A model of the plastic behaviour of polymer-based unidirectional compo
site materials during quasi-static tensile tests is presented. Cases o
f both monotonic and non-monotonic loading are considered. The mechani
cal properties of the unidirectional lamina are supposed to depend on
kinematic parameters, namely the actual shear strain and the extremum
shear strains attained during the loading history. Apart from the usua
l elastic moduli, this model depends on two parameters in the monotoni
c case, plus two parameters to describe the unloading/reloading loops,
and one variable, the maximum shear strain. This model is easy to inc
lude in FEM codes, in incremental non-linear analyses.