The out-of-plane shear response of thick, unidirectional and crossply, AS4/3501-6 and S2 glass/3501-6 laminates was investigated theoretically and experimentally using V-notched beam (Iosipescu) specimens. Strains were monitored in the specimen test sections using conventional strain gages, moiré interferometry and full section strain gages. Crossply laminates exhibited a fairly uniform strain distribution away from the notches, while the unidirectional specimens were characterized by a nonuniform distribution. Measured strains correlated very well with predicted strains from specimen finite element analyses using nonlinear elastic material properties.

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Accurate nonlinear material models must include both material and damage related nonlinearities. Even at the specimen level macromechanical boundary conditions and specimen geometry can significantly affect the measured response. In this study two experimental techniques for determining shear stress strain response are compared and a micromechanical finite element analysis is used to determine the effect of failure theory on predicted nonlinear response.

A point stress criterion based on stress distribution, in conjunction with Hashin's interactive failure criteria for fiber composites, is applied to composite laminates containing throughthickness discontinuities. The point stress criterion assumes that failure occurs when the stress over some distance (characteristic distance) from the discontinuity is equal to or greater than the strength of the material without the discontinuity. The characteristic distance is determined from Vnotched beam specimens cut through the thickness of AS4/3501-6, S2 glass/3501-6, and AS4/PEEK unidirectional laminates. This characteristic distance is then used to estimate the strength of inplane Vnotched beam specimens, transverse flexure specimens, and an AS4/PEEK doublenotched cylinder loaded in axial compression. Good correlation between the predicted and measured strength was obtained for this case. Based on these results, additional investigations with other material systems and more interactive stress states are warranted.