Spot Weld Mechanical Properties
Mechanical Properties
Lesson Objectives
When you finish this lesson you will
understand:
• Peel Chisel and Tensile Mechanical
testing techniques
• Factors which effect performance in
these 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
Mechanical Properties of Spot Welds
• Peel Tests
• Chisel Test
• Tensile Test
• Tensile Shear Ratios
• Torsion Test
• Impact Tests
• Fatigue Test
AWS Spec D8.9-97, 1997
AWS Spec D8.9-97, 1997
AWS Spec D8.9-97, 1997
AWS Spec D8.9-97, 1997
AWS Spec D8.9-97, 1997
AWS Spec D8.9-97, 1997
Dickinson, “Welding in Auto Industry,
AISI, 1981
AWS Spec D8.9-97, 1997
AWS Spec D8.9-97, 1997
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
Geometric Effects on the Peel Test
Distance “x” can
cause a wide
variation in load
results, thus peel
test can NOT be
used with
confidence to
develop
mechanical
property data
Orts, Armco Steel, Private Communication,
Nov 1980
Instrumented Peel Test
Area = Energy
“Static Toughness”
Sawhill, Spot Weldability of High Strength Sheet Steel”,
Welding Journal, Jan 1980
Sawhill, Spot Weldability of High Strength Sheet Steel”,
Welding Journal, Jan 1980
Peel Tested While
Still Warm
Promotes Full
Nugget Pull-Out
Peel Tested When
Cold
Promotes Partial
Nugget Failure
Mechanical Properties of Spot Welds
• Peel Tests
• Chisel Test
• Tensile Test
• Tensile Shear Ratios
• Torsion Test
• Impact Tests
• Fatigue Test
Dickinson, “Welding in Auto Industry,
AISI, 1981
Weld Time
Min. Nugget With Peel Test
Min. Nugget With Chisel
Test
Weld Current
Chisel Test Tends to Expose Nugget Closer to Fusion Line
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?
Mechanical Properties of Spot Welds
• Peel Tests
• Chisel Test
• Tensile Test - Tensile Shear
• Tensile Shear Ratios
• Torsion Test
• Impact Tests
• Fatigue Test
Dickinson, “Welding in Auto Industry,
AISI, 1981
AWS Spec D8.9-97, 1997
Kraus, “A Practical Design approach…”
Welding Journal, Oct 1961
Dickinson, “Welding in Auto Industry,
AISI, 1981
Vanden Bossche, “Ultimate Strength and Failure Mode..”,
SAE paper 770214, Feb 1977
Dickinson, Republic Steel Corp Internal Document, 1978
Tensile Shear Test
Single 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 Shear
Weld Bonding (Nugget plus Adhesive)
Material Thickness – Tensile Shear
In the thinner gages, the lower C
Steels tend to have higher strength
because the higher carbon
materials develop hard brittle
interfacial failures.
Heuschkel, “Some metalurgical aspects of carbon steel spot welding”,
Welding Journal, Oct 1947
Nugget
Diameter –
Tensile
Shear
Increased Tensile Shear
• Nugget Diameter
• Sheet Thickness
• BM Strength
Pollard, Spot Welding Characteristics of HSLA”,
Welding Journal, Aug 1974
Nugget Diameter (Current & Time & BM Strength) –
Tensile Shear
Nugget
Pullout
Increase BM Strength
Interfacial Failure
Increased Weld Current
• Greatly Increased Nugget
• Greatly Increased Tensile
Shear Strength
Increased Weld Time
• Slightly Increased Nugget
• Greatly Increased Tensile
Shear Strength
Increased BM Strength
• Increased Tensile
Shear
Pollard, Spot Welding Characteristics of HSLA”,
Welding Journal, Aug 1974
Nugget
Dia
Tensile
Shear
Strength
Is it Current, or Effect of Current on Nugget Diameter?
Electrode
Face
Combinations of Current and
Electrode Face Diameter gives
Constant Nugget Diameter
Current
Relationship between
Nugget Dia and Strength
Not Current/Strength
Turn to the person sitting next to you and discuss (1 min.):
• 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.
Base Metal Strength
• Solid Solution Strengthening
• Grain Refinement Through Special Processing
• Precipitation Strengthening
• Cold-work Strengthening
• Heat Treatment Strengthening (Hardening)
Effect of Carbon Content
Hard Brittle Martensite
Interfacial Failures
Heuschkel, “Some Metallurgical Aspects….”
Welding Journal, Oct 1947
Effect of Base Metal Strength
Grain Refinement
Precipitation
10o
The Stronger Materials
have less sample rotation
thus they carry greater
tensile shear load than
expected
30o
Pollard, “Spot Weldability of HSLA Steels”,
ASM/ADDRG Seminar, Nov 12&13, 1971
Effect of Structure
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)
Chandel, “Mech & Metallurgical Aspects…”
Metals Technology, Sept 1974
TSS  9.5T1.26UTS 0.76
Defourney, “Spot Welding of HSS,
IIW 646-80, 1980
Heuschkel, “Expression of Spot Weld Properties”,
Weldign Journal Oct 1952
Sawhill, “Spot Weldability of HSS”,
Welding Journal, Jan 1980
Critical Diameter to Thickness Ratio
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)
Vanden Bossche, “Ultimate Strength and Failure Modes…”
SAE 770214, Feb 1977
Effect of Coating
When only Zn-Zn
Bonds lower strength
than bare seel.
When steel-steel bonds
strength equal to or greater
Armco Steel Fabrication Data, 1981
Turn to the person sitting next to you and discuss (1 min.):
• 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 to
inaccuracies?
Hold Time – Tensile Shear
Hold Time Sensitive
Material in Peel Test
Not Hold Time
Sensitive in Tensile
Shear
Hold time appears to have no effect
Sawhill, “Spot weldability for High Strength Steels”,
SAE 810352, Feb 1981
Effect of Post
Weld Furnace
Treatment
>0.2% C Steels
Slight loss in strength
No benefit + Expensive
In Machine Q&T
> 0.2 % C Steels
Up to 300% benefit
Must be done correct
<0.2% Carbon
No Benefit
Balasubramanian et al, “Improvement of Resistance Spot Weld Characteristics”,
Welding Research Abroad, Nov 1978
Effect of Test Temperature for Plain Carbon Steel
Heuschkel, “The Expression of Spot Weld Properties”,
Welding Journal, Oct 1952
Effect of Cross Head Speed on Tensile Testing Machine
Impact
Chandel, “Mech Aspects pf Spot-WeldedJoints…”,
Metals Technology, Jan 1977
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)
Dickinson, “Welding in Auto…”,
AISI, Aug 1981
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
Effect of Increasing Number of Welds
Non-uniform loading on
Outside welds causes
deviation
Hills, “Effect of number of welds in spot welded…”,
Iron & Steelmaking, Vol 23, No 2, 1996
Effect of Sheet Thickness on Double Transverse Spot Welds
Capelli, et al, “Fatigue Strength of Spot-welded Joints..”
Welding of HSLA Steels, ASM, 1978
Effect of Nugget Rotation – Multiple Spot Array
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
Orts, “Fatigue Strength of Spot Weld Joints in HSLA”,
SAR 810355, Feb 1981
Turn to the person sitting next to you and discuss (1 min.):
• 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?
Tensile Test
Single Nugget Test – Tensile Shear
Multiple Nugget Test – Tensile Shear
Weld Bonding (Nugget plus Adhesive)
High Modulus
Adhesive Only
Weld Bond, Relative
Height of Peaks
Depends on Number
of Welds
Low Modulus
Adhesive Only
Spot Weld Only
Hills, “Effect of number of welds in spot welded…”,
Iron & Steelmaking, Vol 23, No 2, 1996
High Modulus Adhesive
Lower Modulus Adhesive
Fewer Welds
Adhesive Dominates
Hills, “Effect of number of welds in spot welded…”,
Iron & Steelmaking, Vol 23, No 2, 1996
Turn to the person sitting next to you and discuss (1 min.):
• We will study more about weld bonding techniques later.
Why is this technique so infrequently used?