MECHANISMS OF FAILURE M.N. Tamin, UTM SME 4133 Failure of Engineering Components and Structures MODULE 4 MECHANISMS OF FAILURE SKMM 4133 Failure of Engineering Components and Structures

MECHANISMS OF FAILURE M.N. Tamin, UTM SME 4133 Failure of Engineering Components and Structures 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 Structures

MECHANISMS OF FAILURE M.N. Tamin, UTM SME 4133 Failure of Engineering Components and Structures Tensile Fracture Cleavage (brittle) fractureDuctile fracture Source: Vander Voort, G.F., Metals Engineering Quarterly, Vol. 16, No. 3, 1976, pp. 33. SKMM 4133 Failure of Engineering Components and Structures

MECHANISMS OF FAILURE M.N. Tamin, UTM SME 4133 Failure of Engineering Components and Structures 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 Structures

MECHANISMS OF FAILURE M.N. Tamin, UTM SME 4133 Failure of Engineering Components and Structures Fracture of Shaft in Torsion Overload Dark spiral indicates plastic deformation by torsion Swirl pattern of fracture surface Fracture surface is flat and perpendicular to axis of shaft Ductile failure of 1035 steel drive shaft due to torsion overload SKMM 4133 Failure of Engineering Components and Structures

MECHANISMS OF FAILURE M.N. Tamin, UTM SME 4133 Failure of Engineering Components and Structures Fig. 4.3, Callister 7ed. Burgers vector b Imperfections in Solid Screw dislocation SKMM 4133 Failure of Engineering Components and Structures

MECHANISMS OF FAILURE M.N. Tamin, UTM SME 4133 Failure of Engineering Components and Structures Particles serve as void nucleation sites. 50  m P. Thornton, J. Mater. Sci., Vol. 6, 1971, pp ) Fracture Process in Ductile Materials Slip by plastic deformation SKMM 4133 Failure of Engineering Components and Structures

MECHANISMS OF FAILURE M.N. Tamin, UTM SME 4133 Failure of Engineering Components and Structures Ductile failure: --one piece --large deformation 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., Used with permission. Ductile Versus Brittle Fracture SKMM 4133 Failure of Engineering Components and Structures

MECHANISMS OF FAILURE M.N. Tamin, UTM SME 4133 Failure of Engineering Components and Structures Ductile Fracture Surface - Dimples in ductile fracture. Transgranular fracture (across grains) SKMM 4133 Failure of Engineering Components and Structures

MECHANISMS OF FAILURE M.N. Tamin, UTM SME 4133 Failure of Engineering Components and Structures Intergranular fracture (between grains) 304 S. Steel (metal) Reprinted w/permission from "Metals Handbook", 9th ed, Fig. 633, p 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 Structures

MECHANISMS OF FAILURE M.N. Tamin, UTM SME 4133 Failure of Engineering Components and Structures Deterioration of a material by initiation and propagation of crack when subjected to repeated load. FATIGUE FAILURE SKMM 4133 Failure of Engineering Components and Structures

MECHANISMS OF FAILURE M.N. Tamin, UTM SME 4133 Failure of Engineering Components and Structures Formation of Fatigue Striations SKMM 4133 Failure of Engineering Components and Structures

MECHANISMS OF FAILURE M.N. Tamin, UTM SME 4133 Failure of Engineering Components and Structures Fatigue Striations SKMM 4133 Failure of Engineering Components and Structures

MECHANISMS OF FAILURE M.N. Tamin, UTM SME 4133 Failure of Engineering Components and Structures PSB – persistent slip bands Fracture Surface Due To Fatigue SKMM 4133 Failure of Engineering Components and Structures