PPT: Failure of Materials | Strength of Materials (SOM) - Mechanical Engineering PDF Download

 Page 1


ISSUES TO ADDRESS...
•  How do cracks that lead to failure form?
•  How is fracture resistance quantified?  How do the fracture 
resistances of the different material classes compare?
•  How do we estimate the stress to fracture?
•  How do loading rate, loading history, and temperature
affect the failure behavior of materials?
Ship-cyclic loading
from waves.
Computer chip-cyclic
thermal loading.
Hip implant-cyclic
loading from walking.
Adapted from Fig. 22.30(b), Callister 7e.
(Fig. 22.30(b) is courtesy of National 
Semiconductor Corporation.)
Adapted from Fig. 22.26(b), 
Callister 7e.
Chapter 8: Mechanical Failure
Adapted from chapter-opening photograph, 
Chapter 8, Callister & Rethwisch 8e. (by 
Neil Boenzi, The New York Times.)
Page 2


ISSUES TO ADDRESS...
•  How do cracks that lead to failure form?
•  How is fracture resistance quantified?  How do the fracture 
resistances of the different material classes compare?
•  How do we estimate the stress to fracture?
•  How do loading rate, loading history, and temperature
affect the failure behavior of materials?
Ship-cyclic loading
from waves.
Computer chip-cyclic
thermal loading.
Hip implant-cyclic
loading from walking.
Adapted from Fig. 22.30(b), Callister 7e.
(Fig. 22.30(b) is courtesy of National 
Semiconductor Corporation.)
Adapted from Fig. 22.26(b), 
Callister 7e.
Chapter 8: Mechanical Failure
Adapted from chapter-opening photograph, 
Chapter 8, Callister & Rethwisch 8e. (by 
Neil Boenzi, The New York Times.)
Fracture mechanisms
• Ductile fracture
– Accompanied by significant plastic 
deformation
• Brittle fracture
– Little or no plastic deformation
– Catastrophic
Page 3


ISSUES TO ADDRESS...
•  How do cracks that lead to failure form?
•  How is fracture resistance quantified?  How do the fracture 
resistances of the different material classes compare?
•  How do we estimate the stress to fracture?
•  How do loading rate, loading history, and temperature
affect the failure behavior of materials?
Ship-cyclic loading
from waves.
Computer chip-cyclic
thermal loading.
Hip implant-cyclic
loading from walking.
Adapted from Fig. 22.30(b), Callister 7e.
(Fig. 22.30(b) is courtesy of National 
Semiconductor Corporation.)
Adapted from Fig. 22.26(b), 
Callister 7e.
Chapter 8: Mechanical Failure
Adapted from chapter-opening photograph, 
Chapter 8, Callister & Rethwisch 8e. (by 
Neil Boenzi, The New York Times.)
Fracture mechanisms
• Ductile fracture
– Accompanied by significant plastic 
deformation
• Brittle fracture
– Little or no plastic deformation
– Catastrophic
Ductile vs Brittle Failure
Very 
Ductile
Moderately
Ductile
Brittle
Fracture
behavior:
Large Moderate %AR or %EL Small
• Ductile fracture is 
usually more desirable 
than brittle fracture!
Adapted from Fig. 8.1, 
Callister & Rethwisch 8e. 
• Classification:
Ductile:
Warning before 
fracture
Brittle:
No 
warning
Page 4


ISSUES TO ADDRESS...
•  How do cracks that lead to failure form?
•  How is fracture resistance quantified?  How do the fracture 
resistances of the different material classes compare?
•  How do we estimate the stress to fracture?
•  How do loading rate, loading history, and temperature
affect the failure behavior of materials?
Ship-cyclic loading
from waves.
Computer chip-cyclic
thermal loading.
Hip implant-cyclic
loading from walking.
Adapted from Fig. 22.30(b), Callister 7e.
(Fig. 22.30(b) is courtesy of National 
Semiconductor Corporation.)
Adapted from Fig. 22.26(b), 
Callister 7e.
Chapter 8: Mechanical Failure
Adapted from chapter-opening photograph, 
Chapter 8, Callister & Rethwisch 8e. (by 
Neil Boenzi, The New York Times.)
Fracture mechanisms
• Ductile fracture
– Accompanied by significant plastic 
deformation
• Brittle fracture
– Little or no plastic deformation
– Catastrophic
Ductile vs Brittle Failure
Very 
Ductile
Moderately
Ductile
Brittle
Fracture
behavior:
Large Moderate %AR or %EL Small
• Ductile fracture is 
usually more desirable 
than brittle fracture!
Adapted from Fig. 8.1, 
Callister & Rethwisch 8e. 
• Classification:
Ductile:
Warning before 
fracture
Brittle:
No 
warning
• Ductile failure:
-- one piece
-- large deformation
Figures from V.J. Colangelo and F.A. 
Heiser, Analysis of Metallurgical Failures
(2nd ed.), Fig. 4.1(a) and (b), p. 66  John 
Wiley and Sons, Inc., 1987.  Used with 
permission.
Example:  Pipe Failures
• Brittle failure:
-- many pieces
-- small deformations
Page 5


ISSUES TO ADDRESS...
•  How do cracks that lead to failure form?
•  How is fracture resistance quantified?  How do the fracture 
resistances of the different material classes compare?
•  How do we estimate the stress to fracture?
•  How do loading rate, loading history, and temperature
affect the failure behavior of materials?
Ship-cyclic loading
from waves.
Computer chip-cyclic
thermal loading.
Hip implant-cyclic
loading from walking.
Adapted from Fig. 22.30(b), Callister 7e.
(Fig. 22.30(b) is courtesy of National 
Semiconductor Corporation.)
Adapted from Fig. 22.26(b), 
Callister 7e.
Chapter 8: Mechanical Failure
Adapted from chapter-opening photograph, 
Chapter 8, Callister & Rethwisch 8e. (by 
Neil Boenzi, The New York Times.)
Fracture mechanisms
• Ductile fracture
– Accompanied by significant plastic 
deformation
• Brittle fracture
– Little or no plastic deformation
– Catastrophic
Ductile vs Brittle Failure
Very 
Ductile
Moderately
Ductile
Brittle
Fracture
behavior:
Large Moderate %AR or %EL Small
• Ductile fracture is 
usually more desirable 
than brittle fracture!
Adapted from Fig. 8.1, 
Callister & Rethwisch 8e. 
• Classification:
Ductile:
Warning before 
fracture
Brittle:
No 
warning
• Ductile failure:
-- one piece
-- large deformation
Figures from V.J. Colangelo and F.A. 
Heiser, Analysis of Metallurgical Failures
(2nd ed.), Fig. 4.1(a) and (b), p. 66  John 
Wiley and Sons, Inc., 1987.  Used with 
permission.
Example:  Pipe Failures
• Brittle failure:
-- many pieces
-- small deformations
• Resulting
fracture
surfaces
(steel)
50 mm
particles
serve as void
nucleation
sites.
50 mm
From V.J. Colangelo and F.A. Heiser, 
Analysis of Metallurgical Failures (2nd 
ed.), Fig. 11.28, p. 294,  John Wiley and 
Sons, Inc., 1987.  (Orig. source:  P. 
Thornton, J. Mater. Sci., Vol. 6, 1971, pp. 
347-56.)
100 mm
Fracture surface of tire cord wire  
loaded in tension.  Courtesy of F. 
Roehrig, CC Technologies, Dublin, 
OH.  Used with pe
Moderately Ductile Failure
• Failure Stages:
necking
s
void 
nucleation
void growth
and coalescence
shearing 
at surface
fracture