FAILURE RESPONSE OF WOVEN CARBON FIBER SPECIMENS WITH DOUBLE-EDGE NOTCHES UNDER STATIC AND FATIGUE LOADING

摘要

Carbon fiber composites are continually seeing increased use in aerospace applications. It isnecessary to understand their failure modes in order to properly design and perform analysis onstructures constructed primarily from them. This paper studies the static and fatigue failures ofwoven carbon fiber laminates with and without edge notches. Test specimens were fabricated ina Tetrahedron plate press under heat and pressure according to Advanced Composites Group'scure cycle instructions for their LTM45EL series woven carbon fiber. Specimens wereconstructed of six layers of LTM45EL woven carbon fiber prepreg. Monotonic tests wereperformed to determine material characteristics. Specimens were tested with and without notchesthat were cut into both edge-wise sides of the rectangular test specimens. Notch depths ranged invalues from a/w = 0.10 to a/w = 0.35. Tensile test results for notched specimens show that thefracture toughness of double-edge notched woven carbon fiber specimens is better related to thecubic root of notch size than the square root of the notch size as predicted by Griffith. Fatiguetests were also performed on the specimens with and without notches. Fatigue tests providedevidence of mixed mode failures in unnotched specimens with delaminations between all pliesspanning the length of the specimens and separated plies tearing at different locations.