A thermal, rheological and mechanical material characterization of an aeronautic epoxy resin from commercial prepreg is reported in this article. The kinetic of the crosslinking reaction of the resin is characterized and modeled. The specific heat, the glass transition temperature, the thermal expansion coefficients, the chemical shrinkage coefficients and the thermo-mechanical properties have been investigated as a function of temperature and degree of cure. Dynamic mechanical measurements are used to determine the gel point. Finally, the residual stresses developed during the curing process are calculated using a finite element simulation, taking into account the material properties evolutions according to proposed models. The results highlight the importance of the characterization accuracy and the associated models.

Material characterization and residual stresses simulation during the manufacturing process of epoxy matrix composites

Sheet molding compounds (SMC) are fiber-reinforced thermosetting semifinished products. They are produced in thin uncured and thickened sheets that can be handled easily before their forming process. To a larger extent, SMC is a generic term that designates such types of compounds together with the process to convert them into large composite parts, which mainly display shell-like geometry. This process is usually compression molding. SMC are widely used in a large diversity of fields of applications (aerospace, agricultural, rail and marine, electrical and energy, domestic appliance, building and construction, and medical sectors), but the automotive and truck industries remain the drivers of SMC technology. After a short introduction, this article gives successively detailed descriptions of (i) the materials used in SMC, (ii) their compounding, (iii) the compression molding process, (iv) the final properties of SMC, and (v) SMC recycling.


Keywords:

sheet molding compounds (SMC);
compression molding;
short fiber-reinforced polymer composites;
hermoset polymer matrix

Sheet Molding Compounds

A model is proposed for the flow, reaction, and heat transfer during compression molding of thin, flat parts. The isothermal Newtonian version of the model is implemented using the finite element method, and is capable of handling arbitrary planar geometries. Automated mesh expansion and boundary condition modification allow the simulation to run without operator interaction. The model accurately predicts mold filling pattern for non-Newtonian and non-isothermal flows.

Model of compression mold filling.

Development of a numerical code that simulates combined heat transfer, resin flow and compaction during composites processing

Predictions of fiber orientation dependent mechanical properties are extremely important in the automotive industry for injection molded fiber-reinforced thermoplastic composites. Prior studies on three-dimensional (3D) numerical computations have not had satisfactory results in the searches for significant deviation in the core region and skin boundary of a fiber orientation pattern, although the orientation in the shell layer was predicted fairly well. To perform the connection between fiber orientation and the mechanical properties in a familiar short-fiber composite, therefore they aim for accurate predictions of the anisotropic fiber orientation at various flow factors in a reliable, 3D injection molding simulation within a new objective fiber orientation model. Comparisons of the predictive fiber orientation and tensile modulus with related experimental data were also made herein, as well as including variation in the modulus along the flow distance from the gate. POLYM. COMPOS., 2017. © 2017 Society of Plastics Engineers

Accurate predictions of orientation dependent modulus in short‐fiber‐reinforced composite with experimental validation

Design of molding tools and molding cycles for sheet molding compounds (SMC) is often expensive and time consuming. Computer simulation of the compression molding process is a desirable approach for reducing actual experimental runs. The focus of this work is to develop a computer model that can simulate the most important features of SMC compression molding, including material flow, heat transfer, and curing. A control volume/finite element approach was used to obtain the pressure and velocity fields and to compute the flow progression during compression mold filling. The energy equation and a kinetic model were solved simultaneously for the temperature and conversion profiles differential scanning calorimetry (DSC) was used to experimentally measure the polymer zation kinetics. A rheometrics dynamic analyzer (RDA) was used to measure the rheological changes of the compound. A series of molding experiments was conducted to record the flow front location and material temperature. The results were compared to simulated flow front and temperature profiles.

R. R. Hill

Papers

Numerical simulation of non‐isothermal SMC (sheet molding compound) molding