1Based on Materials Science and Engineering An Introduction, W.D. Callister, Jr. 5th edition, 2000, Wiley

This material is for educational used only within Wright State University

ME 370/570Materials Science and Engineering-I

Chapter VI

• Instructor: Dr. R. Srinivasan• Mechanical and Materials

Engineering Dept.

2Based on Materials Science and Engineering An Introduction, W.D. Callister, Jr. 5th edition, 2000, Wiley

This material is for educational used only within Wright State University

3Based on Materials Science and Engineering An Introduction, W.D. Callister, Jr. 5th edition, 2000, Wiley

This material is for educational used only within Wright State University

4Based on Materials Science and Engineering An Introduction, W.D. Callister, Jr. 5th edition, 2000, Wiley

This material is for educational used only within Wright State University

5Based on Materials Science and Engineering An Introduction, W.D. Callister, Jr. 5th edition, 2000, Wiley

This material is for educational used only within Wright State University

θθστθσσcossin'

cos' 2

==

6Based on Materials Science and Engineering An Introduction, W.D. Callister, Jr. 5th edition, 2000, Wiley

This material is for educational used only within Wright State University

Simplified Hooke’s Law

γτεσ

GE

==

7Based on Materials Science and Engineering An Introduction, W.D. Callister, Jr. 5th edition, 2000, Wiley

This material is for educational used only within Wright State University

8Based on Materials Science and Engineering An Introduction, W.D. Callister, Jr. 5th edition, 2000, Wiley

This material is for educational used only within Wright State University

9Based on Materials Science and Engineering An Introduction, W.D. Callister, Jr. 5th edition, 2000, Wiley

This material is for educational used only within Wright State University

10Based on Materials Science and Engineering An Introduction, W.D. Callister, Jr. 5th edition, 2000, Wiley

This material is for educational used only within Wright State University

11Based on Materials Science and Engineering An Introduction, W.D. Callister, Jr. 5th edition, 2000, Wiley

This material is for educational used only within Wright State University

12Based on Materials Science and Engineering An Introduction, W.D. Callister, Jr. 5th edition, 2000, Wiley

This material is for educational used only within Wright State University

13Based on Materials Science and Engineering An Introduction, W.D. Callister, Jr. 5th edition, 2000, Wiley

This material is for educational used only within Wright State University

14Based on Materials Science and Engineering An Introduction, W.D. Callister, Jr. 5th edition, 2000, Wiley

This material is for educational used only within Wright State University

15Based on Materials Science and Engineering An Introduction, W.D. Callister, Jr. 5th edition, 2000, Wiley

This material is for educational used only within Wright State University

16Based on Materials Science and Engineering An Introduction, W.D. Callister, Jr. 5th edition, 2000, Wiley

This material is for educational used only within Wright State University

17Based on Materials Science and Engineering An Introduction, W.D. Callister, Jr. 5th edition, 2000, Wiley

This material is for educational used only within Wright State University

18Based on Materials Science and Engineering An Introduction, W.D. Callister, Jr. 5th edition, 2000, Wiley

This material is for educational used only within Wright State University

19Based on Materials Science and Engineering An Introduction, W.D. Callister, Jr. 5th edition, 2000, Wiley

This material is for educational used only within Wright State University

• The tension test is very useful for obtaining many mechanical properties, such as:– yield strength– ultimate tensile strength– elastic modulus, and – ductility in tension.

• However, the test is fairly expensive in terms of the equipment needed and the cost of the specimens. It is also a destructive test.

• An alternative way of getting to some of the information that the tension test provides is by the hardness test.

20Based on Materials Science and Engineering An Introduction, W.D. Callister, Jr. 5th edition, 2000, Wiley

This material is for educational used only within Wright State University

What is Hardness?• Resistance to Abrasion (Moh’s scale)

– Used in mineralogy or geology– Talc = 1; Diamond = 10– Not enough resolution for engineering use

• Resistance to indentation– Brinell– Vickers– Knoop– Rockwell

21Based on Materials Science and Engineering An Introduction, W.D. Callister, Jr. 5th edition, 2000, Wiley

This material is for educational used only within Wright State University

Advantages

• Simple• Inexpensive• Non-destructive• Other properties can be estimated from

hardness test results.

22Based on Materials Science and Engineering An Introduction, W.D. Callister, Jr. 5th edition, 2000, Wiley

This material is for educational used only within Wright State University

23Based on Materials Science and Engineering An Introduction, W.D. Callister, Jr. 5th edition, 2000, Wiley

This material is for educational used only within Wright State University

24Based on Materials Science and Engineering An Introduction, W.D. Callister, Jr. 5th edition, 2000, Wiley

This material is for educational used only within Wright State University

25Based on Materials Science and Engineering An Introduction, W.D. Callister, Jr. 5th edition, 2000, Wiley

This material is for educational used only within Wright State University

26Based on Materials Science and Engineering An Introduction, W.D. Callister, Jr. 5th edition, 2000, Wiley

This material is for educational used only within Wright State University

Variability in Mechanical Properties• Even when using the best of testing procedures the

results show variability• Possible causes

– Test method– Specimen fabrication– Operator bias– Apparatus calibration– Homogeneities– Compositional variations

• Handbook values should be considered average values for hundreds or even thousands of tests, and all designs should allow for the scatter.

27Based on Materials Science and Engineering An Introduction, W.D. Callister, Jr. 5th edition, 2000, Wiley

This material is for educational used only within Wright State University

28Based on Materials Science and Engineering An Introduction, W.D. Callister, Jr. 5th edition, 2000, Wiley

This material is for educational used only within Wright State University

Designing for Variability

• Typically, one designs to a working or allowable stress which is less than the handbook value of the yield stress.

• Where N is the factor of safety (>1)

Ny

w

σσ =