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Overview of VDI 2230 by mifei

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									 Overview of VDI 2230

 An Introduction to the Calculation
Method for Determining the Stress in
           a Bolted Joint
            Important Note
This summary of the VDI 2230 Standard is intended
to provide a basic understanding of the method.
Readers who wish to put the standard to use are
urged to refer to the complete standard that contains
all information, figures, etc.
              Definitions
• Covers high-duty bolted joints with constant
  or alternating loads
• Bolted joints are separable joints between
  two or more components using one or more
  bolts
• Joint must fulfill its function and withstand
  working load
        Aim of Calculation
Determine bolt dimension allowing for:
• Strength grade of the bolt
• Reduction of preload by working load
• Reduction of preload by embedding
• Scatter of preload during tightening
• Fatigue strength under an alternating load
• Compressive stress on clamped parts
      1. Range of Validity
• Steel Bolts
• M4 to M39
• Room Temperature
   2. Choice of Calculation
          Approach
• Dependent upon geometry
  –   Cylindrical single bolted joint
  –   Beam connection
  –   Circular plate
  –   Rotation of flanges
  –   Flanged joint with plane bearing face
  Cylindrical Single Bolted
            Joint
• Axial force, FA
• Transverse force, FQ
• Bending moment, MB
    Beam Geometry, Ex. 1
• Axial force, FA
• Transverse force, FQ
• Moment of the plane of the beam, MZ
    Beam Geometry, Ex. 2
• Axial force, FA
• Transverse force, FQ
• Moment of the plane of the beam, MZ
       Rotation of Flanges
• Axial force, FA (pipe force)
• Bending moment, MB
• Internal pressure, p
   Flanged Joint with Plane
      Bearing Face, Ex. 1
• Axial force, FA (pipe force)
• Torsional moment, MT
• Moment, MB
     Flanged Joint with Plane
        Bearing Face, Ex. 2
•   Axial force, FA (pipe force)
•   Transverse force, FQ
•   Torsional moment, MT
•   Moment, MB
     Flanged Joint with Plane
        Bearing Face, Ex. 3
•   Axial force, FA (pipe force)
•   Transverse force, FQ
•   Torsional moment, MT
•   Moment, MB
   3. Analysis of Force and
         Deformation
• Optimized by means of thorough and exact
  consideration of forces and deformations
  including:
  – Elastic resilience of bolt and parts
  – Load and deformation ratio for parts in
    assembled state and operating state
        4. Calculation Steps
• Begins with external working load, FB
• Working load and elastic deformations may
  cause:
  –   Axial force, FA
  –   Transverse force, FQ
  –   Bending Moment, MB
  –   Torque moment, MT
         Determining Bolt
           Dimensions
• Once working load conditions are known
  allow for:
  – Loss of preload to embedding
  – Assembly preload reduced by proportion of
    axial bolt force
  – Necessary minimum clamp load in the joint
  – Preload scatter due to assembly method
      Calculation Step R1
• Estimation of bolt diameter, d
• Estimation of clamping length ratio, lK/d
• Estimation of mean surface pressure under
  bolt head or nut area, pG
• If pG is exceeded, joint must be modified
  and lK/d re-determined
       Calculation Step R2
• Determination of tightening factor, aA,
  allowing for:
  – Assembly method
  – State of lubrication
  – Surface condition
       Calculation Step R3
• Determination of required average clamping
  load, Fkerf, as either:
  – Clamping force on the opening edge with
    eccentrically acting axial force, FA
  Or
  – Clamping force to absorb moment MT or
    transverse force component, FQ
       Calculation Step R4
• Determination of load factor, F, including:
  – Determination of elastic resilience of bolt, dS
  – Evaluation of the position of load introduction,
    n*lK
  – Determination of elastic resilience of clamped
    parts, dP
  – Calculation of required substitutional cross-
    section, Aers
       Calculation Step R5
• Determination of loss of preload, FZ, due to
  embedding
• Determination of total embedding
       Calculation Step R6
• Determination of bolt size and grade
  – For tightening within the elastic range, select
    bolt for which initial clamping load is equal to
    or greater than maximum initial clamping load
    due to scatter in assembly process
  – For tightening to yield, select bolt for which
    90% of initial clamping load is equal to or
    greater than minimum initial clamping load due
    to scatter in assembly process
       Calculation Step R7
• If changes in bolt or clamping length ratio,
  lK/d, are necessary, repeat Steps R4 through
  R6
      Calculation Step R8
• Check that maximum permissible bolt force
  is not exceeded
       Calculation Step R9
• Determine alternating stress endurance of
  bolt
• Allow for bending stress in eccentric load
  applications
• Obtain approximate value for permissible
  stress deviation from tables
• If not satisfactory, use bolt with larger
  diameter or greater endurance limit
• Consider bending stress for eccentric
  loading
      Calculation Step R10
• Check surface pressure under bolt head and
  nut bearing area
• Allow for chamfering of hole in
  determining bearing area
• Tables provide recommendations for
  maximum allowable surface pressure
• If using tightening to or beyond yield,
  modify calculation
     5. Influencing Factors
• Allow for factors depending upon:
  – Material and surface design of clamped parts
  – Shape of selected bolts and nuts
  – Assembly conditions
       Strength of the Bolt
• Stress caused by:
  – Torsional and axial stresses during tightening
  – Working load
• Should not exceed yield load
           Minimum Thread
             Engagement
• Depends upon:
  –   Thread form, pitch, tolerance, and diameter
  –   Form of the nut (wrenching width)
  –   Bolt hole
  –   Strength and ductility of bolt and nut materials
  –   Type of stress (tensile, torsional, bending)
  –   Friction coefficients
  –   Number of tightenings
    Thread Shear Strength
• Bolt-Nut Strength Matching
• Number for strength grade of nut is
  equivalent to first number of strength grade
  of bolt
Calculation of Required Nut
          Height
• Allows for geometry and mechanical
  properties of joint elements
• Predicts type of failure caused by
  overloading
• Considers:
  – Dimensional values (tensile cross-section of
    bolt thread, thread engagement length, etc.)
  – Thread form & nut form
  – Bolt clearance hole
         Bolt Head Height
• Ensures that failure will occur in free loaded
  thread section or in the shank
• Highest tensile stress in thread < Highest
  tensile stress in bolt head
  Surface Pressure at Bolt
 Head & Nut Bearing Areas
• Calculation determines surface pressure
  capable of causing creep resulting in loss of
  preload
• Surface pressure due to maximum load
  should not exceed compressive yield point
  of clamped material
 Tightening Factor, Alpha A
• Allowance must be made for torsional stress
  caused by pitch and thread friction, and
  axial tensile stress
• Scatter in friction coefficients and errors in
  method of controlling preload create
  uncertainty in level of tensile and torsional
  stress
• Tightening factor, aA, reflects amount of
  required “over-design”
           Fatigue Strength
• Design modifications to improve endurance
  limit of joint
  –   Increase preload
  –   Reduce pitch of screw thread
  –   Reduction of modulus of nut material elasticity
  –   Increase thread engagement
Fatigue Strength -Continued
• Design modifications to improve endurance
  limit of joint
  – Change form of nut
  – Reduce strength of nut material
  – Increase elastic resilience of bolt, lower elastic
    resilience of parts
  – Shift introduction of load toward interface
             Embedding
• Caused by flattening of surface
  irregularities
• Affects forces in joint
• Reduces elastic deformation and preload
       Self-Loosening and
            Prevention
• Preload drops due to:
  – Relaxation as a result of embedment or creep
  – Rotational loosening due to relative movements
    between mating surfaces
   6. Calculation Examples
• Ex. 1, Concentric Clamping and Concentric
  Loading
• Ex. 2, Transverse Shearing Force
• Ex. 3, Torsional Shearing Load
• Ex. 4, Eccentric Clamping and Eccentric
  Loading
• Ex. 5, Eccentric Clamping and Loading

								
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