A STUDY OF THE STRESS-STRAIN BEHAVIOR OF GRAPHITE FIBER COMPOSITES TO ASSESS THE STRESS LEVELS AT WHICH SIGNIFICANT DAMAGE OCCURS

摘要

The purpose of this investigation was to attempt to obtain by experimental means a rigorous definition of the stress level within a composite specimen at which physical damage and/or degradation of mechanical properties was initiated. The goal of the study was to show that the composite material resistance to subsequent loadings is seriously impaired. This purpose and goal are similar to the ones pursued on a cursory basis in a previous report by the authors. In continuing the study on the HTS/ERL-2256 graphite epoxy in (0)C, (0/90)C, (0/ plus or minus 45/0)C, (90/ plus or minus 45/0)C, and (plus or minus 45)C orientations, the axially loaded flat specimen, tube test, and characterization program was continued. In this program, load-introduction problems on tubes were studied along with compression test methods. Additional fatigue data were generated, showing good correlation with significant damage (proportional limit) stress levels. Maximum strain criterion was used to predict the proportional limit (significant damage level) and cultivate strength with considerable success. A large number of tubes was fabricated for testing in the balance of the program and a test plan worked out.