International Journal of Fracture and Damage Mechanics vol 2 issue 2

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IJFDM (2016) 7–9 © JournalsPub 2016. All Rights Reserved Page 7

International Journal of Fracture and Damage Mechanics Vol. 2: Issue 2

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Creep Mechanism in Materials at Elevated Temperature

Manisha Agnihotri* Rajiv Gandhi Proudyogiki Vishwavidyalaya, Bhopal, India

ABSTRACT

Deformation at elevated temperature under constant load is called creep. It depends on the

wire material and the temperature of the room. In this paper we have given a short

communication on Creep occurring in materials and its mechanism at elevated temperature

values. In the meanwhile, structural changes in the material are well explained

Keywords: creep, dislocation, elevated temperature, material deformation, tensile load

INTRODUCTION

Creep occurs when a metal is subjected to

a constant tensile load at an elevated

temperature. Hence it undergoes a time-

dependent increase in length. As the

material is said to have low melting point,

creep usually occurs when the homologous

temperature is > 0.5. When the material is

subjected to high temperature creep test is

performed on the material. Creep test is

performed in influence of constant load on

a tensile specimen at constant temperature.

The resultant graph thus illustrates a

typical creep curve having 3 distinct stages

with different creep rates. After an initial

rapid elongation e0, the creep rate decrease

with time until reaching the steady state.

(1) Primary creep is a period of transient

creep. The creep resistance of the

material increases due to material

deformation. Predominate at low

temperature test such as in the creep of

lead at RT.

(2) Secondary creep provides a nearly

constant creep rate. The average value

of the creep rate during this period is

called the minimum creep rate.

(3) Tertiary creep shows a rapid increase

in the creep rate due to effectively

reduced cross-sectional area of the

specimen.

The shape of creep curve will slightly

change according to the applied stress at a

constant temperature.

CREEP

Many complex processes are taking place

inside the solder alloy during the creep

test. The deformation observed is a result

of the simultaneous application of a load

(the 4.8 kg weight) and the atomic

movement inside the alloy at elevated

temperature. (In this case room

temperature is an “elevated” temperature.)

A creep curve such as the one shown

above is often divided into three portions:

Primary creep: This is the deformation

that occurs just after the load is

applied. In this region, the curve is

downward. This means the

deformation rate is decreasing. During

primary creep, the internal structure of

the alloy is changing in response to the

applied load.

Secondary creep: There is often a stage

where the slope of the creep curve

remains approximately constant, like a

straight line. This is the period of

secondary creep (also called steady

state creep). During secondary creep,

the internal structure of the alloy

remains approximately constant.

IJFDM (2016) 14-16 © JournalsPub 2016. All Rights Reserved Page 14


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A Brief Account of Brittle Fracture in Engineering Materials

Rekha Rani* Lovely Professional University, Punjab, India

ABSTRACT

Fracture is usually undesirable in engineering applications. Flaws such as surface cracks

lower the stress for brittle fracture whereas line defects are responsible for initiating ductile

fractures. Brittle fracture is the failure of a material with minimum of plastic deformation. If

the broken pieces of a brittle fracture are fitted together, the original shape & dimensions of

the specimen are restored. Brittle fracture is defined as fracture which occurs at or below the

elastic limit of a material. The mechanism of Brittle fracture is explained by Griffith theory.

This paper discusses about brittle fracture and gives a brief introduction of Griffith Theory of

brittle fractures.

Keywords: brittle fracture; crack formation, ductile, Griffith theory, plastic deformation

INTRODUCTION

Brittle fracture takes place by rapid crack

propagation and very little plastic

deformation, and yields a relatively flat

fracture surface. For most brittle

crystalline materials, crack propagation

corresponds to the successive and repeated

breaking of atomic bonds along specific

crystallographic planes, this is known as

cleavage.

Cleavage is essentially a low temperature

phenomenon, which can be eliminated if a

sufficiently high deformation temperature

is used. See the section on the ductile-to-

brittle transition. The occurrence of brittle

fracture is also associated with certain

crystal structures, in particular BCC,

where it is more pronounced in the

presence of impurities which form

interstitial solid solutions in metals of this

structure.[1–3]

FRACTURE

It is defined as the separation of a body

into pieces due to stress, at temperatures

below the melting point. Steps in fracture:

crack formation

crack propagation

Fracture Depending on the ability of

material to undergo plastic deformation

before the fracture two fracture modes can

be defined - ductile or brittle

Ductile Fracture – most metals (not too

cold):

Extensive plastic deformation ahead of

crack

energy absorption (“toughness”) before

fracture

Crack is “stable”: resists further

extension unless applied stress is

increased

Brittle Fracture

Some Examples – ceramics, ice, cold

metals:

Relatively little plastic deformation

low energy absorption before fracture

Crack is “unstable”: propagates rapidly

without increase in applied stress

No appreciable plastic deformation

IJFDM (2016) 10-13 © JournalsPub 2016. All Rights Reserved Page 10


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A Short Communication on Tool Wear Mechanism

Priyanka Garg* Department of Physics, University of Madras, Chennai, Tamil Nadu, India

ABSTRACT

Tool wear describes the gradual failure of cutting tools due to regular operation. It is a term

often associated with tipped tools, tool bits, or drill bits that are used with machine tools.

Types of wear include: flank wear in which the portion of the tool in contact with the finished

part erodes. This paper discusses the tool wear mechanism and factors affecting it.

Keywords: abrasive, adhesive, crater, flank wear, tool wear

INTRODUCTION

Evidence indicates that wear is a complex

phenomenon and is influenced by many

factors. The causes of wear neither behave

in the same manner, nor do they always

affect wear to the same degree under

similar cutting conditions. The causes of

wear are not fully understood.

In recent years, great strides have been

made by various researches. Even though

there is some disagreement regarding the

true mechanisms by which wear actually

takes place, most investigators feel that

there are at least five basic causes of wear

as follows:

(1) Abrasive action of hard particles

contained in the work material.

(2) Plastic deformation of the cutting edge.

(3) Chemical decomposition of the cutting

tool contact surfaces.

(4) Diffusion between work and tool

material.

The relative effects of these causes are a

function of cutting velocity or cutting

temperatures. Investigations have also

been made on other possible causes such

as oxidation and electrochemical reactions

in the tool work contact zone.[1–3]

FACTORS INFLUENCING TOOL

WEAR

The most important factor influencing tool

wear is cutting temperature. Of the four

basic causes of wear, temperature has

considerable effect in all but, one cutting

temperatures is important for two basic

reasons:

(1) Most tool materials shown rapid loss

of strength hardness, and resistance to

abrasion above some critical

temperature

(2) The rate of diffusion between work

and tool materials rises very rapidly as

temperature increases past the critical

TYPES OF WEAR

Abrasive wear

Softer material sliding over the face of

hard material may contain appreciable

concentration of hard particles. Hard

particles act as small cutting edge like

grinding wheel. Hard particles result worn

out of tool material. Particles of hard

material are intermittently turn out from

the surface and dragged along the

surface.[2]

The most common type of wear

mechanism, abrasive wear occurs when

the hard particle on chips passes over the

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mechanics and crack-damage repair mechanics. Journals publish both theoretical and experimental

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Focus and Scope of the Journal Elastic instability Gross plastic deformation Tensile instability Creep damage and creep-fatigue interaction Low and high cycle fatigue damage Brittle/elastic damage Ductile/plastic damage Strain softening and strain-rate sensitivity damage Impact damage Modeling and numerical simulation Elastic–plastic fracture mechanics Crack incubation and propagation Crack and fracture repair techniques Damage tolerance and fracture control

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From the Editor's Desk

Dear Readers,

We would like to present, with great pleasure, the inaugural volume of a new scholarly

journal, International Journal of Fracture and Damage Mechanics. This journal is part of

the Engineering Sciences, and is devoted to the scope of present Fracture and Damage

Mechanics from theoretical aspects to application-dependent studies and the validation of

emerging technologies.

This new journal was planned and established to represent the growing needs of Fracture and Damage

Mechanics as an emerging and increasingly vital field, now widely recognized as an integral part of

scientific and technical investigations. Its mission is to become a voice of the Engineering Science

community, addressing researchers and practitioners in this area.

The core vision of International Journal of Fracture and Damage Mechanics in Journals Pub is to

propagate novel awareness and know-how for the profit of mankind ranging from the academic and

professional research societies to industry practitioners in a range of topics in Fracture and Damage

Mechanics in general. Journals Pub acts as a pathfinder for the scientific community to published their

papers at excellently, well-time & successfully.

International Journal of Fracture and Damage Mechanics focuses on original high-quality research in the

realm of Elastic instability, Gross plastic deformation, Tensile instability, Creep damage and creep-fatigue

interaction, Low and high cycle fatigue damage, Brittle/elastic damage etc.

The Journal is intended as a forum for practitioners and researchers to share the techniques of Fracture and

Damage Mechanics and solutions in the area.

Many scientists and researchers have contributed to the creation and the success of the Fracture and

Damage Mechanics community. We are very thankful to everybody within that community who supported the

idea of creating an innovative platform. We are certain that this issue will be followed by many others,

reporting new developments in the field of Fracture and Damage Mechanics

This issue would not have been possible without the great support of the Editorial Board members, and we

would like to express our sincere thanks to all of them. We would also like to express our gratitude to the

editorial staff of Journals Pub, who supported us at every stage of the project.

It is our hope that this fine collection of articles will be a valuable resource for engineering readers and will

stimulate further research into the vibrant area of Fracture and Damage Mechanics.

Puneet Mehrotra

Managing Director

1. Classification of Chains Based on Strength and Reliability in Machines C. Chinglenthoiba, V. Balaji, B. Abbas, A. Madhan Kumar 1

2. Practices Used in Damage Tolerance and Fatigue Control in Aircraft Structures Reema Jaiswal 4

3. Creep Mechanism in Materials at Elevated TemperatureManisha Agnihotri 7

4. A Short Communication on Tool Wear MechanismPriyanka Garg 10

5. A Brief Account of Brittle Fracture in Engineering MaterialsRekha Rani 14

Contents



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Classification of Chains Based on Strength and Reliability in

Machines

C. Chinglenthoiba*, V. Balaji, B. Abbas, A. Madhan Kumar

Department of Mechanical Engineering, Mahendra Engineering College, Affiliated to Anna University,

Namakkal, Chennai, India

ABSTRACT

A chain, a reliable machine component, transmits power by means of tensile forces, used

primarily for power transmission and conveyance systems. The function and uses of chain are

similar to a belt and convenient to sort types of chain by either material of composition or

method of construction. The chains can be broadly divided into six types.

Keywords: compressed air technology, effective renewable alternative energy, zero pollution

vehicle

INTRODUCTION A chain is a reliable machine component,

which transmits power by means of tensile

forces, and is used primarily for power

transmission and conveyance systems. The

function and uses of chain are similar to a

belt.

There are many kinds of chain. It is

convenient to sort types of chain by either

material of composition or method of

construction.[1–7]

We can sort chains into five types:

Cast iron chain

Cast steel chain

Forged chain

Steel chain

Plastic chain

Demand for the first three chain types is

now decreasing; they are only used in

some special situations. For example, cast

iron chain is part of water-treatment

equipment; forged chain is used in

overhead conveyors for automobile

factories.

It is important to note that, roller chain is a

chain that has an inner plate, outer plate,

pin, bushing, and roller.[8–17]

CLASSIFICATION OF CHAINS

Based on the Type of Application

We can sort chains according to their uses,

they can be broadly divided into six types:

(1) Power transmission chain

(2) Small pitch conveyor chain

(3) Precision conveyor chain

(4) Top chain

(5) Free flow chain

(6) Large pitch conveyor chain

The first one is used for power

transmission; the other five are used for

conveyance. In the Applications section of

this book, we will describe the uses and

features of each chain type by following

the above classification.

In the following section, we will explain

the composition of power transmission

chain, small pitch chain, and large pitch

conveyor chain.



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Practices Used in Damage Tolerance and Fatigue Control in

Aircraft Structures

Reema Jaiswal* Chhatrapati Shahu Ji Maharaj University, Kanpur, India

ABSTRACT

This paper discusses the importance of fatigue and damage tolerance analysis procedures,

which are dominant factors in the aircraft structural design process as well as the following

in service life. These concepts are illustrated with typical examples.

Keywords: aerospace structure, aircraft, damage tolerance, fatigue, fracture

INTRODUCTION

In today’s structural design, fatigue and

damage tolerance analysis have become

most important and challenging task for

the designers because of failure of

structure due to different type of damages.

Some of these damages have caused a loss

of entire structure i.e. Whole Aircraft

Itself. The failures associated deal with

structural components serving mechanical

systems. The loading conditions can take a

variety of forms, such as engine noise

during normal operation, or maneuvers

performed during cruise. The analysis of

combined loading conditions provide a

more realistic picture of actual in-service

use, and allow the engineer to assess

system performance more clearly before

any supporting testing may commence.[1]

As a system performs throughout its

intended lifespan, accumulated wear, or

fatigue will inherently occur. This

accumulation has a direct correlation with

the increase probability a failure will

occur, defined as risk.

Fatigue

Fatigue is defined as structural failure due

to repeated loads (cycling), whose

generated stresses are lower than those

found for static failure. Failures occur due

to the natural inhomogeneity of materials

and damage imparted to materials from

manufacturing processes, where

accumulation of damage from loading

occurs due to:

Mechanical or thermally induced

loading

Environmental effects to component

(corrosion, etc.)

Rate of damage is load dependent

(randomized loading vs. constant

loading)

Fatigue damage in large and complex

structures can have multiple sites of

initiations, which is especially true for

large assemblies, such as the aircraft’s

fuselage and wing. Initiation sites are due

to poor design practices or manufacturing

quality. Some examples include improper

corrosion protection (design),

incorporation of jagged edges or notches

(design and/or manufacturing). Such

initiation sites cause local discontinuities

(in the case of corrosion pitting) and/or

geometric aberrations, where sudden

changes in the structural load path promote

stress risers. Quantified geometric

aberrations are termed stress concentration

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