A 6-ring embedded strain sensor

Abstract

The proposed embedded strain sensor consists of six elastic rings, placed in an icosahedral symmetry, whose measured elongations give access to the complete 3D strain tensor in the surrounding matrix. The linear relationship between the ring elongations and the strain tensor in the matrix is given. From this relation it is deduced that the tensor is isotropic, i.e. its sensitivity is independent of the rotation of the strain tensor and that the sensor is more sensitive to hydrostatic strains than to deviatoric strains. The additional perturbation of the strain field in the matrix, induced by the presence of the sensor, is studied by means of a numerical integration of the Kelvin solution and the use two dimensionless factors relating to geometry and elasticity. From this study we obtain, in a generic way, an evaluation of the intensity of this additional strain field and the value of the measurement bias due to the elasticity of the ring, which allows in practice to reduce this bias. A draft of the realisation is proposed, for which it is verified that the disturbance of the strain field in the matrix as well as the bias to be corrected are small.