MODULE 4 - Universiti Teknologi Malaysiataminmn/pdf-files/sme4133_Module_4... · MODULE 4...

SME 4133 Failure of Engineering Components and Structures

MODULE 4

MECHANISMS OF FAILURE M.N. Tamin, UTM

MECHANISMS OF FAILURE

SME 4133 Failure of Engineering Components and Structures

MECHANISMS OF FAILURE

Static failureTensile fractureDuctile and brittle fracture

MECHANISMS OF FAILURE M.N. Tamin, UTM

Ductile and brittle fractureCreep ruptureMorphology of fracture surfaces

Fatigue failureStages of fatigue failureFatigue fracture characteristics

SME 4133 Failure of Engineering Components and Structures

Tensile Fracture

MECHANISMS OF FAILURE M.N. Tamin, UTM

Cleavage (brittle) fracture Ductile fracture

Source: Vander Voort, G.F., Metals Engineering Quarterly, Vol. 16, No. 3, 1976, pp. 33.

SME 4133 Failure of Engineering Components and Structures

Fracture of Bolts in Tensile Overload

(a) Brittle fracture

(Water-quenched to 47 Rockwell C)

MECHANISMS OF FAILURE M.N. Tamin, UTM

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)

SME 4133 Failure of Engineering Components and Structures

Fracture of Shaft in Torsion Overload

Fracture surface is flat and perpendicular to axis of shaft

MECHANISMS OF FAILURE M.N. Tamin, UTM

Dark spiral indicates plastic deformation by

torsion Swirl pattern of fracture surface

Ductile failure of 1035 steel drive shaft due to torsion overload

SME 4133 Failure of Engineering Components and Structures

Imperfections in SolidScrew dislocation

MECHANISMS OF FAILURE M.N. Tamin, UTM

Fig. 4.3, Callister 7ed.

Burgers vector b

SME 4133 Failure of Engineering Components and Structures

necking void nucleation

void growth and linkage

shearing at surface

fracture

σ

Fracture Process in Ductile Materials

MECHANISMS OF FAILURE M.N. Tamin, UTM

Particles serve as void

nucleation sites.

50 µm

P. Thornton, J. Mater. Sci., Vol. 6, 1971, pp. 347-56.)

Slip by plastic deformation

SME 4133 Failure of Engineering Components and Structures

• Ductile failure:--one piece--large deformation

Ductile Versus Brittle Fracture

MECHANISMS OF FAILURE M.N. Tamin, UTM

• Brittle failure:--many pieces--small 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.

SME 4133 Failure of Engineering Components and Structures

Ductile Fracture Surface

• Transgranular fracture(across grains)

MECHANISMS OF FAILURE M.N. Tamin, UTM

- Dimples in ductile fracture.

SME 4133 Failure of Engineering Components and Structures

• Intergranular fracture(between grains)

Brittle Fracture Surfaces

MECHANISMS OF FAILURE M.N. Tamin, UTM

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

SME 4133 Failure of Engineering Components and Structures

Deterioration of a material by initiation and propagation of crack when subjected to

FATIGUE FAILURE

MECHANISMS OF FAILURE M.N. Tamin, UTM

propagation of crack when subjected to repeated load.

SME 4133 Failure of Engineering Components and Structures

Formation of Fatigue Striations

MECHANISMS OF FAILURE M.N. Tamin, UTM

SME 4133 Failure of Engineering Components and Structures

Fatigue Striations

MECHANISMS OF FAILURE M.N. Tamin, UTM

SME 4133 Failure of Engineering Components and Structures

Fracture Surface Due To Fatigue

MECHANISMS OF FAILURE M.N. Tamin, UTM

PSB – persistent slip bands