Design of a biaxial extensometer for measuring strains in cruciform specimens

A biaxial extensometer for measuring strains in flat cruciform specimens is presented. This extensometer allows for the use of two displacement or strain transducers to control and measure strains along mutually orthogonal directions in the plane of the specimen. The measurement and control of strains along each direction are completely independent of each other. The resolution and the measurable strain range of the biaxial extensometer depend on the particular displacement transducers employed. Independently adjustable gage lengths are incorporated along the two directions such that different strain ranges can be measured with the same transducer displacement range. The use of the biaxial extensometer with cruciform specimens and other applications, including the possibility for measuring triaxial strains in a plate specimen, are discussed.