Material Selection

The selection of a material for a machine part or structural member is one of the most important decisions of the designer.  There are systematic and optimizing approaches to material selection. Here, we will only look at how to approach some material properties. One basic technique is to list all the important material properties associated with the design,( strength, stiffness, and cost). This can be prioritized by using a weighting measure depending on what properties are more important than others. Next, for each property, list all available materials and rank them in order beginning with the best material; e.g., for strength, high-strength steel such as 4340 steel should be near the top of the list. For completeness of available materials, this might require a large source of material data. Once the lists are formed, select a manageable amount of materials from the top of each list. From each reduced list select the materials that are contained within every list for further review. The materials in the reduced lists can be graded within the list and then weighted according to the importance of each property.   

Choosing material for any product in design stage, should analyses the product.
 What does it do, who uses it, what should it cost?
 How do the mechanical parts work and interact

Selection of Material Depends on following factors,

• Function
• Material Properties                  
• Failure mode
• Material Cost and Availability 
Material must be priced appropriately (not cheap but right) 
            Material must be available (better to have multiple sources)
• Processing / Manufacturability
Must consider how to make the part, for example: 
            Casting 
            Machining 
            Welding
• Working Environment and Serviceability
         Wear and Corrosion

• Durability and Maintenance

Materials Selection Methodology 

1. Identify the design requirements, The design requirements include the following items:
• Performance requirements
• Reliability requirements
• Size, shape, and mass requirements
• Cost requirements
• Manufacturing and assembly requirements
• Industry standards
• Government regulations
• Intellectual property requirements
• Sustainability requirements

2. Translate the design requirements into materials specifications. It should take into consideration the design Objectives, Function, Constraints and Free variables.
(Objectives- to make it as cheap as possible, or as light as possible, or as safe as possible, or combination of all)
(Function- to support load, or to contain pressure, or to transmit heat)
(Constraints- dimensions are fixed, or withstand load without fail, or it should function in a certain temperature range)

3. List the constraints (e.g. no buckling, high stiffness) of the problem and develop an equation for them, if required.
Develop an equation of the design objective in terms of functional requirements, geometry and materials properties (objective function)

4. Define the unconstrained (free) variables. Substitute the free variable from the constraint equation into the objective function.

5. Group the variables into three groups, functional requirements (F), geometry (G) and materials functions (M), to develop the performance metric (P)

6. Screening out of materials that fail the design constraints and other variables. And Ranking the materials by their ability to meet the requirements.

7. Search for supporting information for the material candidates/Attributes. Analyze and select the appropriate material for safe design.

Some Material And Its Application   

Material	Applications
Ferrous
Cast irons	Automotive parts, engine blocks, machine tool structural parts, lathe beds
High carbon steels	Cutting tools, springs, bearings, cranks, shafts, railway track
Medium carbon steels	General mechanical engineering (tools, bearings, gears, shafts, bearings)
Low carbon steels	Steel structures (mild steel)—bridges, oil rigs, ships; reinforcement for concrete; automotive parts, car body panels; galvanized sheet; packaging (cans, drums)
Low alloy steels	Springs, tools, ball bearings, automotive parts (gears connecting rods, etc.)
Stainless steels	Transport, chemical and food processing plant, nuclear plant, domestic ware (cutlery, washing machines, stoves), surgical implements, pipes, pressure vessels, liquid gas containers
Non-ferrous
Aluminum alloys / Casting alloys	Automotive parts (cylinder blocks), domestic appliances (irons)
Non-heat-treatable alloys	Electrical conductors, heat exchangers, foil, tubes, saucepans, beverage cans, lightweight ships, architectural panels
Heat-treatable alloys	Aerospace engineering, automotive bodies and panels, lightweight structures and ships
Copper alloys	Electrical conductors and wire, electronic circuit boards, heat exchangers, boilers, cookware, coinage, sculptures
Lead alloys	Roof and wall cladding, solder, X-ray shielding, battery electrodes
Magnesium alloys	Automotive castings, wheels, general lightweight castings for transport, nuclear fuel containers; principal alloying addition to aluminum alloys
Nickel alloys	Gas turbines and jet engines, thermocouples, coinage; alloying addition to austenitic stainless steels
Titanium alloys	Aircraft turbine blades; general structural aerospace applications; biomedical implants.
Zinc alloys	Die castings (automotive, domestic appliances, toys, handles); coating on galvanized steel
Polymers: Elastomer
Butyl rubber	Tyres, seals, anti-vibration mountings, electrical insulation, tubing
Ethylene-vinyl-acetate	Bags, films, packaging, gloves, insulation, running shoes
Isoprene	Tyres, inner tubes, insulation, tubing, shoes
Natural rubber	Gloves, tyres, electrical insulation, tubing
Polychloroprene (neoprene)	Wetsuits, O-rings and seals, footware
Polyurethane elastomers	Packaging, hoses, adhesives, fabric coating
Silicone elastomers	Electrical insulation, electronic encapsulation, medical implants
Polymers: Thermoplastic
Acrylonitrile butadiene styrene	Communication appliances, automotive interiors, luggage, toys, boats
Cellulose polymers	Tool and cutlery handles, decorative trim, pens
Ionomer	Packaging, golf balls, blister packs, bottles
Polyamides (nylons)	Gears, bearings; plumbing, packaging, bottles, fabrics, textiles, ropes
Polycarbonate	Safety goggles, shields, helmets; light fittings, medical components
Polyetheretherketone	Electrical connectors, racing car parts, fiber composites
Polyethylene	Packaging, bags, squeeze tubes, toys, artificial joints
Polyethylene terephthalate	Blow molded bottles, film, audio/video tape, sails
Polymethyl methacrylate (acrylic)	Aircraft windows, lenses, reflectors, lights, compact discs
Polyoxymethylene (acetal)	Zips, domestic and appliance parts, handles
Polypropylene	Ropes, garden furniture, pipes, kettles, electrical insulation, astroturf
Polystyrene	Toys, packaging, cutlery, audio cassette/CD cases
Polyurethane thermoplastics	Cushioning, seating, shoe soles, hoses, car bumpers, insulation
Polyvinylchloride	Pipes, gutters, window frames, packaging
Polytetrafluoroethylene (teflon)	Non-stick coatings, bearings, skis, electrical insulation, tape
Polymers: Thermoset
Epoxies	Adhesives, fiber composites, electronic encapsulation
Phenolics	Electrical plugs, sockets, cookware, handles, adhesives
Polyester	Furniture, boats, sports goods
Polymers:Polymer foams
Flexible polymer foam	Packaging, buoyancy, cushioning, sponges, sleeping mats
Rigid polymer foam	Thermal insulation, sandwich panels, packaging, buoyancy
Composites
Alumina	Cutting tools, spark plugs, microcircuit substrates, valves
Aluminum nitride	Microcircuit substrates and heat sinks
Boron carbide	Lightweight armor, nozzles, dies, precision tool parts
Silicon	Microcircuits, semiconductors, precision instruments,
Silicon carbide	High temperature equipment, abrasive polishing grits, bearings, armor
Silicon nitride	Bearings, cutting tools, dies, engine parts
Tungsten carbide	Cutting tools, drills, abrasives
Ceramics
Borosilicate glass	Ovenware, laboratory ware, headlights
Glass ceramic	Cookware, lasers, telescope mirrors
Silica glass	High performance windows, crucibles, high temperature applications
Polymer
CFRP	Lightweight structural parts (aerospace, bike frames, sports goods, boat hulls and oars, springs)
GFRP	Boat hulls, automotive parts, chemical plant