Multi-point forming of sandwich panels with egg-box-like cores and failure behaviors in forming process: Analytical models, numerical and experimental investigations

The manufacturing of shaped sandwich components is a task with technical challenge. In this paper the mechanical feasibility to produce a doubly curved panel from an initially flat sandwich plate was investigated. Experimental results of multi-point forming (MPF) and finite element analyses reveal that the formability of sandwich panel with egg-box-like (EBL) cores in plastic forming process is mainly dominated by the failure modes of face sheet plastic wrinkling, face sheet plastic dimpling and core cell fracture. Analytical models for predicting the face sheet buckling were developed, and limit bending radius for wrinkling and the critical stress for dimpling were determined as the functions of the geometric parameters and material properties of sandwich plate. The stress-based fracture limit curve and associated theoretical formulations to predict the core cell fracture were presented. The developed analytical models have been validated experimentally and using finite element simulations. Multi-point forming experiments were carried out and the feasibility of using plastic forming technique to form EBL-cored sandwich panels was demonstrated finally. (C) 2018 Elsevier Ltd. All rights reserved.