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This and the next image are from:
Boisse P, Hamila N, Madeo A (INSA-Lyon, Universitité de Lyon, Villeurbanne, France),
“Modelling the development of defects during composite reinforcements and prepreg forming”, Philos Trans R Soc A Math Phys Eng Sci 374:20150269, 2016 https://doi.org/10.1098/rsta.2015.0269
ABSTRACT: Defects in composite materials are created during manufacture to a large extent. To avoid them as much as possible, it is important that process simulations model the onset and the development of these defects. It is then possible to determine the manufacturing conditions that lead to the absence or to the controlled presence of such defects. Three types of defects that may appear during textile composite reinforcement or prepreg forming are analysed and modelled in the present paper. Wrinkling is one of the most common flaws that occur during textile composite reinforcement forming processes. The influence of the different rigidities of the textile reinforcement is studied. The concept of ‘locking angle’ is questioned. A second type of unusual behavior of fibrous composite reinforcements that can be seen as a flaw during their forming process is the onset of peculiar "transition zones" that are directly related to the bending stiffness of the fibers. The ‘transition zones’ are due to bending stiffness of fibres. The standard continuum mechanics of Cauchy is not sufficient to model these defects. A second gradient approach is presented that allows to account for such unusual behaviors and to master their onset and development during forming process simulations. Finally the large slippages that may occur during a preform forming are discussed and simulated with meso F.E. models used for macroscopic forming.
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