Ductility potential of brittle epoxies: Thermomechanical behaviour of plastically-deformed fully-cured composite resins

Turk, Mark A.; Hamerton, Ian; Ivanov, Dmitry

doi:10.1016/j.polymer.2017.05.052

Cited by 25 publications

(19 citation statements)

References 23 publications

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“…As it can be seen, the surface fractures were uniform, showing many crack growths. The surfaces are typical of a brittle fracture caused by the absence of plastic deformation [42], which is in accordance to the mechanical properties reported above. One can observe a morphological change in the fracture surface of the partially bio-based epoxy resin that was subjected to post-curing at 125 °-0.1emnormalC, shown in Figure 2c,d.…”

Section: Resultssupporting

confidence: 85%

Optimization of the Curing and Post-Curing Conditions for the Manufacturing of Partially Bio-Based Epoxy Resins with Improved Toughness

et al. 2019

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This research deals with the influence of different curing and post-curing temperatures on the mechanical and thermomechanical properties as well as the gel time of an epoxy resin prepared by the reaction of diglycidyl ether of bisphenol A (DGEBA) with an amine hardener and a reactive diluent derived from plants at 31 wt %. The highest performance was obtained for the resins cured at moderate-to-high temperatures, that is, 80 ° C and 90 ° C , which additionally showed a significant reduction in the gel time. This effect was ascribed to the formation of a stronger polymer network by an extended cross-linking process of the polymer chains during the resin manufacturing. Furthermore, post-curing at either 125 ° C or 150 ° C yielded thermosets with higher mechanical strength and, more interestingly, improved toughness, particularly for the samples previously cured at moderate temperatures. In particular, the partially bio-based epoxy resin cured at 80 ° C and post-cured at 150 ° C for 1 h and 30 min, respectively, showed the most balanced performance due to the formation of a more homogeneous cross-linked structure.

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Section: Resultssupporting

confidence: 85%

Optimization of the Curing and Post-Curing Conditions for the Manufacturing of Partially Bio-Based Epoxy Resins with Improved Toughness

et al. 2019

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“…With the addition of 5% SNPs, the impact strength increased from 64 to 128 lb/in 2 when compared to the epoxy without nanoparticles, while, in the case of scratch resistance, there is an increase from a 6 kg failure load for the epoxy to a 9 kg failure load with the addition of 5% nanoparticles. The epoxy imparts brittle behavior [32,33], and the increase in its mechanical properties is due to the contribution of the SNPs that increase the modulus [34,35]. This induced a plasticizing effect on the coatings, which, in turn, increased the scratch and impact properties.…”

Section: Mechanical Properties and Nanoindentation Testmentioning

confidence: 99%

Enhancement in Nanomechanical, Thermal, and Abrasion Properties of SiO2 Nanoparticle-Modified Epoxy Coatings

et al. 2020

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Epoxy formulations containing 1%, 3%, and 5% SiO2 nanoparticles (SNPs) were produced and applied to mild steel substrates in order to improve their thermal, nanomechanical, and abrasion resistance. Field emission scanning electron microscopy (FE-SEM) was used to analyze the dispersion of nanoparticles in the final coating samples, and Energy-dispersive X-ray spectroscopy (EDX) was used to confirm the presence of nanoparticles. Thermogravimetric analysis (TGA) was employed to measure the thermal resistance of the prepared coatings. Conventional techniques were used to measure the impact and scratch resistance. For nanomechanical testing, nanoindentation was performed using a Berkovich-type indenter. Using a taber abraser, the abrasion properties of the coatings were measured. The FE-SEM images indicated good dispersion of the nanoparticles at all three different loading levels. The scratch, impact, and hardness of coatings improved with the addition of the SNPs. Nanomechanical properties, such as hardness and elastic modulus, improved when compared to the unmodified coatings. The thermal and abrasion resistances of the coatings improved with the increase in the SNPs content of the coatings. The highest mechanical, thermal, and abrasion properties were obtained for the coatings with 5% SNP content.

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“…Towse et al [17] analyzed the defects causing failure and found a correlation between the size of the defects and the failure strain of an aerospace grade epoxy. Turk et al [18] studied the potential of improved ductility of brittle epoxies for use in structural composites. Fiedler et al [19] observed relatively large plasticity in brittle epoxy (Toho-Rayon Ltd) resin specimens under shear.…”

Section: Introductionmentioning

confidence: 99%

Extreme scale-dependent tensile properties of epoxy fibers

Sui¹,

Tiwari²,

Greenfeld³

et al. 2019

Express Polym. Lett.

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Epoxy fibers with different diameters were prepared by hot drawing and their mechanical properties were measured under tension. The stiffness, strength, ultimate strain, and toughness revealed substantial scale-dependent effects as they all significantly increased with a decrease in size. Compared to bulk epoxy, an intrinsically brittle material, thin epoxy fibers displayed a highly ductile behavior under tension. A drop in stress observed immediately beyond the yield point was followed by the development of a stable necking region propagating through the entire fiber length, then by strain-hardening up to final rupture. Necked fiber segments tested in tension were found to have even higher strength and modulus compared to the initial as-prepared fibers. Possible reasons for the highly ductile mechanical behavior and the size effects of epoxy fibers are discussed. Size effects for the strength of epoxy can be elucidated in principle either by means of a classical fracture mechanics argument (strength~1/d 1/2), or via a stochastic model argument (strength~1/d 1/β , where β is a function of the material and is generally larger than 2). In both models the presence and size of critical defects play a key role. However, defects cannot explain the colossal ductility (plastic deformation) seen in our experiments, nor can the presence of defects justify a size effect in an elastic property, namely Young's modulus. Only scarce evidence exists in the literature for similar (milder) size effects in epoxy fibers but without any structural justification. We find here that highly cross-linked necked epoxy fibers exhibit partial macromolecular anisotropy which likely explains the observed high mechanical characteristics.

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Ductility potential of brittle epoxies: Thermomechanical behaviour of plastically-deformed fully-cured composite resins

Cited by 25 publications

References 23 publications

Optimization of the Curing and Post-Curing Conditions for the Manufacturing of Partially Bio-Based Epoxy Resins with Improved Toughness

Optimization of the Curing and Post-Curing Conditions for the Manufacturing of Partially Bio-Based Epoxy Resins with Improved Toughness

Enhancement in Nanomechanical, Thermal, and Abrasion Properties of SiO2 Nanoparticle-Modified Epoxy Coatings

Extreme scale-dependent tensile properties of epoxy fibers

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