Transcript No Slide Title

Welding Design
Design
1998/MJ1/MatJoin2/1
Design
Lesson Objectives
When you finish this lesson you will
understand:
• Mechanical and Physical Properties
(structure sensitive and structure
insensitive)
Learning Activities
1. Read Handbook
pp126-136
2. View Slides;
3. Read Notes,
4. Listen to lecture
5. Do on-line
workbook
6. Do homework
Keywords
Structure Sensitive Properties, Structure Insensitive Properties,
Stress, Strain, Elastic Modulus, Yield Strength, Tensile Strength,
Ductility, Elongation, Proportional Limit, Fatigue, Stress Range,
Stress Ratio, Endurance Limit, Toughness, Charpy, Ductile, Brittle,
Hardness, Creep
Introduction
Welding Design
Welding Design

Welding design involves consideration of
strength requirements, cost, and service
conditions
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
Mechanical & Physical properties
Joint Design
Welding stress and distortion
0.1.1.3.0.T1.95.12
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Welding Design
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Welding Design
Mechanical Properties
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Mechanical Properties
Welding Design
Stress and Strain

Stress is defined as force per unit area
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Pounds per square inch, psi
Megapascals (Newtons/mm2), MPa
Strain is defined as change in dimension divided by
original dimension

Expressed as percent (%)
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Mechanical Properties
Welding Design
Tensile Test
Stress, psi or MPa
Tensile Strength

Tensile test provides a
plot of stress versus
strain

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Yield Strength


Elastic Modulus (E)
Yield strength
Tensile Strength
Ductility
Slope = Modulus
Ductility
Strain
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Welding Design

E

A = Proportional (Elastic) Limit B = 0.2% Offset Yield Strength
C = Ultimate Tensile Strength Slope = Elastic Modulus
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Welding Design
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Turn to the person sitting next to
you and discuss (1 min.):
• The elastic portion of the stressstrain curves for steel, rubber,
aluminum and tungsten are
plotted here. Which material is
which?
Welding Design
Fatigue Design
Fatigue

Tension - Tension
Stress

Fatigue is material failure
due to cyclic loading
Cyclic rather than static
loading



0
Tension - compression
Tension - tension
Occurs at stress levels
below the tensile strength
Tension - Compression
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Welding Design
Stress Range
Stress Ratio
Linnert, Welding Metallurgy
AWS, 1994
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Welding Design
Linnert, Welding Metallurgy
AWS, 1994
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Mechanical Properties
Welding Design
Fatigue Appearance

Distinct fracture surface
has a characteristic
texture

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Initiation
site

Concentric line pattern
Smooth portion referred to
as clamshell texture
Sources of fatigue

Cracks

Notches
Sharp corners
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0.1.1.3.1.T10.95.12
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Welding Design
Endurance Limit
Linnert, Welding Metallurgy
AWS, 1994
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Welding Design
Fatigue Design
Factors Affecting Fatigue
Undercut
Intrusion

Welds have pre-existing
stress risers or initiation
sites from which fatigue
cracks can grow
Slag intrusions
 Undercut
 Weld toe radius
Other factors
 Butt joints vs. lap joints
 Sharp corners, notches
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Smooth weld toe
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Mechanical Properties
Welding Design
Fatigue of Welds
Undercut
Intrusion

In general, welds have
pre-existing stress risers
or initiation sites from
which fatigue cracks can
grow

Butt joint
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Lap joint
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Slag intrusions
Undercut
Hardness variations
Design considerations

Butt joints rather than lap
joints
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Turn to the person sitting next
to you and discuss (1 min.):
• In the previous discussion we
looked at stress cycles where
both the min. and max. stress
were positive. What do you
think might happen if the
minimum stress were
compressive like the bottom
curve?
Turn to the person sitting next
to you and discuss (1 min.):
• In the previous discussion we
looked at stress cycles where
both the min. and max. stress
were positive. What do you
think might happen if the
minimum stress were
compressive like the bottom
curve?
Goodman Diagram
Welding Design
Toughness
Ability of a metal to resist fracture in the presence of
a notch, and to accommodate loads by plastic
deformation
Conditions Influencing Behavior
• Rate of Straining
• Nature of Load - Uniaxial or Multiaxial
• Temperature
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Mechanical Properties
Welding Design
Scale
Toughness
Hammer

Specimen
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Toughness is a measure
of the ability of a material
to absorb energy prior to
failure
Impact energy measured
by the Charpy test
Charpy V-Notch specimen
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Mechanical Properties
Welding Design
Ductile to Brittle Transition
Energy absorbed for fracture

Steels have greatly
reduced toughness at
lower temperatures
Temperature
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Welding Design
Linnert, Welding Metallurgy
AWS, 1994
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Welding Design
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Welding Design
Linnert, Welding Metallurgy
AWS, 1994
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Mechanical Properties
Welding Design
Effect of Discontinuities on Properties
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Fracture mechanics analysis of the failure of
structural materials with
pre-existing flaws
Fracture toughness
testing is used for brittle
materials or thick sections
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Strain rate
Temperature
Thickness
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Turn to the person sitting next
to you and discuss (1 min.):
• Consider the two beams.
Which will experience less
impact stress?
Turn to the person sitting next
to you and discuss (1 min.):
• Consider the two beams.
Which will experience less
impact stress?
(1) For a steady load, doubling the length of the beam will double
the resulting bending stress
(2) For an impact load, doubling the length of the beam will reduce
the resulting impact stress to 70.7% of the original.
See “Design of Weldments” p 3.1-6 Lincoln Arc Welding Foundation
Mechanical Properties
Welding Design
Hardness
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Hardness - resistance to
indentation
Measured by pushing an
indenter into the surface
of a material
Wear resistant materials
have high hardness
Hardness can be
correlated to tensile
strength
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Mechanical Properties
Welding Design
Measures of Ductility
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% Elongation at failure
% Reduction in area
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Welding Design
Linnert, Welding Metallurgy
AWS, 1994
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Welding Design
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Welding Design
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