Axial Load Study

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					 MANE 6980 – Masters Project – Second Progress Report Presentation




            Comparison of Theoretical and
              ANSYS FEA Lug Analysis
                      Christina Stenman
                          3/11/2008




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 MANE 6980 – Masters Project – Second Progress Report Presentation
                                                   Introduction
  •Lugs are connector type elements used a structural supports
  for pin connections
  •During the 1960’s, the United States Air Force issued a
  manual, Stress Analysis Manual, that is the aerospace industry
  standard method for designing lug, link, and pin joints          Bushing                   Link

  •In considering any lug-pin combination, all ultimate failure
  methods must be considered.
        •Tension across the net section resulting from hole Kt
                                                                   Pin
        •Shear tear-out or bearing, closely related failures
                                                                             Lug
        •Hoop tension at the tip of the lug
        •Shearing of the pin
        •Bending of the pin, which can lead to excessive pin
        deflection and the build up of load near the lug shear
        plane
                                                                                   Net Section Tension
        •Excessive yielding of the bushing if one is used
                                                                                      Shear / Bearing
  •With the ever increasing prevalence and usage of FEA, it is
  necessary to determine whether the results obtained from FEA                          Hoop Tension
  analysis concur with those historically acceptable values
  generated from theoretical hand calculations

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 MANE 6980 – Masters Project – Second Progress Report Presentation
                                                         Theory
  •For double shear joints Stress Analysis Manual
  outlines all required calculations to calculated the
  ultimate load the joint can support
        •Ultimate axial and transverse load are
        determined.
        •If the joint is under oblique loading, it can be
        broken into an axial and transverse component.
  •These calculations take into account material
  allowables, joint geometry, ductile/brittle behavior of           Axially Loaded Lug
  the joint materials, and the distribution of load in the
  joint.
  •The lug, link, and pin are allowed to yield while the
  bushing is designed to not yield in compression
  •Initially calculations assume that the pin contacts
  along the length of the lug and lug.
        •If the pin bends excessively, causing load to
        peak near the lug shear planes, additional
        calculations are required to account for the              Transversely Loaded Lug
        decrease of the bending arm, and therefore
        bending moment, on the pin.


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 MANE 6980 – Masters Project – Second Progress Report Presentation
                                        Practical Application Theory




  •All calculations were completed for the theoretical
  geometry shown at left
        •Uniform temperature of 1000°F                        Bushing         Link
        •Lug and Pin are INCO718
        •Link is Waspaloy
        •Bushings are Stellite 6                              Pin
  •Pin is determined to be the limiting joint component                 Lug
  as it bends excessively based on initial calculations
  •Ultimate load on the joint is 1632 lb.




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 MANE 6980 – Masters Project – Second Progress Report Presentation
                         Finite Element Model and Modeling Assumptions
  •A symmetric, parametric, solid model of the double shear joint was
  created in ANSYS
        •SOLID95 elements were used, which are quadratic, brick
        elements
        •Mesh was locally refined in the regions of expected
        plasticity and high load
        •Surface to surface contact (CONTACT174 and
        TAREGT170) was used between the joint components
  •Model constraints:
        •Symmetry boundary conditions were applied to the link and
        pin
        •Lug was grounded in the normal and shear direction at its
        base
        •Mass element (MASS21) was created at the center of the
        pin on the symmetry plane, constrained about the pin’s axis
        and connected to the pin elements on the symmetry plane
        with rigid constraint equations in all directions
  •Load applied to one node on the link face. Couples and constraint
  equations provide a moment constraint and distribute this force
  over the face.


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 MANE 6980 – Masters Project – Second Progress Report Presentation
                                             Preliminary FEA Results
•A mesh density study was undertaken on the purely axially
loaded joint to ensure that the FE model was predicting stress
and strain correctly.
      •The mesh was refined such that predicted stress and
      strain error was less than 10% and contact regions
      stabilized.
•Coefficient of friction between the lug/bushing and
bushing/pin was studied
      •Initially 0.3 was used but this made the joint overly                             Total Strain Plot:
      stiff                                                                              Grey region
                                                                                         shows where link
      •Coefficient decreased to 0.01                                                     is above
                                                                                         proportional limit
•Ensure that the ANSYS model treated the joint components
the same way as the theoretical calculation did, especially
how plasticity was considered
      •Theoretical calculations use a plastic bending
      coefficient to augment the ultimate tensile allowables
      of the pin
      •Thus study underway to determine if pin should be
      modeled as elastic or if plasticity should be taken into
      account.
•Currently, FE model is less conservative than the theoretical
calculations when net section stresses are accounted for and
more conservative when peak stresses/strains are considered            Pin Stress Plot
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 MANE 6980 – Masters Project – Second Progress Report Presentation
                                              Going Forward Plan


            •Continue to refine modeling technique on the axially loaded case until it is certain that the
            joint is modeled correctly.
            •Correlate axially loaded ANSYS model to theoretical calculations
                  •Determine factor if necessary
            •Correlate transversely loaded ANSYS model to theoretical calculations
                  •Determine factor if necessary
            •Compile post processing guidelines
                  •How to determine contact between parts (contact status, contact pressure, etc)
                  •Should peak stress or net section stress be used to determine failure
                  •Should stress or strains be used to calculate margin




3/11/2008                                                                                                    7