Development And Calibration Of Embedded PZT-based Dynamic Tensile Stress Sensors

Concrete materials are easy to crack under the tensile stresses due to its low tensile strength. It is vital to real-time monitor the tensile stress of concrete structures for determining both the cracks and the stress destribution of concrete under dynamic loading. The traditional way of testing the stress in concrete materials is determined from the strain measurement from strain gauges. However, due to concrete materials behave nonlinearly under strong dynamic loading and the strain rate effect of concrete under impact loading, the calculated stress from the strain measurement using Young’s modulus is not reliable. Moreover, most of the currently available strain measurement is based on strain gauge on the surface of concrete specimens and the real stress distribution inside the concrete specimens is still unknown. It is very necessary to develop a new type stress sensor which can directly measuring the internal stress of concrete structures. Due to the direct and reverse pizeoelectric effect, piezoelectric material is an ideal option for making both actuators and sensors. In recent years, piezoelectric material has been successfully applied in monitoring and detecting the performance of concrete structures.In this paper, piezoelectric ceramics(PZT) are picked to manufacture the dynamic internal tensile stress sensor due to its excellent properties, like low price, easy to cut, wide frequency bands and speedy response.The main contents of this study can be summarized as follows:(1)Based on existing research on internal stress sensor, this study set emphasis on developing dynamic internal tensile stress sensor suitable for concrete structures. Standardise the materials and steps of manufacturing in order to ensure the sensor has the waterproof and insulation property and different sensors share a close sensivity.(2)A self-developed unique large-scale drop hammer test facility has been designed and improved, then calibration tests are carried out for the proposed stress sensors. Results show the output voltage of the developed stress sensor has a linear relationship with the applied tensile force and the sensitivities of different sensors with identical PZT patch sensing element are close.(3)An effective method of applying prestress on the PZT patch was developed. Calibration tests are carried out for the proposed stress sensors with different prestress levels and the influence of prestress on PZT patch is also studied in this paper.(4)Embedded the designed PZT-based sensors in the tensile zone of a reinforced concrete beam, and then applied step impact loading to the beam. It proved that the disigned PZT-based sensors can detect the dynamic tensile stress in the reinforced concrete beam.