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Methods For Assessing Honeycomb Sandwich Panel Wrinkling Failures

This document presents the assessment of an accurate yet efficient method for predicting sandwich
panel facesheet wrinkling using the wrinkling stress calculation developed by Heath (1960) and Vinson
(1999) and the combined multiaxial failure criterion developed by Ley et a1. (1999). These closed form
predictions were verified using several finite element analyses with varying levels of detail described in
this report. The closed form method was then implemented into the HyperSizer Structural Sizing
Software (HyperSizer, 2012) as a user-defined failure criterion, and the implemented code was verified
using hand calculations. The motivation for this work was the need for an accurate wrinkling solution that
is also sufficiently computationally efficient so as to be implemented into sizing software, such as
HyperSizer, for accurate and quick wrinkling assessment early in the structural design process.

Facesheet wrinkling, often referred to simply as wrinkling, is a failure mode that is commonly
observed in sandwich panels with thin facesheets and lightweight cores, which do not provide a great deal
of support to the facesheets. The failure is characterized by short wavelength buckling in one or both
facesheets, as shown in Figure 1, and the failure is usually catastrophic soon after the onset of wrinkling
(Collier Research Corporation, 2011). It is thus critical to account for this failure mode when designing
sandwich panels for structural applications.

The existing method in HyperSizer treats sandwich panel facesheet wrinkling as buckling of a simple
beam on elastic foundation and predicts wrinkling failure based on a modification of the equation
developed by Hemp (1948), which is the same equation developed by Yusuff (1955).