TABLE OF CONTENTS Interlaminar shear strength is a measure of the in situ shear strength of the matrix layer between plies. There is no method available for exact determination of this property. Approximate values of the interlaminar shear strength, or apparent interlaminar shear strength, can be obtained by various tests.
The most commonly used test is the short beam under three-point bending (Fig. 8.30). The beam is machined from a relatively thick (at least 16 plies thick) unidirectional laminate with the fibers in the axial direction and is loaded normally to the plies (in the 3-direction). (ASTM D2344-84.) [5] Some doubts have been raised about the validity of results obtained from thin laminates (less than 16 plies thick) because of local compressive failure near the loaded points. Better results are obtained with thicker (approximately 50-plies thick) laminates. [32], [33] Because of its simplicity, the short beam shear test is used as a quality control (qualification) test of the lamination process and related matrix-dominated properties of the composite.
If the beam is sufficiently short compared with its depth, shear failure will take place at the midplane in the form of delamination. This is true only sufficiently far away from the load and reaction points, where a parabolic shear stress distribution through the thickness can be assumed. A finite element analysis has shown that the shear stress distribution is skewed near...
