Sponsored by Boeing Commercial Airplane Company
Due to the high stiffness to weight ratio, sandwich panels with a honeycomb core are being investigated for use as primary structural members in the high speed civilian transport. These panels must meet specified damage tolerance requirements before they can be incorporated into the design. This project is an extension of research and development into damage tolerance in honeycomb structural members started under a previous project at Cornell University.
The objective of previous project is to develop an accurate, cost-effective, computer-based tool to predict damage tolerance in the honeycomb sandwich panels. Several damage mechanisms under various loading conditions were studied. The damage mechanisms consist of crack propagation in a single facesheet, crack propagation from through-penetration, and delamination of a single facesheet. Also, debonding propagation under edge compression loading and damage tolerance under freeze-thaw-evaporation cycles were studied.
The continuing project consists of five technical tasks.
Task 1 : Continue Parametric Studies of Core-to-Facesheet Disbond Growth
Task 2 : Modify Current Approach for Core-to-Facesheet Disbond Growth to Allow a Strength-Based Approach
Rather than explicitly model the core and perform fracture mechanics mechanics-based approach, strength-based approach can be used as long as the notch-sensitivity of the adhesive is negligible. (Task 3) Modifications to the FRANC3D/STAGS system will be made to accept the strength value and to uncouple the common node when it is this value is exceeded.
Task 3 : Develop Test Geometry/Method to Determine Notch Sensitivity of Adhesive
Task 4 : Develop a Pell-Type test Specimen to Measure the Toughness of the Core-to-Facesheet Bond
Task 5 : Modify Existing Orthotropic Toughness Models for Crack Trajectory to Apply to Fibrous, Laminated Composite Materials
The objective of this task is to develop an engineering approach to predicting the trajectory of a crack propagating in a facesheet of a sandwich panel. A major complication is the extreme anisotropy in toughness of the composite laminate--crack growth is much more difficult across fibers than parallel to them. Therefore, crack trajectory is a function of not only the driving stress field, but also the direction-dependent resisting toughness.
The approach to this task will be :