Fracture and Fatigue of Bi-Materials.
Final rept. 1 Dec 79-30 Nov 80,
MASSACHUSETTS INST OF TECH CAMBRIDGE
Pagination or Media Count:
Eighty-nine axially loaded, aluminum honeycomb sandwich specimens with graphite epoxy face sheets of four different laminates were compressively cycled with a minimum to maximum load ratio of R10. Fatigue damage initiation and propagation were monitored on both graphiteepoxy faces of each specimen using Moire interferometry, a method of optically producing surface contour lines. These patterns were photographically recorded at intervals for later analysis. Life, residual strength, cycles to damage initiation and damage growth data are reported. Damage initiation site and mode are compared with the analytically predicted three dimensional stress field at the edge of the hole. The location of first observable damage in all laminates was an experimentally repeatable layup characteristic. All laminate types showed a nearly horizontal initial region of damage growth followed by a second region of gradually increasing damage area growth with loading cycles, and a final region of very rapid growth just prior to failure. Post fatigue inspection showed damage concentrated mainly in the angle plys. No well defined relationship could be established however, between specimen fracture and final damage area. Life to first damage and life to specimen failure for the four laminate types showed that both stacking sequence and ply orientation had an affect on the response of a specimen to cyclic compression loads. Author
- Laminates and Composite Materials