Browsing by Subject "Metals -- Fatigue"
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Item Evaluation of the effectiveness of API-modified Goodman diagram in sucker rod fatigue analysis(Texas Tech University, 2001-08) Nampoothiri, M. P ParameswaranIn petroleum engineering applications an understanding of the fatigue behavior of metals is of great importance primarily in the selection of sucker rods. Of all the components of the oil-well pumping mechanism, sucker rods have the greatest effect on the action and performance of the whole pumping system. The behavior of the sucker rods in the transfer of forces and loads determines the action of the pump. Their inherent characteristics affect the loads imposed on the surface equipment. For years, the Goodman diagram is the basis of analyzing the endurance (fatigue) life of ferrous material. Goodman published the diagram during the year 1908. An American Petroleum Institute (API) Committee suggested several design factors for Goodman Diagram in order to adapt it specifically to specifically sucker-rod pumping installations. The diagram is known as the API Modified Goodman diagram. The committee had suggested the following revisions to original Goodman Diagram. They are: (1) The apex of the diagram should be set at the tensile strength of the material. (2) The >^-intercept should have a factor of safety of two. (3) The safety factor on the material tensile strength apex should be 1.75. The result was the creation of API Modified Goodman Diagram. The design formula for the allowable stress line is given as: S,={T/4+MSmin)SF…………………………………………………………………………………(1) where Sa = Allowable maximum stress, psi, T= Minimum tensile strength, psi, M= Slope of the allowable stress line = 0.5625, Smin = Minimum stress, measured or calculated, psi, SF = Design Safety Factor. Since this diagram is used for the design of permissible stresses for sucker rod installations, it is imperative that the design engineer understands the loads imposed on the sucker rods; however, conventional polish rod dynamometer analysis does not provide sufficient information regarding down-hole load conditions. Since the rods available today is superior due to the improved manufacturing processes and testing facilities, this thesis is an experimental study the effectiveness and accuracy of the "API Modified Goodman Diagram." Tests conducted at 160% of the stress range as specified in the API Modified Goodman Diagram on 5/8 inch. Grade 'D' sucker rod specimens resulted in the following findings: 1. The Y-intercept of the diagram can be changed to r/2.5 as compared to T/4 given by the API Modified diagram. 2. The slope of the allowable stress line is found to be 0.3 as compared to the 0.5625 given by the Modified Goodman diagram. In effect, the test results indicate that the present API Modified Goodman diagram is conservative and the formula for the allowable stress line could be revised to Sa =(T/2.5+ MSmin)SF………………………………………………………………………(2) where, Sa = Allowable stress, psi, T = Minimum Tensile Strength, psi, M= Slope of the allowable stress line = 0.3, Smin= Minimum Stress, psi, SF= Safety Factor.Item Stress-corrosion fatigue cracking of cold expanded components(Texas Tech University, 2002-05) Kunnavakkamvinjamur, RamkumarFasteners like rivets are widely used for assembling parts in the aircraft industry. The fasteners not only help in easy assembly and dismantling of the parts, but also help in proper distribution of the load applied on the body. However, in order to fasten two parts together, a number of holes have to be drilled on both parts and these holes tend to raise the stress in the region surrounding them. This stress concentration effect of the holes reduces the fatigue life of the part when cyclic load is applied to the part. To offset the stress concentration effect of the holes, a technique called Split Sleeve Cold Expansion has been widely used in the aircraft industry. It induces a compressive residual stress in the fastener hole and the region around it, which retards the growth of fatigue crack and thereby improves the fatigue life of the component. The objective of this thesis work was to analyze the effect of Split Sleeve Cold Expansion on the fatigue life of AI-7075 T6 specimen subjected to corrosion. In order to fully understand the interaction between cold expansion, corrosion and fatigue life, two possible cases were considered. In the first case the specimens were cold expanded first and then corroded to required mass loss level. In the second case the specimen were corroded prior to cold expansion. The specimens were corroded using a galvanic corrosion cell. The specimens were then tested for fatigue strength. The results showed that cold expansion improved the fatigue life of un-corroded and mildly corroded specimen by a factor of 20. However, fatigue life of cold expanded specimens dropped exponentially with corrosion. For severely corroded specimens there was no significant improvement in fatigue life due to cold expansion. The results also showed that for specimens subjected to the same degrees of cold expansion and corrosion, the fatigue life of specimens cold expanded after corrosion was lower than the fatigue life of specimens cold expanded prior to corrosion.