On the axial propagation of kink bands in fiber composites : Part i experiments |
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Affiliation: | 1. Department of Mechanical Engineering, Aeronautics Institute of Technology – ITA, Praça Marechal Eduardo Gomes 50, São José dos Campos 12228-900, SP, Brazil;2. Department of Aeronautics, Aeronautics Institute of Technology – ITA, Praça Marechal Eduardo Gomes 50, São José dos Campos 12228-900, SP, Brazil;3. Institute of Science and Technology, Federal University of São Paulo – UNIFESP, Rua Talim 330, São José dos Campos 12231-280, SP, Brazil |
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Abstract: | In many fiber composites, longitudinal compressive failure leads to the formation of kink bands. It has been found that these kink bands, once formed, can be made to propagate (broaden) in a steady-state manner at a constant stress level called the propagation stress (σP) . This is a characteristic stress of the material which, for the AS4⧹PEEK composite used in the study reported here, is approximately 40% of its compressive strength. This phenomenon is investigated experimentally using a special confining set-up that allows direct observation of the propagation process. For the composite studied, the kink bands have a repeatable inclination (β) of approximately 15°, and the fibers within the bands are rotated to about 30° in the absence of a load. When loaded to σP, however, they are found to rotate further to 40°, that is, substantially greater than the 2β reported elsewhere. The mechanism of propagation is found to be a bend-break-rotate sequence undergone by short segments of fibers at the edge of the kink band. It is well known that polymeric matrix composites such as the one used in this study exhibit rate-dependent behavior. Experimental results are presented which show that the kink band propagation stress is also rate dependent. |
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