1. Welding Design 1998/MJ1/MatJoin2/1 Design

2. Lesson Objectives When you finish this lesson you will understand: Mechanical and Physical Properties (structure sensitive and structure insensitive) Learning Activities 1.Read Handbook pp126-136 2.View Slides; 3.Read Notes, 4.Listen to lecture 5.Do on-line workbook 6.Do homework Keywords Structure Sensitive Properties, Structure Insensitive Properties, Stress, Strain, Elastic Modulus, Yield Strength, Tensile Strength, Ductility, Elongation, Proportional Limit, Fatigue, Stress Range, Stress Ratio, Endurance Limit, Toughness, Charpy, Ductile, Brittle, Hardness, Creep Design

3. Welding Design 1998/MJ1/MatJoin2/3 Welding Design l Welding design involves consideration of strength requirements, cost, and service conditions Mechanical & Physical properties Joint Design Welding stress and distortion Introduction 0.1.1.3.0.T1.95.12

4. Welding Design 1998/MJ1/MatJoin2/4

5. Welding Design 1998/MJ1/MatJoin2/5 Mechanical Properties

6. Welding Design 1998/MJ1/MatJoin2/6 Stress and Strain l Stress is defined as force per unit area Pounds per square inch, psi Megapascals (Newtons/mm 2 ), MPa l Strain is defined as change in dimension divided by original dimension Expressed as percent (%) Mechanical Properties 0.1.1.3.1.T2.95.12

7. Welding Design 1998/MJ1/MatJoin2/7 Tensile Test l Tensile test provides a plot of stress versus strain Elastic Modulus (E) Yield strength Tensile Strength Ductility Strain Stress, psi or MPa Yield Strength Tensile Strength Slope = Modulus Ductility Mechanical Properties 0.1.1.3.1.T3.95.12

8. Welding Design 1998/MJ1/MatJoin2/8 A = Proportional (Elastic) Limit B = 0.2% Offset Yield Strength C = Ultimate Tensile Strength Slope = Elastic Modulus

9. Welding Design 1998/MJ1/MatJoin2/9

10. Turn to the person sitting next to you and discuss (1 min.): The elastic portion of the stress- strain curves for steel, rubber, aluminum and tungsten are plotted here. Which material is which?

11. Welding Design 1998/MJ1/MatJoin2/11 Fatigue l Fatigue is material failure due to cyclic loading l Cyclic rather than static loading Tension - compression Tension - tension l Occurs at stress levels below the tensile strength Tension - Tension Tension - Compression Stress 0 Fatigue Design

12. Welding Design 1998/MJ1/MatJoin2/12 Linnert, Welding Metallurgy AWS, 1994 Stress Range Stress Ratio

13. Welding Design 1998/MJ1/MatJoin2/13 Linnert, Welding Metallurgy AWS, 1994

14. Welding Design 1998/MJ1/MatJoin2/14 Fatigue Appearance l Distinct fracture surface has a characteristic texture Concentric line pattern Smooth portion referred to as clamshell texture l Sources of fatigue Cracks Notches Sharp corners Initiation site Mechanical Properties 0.1.1.3.1.T10.95.12

15. Welding Design 1998/MJ1/MatJoin2/15 Linnert, Welding Metallurgy AWS, 1994 Endurance Limit

16. Welding Design 1998/MJ1/MatJoin2/16 Factors Affecting Fatigue l Welds have pre-existing stress risers or initiation sites from which fatigue cracks can grow Slag intrusions Undercut Weld toe radius l Other factors Butt joints vs. lap joints Sharp corners, notches UndercutIntrusion Smooth weld toe Fatigue Design

17. Welding Design 1998/MJ1/MatJoin2/17 Fatigue of Welds l In general, welds have pre-existing stress risers or initiation sites from which fatigue cracks can grow Slag intrusions Undercut Hardness variations l Design considerations Butt joints rather than lap joints Lap joint Butt joint UndercutIntrusion Mechanical Properties 0.1.1.3.1.T11.95.12

18. Turn to the person sitting next to you and discuss (1 min.): In the previous discussion we looked at stress cycles where both the min. and max. stress were positive. What do you think might happen if the minimum stress were compressive like the bottom curve?

19. Turn to the person sitting next to you and discuss (1 min.): In the previous discussion we looked at stress cycles where both the min. and max. stress were positive. What do you think might happen if the minimum stress were compressive like the bottom curve? Goodman Diagram

20. Welding Design 1998/MJ1/MatJoin2/20 Toughness Ability of a metal to resist fracture in the presence of a notch, and to accommodate loads by plastic deformation Rate of Straining Nature of Load - Uniaxial or Multiaxial Temperature Conditions Influencing Behavior

21. Welding Design 1998/MJ1/MatJoin2/21 Toughness l Toughness is a measure of the ability of a material to absorb energy prior to failure l Impact energy measured by the Charpy test Scale Hammer Specimen Charpy V-Notch specimen Mechanical Properties 0.1.1.3.1.T6.95.12

22. Welding Design 1998/MJ1/MatJoin2/22 Ductile to Brittle Transition l Steels have greatly reduced toughness at lower temperatures Temperature Energy absorbed for fracture Mechanical Properties 0.1.1.3.1.T7.95.12

23. Welding Design 1998/MJ1/MatJoin2/23 Linnert, Welding Metallurgy AWS, 1994

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25. Welding Design 1998/MJ1/MatJoin2/25 Linnert, Welding Metallurgy AWS, 1994

26. Welding Design 1998/MJ1/MatJoin2/26 Effect of Discontinuities on Properties l Fracture mechanics - analysis of the failure of structural materials with pre-existing flaws l Fracture toughness testing is used for brittle materials or thick sections Strain rate Temperature Thickness Mechanical Properties 0.1.1.3.1.T8.95.12

27. Turn to the person sitting next to you and discuss (1 min.): Consider the two beams. Which will experience less impact stress?

28. Turn to the person sitting next to you and discuss (1 min.): Consider the two beams. Which will experience less impact stress? (1)For a steady load, doubling the length of the beam will double the resulting bending stress (2)For an impact load, doubling the length of the beam will reduce the resulting impact stress to 70.7% of the original. See “Design of Weldments” p 3.1-6 Lincoln Arc Welding Foundation

29. Welding Design 1998/MJ1/MatJoin2/29 Hardness l Hardness - resistance to indentation l Measured by pushing an indenter into the surface of a material l Wear resistant materials have high hardness l Hardness can be correlated to tensile strength Mechanical Properties 0.1.1.3.1.T5.95.12

30. Welding Design 1998/MJ1/MatJoin2/30 Measures of Ductility l % Elongation at failure l % Reduction in area Mechanical Properties 0.1.1.3.1.T4.95.12

31. Welding Design 1998/MJ1/MatJoin2/31 Linnert, Welding Metallurgy AWS, 1994

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