Fundamentals of Materials Science and Engineering: An Integrated Approach, 3e

GTBL042-07 GTBL042-Callister-v2 August 9, 2007 13:52

214 • Chapter 7 / Mechanical Properties

0.0 0.2 0.4 0.6 0.8 1.0

60

50

40

30

20

10

0

Volume fraction porosity

Modulus of elasticity (10

6 psi)

Modulus of elasticity (GPa)

400

300

200

100

0

Figure 7.20 The influence of porosity on the modulus of elasticity for aluminum oxide at

room temperature. The curve drawn is according to Equation 7.21. (From R. L. Coble and

W. D. Kingery, “Effect of Porosity on Physical Properties of Sintered Alumina,”J. Am.

Ceram. Soc.,39,11, Nov. 1956, p. 381. Reprinted by permission of the American Ceramic

Society.)

a factor of 2. The influence of porosity on strength is rather dramatic; for example, it is

not uncommon that 10 vol% porosity will decrease the flexural strength by 50% from

the measured value for the nonporous material. The degree of the influence of pore

volume on flexural strength is demonstrated in Figure 7.21, again for aluminum oxide.

Experimentally it has been shown that the flexural strength decreases exponentially

with volume fraction porosity (P)as

σfs=σ 0 exp(−nP) (7.22)

Dependence of

flexural strength on

volume fraction

porosity

In this expressionσ 0 andnare experimental constants.

0.0 0.2 0.4 0.5 0.6

40

20

10

250

200

150

50

0

Volume fraction porosity

Flexural strength (10

3 psi)

Flexural strength (MPa)

30

100

0

0.1 0.3

Figure 7.21 The influence of porosity on the flexural strength for aluminum oxide at room

temperature. (From R. L. Coble and W. D. Kingery, “Effect of Porosity on Physical

Properties of Sintered Alumina,”J. Am. Ceram. Soc.,39,11, Nov. 1956, p. 382. Reprinted by

permission of the American Ceramic Society.)