1,721,041 research outputs found
Crack growth in discontinuous glass fibre reinforced polypropylene under dynamic and static conditions
No full textStrain rate dependence of the anisotropic fracture toughness of rubber-modified polypropylene films
No full textA rubber modified cast polypropylene film has been tested by the essential work of fracture method to assess the effect of material orientation on the fracture toughness. The tests have been performed under different quasi-static rates, in order to analyze the strain rate effects on the material toughness: impact rates were also considered, but results are still at a preliminary stage. Results indicate a marked anisotropy with higher essential work of fracture values for cracks propagating transversally to the extrusion direction. Fracture toughness in both direction is substantially independent of testing speed up to 500 mm/min and markedly decreases under impact conditions. Furthermore, the specific essential work of fracture was partitioned into two terms, one representing the specific work for yielding up to the onset of fracture, and another term related to the specific work for subsequent necking and tearing. Scanning electron microscopy observations have been conducted to reveal fracture surfaces morphology
Non-linear dynamic behaviour or rubber compounds: construction of generalized master curves
No full textEnergy storage and strain recovery processes in highly deformed semicrystalline poly(butylene terephthalate)
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Time, temperature, and strain effects on viscoelastic Poisson's ratio of epoxy resins
No full textPoisson's ratio of polymeric materials, although generally assumed as a constant, is known to display a viscoelastic dependence on time, temperature, and strain. This article investigates the phenomenology of this dependence on two crosslinked epoxy systems with different glass transition temperatures. Poisson's ratio measurements are performed by contact extensometers simultaneously measuring the axial and transverse deformations under two different tensile testing conditions: (i) constant deformation rate, in which the effects of strain, strain rate, and temperature are highlighted; (ii) stress relaxation (or constant deformation), where the dependence of Poisson's ratio on time is studied at various strain levels. The viscoelastic Poisson's ratio increases as strain, temperature, and time increases, with trends markedly depending on the materials glass transition
Thermal stability of high density polyethylene-fumed silica nanocomposites
No full textHigh-density polyethylene-based nanocomposites were prepared through a melt compounding process by using surface functionalized fumed silica nanoparticles in various amounts, in order to investigate their capability to improve both mechanical properties and resistance to thermal degradation. The fine dispersion of silica aggregates led to noticeable improvements of both the elastic modulus and of the stress at yield proportionally to the filler content, while the tensile properties at break were not impaired even at elevated filler content. Thermogravimetric analysis showed that the selected nanoparticles were extremely effective both in increasing the decomposition temperature and in decreasing the mass loss rate, even at relatively low filler loadings. The formation of a char enriched layer, limiting the diffusion of the oxygen through the nanofilled samples, was responsible of noticeable improvements of the limiting oxygen index, especially at elevated silica loadings. In contrast with commonly reported literature results, cone calorimeter tests also revealed the efficacy of functionalized nanoparticles in delaying the time to ignition and in decreasing the heat release rate values. Therefore, the addition of functionalized fumed silica nanoparticles could represent an effective way to enhance the flammability properties of polyolefin matrices even at low filler concentrations
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