MODULE 1 INTRODUCTION

1. MODULE 1 INTRODUCTION

2. OPENING REMARKS Fatigue crack in root area of a turbine blade List possible questions regarding this fracture situation

3. Failure Analysis of Metallic Components • Failure • Inability of a component to perform according to its intended function. • Failure Analysis • The examination of a failed component and of the failure situation in order to determine the causes of failure

5. 1.0 Introduction Historical background, origin, detection and prevention of failure, types of mechanical failure: gross yielding, fatigue fracture, buckling, creep rupture, review of stress field and stress concentration, statistical aspect of failure analysis, loading spectrum, metallurgical aspect of component failure. 2.0 Materials Defects Processing-structure-property relationship, metallurgical imperfection, processing defects, NDT methods, surface defects and corrosion, propagation of defects, tools for metallurgical failure analysis 3.0 Failure due to overload Yield failure theories, idealized material behavior, plastic bending of beams, collapse loads, plastic torsion of circular bar, residual stresses after yielding. 4.0 Buckling of Struts and Columns Euler’s column theory, Rankine-Gordon formula, eccentric loading, inelastic buckling. COURSE CONTENT

6. 5.0 Fatigue Failure High-cycle fatigue, Strength-life (S-N) curves, cumulative damage concept, life prediction and fracture control; low-cycle fatigue, strain cycling concept, strain-life curve and low-cycle fatigue relations, influence of non-zero mean strain and non-zero mean stress. 6.0 Creep and Stress Rupture Theories for predicting creep behavior, Larson-Miller and Manson-Haferd parameters, uniaxial and multi-axial state of stress, cumulative creep concept, creep-fatigue interaction. 7.0 Fatigue Crack Propagation and Control Basics of fracture mechanics, linear elastic and elastic-plastic fracture mechanics, stress intensity factor range, fatigue crack growth rate, factors affecting crack propagation, fatigue fracture mechanisms in metals. COURSE CONTENT (Continued)

7. COVERAGE • CONCEPT • FUNDAMENTAL THEORY • ESTABLISHED WORK • STATISTICS • CASE STUDIES

8. REQUIREMENTS FOR FAILURE ANALYSIS • Mechanical design and analysis • Force analysis • Stress analysis • Chemical analysis • Metallography • Fractography • Mechanical testing • Failure simulation SCOPE • MODES OF FAILURE • Gross Yielding • Fatigue Fracture • Creep Rupture • Buckling • Static Delayed Fracture

9. Classification of the causes of failure • Faulty design considerations/ misapplication of materials • Ductile failure – excessive deformation (elastic or plastic), tearing or shear fracture). • Brittle fracture – from flaws and critical stress raisers. • Fatigue failure – due to time-varying load, thermal cycling, corrosion fatigue. • High-temperature failure – creep, oxidation, local melting, warping. • Static delayed fracture – hydrogen embrittlement, • Severe stress raiser inherent in design. • Inadequate stress analysis • Mistake in designing on basis of static tensile properties only

10. Classification of the causes of failure • Faulty processing • Flaws due to faulty composition – wrong material, inclusions, embrittling impurities. • Defects originating in ingot making and casting – porosity, non-metallic inclusions, segregation. • Defects due to working – laps, seams, hot-short splits, excess local deformation • Irregularities / mistakes due to machining, grinding or stamping – burns, tearing, cracks. • Welding defects – voids, undercuts, residual stresses, HAZ, lack of penetration. • Abnormalities due to heat treatment – grain growth, precipitation, excessive retained austenite, decarburization. • Flaws due to case hardening – intergranular carbides, soft core. • Defects due to surface treatment – plating, chemical diffusion, hydrogen embrittlement. • Parting-line failure in forging - due to poor transverse properties. • Careless assembly – mismatch of mating parts, residual stress, gouges.

11. Classification of the causes of failure • Deterioration in service • Overload / unforeseen loading conditions • Wear – erosion, galling, seizing, cavitation. • Corrosion – chemical attack, stress corrosion, dezincification. • Inadequate / misdirected maintenance or improper repair – welding, grinding, cold straightening. • Disintegration by chemical attack, attack by liquid metals or plating at elevated temperature • Radiation damage - decontamination may destroy evidence for the cause of failure. • Accidental condition – abnormal operating temperature, severe vibration, impact, thermal shock.

12. Steps in Performing Failure Analysis • Description of the failure situation – Background information, history of usage, design of component. • Visual inspection – DO NOT damage the fracture surface. • Mechanical design analysis (stress analysis) – to establish the cause of failure. Was the part of sufficient size? • Chemical design analysis –to establish the suitability of the material wrt corrosion resistance. • Fractography – examine fracture surface to establish the mechanism of fracture. • Metallographic examination – to help establish such facts as whether the part has correct heat treatment. • Determine properties – to establish properties pertinent to the design. • Failure simulation - to establish response of identical component under exact condition of loading, numerical simulation. • Formulation of conclusions, Report writing (may include recommendations)