2. Basics of relevant thermomechanical modeling

Thermoplastic shaping processes are essentially driven by mechanical and thermal phenomena. They consist of three stages (figure 1 ):

• melting, i.e. the transition from a solid (in powdered or granulated state) to a sufficiently homogeneous fluid molten state. The term "melting" covers several different physical phenomena, depending on whether the polymer is semi-crystalline or amorphous;

• shaping in the molten state, by flowing under pressure through a die or into a mold;

• shaping and cooling, possibly including stretching, biaxial-stretching, blowing operations...

The properties of the produced object depend, of course, on the chosen polymer, but...