Some models of crack growth in brittle materials

This work is devoted to the study of models of fractures growth in brittle elastic materials; it collects the results obtained during my Ph.D., that are contained in [77, 76, 78]. We consider quasi-static rate-independent models, as well as rate-dependent ones and the case in which the first ones are limits of the second ones when certain physical parameters vanish. The term quasistatic means that, at each instant, the system is assumed to be in equilibrium with respect to its time-dependent data; this setting is typical of systems whose internal time scale is much smaller than that of the loadings. By rate-independent system we mean that, if the time-dependent data are rescaled by a strictly monotone increasing function, then the system reacts by rescaling the solutions in the same manner

Biocomposites including nano-scale dispersed phase and polymers from renewable resources

Poly(lactic acid) (PLA) was physically modified by filling with an inorganic additive, natural fibres as well as with a tributyl citrate (TBC). PLA composites were prepared with a film stacking method and analysed by scanning electron microscopy (SEM), thermogravimetry (TGA), thermomechanometry and differential scanning calorimetry (DSC) to investigate the physical and mechanical properties of the hybrid composites. PLA composites reinforced with hemp fibres in combination with nanosilica are thermally stable as the maximum rate of weight loss of the composites shifted to the highest temperature observed in TGA results. Dynamic mechanical properties of PLA composites showed that the reinforcement of hemp fibre and nanosilica strongly affected the mechanical properties of the composites. The highest storage modulus improvements were reached by addition of hemp fibre and nanosilica without plasticiser. An increase in storage modulus monitored in the temperature region from 70 to 100 °C reflected an increase in structural stiffness due to recrystallisation activity in the composites. The addition of TBC reduced the modulus though initiated the crystallisation on cooling, enhanced the nucleating ability of the fillers and chain mobility in PLA composites. The melting and crystallisation behaviour of PLA composites was explored with non isothermal DSC at various scanning rates. The characteristics of the crystallisation and melting behaviour of PLA composites were explained by the slow rate of crystallisation and recrystallisation, which is in agreement with DMA results. Non-isothermal crystallization kinetics shows that the crystallization rate of PLA composites was higher than of neat PLA and further increased with presence of TBC, indicating that the addition of plasticiser and nucleating agents enhanced the transportation ability of polymer chains. SEM revealed a good distribution of nanosilica for composites with and without TBC. A great transfer of stress between hemp fibres and PLA nanosilica matrix resulted in improved of physical and mechanical properties as evidenced by DMA and DSC results

Continuous precipitation of yttrium hydroxycarbonate spheres of narrow size distribution

Submicron spherical particles of the yttria precursor Y(OH)CO[subscript]3·H[subscript]2O were continuously precipitated in three types of reactors: (1) mixed-suspension mixed-product removal (MSMPR), (2) semi-batch, and (3) packed bed. The homogeneous precipitation occurred as a result of the thermal decomposition of urea in an aqueous yttrium nitrate solution;A wide variety of particle size distributions were produced from these reactors. Mathematical models, which assumed that particle growth was by a diffusion mechanism, successfully allowed the size and shape of the particle size distributions to be predicted and controlled. It was shown that the concentration of the rate-limiting diffusing species could be calculated from a simple analysis of the particle size distribution from the MSMPR reactor. From such an analysis, it appeared that carbonate was the rate-limiting diffusant

Global Constraint Catalog, 2nd Edition

This report presents a catalogue of global constraints where each constraint is explicitly described in terms of graph properties and/or automata and/or first order logical formulae with arithmetic. When available, it also presents some typical usage as well as some pointers to existing filtering algorithms

Global Constraint Catalog, 2nd Edition (revision a)

This report presents a catalogue of global constraints where each constraint is explicitly described in terms of graph properties and/or automata and/or first order logical formulae with arithmetic. When available, it also presents some typical usage as well as some pointers to existing filtering algorithms