Long-term creep and recovery models (master curves) were developed from short-term data using the time temperature superposition principle (TTSP) for kiln-dried southern pine loaded in compression parallel-to-grain and exposed to constant environmental conditions (~70°F, ~9%EMC). Short-term accelerated creep (17 hour) and recovery (35 hour) data were collected for each specimen at a range of temperature (70°F-150°F) and constant moisture condition of 9%. The compressive strain was measured using bonded electrical resistance strain gages. For each specimen, the compliance curves for all the temperature levels were plotted against log-time on the same plot. The curve segments at successively higher temperature levels were shifted along the log-time axis with respect to the curve section at 70°F to construct a master curve for each specimen. The extrapolation of the developed master curves ranged from 0.23 to 6.4 years. The requirement that the shift factors below glass transition temperature follow Arrhenius formulation was satisfied by the empirical shift factors. The activation energy for creep and recovery of kiln-dried southern pine derived from the slope of the plot of horizontal shift factor and the inverse of the absolute temperature was 28 KCal/mole. Creep and recovery master curves were represented by power functions and the nonlinear regression analysis was used to estimate the model parameters. Linear regression models were developed to predict one parameter in creep and recovery models from Young's modulus. The other model parameter showed weak correlations with material properties; therefore, an average value was recommended. The validity of the master curves for predicting creep of wood exposed to normal interior environmental conditions in buildings was tested by conducting long-term (10 month) creep tests in a heated/cooled laboratory environment. The fluctuating test environmental conditions caused geometry changes in the surface of the wood specimens in addition to mechanosorptive creep leading to fluctuating long-term data. Therefore, a good agreement between the master curves and long-term data was not found. Creep behavior of shallow southern pine arches was studied to demonstrate the application of the finite element method, incorporating the long-term curves based on TISP, to predict creep in wood structures. Creep tests were conducted at various load levels applied at ambient environmental conditions for two months. One arch failed (i.e., snapped-through) nine days after the tests began indicating that creep can indeed cause instability failure in shallow structures. It was found that the supports in the arch test fixture deflected elastically; therefore, the arches were modeled as three pin structures with base pin joints supported by zero-length linear elastic springs. However, the elastic analysis results revealed the presence of other factors affecting the experimental response which complicated the modeling procedure. The creep analysis was performed using a finite element model incorporating the developed creep master curves; however, due to the complexity in the creep experimental apparatus, the numerical predictions were not validated experimentally. / Ph. D.

Past efforts at implementing Load Spectrum Generation and Neuber Control have centered around minicomputers and analog circuits. The use of a personal computer to implement the tasks is presented. On implementation of the load Spectrum Generation software, the response of the Materials Testing System was investigated for distortion and attenuation. In particular, the effect of the resolution of the waveform on the test system response was noted. There was negligible attenuation for full scale frequencies of up to 20 Hz. Greater waveform resolution was required at lower frequencies than at higher frequencies. On implementation of the Neuber Control program, the accuracy obtained at the Neuber hyperbolas was noted. Better accuracy was obtained at ramp frequencies below 0.1 Hz. Based on the results obtained after implementing the Load Spectrum Generator program and the Neuber Control program, the performance of the personal computer in controlling fatigue tests is evaluated. Cost effectiveness and versatility favor the use of a personal computer for the control of fatigue tests. / Master of Science

To date there are no long-term creep models or practical methods to investigate the effect of creep on the safety and serviceability of modem wood structures and structural wood composites. Long-term creep models were developed for wood in tension and compression using the Time-Temperature Superposition Principle (TTSP). The principle states that the long-term response of a polymer at lower temperature is equivalent to the short-term response at a higher temperature. Accelerated creep tests were conducted in tension and compression using small clear specimens of Douglas-fir, southern pine and yellow-poplar. The specimens were tested at moisture contents of 6 %, 9 %, and 12 %, and at temperatures between 20°C and 80°C. The strain was measured using bonded strain gages. The individual creep compliance for each temperature was shifted along the log-time axis to obtain a "master" curve that describes the creep response of the specimens. All compliance curves also required vertical shifting. The experimental horizontal shift factors followed the Arrhenius formulation that describes the shift factor relation for polymers in the glassy region. / Master of Science

Ultrasonic velocity and attenuation were both measured on samples containing various degrees of damage due to high temperature creep. These results were compared with parameters associated with creep damage such as strain and cavity formation, in order to better understand the mechanisms of creep in Si/SiC and to determine if ultrasonics can be used in evaluating the severity of damage. The data indicated that both ultrasonic velocity and attenuation are directly related to creep strain and can be used in evaluating creep damage. Ultrasonic velocity was found to be exponentially related to creep strain. Cavity formation was found not to significantly affect either of the measured ultrasonic properties. The results indicated that Si/SiC behaves as a two phase material in that high frequency ultrasound propagates primarily through the silicon carbide phase and not by the silicon phase. / Master of Science

Thesis (Ph. D.)--Electrical and Computer Engineering, Georgia Institute of Technology, 2008. / Committee Chair: Michaels, Jennifer; Committee Member: Habetler, Thomas; Committee Member: Jacobs, Laurence; Committee Member: Michaels, Thomas; Committee Member: Vachtsevanos, George.

Thesis (doctoral)--Helsinki University of Technology, 2004. / Includes bibliographical references (p. 146-154). Also available on the World Wide Web.

Thesis (MTech (Mechanical Engineering))--Cape Peninsula University of Technology, 2017. / Material testing is an important test to researchers in material science fields and other engineering related fields. This is the base for material evaluation prior to the application. This test is used in the engineering field to determine the strength of materials which is an aspect of assigning materials to different functions. The uniaxial tensile testing of material is the most common form of testing the strength of metallic material - usually to investigate whether or not the material is worthy of the intended application. Material testing is normally performed under uncontrolled conditions in most laboratories. Numerous attempts had been previously made in attempt to control the temperature conditions when performing the tensile test on special materials such as shape memory alloys (SMA) and other smart materials. Various methods had been employed to control the temperature during tensile testing, methods such as induction heating, warm liquid baths, etc. The aim of this study was to develop a temperature controlled environment for the Houndsfield tensile testing machine which is found at the Cape Peninsula University of Technology in the Mechanical Engineering Department workshop. This was achieved through designing and manufacturing of a thermally controlled chamber -better known as a furnace. This chamber was tested for the optimal combination of proportional, integral and derivative parameters which were tuned on the proportional integral derivative (PID) controller. Performing the tensile test under controlled thermal conditions will allow the analysis of SMAs and other materials behaviour at different temperatures. With the aid of the manufactured chamber, the superior features of the SMA will be able to be studied. The manufactured thermal chamber which is electrically powered is insulated with a special ceramic refractory material to prevent the heat from escaping the chamber. The PID controller was used to control the temperature and heating elements act as the heat source. The manufactured chamber could withstand the maximum temperature 350oC that it was initially designed for. However, the challenge of having the specimen to be tested fully inside the chamber was overcame by designing specimen connectors that connected the specimen to the tensile testing machine. Tensile tests were conducted on the SMA wire at room temperature and other various controlled temperatures and different behaviours were observed on the stress-strain graphs.

In the thesis lubrication and wear at metal/HDPE contacts was addressed. In particular this type of contact occurs in artificial joint replacements. Wear of HDPE was recognized as a major factor limiting device performance. In the thesis, fully implicit fully coupled numerical approach was developed to simulate lubrication and wear. Approach allows solving stationary and transient problems for rough surfaces in a wide range of parameters. Wear coefficients were estimated from experimental data. Wear particles formed in wear process were investigated. Particles were found to be approximately 100 nm in diameter and spherical in shape. Considering theoretical solutions, it was concluded that debris may play a role of third-body abrasive wear particles. In the summary section, some discussion was provided on the topic of theoretical modeling of friction and wear and recommendations for future research were formulated.

A dissertation submitted to the Faculty of Engineering, University of the Witwatersrand, in fulfilment of the requirements for the degree of Master of Science in Engineering, Johannesburg, 1998 / This research examines fatigue in WC-Co, both under compressive and tensile loading conditions. A new macro-mechanism for compression fatigue crack propagation is put forward, which contradicts existing data on compression fatigue cracks as being self-limiting. Evidence of this macro-mechanism is presented in the form of final crack length versus number of cycles data, and micrographs of the compression fatigue cracks. A finite element study of the stress distribution in the WC-Co microstructure during compression fatigue loading has been developed. This model verifies possible methods of compression fatigue crack initiation. Examination of tensile fatigue and fast: fracture surfaces is used to show that fatigue is a separate mechanism to fast fracture in WC-Co. Characteristic features of the fatigue fracture surface are presented. A possible fatigue crack propagation mechanism is also presented. Finally, fatigue crack growth rate data in the form of the Paris equation is presented for WC-Co grades T6 and G6. / MT2017

The theory of a rigid-perfectly plastic solid when impact loaded was used to relate the dynamic yield strength and MIBANT bend angle of driven steel fasteners. Static yield strength values for pallet nails were found to values (p > 0.0001 be linearly related to the dynamic 2 and R² = 0.950) and hence MIBANT bend angles. Static yield strength values were also related to MIBANT bend angles (p > 0.209 and R² = 0.896) for staples. The Vickers hardness number and carbon content of pallet nails are related to material properties. Vickers hardness number was found to be linearly related to static yield strength(? > 0.0001 and R² = 0.835). Vickers hardness number was also related to and MIBANT bend angle ( P > 0.0001 and R² = 0.845). Carbon content was logarithmically related to static 2 yield strength of hardened nails (P > 0.0001 and R² = C.93) and linearly related to static yield strength of non-hardened nails (P > 0.0001 and R²) Carbon content was related to logarithm of the bend angle of hardened nails (P > 0.0001 and R² = 0.781) and non-hardened nails (P > 0.0081 and R² = 0.486). Problems emanating from the impact test procedure are discussed. Recommendations include utilizing the BRAT tester for impact tests on driven fasteners for wood. / M.S.