1,721,092 research outputs found
Strain 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
Post-yield deformation of an epoxy resin and of an epoxy/layered silicate nanocomposite as investigated by strain recovery experiments
No full textTime, 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
Strain recovery kinetics of epoxy resins deformed above yielding: effect of the cross-link density
No full textStrain recovery and stored energy release of a post-yield deformed epoxy resin and its epoxy/layered silicate nanocomposite
No full textThe strain recovery behaviour of an epoxy resin and of an epoxy-layered silicate nanocomposite deformed at high nominal strain levels (50%) was investigated in isothermal recovery experiments. By representing the whole recovery process in terms of strain recovery master curves, it was possible to evidence differences in the recovery features of the two materials. Further, the study of the energy stored in the materials and of its release process permitted to distinguish the part of recovery occurring with heat release from that occurring after that all the stored energy is released
Strain Recovery Behavior Of Post-Yield Deformed Epoxy Resins: Effect Of The Resin/Hardener Ratio
No full textThe effect of the resin/hardener ratio on the strain recovery kinetics of various post-yield deformed epoxy resins is investigated in isothermal tests and in thermally stimulated recovery tests. Recovery is seen to take place following a two-stage process, in which the different stages can be distinguished on the time and temperature scales. These two recovery contributions are differently affected by the resin/hardener ratio and by the applied deformation
Filler Networking and Nonlinear Viscoelastic Behaviour of Natural Rubber/Clay Nanocomposites
No full textStrain recovery of post-yield compressed semicrystalline poly(butylene terephthalate)
No full textCubic specimens of a semicrystalline poly(butylene terephthalate) (PBT) have been compressed up to post-yield deformation levels with a fast (3.0 102 s1) and a slow (1.5 104 s1) strain rate at three different temperatures (25 C, 45 C, and 100 C, i.e. below, close and above the glass transition temperature of the material, Tg, respectively). Differently from literature results reported for amorphous polymers, semicrystalline PBT shows that, after a post-yield deformation, recovery occurs also at temperatures higher than Tg, and that an irreversible deformation, 3irr, is set in the material. The irreversible strain component has been evaluated as the residual deformation after a thermal treatment of 1h at 180°C.
After unloading, isothermal strain recovery has been monitored for time periods of 1 h at various temperatures. From the obtained data, strain recovery master curves have been constructed by a timeetemperature superposition scheme. The features of the recovery process for the various deformation conditions have been analysed. In particular, it appears that specimens deformed below Tg show a lower irreversible component, whereas, when deformed above Tg, they display a higher irreversible deformation and a slower recovery process. Moreover, the effect of deformation rate appears particularly marked for samples deformed above Tg
Energy storage and recovery of post-yield deformed semicrystalline poly(butylene terephthalate): deformation temperature and rate effects
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