METHOD FOR DETERMINING THE MIXED COEFFICIENT OF TSAI-WU FAILURE CRITERION FOR LONG FIBRE COMPOSITE MATERIALS

摘要

The invention relates to a method for determining the mixed coefficient Fof the Tsai-Wu failure criterion used for characterizing long fiber reinforced composite materials, for the plane state, said criterion defining a failure surface within the three-dimensional space of the components ( &sgr;, &sgr;, and &sgr;) of stress tensor which represents the normal stresses oriented along the direction of the fibres ( &sgr;), perpendicular on the fibres ( &sgr;) and the shear stress ( &sgr;) which are in a relation : F&sgr;+ F&sgr;+ F&sgr;+ 2 F&sgr;&sgr;+ F&sgr;+F&sgr;= 1. According to the invention, the method consists in the experimental determination on plane specimens of the mixed coefficient Fby creating a controlled biaxial state of stress which increases progressively up to the specimen failure by performing a tensile test upon the specimen according to the direction Θfor annulling the shear and elongation effects, the corresponding point P within the stress tensor space will have the coordinates Q cosΘ, QsinΘ, 0 where Q represents the ultimate failure value and by noting with c = cos Θand with s = sin Θand by imposing on the coordinates of point P the condition to verify the equation of failure surface, there is determined the final form of the expression of the mixed coefficient F=( 1/2csQ)(1 - FcQ - FsQ - FcQ- FsQ+ FscQ).