Honeycomb Core and the Myths of Moisture Ingression

Abstract

While it is true that honeycomb core can trap moisture, it is a myth that widespread moisture ingression is an inevitable outcome when honeycomb sandwich structures are exposed to real world environments. It is also a myth that when moisture ingression occurs, progressive weight gain and strength loss are inevitable outcomes. Using a rebuttal of a 2004 honeycomb-critical paper as the focal point, this paper summarizes multiple sources which indicate both that moisture ingression is preventable and, even if it does occur, that proper material choices can prevent severe consequences. These claims are further supported by results from in-plane compression testing of typical (0.064 g/cm 3 aramid-paper/phenolic core with 0.116 cm carbon/epoxy faces) composite honeycomb sandwich specimens after impacting, water submersion, and extensive thermal cycling.

Effects of moisture ingressions on mechanical properties of honeycomb-structured fiber composites for aerospace applications

“…In that case, more analysis is required to determine the diffusion rate [8][9][10][11][12]. Pilli et al [11] stated that the moisture diffusion coefficient can be determined through Fick's second law.…”

Investigating the effects aviation fluids have on the flatwise compressive strength of Nomex® honeycomb core material

“…There are many possible ways that fluids can intrude into a honeycomb sandwich structure. Fluid ingresses into the structure through joints, closeouts, and inserts of sandwich structure [11], [15]. Skin damage, such as a crack, can provide an intrusion path for moisture [1], [7], [11], [15], [16].…”

“…Fluid ingresses into the structure through joints, closeouts, and inserts of sandwich structure [11], [15]. Skin damage, such as a crack, can provide an intrusion path for moisture [1], [7], [11], [15], [16]. Possible pathways of moisture ingression are negative gage pressure in the cell caused during the curing process, which draws the moisture into the cell [7].…”

“…Possible pathways of moisture ingression are negative gage pressure in the cell caused during the curing process, which draws the moisture into the cell [7]. Even when there is no damage to the skin panel, moisture can diffuse through porosity and micro-cracks that are induced from thermal cycles [7], [15], [16]. When moisture ingresses into a honeycomb structure, the pattern of the infiltration is very random and unpredictable [17].…”

“…If there is moisture inside of the honeycomb cell, repeated freeze and thaw mechanism caused by temperature change causes destruction of the honeycomb core and the bond between facesheets and the core [1], [7]. However, Fogarty [15] reported that honeycomb sandwich structure can trap some moisture in a real operational environment, but it is not true that wide spread ingression of moisture for entire structure is inevitable. Fogarty [15] showed that many researchers found that moisture ingression can be prevented.…”