BS in Materials Engineering
Materials Engineering Department
The use of composite sandwich panels has increased in the aerospace industry. Prediction of a theoretical composite construction's flexural properties is important for efficient composite product designs. Utilizing the four point flexure geometry defined by Zodiac Aerospace, Santa Maria, CA, a mechanical model was derived to predict the flexural behavior of a theoretical honeycomb core sandwich composite using laminate tensile properties. The most common failure mode of Zodiac Aerospace’s four point bend test is a failure in tension of the bottom laminate. Given this information, ASTM D3039 (Standard Test Method for Tensile Properties of Polymer Matrix Composite Materials) was chosen to test ply tensile properties. Based on the ASTM standard, a sample size of 30 specimens for each laminate was examined to account for any statistical variance. Specimen width was 1 inch, as suggested by the ASTM standard, and the thickness was 0.01 inches per ply on average. A high strength epoxy was used to adhere medium density fiberboard tabs to the fiberglass specimen to ensure failure occurred within the gage length. The tensile strength of a phenolic woven-fiberglass laminate construction with 1-ply, 2-ply, and 3-ply thicknesses was tested, inserted into the mechanical model, and compared to existing flexural data on sandwich panels tested by Zodiac Aerospace. The results indicate that the tensile strength increases as the number of plies are increased. The average tensile strength value for one, two and three ply are 38.8 ksi, 64.67 ksi and 71.22 ksi respectively. Although the flexural load of a sandwich panel with given dimensions was calculated using the ply tensile strength, the predicted loads may not be representative of the flexural loads measured in industry because the plies tested did not come from a population of batches, but from one batch.