1. Chapter 3 – Mechanical Properties of Material
Recall, for design and analysis, material properties are needed!! Why??
Design:
sallow = sfailure/F.S. - select geometry to satisfy this!
Analysis:
Want s < sallow – analyze structure to make sure this is true!!
Both cases need sfailure – what is sfailure and how is it determined??? Also, how much does it deform and strain under load?? MATERIAL PROPERTIES!!

2. Both cases need sfailure – what is sfailure and how is it determined???
First, sfailure can be either:
sY = Yield strength – stress level at which material yields (i.e. permanent deformation. OR
su = Ultimate strength – stress level at which material fails (i.e. catastrophic failure)
Next, where do they come from??

3. ANSWER: The Tension Test:
Figure: 03-02

4. Round material specimen:
Figure: UN

5. Figure: 03-04

6. Ductile Fracture: Steps to fracture:
Linear, yield, strain hardening, necking then fracture!!
Figure: UN

7. Example: find yield strength and ultimate
Figure: 03-06

8. Example: find yield strength and ultimate for material that does not exhibit knee behavior
Figure: 03-07

9. Hooke’s Law (key material property = Young’s Modulus:
Slope of linear portion of stress-strain curve.
Measure of material stiffness
E = s/e
s = E * e
What is E for the above curves?? How is it different for the steel curve vs the aluminum??
Known as Hooke’s Law

10. All these curves are steels. What do they have in common?
What is different?
Figure: 03-13

11. All these curves are steels. What do they have in common?
What is different?
Figure: 03-17

12. Other properties determined from stress strain curve:
Figure: 03-16a

13. Strain Hardening (i.e. cold working):
Figure: 03-14a

14. More Examples of Stress-Strain Curves

15. Rubber – VERY ELASTIC!!!!
Figure: 03-08

16. Cast Iron – Ductile or Brittle??
Figure: 03-09

17. Figure: 03-10a

18. Concrete: Ductile or Brittle??
Figure: 03-11

19. Plastic – highly non-linear behavior, why??
Figure: 03-12

20. Example: Find yield, tensile, E:
Figure: 03-18Ex3.01

21. Figure: P3.8

22. EX: Su = ultimate Strength = 47,820 psi
Sy = Yield Strength = 44,200 psi
E = Young’s Modulus = (34,640 – 10,597)/( ) = 9.6 E6
% Elongation = 11.5%
.002 = .2% offset

23. Final Concept: Poisson’s Ratio, n:
Figure: 03-21a