The present paper purposes a new factor of Acoustic Emission (AE) to estimate the damage of factor in fiberglass-epoxy composites. Both notched and unnotched specimens were prepared for the tests. AE signal was monitored during the tensile, the loading-holding, and the unloading-reloading testings on this material. History of amplitude or energy distribution of AE showed that the factor process during the tensile testing is dependent upon the specimen geometry. Although the source locations of the events during the tensile testing were widely distributed over the specimen, the damage area leading to final failure could be clearly located by the cumulative AE energy. In the loading-holding testing specimens were subjected to similar loading procedure to that of the ASME standard (Section 5, 11). The ratio (H=N
l/N
n) of event counts during holding (N
n) and during loading was shown to be a good indicator to predict the ultimate stress. Kaiser Effect Ratio (Felicity Ratio) was carefully studied during the sequential loading and unloading cycles. It is concluded that the ratio (Damage Factor, (DF=E
u/E
l) of event counts during unloading (E
u) to that during loading (E
l) is to be a good indicator to predict the generated micro crack from AE results and SEM observations.
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