The main purpose of the present investigation was to determine the damages generated by the low velocities with the help of the experimental method (Impact by a drop test) and the finite element method. The commercial transient finite element package LS-dyna used to model the effect of slug impactor and circular notch induced damage in composite material IntroductionThe fibrous composites are being increasingly used in load bearing structures due to number of advantages over conventional materials: high specific strength and stiffness, good fatigue performance and corrosion resistance. A serious obstacle to more widespread use is their sensitivity to impact and static loads in the thickness direction. As composites have demonstrated to be very venerable to out of plane impact, which cause barely visible impact damage (BVID) reportedly contributes up to 60 % loss in structures' compressive strength and major reason of catastrophic failures. The energy absorbed during impact is mainly dissipated by a combination of matrix damage, fibre fracture and fibre-matrix de-bonding, which leads to significant reductions in the resistance. In ballistic impacts the damage is localized and clearly visible by external inspection, while low velocity impact involves long contact time between impactor and target, which produces global structure deformation with undetected internal damage at points far from the contact region. Low velocity impact is often simulated by simple static indentation-flexure tests, neglecting the influence of dynamic effects. It is also suggested the complete model to take into account the full dynamic behavior of the laminates. Abrate et al. [1] have investigated the delamination of two laminated composite graphite/PEEK and graphite/BMI under low velocity impact. The range number of layers varies from 9 to 95 plies. The obtained result shown a higher delamination threshold load and higher damage resistance. The resulting damage is not normally visible on the specimen surface nor is easily detected and grows rapidly during normal service. The area has been under active research for a quite some time. Some of the relevant articles addressing this issue found in the literature are presented below. The strategy of reducing the stiffness of damaged plies to a certain fraction without considering the degree of damage was used by some investigators [2,3]. Other researchers applied damage theory of continuum mechanics to address the internal damage. They initiated the stress-strain relation for the actual damaged by introducing a fourth-order damage operator to transform the compliance matrix according to the damage states. Based on this work, several investigations

This work deals with the application of the genetic algorithm to the determination of optimal safety factor of layered structure subjected to low velocity impact damage. These genetic algorithms are optimization algorithms based on the techniques derived from genetics and the natural evolution; crossovers, mutations, selection. The numerical modeling was carried out by the finite element software LS dyna which is coupled to the optimization program Ls-optui. The aim of this work is to minimize the safety factor based on the Tsai-Wu criterion for laminate.The optimization is held by evaluating the maximal energy that can undergo the material for a minimum safety factor. In this case a composite laminate of stacking [0/30/45/60/90/45]s with a circular notch drilled at defined location, then a laminate was targeted at the center by four impactors (cylinder, hemispherical, ball and truncated cone). The optimization was held in two phases; first without taking account the function of delamination and in the second phase with the function of delamination.

The main purpose of the present investigation was to determine the damages generated by the low velocity impact by mean of the finite element method. The commercial transient finite element package LS-dyna used to model the effect of slug impactor induced damage in composite material subjected to low velocity impact. Four types of weaving were considered; serge (2/2), serge (0/30/-30/0), serge (0/45-45/0) and taffeta. The Texgen package was used to build the laminate pattern weaves. The composite material was subjected to stainless steel slug impactor in the transverse direction dropping the composite laminate at the center with a velocity about of 15m/s. The analysis was carried out using the model 001-ELASTIC for matrix, 002-ORTHOTROPIC_ELASTIC for fibersand a rigid body model MAT20 for the slug impactor. The contact automatic single surface has been used between the yarns and the automatic_surface_to_surface between the matrix and the impactor and the contact automatic_surface_to_surface_tiebreak between the matrix and yarns and the contact automatic_surface_to_surface_tiebreak between layers.The impact load, energy, displacements were reported as function of impact time. The delamination area was represented at the layer interfaces for each material.