MECHANISMS OF FAILURE SKMM 4133 Failure of Engineering Components and Structures MECHANISMS OF FAILURE Static failure Tensile fracture Ductile and brittle fracture Creep rupture Morphology of fracture surfaces ID: 178660
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MODULE 4MECHANISMS OF FAILURE
SKMM 4133 Failure of Engineering Components and StructuresSlide2
MECHANISMS OF FAILURE
Static failure Tensile fracture Ductile and brittle fracture Creep rupture Morphology of fracture surfaces Fatigue failure Stages of fatigue failure Fatigue fracture characteristics
SKMM 4133 Failure of Engineering Components and StructuresSlide3
Tensile Fracture
Cleavage (brittle) fracture
Ductile fractureSource: Vander Voort, G.F., Metals Engineering Quarterly, Vol. 16, No. 3, 1976, pp. 33.
SKMM 4133 Failure of Engineering Components and StructuresSlide4
Fracture of Bolts in Tensile Overload
(a) Brittle fracture
(Water-quenched to 47 Rockwell C)(b) Ductile fracture(Annealed to 15 Rockwell C)(c) Extensive necking and cup-and-cone fracture of an annealed bolt(d) Brittle fracture of a quenched bolt. No obvious plastic deformation
(a) (b) (c) (d)
SKMM 4133 Failure of Engineering Components and StructuresSlide5
Fracture of Shaft in Torsion Overload
Dark spiral indicates plastic deformation by torsion
Swirl pattern of fracture surfaceFracture surface is flat and perpendicular to axis of shaftDuctile failure of 1035 steel drive shaft due to torsion overload
SKMM 4133 Failure of Engineering Components and StructuresSlide6
Fig. 4.3, Callister 7ed.
Burgers vector
b
Imperfections in Solid
Screw dislocation
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Particles serve as void nucleation sites.
50
mmP. Thornton, J. Mater. Sci
., Vol. 6, 1971, pp. 347-56.)
Fracture Process in Ductile Materials
Slip by plastic deformation
SKMM 4133 Failure of Engineering Components and StructuresSlide8
• Ductile failure:
--one piece
--large deformation• Brittle failure: --many pieces --small deformationFigures 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.
Ductile Versus Brittle Fracture
SKMM 4133 Failure of Engineering Components and StructuresSlide9
Ductile Fracture Surface
- Dimples in ductile fracture.
• Transgranular fracture (across grains)SKMM 4133 Failure of Engineering Components and StructuresSlide10
• Intergranular fracture
(
between grains)304 S. Steel (metal)Reprinted w/permission from "Metals Handbook", 9th ed, Fig. 633, p. 650. Copyright 1985, ASM International, Materials Park, OH. (Micrograph by J.R. Keiser and A.R. Olsen, Oak Ridge National Lab.)
4 mm
Brittle Fracture Surfaces
SKMM 4133 Failure of Engineering Components and StructuresSlide11
Deterioration of a material by initiation and propagation of crack when subjected to repeated load.
FATIGUE FAILURE
SKMM 4133 Failure of Engineering Components and StructuresSlide12
Formation of Fatigue Striations
SKMM 4133 Failure of Engineering Components and StructuresSlide13
Fatigue Striations
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PSB – persistent slip bands
Fracture Surface Due To Fatigue
SKMM 4133 Failure of Engineering Components and Structures