Determination of mechanical properties by nanoindentation in the case of viscous materials A mechanical model based on a generalized Kelvin-Voigt model has been developed to explain and fit the nanoindentation curves realized on three amorphous polymers (PC, PMMA and PS). This model includes the responses of quadratic elastic (spring), viscoelastic (two Kelvin-Voigt elements), plastic (slider) and viscoplastic components (dashpot). It is able to fit nanoindentation curves during loading, unloading and hold time periods. With the values of the model parameters and the value of the contact area calculated with the Oliver and Pharr method, it is possible to calculate the values of the mechanical properties of the polymers. A good agreement is found between these values and those obtained with conventional methods.
The aim of the present study is to investigate the mechanical behavior of carbon/flax hybrid composites under static and fatigue tensile loading. The failure characteristics and parameters used in the fatigue tests were deduced from the static ones. The effect of the applied stress level, hybridization and stacking sequences on the stiffness, hysteresis loops, dissipated energy and damping, were studied for a various number of cycles during fatigue tests. The Wohler S-N curves were constructed to investigate the effect of hybridization on the fatigue behavior. The results obtained show that the fatigue performance as well as the fatigue resistance increase with the increase of the volume fraction of carbon fiber. Nevertheless, the damping ratio and the fatigue life increase with the increase of the flax fiber volume fraction.
This manuscript deals with the effects of recycling on the static and dynamic properties of flax fibers reinforced thermoplastic composites. The corresponding thermoplastic used in this work is Elium resin. It's the first liquid thermoplastic resin that allows the production of recycled composite parts with promising mechanical behavior. It appeared on the resin market in 2014. But until now, no studies were available concerning how it can be recycled and reused. For this study, a thermocompression recycling process was investigated and applied to Elium resin. Flax fiber-reinforced Elium composites were produced using a resin infusion process and were subjected to different thermomechanical recycling operations. For each material, five recycling operations were carried out on the raw material. A total of 10 different materials were investigated and tested by means of tensile and free vibration tests to evaluate the effect of recycling on their behavior. In addition, a finite element model of the dynamic problem was developed to evaluate the loss factor and natural frequencies regarding different cases. The results obtained show that the failure tensile properties of Elium resin as well as flax fiber reinforced composites decrease during recycling operations. Conversely, recycling induces a rise in the elastic modulus. Moreover, improvement in the dynamic stiffness was observed with recycling operations. But repeated recycling appeared to have negligible effects on the loss factor of the recycled materials. The results obtained from the experiment and the numerical analyses were in close agreement.
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