| Summary: | Although composites have gained widespread use, we do not, as yet, have a precise and complete understanding of the mechanisms of damage development in composite materials. Recent research results have pointed out the need to treat damage as a collective condition-that is, a damage state, rather than as an assembly of discrete and independent damage modes. This paper presents the results of an investigation to determine the damage states which develop in two quasi-isotropic graphite/epoxy laminates with center holes due to tension-tension cyclic loads, to determine the influence of stacking sequence on the initiation and interaction of damage modes and the process of damage development, and to establish the relationships between the damage states and the strength, stiffness, and life of the laminates. Damage was monitored nondestructively throughout the loading history using X-ray radiography, moiré interferometry, and stiffness change. Some specimens were deplied after specific numbers of cycles to determine the distribution of damage in each ply around the hole and to confirm the components and size of the damage state observed nondestructively. Fatigue life and residual strength tests were also performed
|
|---|