Die mechanischen Eigenschaften von quasi-unidirektionalem gewebeverstärktem Polypropylen bei verschiedenen Lastfällen
In structural applications, laminated composites are generally used in the form of a series of thin unidirectional plies with definite orientation that form cross-plies and quasi-isotropic laminates. As an efficient alternative to unidirectional plies, quasi-unidirectional fabrics, which contain few fibers in weft direction, can improve some properties of the resulting composites such as transverse and shear properties while maintaining high performance in the prominent direction. However, to use the benefits of quasi-UD fabric in structural application, a thorough study of the mechanical behavior of quasi-UD composites is very important.
In this work, the temperature-, and time-dependent mechanical behavior of one particular type of quasi-unidirectional fabric reinforced polypropylene composites were investigated. On the basis of experimental results, it was found that the effects of temperature and strain rate on quasi-UD composites can be explained by the interaction of two main phenomena: the local and global behavior of matrix and the properties at the fiber-matrix interface. In fact, mechanical characteristics of composites, in terms of the overall mechanical behavior, damage initiation and damage kinetic, have been found to depend on loading conditions. In addition, to find the contributors to the nonlinearity in quasi-UD composites under off-axis tensile loading, cyclic loading-unloading tensile tests were introduced. The damage and plasticity master curves depending on loading temperature and strain rate were determined. Based on the results, a temperature- and strain rate-dependent nonlinear constitutive model for quasi-UD composites is built. This type of data consisting of plastic and damage accumulation in composites can help better the understanding of the mechanical behavior of quasi-UD based multiply composites under various loading conditions.