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

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 Material lower Strength Because Brittle Nuggets

Effect of Weld Current (Sheet Thickness) On Cross Tension Tensile Shear Pollard, “Spot Welding Characteristics…” Welding Journal, Aug 1974

Effect of Nugget Size (Current) Small Nugget Interfacial Tearing Strength Determined By Nugget Size Strength Determined By Weld Ductility Above Expulsion Erratic Behavior

Effect of Weld Time Low Current Intermediate Current High Current High 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 Tension Tensile Shear 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 , 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

Effect of Steel Cleanliness Small Nugget Interfacial Tearing Strength Determined By Nugget Size Strength Determined By Weld Ductility Above Expulsion Erratic Behavior Lamellar Type Tears 50% lower

Effect of Base Metal Strength Slightly Raises Cross Tension Strength Small Nugget Interfacial Tearing Strength Determined By Nugget Size Strength Determined By Weld Ductility Above Expulsion Erratic Behavior Lamellar Type Tears 50% lower Yamauchi, “Spot Weldability of High …” IIW III , 1980

Effect of Post Weld Temper

Upslope/Downslope, Hold Time, & Temper Weld Current Temper Current Electrode Pressure Current Squeeze Time Weld Time Off Time Hold Time Upslope 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 ( Ductility) Ratios Torsion Test Impact Tests Fatigue Test

Balasubramanian, S. et al “Improvement of Resistance Spot Weld Characteristics”, Welding Research Abroad, Nov 1978 Pollard, B., “Spot Weldability of HSLA Steels”, ASM/ADDRG Seminar on the Application of High-Strength-to-Weight Metals for Automotive Components, Nov 1974.

Heuschkel, J. “Some Metalurgical Aspects of Carbon Steel Spot Welding”, Welding Journal, Oct 1947.

Williams, NT, “Spot Weld Size and Fracture Mode in Low Carbon Mild Steels”, Metal Construction, Oct 1979

Cold Rolled Steels Hot Rolled Steels Sawhill, J, “Spot Weldability Tests for High Strength Steels”, SAE Paper , Feb 1981

Schneider, EJ Pollard, B, “Titanium-Bearing High Strength Cold Rolled Steels”, Proceedings of the AIME Mechanical Working Conference Oct 1980.

Balasubramanian, S. et al “Improvement of Resistance Spot Weld Characteristics”, Welding Research Abroad, Nov 1978

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 as Failure Angle

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 Bibber, “Spot Weldability of Low Carbon….” Welding Journal, Dec 1943 Sheet Buckling Twist Angle Reduces With Increased Thickness Stronger Material

Nugget Defects At Short Hold Martensite Harder Martensite 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 , Feb, 1981

Effect of Steel Type on Angle and Torque French “A Comparison of Methods of Assessing….” British Welding Journal, Nov 1957

High Tensile Loaded Joint Assignment 3