M.Ing. / This thesis demonstrates the measurement of temperature distribution across a metal plate and the non-contact measurement of torsion in a rotating shaft. After a thorough theoretical study of the origin of fibre Bragg gratings, methods of fabrication and erasing of gratings, methods of demodulating the signals from gratings, and methods of discriminating between strain and temperature variations in gratings, simulations and experiments were done to prove the feasibility of both temperature distribution measurement and non-contact torsion measurement. For the measurement of temperature distribution, a 450 x 450 x 1.6 mm type 304 stainless steel plate was used. Two 4,7Ω 25W resistors were used as heat sources, and five fibre Bragg gratings measured the temperature at strategic points on the plate. The measured values were interpolated appropriately and a three-dimensional representation of the temperature distribution was shown on a personal computer monitor. The measurement of torsion was first done on a non-rotating 25 mm diameter solid shaft with torque applied. Both resistive strain gauges and fibre Bragg gratings were attached to the shaft and the measurement results compared well. Up to 90 Nm of torque was applied to the shaft. The non-contact measurement of torsion on a rotating shaft was done with fibre Bragg gratings and involved the use of graded index (GRIN) lenses for transmitting optical information between the light source, the gratings, and back to the spectrum analyser through free space. A special Böhler steel with high yield strength was used, and the set-up was mounted on a lathe. The one end of the shaft was clamped in the lathe chuck, and the other was fixed to an automobile drum brake system, allowing the application of torque on the rotating shaft. Up to 97 Nm of torque was applied to the shaft rotating at 190 rpm, and the results are within 10% of the expected values. As far as we are aware, this is the first time that torsion is measured by fibre Bragg gratings without the need to have physical contact with the shaft, i.e. slip rings, to transmit the information to and from the sensors. The experimental results of this thesis confirm that fibre Bragg grating sensors can be applied usefully in temperature distribution measurement, as well as in the measurement of torsional stress in rotating shafts.

Ordinary chondrites are the most common type of meteorite to fall to Earth and are composed of lithified primitive nebular materials which have experienced variable extents of thermal metamorphism and shock processing. They were subjected to radiogenic heating by incorporation of unstable short lived radionuclides such as 26Al in the early solar system. The relationship between metamorphism and impact processing in ordinary chondrites is not fully understood. An unresolved issue in the study of ordinary chondrites is whether their original parent bodies were fragmented by impacts into rubble-pile bodies while they were still hot, or whether they retained their onion-shell structures until they had shed their radiogenic heat. Heat is lost more quickly due to catastrophic impacts because warm material from the interior is exposed directly to the space environment until the impact debris re-accretes into a rubble-pile body, and is then distributed evenly between the surface and the interior of the new rubble-pile body. The extent of retrograde metamorphism possible in ordinary chondrites would therefore largely be dictated by the extent to which their parent bodies were broken up by impacts. Disaggregation caused by an impact would record fast cooling between the temperature at the time of breakup and the temperature at the time of re-accretion. In this thesis project, five H6 chondrites (Butsura, Estacado, Kernouve, Portales Valley, Queen's Mercy) and five L6 chondrites (Bruderheim, Holbrook, Leedey, Morrow County, Park) were subjected to three different thermometry analyses (pyroxene, olivine spinel, and metallographic) to determine their cooling profiles and evaluate same set of samples. Cooling rates for pyroxene and olivine--spinel thermometry systems are determined using the formulation of Dodson (1973) as modified by Ganguly & Tirone (1999). Cooling rates for the metallographic system are determined using the method developed by Wood (1967) as modified by Willis & Goldstein (1981). At temperatures higher than ~600 degrees C, all samples experienced cooling rates which are orders of magnitude faster (100's to 1000's of degrees C/kyr) than what is predicted for onion--shell thermal evolution (10's of degrees C/Myr) by e.g. Monnereau et al. (2013). At temperatures below ~600 degrees C, i.e. those recorded by the metals, cooling rates are much slower in comparison to the silicate/oxide systems, with the exception of Park, which continued to cool quickly. The discrepancy between high-- and low--temperature cooling rates for both H-- and L--chondrites can best be accounted for by a catastrophic impact which occurred while each body was still near its peak metamorphic temperature, followed by re--accretion into a rubble--pile, which would then cool slowly due to the poor thermal conductivity of rubble--piles. Shock heating does not appear to affect silicate--oxide thermometers.

M.S.

No description available.

Experimental measurements of surface temperatures produced during dry sliding contact were made by using an advanced infrared microscope which receives radiation from a very small target area e.g., 1.78 x 10⁻⁵m in diameter for a 36X objective, allowing temperature measurements within a general region of contact. The sliding system consisted of an Armco iron pin, with a hemispherical end loaded against a rotating sapphire disk. A statistical study was made concerning the effect of environment, load, and velocity on temperature, wear, and coefficient of friction. The formation of iron oxides and its influence on emissivity and possible correlation with wear and friction is discussed. Comparison between the experimental results and the flash temperature theories by both Jaeger and Archard is made. / Master of Science

Call number: LD2668 .T4 1979 L64 / Master of Science

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2009. / The PBMR has called for research into the possibility of distributed in-core temperature measurement. In this thesis, several methods for distributed temperature measurement in high-pressure, -radiation and -temperature environments have been investigated by means of a literature study. The literature study has revealed FBG temperature sensors as the most feasible solution to the temperature measurement challenge. Various parameters affecting the propagation of light in optical fibres and consequently the FBG reflection profile was researched. The differential equations describing FBG structures were solved and implemented in Matlab in order to simulate WDM of a distributed FBG sensing system. Distributed sensing with apodized FBGs written in sapphire optical fibre show the most promise of becoming a solution to the measurement challenge. However, practical testing of sapphire FBGs exposed to the environment in the PBMR core is required. With this long-term goal in mind, a general test platform for FBG temperature sensors was assembled. A heater controller was built for a specialized fibre heating element capable of controlling the temperature of a single FBG up to 1600 C. Temperature measurement using wavelength division multiplexing of apodized FBGs written in silica optical fibre were demonstrated in the test platform with great success. The measured results corresponded very well with the theory. Finally, the implementation of FBGs in the PBMR is discussed and recommendations are made for future work

Several different laser remote sensing techniques related to the detection of trace chemical species were studied. In particular, a Differential-Absorption lidar (DIAL), a Laser-Induced-Breakdown Spectroscopy (LIBS) lidar, and a Raman lidar were studied. Several of the laser spectroscopic techniques that were used were common throughout these different studies. More precisely, 10.6 μm CO2 laser related spectroscopy was common for the DIAL and LIBS studies, and 266 nm Nd:YAG laser related spectroscopy was used for the LIBS and Raman studies. In the first system studied a tunable CO2 DIAL system was developed for the first time to our knowledge for the potential detection of the explosive Triacetone Triperoxide (TATP) gas clouds. The system has been used to measure gas samples of SF6, and has shown initial absorption measurements of samples of TATP contained within an enclosed optical absorption cell. DIAL/Lidar returns from a remote retroreflector target array were used for the DIAL measurements after passage through a laboratory cell containing the TATP gas. DIAL measured concentrations agreed well with those obtained using a calibrated Ion Mobility Spectrometer. DIAL detection sensitivity of the TATP gas concentration in the cell was about 0.5 ng/μl for a 0.3 m path-length. However, the concentration of TATP was found to be unstable over long periods of time possibly due to re-absorption and crystallization of the TATP vapors on the absorption cell windows. A heated cell partially mitigated these effects. In the second set of studies, a Deep UV LIBS system was developed and studied for the remote detection of solid targets, and potentially chemical, biological, and explosive substances. A 4th harmonic Q-Switched Nd:YAG laser operating at 266 nm was used for excitation of the LIBS plasma at standoff ranges up to 50 m . The LIBS plasma emission covering the range of 240 – 800 nm was enhanced by use of a nearly simultaneous 10.6 μm CO2 laser that increased the LIBS plasma emission by several orders of magnitude. The emission spectrum was used to detect and identify the species of interest. Plasma temperatures on various solid substrates were measured. An increase in the plasma temperature of about 5000 K was measured and analyzed, for the first to our knowledge, due to the addition of the CO2 laser pulse to the LIBS plasma generated by the Nd:YAG laser. An optimum temporal overlap of the two laser pulses was found to be important for the enhancement. Finally, in a third related lidar system, initial 266 nm Raman lidar studies were conducted at detection ranges of 15 m. However, significant spectroscopic background interferences were observed at these wavelengths and additional optical filtering is required.

Digital Image Correlation (DIC) is a technique which uses images taken before and after deformation to determine displacement and strain data over the surface of the sample. In order to obtain this data for both in-plane as well as out-of-plane direction, multiple views of the sample are required. Typically, this is accomplished using multiple cameras, but it is possible to use diffraction gratings to bend the light coming from the specimen in order to allow a single camera to capture multiple views. This technique is referred to as Diffraction Assisted Image Correlation (DAIC) and has been previously demonstrated at room temperature. This work expands this method for use at high temperatures by incorporating the use of ultraviolet (UV) lights for illumination and filtering out the light in the visible spectrum. This increases the temperature at which useful images can be captured by reducing the glow that specimens produce at elevated temperatures. When not filtered out, this glow saturates the camera sensor making DIC impossible. This new technique is referred to as Ultraviolet Diffraction Assisted Image Correlation (UV-DAIC).

Abstract not available