2a4 Spot Weld Mech Prop

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Spot Weld Mechanical Properties


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Mechanical Properties

Lesson ObjectivesWhen you finish this lesson you will

understand:

Peel Chisel and Tensile Mechanical

testing techniques

Factors which effect performance inthese mechanical tests

The importance of these test for part

design

Learning Activities

1. View Slides;2. Read Notes,

3. Listen to lecture

4. Do on-line

workbook

Keywords

Peel Test, Chisel Test, Tensile Shear Test, Multiple Nugget Test,

Weld Bond Tensile Test, Coupon Dimensions, Weld Spacing,

Electrode Conditioning, Button Shape, Plastic Hinge


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Mechanical Properties of Spot Welds

Peel Tests Chisel Test

Tensile Test

Tensile Shear Ratios Torsion Test

Impact Tests

Fatigue Test


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AWS Spec D8.9-97, 1997


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AWS Spec D8.9-97, 1997


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AWS Spec D8.9-97, 1997


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AWS Spec D8.9-97, 1997


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AWS Spec D8.9-97, 1997


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AWS Spec D8.9-97, 1997


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Dickinson, Welding in Auto Industry,

AISI, 1981


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AWS Spec D8.9-97, 1997


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AWS Spec D8.9-97, 1997


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Advantages of Peel Test Ease of Performance

Low Cost

Ability to use on Shop Floor as quality control test

Disadvantages of Peel Test

Only in restricted cases are quantitative values

relating to the strength of the weld nugget or its

performance in service obtained Nugget fracture appearance is not a reliable

predictor of load-carrying capacity or impact

resistance


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Geometric Effects on the Peel Test

Orts, Armco Steel, Private Communication,

Nov 1980

Distance x can

cause a wide

variation in load

results, thus peeltest can NOT be

used with

confidence to

develop

mechanical

property data


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Instrumented Peel Test

Area = EnergyStatic Toughness

Sawhill, Spot Weldability of High Strength Sheet Steel,

Welding Journal, Jan 1980


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Sawhill, Spot Weldability of High Strength Sheet Steel,



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Peel Tested While

Still Warm

Peel Tested WhenCold

Promotes Full

Nugget Pull-Out

Promotes Partial

Nugget Failure


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Tensile Test


Impact Tests

Fatigue Test


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Dickinson, Welding in Auto Industry,AISI, 1981


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Weld Current

WeldTime

Chisel Test Tends to Expose Nugget Closer to Fusion Line

Min. Nugget With Peel Test

Min. Nugget With Chisel

Test


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Turn to the person sitting next to you and discuss (1 min.):

Why do automotive manufactures prefer the chisel test on

the production line over the peel test?


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Tensile Test - Tensile Shear


Impact Tests

Fatigue Test


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AWS Spec D8.9-97, 1997


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Kraus, A Practical Design approach

Welding Journal, Oct 1961


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Vanden Bossche, Ultimate Strength and Failure Mode..,

SAE paper 770214, Feb 1977


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Dickinson, Republic Steel Corp Internal Document, 1978


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Tensile Shear TestSingle Nugget Test Tensile Shear

Material Thickness

Nugget Size (Current & Time)

BM Strength

Carbon Content

BM Structure

Coatings

Hold Time

Post Weld Furnace Treatment

Test Temperature

Test Cross Head Speed

Multiple Nugget Test Tensile ShearWeld Bonding (Nugget plus Adhesive)


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Material Thickness Tensile Shear

Heuschkel, Some metalurgical aspects of carbon steel spot welding,


In the thinner gages, the lower C

Steels tend to have higher strength

because the higher carbon

materials develop hard brittleinterfacial failures.


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Nugget

Diameter Tensile

Shear

Pollard, Spot Welding Characteristics of HSLA,

Welding Journal, Aug 1974

Increased Tensile Shear Nugget Diameter

Sheet Thickness

BM Strength


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Nugget Diameter (Current & Time & BM Strength)

Tensile Shear

Increase BM Strength

Increased Weld Current

Greatly Increased Nugget

Greatly Increased Tensile

Shear Strength

Pollard, Spot Welding Characteristics of HSLA,

Welding Journal, Aug 1974

Increased Weld Time

Slightly Increased Nugget

Greatly Increased Tensile

Shear Strength

Interfacial Failure

Nugget

Pullout

Increased BM Strength

Increased Tensile

Shear


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Is it Current, or Effect of Current on Nugget Diameter?

Current

Electrode

Face

Nugget

Dia

Tensile

Shear

Strength

Combinations of Current and

Electrode Face Diameter gives

Constant Nugget Diameter

Relationship between

Nugget Dia and Strength

Not Current/Strength


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What criteria do you suppose automotive and appliance

designers use when selecting the type of weld joint they will

recommend for their products? Think about the joint

designs in cars and appliances.


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Base Metal Strength

Solid Solution StrengtheningGrain Refinement Through Special Processing

Precipitation Strengthening

Cold-work Strengthening Heat Treatment Strengthening (Hardening)


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Effect of Carbon Content

Heuschkel, Some Metallurgical Aspects.


Hard Brittle Martensite

Interfacial Failures


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Effect of Base Metal Strength

Pollard, Spot Weldability of HSLA Steels,

ASM/ADDRG Seminar, Nov 12&13, 1971

Grain Refinement

Precipitation

30o

10o The Stronger Materials

have less sample rotation

thus they carry greatertensile shear load than

expected


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Effect of Structure

Chandel, Mech & Metallurgical Aspects

Metals Technology, Sept 1974

Tensile Shear Strength Increases when a material is giving the following

Annealed

Bainitic (Heat Treated) Martensitic (Heat Treated)

Cold-rolled (Lower at higher currents due to HAZ softening)


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Heuschkel, Expression of Spot Weld Properties,

Weldign Journal Oct 1952

Sawhill, Spot Weldability of HSS,


76.026.1UTST5.9TSS !

Defourney, Spot Welding of HSS,

IIW 646-80, 1980


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Critical Diameter to Thickness Ratio

Vanden Bossche, Ultimate Strength and Failure Modes

SAE 770214, Feb 1977

d = nugget diameter

t = sheet thickness

ysbm= yield strength base metal

yswm = yield strength weld metal

Thus, higher strength materials

should have larger nuggets (electrode)


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Effect of Coating

Armco Steel Fabrication Data, 1981

When only Zn-Zn

Bonds lower strength

than bare seel.

When steel-steel bonds

strength equal to or greater


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We have looked at some factors which effect tensile shear

strength. And some people have developed empirical

equations to calculate tensile shear strength. How reliable

are these equations? What factors might lead toinaccuracies?


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Hold Time Tensile Shear

Hold time appears to have no effectSawhill, Spot weldability for High Strength Steels,

SAE 810352, Feb 1981

Hold Time Sensitive

Material in Peel Test

Not Hold Time

Sensitive in TensileShear


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Effect of Post

Weld Furnace

Treatment>0.2% C Steels

Balasubramanian et al, Improvement of Resistance Spot Weld Characteristics,

Welding Research Abroad, Nov 1978

Slight loss in strength

No benefit + Expensive

In Machine Q&T

> 0.2 % C Steels

Up to 300% benefit

Must be done correct


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Effect of Test Temperature for Plain Carbon Steel

Heuschkel, The Expression of Spot Weld Properties,



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Effect of Cross Head Speed on Tensile Testing Machine

Impact

Chandel, Mech Aspects pf Spot-WeldedJoints,

Metals Technology, Jan 1977


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Tensile Test

Single Nugget Test Tensile Shear

Multiple Nugget Test Tensile Shear Total Spot Weld Area

Sheet Thickness

Nugget Rotation (spot pattern)

Weld Bonding (Nugget plus Adhesive)


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Dickinson, Welding in Auto,

AISI, Aug 1981


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Effect of Total Nugget Area on Double Transverse Spot Welds

Capelli, et al, Fatigue Strength of Spot-welded Joints..Welding of HSLA Steels, ASM, 1978


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Effect of Increasing Number of Welds

Hills, Effect of number of welds in spot welded,Iron & Steelmaking, Vol 23, No 2, 1996

Non-uniform loading on

Outside welds causesdeviation


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Capelli, et al, Fatigue Strength of Spot-welded Joints..Welding of HSLA Steels, ASM, 1978

Effect of Sheet Thickness on Double Transverse Spot Welds


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Effect of Nugget Rotation Multiple Spot Array

Orts, Fatigue Strength of Spot Weld Joints in HSLA,SAR 810355, Feb 1981

Load = f(load per weld, stiffness)

Max load per weld reduced by:

Closely Spaced Welds

In line with load

Increased Nugget Size

Stiffness Increased by:

Closely Spaced Welds inline Specimen Width


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We have examined tensile shear strength on single welds

and on combinations of multiple welds. Does anything

surprise you about the multiple weld samples? Why are so

few reports presented with multiple weld data?


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Tensile Test

Single Nugget Test Tensile Shear

Multiple Nugget Test Tensile ShearWeld Bonding (Nugget plus Adhesive)


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High Modulus

Adhesive Only

Low Modulus

Adhesive Only

Spot Weld Only

Weld Bond, Relative

Height of PeaksDepends on Number

of Welds



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High Modulus Adhesive Lower Modulus Adhesive

Fewer Welds

Adhesive Dominates


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We will study more about weld bonding techniques later.

Why is this technique so infrequently used?

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2a4 Spot Weld Mech Prop