Gedvilas R. Determination of fatigue curves parameters and lifetime at low cycle straining for stainless steels: Master thesis of mechanical engineer / research advisor associate professor dr. R. Šniuolis; Šiauliai University, Technological Faculty, Mechanical Engineering Department. – Šiauliai, 2006. - 58 p. Cycle fracture parameters of structural materials at low cycle straining are understood as lifetime or low cycle fatigue curves that are constructed in coordinates or according to the number of loading cycles N. The lifetime of material at low cycle straining in elastic plastic area is expressed by Coffin’s equation. Parameter of Coffin’s equation C markedly differs from the experimental, therefore high errors occur in evaluating lifetime of the material. It is noticed in many works that parameter proposed by Coffin is close to experimental. Parameter m=0,5, proposed by Coffin, is determined according the low cycle fatigue curves in coordinates for structural materials. Parameters of low cycle fatigue curves mp, Cp for stainless steels according to Coffin were specified and parameters me, Ce according to elastic strain at low cycle straining at room and elevated temperature were determined. Analytic dependences of low cycle fatigue curve parameters on modified plasticity (su/sy)y were proposed, lifetime for stainless steels at room and elevated temperature was calculated in this work. Statistical analysis of results of low cycle fatigue fracture parameters and... [to full text]

The purpose of this project was to show the updated procedures and to make additions to the computer program called Tmin designed by E. I. DuPont De Nemours and Company. This program is used as a screening tool for determining the largest of the minimum pipe-wall thicknesses in a piping system. This project involved several additions that will be released in the next version of the Tmin computer program. The first major additions to be implemented are four alternating Stress-to-Number of cycles curves: Aluminum 1100, Aluminum 3003-0, Aluminum 6061-T6, and Nickel 200. In addition, procedures of the ASME for fatigue curve analysis and implementation of fatigue data were investigated. These four stress-to-number of cycles (S-N) fatigue curves were added to Tmin's internal Microsoft Access® database. Next, a 2-D vertical piping span configuration was incorporated. Finally, DuPont required a Microsoft Word® document output of the pipe-wall thickness data including the piping span model information. Other user-friendly additions were included. Since this computer program was to be American Society of Mechanical Engineers (ASME) compliant, a study of the ASME Pressure Vessel and Piping standards and codes was made to determine how pipe-wall thickness calculations were to be processed. The 2-D vertical piping span calculation procedures were investigated. Once the 2-D vertical piping span analysis was complete, the largest pipe-wall thickness value calculated were passed to a Microsoft Word® document. The last implementation is the inclusion of help files. Help file button additions in all input boxes allowed for the user to know exactly what was needed before a data entry was made. / Master of Science