Metal / Metallic materialsGenerally classified as ferrous and nonferrous

Ferrous materials consist of steel and cast ironEg. Carbon steel, high alloy steel, stainless steel

Nonferrous materials consist of the rest of the metals and alloys

Eg. Aluminum, magnesium, titanium & their alloys

Materials from each group are further classified and given certain designation according to the ASTM standard

Engineering materials

Each has their own unique number/code that represent main alloying elements, cast or wrought and in case of plain carbon – amount of carbon.Steel can be classified or grouped according to some common characteristic.The most common classification is by their

i. CompositionExample : 10xx, 15xx

ii. StrengthMost common material used in construction of structure such as bridge, building and ships

Engineering materials

Low yield strength, less < 40 psiEg : A36 – Carbon steel plates, bars and shapes

High strength, between 40 psi and 120 psiEg. A440- Carbon steel plates, bars and shapes of

high tensile strength

Ultra-high strength > 200 psiiii. Product shape, finish processing and quality

descriptorsTypical product classification of flat hot-rolled carbon & low alloy steel

According to the thickness and width

Engineering materials

For ‘shape’ product formseg. I beam and special shapes ( designed for specific application ), bar ( also included round, squares, hexagon in cross section )

Finishing processThe last processing that the steel undergone.The mot common are hot-rolled, cold—rolled or cold finished, annealed, normalized, quenched and tempered, coating process.

Engineering materials

Design and selection for metals

One of the major issues for structural components is deflection under service load.

A function of the applied forces and geometry, and also stiffness of material.

So suitable material and design are needed.

Load carrying capacity of component can be related to the yield strength, fatigue strength or creep strength depending on loading & service condition.

All are structure sensitive.Changed, chemical composition of the alloy, method and condition of manufacturing, as well as heat treatment

Engineering materials

Electrical & thermal conductivities

Thermal conductivity, KIs measure of the rate at which heat is trnasfered through a material

Manufacture of component where electrical conductivity is primary requirement

Al & Co

Corrosion resistance & specific gravity limits the materials.

Engineering materials

x

Tk

A

Q

Manufacturing considerationWrought m/str usu stronger and more ductile than cast.

Precision / size tolerances, surface finish, heat treatment – stress relief etc., other secondary treatment & finishing.

Weldability – a function of material composition. So structure involve welding of the components need to consider. Also for other joining means.

Machinability – improvement by heat treatment or alloying elements.

Economic aspects - perform function at lowest cost.

Engineering materials

Design for polymerPolymer – low density, good thermal & electrical insulation, high resistance to most chemicals and ability to take colours and opacities.

But if unreinforced bulk polymer are mechanically weaker, lower elastic moduli & high thermal expansion coefficients.

Improvement – Reinforced variety of fibrous materials

Composites (PMC).

Advantages : ease of manufacturing & versatility.

Can manufacture into complicated shapes in one step with little need for further processing or surface treatment.

Engineering materials

Versatility : ability to produce accurate component, with excellent surface finish and attractive color, at low cost and high speed

Basic manufacturing processes for polymer parts are extrusion, molding, casting and forming of sheet.

Thermoset & thermoplastic

Differ in the degree of their inter-molecular bonding

Rubber are similar to plastic in structure and the difference is largely based on the degree of extensibility or stretching.

Design : avoid limitations, must remember that strength & stiffness vary with T, many have low impact strength, i.e brittle so avoid stress raisers.

Engineering materials

Design consideration for polymer

Structural part

When the parts is to carry load

Should remember the strength and stiffness of plastics vary with temperature.

Long term properties

Eg. Creep behavior

Stress raiser

Engineering materials

Design for ceramicsCeramics – inorganic compounds of one or more metals with a nonmetallic element. Eg Al2O3, SiC, Si2N3.Crystal structure of ceramic are complex

They accommodate more than one element of widely different atomic size.

The interatomic forces generally alternate between ionic & covalent.

usually heat & electrical insulators.Strong ionic & covalent bonds give high hardness, stiffness & stability (thermal & hostile env.).(1) Amorphous or glass, (2) crystalline (arrange) & (3) crystalline bonded by glassy matrix.

Engineering materials

Whitewares, glass, refractories, structural clay products & enamels.Disadvantages

Brittleness, low mechanical & thermal shock

Design consideration for ceramicsSensitive to stress concentration

Avoid stress raiser during design.Dimensional change take place during drying and firing, should be considerLarge flat surface can cause wrappingLarge changes in thickness of product can lead to nonuniform drying and cracking.

Engineering materials

Design for compositeA composite material can be broadly defined as an assembly two or more chemically distinct material, having distinct interface between them and acting to produce desired set of properties

Composites – MMC, PMC & CMC.

The composite constituent divided into two

Matrix

Structural constituent / reinforcement

Properties / behavior depends on properties, size & distribution, volume fraction & shape of the constituents, & the nature and strength of bond between constituents.

Engineering materials

Mostly developed to improve mechanical properties i.e strength, stiffness, creep resistance & toughness.

Three type of composite

(1) Dispersion-strengthened, (2) Reinforcement – continuous & discontinuous (3) Laminated.

Designing with composite

A composite materials usually are more expensive on a cost.

Important factors when designing with composite materials is that their high strength are obtained only as a result of large elastics strains in the fiber

Fatigue behavior at low stress level because fibrous composites may have many crack, which can be growing and propagate through the matrix

Engineering materials