Micro-mechanical simulations of advanced materials can be employed to better understand the impact of microscopic phenomena on the structural response, to design the material microstructure, or to generate data required to build surrogate macroscopic models, for instance. However, an accurate description of the micro-constituents is required. In the case of carbon-fibre-reinforced composites, recent studies [1,2] revealed that classical elasto-plastic constitutive models are not able to capture the strain fields accurately, especially in regions of the matrix close to the fibres, where excessive strain localisation is predicted. Enriched continua like strain gradient plasticity may be adequate for a better description of the matrix deformation in these regions, as well as to capture the macroscopic strength that is often underestimated with classical models for the matrix. In this contribution, a classical pressure-sensitive elasto-plastic model is re-formulated to comply with a strain-gradient plasticity approach. A systematic analysis of the influence of the additional constitutive parameters is performed, and these are calibrated. Experimental data available from the micro-scale is employed to assess the enhanced model. This project has received funding from the European Union’s Horizon Europe research and innovation programme under grant agreement No. 101056682. REFERENCES [1] J. Chevalier, P. P. Camanho, F. Lani, and T. Pardoen. Multi-scale characterization and modelling of the transverse compression response of unidirectional carbon fiber reinforced epoxy. Compos. Struct., 209:160-176, 2019. [2] N. Klavzer, S. F. Gayot, M. Coulombier, B. Nysten, and T. Pardoen. Nanoscale digital image correlation at elementary fibre/matrix level in polymer–based composites. Compos. Part A Appl. Sci. Manuf., 168:107455, 2023.