This paper elucidates a modified Classical Nucleation Theory (CNT) that considers the effects of stress variations and existence of microvoids in plastic foaming processes. The stress effect has been incorporated into the CNT by a local pressure variation term that describes the dynamic conditions of industrial plastic foaming processes (e.g., extrusion foaming, injection foam molding). Also, the free energy barrier equation has been modified to include nucleation events from existing gas clusters. Both phenomena have been observed experimentally via in-situ plastic foaming visualization to confirm the modified theory. Combining the stress and preexisting gas clusters considerations, the modified CNT described in this paper improves the traditional CNT in describing cell nucleation phenomena in plastic foaming processes.

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