MATERIAL SELECTION IN DESIGN

Materials of Construction can be classified into two groups

1.Metallic Materials2.Non-Metallic Materials

Metallic Materials1. Ferrous materials2. Non-Ferrous materials

Ferrous: Iron & its iron alloys such as grey cast iron, malleable cast iron, wrought cast iron and steels of low and high carbon content.

Non-ferrous: Copper, zinc, tin, lead and their alloys like brass, bronze, gun metal, duralumin.

Non-metallic materials: Plastics, rubber, leather, carbon, wood, glass.

PROPERTIES OF MATERIALS

Need for Material SelectionMany new materialsMany new material typesNew manufacturing methodsProperties of existing materials improvedIncreased use of advanced materialsEntirely new design configurations feasibleIncreased competition between materials

Selection of Materials in Mechanical Design

A systematic approach:1.Conventional practices and individual

experiences determine the type of the material to be used in the application.

2.This practice saves the design time.3.It overlooks the objectives of the product for

which the materials are being selected.

Stepwise details of the approach1.Define the material requirements.

2. Find possible materials

3.Make a choice

S.NO PRODUCT OBJECTIVE

MATERIAL REQUIREMENT

1 Initial cost Materials, Transportation2 Processing cost Machineability, Forgability, hot/cold rolled,

Weldability, Heat treatment characteristics.3 Maintenance cost Wear , lubrication , corrosion and failure

characteristics4 Efficiency Surface properties , corrosion characteristics

and thermal characteristics.5 Mass production Castability , machinability , forgebility and

other processing characteristics.6 Accuracy Wear characteristics, surface finish obtainable,

hardness and stiffness.7 Aesthetics Natural appearance, adaptability for surface

coatings.8 Noise Damping characteristics, lubrication properties,

stiffness and others.9 Safety Chemical properties, failure characteristics and

others.10 Functional

requirements for reliable performance

Strength, endurance limit, yield characteristics, hardness, impact resistance, magnetisation and others.

11 Weight Specific weight, strength and others.12 Delivery time Processing characteristics and others.13 Life Wear resistance, corrosion resistance, failure

characteristics and others.

S.NO Class of influencing factors

Influencing factors

1 Resources limitations Availability of materialsManufacturing process availableAvailable modes of transportation and others

2 User’s Restrictions Maximum permissible costMaximum permissible noise levelMaximum acceptable lifeDesired qualityDesired delivery dateInhibitions for aestheticsMaximum acceptable weightMaintenance level acceptable and others

3 Environmental conditions Restriction on utilization of indigenous resources

Environmental conditions for service life

Material selection is a step in the process of designing any physical object.

This selection process can be defined by

application requirements, possible materials, physical principles, and selection.

Material Selection Process

Requirements involved in material selection

Service requirementFabrication requirementsEconomic requirements

SERVICE REQUIREMENTSDimensional stabilityCorrosion resistance Adequate strength Hardness Toughness Heat resistance.

Fabrication Requirements

MECHANICAL PROPERTIES:

Strength RigidityQuality Durability

Economic Requirements

Material cost:

Initial costProcessing costMaintenance cost

transparentabsorbentmalleable

flexibleopaque

strongsmooth

roughshinydull

hard

suitablecost

Materials used

Properties

transparentstrong

flexible

soft

keeps heat in

malleable

strong

wool forjumpers

steel forcars

glass forwindows

Characteristics of materials

APPLICATIONS BASED ON MATERIAL PROPERTIES

Pre-Selection of materials:

Purpose of Pre-SelectionExamples for pre-SelectionSystematic ApproachBase Material for Pre-Selection

Purpose of Pre-Selection/Sifting of Material

Type of Material

Manufacturing Process

Function Specification

Systematic Approach