This work aims to analyse the response under crashworthiness impact of an automotive crash box composite consisting on short glass fibres that are embedded within graphene reinforced polymer composite. Analytical as well as finite element techniques are employed to derive the overall composite response and mechanical characterisation for a macroscopic structural crashworthiness application. Graphene sheets are considered as platelets GPL embedded within an elasto plastic polymer matrix phase leading to a 2-phases graphene/polymer composite. The modelling of 3-phases short glass fibres/graphene polymer composite consists on a double-scale approach combining the 2-phases graphene polymer composite as matrix phase in which are embedded the glass fibres. The full structure crash box is simulated at each Gauss integration point by implementing the constitutive 3-phases composite using a user-defined materials subroutine.