chapter 9 welding, bonding, and the design of permanent joints lecture slides the mcgraw-hill...
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Chapter 9
Welding, Bonding, and the Design of Permanent
Joints
Lecture Slides
The McGraw-Hill Companies © 2012
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Chapter Outline
Shigley’s Mechanical Engineering Design
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Welding Symbols
Welding symbol standardized by American Welding Society Specifies details of weld on machine drawings
Shigley’s Mechanical Engineering Design
Fig. 9–4
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Welding Symbols
Shigley’s Mechanical Engineering Design
Fig. 9–1
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Welding Symbols
Arrow side of a joint is the line, side, area, or near member to which the arrow points
The side opposite the arrow side is the other sideShape of weld is shown with the symbols below
Shigley’s Mechanical Engineering Design
Fig. 9–2
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Welding Symbol Examples
Shigley’s Mechanical Engineering Design
Weld leg size of 5 mmFillet weldBoth sides
Intermittent and staggered 60 mm along on 200 mm centers
Leg size of 5 mmOn one side only
(outside)Circle indicates all the
way around
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Welding Symbol Examples
Shigley’s Mechanical Engineering Design
Fig. 9–5
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Welding Symbol Examples
Shigley’s Mechanical Engineering Design
Fig. 9–6
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Tensile Butt Joint
Simple butt joint loaded in tension or compressionStress is normal stress
Throat h does not include extra reinforcementReinforcement adds some strength for static loaded jointsReinforcement adds stress concentration and should be ground
off for fatigue loaded joints
Shigley’s Mechanical Engineering DesignFig. 9–7a
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Shear Butt Joint
Simple butt joint loaded in shearAverage shear stress
Shigley’s Mechanical Engineering Design
Fig. 9–7b
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Transverse Fillet Weld
Joint loaded in tensionWeld loading is complex
Shigley’s Mechanical Engineering Design
Fig. 9–8
Fig. 9–9
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Transverse Fillet Weld
Summation of forces
Law of sines
Solving for throat thickness t
Shigley’s Mechanical Engineering Design
Fig. 9–9
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Transverse Fillet Weld
Nominal stresses at angle
Von Mises Stress at angle
Shigley’s Mechanical Engineering Design
Fig. 9–9
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Transverse Fillet Weld
Largest von Mises stress occurs at = 62.5º with value of ' = 2.16F/(hl)
Maximum shear stress occurs at = 67.5º with value of max = 1.207F/(hl)
Shigley’s Mechanical Engineering Design
Fig. 9–9
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Experimental Stresses in Transverse Fillet Weld
Experimental results are more complex
Shigley’s Mechanical Engineering Design
Fig. 9–10
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Transverse Fillet Weld Simplified Model
No analytical approach accurately predicts the experimentally measured stresses.
Standard practice is to use a simple and conservative modelAssume the external load is carried entirely by shear forces on
the minimum throat area.
By ignoring normal stress on throat, the shearing stresses are inflated sufficiently to render the model conservative.
By comparison with previous maximum shear stress model, this inflates estimated shear stress by factor of 1.414/1.207 = 1.17.
Shigley’s Mechanical Engineering Design
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Parallel Fillet Welds
Same equation also applies for simpler case of simple shear loading in fillet weld
Shigley’s Mechanical Engineering Design
Fig. 9–11
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Fillet Welds Loaded in Torsion
Fillet welds carrying both direct shear V and moment M
Primary shear
Secondary shear
A is the throat area of all welds
r is distance from centroid of weld group to point of interest
J is second polar moment of area of weld group about centroid of group
Shigley’s Mechanical Engineering Design
Fig. 9–12
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Example of Finding A and J
Rectangles represent throat areas. t = 0.707 h
Shigley’s Mechanical Engineering Design
Fig. 9–13
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Example of Finding A and J
Note that t3 terms will be very small compared to b3 and d3
Usually neglectedLeaves JG1 and JG2 linear
in weld widthCan normalize by
treating each weld as a line with unit thickness t
Results in unit second polar moment of area, Ju
Since t = 0.707h,
J = 0.707hJu
Shigley’s Mechanical Engineering Design
Fig. 9–13
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Common Torsional Properties of Fillet Welds (Table 9–1)
Shigley’s Mechanical Engineering Design
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Common Torsional Properties of Fillet Welds (Table 9–1)
Shigley’s Mechanical Engineering Design
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Example 9–1
Shigley’s Mechanical Engineering Design
Fig. 9–14
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Example 9–1
Shigley’s Mechanical Engineering Design
Fig. 9–15
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Example 9–1
Shigley’s Mechanical Engineering Design
Fig. 9–15
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Example 9–1
Shigley’s Mechanical Engineering DesignFig. 9–15
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Example 9–1
Shigley’s Mechanical Engineering Design
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Example 9–1
Shigley’s Mechanical Engineering Design
Fig. 9–16
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Example 9–1
Shigley’s Mechanical Engineering DesignFig. 9–16
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Fillet Welds Loaded in Bending
Shigley’s Mechanical Engineering Design
Fig. 9–17
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Bending Properties of Fillet Welds (Table 9–2)
Shigley’s Mechanical Engineering Design
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Bending Properties of Fillet Welds (Table 9–2)
Shigley’s Mechanical Engineering Design
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Strength of Welded Joints
Must check for failure in parent material and in weldWeld strength is dependent on choice of electrode materialWeld material is often stronger than parent materialParent material experiences heat treatment near weldCold drawn parent material may become more like hot rolled in
vicinity of weldOften welded joints are designed by following codes rather than
designing by the conventional factor of safety method
Shigley’s Mechanical Engineering Design
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Minimum Weld-Metal Properties (Table 9–3)
Shigley’s Mechanical Engineering Design
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Stresses Permitted by the AISC Code for Weld Metal
Shigley’s Mechanical Engineering Design
Table 9–4
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Fatigue Stress-Concentration Factors
Kfs appropriate for application to shear stresses
Use for parent metal and for weld metal
Shigley’s Mechanical Engineering Design
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Allowable Load or Various Sizes of Fillet Welds (Table 9–6)
Shigley’s Mechanical Engineering Design
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Minimum Fillet Weld Size, h (Table 9–6)
Shigley’s Mechanical Engineering Design
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Example 9–2
Shigley’s Mechanical Engineering Design
Fig. 9–18
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Example 9–2
Shigley’s Mechanical Engineering Design
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Example 9–2
Shigley’s Mechanical Engineering Design
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Example 9–3
Shigley’s Mechanical Engineering Design
Fig. 9–19
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Example 9–3
Shigley’s Mechanical Engineering Design
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Example 9–3
Shigley’s Mechanical Engineering Design
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Example 9–3
Shigley’s Mechanical Engineering Design
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Example 9–3
Shigley’s Mechanical Engineering Design
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Example 9–3
Shigley’s Mechanical Engineering Design
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Example 9–4
Shigley’s Mechanical Engineering DesignFig. 9–20
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Example 9–4
Shigley’s Mechanical Engineering Design
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Example 9–4
Shigley’s Mechanical Engineering Design
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Example 9–4
Shigley’s Mechanical Engineering Design
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Example 9–5
Shigley’s Mechanical Engineering DesignFig. 9–21
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Example 9–5
Shigley’s Mechanical Engineering Design
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Example 9–5
Shigley’s Mechanical Engineering Design
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Example 9–6
Shigley’s Mechanical Engineering Design
Fig. 9–22
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Example 9–6
Shigley’s Mechanical Engineering Design
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Example 9–6
Shigley’s Mechanical Engineering Design
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Resistance Welding
Welding by passing an electric current through parts that are pressed together
Common forms are spot welding and seam weldingFailure by shear of weld or tearing of memberAvoid loading joint in tension to avoid tearing
Shigley’s Mechanical Engineering DesignFig. 9–23
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Adhesive Bonding
Adhesive bonding has unique advantagesReduced weight, sealing capabilities, reduced part count, reduced
assembly time, improved fatigue and corrosion resistance, reduced stress concentration associated with bolt holes
Shigley’s Mechanical Engineering DesignFig. 9–24
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Types of Adhesives
May be classified by◦Chemistry
Epoxies, polyurethanes, polyimides◦ Form
Paste, liquid, film, pellets, tape◦ Type
Hot melt, reactive hot melt, thermosetting, pressure sensitive, contact
◦ Load-carrying capability Structural, semi-structural, non-structural
Shigley’s Mechanical Engineering Design
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Mechanical Performance of Various Types of Adhesives
Shigley’s Mechanical Engineering Design
Table 9–7
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Stress Distributions
Adhesive joints are much stronger in shear loading than tensile loading
Lap-shear joints are important for test specimens and for practical designs
Simplest analysis assumes uniform stress distribution over bonded area
Most joints actually experience significant peaks of stress
Shigley’s Mechanical Engineering DesignFig. 9–25
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Double-lap Joint
Classic analysis of double-lap joint known as shear-lag modelDouble joint eliminates complication of bending from
eccentricity
Shigley’s Mechanical Engineering DesignFig. 9–26
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Double-lap Joint
Shear-stress distribution is given by
Shigley’s Mechanical Engineering DesignFig. 9–26b
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Example 9–7
Shigley’s Mechanical Engineering DesignFig. 9–26
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Example 9–7
Shigley’s Mechanical Engineering Design
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Example 9–7
Shigley’s Mechanical Engineering DesignFig. 9–27
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Example 9-7
Shigley’s Mechanical Engineering Design
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Example 9-7
Shigley’s Mechanical Engineering Design
![Page 70: Chapter 9 Welding, Bonding, and the Design of Permanent Joints Lecture Slides The McGraw-Hill Companies © 2012](https://reader036.vdocuments.us/reader036/viewer/2022082216/56649d345503460f94a0b0a8/html5/thumbnails/70.jpg)
Single-lap Joint
Eccentricity introduces bendingBending can as much as double the resulting shear stressesNear ends of joint peel stresses can be large, causing joint failure
Shigley’s Mechanical Engineering DesignFig. 9–28
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Single-lap Joint
Shear and peal stresses in single-lap joint, as calculated by Goland and Reissner
Volkersen curve is for double-lap joint
Shigley’s Mechanical Engineering DesignFig. 9–28
![Page 72: Chapter 9 Welding, Bonding, and the Design of Permanent Joints Lecture Slides The McGraw-Hill Companies © 2012](https://reader036.vdocuments.us/reader036/viewer/2022082216/56649d345503460f94a0b0a8/html5/thumbnails/72.jpg)
Adhesive Joint Design Guidelines
Design to place bondline in shear, not peel.Use adhesives with adequate ductility to reduce stress
concentrations and increase toughness to resist debond propagation.
Recognize environmental limitations of adhesives and surface preparation.
Design to facilitate inspection.Allow sufficient bond area to tolerate some debonding before
becoming critical.Attempt to bond to multiple surfaces to support loads in any
direction.Consider using adhesives in conjunction with spot welds, rivets, or
bolts.
Shigley’s Mechanical Engineering Design
![Page 73: Chapter 9 Welding, Bonding, and the Design of Permanent Joints Lecture Slides The McGraw-Hill Companies © 2012](https://reader036.vdocuments.us/reader036/viewer/2022082216/56649d345503460f94a0b0a8/html5/thumbnails/73.jpg)
Design Ideas for Improved Bonding
Shigley’s Mechanical Engineering DesignFig. 9–29
![Page 74: Chapter 9 Welding, Bonding, and the Design of Permanent Joints Lecture Slides The McGraw-Hill Companies © 2012](https://reader036.vdocuments.us/reader036/viewer/2022082216/56649d345503460f94a0b0a8/html5/thumbnails/74.jpg)
Design Ideas for Improved Bonding
Shigley’s Mechanical Engineering DesignFig. 9–29
![Page 75: Chapter 9 Welding, Bonding, and the Design of Permanent Joints Lecture Slides The McGraw-Hill Companies © 2012](https://reader036.vdocuments.us/reader036/viewer/2022082216/56649d345503460f94a0b0a8/html5/thumbnails/75.jpg)
Design Ideas for Improved Bonding
Shigley’s Mechanical Engineering DesignFig. 9–29