Book Description

In typical applications like in the top skin of the wing or in control surfaces of an airframe, laminated composites are often found to be buckling-critical. Under excessive compression loading composite panels may undergo buckling and failure mechanisms would generally involve delamination or fiber breakage. Tapered composite panels with ply drops, when employed in wing skin, are expected to be more prone to the above mode of failure. This is one important area of concern to the designers of composite structures and both analysis and experimental verification of the buckling behavior is recommended as a part of design validation effort. However, data from such analysis are scarce in open literature. In this paper, results of a study on buckling and fracture behavior of laminated Carbon Fiber Composite (CFC) panels containing ply drops are presented. CFC panels of varying thickness with normal and inclined ply drop were tested under compression loading until buckling and ultimate failure. Nearly simply supported boundary conditions at the ends and along the edges were simulated with the help of specially designed test fixtures. Tests were conducted both under room temperature and hot-wet (100°C ± 3 °C and ? 85% RH) environmental conditions. Back-to-back strain gage output and out-of-plane deformation data were recorded and analyzed to determine the critical buckling loads and corresponding mode shapes. Finite element analysis using MSC NASTRAN was also made in order to predict critical buckling loads and corresponding mode shapes. These results were compared with those obtained from experiments and the agreement was found to be good in most cases. It was also found that under hot-wet conditions, both critical buckling loads and failure loads were lower compared to the room temperature values.