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Spot Weld Mechanical Properties 2
Cross TensionDuctility RatioTorsion Test
Mechanical Properties 2
Lesson ObjectivesWhen you finish this lesson you will understand:• Cross Tensile and Torsion Mechanical testing techniques• Factors which effect performance in these mechanical tests• The importance of these test for part design
Learning Activities1. View Slides; 2. Read Notes, 3. Listen to lecture4. Do on-line
workbook5. Do Homework
KeywordsCross Tensile Test, Ductility Ratio, Torsion Test, Twist Angle
Mechanical Properties of Spot Welds
• Peel Tests• Chisel Test• Tensile Test – Tensile Shear• Tensile Test - Cross Tension• Tensile Shear Ratios• Torsion Test• Impact Tests• Fatigue Test
Dickinson, “Welding in Auto Industry,AISI, 1981
Direct Tension Testing
Tensile Shear
Material Thickness on Direct Tension
Heuschkel, “Some Metallurgical Aspects…”Welding Journal, Oct 1947
Higher Carbon Materiallower Strength Because Brittle Nuggets
Effect of WeldCurrent (Sheet Thickness)
On Cross Tension
Tensile Shear
Pollard, “Spot Welding Characteristics…”Welding Journal, Aug 1974
Weld Current
Cro
ss T
ensi
on
Str
eng
thEffect of Nugget Size (Current)
Small NuggetInterfacial Tearing
Strength Determined ByNugget Size
Strength Determined By Weld Ductility
Above ExpulsionErratic Behavior
Weld Time
U T
ensi
le S
tren
gth
Effect of Weld Time
Low Current
Intermediate Current
High CurrentHigh Currents = increase heat input to HAZ reducing cooling rate so that less hard martensite present
Thus peak may be chemistry dependent
Increase in time = larger nuggets thus higher direct tensile strength
Effect of Hold Time - Direct TensionTensile Shear
The More the Interfacial ModeThe lower the Direct Tensile Strength
Note Difference between Tensile Shear and Direct Tensile Sawhill, “Spot weldability for High Strength Steels”,
SAE 810352, Feb 1981
Effect of Carbon Content
Tensile Shear
Note Difference between Tensile Shear and Direct Tension
Heuschkel, “The Expression of Spot Weld Properties”,Weldign Journal, Oct 1952
Weld Current
Cro
ss T
ensi
on
Str
eng
thEffect of Steel Cleanliness
Small NuggetInterfacial Tearing
Strength Determined ByNugget Size
Strength Determined By Weld Ductility
Above ExpulsionErratic Behavior
Lamellar Type Tears
50% lower
Effect of Base Metal StrengthSlightly Raises Cross
Tension Strength
Weld Current
Cro
ss T
ensi
on
Str
eng
th
Small NuggetInterfacial Tearing
Strength Determined ByNugget Size
Strength Determined By Weld Ductility
Above ExpulsionErratic Behavior
Lamellar Type Tears
50% lower
Yamauchi, “Spot Weldability of High …”IIW III-644-80, 1980
Effect of Post Weld Temper
Upslope/Downslope, Hold Time, & Temper
Weld Current
Temper Current
Ele
ctro
de
Pre
ssu
reC
urr
ent
Squeeze Time Weld Time Off Time Hold TimeUpslope Downslope Temper
Temper Improvement Degradation
Analytical Approach
Heuschkel, J. “The Expression of Spot Weld Properties”, Welding Journal, Oct. 1952
Mechanical Properties of Spot Welds
• Peel Tests• Chisel Test• Tensile Test• Tensile Shear Ratios• Torsion Test• Impact Tests• Fatigue Test
Dickinson, “Welding in the Automotive …”AISI, !981
Dickinson, “Welding in the Automotive …”AISI, !981
Angle taken asFailure Angle
Torsion TestFactors Affecting Angle of Twist (Ductility)• Sheet Thickness• Material Strength • Carbon Content & Chemistry• Post Weld Heat
Factors Affecting Torque• Sheet Thickness• Material Strength• Post Weld Temper• Hold Time
Effect of Sheet Thickness & Material Strength
Bibber, “Spot Weldability of Low Carbon….”Welding Journal, Dec 1943
SheetBuckling
Twist Angle Reduces With• Increased Thickness• Stronger Material
Nugget DefectsAt Short Hold Martensite
HarderMartensite
Effect of Hold Time, Carbon Content, Post Weld Temper
Joumat, P. “Assessment of Spot Quality…”British Welding Journal, May 1955
Effect of Chemistry
Heuschkel “The Expression of Spot Weld Prop..”Welding Journal, Oct 1952
Effect of Post Weld Heat on • Twist Angle• Torque
Joumat, P. “Assessment of Spot Quality…”British Welding Journal, May 1955
Effect of Hold Time on Torque
Sawhill, “Spot Weldability for HS Steels” SAE Paper 810352, Feb, 1981
Effect of Steel Type on Angle and Torque
French “A Comparison of Methods of Assessing….”British Welding Journal, Nov 1957
