toughness without affecting the glass transition temperature of the epoxy. Here glass beads or ceramic (e.g. silica or alumina) particles with a diameter of between 4 and 100 μm are typically used, e.g. [9][10][11][12][13][14].However, these relatively large particles also significantly increase the viscosity of the resin, reducing the ease of processing. In addition, due to the size of these particles they are unsuitable for use with infusion processes for the production of fibre composites as they are strained out by the small gaps between the fibres.More recently, a new technology has emerged which holds promise for increasing the mechanical performance of such thermosetting polymers. This is via the addition of a nanophase structure in the polymer, where the nanophase consists of small rigid particles of silica [15][16][17][18]. Such nanoparticle-modified epoxies have been shown to not only increase further the toug...

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Molecular fracture in polymers

Cited by 65 publications

References 49 publications

Toughened carbon fibre-reinforced polymer composites with nanoparticle-modified epoxy matrices

Toughened carbon fibre-reinforced polymer composites with nanoparticle-modified epoxy matrices

Graphene nanoplatelet-modified epoxy: effect of aspect ratio and surface functionality on mechanical properties and toughening mechanisms

Toughening mechanisms of nanoparticle-modified epoxy polymers

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