This work investigated the mechanical properties of glass/epoxy laminates reinforced by kaolin powder with graded properties by performing tensile, 3-point bending, impact tests, and compression after impact (CAI) tests. Firstly, we evaluated the effects of mixing parameters on particle dispersion and the effect of kaolin powder rate on the epoxy properties. It was found that the optimal parameters for a good distribution are a temperature of 60°C with 10 min of stirring time and the optimum kaolin powder rate is 5 wt %. Secondly, four graded heterogeneous laminates were elaborated with increased powder rate at each 1, 2, 3, and 4 layers named models 1/1, 2/2, 3/3, and 4/4, respectively. The test results showed that the powder gradient distribution considerably influences the behavior of the composite, with a significant improvement in mechanical properties compared to unreinforced glass/epoxy laminates. The model 1/1 on the top side exhibits the most significant increase in flexural modulus and maximum flexural strength, respectively, compared to the unfilled specimen. The impact tests showed that the powder distribution gradient is essential in absorbing the leading force and energy. The model 1/1 on the top side showed the best impact strength. According to this previous finding, adding ceramic particles in a polymer matrix; with a particular gradient distribution; significantly enhances the composite laminates' properties, especially under bending load. This heterogeneous composite type finds its application in closed structures where the load side is known, such as tanks and aircraft wings, and will allow a considerable weight gain.

In this study, the strain rate sensitivity of a discontinuous short fiber reinforced composite and the strain rate effect on the damage evolution are investigated. The studied material is a polymeric composite with a polyamide 6.6 matrix reinforced with oriented randomly short glass fibers at a 50% weigh ratio (PA6.6GF50). Tensile tests at low and high strain rate are conducted. In addition, interrupted tensile tests are carried out to quantify the damage at specific stress levels and strain rates. To perform the interrupted tensile tests, an intermediate fixture is realized via double notched mechanical fuses with different widths designed to break at suitable stress levels. The damage is estimated by the fraction of debonded fibers and matrix fractures. Based on the experimental observations, it is concluded that the ultimate stress and strain, and the damage threshold are mainly governed by the strain rate. Furthermore, it is established that the considered composite has a non-linear dynamic behavior with a viscous damage nature.

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