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Probabilistic Characterization of Interlaminar Toughness for Reliability Analysis of Aircraft Composite Structures



Interlaminar areas are usually the weakest links in composite primary structural elements, and objectives of this work are the development of a methodology for efficient probabilistic characterization of Mode II interlaminar toughness; its demonstration on examples of typical laminated carbon-fiber composite materials; and generation of representative data quantifying its statistical scatter and distribution trends. The developed methodology is based on the assumption that, in contrast with average properties, parameters of variability can be sensitive to considered statistical populations. Therefore, it is based on analysis of variability at different scales, namely, within a relatively small area of materials (e.g., one beam-type coupon), larger domains (e.g., square panels), and populations of multiple panels. In addition, effects of material thickness are captured through consideration of composites with different numbers of layers. For efficient testing, a modified variant of Mode II characterization was suggested and successfully implemented. A systematic test program was planned and performed to generate a significant population of results sufficient to make conclusions on statistical variability with high confidence. Typical uni-directional IM7/8552 carbon-fiber laminated composites with 20, 30, and 40 individual layers were used as representative examples for the demonstration. Finally, applicability of the generated results to probabilistic Finite Element Analysis for damage tolerance based analysis was suggested.

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