Search

In this work, the properties of microcellular ABS were studied. Foamed samples exhibited a solid skin/foamed core struc- ture, with some elongated cells in the flow direction, while spherical cells were mostly observed in the transversal direction. The flex- ural modulus, flexural strength, and fracture toughness K Ic decreased with the density. However, the crack tip opening displacement (CTOD) was found to increase with the foaming ratio. The evolution of the mechanical properties and fracture toughness was well described by prediction models considering the skin/core morphology of these microcellular materials. Foaming increased the aniso- tropic behavior of the material, due to the cell elongation caused by the fountain flow during injection

The study of polymer and composite behavior under high strain rates is of fundamental relevance to determine the material suitability for a selected application. However, the impact phenomenon is a very complicated event, mainly due to the short duration, large deformation, and high stresses developed in the sample. In this work, we have performed impact tests over a carbon fiber reinforced epoxy using low-energy in the striker. A nonconservative and nonlineal spring-dashpot series model has been proposed to reproduce the material behavior. The model considers simultaneously both flexural and indentation phenomena accounting for energy losses by means of the restitution coefficient. Using this model, an excellent fit between the predicted and the experimental force-time trace has been obtained below the composite failure point, which was recognized by a separation of both mentioned curves. As the epoxy-fiber laminate has a very low viscoelasticity, the high strain rate Young's modulus obtained from the model was compared with that extracted from a conventional three point bending test, finding a very good match between the values. The study of the dashpot coefficients allows concluding that the dominant mechanism is the composite flexion, while the indentation effects contribution takes on importance at low impact velocities. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 2256–2263, 2005

Instrumented falling weight impact tests were carried out to characterize the mechanical behavior of a material pattern formed by polystyrene and different amounts of glass beads. This characterization was performed at high strain rate using two different impact arrangements: the first uses high impact energy at the striker, whereas the second uses a low-impact energy. Starting from a conservative model, a nonconservative one has been proposed for the low-energy impact configuration as a better approach to the material behavior. In this latter model, the energy losses were quantified through the restitution coefficient. Two alternative methods for its calculation are described. The results shows good agreement between the flexural modulus and break stresses calculated in either the low- or the high-energy arrangement; however, the low-energy impact method yields more confidence results. Using the proposed model, the composites' fracture onset was determined, and also in the samples with low content of glass beads, it was possible to assess the micromechanism of failure, given the estimation for the stress to produce crazing. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1271–1284, 2004

Films of an architecturally modified poly(lactic acid) (PLAREx) with three different types of fumed silica nanofillers (SiO2) were processed through reactive extrusion-calendering in a pilot plant. The effects of the SiO2 type on both the dispersion and the crystallization behaviour under dynamic and isothermal conditions are investigated using transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). The mechanical properties are assessed by tensile testing. TEM micrographs showed that the improved chemical affinity of both surface-treated SiO2 towards PLAREx end groups did not improve particle dispersion. DSC results revealed that untreated SiO2 nucleated PLAREx more efficiently than both surface-modified silicas. The activation energy for the isothermal crystallization process, as determined by an Arrhenius method, suggests that addition of untreated SiO2 enhances the crystallization rate of PLAREx. However, it seems that the tensile behaviour remained unchanged whether silicas were added or not.