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In this work, the effect of a biaxial preload in the behaviour of glass/polyester woven laminate plates subjected to high velocity trans versal impact was studied. For this, an analytic model based on energy considerations that include the presence of an in plane preload was used. The results of the analytic model for the biaxial preload state were compared with those found for a non preload plate, the difference between them being minimal for the pre stressed level reached in the tests (31% of the static UTS). Therefore, numerical simulations were made in order to study the effect of the preload in greater detail; furthermore, experimental tests were conducted, validating the analytic and numerical model. In general, the two methods revealed minimal differences between the values of the ballistic limit and those of the residual velocity.

a b s t r a c t a r t i c l e i n f o Keywords:Composite materials Sandwich Multiplate structure Impact behaviour Aerospace materialsIn this paper the ballistic behaviour of several glass/polyester laminate structures was studied, evaluating the residual velocity of the projectile and the damage area. Three monolithic laminates of different thicknesses and two multiplate laminate structures were analyzed: one of a sandwich type with face sheets of glass/ polyester and a foam core, and another made with the same face sheet, which were separated by a distance equal to the thickness of the core. It was found that laminates of greater thickness show a larger damage area and a greater ballistic limit. The influence of the core on the ballistic limit of multiplate laminate structures is negligible but, nevertheless, the extension of the damage area in the back face sheet is increased.

Damage evolution of notched composite laminates is analysed in this work using a discrete damage model, which estimates matrix damage evolution and fibre failure. The fibre damage is regularized with a Weibull distribution, and a Regula Falsi method has been used to improve numerical convergence. The model is compared and validated with several experimental results taken from the scientific literature, which consider different materials, laminate stacking sequences and specimen geometries. A good correlation has been found for the failure strength and the stress-strain curve of notched and un-notched laminates subjected to in plane loads. The influence of the Weibull modulus on the matrix and fibre damage evolution, and the failure strength, is analysed.

This is a postprint version of the following published document:Iváñez, I.; Moure, M. M.; García-Castillo, S. K.; Sánchez-Sáez, S. (2015). The oblique impact response of composite sandwich plates.