Theses and Dissertations from UMD
Permanent URI for this communityhttp://hdl.handle.net/1903/2
New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
More information is available at Theses and Dissertations at University of Maryland Libraries.
Browse
2 results
Search Results
Item CONCRETE SHRINKAGE PREDICTION USING MATURITY AND ACTIVATION ENERGY(2009) Clarke, Christopher Steven; Goulias, Dimitrios G.; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Shrinkage is a complex material response that often affects concrete in an adverse manner. The characteristics of the natural environment in which concrete is placed and the rate of strength development have been used to model the rate of shrinkage development. Furthermore, concrete maturity has been used to predict the rate of strength development of concrete cured at different temperatures. This study sought to find a correlation between activation energy based concrete maturity and concrete shrinkage. A single concrete mixture was tested to determine the apparent activation energy of the mixture and the shrinkage under varying environmental conditions. A shrinkage model incorporating relative humidity and temperature was developed to predict the shrinkage of the concrete mixture. A relationship between concrete shrinkage and activation energy based maturity was investigated.Item Investigation of Low Temperature Creep Deformation Behavior of a Metastable Beta Titanium-14.8Wt%Vanadium Alloy(2004-07-13) Hudson, Candi Monica; Ankem, Sreeramamurthy; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation presents the results of investigated low temperature creep behavior of a metastable beta phase Ti-14.8Weight%V alloy (Ti-14.8V). It is the first such study which relates the activation energy and microstructure with low temperature creep deformation mechanisms in the temperature range of 298K to 800K. A Ti-14.8V alloy with a grain size of 350 m was tensile and creep tested in the temperature range of 298 - 458 K; creep tests were conducted at 95% of the 0.2% yield stress. Activation energies were determined by utilizing strain rate models and resulting least squared Arrhenius plots, which were found to be in the range of 36.6-112.42 kJ/mole for the measured temperature range of 298 - 458K. The resulting activation energies plotted as a function of strain was found to be linear dependent. The determined activation energy values of 36.6 57.55 kJ/mole at the low end of the strain are within the range of activation energy values for dislocation motion. The higher activation energy value of 112.42 kJ/mole is within range of for activation energy value for diffusion of oxygen in beta titanium alloy. These activation energy values are consistent with SEM and TEM observations of deformation mechanisms as dislocations, slip, and stress induced plates (SIP) in the form of twinning were the dominant creep deformation mechanisms for this alloy. The deformation mechanisms changed from predominantly slip to SIP in the form of twins at the higher test temperatures. Further, these findings are consistent with observations, characterization by TEM analysis identified slip dislocations of the 1/2<111> type and twins of the {332}<113> type, which are consistent with time dependent twinning deformation. The results strongly support the mechanism of oxygen controlled time dependent twinning deformation as proposed earlier.