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Buckling of polymer (thermoplastic) encapsulated materials

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(@jflou)
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I have a multi-layered laminated structure of approximately 2 mm thick. It is about 2 m long. This laminated structure is basically thin metal ribbons (~0.1 mm thick) encapsulated between thermoplastic polymers (on top and bottom both). We can think of the layup as polymer/polymer/periodic ribbons/polymer/polymer. These polymers are all of the same size. The metallic ribbons are periodically arranged in the same plane, one adjacent to other, with ~1 mm gap between them. This whole layup is laminated at a high temperature to bond the layers together.

Quite rarely, in a thermal cycle, this structure tends to show small bumps (possibly representing a buckle mode). However these bumps are not more than 1 mm to 2 mm range. The polymers and the metal between at any cross-section through the length have the same curvature. I am modeling the metallic ribbons as elastic plastic and polymers as elastic (temperature dependent moduli obtained from DMA). However, I am unable to simulate such buckling modes. I am using a constant CTE (not temperature dependent) for the polymers. I am wondering if my modeling of polymers is fundamentally wrong. Is there any shrinkage that needs to be accounted for? In a way it appears from experiments that the ribbon takes the buckling mode shape (stiffness and CTE mismatch) and the polymers around the ribbons are locking the ribbon in this mode shape. And this mode shape doesnt seem to relax at high temperatures (~100C) during the thermal cycle.

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