Volume 20, Issue 2 (June 1997)
Calibration and Use of Grid-Based Tactile Pressure Sensors in Granular Material
A revolutionary technology is introduced enabling the measurement and presentation of normal stress distribution over an area in real time. A flexible, grid-based, tactile pressure sensor allows pressure to be measured in up to 2288 (52 × 44) sensing locations. The overall shape and size of the measured area can vary with sensors up to 427 by 488 mm in size. Pressure ranges are possible up to 172 MPa (25 ksi). The system was originally developed for dental purposes and has been used in other medical and mechanical applications as well.
The implementation of the system is complex due to three factors: (a) the measurements are relative and hence absolute calibration is required; (b) the measurements are carried out simultaneously at a large number of points, and a calibration system calls for the development of “known” conditions at each point; and (c) the novel technology makes use of new principles and materials that can be influenced by loadrate, post-loading effects, creep, and hysteresis in addition to unfamiliar problems like trapped air.
The preliminary examination of the technology for geotechnical applications is introduced through tests with ideal granular material. A calibration system was developed, and the sensors were examined through various loading and unloading rates as well as unchanging pressure conditions. The mean stress measurement depends on the pressure application sequence (stress history) with overall high accuracy compared to existing intruding soil pressure measurement techniques. The ability to examine stress variations over an area in real time is unmatched by any other existing means. The measurements of stresses developed along the front boundary of an interfacial shear device are used for demonstrating the system's application.