The Experts below are selected from a list of 2079 Experts worldwide ranked by ideXlab platform

Toshimichi Fukuoka - One of the best experts on this subject based on the ideXlab platform.

  • Evaluation of Specific Mechanical Behavior of Fine Screw Threads by Finite Element Analysis and Experiments
    Volume 2: Computer Technology and Bolted Joints, 2014
    Co-Authors: Toshimichi Fukuoka, Masataka Nomura, Misato Sasai
    Abstract:

    Fine screw Threads are widely used for the bolted joints under severe running conditions. It is well known that they are effective to prevent Thread loosening due to fine pitch. As for other mechanical characteristics, it has been reported in the previous paper using complex stress functions that the stress concentration at bolt Thread Root is higher than coarse screw Threads and the fatigue strength of Threaded fasteners shows a minimum value for varying pitch. However, the latter is questionable since the calculations were conducted under lots of hypotheses. In this study, stress concentration and stress amplitude along Thread Root are evaluated by three-dimensional finite element analysis, in which numerical models of the bolted joints are constructed so as to accurately represent the effect of Thread helical geometry. It is shown that the stress concentration at Thread Root of fine screw Threads is higher than that of coarse screw Threads, and the maximum stress amplitude is likely to be lower on the contrary. Meanwhile, it is sometimes recognized that clamping forces of fine screw Threads are smaller comparing to those of coarse screw Threads when tightened with same torque. To clarify this contradictory phenomenon, tightening experiments are conducted, and it is found that the difference of the energy needed for tightening screw Threads is found to be the major cause.Copyright © 2014 by ASME

  • Finite Element Analysis of the Cyclic Stress Amplitude of Threaded Fasteners Using Helical Thread Models
    Journal of Pressure Vessel Technology-transactions of The Asme, 2011
    Co-Authors: Toshimichi Fukuoka, Masataka Nomura, Takashi Fuchikami
    Abstract:

    Fatigue failures of bolted joints frequently lead to serious accidents in machines and structures. It is well known that fatigue failure is likely to occur around the first Thread Root of the bolt adjacent to the nut loaded surface and the run-out of bolt Thread. That is because high stress amplitudes are generated there due to alternating external forces. Accordingly, it is significantly important to evaluate the stress amplitudes along the Thread Root in order to rigorously examine the fatigue failure mechanism of bolted joints. In this study, stress amplitude distributions along the Thread helix including the Thread run-out are analyzed by threedimensional finite element analysis. The numerical models of the bolted joints are constructed so as to accurately represent the effect of Thread helical geometry, using the modeling scheme proposed in the previous study which analyzed the stress concentrations at the Thread Root. The analytical objectives are bolted joints with axisymmetric geometry except for the helicalshaped Threaded portions that are subjected to axisymmetric external forces. It has been substantiated, based on the stress amplitude distributions along the Thread helix, which the fatigue failures are likely to originate from the first bolt Thread, as in the case of the maximum stress, and the run-out of Threads. It has also been shown that a bolt with reduced diameter is effective for the purpose of lowering the stress amplitude at the first Thread Root of bolt. [DOI: 10.1115/1.4004559]

  • Analysis of the Tightening Process and the Cyclic Stress Amplitude of Studs and Tap Bolts
    Volume 2: Computer Technology and Bolted Joints, 2011
    Co-Authors: Toshimichi Fukuoka, Masataka Nomura, Yosuke Takeda, Uichiro Mori
    Abstract:

    When subjected to alternating external forces, a fatigue failure of bolted joint is most likely to occur around the first bolt Thread for the case of bolt-nut connections. It has been substantiated in the previous paper by three-dimensional finite element analysis, in which the numerical models of bolted joints are constructed so as to accurately take account of the effect of Thread helical geometry. In the cases of bolted joints clamped by studs and tap bolts, however, fatigue failures sometimes occur at other than the first bolt Thread and frequently initiate around the far end female Threads. In this paper, using the FE models with correct helical Thread geometry, stress amplitude distributions along the Thread Root including the Thread run-out are evaluated for both male and female Threads. It is shown that the maximum stress amplitude in the male Threads occurs at the Thread Root slight away from the first Thread and the maximum value in the female Threads is generated near the far end of the engaged Threads. Also shown is the contact pressure distribution pattern at the interface between the plate and the block, which is inherent to the bolted joints clamped by studs and tap bolts and may be the major source of the specific stress amplitude distributions.© 2011 ASME

  • Finite Element Analysis of the Fatigue Strength of Threaded Fasteners Using Helical Thread Models
    Volume 3: Design and Analysis, 2009
    Co-Authors: Toshimichi Fukuoka, Masataka Nomura, Takashi Fuchikami
    Abstract:

    Fatigue failures of bolted joints frequently lead to serious accidents of machines and structures. It is well known that fatigue failure is likely to occur around the first Thread Root of bolt adjacent to the nut loaded surface and the run-out of bolt Thread. That is because high stress amplitudes are generated there due to alternating external forces. Accordingly, it is significantly important to evaluate the stress amplitudes along the Thread Root in order to better define the fatigue failure mechanism of bolted joints. In this study, stress amplitude distributions along the Thread helix including the Thread run-out are analyzed by three-dimensional finite element analysis, where the numerical models of bolted joints are constructed so as to accurately take account of the effect of Thread helical geometry, using the modeling scheme proposed in the previous paper. The analytical objectives are bolted joints with axi-symmetric geometry except for the helical-shaped Threaded portions, and are subjected to axi-symmetric external forces. It has been substantiated, based on the stress amplitude distributions along the Thread helix, that the fatigue failures are likely to originate from the first bolt Thread, as in the case of the maximum stress, and the run-out of Threads. Also shown is that the fatigue failure location varies depending on the distance between the target bolt and the loading position and whether or not there is a separation at the plate interface.Copyright © 2009 by ASME

  • Proposition of Helical Thread Modeling With Accurate Geometry and Finite Element Analysis
    Journal of Pressure Vessel Technology-transactions of The Asme, 2008
    Co-Authors: Toshimichi Fukuoka, Masataka Nomura
    Abstract:

    Distinctive mechanical behavior of bolted joints is caused by the helical shape of Thread geometry. Recently, a number of papers have been published to elucidate the strength or loosening phenomena of bolted joints using three-dimensional finite element analysis. In most cases, mesh generations of the bolted joints are implemented with the help of commercial software. The mesh patterns so obtained are, therefore, not necessarily adequate for analyzing the stress concentration and contact pressure distributions, which are the primary concerns when designing bolted joints. In this paper, an effective mesh generation scheme is proposed, which can provide helical Thread models with accurate geometry to analyze specific characteristics of stress concentrations and contact pressure distributions caused by the helical Thread geometry. Using the finite element (FE) models with accurate Thread geometry, it is shown how the Thread Root stress and contact pressure vary along the helix and at the nut loaded surface in the circumferential direction and why the second peak appears in the distribution of Mises stress at Thread Root. The maximum stress occurs at the bolt Thread Root located half a pitch from nut loaded surface, and the axial load along engaged Threads shows a different distribution pattern from those obtained by axisymmetric FE analysis and elastic theory. It is found that the second peak of Mises stress around the top face of nut is due to the distinctive distribution pattern of σ z .

A G Callagy - One of the best experts on this subject based on the ideXlab platform.

  • MALFUNCTIONS OF A STEAM TURBINE MECHANICAL CONTROL SYSTEM
    Failure Analysis Case Studies II, 2001
    Co-Authors: J.h. Bulloch, A G Callagy
    Abstract:

    This paper is aimed at elucidating the cause of a series of malfunctions involving the bending or breaking of main steam turbine throttle valve spindles which occurred at service times ranging from hundreds to several thousand hours in a number of 270 MW steam raising units. It was clearly established, by two distinct approaches (one engineering, one micromechanistic) that the stresses which produced these malfunctions were bending in nature and were the result of out-of-alignment deflections. In the case of the bent spindles the stresses were very high and approached flow strength levels of around 8000 MPa while the broken spindles were the results of fatigue initiation and subsequent growth from a Thread Root (stress concentration) location on the spindle. Using relevant fatigue crack propagation data for the valve spindle material at 300°C it was demonstrated that fatigue failures occurred at spindle deflections of between 0.9 and 1.6 mm. Finally, it was demonstrated that the fatigue breakage problem could be significantly reduced, especially at the lower end of the valve spindle deflection range, by a combination of re-profiling the Thread Root and shot peening. © 1998 Published by Elsevier Science Ltd. All rights reserved.

  • Malfunctions of a steam turbine mechanical control system
    Engineering Failure Analysis, 1998
    Co-Authors: J.h. Bulloch, A G Callagy
    Abstract:

    This paper is aimed at elucidating the cause of a series of malfunctions involving the bending or breaking of main steam turbine throttle valve spindles which occurred at service times ranging from hundreds to several thousand hours in a number of 270 MW steam raising units. It was clearly established, by two distinct approaches (one engineering, one micromechanistic) that the stresses which produced these malfunctions were bending in nature and were the result of out-of-alignment deflections. In the case of the bent spindles the stresses were very high and approached flow strength levels of around 8000 MPa while the broken spindles were the results of fatigue initiation and subsequent growth from a Thread Root (stress concentration) location on the spindle. Using relevant fatigue crack propagation data for the valve spindle material at 300°C it was demonstrated that fatigue failures occurred at spindle deflections of between 0.9 and 1.6 mm. Finally, it was demonstrated that the fatigue breakage problem could be significantly reduced, especially at the lower end of the valve spindle deflection range, by a combination of re-profiling the Thread Root and shot peening.

Zhonghua Li - One of the best experts on this subject based on the ideXlab platform.

J.h. Bulloch - One of the best experts on this subject based on the ideXlab platform.

  • MALFUNCTIONS OF A STEAM TURBINE MECHANICAL CONTROL SYSTEM
    Failure Analysis Case Studies II, 2001
    Co-Authors: J.h. Bulloch, A G Callagy
    Abstract:

    This paper is aimed at elucidating the cause of a series of malfunctions involving the bending or breaking of main steam turbine throttle valve spindles which occurred at service times ranging from hundreds to several thousand hours in a number of 270 MW steam raising units. It was clearly established, by two distinct approaches (one engineering, one micromechanistic) that the stresses which produced these malfunctions were bending in nature and were the result of out-of-alignment deflections. In the case of the bent spindles the stresses were very high and approached flow strength levels of around 8000 MPa while the broken spindles were the results of fatigue initiation and subsequent growth from a Thread Root (stress concentration) location on the spindle. Using relevant fatigue crack propagation data for the valve spindle material at 300°C it was demonstrated that fatigue failures occurred at spindle deflections of between 0.9 and 1.6 mm. Finally, it was demonstrated that the fatigue breakage problem could be significantly reduced, especially at the lower end of the valve spindle deflection range, by a combination of re-profiling the Thread Root and shot peening. © 1998 Published by Elsevier Science Ltd. All rights reserved.

  • Malfunctions of a steam turbine mechanical control system
    Engineering Failure Analysis, 1998
    Co-Authors: J.h. Bulloch, A G Callagy
    Abstract:

    This paper is aimed at elucidating the cause of a series of malfunctions involving the bending or breaking of main steam turbine throttle valve spindles which occurred at service times ranging from hundreds to several thousand hours in a number of 270 MW steam raising units. It was clearly established, by two distinct approaches (one engineering, one micromechanistic) that the stresses which produced these malfunctions were bending in nature and were the result of out-of-alignment deflections. In the case of the bent spindles the stresses were very high and approached flow strength levels of around 8000 MPa while the broken spindles were the results of fatigue initiation and subsequent growth from a Thread Root (stress concentration) location on the spindle. Using relevant fatigue crack propagation data for the valve spindle material at 300°C it was demonstrated that fatigue failures occurred at spindle deflections of between 0.9 and 1.6 mm. Finally, it was demonstrated that the fatigue breakage problem could be significantly reduced, especially at the lower end of the valve spindle deflection range, by a combination of re-profiling the Thread Root and shot peening.

W.d. Dover - One of the best experts on this subject based on the ideXlab platform.

  • Controlled failure design of drillstring Threaded connections
    Fatigue & Fracture of Engineering Materials & Structures, 2003
    Co-Authors: M. J. Knight, Feargal Brennan, W.d. Dover
    Abstract:

    The Threaded connection of the type used in hydrocarbon exploration is a critical component of the drillstring that is highly susceptible to fatigue damage. Fatigue crack growth can either lead to a catastrophic failure of the connection, known as a twist-off, or can be a non-critical failure, known as a wash-out. The design philosophy of Controlled Failure Design has been used in order to promote a ‘friendly’ non-critical failure in the connection, by the controlled application of compressive residual stresses. The influence of compressive residual stress and its effect on controlling fatigue crack shape has been experimentally investigated with the development of Thread Root cold rolling equipment. Through the control of the cold rolling process, it has been demonstrated that fatigue crack growth can be controlled to produce a localized, non-critical failure in the connection.

  • Stress intensity factors for Threaded connections
    Engineering Fracture Mechanics, 1995
    Co-Authors: Feargal Brennan, W.d. Dover
    Abstract:

    Abstract A generic stress intensity factor (SIF) solution for Threaded connections is presented in this paper. This is based on multiple reference state weight function theory, making it applicable to any mode I crack emanating from a Thread Root. The reference SIFs required for the solution are a combination of published results representing geometrical features encountered in Threaded components. These constitutive components of the reference solutions can easily be replaced in the event of more comprehensive or appropriate solutions becoming available. For this reason it is considered prudent to present the structure of the solution rather than a rigid set of parametric expressions so that specific solutions can be fashioned for particular applications. The new solution is rigorously examined, comparing it with published SIF solutions for Threaded and related components.

  • Stress analysis of drillstring Threaded connections using the finite element method
    International Journal of Fatigue, 1993
    Co-Authors: Azam Tafreshi, W.d. Dover
    Abstract:

    Abstract Stress analysis of drillstring Threaded connections under axial, bending and torsion loadings has been carried out using the finite element method in order to determine the regions of highest stress concentration. This information is required for fatigue and fracture mechanics analysis. For axial loading, two-dimensional axisymmetric models of the Threaded joints have been used for the connector types, in standard form and with bore back and stress relief, and also in standard form with some slight modification to Thread Root geometry. Full three-dimensional models of the connectors, but ignoring the helix angle, were studied for bending and torsion loading. The peak stress concentration factors in all cases were at the Thread Root of the first loaded tooth in the pin and the last loaded tooth in the box. In comparison with axial loading, bending showed lower stress concentration factor values, but for torsion the values were very small. The study showed clear advantages in the use of bore back and stress relief in reducing stress concentration factor. It was found that a further decrease in stress concentration factor is possible with minor changes to the Thread geometry. Sensitivity analysis on the effect of Thread profile on stress concentration factor showed that the fatigue life could be increased by an improved profile Thread design.