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THE UNCERTAINTIES DEFORMATION AND STRESS USING THE STRAIN GAUGES
Dokoupil, Pavel ; Vlk, Miloš (referee) ; Koška, Petr (referee) ; Habán, Vladimír (advisor)
The dissertation thesis deals with the determination of uncertainty of strain measurement and the stress using resistance strain gages. You can find two methods to define the uncertainty in the thesis, GUF and MMC, and both are applied for measurements carried out with resistance strain gages. Definition of the measurement uncertainty was set for the strain measured by uniaxial and biaxial strain gages. The uncertainty of the stress was defined for linear strain gages, T Rosettes and Rosettes. There were universal mathematic-technical models defined to measure strain and stress, these models can be used either for standard and special measurements i.e. high-temperature, or for measurements in radiation field. Each part of the strain uncertainty and stress is analyzed from the point of view of a size of uncertainty and a form of probability of the function that strain and stress can adopt. The maximum focus was dedicated to the mistakes influencing measured strain like strain gage properties, installation and operating influences, external influences, time effects and the influence of the measured object. There are two mistakes influencing the stress described and analyzed in the thesis, the mistake of the Young’s modulus of elasticity and the mistake of the Poisson’s ratio. The thesis is conceived as a complex of information related to the measurement uncertainties using the resistance strain gages and methods of defining the measurement uncertainty in a way that the experimenter can apply the gained info and methods in the required measurements. The final chapters give representative examples to define measurement uncertainties for uniaxial and biaxial stress applying GUF and MMC method. The thesis also includes the experiment that compares measured values of strain, stress and measurement uncertainties, using several different types of strain gages at different temperatures, with theoretical calculation of strain and with stress. The experiment was carried out using the displacement sensor that works on an elementary principle of bending load.
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