Luigi Grassia

Enthalpy relaxation of an epoxy matrix/carbon nanotubes

The enthalpy recovery of an Epoxy/Carbon Nanotube systems (E/CNT) manufactured at low nanotube content, have been investigated by using Differential Scanning Calorimetry. Two different nanotube concentration were considered, 0.5 and 0.1 w/w and results compared with the behaviour of the neat epoxy material. Final results reveal that the aging phenomenon is not monotone with the nanofiller content but a significant “depression” of the physical aging seems be highlighted by the lowest nanotube content, i.e. 0.5 w/w. This observation has not been rationalised yet, although it seems reasonable to correlate this later effect with the topological feature of nanotube network within the hosting epoxy. Future work will verify this hypothesis

Modeling the Fatigue Behavior of Glass Fiber Reinforced Thermoplastic and Thermosetting Matrices

The flexural fatigue behavior of continuous and short glass reinforced composites was investigated under four-point bending loading. The effect of mean stress and stress amplitude was identified. It was found that the fatigue life decreased rapidly with the decreasing stress ratio (i.e. the ratio between the minimum and the maximum stress). Further, the specimen lifetime for any loading mode increased with : (a) decreasing load range and decreasing stress ratio and (b) decreasing mean load and increasing stress ratio. From the above observations a brand new two-parameter model based on strength degradation was developed accounting for both the mean load and the load range, in order to express analytically the strength variation during fatigue cycle evolution.

On The Inter-Conversion Between Viscoelastic Material Functions of Polycarbonate

Amorphous polymers show a time dependent response to an external solicitation. The time dependent response is usually measured in terms of shear response, whereas the bulk response is a more difficult to measure. In the framework of linear viscoelasticity at least two viscoelastic functions are needed in order to evaluate the mechanical behavior of viscoelastic amorphous polymers. Often the one of viscoelastic function is available in terms of creep compliance and the other one is available in terms of relaxation modulus: a reliable procedure for the inter-conversion is needed. Here the inter-conversions between relaxation moduli and creep compliances are described and a numerical method for the inter-conversion is presented. It is showed that the numerical solution lays on the analytical one and it is also less time consuming.