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INTRODUCTION M.N. Tamin, UTM

SME 4133 Failure of Engineering Components and Structures

MODULE 1

INTRODUCTION

SKMM 4133 Failure of Engineering Components and Structures



Fatigue crack in root area of

a turbine blade

List possible questions regarding this fracture situation

OPENING REMARKS




• 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

Failure Analysis of Metallic Components



SME 4133 Failure of Engineering Components and StructuresSKMM 4133 Failure of Engineering Components and Structures

Week Date

(Sun.)

Lecture & Topics

TopicsLecture

1

Lecture

2

Lecture

3

1 07 Sep A A A

A – Introduction

- Overview

- Requirements and approach

B – Static failure due to overload

and instability.

C – Fatigue failure

- High-cycle fatigue

- Low-cycle fatigue

D – Creep and stress rupture

E – Fatigue crack propagation

(OPTIONAL) – Computational aspects of

failure analysis

2 14 Sep A A A

3 21 Sep B B B

4 28 Sep B B B

5 05 Oct C C C

6 12 Oct C C C

7 19 Oct SEMESTER BREAK

8 26 Oct Test1 C C

9 02 Nov C C C

10 09 Nov C C C

11 16 Nov D D D

12 23 Nov D D D

13 30 Nov E E E

14 07 Dec E E E

15 14 Dec E Test 2 Closure

16 21 Dec STUDY LEAVE

17 28 Dec FINAL EXAMINATION



COURSE CONTENT

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 (Continued)

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.




COVERAGE

• CONCEPT

• FUNDAMENTAL THEORY

• ESTABLISHED WORK

• STATISTICS

• CASE STUDIES




SCOPE

MODES OF FAILURE

• Gross Yielding

• Fatigue Fracture

• Creep Rupture

• Buckling

• Static Delayed Fracture

REQUIREMENTS FOR FAILURE

ANALYSIS

• Mechanical design and analysis

• Force analysis

• Stress analysis

• Chemical analysis

• Metallography

• Fractography

• Mechanical testing

• Failure simulation




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

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.





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.





• 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)

Steps in Performing Failure Analysis
