4. Iosipescu Shear Test:

This test was developed by Iosipescu in 1967. The original test was designed for a round specimen with a V-notch groove for shear testing of metals. This was extended to flat composite laminates by Bergner et al. The flat specimen has two identical V notches symmetrically placed about the center line at mid length. When the specimen is loaded in shear, a region of nearly uniform, pure shear stress is present in the test section (between the notches). The actual stress distribution is a function of the material properties and fiber orientation. In general, laminae with  and  orientation are used for this test.

The two bi-axial strain gages, one on each face, in the area between the notches are bonded. The strain gauges should have a gauge length of 1 mm or 2 mm, to keep within the region of uniform stress, and are aligned at  ±45° to the longitudinal axis of the specimen.

The average shear strength is given as

(8.26)

and the average shear modulus is given as

(8.27)

where    is ultimate failure load,  is the distance between the notches,   is the specimen thickness,  is the change in applied load and   and  are the corresponding changes in normal strain in   and  and  strain gages. Again, it should be noted that the shear modulus is obtained as initial slope in some range of strain.

More details on this test can be seen in ASTM D5379.