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Modeling and Monitoring of Composite Processing

Involved People: Alfonso Maffezzoli, Antonio Greco
A large experience on all aspects of processing has been accomplished since 1987. Several papers deals with the numerical solution of an energy balance coupled with a kinetic equation capable to fit isothermal and non-isothermal cure data obtained by DSC. These two differential equation are coupled and provide the temperature (T) and the degree of reaction (α) as a function of time and space variables (figure 1). The resin viscosity can be now calculated as a function of T and α. Original models for cure kinetics and chemorheology (Figure 2) have been proposed either for polyester resins either for epoxy resin. In particular the effect of vitrification is originally accounted by a simple and effective modification of classic n order kinetic equations (1-4, 8).
This experience of reactive processes in fiber reinforced composites was transferred to similar problems such as those occurring in some biomaterials applications, namely curing of dental composites and bone cements in total hip implant. Also in this case the analysis of heat transfer was coupled with original models for radical polymerization of acrylic reactive mixtures. The numerical solutions provided fundamental indications for dentists and surgeons for a proper processing route leading to limited exothermal effects. The collaboration with prof. Berglund also lead to a theoretical prediction of residual stress in dental composites (figure 3) (5 -7. 9, 14).
Finally, the attention was also paid to the development of experimental and theoretical tools for cure monitoring. First a dielectric properties were studied developing the first quantitative correlation between normalized ionic conductivity and the degree of reaction (figure 1) (3, 4). Then an extensive research work was devoted to the application of ultrasonic wave propagation to cure monitoring (figure 4). The correlation between the degree of reaction and the normalized ultrasonic longitudinal modulus was used to detect gelation and vitrification. The last developments deals with the fabrication of an ultrasonic air coupled device for the cure monitoring of polyester resins (figure 5) (10,-13, 15-17).

Figure 1 (from ref 3) results of numerical solution of an energy balance coupled with the heat generation arising from resin cure during pultrusion of an epoxy matrix composite a) Temperature b) degree of reaction, c) viscosity
Figure 2 (from ref 4) Viscosity as a function of time during epoxy resin heating: experimental data and theoretical predictions
Figure 3 (from ref 14) Effect of temperature on vitrification: maximum degree of reaction as a function of cure temperature for acrilic dental composites
Figure 4 (from ref. 13) comparison between the evolution of bulk modulus measured by contact ultrasonic wave propagation and degree of reactionmeasured by calorimetric aanalysis.

Figure 5 (from ref. 17). Comparison between the aircoupled and contact ultrasonic measurements


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University of Salento   FacoltÓ di Ingengeria    Department of Engineering for Innovation