Browsing by Author "Cheatham, John B."
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Item An analysis of the performance of clamp-type flowline connectors with tapered hub faces(1983) Hirschberg, Alan J.; Walker, William F.; Paslay, Paul R.; Cheatham, John B.; Douglas, Andrew S.The use of clamp-type connectors with flat hub faces for flaw-line applications results in undesirable separations between the hub faces in the area of the pressure seal. Tapered hub faces are proposed as a design solution to the seal separation problem and a displacement analysis is presented. The axial symmetry of the problem and the symmetry about the radial plane of the hub faces interface are both utilized in the analysis. The equations resulting from the analysis are incorporated into a FORTRAN computer program allowing parametric studies to be conducted easily. The results from these studies provide a basis for the effective design of the tapered hubs. Finite element analyses of a particular clamp-type connector with flat and then tapered hub faces are conducted for the dual purposes of comparison with the thesis analytical solutions for the same design and detailed examination of the stress levels induced under various loading conditions.Item An idealized model of the influence of drill string mechanics on the hole deviation problem(1977) Ho, Cheng-Yo; Cheatham, John B.A simplified theoretical model for the directional drilling tendency of a drill bit in anisotropic rocks is proposed. Deviational forces play a very important role in this model. To analyze the deviational forces a three-dimensional mathematical model of the static deformation of drill strings is presented. The effect of twisting torque on deviational force is studied with this model. The results show that the torque has very little effect on the deviational force in the plane of the gravitational force and a linear but negligible effect on the deviational force in the perpendicular plane. So the effect of torque is ignored and the analysis is reduced to two dimensions. A method is developed using singularly functions to represent the concentrated load in the simplified 2-D analysis of the drill string with stabilizers. Application of this method to the study of the effects of stabilizers and deviational forces produces satisfactory results. Further studies of the three-dimensional rock failure characteristics are needed to complete the theoretical model for directional drilling.Item Anisotropic hardening of an initially isotropic porous limestone(1975) Celle, Cesare Cafferata; Cheatham, John B.The lack of a good description of the behavior of a compacting material that exhibits yield-strength dependence upon hydrostatic pressure, prompted the present study to determine experimentally a yield envelope that would predict the material behavior more accurately. True triaxial tests were performed on Cordova Limestone in order to find detailed information about the stressstrain behavior of this material. From the results of these tests a yield surface was obtained and the experimental data showed normality to be a very good approximation for the actual plastic strains produced by the initial yielding of the material studied. Subsequent yield surfaces were obtained experimentally and it was found that the yield surface displaces in the stress space as hardening takes place. Different tests were performed in order to obtain the shape of the low hydrostatic stress region of the yield envelope. Induced anisotropy due to hardening led to a closing of this yield envelope and a kinematic hardening rule completed the description of the limestone's plastic behavior. The consistency between the predicted and observed stress-strain behavior indicates that the proposed yield envelope model and a kinematic hardening rule correspond to a proper description of the behavior of this limestone.Item Approximation of the plastic behavior of rocks at elevated mean pressures using a bi-linear yield envelope(1980) Gerecci, Gultekin S.; Cheatham, John B.; Wilhoit, James C.; Merwin, John E.In this study, the stress-strain curves of four different rocks are obtained by using true tri-axial test apparatus. First, results using this test apparatus are compared with results using conventional tri-axial test equipment and the dependability is confirmed. Mohr circles, based on the stress-strain curves have been drawn to provide yield envelopes for the rocks tested in this study. The yield envelope is approximated by a bi-linear curve and by extending the wedge indentation theory for this case, the penetration force equation is derived. The calculated values for the penetration force are then compared with the experimental results obtained by previous investigations. The rocks tested are: Danby Marble, Carthage Marble, Ohio Sandstone and Indiana Limestone. These rocks are tested under confining pressures of 25, 5, 75, 1,, 2, and 3, psi.Item Isotropic modeling of transversely isotropic wedge indentation(1977) Marshall, Tom Stanley; Cheatham, John B.The need has become evident for a more thorough understanding of the causes of hole deviation when drilling through stratified formations. The approach to this problem herein is to analyze the forces between the bit teeth and rock and how they might affect horizontal deflection of the drill bit. This study is specifically concerned with methods of modeling the rock and bit tooth interaction so that valid predictions can be made of the actual behavior. The rock and bit tooth interaction is modeled by a vertical wedge indentation into the flat, level surface of an arbitrarily oriented transversely isotropic rigid - perfectly plastic medium. The transversely isotropic wedge is itself modeled by vertical wedge indentation into the flat, inclined surface of an isotropic medium with arbitrary orientation of the direction of maximum slope. An upper bound approximation method for predicting horizontal and vertical loads is developed using fundamental principles of plasticity theory and an experimental study conducted as verification of the method. It is demonstrated herein that the experimental behavior has been satisfactorily predicted by the theoretical analysis and that a limit analysis solution to the isotropic wedge indentation problem has been obtained. An approach to the analysis of the transversely isotropic problem is outlined as a possible introduction to further work on this problem.Item Natural and induced anistropy in rocks under plastic conditions(1981) Allen, Michael Bruce; Cheatham, John B.; Bowen, Ray M.; Merwin, John E.The object of this study was to investigate the effect of anistropy on wedge indentation tests. These tests are used to qualitatively investigate the deviation forces encountered when drilling through an anisotropic medium. The preliminary investigation of anisotropic rocks lead to the study of an elastic - linear hardening limestone, Cordova Cream Limestone, also known as Austin Chalk. A yield condition and hardening rule, which could accurately account for the strain induced anisotropy, were developed. After carefully weighing the advantages and disadvantages of using this rock in wedge indentation tests, it was decided not to proceed further with this material. Instead, Pierre Shale was used, because preliminary tests indicated a high degree of anisotropy. Conventional triaxial tests were performed, in order to establish a yield condition. This yield condition was used in conjunction with four different theories to predict the vertical and horizontal forces encountered in wedge indentation tests. The four theories consisted of an adaptation of R. McLamore's preferred chip analysis, a plane strain slip-line field solution assuming no lip and a perfectly rough wedge, and two limit analysis solutions using the plane strain yield condition; one assumed a perfectly rough wedge while the other assumed the wedge to be frictionless. The slip-line field solution and the limit analysis solutions successfully bounded the vertical force data. The slip-line and limit analysis solutions for the horizontal force very nearly coincided. Although the scatter in the horizontal force data prevented quantitative confirmation of any of the above theories, the general trends, direction of forces and symmetry, were supported. The scatter in the data also did not convincingly confirm or contradict McLamore's theory, although previous observations and experiments do contradict this theory while supporting the plasticity solutions. Additional tests with various wedge and rock orientations were also performed to investigate the effects on the problem. The conclusions that can be made from this study are: (1) That the strength characteristics of Cordova Cream Limestone can be modeled successfully with Ziegler's modification of Prager's hardening rule in the principal stress space. (2) That plasticity theory can successfully predict the forces on a wedge penetrating anisotropic Pierre Shale. The consequences of this study are that the forces on the wedges and therefore on a drill bit are in the up-dip direction when the bedding plane is inclined less than 45°, while the forces are in the down-dip direction for inclinations greater than 45°.Item The use of plasticity theory in predicting the deformational behavior of ice and sand-ice systems(1974) Smith, Leonard L.; Cheatham, John B.Results of triaxial and indentation tests on ice and sand-ice samples are reported. The main parameters studied in the triaxial tests were temperature (-12 to 35°F), confining pressure (atmospheric to 4, psi), and loading rate (2.5 - 25 psi/sec). All of the indentation tests were conducted at atmospheric pressure and at a temperature of about -12°F. Most of the wedge indentation tests were conducted at a constant displacement rate of .12 in/min, which is approximately the same as the initial displacement rate in the triaxial test at 25 psi/sec. Flat punch tests were also performed at both .12 and 1. in/min. Results of theoretical calculations for wedge indentation of ice and sand-ice samples based on results of triaxial tests are compared with experimental results. All experimental results for wedge indentation of ice were bounded by the calculated results for perfectly rough and perfectly smooth wedges; however, the experimental results for the wedge indentation force on sand-ice samples were somewhat higher than the calculated results for a perfectly rough wedge. The experimentally measured force for a flat punch indenting both ice and sand-ice were greater than the calculated yield force. From the comparison of results between experimental and calculated force-displacement-relationship, it appears that plasticity theory is applicable for approximating the force-deformation relationships for both ice and sand-ice samples.