1

1Chapter 8 Failure

Ductile and brittle fracture

2Chapter 8 Failure

Moderately ductile fracture

100 mm

2

3Chapter 8 Failure

Brittle fracture

4Chapter 8 Failure

3 mm

4 mm160 mm

1 mm

Brittle fracture surfaces

3

5Chapter 8 Failure

Stress concentration factor

σmax

2aσa

ρt

6Chapter 8 Failure

Fracture modes

!

a

4

7Chapter 8 Failure

Temperature effect on impact energy

Impa

ct E

nerg

y

Temperature

σ

Ductile-to-brittle

8Chapter 8 Failure

Cyclic loading

σmax

σmin

σ

time

σmS

5

9Chapter 8 Failure

Cyclic stress

uniaxial loading

torsional loading

flexural loading

10Chapter 8 Failure

Fatigue Design Parameters

Sfat

N = Cycles to failure103 105 107 109

S = stress amplitude

N = Cycles to failure103 105 107 109

S = stress amplitude

6

11Chapter 8 Failure

The S-N curveSt

ress

am

plitu

de, S

(MPa

)

Cycles to failure, N

12Chapter 8 Failure

crack origin

Fatigue Mechanism

7

13Chapter 8 Failure

14Chapter 8 Failure

8

15Chapter 8 Failure

Creep - temperature dependence

secondary

tertiary

16Chapter 8 Failure

Secondary Creep

10-2 10-1 1Steady state creep rate (%/1000hr)ε s

102040

100200 Stress (MPa)

427°C

538°C

649°C

9

17Chapter 8 Failure

Prediction of Creep Rupture Lifetime

103 L (K-h)

Stre

ss (1

03 ps

i)

100

10

112 20 24 2816

data for S-590 Iron

20

24

17

18Chapter 8 Failure 1818

103 L (K-h)

Stre

ss (1

03 ps

i)

100

10

112 20 24 2816

data for S-590 Iron

20

24