Core Crush Mechanisms and Solutions in the Manufacturing of Sandwich Structures

Abstract

Core crush is a manufacturing defect occurred during the autoclave curing process of composite honeycomb sandwich structures. It usually leads to costly part rejections since the defect is non-repairable. In addition, this problem has posted constraints on aircraft engineers by limiting the ranges of core density and core thickness that could be used when designing these types of structures. In commercial production, several techniques (e.g., ply tie-down, pre-cured adhesive over the core) have been applied to restrain the core from collapsing inward; however, these approaches require additional labor, time and material cost and thus may not be the best solutions. This paper discusses the recent understandings in core crush mechanisms and the subsequent developments in core crush resistant prepreg based on that foundation. It shows that the prepreg frictional resistance is the key factor in controlling core crush. While past research in the scientific community has mainly focused on resin effects in core crush, studies conducted in Hexcel show that the core crush can also be significantly reduced by controlling construction of the fiber tow shape and fabric architecture. Rounder fiber tow or more open fabric produces rougher prepreg surface and thus yields higher prepreg frictional resistance to reduce core crush. Experimental results show that, without changing the resin, the developed core crush resistant prepreg increases the prepreg frictional resistance and effectively reduces the core crush.