Syntactic foam core material for composite structures

Abstract

A syntactic structural foam product in flat sheet form or curved three-dimensional form adaptable to such uses as a light weight structural core for composite laminates, is made of a mixture of hollow ceramic microspheres and dry resin powder, of either thermosetting or a high-temperature thermoplastic resin, distributed in the interstices of the mass of microspheres for integration of the mixture into desired form upon heating and cooling. The dry resin powder in an other embodiment of the invention includes unexpanded expandable powder which will expand into microballoons in the confined spaces in which they reside and effect a bonding relation with surrounding particles upon supply of heat to the mixture. The foam product is produced by thoroughly intermixing and depositing the mixture as a layer over a surface having a release agent thereover within a dimension defined region and then supplying heat with or without pressure to the layer at a temperature and for a time period sufficient to effect a melting or softening of the resin powder and thereafter cooling the resin to a hardened condition to integrate the mixture into the product desired after which the product is withdrawn from the forming zone. Reinforcing elements such as glass or carbon fibers can be selectively included in the mixture for predeterminable desired physical and mechanical properties.