Iosipescu Test (ASTM D 5379)

Following ASTM D 5379 the Iosipescu shear test induces a state of pure shear at the specimen mid-section by applying two counteracting moments. The two opposing sections of the apparatus can be moved in opposite directions. A composite specimen is gripped at the rim of each side and the force is induced via four points. Ninety-degree notches are machined in the specimen and determin the area of failure. The central region is assumed to be in pure shear.

For determining shear strength using Iosipescu, there are some uncertainties in the test results:

  • The method is limited to small deformations only. Large deformations lead to load shift for horizontal fibre orientation.
  • Shear stress decreases at the central region of the specimen (by 20% for longitudinal and by 10% for transversal orientation). There is no homogenious stress distribution in the cross section.
  • The machining of the notch produces varying stress situations in the notch area which makes the specimen fail at different loads.
  • The test applies concentrated forces to the specimen which can cause local crushing on the edges of the specimen.

On the other hand, the Iosipescu method provides an inexpensive and flexible way of testing shear strength. Varying laminate orientations can be tested easily using only one testing method.