| Popis: |
Laminates of epoxy fiberglass composite (C1D-101 epoxy, woven S-2 glass fabric, volume ~ 56%) were held under constant tensile stress at 76 K for up to 650 hours to measure creep response. Up to 5 specimens were simultaneously loaded under dead weight to various percentages (16% to 33%) of the ultimate tensile strength, and significant creep rates were detected. Two stages of creep were observed, an initial rapid stage, and a secondary, steady-state, creep stage. The tests were terminated before specimen failure occurred. Two equations (linear and power curve) were fit to the second stage data to predict creep behavior beyond the duration of the tests. Static tension tests were also performed to determine the baseline properties of the composite, which revealed transverse microcracking (90° to loading direction) at stresses as low as 22% of the ultimate strength. Therefore, creep behavior at stress levels above 22% is influenced by microcracking, crazing, and probably plastic and viscoelastic mechanisms. |
