Estudio del comportamiento de la fibra de carbono mediante ensayos de compresión tras impacto

Abstract

[EN] Impact performance is a particularly important factor in the design of components made of laminated composite materials. These impacts can create damages which may involve in indentations, matrix crackings and delaminations possibly causing a material failure. Even when no sign of impact damage is observed at the surface, interlaminar breakages can occur. In order to quantify such mechanical complexity, the proper realization of standard test methods to determine the damage resistance of multidirectional polymer matrix composite samples is mandatory. For this reason, the aim of this project was to propose improvements in the experiments carried out at the Leichtbaulabor of the HAW Hamburg required, at a laboratory scale, to better measure the impact damage in carbon fiber reinforced plastic (CFRP) sample plates. Hence, in order to determine the best criteria and workings conditions for measuring the damage resistance of CFRP samples, the applicable industrial standards (DIN 65561 / AITM 1-0010 / D7136 / D7136M) and the results of previous studies were taken into account. The production of the CFRP sample plates (according to the selected conditions), along with the adjustments and improvements of the equipments were necessary to redefine the experiments. All this was done to fulfil, to the maximum possible extent, the standards´ requirements with the materials available at the laboratory where this study was carried out. In this line, the modification (impact mass and support frame) of the pendulum impact test available permitted the amelioration of the damage conditions of the CFRP sample plates in comparison to previous experiences. In the present study, Prepreg EP137-CR527 was used for the composition of the samples. Three different thicknesses (2.31, 3.05 and 3.79 mm) were considered with the aim of covering a wide spectrum to include the standards specifications. Optical and ultrasonic devices were used to analyse the behaviour of the damages in the inner and outer layers of the specimens. A potentiometer and multimeter was introduced for the first time to improve the data acquisition and measure the angle and angular speed of the pendulum. As a result, an accurate calculation of the impact energy (kinetic and potential) could be obtained and therefore it was possible to determine the effectiveness of the changes added to the pendulum test bench. As a result of the newly introduced improvements, the samples could be properly damaged with a single impact, regardless of their thickness, which was one of the main goals to achieve for the realization of this study. However, a compression after impact test showed, that only the 2.31 and 3.05 mm thick plates could be correctly damaged. The findings of this research will be helpful to further ameliorate the procedures in the line of work of impact damage in CFRP in the “Leichtbaulabor” of the HAW Hamburg. As a future approach, attempts should be, for instance, to avoid the formation of air bubbles during the production CFRP laminates and to improve the placement of the additional masses in the pendulum test bench.