Volume 5, Issue 5 (September 1977)
Fatigue Damage: Stiffness/Strength Comparisons for Composite Materials
Boron/epoxy laminates in a [0-deg/ + 45-deg/ - 45-deg/ 0-deg/0-deg/ + 45 -deg/ - 45-deg/0-deg] layup were tested statically for initial strength and fracture strain and were tested in strain-controlled fatigue loading at 30 Hz, with a strain-amplitude ratio of one tenth for five different testing sequences.
A reduced stiffness analysis was used in conjunction with laminated plate theory to predict stiffness changes based on observed debonding and fiber breakage. Specimens used for strength analysis either fractured during fatigue or were loaded statically to failure after fatigue. All specimens were leached with a heated acid, and fiber breakage was recorded. Correlations are noted between matrix damage and stiffness changes as well as between fiber breakage and strength reduction.