Modeling of Thermoforming of Low-density Glass Mat Thermoplastic

The glass mat thermoplastic (GMT) is made from random-chopped glass fibers and polypropylene in a sheet form. This low-density compressible material is used extensively in the automotive industry for making panels. The mechanical behavior of this material in large deformation and at thermoforming process temperature is far from being well understood. The objective of this research is to determine a constitutive law of this Azdel thermoplastic composite used for thermoforming process. A series of biaxial tests was performed to study the stress-strain behavior of the low-density thermoplastic sheet reinforced with 55% glass fiber. Different strain rates and temperatures were employed to study their effects on the mechanical behavior. Pressure-thickness model parameters were obtained using a laboratory press. A nonisothermal hyperelastic model was used for modeling this material. The results of the simulation are compared with data from a laboratory thermoforming machine and a small, simple mold.