Rheological characterization of unsaturated polyester resin sheet molding compound

Abstract

This paper presents a theoretical and experimental analysis of the rheological behavior of sheet molding compound (SMC). The work analyses the squeeze flow in a parallel plate plastometer of SMC discs which contain 25 percent of fiber glass by weight. This method of flow characterization gives a good insight into the basic rheological behavior of SMC for the compression molding process when producing flat parts. The theoretical analysis applies to thickened and matured SMC at room temperature. The analysis treats SMC as a viscoelastic material having an equation of state with viscous, elastic and yield elements. The time variation of compressive force when squeezing SMC discs between two parallel plates (one fixed and one mobile) has been derived from the equation of state. The values of the viscous, elastic and yield parameters were determined by using a least squares method of curve fitting to the experimental results. There are two aspects to the reported experimental work. One aspect is concerned with showing that the three element model for the equation of state provides a realistic mathematical basis for characterizing the rheological behavior of SMC at room temperature. The other shows how the parallel plate plastometer can be used to give data which characterize SMC flow behavior under conditions similar to those of the actual compression molding process.

Anisotropic viscous behavior of sheet molding compounds (SMC) during compression molding

“…Such a high value is commonly encountered in the study of SMC rheology (Silva-Nieto et al, 1981;Kim et al, 1997;Le Corre et al in press). Results are certainly affected by the rather irregular initial thickness h 0 of the samples (Áh 0 /h 0 % AE10%), the inaccuracy of L 0 , l 0 or D 0 (ÁL 0 /L 0 % Ál 0 /l 0 % ÁD 0 /D 0 % AE2%) and the error on the strain rate D 33 (ÁD 33 /D 33 % AE5%).…”

“…In contrast with the high number of experimental studies devoted to the process, references to the rheological properties of these compounds during the compression stage are quite scarce and incomplete (Silva-Nieto et al, 1981;Lee et al, 1981;Michaeli et al, 1990;Kim et al, 1992Kim et al, , 1997Lin et al, 1997;Lin and Weng, 1999). A better knowledge of their properties would contribute to the improvement of rheological models implemented in simulation software (Lee et al, 1984;Barone and Caulk, 1986;Castro and Tomlinson, 1990).…”

“…On the other hand, this implies to use a powerful testing machine to carry out tests on large samples. Silva-Nieto et al (1981) first studied the SMC behavior by squeezing some cylindrical samples (40 mm in diameter) between parallel and non-lubricated plates. Only one glass fiber weight fraction of 25% was tested at room temperature and at constant plate-closure speeds ranging from 0.016 to 0.8 mm s…”

Experimental and analytical procedures for flow dynamics of sheet molding compound (SMC) in compression molding

“…In addition, it also indicates the possibility of bulging of the charge in the middle of the moving flow front, as shown by timing of the responses of the sensors near the left and right sides of the charge in Fig. 10. Such bulges have been predicted for both shear flow (9, 18) and extensional flow with friction (19).…”

Towards the simulation of mould filling with polymer composites reinforced with mineral fillers and short fibres

“…when the suspending fluid is also a concentrated granular suspension [15]. For example, some studies were carried out to understand the rheology of Sheet Moulding Compounds (SMC), a fibre-bundle reinforced thermoset polymer composites with a matrix, which is similar to that of the BMC [1,14,20,30,[34][35][36]50].…”