An Embedded 3D Strain Tensor Sensor Based on the Eshelby’s Inclusion

A new design for an embedded strain sensor is proposed in this paper. Based on Eshelby’s inclusion model, it may be used to measure the full 3D strain or stress tensor within any solid body. Currently, common embedded strain sensors are only capable of 1D measurements. The spherical shape of our sensor allows the stress or strain that would exist in the structure without the sensor to be calculated with the aid of the Eshelby theorem (in the case of elastic behavior). We used fiber Bragg gratings to measure the deformation of the sphere - other techniques are also available. Experimental testing was performed in two settings. The first test measured the performance of a polymethylmethacrylate prototype under fluid pressure load. In a second test, a steel prototype sensor was embedded in a standardized concrete specimen under axial compression, and was successfully used to measure 3D strain in real conditions.