Fracture, Fatigue & Creep Deformation

jove20020

C15: FRACTURE FATIGUE AND CREEP DEFORMATION Catherine Rae 12 Lectures Synopsis Introduction: This course examines the use of fracture mechanics in the prediction of mechanical failure. We explore the range of macroscopic failure modes; brittle and ductile behaviour. We take a closer look at fast fracture in brittle and ductile materials – characteristics of fracture surfaces; inter-granular and intra-granular failure, cleavage and micro-ductility. We describe the range of fatigue failure and apply fracture mechanics to the growth of fatigue cracks. Finally we look at the processes of creep and how it combines with fatigue. Griffiths analysis: Revision of concept of energy release rate, G, and fracture energy, R. Modification for ductile materials, loading conditions. Concept of R curves. Linear Elastic Fracture Mechanics, (LEFM). We look at the three loading modes and hence the state of stress ahead of the crack tip. This leads to the definition of the stress concentration factor, stress intensity factor and the material parameter the critical stress intensity factor. The effect of Constraint, definition of plane stress and plane strain and the effect of component thickness. The plasticity at the crack tip and the principles behind the approximate derivation of plastic zone shape and size. Limits on the applicability of LEFM. Elastic-Plastic Fracture Mechanics; (EPFM). The definition of alternative failure prediction parameters, Crack Tip Opening Displacement, and the J integral. Measurement of parameters and examples of use. The effect of Microstructure on fracture mechanism and path, cleavage and ductile failure, factors improving toughness, Fatigue: definition of terms used to describe fatigue cycles, High Cycle Fatigue, Low Cycle Fatigue, mean stress R ratio, strain and load control. S-N curves. Adapting data to real conditions: Goodmans rule and Miners rule. Micromechanisms of fatigue damage, fatigue limits and initiation and propagation control, leading to a consideration of factors enhancing fatigue resistance. Total life and damage tolerant approaches to life prediction. Creep deformation: the evolution of creep damage, primary, secondary and tertiary creep. Micro-mechanisms of creep in materials and the role of diffusion. Ashby creep deformation maps. Stress dependence of creep – power law dependence. Comparison of creep performance under different conditions – extrapolation and the use of Larson-Miller parameters. Examples.

2 T2 K: [5 u* O2 MBooklist:
. e+ T+ h- |8 h: E3 r7 J1 lT.L. Anderson, Fracture Mechanics Fundamentals and Applications, 2nd Ed. CRC
) g' g5 B. P* J" {* S* |press, (1995) (Fracture mechanics and it’s application to fatigue)
7 e* {" m( o( F1 s1 x  FB. Lawn, Fracture of Brittle Solids, Cambridge Solid State Science Series 2nd ed
1993. (Exactly as it says on the label)
.J.F. Knott, Fundamentals of Fracture Mechanics, Butterworths (1973)
7 d9 m& c4 H( I+ U+ eJ.F. Knott, P Withey, Worked examples in Fracture Mechanics, Institute of
. p! i  T* U; w7 S7 R1 bMaterials. (Excellent short summary of fracture mechanics and good worked
7 d+ U3 p& O+ S$ Mexamples)
3 a) `3 d  F/ R; G* @" ~) s9 PH.L.Ewald and R.J.H. Wanhill Fracture Mechanics, Edward Arnold, (1984)
' b2 {  Z' Z( D7 k4 D6 \S. Suresh, Fatigue of Materials, Cambridge University Press, (1998)
(Excellent on fatigue but not very readable)
4 a7 e; j5 E6 h0 d/ s; ~% b4 QG. E. Dieter, Mechanical Metallurgy, McGraw Hill, (1988)
(General mechanical properties)
D.C. Stouffer and L.T. Dame, Inelastic Deformation of Metals, Wiley (1996)
! e/ B! S* E' Y0 `7 Q0 I(Particularly chapters 2 and 3 for creep and fatigue)
F.R.N. Nabarro, H.L. deVilliers, The Physics of Creep, Taylor and Francis, (1995)
(Creep of superalloys)