ISSUES TO ADDRESS...

1. CHAPTER 6: MECHANICAL PROPERTIES

2. INTRODUCTION (I) The need for standardized language for expressing mechanical properties of materials: STRENGTH, HARDNESS, DUCTILITY, and STIFFNESS standardized test methods: American Society for Testing and Materials Standards and others�

3. INTRODUCTION (II)

4. Basic Concepts of Stress and Strain Need to compare load on specimens of various size and shapes: For tension and compression Engineering Stress, s = F / A0 , where F is load applied perpendicular to speciment crosssection and A0 is cross-sectional area (perpendicular to the force) before application of the load. Engineering Strain, e = ?l / l0 ( x 100 %), where ?l change in length, lo is the original length. These definitions of stress and strain allow one to compare test results for specimens of different cross-sectional area A0 and of different length l0.

5. Basic Concepts of Stress and Strain Need to compare load on specimens of various size and shapes: For tension and compression Engineering Stress, s = F / A0 , where F is load applied perpendicular to speciment crosssection and A0 is cross-sectional area (perpendicular to the force) before application of the load. Engineering Strain, e = ?l / l0 ( x 100 %), where ?l change in length, lo is the original length. For shear Shear Stress, t = F / A0 , where F is load applied parallel to upper and lower specimen faces of area A0. Shear Strain, ? = tan ? ( x 100 %), where ? is the strain angle.

6. ENGINEERING STRESS

7. ENGINEERING STRAIN

8. COMMON STATES OF STRESS

9. OTHER COMMON STRESS STATES (1)

10. OTHER COMMON STRESS STATES (2)

11. OTHER COMMON STRESS STATES (3)

12. SIMPLE STRESS-STRAIN TESTING

13. Stress-Strain Testing

14. Other Types of Application of Load

15. How does deformation take place in the material at an atomic scale ? Two types of deformation : Elastic Reversible, no change in the shape and the size of the specimen when the load is released ! When under load volume of the material changes ! Plastic Irreversible, dislocations cause slip, bonds are broken, new bonds are made. When load is released, specimen does not return to original size and shape, but volume is preserved !

16. STRESS-STRAIN CURVE

17. ELASTIC DEFORMATION

18. LINEAR ELASTIC PROPERTIES

19. NON-LINEAR ELASTIC PROPERTIES Some materials will exhibit a non-linear elastic behavior under stress ! Examples are polymers, gray cast iron, concrete, etc�

20. Linear Elastic Deformation (Atomic Scale)

21. Other Elastic Properties

22. YOUNG�S MODULI: COMPARISON

23. USEFUL LINEAR ELASTIC RELATIONS

24. PLASTIC DEFORMATION (METALS)

25. PLASTIC (PERMANENT) DEFORMATION

26. YIELD STRENGTH, sy

27. HARDENING

28. YIELD STRENGTH: COMPARISON

29. TENSILE STRENGTH, TS

30. TENSILE STRENGTH: COMPARISON

31. DUCTILITY, %EL

32. Mechanical Strength of Materials

33. TOUGHNESS & RESILIENCE

34. Resilience, Ur Ability of a material to store energy Energy stored best in elastic region

35. TRUE STRESS & STRAIN

36. HARDNESS

37. Hardness: Measurement Rockwell No major sample damage Each scale runs to 130 but only useful in range 20-100. Minor load 10 kg Major load 60 (A), 100 (B) & 150 (C) kg A = diamond, B = 1/16 in. ball, C = diamond HB = Brinell Hardness TS (psia) = 500 x HB TS (MPa) = 3.45 x HB

38. Hardness: Measurement

39. HARDNESS !!

40. Variability in Material Properties Elastic modulus is material property Critical properties depend largely on sample flaws (defects, etc.). Large sample to sample variability. Statistics Mean Standard Deviation All samples have same value Because of large variability must have safety margin in engineering specificationsAll samples have same value Because of large variability must have safety margin in engineering specifications

41. Design or Safety Factors

43. SUMMARY

44. ANNOUNCEMENTS