Core Crush Problem in the Manufacturing of Composite Sandwich Structures: Mechanisms and Solutions

Manufacturing of composite honeycomb sandwich structures is significantly impacted by poor production yields caused by the core crush problem that occurs during the autoclave curing process. It is a major manufacturing defect that leads to costly part rejects because the defects are nonrepairable. This failure mechanism also constrains aircraft engineers, limiting the design range of core density and core thickness in attempts to mitigate core crush. Recent studies that have led to basic understanding of core crush mechanism are discussed. It was found that the prepreg frictional resistance is the key factor in controlling core crush. Research in the scientific community has mainly focused on resin effects in core crush. However, studies conducted show that core crush can also be significantly reduced by controlling construction of the fiber tow shape and the fabric architecture. Rounder fiber tow or more open fabric produces rougher prepreg surface, which results in a higher prepreg frictional resistance, reducing the effects of core crush. Experimental results indicate that a developed core crush resistant prepreg increases the prepreg frictional resistance and effectively reduces core crush, without changing the resin system.