Miniature load cell instrumentation for finite deformation biaxial testing of elastomers

Accuracy of biaxial-test equipment to examine the nonlinear mechanical behavior of thin-sheet specimens of elastomeric materials has been hampered by lack of precise determination of the force distribution along the sides of the specimen. It has been necessary to use an effective width established by approximate means to obtain the stress from the overall force applied along the edges. To avoid this experimental difficulty, individual miniature proof-ring load cells utilizing semiconductor strain gages have been designed and applied to the support hooks for the thin-sheet specimens. Typical results are shown for time-dependent stress distributions for all degrees of biaxiality. An accurate evaluation of the effective specimen width is now possible, a fact which offers improvement in both accuracy and economy for future testing.