Evaluation of Failure Behavior of Transversely Loaded Unidirectional Model Composites |
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Authors: | D C Foster G P Tandon M Zoghi |
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Institution: | (1) Air Force Research Laboratory, 2941 Hobson Way, Bldg 654, Rm 136, Wright-Patterson AFB, OH 45433-7750, USA;(2) University of Dayton Research Institute, 300 College Park, Dayton, OH 45469-0168, USA;(3) University of Dayton, 300 College Park, Dayton, OH 45469-0243, USA |
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Abstract: | A leading reason for the limited use of laminated composite materials in primary structural applications is that the failure
initiates in the ply oriented transverse to the direction of the applied load at a much lower strain level than that which
would cause the ultimate failure of the laminate. Previous studies indicate that transverse failure is manifested as either
cavitation-induced failure of the matrix system or fiber-matrix debonding. The mechanism causing the failure initiation event
is not decidedly known and depends on the local stress field of the constrained matrix that is a function of fiber spacing.
In the present study a model composite system using a transparent matrix is employed in a cruciform-shaped specimen to evaluate
the viability of several transverse failure theories. The cruciform-shaped specimen utilizes a low strain-to-failure 828/D230
RT cured epoxy and stainless steel wires arranged such that a fiber is placed at the intersection of face diagonals of four
remaining fibers located at corners of a square. The transverse failure mechanism is observed in-situ via the reflected light
method and recorded utilizing high resolution, high magnification microscope cameras. A parametric study is conducted using
three dimensional finite element models to analyze the stress state in the cruciform specimen as a function of fiber spacing.
The result of the 3-D FE models in conjunction with experimental observations are used to evaluate the transverse failure
theories suggested in the literature. In addition this data will be used to develop a comprehensive failure criterion for
transversely loaded multi-fiber composites that encompasses the dependence on fiber spacing. |
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Keywords: | Cruciform specimen Cavitation Fiber-matrix debonds Transverse failure |
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