Spot Weld Mechanical Properties 2
Cross Tension
Ductility Ratio
Torsion Test
Mechanical Properties 2
Lesson Objectives
When 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 Activities
1. View Slides;
2. Read Notes,
3. Listen to lecture
4. Do on-line
workbook
5. Do Homework
Keywords
Cross 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
Direct Tension Testing
Dickinson, “Welding in Auto Industry,
AISI, 1981
Material Thickness on Direct Tension
Tensile Shear
Higher Carbon Material
lower Strength Because
Brittle Nuggets
Heuschkel, “Some Metallurgical Aspects…”
Welding Journal, Oct 1947
Tensile Shear
Effect of Weld
Current
(Sheet Thickness)
On Cross Tension
Pollard, “Spot Welding Characteristics…”
Welding Journal, Aug 1974
Cross Tension Strength
Effect of Nugget Size (Current)
Strength Determined By
Nugget Size
Small Nugget
Interfacial Tearing
Strength Determined
By Weld Ductility
Weld Current
Above Expulsion
Erratic Behavior
Effect of Weld Time
U Tensile Strength
High Current
High Currents = increase heat input
to HAZ reducing cooling rate so that
less hard martensite present
Thus peak may be chemistry dependent
Intermediate
Current
Low Current
Weld Time
Increase in time = larger nuggets
thus higher direct tensile strength
Tensile Shear
Effect of Hold Time - Direct Tension
The More the
Interfacial Mode
The 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
Cross Tension Strength
Effect of Steel Cleanliness
Strength Determined By
Nugget Size
Small Nugget
Interfacial Tearing
Strength Determined
By Weld Ductility
50% lower
Lamellar Type Tears
Weld Current
Above Expulsion
Erratic Behavior
Effect of Base Metal Strength
Cross Tension Strength
Slightly Raises Cross
Tension Strength
Strength Determined By
Nugget Size
Yamauchi, “Spot Weldability of High …”
IIW III-644-80, 1980
Small Nugget
Interfacial Tearing
Strength Determined
By Weld Ductility
50% lower
Lamellar Type Tears
Weld Current
Above Expulsion
Erratic Behavior
Effect of Post Weld Temper
Current
Electrode
Pressure
Upslope/Downslope, Hold Time,
& Temper
Weld Current
Temper Current
Upslope
Downslope
Temper
Squeeze Time
Weld Time
Off Time
Hold Time
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
Angle taken as
Failure Angle
Dickinson, “Welding in the Automotive …”
AISI, !981
Torsion Test
Factors 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
Sheet
Buckling
Twist Angle Reduces With
• Increased Thickness
• Stronger Material
Bibber, “Spot Weldability of Low Carbon….”
Welding Journal, Dec 1943
Effect of Hold Time, Carbon Content, Post Weld Temper
Nugget Defects
At Short Hold
Martensite
Harder
Martensite
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
Assignment 3
High Tensile Loaded Joint