2. Equations to solve

The various processes described above have the following points in common:

• they concern the deformation of thin structures (the thickness of the material being blown or thermoformed is small compared to the other dimensions of the part);

• deformations are significant (deformations of the order of 5 can be encountered) and essentially elongational in nature. However, in certain areas and for certain processes (e.g. blowing and beaming), shear stresses can be significant;

• deformation speeds can be high (up to 100 s ^–1 locally), the power dissipated during deformation is not negligible and blowing or thermoforming operations cannot always be considered isothermal even before the sheet (or tube) and mold come into contact;

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