Abstract: This research deals with the problem of theoretical estimation of hybrid effect in tensile experiment of sandwich, interply and intraply hybrid composites, a microstructural parameter--dispersion coefficient((?)) is defined for the description of the dispersion of different kinds of fibres in hybrid composites and it can be used for quantitative comparison of dispersion of fibres in different hybrid composites. The research reveals the quantitative relationship among hybrid effect and hybrid ratio, and the dispersion of low-elongation and highelongation fibres in hybrid effect. An empirical formula is formed to estimate hybrid effect. The estimated values are in good agreement with experimental data.

Key words: hybrid composite, hydrid effect, mechanical properties, mechanical testing.