Hasbullah Nawir

A comprehensive characterization of a linear deformation sensor for applications in triaxial compression tests

A linear deformation transducer (LDT), which will be applied to triaxial tests for determining deformation behavior of soils, was designed. It, which is made from a thin and flexible steel strip and a strain gage (KFG-5-120-C1-16L1M2R) bonded on the strip using an adhesive, was characterized systematically. Soil deformation was simulated by applying a certain force to the steel strip. The deformed steel strip was converted into a resistance by the strain gage. A full Wheatstone bridge was used to change the resistance into a small analog voltage. The small analog voltage was then amplified by an instrumentation amplifier. This analog voltage was finally processed by a digital data acquisition system consisting of a 12-bit analog to digital converter (ADC) and a microcontroller. It was found that the Wheatstone bridge output voltage obtained by applying a positive change in deformation (the present deformation is bigger than the previous one) is the same as that achieved by its negative change. When an input voltage was supplied to the bridge, the strain gage resistance reduces slightly with the maximum reduction about 1 ohm, from its static resistance of 119.6±0.4 ohm, depending on the force applied to the steel strip and the input voltage supplied to the bridge. For achieving the maximum deformation of 15 mm, the instrumentation amplifier used the supply voltage of 12 V and the gain resistor of 240±1% to get an amplification or gain of 204.8.

Color Image processing for measuring length deformation in compression test

An image processing method was used to measure sample deformation during a compression test. The images were first calibrated from pixels to millimeters using a ruler which was included in the scene. Analyzing is done by discriminating objects by their colors. The results showed a good agreement with the actual values measured by a compression test instrument with errors up to 0.058 cm.

A Simple Unconsolidated Undrained Triaxial Compression Test Emulator

An unconsolidated undrained (UU) test is one type of triaxial compression tests based on the nature of loading and drainage conditions. In order to imitate the UU triaxial compression tests, a UU triaxial emulator with a graphical user interface (GUI) was developed. It has 5 deformation sensors (4 radial deformations and one vertical deformation) and one axial pressure sensor. In addition, other inputs of the emulator are the cell pressure, the height of sample, and the diameter of sample, which are provided by the user. The emulator also facilitates the analysis and storage of measurement data. Deformation data fed to the emulator were obtained from real measurements [H. Nawir, Viscous effects on yielding characteristics of sand in triaxial compression, Dissertation, Civil Eng. Dept., The University of Tokyo, 2002]. Using the measurement data, the stress vs radial strain, stress vs vertical strain, and Mohr-Coulomb circle curves were obtained and displayed by the emulator.

A simple and inexpensive vertical deformation measurement system for soil compression tests

A simple and low cost system to measure vertical deformations during soil compression tests was successfully developed. It consisted of a vertical deformation sensor, a signal conditioner, an analog to digital converter (ADC), a microcontroller, and a display. The vertical deformation sensor was made from a rotary potentiometer. The deformation was converted to an analog voltage output by the rotary potentiometer. A signal conditioner was required to make the analog voltage output ready for being used by the ADC. The ADC then converts the analog voltage output into digital one. The digital data was later processed by the microcontroller and finally readout by the display. The resolution of the developed system was about 0.038 mm. The calibration was done by comparing the vertical deformations obtained from the potentiometer with those measured by a micrometer. It was found that the developed system can measure a maximum vertical deformation of about 40 mm.