Análisis experimental y optimización numérica del efecto del mecanismo iniciador en las capacidades de absorción de energía de estructuras tubulares de material compuesto bajo carga de impacto

Abstract

[EN] This Thesis was conducted in collaboration with the Cranfield Impact Centre. The main aim of the project was to perform an experimental characterisation of how different trigger mechanisms affect the performance of composite tubular energy absorbers and use the results to create and validate an FEA model in order to develop a triggers’ redesign. CFRP tubular samples were manufactured through a hand lay-up process. Three tubes were produced to test bevel triggers at 30º and 60º as well as a tulip trigger with 4 tips at 60º. Samples were tested in a drop tower rig with a mass of 80 kg at 5 m/s. Experimental results proved that 30º chamfer produced higher SAE and lower peak force than chamfer at 60º. Tulip type specimen presented lower SAE results than bevel type but a smooth force response interesting for crashworthiness purposes. A numerical model was created using LS-Dyna. The model was used to explore further the experimentally studied triggers. Bevel triggers at 15º, 30º, 45º and 60º were compared as well as 4 and 6 tips tulips at 60º and 90º. In overall, chamfer tubes performed better in all cases than the tulip tubes. Within these, chamfer at 45º presented the best results with a SAE of 43.6 kJ/kg. Regarding the tulip triggers, it was proved that increasing the tips’ angle is more effective than increasing the number of tips, however it can produce instabilities in the triggers’ crushing. By contrast, tulip models with a higher number of tips showed more stable crushing behaviours. Combining both benefits, the tulip geometry with 6 tips at 90º exhibited the best results for this trigger, with a SAE of 39.4 kJ/kg improving the experimental baseline an 8.8%.

[ES] La activación es un proceso que inicia el fallo y evita la transferencia de carga al conjunto de la estructura a través de la formación de concentradores de tensiones en los bordes del perfil de la geometría, previniendo que las estructuras de material compuesto fallen de manera catastrófica. Una selección adecuada del iniciador ayuda al fallo progresivo de modo que la carga de rotura es la máxima permisible y la carga se sostiene en un nivel considerable debido a diversos mecanismos de fractura como apertura, fragmentación, etc. El principal objetivo de este proyecto es investigar la influencia de diversos mecanismos iniciadores en los modos de fallo progresivo y las capacidades de absorción de energía de estructuras tubulares de materiales compuestos de fibra de carbono para la absorción de energía bajo carga de impacto. Los tubos son ensayados en el Cranfield Impact Centre (CIC) para obtener pulsos de fuerza para su aplicación en estructuras de vehículos. Simulación por elementos finitos y ensayos físicos serán realizados durante el proyecto.