Residual state of stress in structural materials affect positively or negatively behaviour of component parts. The goal of this scope is not to deal with possible process of creating residual stresses neither about elimination of residual stress, but is focused how to determine magnitude of residual stress by hole-drilling method. We need to know magnitude and direction (angular orientation) of principal stresses to determine how residual state of stress affects behaviour of specimen. The most widely used modern technique for measuring residual stresses is hole-drilling strain-gage method. Hole-drilling method is in scope of this paper and is restricted only for measuring uniform residual stresses of steel specimens with finite dimensions. Structural, linear, elastic and isotropic material model is used with material properties =0,3 and E=2,1[10]^5 MPa. For correct application of this method we need to determine calibration coefficients “a“ and “b“ first. These coefficients are used to determine magnitude and direction of residual stresses in specific depth and diameter of drilled hole for materials with finite dimensions. Geometry and shape of model is simply represented by block with planar faces. Note that numerical determination of calibration coefficients is useful only for one type of strain gauge rosette RY 61 S. Main goals of this thesis are motivation and request to clearly report effectiveness, accuracy and applicability of calibration coefficients in relation to thickness of specimen, dimensions of drilled hole, condition of “through” or “blind” hole and number of drilled increments. High quality and accuracy of created numerical model is necessary too. Numerical simulation of residual stresses by MKP needs to be done to obtain requested results. All results are presented by 3D, 2D graphs and tables and compared with analytical results or results from other authors. Although is this publication focused on numerical modeling using FEM, hole-drilling method has many significant restrictions. The most substantial of them is influence of eccentricity of drilled hole, creation of stress concentration near drilled area and subsequent plastification, influence of geometrical inaccuracy of hole, etc. All these aspects have significant influence of determining calibration coefficients and can not be included into numerical simulation. These problems are closely discussed in background research. All obtained results should be helpful for practical use of calculated calibration coefficients to determine uniform residual stresses of specimens with various thickness and drilled hole. All these results are also applicable only for one type of strain gauge rosette, which is RY 61 S.

No description available.

An investigation of the microstructure-mechanical property relationships for gray cast iron and a vintage ASTM A7 steel are presented herein. Gray cast iron was shown to have a moderate sensitivity to strain rate and a large disparity in behavior between compression, tension, and torsion. ASTM A7 steel was shown to behave in a more complex manor with the strain rate sensitivity having a negative relationship in tension and positive relationship in compression and torsion, the tensile stress-state producing the highest stress response, and the material producing a higher stress response when exposed to elevated temperatures. The counterintuitive behavior observed in A7 steel was attributed to dynamic strain aging. The Mississippi State University Internal State Variable Plasticity-Damage model was updated to accurately capture negative strain rate sensitivity and DSA embrittlement by developing kinematic, thermodynamic, and kinetic constitutive relationships for dynamic strain aging. A parametric study was performed to elucidate the behavior of the new internal state variable for dynamic strain aging. Gray cast iron was successfully calibrated to a pre-DSA version of the plasticity-damage model and A7 steel was successfully calibrated to the updated plasticity-damage model.

One of the current testing method (the Dry Flow test) to qualify resin for use in production in the rotomolding process has been shown to have many flaws in both equipment and procedure. Research was done here to investigate a possible alternative that could eliminate some of these testing deficiencies. By reducing equipment and operator errors, the testing of materials becomes more valuable of an exercise. The Angular Flow test developed in this research can increase repeatability. By coming to understand the rotational molding process better, an evaluation that can give more valid information was devised.

Submitted by Johnny Rodrigues (johnnyrodrigues@ufcg.edu.br) on 2018-03-23T21:32:45Z No. of bitstreams: 1 JOÃO PAULO DANTAS DE CARVALHO - DISSERTAÇÃO PPGEQ 2015..pdf: 1534561 bytes, checksum: 93959f6eca85fa51565d250b6a984284 (MD5) / Made available in DSpace on 2018-03-23T21:32:45Z (GMT). No. of bitstreams: 1 JOÃO PAULO DANTAS DE CARVALHO - DISSERTAÇÃO PPGEQ 2015..pdf: 1534561 bytes, checksum: 93959f6eca85fa51565d250b6a984284 (MD5) Previous issue date: 2015-11-11 / CNPq / Desde a sua descoberta, em 1864 por Cailletet, a fragilização de metais por hidrogênio, foi sujeito a inúmeras investigações, sendo primeiramente estudado com a injeção de hidrogênio gasoso em metais e ligas. Devanathan e Stachurski (1962) desenvolveram a técnica eletroquímica de permeação de hidrogênio em metais e ligas, tornando o estudo mais prático, esta metodologia se baseia em uma dupla célula eletroquímica dispostas simetricamente onde o metal a ser estudado é inserido entre elas. Uma delas conhecida como célula de carga irá gerar o H2 a ser permeado através do corpo de prova e na outra, conhecida como célula de detecção, o mesmo será oxidado e quantificado seu fluxo. Toda a detecção é realizada potenciostaticamente, mas a geração pode ser realizada por meio galvanostático (método galvanostático-potenciostático), potenciostacamente (método duplo-potenciostático) ou por permeação em circuito aberto em meio ácido, chamado de „PCAA‟. As normas ASTM 148-97 (2003) e ISO 17081 (2004) padronizam os experimentos de permeação eletroquímica de hidrogênio. Como os diferentes métodos são baseados em soluções de contorno diferenciados para solução da segunda lei de Fick, tais normas não levam isto em consideração adotando o cálculo da difusividade do hidrogênio apenas pelo método duplo potenciostático, mesmo para aqueles que estudam o fenômeno, diga-se de passagem, em sua grande maioria, utilizando a metodologia galvanostático-potenciostático. Autores como McBreen et al (1966) e Boes & Zuchner (1972) descrevem o fenômeno de permeação de hidrogênio em metais de forma matemática, a partir da solução da segunda de lei de Fick, estes trabalhos atestam a diferença entre os métodos duplo-potenciostatico e galvanostático-potenciostático, porém nunca foi proposto um modelo que descreva o comportamento do método PCAA. Com isso, o trabalho tem como objetivo elucidar o emprego dos modelos matemáticos para determinação do coeficiente de difusão do hidrogênio em metais através das distintas técnicas eletroquímicas de permeação, utilizando os aços API 5L X70 e X65, além disto procurou-se um modelo matemático para o caso em que a geração de hidrogênio seja realizada pelo método PCAA. Neste trabalho atesta-se que que o uso das equações proposta pela norma, a princípio, subestimam o valor da difusividade. A equação proposta para o método PCAA, apresentou um perfeito ajuste de dados experimentais de permeação. A correlação proposta para o cálculo da difusividade mostrou-se coerente para estimar este parâmetro, não só para o caso PCAA, como também para todos os casos. / Since its discovery in 1864 by Cailletet, hydrogen embrittlement of metals, was subjected to numerous investigations, first being studied with the injection of gaseous hydrogen in metals and alloys. Devanathan and Stachurski (1962) developed the electrochemical technique of hydrogen permeation in metals and alloys, making it the study more practical this methodology is based on a dual symmetrically arranged electrochemical cell where the metal to be studied is inserted between them. One known as load cell will generate H2 to be permeated through the specimen and the other, known as the detection cell, it will be oxidized and its flow quantified. All detection is performed potentiostaticly, but the generation can be performed by galvanostatic (galvanostaticpotentiostatic method), potentiostaticly (double- potentiostatic method), or by hydrogen permeation on acid environment method known as a PCAA. The regulations ASTM 148-97 (2003) and ISO 17081 (2004) standardize the electrochemical hydrogen permeation experiments. How different methods are based on different workarounds for solution of the second Fick's law, such rules do not take this into account by adopting the calculation of the hydrogen diffusivity only by the dual voltage method, even for those who study the phenomenon, say passing for the most part, using the galvanostatic-potentiostatic methodology. Authors such as McBreen et al (1966) and Boes & Züchner (1972) describe the hydrogen permeation phenomenon in mathematical form of metal from the solution of the second Fick law, these works attest to the difference between the double-potentiostatic methods and galvanostatic-potentiostatic, but has never proposed a model that describes the behavior of the PCAA method. Thus, the study aims to elucidate the use of mathematical models to determine the hydrogen diffusion coefficient in metals through the different electrochemical techniques permeation using the API 5L steels X70 and X65, in addition sought a mathematical model for the case where the hydrogen generation is performed by the PCAA method. This work testifies that the use of the equations proposed by the standard at first underestimate the value of diffusivity. The equation proposed for the PCAA method, presented a perfect fit experimental permeation data. The proposed correlations for calculating the diffusivity was found to be consistent to estimate this parameter not only to the case PCAA, but also for all cases.

<p>This dissertation focused on the development of mass spectrometric methodologies, separation techniques, and engineered devices for the optimal analysis of complex mixtures relevant to the energy sector, such as alternative fuels, petroleum-based fuels, crude oils, and processed base oils. Mass spectrometry (MS) has been widely recognized as a powerful tool for the analysis of complex mixtures. In complex energy samples, such as petroleum-based fuels, alternative fuels, and oils, high-resolution MS alone may not be sufficient to elucidate chemical composition information. Separation before MS analysis is often necessary for such highly complex energy samples. For volatile samples, in-line two-dimensional gas chromatography (GC×GC) can be used to separate complex mixtures prior to ionization. This technique allows for a more accurate determination of the compounds in a mixture, by simplifying the mixture into its components prior to ionization, separation based on mass-to-charge ratio (<i>m/z</i>), and detection. A GC×GC coupled to a high-resolution time-of-flight MS was utilized in this research to determine the chemical composition of alternative aviation fuels, a petroleum-based aviation fuel, and alternative aviation fuel candidates and blending components as well as processed base oils.</p> Additionally, as the cutting edge of science and technology evolve, methods and equipment must be updated and adapted for new samples or new sector demands. One such case, explored in this dissertation, was the validation of an updated standardized method, ASTM D2425 2019. This updated standardized method was investigated for a new instrument and new sample type for a quadrupole MS to analyze a renewable aviation fuel. Lastly, the development and evaluation of a miniaturized coreflood device for analyzing candidate chemically enhanced oil recovery (cEOR) formulations of brine, surfactant(s), and polymer(s) was conducted. The miniaturized device was used in the evaluation of two different cEOR formulations to determine if the components of the recovered oil changed.

No description available.

An effective procedure and parameter window was developed for underwater friction stir welding (UWFSW) 304L stainless steel with a PCBN tool. UWFSW produced statistically significant: increases in yield strengths, decreases in percent elongation. The ultimate tensile strength was found to be significantly higher at certain parameters. Although sigma was identified in the UWFSWs, a significant reduction of sigma was found in UWFSWs compared to ambient FSWs. The degree of sensitization in UWFSWs was evaluated using double loop EPR testing and oxalic acid electro-etched metallography. Results were compared to base metal, ambient FSW, and arc welds. Upper and lower sensitization localization bands were identified in the UWFSWs. Although higher sensitization levels were present in UWFSWs compared to the arc weld, ambient FSW, and heat treated base metals, the UWFSWs were found less susceptible to corrosion than arc welds due to the subsurface location of the sensitization bands. A SCC analysis of UWFSWs relative to base metal and arc weldments was performed. U-bends were exposed to two 3.5% NaCl cyclic immersion experiments at 21 °C and 63 °C for 1000 hours each. A tertiary test was conducted in a 25% NaCl boiling solution. The UWFSW u-bends were no more susceptible to SCC than base metal in the cyclic immersion tests. In the boiling NaCl test, the SCC of the UWFSWs showed significant improvement over the SCC of arc welds. Arc u-bends cracked entirely within the weld bead and HAZ, while SCC in the UWFSWs showed no cracking localization.