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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