A Single Fracture Toughness Parameter for Fibrous Composite Laminates
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION HAMPTON VA LANGLEY RESEARCH CENTER
Pagination or Media Count:
A general fracture toughness parameter Q sub c was previously derived and verified to be a material constant, independent of lay up, for centrally cracked boron aluminum composite specimens. The specimens were made with various proportions of O deg and or - 45 deg plies. Moreover, a limited amount of data indicated that the ratio Q sub cepsilon sub tuf where epsilon sub tuf is the ultimate tensile strain of the fibers, might be a constant for all composite laminates, regardless of material and layup. In that case, a single value of Q sub cepsilon sub tuf could be used to predict the fracture toughness of all fibrous composite laminates from only the elastic constants and epsilon sub tuf. To verify that Q sub cepsilon sub tuf is indeed a constant, values of Q sub cepsilon sub tuf were calculated for centrally cracked specimens made from graphitepolyimide, graphiteepoxy, E-glassepoxy, boronepoxy, and S-glass-graphiteepoxy materials with numerous layups. Within ordinary scatter, the data indicate that Q sub cepsilon sub tuf is a constant for all laminates that did not split extensively at the crack tips or have other deviate failure modes. Using a single value of Q sub cepsilon sub tuf for all the layups and materials, strengths were predicted for the test specimens. The predicted and test values agree well except for laminates that split extensively. Then, the predicted strengths are usually conservative.
- Laminates and Composite Materials