comparitive study of mechanical properties of engineering material by following suitable testing...

8/7/2019 Comparitive Study of Mechanical Properties of Engineering Material by Following Suitable Testing Procedures- II

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COMPARITIVE STUDY OF MECHANICAL

PROPERTIES OF ENGINEERING MATERIAL

BY FOLLOWING SUITABLE TESTING

PROCEDURES

Submitted by

Sayantan Mukherjee (071160132020)

Debarghya Mukherjee (071160132002)Rashmi Sharma (071160132048)

Md. Sadique Gazi (071160132015)

Sayak Sen (071160132027)

Puranjoy Banerjee (071160132002)

Under the supervision ofMr. Manik Chandra Das

REPORT SUBMITTED IN FULFILLMENT OF THE REQUIREMENT FOR

THE DEGREE OF BACHELOR OF TECHNOLOGY IN AUTOMOBILE

ENGINEERING OF WEST BENGAL UNIVERSITY OF TECHNOLOGY

2010-2011 SESSION

DEPARTMENT OF AUTOMOBILE ENGINEERING

MCKV INSTITUTE OF ENGINEERING

243 G.T. ROAD (NORTH) LILUAH

HOWRAH-711204


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CONTENTS

Topics Page No.

1) The Background 03

2) The Push for Alternative Materials 04

3) The Outlook 07

4) All about Steel 07

5) Material Failure Types 13

6) Research Works Already Performed 23

7) Materials under Consideration 24

8) The Project Work in Details 24

9) Experimental Results 26

10) Comparative Study of the Stress-Strain Curves Obtained for the

Different Material 27

11) Comparative Study of the Fatigue Testing for the Different Materials 30

12) Generalized Summary of the comparative Study 31

13) Acknowledgement and Conclusion 31

References 32


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THE BACKGROUND

Tomorrows cars will handle better, offer improved acceleration, braking and cornering,

be lighter and more fuel efficient, and cause less pollution. But light weight at any priceis not the sole objective. Safety and style, technical feasibility, environmental impact and

affordability, are vital factors.

Audis launch of the aluminum A8 and its 47m joint venture manufacturing facility with

Alcoa, have further highlighted the automotive industrys increasing interest in

alternative materials for the body-in-white. These, and similar, developments threaten

the dominant position of steel as the quintessential automotive material.

MATERIAL TRENDS IN AUTOMOTIVE INDUSTRY

Aluminium alloys, plastics and composites are the new materials for the automotiveindustry (some of them have existed, in various forms, for two or three decades) andtheir publicity has eclipsed that for similar advances in steel production and technology.Todays average European car contains 70 kg of aluminium and up to 120 kg of plastics(both almost double the 1980 figures). Sheet steel contributes 400 kg, and all steels intotal account for 55-60% of typical vehicle weight (as they have for 14 years, even afterconsiderable weight reductions). Despite, or because of, steels dominance in highvolume car production, it is increasingly seen as yesterdays material, and the fact thatover 50% of modem automotive steels have been introduced since the mid 1980s isfrequently overlooked by the motoring media and public eager for more attractive

alternatives.

STEELS

The automotive steels of the 1990s have better formability, greater capacity forlocalized/necking elongation, higher forming limits, smaller bend radii limits, less spring back in pressing operations, and lower sensitivity to galling and surface damage thanalternative materials. The new hot rolled, high-strength carbon-manganese and carbon-manganese-silicon sheet steels combine yield and tensile strength with cold formabilityand they can now increase component strength, or achieve equivalent strength for less

weight (useful in underbody applications). Bake hardenable steels, in which strength anddent resistance increase after stowing in the paint shop, are particularly useful in panelsexposed to minor knocks and scrapes, such as doors and boot lids.


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THE PUSH FOR ALTERNATIVE

MATERIALS

The arguments for alternative materials concentrate on weight reduction and fuel

efficiency, better performance, tooling cost, and environmental friendliness.

In North America legislative pressure to reduce fuel consumption has sparked the search

for a lighter car. Aluminium and plastics can indeed produce vehicles that are lighter than

current steel models. And these lighter vehicles also have other benefits, such as fewer

parts, by using space frame construction though steel could also do this. An aluminium

panel weighs about half as much as a steel panel of equivalent strength, and using more

aluminium could, it is claimed, also meet other criteria, although the past 15 years have

seen considerable savings (albeit offset by luxury fittings and safety features) achieved

through rationalization of car body structures and the use of lighter gauge, higher strength

steels.

At present, alternative materials are most competitive in low volume production where

tooling, rather than materials, most affects unit cost. Aluminium could reduce body

weight by up to 40%, but new steel technologies promise reductions of up to 35%,

leaving aluminium only just ahead.

LIGHTER STEELS

Weight reduction also improves overall performance and handling. A 10% weight losscan reduce acceleration time from 0 to 60mph by about 8%. Research using finite

element and design sensitivity analysis shows that a 20% or greater reduction in bodyweight can be achieved by combining new steels and manufacturing technologies (suchas adhesives and weld bonding). Work involving the American Iron and Steel Institute(AISI), Ford and Porsche Engineering Services, has shown that structures 15% stiffer andnearly 20% lighter than existing base saloon cars, could give savings of about 140lbs pervehicle. As steel is used almost universally in the automotive industry, reductions couldbe introduced into existing facilities almost immediately, increasing the cost advantagesof weight reduction using steels rather than other materials.

PLASTICS- A SUITABLE ALTERNATIVE

In contrast, potential savings with plastics are less clear. Lower densities, relative to steel,

are offset by the need for thicker panels to achieve equivalent stiffness, inherent problems

with consistent panel quality in high volume manufacture, and a tendency to crack on

impact. New manufacturing equipment, such as injection moulding tools, represent a

significant price barrier to a plastic body-in-white, especially for manufacturers with

substantial investment in stamping and pressing equipment. Although high corrosion

resistance, shape flexibility, and dent and stone chipping resistance, make plastics useful


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for vulnerable parts, such as bumpers, they are never cheaper than steels of equivalent

strength and sometimes cost four times as much.

The weight, size and design (including materials) of a car body all contribute to its

behaviour in an accident (crashworthiness) and the safety of the passengers. Aluminium

structures are capable of absorbing energy equivalent to those using steels. But the

proven performance of steel-bodied cars in a wide range of countless real life crashescannot be reproduced easily. Aluminium costs five times as much as mild steel, however,

and while bare aluminium is undoubtedly more resistant to atmospheric corrosion than

bare steel, new coatings and galvanized steels mean that corrosion is no longer the

primary determinant of a car's lifespan.

INFRASTRUCTURE

The largest, and most immediate problem in high-volume production with alternativematerials is the expense of a new infrastructure to handle design, manufacture and repair.

Much of that used for steel cars is either unsuitable or incompatible. For example,aluminium and plastics cannot use presses with magnetic handling so new handling andpost stamping facilities would be needed. Plastics pose problems with fixing and paintingand, like aluminium, are difficult to integrate with monocoque steel body design, so newjoining techniques would be needed.

WELDING

Aluminium welding poses special problems. It requires more welding spots tocompensate for lower fatigue strength. Fusion welding is difficult because of oxideformation, frequently making MIG/TIG welding necessary. And aluminium's higher

surface reflectivity makes laser welding more difficult. Steels require lower weldingcurrents and lower contact pressures, while electrode life is longer, and energyconsumption three times less.

SPACEFRAMES

The constraints on manufacturing and cost have led to non-traditional body structures,such as the spaceframe which is made up of aluminium extrusions capable of being bentor formed, with castings for connection points and aluminium sheet panels. This uses halfas many parts and fewer joints than a sheet metal body and has led to claims of a 35%reduction in primary body structure weight and a 50% cut in tooling cost, compared with

traditional methods.

DISADVANTAGES OF ALUMINIUM AND SPACEFRAMES

Yet for all their ability to be readily extruded, compared with autobody steels, aluminiumalloys have a lower formability and a greater tendency to spring back in press forming.They are also more prone to handling damage by denting and scraping, and require pre-lubricated strip or protection during pressing. This has an impact on repair, as well as


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manufacturing processes and a specialized panel and frame repair system, including anetwork of dedicated repair shops, would be needed. Shaping and straighteningaluminium parts requires greater temperature control and special paints to detectoverheating or micro cracks, and separate tools and equipment to prevent iron depositsfrom corrupting aluminium welds. Spaceframes may require even more sophisticated

facilities, particularly to correct body misalignment, and complex repairs may beimpossible, leading to automatic replacement of damaged parts and higher insurancepremiums.

ENVIORNMENTAL CONSIDERATIONS

Environmental issues increasingly influence automotive design, particularly noise,recycling and life-cycle pollution. In theory, an aluminium structures resistance tovibration is one third that of an identical steel structure. This means 10 db more noise,while steel's higher sound-damping capacity reduces road noise. Aluminium cars cancompete by alternative designs or insulation, but the penalty is extra cost in materials and

more weight. Passenger comfort may also be reduced: aluminium's thermal conductivityis five times that of steel. This presents problems with external and internal temperatureson hot days so air conditioning may become a necessary extra.

RECYCLABILITY

Legislation in Germany and North America appears to be heading towards the 100%

recyclable car. Marketing campaigns have presented aluminium as a highly recyclable

material. Pound for pound it has ten times the value of steel sheet scrap. Aluminium, the

material, is potentially recyclable with an appropriate infrastructure and a limited mix of

alloys.

But recycling aluminium cars is highly complex; the different products and alloys likely

to be used are incompatible for recycling into wrought products for car bodies, and it will

take 10-15 years to create an adequate stockpile of scrap, by which time the alloys in use

today may be obsolete.

But steel is the worlds most recycled material and recycling is as old as steel production

itself. Over 400m tons are recycled worldwide each year. This is about ten times the

combined total of all other automotive body materials. Secondary aluminium production

in Europe in 1991 was only 1.6m tonnes. These 400m tons include 20m tons of

automotive steel scrap in the USA and Europe using existing recycling networks. Plastics

recycling is minimal and automotive plastics are causing problems with landfill space.

Steel can be separated magnetically, while plastic resins or aluminium alloys must besegregated with 100% accuracy, because of their low tolerance to impurities. Different

molten aluminium alloys could be mixed, but only at the expense of downgrading.

Some 80% of todays car is recycled (including over 95% of the steel), requiring much

less energy than refining from ore. The energy required for primary aluminium

production is five times that of steel, and producing a part from aluminium, rather than

steel, needs almost three times the energy. Although the excess energy in vehicle parts


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manufacture is paid back during its life, there is an overall deficit because of increased

emission of greenhouse gases in primary aluminium production, and other problems,

such as the caustic red mud produced in alumina extraction, and disposal of toxic

potliners containing cyanides and fluorides.

THE OUTLOOK

Car manufacturers are examining future options, but have already decided the way ahead

for the near future. Very few of the future models are known to include significant

amounts of aluminium or plastic body panels. Meanwhile, Chrysler is replacing the

plastic wing on its LHS with steel, and problems with the Viper's plastic bumper led to

66% of 1993 production being lost.

Radical new designs, such as spaceframes, could make aluminium and plastic panels

viable, but are still at the experimental stage. Monocoque bodies - the most economicalconstruction - are designed for steel panels and substituting alternatives would lead to

problems. Few manufacturers have worked with aluminium in mass production, and

introducing new product forms and working practices will take time and money. While

aluminium alloys and plastics undoubtedly offer some benefits, car manufacturers are

nothing if not realistic and the bottom line is: alternative materials may exist, but are they

cost-effective in producing safer, greener cars? With today's steels, an annual run of just

25,000 units could save US$140 per car (IISI study Competition between steel and

aluminium for the passenger car), or US$525 on a run of 200,000 units.

By the time the claims made for aluminium, plastic and composite exteriors have been

examined and proven (or not) steel will probably have evolved still further, maintaining,or even improving, its current advantage and preventing mass penetration of the all-

important high volume markets.

ALL ABOUT STEEL

Steel Alloys can be divided into five groups

Carbon Steels

High Strength Low Alloy Steels

Quenched and Tempered Steels

Heat Treatable Low Alloy Steels

Chromium-Molybdenum Steels


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Steels are readily available in various product forms. The American Iron and SteelInstitute defines carbon steel as follows:

Steel is considered to be carbon steel when no minimum content is specified or requiredfor chromium, cobalt, columbium [niobium], molybdenum, nickel, titanium, tungsten,

vanadium or zirconium, or any other element to be added to obtain a desired alloyingeffect; when the specified minimum for copper does not exceed 0.40 per cent; or whenthe maximum content specified for any of the following elements does not exceed the percentages noted: manganese 1.65, silicon 0.60, copper 0.60. Carbon steels arenormally classified as shown below.

Low-carbon steels contain up to 0.30 weight percent C. The largest category of this classof steel is flat-rolled products (sheet or strip) usually in the cold-rolled and annealedcondition. The carbon content for these high-formability steels is very low, less than 0.10weight percent C, with up to 0.4 weight percent Mn. For rolled steel structural plates andsections, the carbon content may be increased to approximately 0.30 weight percent, with

higher manganese up to 1.5 weight percent.

Medium-carbon steels are similar to low-carbon steels except that the carbon ranges from0.30 to 0.60 weight percent and the manganese from 0.60 to 1.65 weight percent.Increasing the carbon content to approximately 0.5 weight percent with an accompanyingincrease in manganese allows medium-carbon steels to be used in the quenched andtempered condition.

High-carbon steels contain from 0.60 to 1.00 weight percent C with manganese contentsranging from 0.30 to 0.90weight percent.

High-strength low-alloy (HSLA) steels, or microalloyed steels, are designed to providebetter mechanical properties than conventional carbon steels. They are designed to meetspecific mechanical properties rather than a chemical composition. The chemicalcomposition of a specific HSLA steel may vary for different product thickness to meetmechanical property requirements. The HSLA steels have low carbon contents (0.50 to~0.25 weight percent C) in order to produce adequate formability and weldability, andthey have manganese contents up to 2.0 weight percent. Small quantities of chromium,nickel, molybdenum, copper, nitrogen, vanadium, niobium, titanium, and zirconium areused in various combinations.

Below is a list of some SAE-AISI designations for Steel (the xx in the last two digitsindicate the carbon content in hundredths of a percent)

Carbon Steels

10xx Plain Carbon

11xx Resulfurized

12xx Resulfurized and rephosphorized

Manganese steels

13xx Mn 1.75


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Nickel steels

Illustration of Effect of Cacontent on Steel Hardness

23xx Ni 3.5

25xx Ni 5.0

Nickel Chromium Steels

31xx Ni 1.25 Cr 0.65-0.80

32xx Ni 1.75 Cr 1.0733xx Ni 3.50 Cr 1.50-1.57

34xx Ni 3.00 Cr 0.77

Chromium Molybdenumsteels

41xx Cr 0.50-0.95 Mo 0.12-0.30

Nickel ChromiumMolybdenum steels

43xx Ni 1.82 Cr 0.50-0.80 Mo 0.25

47xx Ni 1.05 Cr 0.45 Mo 0.20 0.35

86xx Ni 0.55 Cr 0.50 Mo 0.20Nickel Molybdenum steels

46xx Ni 0.85-1.82 Mo 0.20

48xx Ni 3.50 Mo 0.25

Chromium steels

50xx Cr 0.27- 0.65

51xx Cr 0.80 1.05

Effects of Elements on Steel

Steels are among the most commonly used alloys. The complexity of steel alloys is fairly

significant. Not all effects of the varying elements are included. The following text givesan overview of some of the effects of various alloying elements. Additional researchshould be performed prior to making any design or engineering conclusions.

Carbon has a major effect on steel properties. Carbon is the primary hardening elementin steel. Hardness and tensile strength increases as carbon content increases up to about0.85% C as shown in the figure above. Ductility and weldability decrease withincreasing carbon.

Manganese is generally beneficial to surface quality especially in resulfurized steels.Manganese contributes to strength and hardness, but less than carbon. The increase in

strength is dependent upon the carbon content. Increasing the manganese contentdecreases ductility and weldability, but less than carbon. Manganese has a significanteffect on the hardenability of steel.

Phosphorus increases strength and hardness and decreases ductility and notch impacttoughness of steel. The adverse effects on ductility and toughness are greater inquenched and tempered higher-carbon steels. Phosphorous levels are normally controlled


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to low levels. Higher phosphorus is specified in low-carbon free-machining steels toimprove machinability.

Sulfurdecreases ductility and notch impact toughness especially in the transversedirection. Weldability decreases with increasing sulfur content. Sulfur is found primarily

in the form of sulfide inclusions. Sulfur levels are normally controlled to low levels. Theonly exception is free-machining steels, where sulfur is added to improve machinability.

Silicon is one of the principal deoxidizers used in steelmaking. Silicon is less effectivethan manganese in increasing as-rolled strength and hardness. In low-carbon steels,silicon is generally detrimental to surface quality.

Copperin significant amounts is detrimental to hot-working steels. Copper negativelyaffects forge welding, but does not seriously affect arc or oxyacetylene welding. Coppercan be detrimental to surface quality. Copper is beneficial to atmospheric corrosionresistance when present in amounts exceeding 0.20%. Weathering steels are sold having

greater than 0.20% Copper.

Lead is virtually insoluble in liquid or solid steel. However, lead is sometimes added tocarbon and alloy steels by means of mechanical dispersion during pouring to improve themachinability.

Boron is added to fully killed steel to improve hardenability. Boron-treated steels areproduced to a range of 0.0005 to 0.003%. Whenever boron is substituted in part for otheralloys, it should be done only with hardenability in mind because the lowered alloycontent may be harmful for some applications.

Boron is a potent alloying element in steel. A very small amount of boron (about0.001%) has a strong effect on hardenability. Boron steels are generally produced withina range of 0.0005 to 0.003%. Boron is most effective in lower carbon steels.

Chromium is commonly added to steel to increase corrosion resistance and oxidationresistance, to increase hardenability, or to improve high-temperature strength. As ahardening element, Chromium is frequently used with a toughening element such asnickel to produce superior mechanical properties. At higher temperatures, chromiumcontributes increased strength. Chromium is a strong carbide former. Complexchromium-iron carbides go into solution in austenite slowly; therefore, sufficient heatingtime must be allowed for prior to quenching.

Nickel is a ferrite strengthener. Nickel does not form carbides in steel. It remains insolution in ferrite, strengthening and toughening the ferrite phase. Nickel increases thehardenability and impact strength of steels.

Molybdenum increases the hardenability of steel. Molybdenum may produce secondaryhardening during the tempering of quenched steels. It enhances the creep strength of low-alloy steels at elevated temperatures.


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Aluminum is widely used as a deoxidizer. Aluminum can control austenite grain growthin reheated steels and is therefore added to control grain size. Aluminum is the mosteffective alloy in controlling grain growth prior to quenching. Titanium, zirconium, andvanadium are also valuable grain growth inhibitors, but there carbides are difficult todissolve into solution in austenite.

Zirconium can be added to killed high-strength low-alloy steels to achieve improvementsin inclusion characteristics. Zirconium causes sulfide inclusions to be globular ratherthan elongated thus improving toughness and ductility in transverse bending.

Niobium (Columbium) increases the yield strength and, to a lesser degree, the tensilestrength of carbon steel. The addition of small amounts of Niobium can significantlyincrease the yield strength of steels. Niobium can also have a moderate precipitationstrengthening effect. Its main contributions are to form precipitates above thetransformation temperature, and to retard the recrystallization of austenite, thuspromoting a fine-grain microstructure having improved strength and toughness.

Titanium is used to retard grain growth and thus improve toughness. Titanium is alsoused to achieve improvements in inclusion characteristics. Titanium causes sulfideinclusions to be globular rather than elongated thus improving toughness and ductility intransverse bending.

Vanadium increases the yield strength and the tensile strength of carbon steel. Theaddition of small amounts of Vanadium can significantly increase the strength of steels.Vanadium is one of the primary contributors to precipitation strengthening inmicroalloyed steels. When thermomechanical processing is properly controlled theferrite grain size is refined and there is a corresponding increase in toughness. The

impact transition temperature also increases when vanadium is added.

All microalloy steels contain small concentrations of one or more strong carbide andnitride forming elements. Vanadium, niobium, and titanium combine preferentially withcarbon and/or nitrogen to form a fine dispersion of precipitated particles in the steelmatrix.

One of the main factors contributing to the utility of steels is the broad range ofmechanical properties which can be obtained by heat treatment. For example, easyformability and good ductility may be necessary during fabrication of a part. Onceformed very high strength part may be needed in service. Both of these materialproperties are achievable from the same material.

All steels can be softened to some degree by annealing. The degree of softening dependson the chemical composition of the particular steel. Annealing is achieved by heating toand holding at a suitable temperature followed by cooling at a suitable rate.

Similarly, steels can be hardened or strengthened. This can be accomplished by coldworking, heat treating, or an appropriate combination of these.


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Cold working is the technique used to strengthen both low carbon low alloyed steels andhighly alloyed austenitic stainless steels. Only reasonably high strength levels can beattained in the carbon low alloyed steels, but the highly alloyed austenitic stainless steelscan be cold worked to rather high strength levels. Most steels are commonly supplied tospecified minimum strength levels.

Heat treating is the primary technique for strengthening the remainder of the steels.Some common heat treatments of steels are listed below:

Martensitic hardening Pearlitic transformation Austempering Age hardening

Figure 1 Schematic of Time Temperature Transformation Diagram

Carbon and alloy steels are Martensitic hardened by heating to the Austenitizingtemperature followed by cooling at the appropriate rate. One requirement for fulltransformation to Martensite is that cooling must occur prior to the nose of thetransformation start curve in Figure 1. Cooling frequently occurs by quenching in oil orwater. Some steels are capable of Martensitic transformation when air cooled.


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Ms is when the Martensite transformation starts. Mfis when the Martensitetransformation finishes. Martempering is a martensitic transformation where the part iscooled rapidly to above the Ms and held until the temperature becomes uniform across thecross section.

After Martensitic transformation the steel is then tempered. Tempering consists ofreheating the steel to an intermediate temperature. Tempering causes microstructuralchanges in the steel in addition to relieving internal stresses and improving toughness.

The maximum hardness of carbon and alloy steels, after rapid quenching to avoid thenose of the isothermal transformation curve, is a dependent on the alloy content, predominantly the carbon content. The maximum thickness for complete hardening orthe depth to which an alloy will harden is measure of steels hardenability.

Pearlitic transformation is another transformation for austenite during cooling. If coolingof austenite is not quick enough some or all of the steel may transform to Pearlite instead

of Martensite. While Pearlite is not as hard as Martensite, the steels properties are stillquite good and Pearlitic structures are used in many applications.

Austempering is another heat treatment for steels. In this heat treatment steels areAustenitized followed by rapidly quenching avoid transformation of the austenite toPearlite. The steel is held at a temperature below temperatures that promote Pearliteformation and above the Martensite start transformation range. While held at thistemperature range the austenite transforms isothermally to a completely Bainiticmicrostructure. Finally the steel is cooled to room temperature. The intention ofAustempering is to acquire increased ductility or notch toughness at high hardness levels,or to decrease the possibility of cracking and distortion that might occur by traditional

quenching and tempering.

Some steels have been developed that are strengthened by age hardening. These steelsare heat treated to dissolve certain constituents in the steel into solution followed bycooling. Subsequently these steels are age hardened to precipitate the constituents insome favored particle size and distribution.

MATERIAL FAILURE TYPES

The reason why we are in a constant search of alternate materials is costing, fueleconomy due to lighter weight etc. though researchers have found some really goodalternate materials to key metals still the question remains.is that fully safe? Thus nowresearchers are in a process of studying the different types of failures common fordifferent parts of an automobile. The typical root cause failure mechanisms for differentmaterials are:-

1. Fatigue failures2. Corrosion failures3. Stress corrosion cracking
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4. Ductile and brittle fractures5. Hydrogen embrittlement6. Liquid metal embrittlement7. Creep and stress rupture

Fatigue Failures

Metal fatigue is caused by repeatedcycling of of the load. It is a progressive localized damage dueto fluctuating stresses and strainson the material. Metal fatiguecracks initiate and propagate inregions where the strain is mostsevere.

The process of fatigue consists ofthree stages:

Initial crack initiation Progressive crack growth

across the part Final sudden fracture of

the remaining cross section

Schematic of S-N Curve, showing increase in fatiguelife with decreasing stresses.

Stress Ratio

The most commonly used stress ratio is R, the ratio of the minimum stress to themaximum stress (Smin/Smax).

If the stresses are fully reversed, then R = -1. If the stresses are partially reversed, R = a negative number less than 1. If the stress is cycled between a maximum stress and no load, R = zero. If the stress is cycled between two tensile stresses, R = a positive number less

than 1.

Variations in the stress ratios can significantly affect fatigue life. The presence of a mean

stress component has a substantial effect on fatigue failure. When a tensile mean stress isadded to the alternating stresses, a component will fail at lower alternating stress than itdoes under a fully reversed stress.
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Preventing Fatigue Failure

The most effective method of improving fatigue performance is improvements in design:

Eliminate or reduce stress raisers by streamlining the part

Avoid sharp surface tears resulting from punching, stamping, shearing, or otherprocesses

Prevent the development of surface discontinuities during processing. Reduce or eliminate tensile residual stresses caused by manufacturing. Improve the details of fabrication and fastening procedures

Fatigue Failure Analysis


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Metal fatigue is a significant problem because it can occur due to repeated loads belowthe static yield strength. This can result in an unexpected and catastrophic failure in use.

Because most engineering materials contain discontinuities most metal fatigue cracksinitiate from discontinuities in highly stressed regions of the component. The failure may

be due the discontinuity, design, improper maintenance or other causes. A failureanalysis can determine the cause of the failure.

Corrosion Failures

Corrosion is chemically induced damage to a material that results in deterioration of thematerial and its properties. This may result in failure of the component. Several factorsshould be considered during a failure analysis to determine the affect corrosion played ina failure. Examples are listed below:

Type of corrosion Corrosion rate The extent of the corrosion Interaction between corrosion and other failure mechanisms

Corrosion is a normal, natural process. Corrosion can seldom be totally prevented, but itcan be minimized or controlled by proper choice of material, design, coatings, andoccasionally by changing the environment. Various types of metallic and nonmetalliccoatings are regularly used to protect metal parts from corrosion.

Stress corrosion cracking necessitates a tensile stress, which may be caused by residualstresses and a specific environment to cause progressive fracture of a metal. Aluminumand stainless steel are well known for stress corrosion cracking problems. However, allmetals are susceptible to stress corrosion cracking in the right environment.

Laboratory corrosion testing is frequently used in analysis but is difficult to correlate withactual service conditions. Variations in service conditions are sometimes difficult toduplicate in laboratory testing
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Corrosion Failures Analysis

Identification of the metal or metals, environment the metal was subjected to, foreignmatter and/or surface layer of the metal is beneficial in failure determination. Examplesof some common types of corrosion are listed below:

Uniform corrosion Pitting corrosion Intergranular corrosion Crevice corrosion Galvanic corrosion Stress corrosion cracking

Not all corrosion failures need a comprehensive failure analysis. At times a preliminaryexamination will provide enough information to show a simple analysis is adequate.

Stress Corrosion Cracking

Stress corrosion cracking is a failure mechanism that is caused by environment,susceptible material, and tensile stress. Temperature is a significant environmental factoraffecting cracking.

For stress corrosion cracking to occur all three conditionsmust be met simultaneously. The component needs to bein a particular crack promoting environment, thecomponent must be made of a susceptible material, andthere must be tensile stresses above some minimum

threshold value. An externally applied load is notrequired as the tensile stresses may be due to residualstresses in the material. The threshold stresses arecommonly below the yield stress of the material.

Stress Corrosion Cracking Failures

Stress corrosion cracking is an insidious type of failure asit can occur without an externally applied load or at loadssignificantly below yield stress. Thus, catastrophicfailure can occur without significant deformation or

obvious deterioration of the component. Pitting iscommonly associated with stress corrosion crackingphenomena.

Aluminum and stainless steel are well known for stress corrosion cracking problems.However, all metals are susceptible to stress corrosion cracking in the rightenvironment.
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Controlling Stress Corrosion Cracking

There are several methods to prevent stress corrosion cracking. One common method isproper selection of the appropriate material. A second method is to remove the chemicalspecies that promotes cracking. Another method is to change the manufacturing process

or design to reduce the tensile stresses. AMC can provide engineering expertise toprevent or reduce the likelihood of stress corrosion cracking in your components.

Ductile and Brittle failure

Ductile metals experience observable plastic deformation prior to fracture. Brittle metalsexperience little or no plastic deformation prior to fracture. At times metals behave in atransitional manner - partially ductile/brittle.

Ductile fracture has dimpled, cup and cone fracture appearance. The dimples canbecome elongated by a lateral shearing force, or if the crack is in the opening (tearing)

mode.

Brittle fracture displays either cleavage (transgranular) or intergranular fracture. Thisdepends upon whether the grain boundaries are stronger or weaker than the grains.

The fracture modes (dimples, cleavage, or intergranular fracture) may be seen on thefracture surface and it is possible all three modes will be present of a given fracture face.

Schematics of typical tensile test fractures are displayed above.

Brittle Fractures

Brittle fracture is characterized by rapid crack propagation with low energy release andwithout significant plastic deformation. The fracture may have a bright granularappearance. The fractures are generally of the flat type and chevron patterns may bepresent.


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Ductile Fractures

Ductile fracture is characterized by tearing of metal and significant plastic deformation.The ductile fracture may have a gray, fibrous appearance. Ductile fractures areassociated with overload of the structure or large discontinuities.

Hydrogen Embrittlement

When tensile stresses are applied to hydrogen embrittled component it may failprematurely. Hydrogen embrittlement failures are frequently unexpected and sometimescatastrophic. An externally applied load is not required as the tensile stresses may be dueto residual stresses in the material. The threshold stresses to cause cracking arecommonly below the yield stress of the material.

High strength steel, such as quenched and tempered steels or precipitation hardened steelsare particularly susceptible to hydrogen embrittlement. Hydrogen can be introduced intothe material in service or during materials processing.

Hydrogen Embrittlement Failures

Tensile stresses, susceptible material, and the presence of hydrogen are necessary tocause hydrogen embrittlement. Residual stresses or externally applied loads resulting instresses significantly below yield stresses can cause cracking. Thus, catastrophic failurecan occur without significant deformation or obvious deterioration of the component.


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Very small amounts of hydrogen can cause hydrogen embrittlement in high strengthsteels. Common causes of hydrogen embrittlement are pickling, electroplating andwelding, however hydrogen embrittlement is not limited to these processes.

Hydrogen embrittlement is an insidious type of failure as it can occur without an

externally applied load or at loads significantly below yield stress. While high strengthsteels are the most common case of hydrogen embrittlement all materials aresusceptible.

Liquid Metal Embrittlement

Liquid metal embrittlement is the decrease in ductility of a metal caused by contact withliquid metal. The decrease in ductility can result in catastrophic brittle failure of anormally ductile material. Very small amounts of liquid metal are sufficient to result inembrittlement.

Some events that may permit liquid metal embrittlement under the appropriatecircumstances are listed below:

Brazing Soldering Welding Heat treatment Hot working Elevated temperature service

In addition to an event that will allow liquid metal embrittlement to occur, it is also

required to have the component in contact with a liquid metal that will embrittle thecomponent.

Liquid Metal Embrittlement Failures

The liquid metal can not only reduce the ductility but significantly reduce tensilestrength. Liquid metal embrittlement is an insidious type of failure as it can occur atloads below yield stress. Thus, catastrophic failure can occur without significantdeformation or obvious deterioration of the component.

Intergranular or transgranular cleavage fracture is the common fracture modes associated

with liquid metal embrittlement. However reduction in mechanical properties due to de-cohesion can occur. This results in a ductile fracture mode occurring at reduced tensilestrength. An appropriate analysis can determine the effect of liquid metal embrittlementon failure.


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Creep and Stress Rupture

Creep occurs under load at high temperature. Boilers, gas turbine engines, and ovens aresome of the systems that have components that experience creep. An understanding ofhigh temperature materials behavior is beneficial in evaluating failures in these types of

systems.

Failures involving creep are usually easy to identify due to the deformation that occurs.Failures may appear ductile or brittle. Cracking may be either transgranular orintergranular. While creep testing is done at constant temperature and constant loadactual components may experience damage at various temperatures and loadingconditions.

Creep of Metals

High temperature progressive deformation of a material at constant stress is called creep.

High temperature is a relative term that is dependent on the materials being evaluated. Atypical creep curve is shown below:

In a creep test a constant load is applied to a tensile specimen maintained at a constanttemperature. Strain is then measured over a period of time. The slope of the curve,identified in the above figure, is the strain rate of the test during stage II or the creep rateof the material.


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Primary creep, Stage I, is a period of decreasing creep rate. Primary creep is a period ofprimarily transient creep. During this period deformation takes place and the resistanceto creep increases until stage II. Secondary creep, Stage II, is a period of roughlyconstant creep rate. Stage II is referred to as steady state creep. Tertiary creep, Stage III,occurs when there is a reduction in cross sectional area due to necking or effective

reduction in area due to internal void formation.

Stress Rupture

Stress rupture testing is similar to creep testing except that the stresses used are higherthan in a creep test. Stress rupture testing is always done until failure of the material. Increep testing the main goal is to determine the minimum creep rate in stage II. Once adesigner knows the materials will creep and has accounted for this deformation a primarygoal is to avoid failure of the component.


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Stress rupture tests are used to determine the time to cause failure. Data is plotted log-logas in the chart above. A straight line is usually obtained at each temperature. Thisinformation can then be used to extrapolate time to failure for longer times. Changes inslope of the stress rupture line are due to structural changes in the material. It issignificant to be aware of these changes in material behavior, because they could result in

large errors when extrapolating the data.

Failure Analysis

High temperature failures is a significant problem. A failure analysis can identify theroot cause of your failure to prevent reoccurrence. AMC can provide failure analysis ofhigh temperature failures to identify the root cause of your component failure.

RESEARCH WORKS ALREADY

PERFORMED

In a recent study released by the University of Toledo, forged steel crankshafts were

shown to have 36 percent higher fatigue strength than cast iron crankshafts, resulting in a

usage life six times longer for the forged steel crankshaft. The study also explored

strength, ductility and impact toughness of the two materials and found forged steel to be

superior to the ductile cast iron. Professor Ali Fatemi led a research team in conducting

the study for the Forging Industry Educational and Research Foundation (FIERF) and the

American Iron and Steel Institute (AISI).

Figure 1 - The crankshafts that were tested are shown in their final machined conditions:

the forged steel crankshaft, 3.9 kg (top) and the cast iron crankshaft, 3.7 kg (bottom).

A crankshaft experiences a large number of load cycles during its service life.

Therefore, fatigue performance and durability are key considerations in this components

design and performance, said Professor Fatemi.

Another aspect of the study was the design optimization of the forged steel crankshaft.

The dimensions and geometry of the crank webs were changed while maintainingdynamic balance, resulting in an 18 percent weight reduction. This optimally designed

crankshaft was found to have no degradation in performance. The weight reduction of a

rotating engine component is important, as fuel efficiency improvements will be realized

by the vehicle and the consumer.


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This study continues to prove to powertrain design engineers that forged steel

outperforms other materials in critical safety component applications, said David

Anderson, director of AISIs Long Product Market Development Group.

MATERIALS UNDER CONSIDERATION

Depending upon the desired mechanical property possessed by some of the materials wechoose the different materials for the experimentation purpose. The main aim of the project was to study the characteristics of the materials used in most auto parts as acommon practice and suggest any alternative low cost materials for the same. But due to,shortage of time, resources, experimental setups and other unavoidable circumstances weare bound to complete our research work experimenting on some market-availablematerials only.

The materials on which we experimented:-1) Nickel Chromium Steel2) Mild Steel3) Silicon Manganese Steel

The main aim is to perform experiments to test the tensile and compressive stress,toughness, fatigue and hardenability of all these materials. On the basis of the obtainedresults we will be in a position to describe and comment on why one type of material isspecially used for a particular auto part and is considered the best over others.

THE PROJECT-WORK IN DETAILSWe initially bought the materials from the market. The course of work was thus made indetails. We were supposed to perform hardness testing, fatigue testing and testing in theUniversal Testing Machine. Samples for these experiments to be performed are nevermarket available. All we need to do is to estimate the amount of required material withapproximate dimensions and buy the materials accordingly. So, we bought samples oflength 92 cm and 15mm diameter for each of the different materials under consideration.

The next major task was of manufacturing. The big samples were cut into requisite piecesas was required for the experiments. The first experiment to be performed was that of the

Rockwell Hardness. For this purpose we cut 2 similar sized samples (2.5cm each) foreach of the three materials from the original big sample.


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The next step was to machine the small samples and prepare them for the experiments.


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EXPERIMENTAL RESULTS

The following are the results obtained when the hardness test was performed.

Sample 1- Nickel Chromium Steel

No. of Observations Scale Load RA Scale

1 C-Scale 150 Kg 55

2 57

3 53

4 59

5 62

6 60

7 53

8 609 55

10 57

11 65

12 53

13 61

14 62

Sample 2- Mild Steel


1 B-Scale 100 Kg 812 73

3 82

4 75

5 78

6 70

7 75

8 76

9 72

10 77

11 81

12 7013 75

14 75

Sample 3- Silicon Manganese Steel


1 C-Scale 150 Kg 61


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2 61

3 66

4 65

5 62

6 65

7 638 65

9 62

10 63

11 65

12 64

13 63

14 65

Taking the average of all the hardness values obtained by the Rockwell Hardness testerwe get a comparative study of the BHN for each of the three samples.

Type of Sample Average RA Scale Brinell Hardness Number

Nickel Chromium Steel 55 (C-Scale) 241

Mild Steel 75 (B-Scale) 143

Silicon Manganese Steel 65 (C-Scale) 242

Comparative Study of the Stress-Strain

Curves Obtained for the Different Materials

There were three materials under considerations. They were examined for three basic purposes. The aim was to conclude from the performed tests the reason a particularelement is preferred over the others when it comes to use in major auto parts. It is foundthat connecting rod found the Ni-Cr steel as its best component. When considered ingeneral, we can summaries that a connecting rod requires being strong in terms of tensileand compressive stress. The material by which a connecting rod is made needs to be veryductile. Now the comparison among the materials will give a clear view of why Ni-Crsteel is used as a perfect material for the making of a connecting rod. Consider the graphbelow:-


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From the graph we can find that the ultimate stress for the Ni-Cr steel is 40KN while thebreaking stress is 38KN. The material had a percentage elongation of 16/85 or 18.8%.This is a high yield very much suitable for a material exposed to constant tensile andcompressive stress.Now consider the next graph.


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This is the stress-strain graph obtained for the carbon steel. Here again the obtainedultimate stress and the breaking stress are pretty much close to that of the Ni-Cr steel.Again the percentage elongation is found to be 12.6/85.3 or 14.77%.Finally we go for the Si-Mn steel as well. The graph says:-

The Si-Mn steel has an interesting stress-strain graph. The ultimate stress and thebreaking stress are very high for this material. It is very hard but the curve shows that thebreaking stress obtained is at the constant strain developed. This means that though thesubstance is good for hardenability and machinability it never yields much under tensileand compressive stress. The percentage elongation for this material is 14/87.66 or15.97%.From the above three results obtained a very simple and convincing comparison can bedone. The carbon steel is the least yielding material. It has low ultimate and breakingstress. Properties that a material making up the connecting rod should have are not foundin this material. Thus the carbon steel is not the very best option for the connecting rod.Next comes the Si-Mn steel. In terms of high ultimate and breaking stress it is tougherthan the other two materials. But when it comes to elongation due to tensile stress whichis most important while considering connecting rod, it is not better than Ni-Cr steel. Duethe high percentage of elongation as compared to the other two materials Ni-Cr steel canbe best used for use in connecting rod. Though Ni-Cr steel is more costly than Si-Mnsteel due to its mechanical properties it is preferred over Si-Mn steel. This is the reasonwhy Ni-Cr steel is predominantly used in the making of connecting rod.


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Comparative Study of the Fatigue Testing for

the Different Materials

Crankshaft is one of the vital auto components. Crankshafts undergo constant stressreversal. For this reason crankshaft material needs to be fatigue enduring. We haveundergone the fatigue testing on all the three materials under consideration. The materialsustaining the most number of cycles was supposed to be the best in terms of fatiguestrength. Each material was tested for two observations.

Below is the comparison of the fatigue strength for the three materials underconsideration.

Type of Material Ni-Cr Steel Carbon Steel Si-Mn Steel

No. of Cycles46691 82315 59027

43227 79075 60034

From the obtained data we can have an easy conclusion that carbon steel is far better interms of fatigue strength in comparison to Ni-Cr steel and Si-Mn steel. Carbon steel thuscan be easily declared the best material for crankshaft manufacturing. This is the reasonwhy carbon steel finds vast application in the manufacturing of one of the most importantauto-component.


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Generalised Summary of the Comparative

Study

The obtained results for the hardness test gives us an idea about which type of material isbest to form the automotive chassis. The BHN for the carbon steel is the least. So it isnever a very hard material and can never be a good choice for the automotive chassis.Automotive chassis needs to be made up of such material that has the ability to opposeany scratch or abrasion. In this respect carbon steel proved to be very weak. But of theother two materials Si-Mn steel finds extreme application as automotive chassiscomponent. The hardness test performed on the materials showed almost similar BHN forthe Si-Mn and Ni-Cr steel. But Si-Mn steel is cheaper than Ni-Cr steel though in terms ofmechanical properties Ni-Cr steel can be a good alternative to Si-Mn steel.

Acknowledgement and Conclusion

Value engineering (VE) is a systematic method to improve the "value" of goods orproducts and services by using an examination of function. Value, as defined, is the ratioof function to cost. Value can therefore be increased by either improving the function orreducing the cost. It is a primary tenet of value engineering that basic functions be preserved and not be reduced as a consequence of pursuing value improvements. Theresearch work performed had the aim of contributing in the field of value engineering. Itis never easy to suggest an alternative to an already existing material. It requires precisejudgment, testing and impact. The shortage of time and experimental setups bound us to

perform the research work on some chosen auto components and their normally usedmaterials only. The ultimate aim is however fulfilled. We aimed to find the reason why a particular material finds extreme application in the making of a certain type ofcomponent. The very first stage of value engineering is information gathering. This askswhat the requirements are for the object. Function analysis, an important technique invalue engineering, is usually done in this initial stage. It tries to determine what functionsor performance characteristics are important. It asks questions like; What does the objectdo? What must it do? What should it do? What could it do? What must it not do? We didthe same. Finding out the actual mechanical properties for which one material is superiorto other was the purpose of our project. We thank Dhiman sir for his tiring effort inhelping us perform flawless experiments. All staffs of the workshop helped us a lot while

making the samples. Specially, Ajit sir deserves thanks for being always with us and forhelping us in making samples of actual required dimensions. Our mentor, our respectedH.O.D sir, Mr. Manik Chandra Das had always been with us from the very beginning ofthe project work. His assistance, zeal and encouragement drove us to be perfect inwhatever we did. All the team-mates worked hand in hand to make the project successful.At the end of the second session of project work we proudly conclude that we lived up tothe expectations of all those involved in the project.
http://en.wikipedia.org/wiki/Costhttp://en.wikipedia.org/wiki/Costhttp://en.wikipedia.org/wiki/Costhttp://en.wikipedia.org/wiki/Cost


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1) Song Jeng Huang,Yo Zhi Dai, Yeau Ren Jeng; Volume Fraction Effects of SiliconCarbide on the Wear Behavior of sicp- Reinforced Magnesium Matrix Composites;

Advanced Materials Research (Volumes 152 - 153)

2) Ken Lowe; Materials World, Vol. 2 no. 11 pp. 577-79, November 1994

3) T.V. Christy1, N. Murugan and S. Kumar; A Comparative Study on theMicrostructures and Mechanical Properties of Al 6061 Alloy and the MMC Al6061/tib2/12P; Journal of Minerals & Materials Characterization & Engineering, Vol. 9,No.1

4) Donald Gerwin; An Agenda For Research on the Flexibility of ManufacturingProcesses; International Journal of Operations & Production Management, Volume 25

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6) Jeff R. Dieffenbach, Jacqueline A. Isaacs; Economic Analysis of the Ultra Light SteelAuto Body; International Body Engineering Conference & Exposition, September 1998

7) Erica R.H. Fuchs; Strategic materials selection in the automobile body: Economicopportunities for polymer composite design; Composites Science and Technology,Volume 68, Issue 9

8) Cooper, Robin; Target costing and value engineering; Book (ISBN 1563271729) 379 p

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USING THE TECHNIQUE OF CRACK MODELLING; Fatigue & Fracture of

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