Abstract: It is proved that the ultimate strength of postbuckling for simply supported rectangular composite thin plates under compression is far higher than their buckling stress through the tests of 283 rectangular composite thin laminates in this paper.The ultimate strength of the composite thin plates is studied using large-deflection theory and small-deflection theory of thin plates.According to the failure criterion of the composites ultimate strength is found finally.It is in accordance with the experimental values,for the plates having 45 degrees off-axial,and for longitudinal and latitudinal plates.when β< 0.11,the theoretical values are higher.The coefficientC given in this paper may be referred to in product designing.

Key words: compression, failure criterion, composites, postbuckling, ultimate strength