Browsing by Author "Penny, R K"

Now showing 1 - 6 of 6
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    Creep predictions for turbomachinery components
    (1989) Sieburg, H O; Penny, R K
    Several theories of creep and creep rupture are reviewed. Specific attention is devoted to the brittle damage theory proposed by Kachanov. Creep, damage and life predictions for rectangular or circular cross section beams under bending and tensile loads are presented. Comparison with data for a Ni Superalloy showed life predictions could be 30X in excess of experimental values. This beam model also revealed that it is imperative that no bending moments be inadvertently applied during tensile creep testing. The creep-damage material model is extended to multidimensional situations. A refinement, whereby no damage accumulates in compression, is incorporated. A User-Material subroutine for this constitutive model has been formulated, and incorporated into the ABAQUS FEM package. Several verification examples are presented; one example is the creep-damage behaviour of a notched bar in tension. The value of reference stress techniques is discussed. Reference stress estimates for a centrifugally loaded bar, as well as for a cantilever under distributed loads, are presented. These could be useful in turbine blade design. Bibliography: pages 91-92.
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    Design procedures for high temperature components using finite element methods
    (1993) Hulett, Cameron; Penny, R K
    A procedure for design and redesign of high temperature components is developed. The thesis begins with a description of an engineering problem, namely the failure of a steel plant pre-reduction kiln, which incorporates a number of commonly occurring design problems. A redesign procedure, which follows a more prescriptive rather than a descriptive method, is established for the case study. An investigation of the material properties, loading conditions and component failure is undertaken. Each investigation begins with an overall view of the topic, which is then narrowed to suit the case study. The procedure developed during the investigations begins by using conventional theoretical techniques to determine the material properties and loadings involved. Simple and then more detailed finite element modelling establishes more accurate results for so.me complicated problems. In particular the thermal loading of the kiln is found to be considerably larger than the self weight loading. Failure analysis techniques together with a sophisticated non-destructive testing technique, Holographic Interferometry, are employed to investigate flaws and failure modes. The technique developed enables the qualification and quantification of material properties and flaws for in situ components. The dominant failure mode for the kiln is stress corrosion which can be prevented by avoiding corrosion and lowering the thermal stresses. However the existence of flaws enables fatigue failure to occur. The procedure continues with a life assessment due to fatigue, however in the kiln case study, the validity of this is uncertain due to insufficient test data. Recommendations for redesign are then given. The design procedure enables an ordered and effective means of solving in situ component failure and redesign problems.
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    Dynamic hardness testing challenges conventional tests
    (1993) Kohlhöfer, Walter; Penny, R K
    The design and use of a portable dynamic hardness tester is described. The thesis begins with a description of the more common static hardness tests and the usefulness of such tests in industry. It shows a correlation between the different types of hardness and also between hardness and other material parameters such as tensile strength. A thorough investigation of the principles involved in the indentation processes using conical and spherical indenters under static and dynamic loading is given so that the reasons for the correlations may be more clearly understood. A series of test specimens tested by conventional static hardness tests (Brinell, Vickers and Rockwell) are used as calibration specimens for the dynamic tester. Both a spherical and conical tip are used. The results of these tests are compared and analyzed. The dynamic tester may then be programmed so that it correlates with the results of the static tests. A set of guidelines for the use of such a portable tester is then given.
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    ROPES : an expert system for condition analysis of winder ropes
    (1990) Williamson, Lance K; Penny, R K
    This project was commissioned in order to provide engineers with the necessary knowledge of steel wire winder ropes so that they may make accurate decisions as to when a rope is near the end of its useful life. For this purpose, a knowledge base was compiled from the experience of experts in the field in order to create an expert system to aid the engineer in his task. The EXSYS expert system shell was used to construct a rule-based program which would be run on a personal computer. The program derived in this thesis is named ROPES, and provides information as to the forms of damage that may be present in a rope and the effect of any defects on rope strength and rope life. Advice is given as to the procedures that should be followed when damage is detected as well as the conditions which would necessitate rope discard and the urgency with which the replacement should take place. The expert system program will provide engineers with the necessary expertise and experience to assess, more accurately than at present, the condition of a winder rope. This should lead to longer rope life and improved safety with the associated cost savings. Rope assessment will also be more uniform with changes to policy being able to be implemented quickly and on an ongoing basis as technology and experience improves. The program ROPES, although compiled from expert knowledge, still requires the further input of personal opinions and inferences to some extent. For this reason, the program cannot be assumed infallible and must be used as an aid only.
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    Stochastic structural analysis of engineering components using the finite element method
    (1993) Weber, Marc Anton; Penny, R K
    This thesis investigates probabilistic and stochastic methods for structural analysis which can be integrated into existing, commercially available finite element programs. It develops general probabilistic finite element routines which can be implemented within deterministic finite element programs without requiring major code development. These routines are implemented in the general purpose finite element program ABAQUS through its user element subroutine facility and two probabilistic finite elements are developed: a three-dimensional beam element limited to linear material behaviour and a two-dimensional plane element involving elastic-plastic material behaviour. The plane element incorporates plane strain, plane stress and axisymmetric formulations. The numerical accuracy and robustness of the routines are verified and application of the probabilistic finite element method is illustrated in two case studies, one involving a four-story, two-bay frame structure, the other a reactor pressure vessel nozzle. The probabilistic finite element routines developed in this thesis integrate point estimate methods and mean value first order methods within the same program. Both methods require a systematic sequence involving the perturbation of the random parameters to be evaluated, although the perturbation sequence of the methods differ. It is shown that computer-time saving techniques such as Taylor series and iterative perturbation schemes, developed for mean value based methods, can also be used to solve point estimate method problems. These efficient techniques are limited to linear problems; nonlinear problems must use full perturbation schemes. Finally, it is shown that all these probabilistic methods and perturbation schemes can be integrated within one program and can follow many of the existing deterministic program structures and subroutines. An overall strategy for converting deterministic finite element programs to probabilistic finite element programs is outlined.
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    The study of creep in machine elements using finite element methods
    (1990) Weber, Marc Anton; Penny, R K
    In this thesis a simplified analysis procedure is developed, in which creep laws are decoupled from damage laws, for the purposb of constructing methods of use in the early stages of high temperature design. The procedure is based on the creep and damage laws proposed by Kachanov and Rabotnov. The creep laws are normalised. with respect to a convenient normalising stress. As a consequence of this normalisation, the dependence of the creep law on the stress constant, the time and temperature functions, and the actual load level is removed. In addition, if the reference stress of the component is chosen as the normalising stress, the creep law becomes insensitive to the stress exponent. The non-dimensional creep laws are then implemented in a standard finite element scheme, from which the results of a stationary state creep analysis are then in non-dimensional form. In order to estimate rupture times, the maximum stationary stresses in a component are used together with the damage laws. Conservative failure criteria are derived from the creep and damage laws to extend the method to residual life assessment and damage monitoring. The procedure is illustrated and tested against simple examples and case studies.