# Axial Load Study by nikeborome

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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

3/11/2008                                                            1
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

3/11/2008                                                                                                2
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.

3/11/2008                                                                                   3
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
•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.

3/11/2008                                                                            4
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.

3/11/2008                                                                5
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
•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
3/11/2008                                                                                                     6
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

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