A reusable biaxial strain transducer

This paper describles a transducer which is, in effect, a reusable strain-gage rosette. The sensitive member of the instrument is a flat element shaped in the form of a hollow equilateral triangle. At the corners of the triangle are styli mounted perpendicular to the plane of the triangular element. On each side of each arm, an electric-resistance strain gage is centrally mounted parallel to the edges of the arm. The two gages on an arm form a temperature-compensated pair. In operation, the styli are pressed into the test surface, and subsequent straining of the surface induces bending and twisting strains in the arms of the element. The bending strain in an arm is detected by the strain gages mounted thereon and is proportional to the strain in the test surface in the direction parallel to the arm. The bending strain in a particular arm is unaffected by the forces in the other two arms. The theory of the transducer is discussed and experimental evidence which supports the theory is provided.