A Single Fracture Toughness Parameter for Fibrous Composite Laminates
Abstract
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 c/epsilon 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 c/epsilon 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 c/epsilon sub tuf is indeed a constant, values of Q sub c/epsilon sub tuf were calculated for centrally cracked specimens made from graphite/polyimide, graphite/epoxy, E-glass/epoxy, boron/epoxy, and S-glass-graphite/epoxy materials with numerous layups. Within ordinary scatter, the data indicate that Q sub c/epsilon 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 c/epsilon 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.
Document Details
- Document Type
- Technical Report
- Publication Date
- Mar 01, 1981
- Accession Number
- ADA303771
Entities
People
- C. C. Poe Jr
Organizations
- National Aeronautics and Space Administration