material selection and design consideration

8/10/2019 Material Selection and Design Consideration

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MaterialSelection and

DesignConsideration

Submitted to: Engr. Mary Jeanne Servigon

Submitted by: Jean Clauden C. Banks ChE4

Cloe Ferolino ECE 3

Mark Christian Basbano


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What is Material Selection?

It is the foundation of all engineering applications and design.

It is the step in the process of designing any physical object.

The main goal of material selection is to minimize cost while meeting productperformance goals.

What is Design Consideration?

They are not requirements, but do present information that is important to consider in thedesign, construction and maintenance of improvements within public rights-of-way.

As an engineer, you dont want to be famous for designing a component that failed.

Why Study Material Selection and Design Consideration?

An engineering student should be familiar with and versed procedures and protocols thatare normally employed in the process.

Inappropriate or improper decisions can be disastrous from both economic and safety perspectives.

An important task for an engineer to perform is that of material selection with regard tocomponent design.

Material Selection and Design Consideration Involves

Selecting a material,

How to wisely select a material;

Choosing a manufacturing process.


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Materials

The matter from which a thing is or can be made.

The substance or substances out of which a thing is or can be made.

A physical object, as opposed to something spiritual or mental, or something that isessential and relevant.

Types of Materials

Ceramics

A ceramic is a non-metallic material composed of

inorganic molecules, normally prepared by heating

and subsequent cooling.


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Polymers/ Plastics

Plastics/polymers are made up of millions of

repeated links to make a long molecule.

Metals

Metals are materials that are easily shaped by forming.

They are excellent conductors of electricity and heat.

Metals have an orderly arrangement of atoms,

resulting in a crystalline structure.

Composites

Composites are the mixture of two materials,

which in combination, offer superior properties

to the materials alone.


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Properties of Materials

When studying materials and especially when selecting materials for a project / design, itis important to understand key properties.

The expected level of performance from the material

Metallic and Nonmetallic Materials

It is the most common, and useful classification of a material. Metallic materials are thosewhich are metals. The most common metals are iron, steel, bronze, copper and aluminum.The nonmetallic group includes materials such as wood, brick, concrete, rubber and

plastic.

Importance: Metals will be the more important of the two groups from theviewpoint of production, the relative importance of the nonmetallic group is increasingand will undoubtedly continue to do so BUT the selection of materials from either groupis dependent, in the main, upon properties and cost.

Physical and Mechanical Properties

In order to distinguish one material from another the physical properties are considered as

the: color, density, specific heat, coefficient of thermal expansion/ conductivity, electricalconductivity, strength and hardness.

Importance: Some of these are of prime importance in selecting materials for specific usesin the electrical or nuclear fields

Physical properties describe the reaction of a material to mechanical usage these often arecalled the mechanical properties of materials. To determine their mechanical properties,materials are subjected to standardized laboratory tests, wherein the influencing conditions arecontrolled. In this manner the reaction to changes in the variables may be determined.

Importance: The results will be useful only to the extent to which service conditionsduplicate the test conditions


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Stress and Strain

When materials are used in mechanisms or structures they are subjected to applied forces.

For example a weight, W is suspended by means of a bar, the bar will elongate an amount

equal to, L elongation.

The internal reactive forces are called stress. Stress is measured quantitatively as thestress per unit area s-W/Ao, where Ao is the original cross-sectional area of the bar.

The weight tends to lengthen the bar it is called a tensile strain and the stress is calledtensile strain.


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Strength

The ability of a material to stand up to forces being a

applied without it bending, breaking, shattering or deforming

in any way.

Tensile Strength

The ability of a material to stretch without

breaking or snapping.

.

Ductility

The ability of a material to change shape

(deform) usually by stretching along its length.


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Plasticity

The ability of a material to be change

in shape permanently.

The technician and his twin brother

demonstrate the plasticity of a molten

aluminum by pouring it into a mould.

Once the aluminum has cooled down,

it can be removed from the casting sand. It has a new shape.

Elasticity

The ability of a material to absorb force and

flex in different directions, returning to

its original position.


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Material Selection Charts

Allow you to view the selection charts.

Enable you to interactively 'explode' particular classes of materials.

Give brief definitions of the properties on the chart

Provide general information about each chart and some insights into the physical reasons underlying it

Youngs Modulus - Density

'

Stiffness' measures how much something stretches when a load isapplied. Young's modulus measures stiffness and is a material constant,i.e. it is the same whatever the size of the test-piece.

Many applications require stiff materials, e.g. roof beams, bicycle frames- these materials lie at the top of the chart

Many applications require low density materials, e.g. packaging foams -these materials lie to the left of the chart.


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Young's Modulus - Cost

Young's modulus measures stiffness and is a material constant, i.e. it is thesame whatever the size of the test-piece.

Many applications require stiff materials, e.g. roof beams, bicycle frames -these materials lie at the top of the chart

Many applications require low cost materials, e.g. packaging foams - thesematerials lie to the left of the chart.

Cheap stiff materials lie towards the top left of the chart mostly metals andceramics.


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Strength-Toughness

Strength measures the resistance of a material to failure, given by the applied stress(or load per unit area)

The chart shows yield strength in tension for all materials, except for ceramics forwhich compressive strength is shown (their tensile strength being much lower)

Toughness measures the energy required to crack a material; it is important forthings which suffer impact

There are many cases where strength is no good without toughness, e.g. a carengine, a hammer

Increasing strength usually leads to decreased toughness

Tempered steel is tougher but less strong than after quenching.


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Strength-Cost

Strength measures the resistance of a material to failure, given by the appliedstress (or load per unit area)

The chart shows yield strength in tension for all materials, except for ceramicsfor which compressive strength is shown (their tensile strength being much

lower)

Many applications require strong materials, e.g. screw drivers, safety belts -these lie at the top of the chart

Unfortunately there are few cheap high strength materials (top left)


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Electrical Resistivity

This chart is important for designing components requiring good electrical

insulation (e.g. plug casings) or good electrical conductivity (e.g. electric POWERCABLES) at a good price

Good electrical conductors are usually good thermal conductors and goodelectrical insulators are good thermal insulators

The similarity between electrical and thermal properties means that the chart canalso be used to identify materials requiring good thermal insulation (e.g. for kilnwalls) or thermal conductivity (e.g. for FRYING PANS)


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How To Select a Material

Material selection is a step in the process of designing any physical object. Themain goal of material selection is to minimize cost while meeting product

performance goals.[Systematic selection of the best material for a given application begins with properties and costs of candidate materials. Material selection is a stepin the process of designing any physical object. In the context of product design,the main goal of material selection is to minimize cost while meeting product

performance goals. Systematic selection of the best material for a given application begins with properties and costs of candidate materials.

Criteria when selecting material:

thermal stress

mechanical stress

chemical stress


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physiological harmlessness

thermal conduction / insulation

electrical requirements

optical requirements

fire behavior

weather resistance

radiation exposure

special specifications

When Selecting a Material for a Particular Design

Mechanical properties

Wear of materials

Corrosion

Ability to manufacture

Mechanical properties

Cost

When a certain design is going to be actually produced it must be subjectedto a number of manufacturing practices depending on the material and the

design process.

Its important for any material which is going to be subjected to mechanicalforces in use.

These forces cause the material to deform (i.e. change shape) and may causeit to fail (i.e. break).


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Examples of Failures

A 737 engine; one of the turbine blades broke away and exited through theengine casing, nearly taking someones head off!


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Wear of materials

Wear is a problem when the materials are contacting each other in a product.So it must be ensured that the selected materials have sufficient wear

resistance. This is also very important factor to consider when selecting amaterial for a particular design. In the engineering design process this has to be considered with great care.

Cost

Cost is a critical fact to consider when selecting materials for a certaindesign for most products because they are facing a severe competition in themarket.

Corrosion

Some materials are very likely to be corroded in the service depending on theservice environment. Therefore it must be assured that the material is capableof being employed for the particular design before selecting it.

Ability to manufacture

To make the dimensions more accurate it has to be machined in the

production. If this selection criteria is neglected the manufacture processmight be very costly making it unprofitable as a commercial product. Sobefore selecting the materials this fact also must be considered.

Material Cost and Availability

Material must be priced appropriately (not cheap but right)

Material must be available (better to have multiple sources)


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Manufacturing a Product

Thought processes and procedures involved in designing and manufacturing common products. Example: Paper Clip

Must meet its basic functional requirement: hold pieces of paper together withsufficient clamping force so that the papers do not slip away from each other.

Design based on strength of materials and mechanics of solids, dealingwith the stressesand strains involved during manufacturing and during normal use of the product.

Material selected must have certain stiffness and strength: Force to open the clip toohigh? Not enough clamping force on the paper? Permanent bend during use due to lowyield stress?

Manufacturing a ProductOther considerations:

Style, appearance, surface finish or texture of clipCorrosion properties: rust marks on paper

Production concerns: Bending of selected material during manufacturing without

cracking or breakingCutting the wire from a long piece without excessive wearCutting the wire with a smooth edgeThe most economical way of manufacturing the clip to make a

profitConsider the design, material selection, and processing methods involved in

manufacturing a jet engine!

Criteria for Selecting a Manufacturing Process

Shape of the final product and raw material Type of material and its basic properties:

Brittle and hard materials cannot be formed easily, but they canbe cast or machined.

Manufacturing process often alters the properties of thematerials: metals that are formed at room temperature becomestronger, harder, and less ductile than prior to processing.

Design requirements


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Additional Criteria

Dimensional and surface finish requirements: Size, thickness, and shape complexity: parts with thin cross-

sections cannot be cast properly; complex parts cannot be formed

easily.Tolerances and surface finish: better in hot-working vs. cold-

working; dimensional changes, warpage, surface oxidation atelevated temperatures.

Additional operations: grinding, polishing (better finish but moreexpensive!)

Operational and Cost considerations: Design and cost of toolingLead time required to begin productionEffect of workpiece material on tool and die lifeExpensive materials: minimize scrap (e.g., machining produces

too much scrap)Availability of machines and equipmentNumber of parts or products required and desired production

rateEnvironmental concerns

Manufacturing Processes for Metals

Casting: expendable mold and permanent mold Forming and Shaping: rolling, forging, extrusion, drawing, sheet forming,

powder metallurgy, molding Machining: turning, boring, drilling, milling, planing, shaping, broaching,

grinding, ultrasonic machining, chemical machining, electrical dischargemachining (EDM), electrochemical machining, high-energy beam machining

Joining: welding, brazing, soldering, diffusion bonding, adhesive bonding,mechanical joining

Finishing Operation: honing, lapping, polishing, burnishing, deburring, surfacetreating, coating, plating


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Choosing Methods of Production

Casting Processes

Among the oldest methods of manufacturing: used to make arrowheads,ornaments, about 4000 B.C.

Introduction of molten metal into a mold cavity; upon solidification, metalconforms to the shape of the cavity

Capable of producing intricate shapes, with internal cavities, in a single piece Very large, very small, and hollow parts can be produced economically Typical cast products: engine blocks, crankshafts, pistons, valves, railroad

wheels

Expendable mold casting : molds made of sand, plaster, ceramics, investment casting

Permanent mold casting : molds, made of metals, can be re-used; pressure casting,die-casting, centrifugal casting


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Forming and Shaping Processes

Bulk deformation processes induce shape changes by plastic deformationunder forces applied by tools and dies

Take cast metal and roll it down into general shapes such as slabs, plates,billets, then forge it into near-net shape

Forging : plastic deformation carried out by compression into a die (e.g., crankshafts,connecting rods, turbine disks, gears, wheels, bolt heads, hand tools,...)

Rolling : reducing the thickness or changing the cross-section of a long workpiece bycompression through a set of rolls (e.g., plates for ship hulls, bridges, machine

structures, nuclear vessels; sheets for automobile bodies, appliances, containers forfood and beverages, ...)

Extrusion: forcing a billet through a die opening by compression, hot or cold


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Drawing: reducing the cross-section of a bar by pulling it through a converging die bytension (rods used for small components;wires used for cables, springs, musicalinstruments, fencing, shopping carts)

Sheet-Metal Forming Processes

Producing thin sheets of metal at room temperature (metal desks, appliance

bodies, aircraft panels, beverage cans, car bodies) Shearing : cutting a sheet metal by subjecting it to shear stress, between a punch and

a dieBending : used to form flanges, curls, seams, corrugationsDrawing : a flat sheet-metal blank is formed into a cylindrical or box-shaped part by

means of a punch that presses the blank into the die cavity


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Spinning : forming assymetric parts over a rotating mandrel with the use of rigid tools orrollers

Machining Processes

Material removal from a workpiece: cutting, grinding, nontraditional

machining processes Finishing operations that remove small amounts of material

Pros: improves dimensional accuracy, can create hard-to-obtainfeatures (e.g., sharp corners), can control surface finish

Cons: expensive, generates waste, can have adverse effects on surfacequality and properties of product

Cutting to produce round shapes (e.g., shafts, pistons, cylinders, gun

Drilling : making holes

Turning : removing material while part turns (e.g., shafts, spindles,pins, handles, and various machine components)

Facing, boring, parting Cutting to produce various shapes:

Milling : cutting with a multi-tooth tool which rotates


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Broaching : cutting with a multi-tooth tool which makes progressivelydeeper cuts (e.g., holes of circular, square, or irregular section, keyways,teeth of internal gears, ...)

Planing, shaping, sawing, filing Workpiece material is too hard or brittle, or its shape is difficult to produce with

sufficient accuracy by cutting

Grinding : cutting with a rough wheel to finish a surface

Surface grinding, cylindrical grinding, internal grinding, centerlessgrinding


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Joining ProcessesIncludes welding, brazing, soldering, adhesive bonding, mechanical

joining Reasons for importance:

Product is impossible to manufacture as a single pieceProduct is easier and more economical to manufacture asindividual components

Products may have to taken apart for repair or maintenanceTransporting the product in individual components and

assembling them later may be easier and less costlyManufacturing Processes for Plastics

Plastics are shipped to manufacturing plants as pellets or powders and aremelted just before the shaping process. Polymers melt at relatively lowtemperatures and, unlike metals, are easy to handle and require less energy to

process. Plastics can be molded, and formed, as well as machined and joined, into many

shapes with relative ease and with little or no additional operations required.

Extrusion : Raw powder is placed into a hopper and fed into the extruder barrel; thebarrel has a screw that blends and conveys the powder down the barrel; the powder isheated and liquefied; the molten plastic is then forced into a die.

Injection Molding : the powder is melted inside a heated chamber; the melt is forcedinto a split-die chamber either by a hydraulic plunger or by a rotating screw (cups,containers, knobs, toys,...)

Blow Molding : a tube is extruded and clamped into a mold cavity and then blownoutward to fill the mold (e.g., hollow containers)


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Thermoforming : a sheet is heated to the softening point and placed over a mold and

pulled against the mold through the application of vacuum (e.g., advertising signs,packaging, panels for shower stalls,...)

Compression Molding : a preshaped part or premeasured amount of powder isplaced directly in a heated mold cavity; forming is done under pressure with a plug (e.g.,dishes, handles, fittings, container caps,...)

material selection and design consideration

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