During the past decades there has been a great accumulation of important data on the diffusion of water molecules in polymeric solids and its effect on the mechanical and viscoelastic behavior of polymers. It has become apparent that in many cases diffusion in polymers as well as its effect exhibits features that cannot be expected from classical theories and that such departures are related to the molecular structure characteristics of polymers. In the present investigation, the mechanical and viscoelastic behavior of an epoxy resin system is studied as a function of absorbed water, temperature, and time of immersion. Water sorption was achieved by immersing the material in distilled water at constant temperature of 60°C and 80°C for 2,5,8,13, 32, 74, 128, 266, 512, 1024, and 1536 h. Subsequently the specimens were tested in static and dynamic three-point bending tests to study their mechanical and viscoelastic behavior. The variation of T g , tan ␦, bending modulus, and strength was measured as a function of exposure time and respective percentage of water uptake for both temperatures. Some anomalies in their behavior due to water absorption were observed, and a model for the description of the experimentally observed mechanical behavior due to hygrothermal aging is proposed. The results show that the model predictions are in good agreement with experimental findings.

Abstract. This work presents an insight into the effect of preparation procedure and the filler content on both electrical and mechanical properties of a nanocomposite system. For the preparation of the nanocomposites diglycidyl ether of bisphenol A (DGEBA) was used with triethylenetetramine (TETA) as a curing agent. As fillers carbon black (CB) nanoparticles with size from 25 to 75 nm were used. The characterization was done using Dynamic Mechanical Analysis (DMA), Dielectric Relaxation Spectroscopy (DRS), Differential Scanning Calorimetry (DSC), Wide Angle X-ray Diffraction (WAXD) and electrical conductivity measurements. The dependence of the dynamic mechanical and dielectric parameters (E′, E″, tanδ, ε′, ε″, σ and Tg) is associated with the filler content and is controlled by the employed curing conditions. An increase in electrical conductivity, which is observed at about 1% w/w of carbon black, indicates the creation of conducting paths and is associated with the Maxwell Wagner Sillars (MWS) relaxation, probably due to the formation of aggregated microstructures in the bulk composite.

The finite element method is used to investigate the load-carrying characteristics and the stress profiles in unidirectional short fiber polymeric composites. The micromechanics composite model incorporates a hybrid interphase region surrounding the fiber. The new interphase concept involves different domains of interaction between different material properties depending on the corresponding properties of primary constituents, volumetric composition and macroscopic characterization of the composite. Thus, the hybrid interphase is not defined within a unique thickness, its outer radius being a function of the material property under consideration. The model describes also imperfect adhesion conditions by immediate softening of material properties. Numerical results are illustrated and discussed for a variety of the involved parameters. These results referring mainly to hoop and radial stresses along the fiber length confirm the intense variation of stress in this area. Parametric studies have been conducted accounting for different degrees of adhesion and shapes of the fiber tip and where it is possible comparisons with existing theories and experimental results taken from literature are illustrated.

This article describes the results of a series of tests conducted to support the development of a semiempirical model, for predicting the mechanical degradation of a satin weave glass fabric composite, with throughthickness damage in the form of a crack-like edge-centered notch. Test specimens were subjected to loading in both static three-point bending and dynamic mechanical thermal analysis (DMTA) tests. The effect of both notch length and displacement rate, on the static and that of notch length on the dynamic behavior of the materials tested, was evaluated and compared with respective predictions, as derived from the application of the residual property model. A satisfactory agreement between the experimental results and theoretical predictions was observed in all cases. Scanning electron microscopy was applied to observe the failure topographical characteristics of the DMTA specimens that were off-plane loaded.

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