MULTIVARIABLE OPTIMISATION OF FIBRE REINFORCED HONEYCOMB SANDWICH PANELS

摘要

Sandwich construction, consisting of strong, stiff facings bonded to a relatively thick, low density core, is common in many structural applications of polymer composites. A wide variety of core materials (aluminium, Kevlar, polypropylene, etc.) are available, each having its own advantages and disadvantages. In a recent article, a relatively novel concept using short fibres as reinforcement in the cell walls of the honeycomb cores has been reported in Rao. et.al [1], the cores are not only structurally viable but also provide the advantage of being reprocessed. Several other properties such as energy absorption due to impact loading, sound absorption etc. are reported in [2-4]. Typically, sandwich panels are used in flexural applications where they behave similar to I-beam, where the facings sustain the bending stresses and the core takes the shear. Using a weak core assumption [5], common failures observed in panels under such loading may be faceplate fracture, shear failure of the core, wrinkling of the faceplate into the core or outwards due to delamination at their interface, and each of which can be determined by testing them individually. The results from these simplified tests will be helpful in setting failure criteria or stress constraints for sandwich panels as a whole during the design stage. For example, faceplate wrinkling in a sandwich panel can be avoided by designing a faceplate to withstand wrinkling stresses by considering it to be subjected to compressive edge loading and assuming one side of it to be resting on infinite elastic medium [6,7]. The buckling load during testing will give an indication of the maximum stress at which the faceplates would start to wrinkle, and by setting this critical stress as a failure criterion for faceplate wrinkling, the sandwich panel could be designed against that failure mode. Similarly, to avoid face dimpling into the core, the face dimpling or the intercellular buckling stress is calculated by using plate buckling theory for the in-plane stresses in the facings at which the face plate buckles at regions that are unsupported by the cell walls [8]. By using these simplified tests, failure criteria in terms of mathematical equations are setup and analytical solutions [9] for the whole panel are developed which in essence would reduce experimentation.