# Prediction of Load-Displacement Curve for Weld-Bonded Stainless Steel Using Finite Element Method - PowerPoint PPT Presentation

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## Prediction of Load-Displacement Curve for Weld-Bonded Stainless Steel Using Finite Element Method

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### Prediction of Load-Displacement Curve for Weld-Bonded Stainless Steel Using Finite Element Method Essam Al-Bahkali Jonny Herwan Department of Mechanical Engineering – PowerPoint PPT presentation

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Title: Prediction of Load-Displacement Curve for Weld-Bonded Stainless Steel Using Finite Element Method

1
Weld-Bonded Stainless Steel Using Finite Element
Method
• Essam Al-Bahkali
• Jonny Herwan
• Department of Mechanical Engineering
• King Saud University,
• P.O.Box 800, Riyadh 11421, Saudi Arabia
• Multiphysics Dec 09-11, 2009
• Lille, France

2
Background
• It is one of the oldest cost effective, less
labor and readily automated electric welding
techniques that is used to join similar and
dissimilar metals.
• Introducing an adhesive layer in conjunction with
a spot weld nugget helps strengthening welded
joints and balancing stresses in the weld nugget
area.
• Optimum welding quality of a spot welded or a
weld-bonded joints, Required optimum welding
parameters, i.e. welding current, electrode
force, and welding time.

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• The advantages of resistance welding process
include
• short process times
• heat focused at the material interfaces.
• easily be automated
• While experimental work provides the necessary
physical insight about the behavior of
spot-welded joints, predictive tasks such as
design analysis and evaluation of spot-welded
structures are often carried out by computational
methods
• In predicting stress distribution, stress
concentration and failure modes of a weld-bonded
or a spot welded nugget, a finite element
modeling can do an excellent job in this regard.

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• Engineers use the process of adhesive bonding to
join materials
range of materials such as metal to metal, metal
to ceramic, metal to polymer, etc.
• Reducing weight
• Uniform stress distribution
• Fatigue resistance
• Ability to join thick with thin materials as well
as the ability to join dissimilar materials.
• No stress concentration

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• There are two types of Bonded structure
• Bonded-Welded
• Bonded-Riveted
• Bonded Screwed connections
• The combined connections ensure high fatigue
strength of the structures.
• Single lap welded joint is one of the important
method used to join two plates together.

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Objective
• In present work
• Manufacturing point of view
• To develop a finite element model of weld-bonded
that can represent a complete load-displacement
curve
• Minimize the experimental or trial in industrial
application
• Design point of view
• To obtain the representative weld-bonded model
which has reasonable deformation shape and
fracture initiation.
• To design the position and the effective number
of these joints in the mechanical structures

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The scope of research
Size, Properties of Nugget, and HAZ
• Process Parameters
• welding current
• welding time
• electrode force
• etc

Deformation and Fracture of the Joints
• Already done by some researchers
• A. De, et al 2003
• E. Feulvarch, et al 2004
• J. Z. Chen, et al 2006
• There was Sorpass Software that can analyze the
temperature distribution, size of nugget and Heat
Affected zone (HAZ)

Our research !
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Experimental Analysis
9
Finite Element Analysis
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FE Modeling and Boundary Conditions
Strip - A
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Assumptions
• 3-D FE model
• Half of the model was considered to save
computation time
• The elastic-plastic FE model was considered in
current analysis for verifying the model with the
experimental test
• There is no adhesive layer in a zone 1 mm around
the circumference of the welds
• The damage evolutions were chosen arbitrary in
term of displacement because the failure
propagation is not considered

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Finite Element Meshes
• The FE mesh was modeled using eight-node linear
brick reduced integration elements for strips and
nugget
• The FE mesh for adhesive layer was modeled using
eight-node 3-D cohesive element

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• Fine mesh was used in strips around the nugget,

Nugget Part
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Stress Triaxiality
• In Abaqus, the ductile fracture limits are in
term of stress triaxiality
• The stress triaxiality equation can be written
as
• Where
• Stress triaxiality can be obtained through
equivalent fracture strain.
• This can be done by conducting standard tensile
test to record the true strains at the fracture
limit.
• The value of the stress triaxiality were
calculated numerically using finite element
modeling of the notch tensile test

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Hardness Measurement and Indentation Test
• Micro-hardness test was used to define the
location of the weld nugget and heat affected
zone (HAZ)
• The hardness measurement started from the center
of the nugget and move a way from the center to
the heat affected zone with a step of 0.25mm.
• To obtain the plastic properties of each region,
spherical indentation ( 2mm diameter) was carried
• Spherical indentation data can be transferred to
true stress-true strain curve using Ahn-Equation
• Where
• s is the true stress, e is the true strain, f is
the plastic constrain factor 3.6, P is the load,
Pm is the mean pressure, a is the adjustment
constant 0.14, ac is the contact radius between
the indenter and material, R is the indenter

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Micro-hardness and Spherical Indentation Results
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Tensile Test Comparison between Experimental and
Finite Element Model
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Load- Displacement Curve of Spot Welding
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Initial Failure Comparison between Experimental
and Finite Element Model
Failure Initiation from Experimental and Finite
Element Model at HAZ
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Conclusions
• The ductile fracture limit criteria were
developed to predict the deformation and fracture
initiation of the model.
• Detailed material properties of each zone of
resistance spot welding (nugget, heat affected
zone, and base metal) are essential to accurately
simulate the model.
• Reverse engineering analysis is introduced to get
those material properties by modeling the
indentation process using finite element
software, and conduct some iteration of models
until the load-displacement curve of indentation
agree with the experimental curve.
• The results in general for the load-displacements
curve from finite element model shows a good
agreement with the experimental data.

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