Rheology of asphalts modified with glycidylmethacrylate functionalized polymers

Asphalt is known to be a colloidal suspension in which asphaltenes are covered by a stabilizing phase of polar resins and form complex micelles that are dispersed in the oily maltenic phase. In order to enhance its mechanical properties (e.g., in road paving), asphalts are often loaded with polymeric materials, thereby obtaining blends that can have different physical or chemical structures, depending on the composition of the added polymer. Asphalts modified by the addition of reactive ethylene terpolymers were prepared and their dielectric and rheological properties were measured both before and after a cure at high temperature. Even if it is not possible to determine the exact nature of the chemical interactions between asphalt and polymer, master curves obtained from dynamic data clearly show that during the cure the material tends to the behavior of a cross-linked network.     

On continuum theories involving quasilinear first order non-conservative systems with involutions and a supplementary inequality

In this note we give a result of hyperbolicity for linearized quasilinear first ordernon-conservative systems with involutions and a supplementary inequality of conservative form. We also indicate some of the circumstances in which, for studying the evolution systems for a class of continua near their equilibria, such result can be applied. Some remarkable examples are the cases of a certain generalization of Landau's two-fluid scheme for superftuid Helium II, of a hyperelastic body acted upon by suitable live body forces, and of various other models appeared in the literature.     

One-dimensional quasistatic nonisothermal evolution of shape-memory material inside the hysteresis loop

We study in this paper the quasistatic nonisothermal processes of a onedimensional bar consisting of a two-phase shape-memory material. The system of p.d.e.'s governing the evolution of the bar is obtained by means of a temperature-dependent hysteretic stress-strain law that we formulate as a plasticity criterion and a hysteresis operator. The constitutive theory is developed here on the basis of the mixture approach proposed by Mtiller [t] and of a natural extrapolation of the isothermal experimental data regarding the behavior of the material inside the hysteresis loop recently described by Miiller and Xu [2]. Numerical simulations are presented for three initial and boundary-value problems of interest with regard to uniaxial stretching experimental tests.     

Rheological properties of asphalt/SBS/clay blends

The effect of the addition of clay as a third component in polymer modified asphalts has been investigated. After a preliminary investigation on the binary asphalt/clay and polymer/clay blends, the tertiary blends were prepared by adding the clay and polymer to the asphalt, either separately or in the form of a premixed master batch. Intercalated nanocomposites with comparable interlayer distances and glass transition temperatures were obtained in both cases. However, the results show that the mixing procedure significantly affected the final rheological properties. The master curves built in the linear viscoelastic range and represented in both the frequency and the temperature domains help to visualize and evaluate such differences.     

Hysteresis in discrete systems of possibly interacting elements with a double-well energy

Summary We study in this paper the hysteretic behavior of a discrete system constituted by a finite number of elements (snap-springs) whose energy has two parabolic wells. The guideline idea is that, in many circumstances, hysteresis can be due to the presence of relative minimizers of a potential (metastable states) in which the system might get locked during its quasistatic evolution. A careful investigation is thus carried out of the relative minimizers of the total energy of our system of snap-springs under imposed total displacement, and of the barriers separating them. This is done both in the case of noninteracting elements and in the case in which some interaction is present that gives rise in the energy to an extra coherence term of special form. The results allow discussion of various hysteretic phenomena, also in the presence of vibrational motion of the elements. This study of a simple but suggestive discrete system will hopefully prove itself of help in understanding the implications regarding hysteresis of certain continuum theories recently proposed to model phase transitions in the solid state, in which the energy density is assumed, as here, to be biparabolic, and in which the coherence energy term we adopt arises in a natural way when equilibria involving mixtures of kinematically noncoherent phases are considered. In these cases the optimal microstructures are known to be layered, and physically this gives a good basis to our discrete calculation.     

Martensitic transformations: from continuum mechanics to spin models and automata

We present a new procedure for the systematic reduction of a continuum theory of martensitic transformations to a spin system whose dynamics can be described by an automaton. Our prototypical model reproduces most of the experimental observations in martensites associated with criticality and power-law acoustic emission. In particular, it explains in a natural way why cyclic training is necessary to reach scale-free behavior.