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Caterpillar: Confidential Green

SELECTION OF MATERIALS FOR ENGINEERINGAPPLICATIONS

• G.S. SHANKAR


OUTLINE

• INTRODUCTION

• THE DESIGN PROCESS

• ENGINEERING MATERIAL AND THEIR PROPERTIES

• MATERIAL SELECTION CHARTS

• MATERIAL SELECTION BASICS

• MATERIAL SELECTION- EXAMPLES & CASE STUDIES

• MATERIAL & SHAPES

• MATERIAL PROCESSING & SELECTION

• MATERIAL AESTHETICS


‘MATERIALS, OF THEMSELVES, AFFECT US LITTLE; IT IS THE WAY WE USE THEM WHICH INFLUENCES OURLIVES’. EPICTETUS, AD 50-100,

DISCOURSES BOOK 2, CHAPTER 5.


INTRODUCTION

• STARTS WITH DESIGN

• BE IT AN AIRCRAFT ENGINE OR A CHILEDREN’S TOY, IT ALL STARTS AT THE DRAWING BOARD

• DESIGN IS THE PROCESS OF TRANSLATING A NEW IDEA

• EACH OF ITS STAGES REQUIRES DECISIONS ABOUT THE MATERIALS FROM WHICH THE PRODUCT IS TO BE

MADE AND THE PROCESS FOR MAKING IT.

• THE NUMBER OF MATERIALSAVAILABLE TO THE ENGINEER IS VAST: 80 000+ WITH ADDITION OF

NEW MATERIALS EVERY YEAR

• THE CHOICE OF MATERIAL CANNOT BE MADE INDEPENDENTLY OF THE CHOICE OF PROCESS BY WHICH

THE MATERIAL IS TO BE FORMED, JOINED, FINISHED, OR HEAT TREATED.

• THE AGES IN WHICH MAN HAS LIVED ARE NAMED FOR THE MATERIALS HE USED: STONE, BRONZE, IRON.

AND WHEN HE DIED, THE MATERIALS HE TREASURED WERE BURIED WITH HIM

• IF THEY HAD LIVED AND DIED TODAY, WHAT WOULD THEY HAVE TAKEN WITH THEM? THEIR TITANIUM

WATCH PERHAPS ,THEIR CARBON-FIBRE REINFORCED TENNIS RACQUET, THEIR METAL-MATRIX COMPOSITE

MOUNTAIN BIKE,HER-ETHYL-KETONE CRASH HELMET.

• THE EARLIER THINKING IS ENGINEERING MATERIALS MEANS ‘METALS’. NOW WE ARE IN THE AGE OF THE

AGE OF ADVANCED MATERIALS. METALS, PLASTIC, RUBBER, ELECTRONIC/ MAGNETIC / NANO MATERIALS

HAVE COME.

• THIS RAPID RATE OF CHANGE OFFERS OPPORTUNITIES WHICH THE DESIGNER CANNOT AFFORD TO

IGNORE. (EXAMPLE >>>>).

• LAST BUT NOT THE LEAST COST SHOULD BE SUCH THAT THE PRODUCT SHOULD SELL IN THE MARKET

1905

Wood &

Leather

2017

Polymer


THE DESIGN PROCESS

• DESIGN IS AN ITERATIVE PROCESS. THE STARTING POINT IS A MARKET NEED OR A NEW IDEA; THE END POINT

IS THE FULL SPECIFICATIONS OF A PRODUCT THAT FILLS THE NEED OR EMBODIES THE IDEA.

• THE PRODUCT ITSELF IS CALLED A TECHNICAL SYSTEM. A TECHNICAL SYSTEM CONSISTS OF ASSEMBLIES,

SUBASSEMBLIES AND COMPONENTS, PUT TOGETHER IN A WAY THAT PERFORMS THE REQUIRED TASK.

• THE DESIGN CONVERTS THE INPUTS INTO THE OUTPUTS.

• DESIGN TOOLS AND MATERIAL DATA: CAD / CAM/ DFM/ DFA/ MODELLING- SOLID WORKS / 3D /FEA /

CFD ETC.

• MATERIALS SELECTION ENTERS EACH STAGE OF THE DESIGN- CONCEPT / PROTO / PRODUCTION

• THE FINAL STAGE OF DETAILED DESIGN REQUIRES A STILL HIGHER LEVEL OF PRECISION AND DETAIL, BUT FOR

ONLY ONE OR A VERY FEW MATERIALS.

• FUNCTION, MATERIAL, SHAPE AND PROCESS : THE SELECTION


TYPES OF DESIGN

Concept

of

Design

Original

design

Adaptive

design

Variant

design

New ideas, Innovative ideas,

Eg: concept of a computer, compact

disc, high purity silica for optical

fiber, train, ship, concept of gas

turbine (not a flight), concept of

internet

Improvement in performance,

Refinement in working principle,

Eg: OHP to DLP, Progress in the

design of automobiles, aircrafts

etc.,

Change is inevitable for

technological

advancements

Scaling up/down of systems

Eg: balsa wood to Al alloys (airplanes)

Retain function, change

material


DESIGN FLOWCHART/PROCESS


DESIGN FLOWCHART/PROCESS

Need

Concept

Final product

Embodiment

Detail

Material selection

process

All known materials

Precise selection of

acceptable

materials

Best material that

satisfies all the

design requirements

Materials

science

Atomic/

crystal

structure

Properties

Mech.

Thermal

Electrical

Optical

Magnetic

Processing

Manufacture

Design tools

Viability analysis

Approximate

analysis

Optimization

More perfect

analysis

Engg.

concepts

Mechanics

Solid

Fluid

Thermo-

dynamics

Modeling

techniques

Numerical

techniques


PROBLEM OF MATERIALS SELECTION

Choice of

Material

Function

Shape Process

Influence of interaction

Eg:

I-section of

rails

Aerodynamic

shapes

Honeycomb,

cellular

structures

Eg: Load bearing,

Temperature, Pressure

etc..

Eg:

Forming, Joining,

Near-net shape

manufacturing,

New processing

technologies


ENGINEERING MATERIAL AND THEIR PROPERTIES• THE CLASSES OF ENGINEERING MATERIAL: CLASSIFY THE MATERIALS OF

ENGINEERING INTO THE SIX BROAD CLASSES - METALS, POLYMERS, ELASTOMERS,

CERAMICS, GLASSES AND COMPOSITES.

• EACH CLASS OF MATERIAL IS DEFINED BY ITS SPECIFIC PROPERTIES. METALS-

STRENGTH, CERAMIC – HIGH TEMPERATURES.

• COMPOSITES COMBINE THE ATTRACTIVE PROPERTIES OF THE OTHER CLASSES OF

MATERIALS WHILE AVOIDING SOME OF THEIR DRAWBACKS. EG: POLYESTER,

USUALLY – REINFORCED BY FIBRES OF GLASS, CARBON OR KEVLAR.

• EACH MATERIAL HAS A SET OF ATTRIBUTES: ITS PROPERTIES. IT IS NOT A MATERIAL,

PER SE, THAT THE DESIGNER SEEKS; IT IS A SPECIFIC COMBINATION OF THESE

ATTRIBUTES: A PROPERTY-PROFILE. THE MATERIAL NAME IS THE IDENTIFIER FOR A

PARTICULAR PROPERTY-PROFILE.


MATERIALS SELECTION CHARTS

• MATERIALS SELECTION CHART IS A NOVEL GRAPHICAL WAY OF

PRESENTING MATERIAL PROPERTY DATA.

• LOGARITHMIC SCALES ARE USED ON THESE CHARTS SINCE THE

PROPERTIES (FOR VARIOUS MATERIALS) CAN EXTEND OVER SEVERAL

ORDERS OF MAGNITUDE.

• THESE 2D PLOTS, DEALS WITH TWO PROPERTIES AT A TIME, AND THERE

ARE NECESSARY DESIGN GUIDELINES TO HELP IN THE SELECTION OF

MATERIALS


MATERIALS SELECTION CHARTS

Eg: Fracture Toughness Vs Strength chart


MATERIAL SELECTION BASICS

South Africa’s Olympian Oscar Pistorious (www.gearpetrol.com)

CFRP leg


METAL STRENGTH VS LOADING

• PARTS ARE DESIGNED TO CARRY LOADS WITHOUT BREAKING

• PARTS CAN FAIL WHEN- 1. OVERLOADED 2.DAMAGE ON THE PART

• PARTS FAIL AT THE WEAKEST LINK.

• STRENGTH OF METAL DECREASES WITH RISE IN TEMPERATURE


METAL STRENGTH VS LOADING

• Parts should not fail under fatigue if the loads are below endurance limit

• If the parts are loaded to ½ endurance limit, then factor of safety is 2


STRESS RISERS

• Stress risers are physical irregularities that concentrate applied stress resulting in increased stress at the irregularity

-Round Groove: 1.5 times

-V Notch: 3.0 times

-Crack: 8 times

• Sharper the irregularity, higher the multiplying factor

• The designer should design parts with enough strength which have geometrical stress risers.

• Un-expected stress risers like material flaws, manufacturing defects and physical abuse can cause parts to experience excessive stress above endurance limit


MATERIAL SELECTION - THE BASICS

‘the component must function at

250”C’, or that ‘the component must work in oil- similar to

job ads- ‘degree in metallurgy’

it is descriptive, graphical or pictorial: case studies of

previous uses of the material- design data book etc.,

The final choice between competing candidates will

often depend on local conditions: on the existing

in-house expertise or equipment, on the availability

of local suppliers,


MATERIAL SELECTION- EXAMPLES & CASE STUDY

• WE WILL SEE SOME OF THE COMMON MATERIALS USED IN THE AUTO COMPONENT INDUSTRY

• GEARS – LOW CARBON ALLOY STEELS (EN 353, 16MNCR5, 20MNCR5, EN 354, 355 ETC..

• SHAFTS – OIL / WATER PUMP, CAM SHAFTS – EN8D, CK-45

• AXLE SHAFTS – EN18

• FUEL TANKS – XL POLY ETHYLENE

• ROPS, FOPS, CHASSIS, CAR BODIES, DOORS – HIGH STRENGTH LOW ALLOY STRUCTURAL STEELS

• GEAR / AXLE HOUSINGS / ENGINE AND CYLINDER BLOCK – CAST IRON / ALUMINIUM

• SPRING / THRUST WASHERS- 1070, 1080 , 42J

• U-BOLTS – EN19

• DUMP BODIES OF TRUCKS – HIGH ALLOY STEELS

• ENGINE VALVES – NI BASED , TITANIUM , HIGH NITROGEN STEELS (21-4N ETC)

• TRANSMISSION AND ENGINE TIMING CHAINS- MEDIUM CARBON PLATES , LOW CARBON ALLOY STEEL ROLLERS, PINS


CASE STUDY – FUEL TANKS

• REQUIREMENTS:

• FUEL TANK NEEDS TO BE RESISTANT TO CORROSION

• LEAK PROOF

• TIGHTNESS TEST AT AN INTERNAL PRESSURE APPROXIMATELY EQUAL TO TWICE OF THE MAXIMUM OPERATING

PRESSURE

• LESS WEIGHT

• EASE OF MANUFACTURING

• PASS THE FIRE RESISTANCE TEST

• ETC…


• POSSIBLE CANDIDATES:

• STEEL , PLASTIC

• LET US COMPARE THESE CANDIDATE MATERIALS VIS-À-VIS THE REQUIREMENTS


Requirement Steel Plastic Remarks

Corrosion Resistance X Good Plastic is better

Leak Proof ???? ?? Seam welding Vs

Roto molding-

process consistencyPass internal pressure

test

????? ??

Ease of

manufacturing

Poor Very Good Good raw material

control, less manual

Fire Resistance Poor Passes ECE R34 regulation

Low temperature

operating conditions

Poor Passes

Impact Test Poor Passes Drop weight test

Weight More Less

Colour Not Possible Possible Restricted Colours


• NOW WE SEE THAT A PLASTIC FUEL TANKS SEEM TO BE A BETTER CHOICE

• BUT OUT OF THE LARGE NUMBER OF PLASTIC MATERIAL AVAILABLE, POLY ETHYLENE HAS BEEN

PROVEN (DATA AVAILABLE).

• FINALLY IT NARROWS DOWN TO XL- CROSS LINKED POLYETHYLENE IS INDEED A BETTER

CHOICE



MATERIAL & SHAPES

• SHAPED SECTIONS CARRY BENDING, TORSIONAL AND AXIAL-COMPRESSIVE LOADS MORE EFFICIENTLY THAN

SOLID SECTIONS

• ‘SHAPED' MEANS THAT THE CROSS-SECTION IS FORMED TO A TUBE, A BOX-SECTION, AN I-SECTION ETC.,

• BY 'EFFICIENT' IT MEANS THAT, FOR GIVEN LOADING CONDITIONS, THE SECTION USES AS LITTLE MATERIAL,

AND IS THEREFORE AS LIGHT, AS POSSIBLE.

• TUBES, BOXES AND I-SECTIONS WILL BE REFERRED TO AS 'SIMPLE SHAPES'.

• EVEN GREATER EFFICIENCIES ARE POSSIBLE WITH SANDWICH PANELS (THIN LOAD-BEARING SKINS BONDED

TO A FOAM OR HONEYCOMB INTERIOR- RADIATOR CORES ETC)

• HERE COMES THE CONCEPT OF ‘SHAPE FACTOR’ SIMPLE NUMBERS WHICH CHARACTERIZE THE EFFICIENCY

OF SHAPED SECTIONS.

• TAKE THE EXAMPLE OF A BICYCLE: ITS FORKS. THEY ARE LOADED IN BENDING. IT COULD, SAY, BE MADE OF

STEEL OR OF WOOD -EARLY BIKES WERE MADE OF WOOD. BUT STEEL IS AVAILABLE AS THIN-WALLED TUBE,

WHEREAS THE WOOD IS NOT; WOOD, USUALLY, HAS A SOLID SECTION. A SOLID WOOD BICYCLE IS

CERTAINLY LIGHTER AND STIFFER THAN A SOLID STEEL ONE, BUT IS IT BETTER THAN ONE MADE OF STEEL

TUBING? MIGHT A MAGNESIUM I-SECTION BE BETTER STILL? WHAT ABOUT A WEBBED POLYMER

MOULDING? HOW, IN SHORT, IS ONE TO CHOOSE THE BEST COMBINATION OF MATERIAL AND SHAPE?


MATERIAL PROCESSING & SELECTION

• MATERIAL PROCESSING REFERS HERE TO TWO ASPECTS.

• 1. THE DESIGN SHOULD BE IN SUCH A WAY THAT THE COMPONENT SHOULD BE MADE BY ONE OF THE

NUMEROUS MANUFACTURING ‘PROCESSES’ AVAILABLE.

• A PROCESS IS A METHOD OF SHAPING, FINISHING OR JOINING A MATERIAL. SAND CASTING, INJECTION

MOULDING, FUSION WELDING ARE ALL PROCESSES.

• THE SECOND ASPECT IS A PROCESS THAT ENHANCES ITS PROPERTIES TO MEET THE PERFORMANCE

REQUIREMENTS- HEAT TREATMENT, PLATING, PAINTING.

• HEAT TREATMENT PROCESSES ARE DESIGNED IN SUCH A WAY THAT IT CAN INCREASE THE STRENGTH, WEAR

RESISTANCE, FATIGUE RESISTANCE EYC.

• MATERIAL AND PROCESS SELECTION AND DESIGN GO HAND IN HAND.


MATERIAL AESTHETICS• GOOD DESIGN WORKS. EXCELLENT DESIGN ALSO GIVES PLEASURE

• PLEASURE DERIVES FROM FORM, COLOUR, TEXTURE, FEEL

• THESE DAYS THE DEMAND FOR AESTHETICS IS EVER INCREASING.

• EXAMPLES- CHROME PLATED CAR DOOR HANDLES , PAINT, BODY COLOURED BUMPERS,

INTERIORS OF A CAR ETC.

• THE DEMAND FROM CUSTOMERS FOR PRODUCTS LIKE FARM TRACTORS AND MINING TRUCKS

IN TERMS OF AESTHETICS IS MIND BOGGLING.

• POLYMERS FOR EXAMPLE LEND THEMSELVES TO BRIGHT COLOURS, SATISFYING TEXTURES AND

GREAT FREEDOM OF FORM; THEY HAVE OPENED NEW STYLES OF DESIGN- MOBILES, PENS


• REFERENCE:

• MATERIALS SELECTION IN MECHANICAL DESIGN,

- M. F. ASHBY, ROYAL SOCIETY RESEARCH PROFESSOR, ENGG. DESIGN CENTRE

ENGG. DEPT., UNIVERSITY OF CAMBRIDGE, UK, PERGAMON PRESS.


THANK YOU

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SELECTION OF MATERIALS FOR ENGINEERING ...iim-kalpakkam.in/images/Conferences/Technical_Programs/...• MATERIALS SELECTION ENTERS EACH STAGE OF THE DESIGN- CONCEPT / PROTO / PRODUCTION