The paper presents the results of experimental studies and numerical analyses using the Finite Elements Method for a planar structure subjected to pure shear. The test specimen was made using an Fused Filament Fabrication incremental technique. In order to correctly represent the mechanical properties of the structure, a series of tests were performed to determine the physical constants of the model material used. Due to the perfect physical nature of the numerical model, in contrast to experimental phenomena, a suitable method was employed to induce the post-critical deformations in the analysed structure.