Development of Test Methods for Measuring Fiber Misalignment and Warping in Honeycomb-Core Composite Panels

Zodiac Aerospace manufactures honeycomb-core composite panels to be used in aircraft cabin interior components. During the manufacturing process, some panels become warped such that they cannot be used for their designated aircraft cabin components. As a result, these panels are scrapped because they cannot be recycled. About 44 to 90% of panels become warped during manufacturing. Warping is caused by many factors, including layer misalignment, processing parameters such as temperature and pressure gradients, and fiber misalignment in the prepregs. Currently, Zodiac does not have any data on the effect of fiber misalignment on panel warpage, so a testing protocol was developed to determine if there was a correlation between these parameters. Fiber misalignment measurements were performed on a selection of glass fiber/phenolic prepregs obtained from multiple shipments. To determine fiber misalignment in the prepregs, the phenolic resin was removed, leaving the raw fibers exposed and able to be measured. Warpage measurements were performed on cured composite panels cut from the same prepreg rolls. Test methods for the maximum deflection and twist angle of the panels was developed, then this data was plotted to determine if a relationship existed between the measurements. The plots showed no correlation between the fiber misalignment and warpage measurements. To provide additional conformation, a one-way analysis of variance (ANOVA) was conducted using an alpha value of 0.05. The ANOVA analysis confirmed that there was no correlation between the fiber misalignment and warpage measurements. Recommendations for further study would be to analyze the effects of temperature and pressure gradients on warping of the panels and construct a fixture to hold the prepreg in the acetone bath