This work contributes to the modelling of manufacturing process of thermoplastic composites. The main aspect of the research is the modelling of possible damages and defects nucleation in thermoplastic composites, which caused by manufacturing temperature cycles. Stress states of thermoplastic matrix material in the case of transversal loading of unidirectional composite are analyzed. Random placement of fibers are imposed into modelling of periodical cells of composites. It is shown for transversal tension loading of unidirectional composite that the most of the matrix material is loaded by biaxial tension. Material model for thermoplastic polymer with taking into account susceptibility to the stress state type is performed. All constants required for stress analysis based on polyetheretherketone (PEEK) thermoplastic material are performed.