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
Prediction of Load-Displacement Curve for
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
  • Adhesive bonding can be used to adhere a wide
    range of materials such as metal to metal, metal
    to ceramic, metal to polymer, etc.
  • Some advantages of adhesive bonding
  • 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
  • Purely Adhesive
  • Adhesive/Mechanical Connection.
  • 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
  • Isotropic adhesive layer
  • 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, and adhesive layers

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
    out at several loads.
  • 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
    radius.

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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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Load- Displacement Curve of Adhesive Bonded
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Load- Displacement Curve of Weld-Bonded
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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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