Abstract
We address in this paper the problem of blow molding for a polymer exhibiting a deformation induced crystallization (e.g. Poly EthyleneTerephthalate or PET). In a first part, we give the equations of a model that couples the mechanics to the crystallization for a class of molecular models (e.g. Maxwell or POM-POM models). In a second part, without a real stabilities analysis, we follow the Swift analysis for biaxial deformations. We conclude this study in showing that it is possible to quantify how crystallization during the process stabilizes it. In enhancing strongly the strain hardening, crystallization is namely a stability factor against necking.
Highlights
Blow molding is a process enabling to manufacture bottles
The material is subjected to very high deformation [1] and this deformation induces a crystallization, which varies form point to point with respect of the materials mechanical history
This situation evidences a strain hardening and a shift of the limit deformation before necking, that increase both with crystallization and strain rate. This strain hardening is effectively due to crystallization as can be seen on figure 5, where are plotted the relative degree of crystallinity during the test
Summary
Blow molding is a process enabling to manufacture bottles. A preform is injected molded and cooled quickly. For PET bottles this cooling time is too short to allow the material to crystallize. The final shape of the bottle is obtained with a combination of axial deformation and air blowing (figure 1). During this final stage, the material is subjected to very high deformation [1] and this deformation induces a crystallization, which varies form point to point with respect of the materials mechanical history (strain, strain rate, temperature ...)
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