Structural performance of spacecraft honeycomb panels

Abstract

Honeycomb sandwich structures (commonly referred to as honeycomb sandwich panels) have found wide spread application in the aerospace industry thanks to their excellent properties, in particular their high strength-to-weight and high stiffness-to-weight ratios. Surrey Satellite Technology Ltd. (SSTL), like many other space companies, often use honeycomb sandwich panels as part of the primary and secondary structures of the small satellites they develop.

Although honeycomb panels have been used for the past 50 years gaining a better understanding of these sandwich structures, and the methods and solutions used to produce
structural assemblies from them is still a major concern in the aerospace industry. Whether directly or indirectly, there are still significant research efforts ongoing that affect these areas. This work focuses on some of these issues and covers several research fields including material science, tribology and adhesive bonding technology.

The first area of focus of this work deals with the structural performance of honeycomb panels alone and mainly concentrates on hexagonal honeycomb cores. An experimental
investigation using the rail shear test was conducted to study the shear behaviour of hexagonal honeycomb cores. This involved both static and fatigue tests using numerous honeycomb panel test samples with the loading direction at various angles to the core ribbon. From these tests it was found that core shear strength did not have a linear relationship with loading orientation and that contrary to what is commonly assumed the transverse direction (to the ribbon) is not always necessarily the weakest orientation.

The optimal design and performance of the load introduction points was the second area of focus for this work which covers equipment inserts and bolted joints. Two types of inserts where investigated in this work: hot bonded inserts and cold bonded inserts. A study on hot bonded and cold bonded inserts was conducted to assess their performance and effectively compare the two insert systems. A large portion of the study was experimental and involved
carrying out numerous insert pull-out tests to measure static pull strength capability. From the study it was found that contrary to what was expected cold bonded potted inserts outperformed the hot bonded inserts in terms of static strength capability. Using finite element it was found that this was due to the different filler materials used for the two insert systems.

The last area covered in this work concerns friction grip bolted joint between honeycomb panels. Here a simple method to analyze the efficiency of shear joint units is proposed. An extensive test campaign was also carried out to determine the influence of various parameters on the friction coefficient. Surface abrasion was found to be a reliable way of achieving high values of friction coefficient.

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