Assessment of a Crack Tip Element-Based Approach for Predicting Delamination Growth in Interlayer-Toughened Composite Skin-Stringer Panels
Abstract
A crack tip element approach to predict delamination growth is reviewed and then used to predict delamination growth in two stiffened-skin geometries that are typical of aircraft configurations. Predictions by this approach are then compared with experimental results. Test specimens were fabricated from T800H/3900-2, which is a graphite/epoxy material system toughened by a thermoplastic interlayer. Experiments were then performed, and predictions were compared to the observed results. Predictions that incorporated previously generated toughness data gave poor correlation to experiments. It was found that the fracture behavior of those specimens used to determine the toughness versus mode mix data was significantly different than that observed in the stiffened-skin elements. Specifically, the thermoplastic interlayer was relatively thin and dispersed in the interply regions of the skin-stringer elements, and delamination advance occurred through the low toughness base matrix and/or through the base resin/thermoplastic interlayer interface. Through scanning electron microscope observations, two distinct reasons were found to be the cause of lack of thermoplastic layer in the stiffened-skin specimens. The first of these is that the noncritical end of the delamination (i.e., away from the crack tip) terminated at a free surface that was reasonably close to the crack tip. This provided a path through which, during manufacture of the specimens, the toughening material could flow out of the inter-ply region. The second contributing factor was the relative angle of the plies bounding the delamination as compared to the direction of delamination advance. The fibers in these bounding plies compress the thermoplastic interlayer into a sinusoidal grid whose peaks and valleys are not aligned with the direction of crack growth.
Document Details
- Document Type
- Technical Report
- Publication Date
- Dec 01, 2002
- Accession Number
- ADA412023
Entities
People
- B. D. Davidson
- L. M. Rao
Organizations
- Syracuse University