Mechanical Properties of Materials

Introduction and Agenda

Materials Properties- helps to determine how to make things with it- helps to determine the processing conditions- helps and constrains process optimization

Processes- forming, cutting, non-traditional, joining, surface treatments, electronics components, …

Materials

Nanomaterials, shape-memory alloys, superconductors, …

Ferrous metals: carbon-, alloy-, stainless-, tool-and-die steels

Non-ferrous metals: aluminum, magnesium, copper, nickel, titanium, superalloys, refractory metals, beryllium, zirconium, low-melting alloys, gold, silver, platinum, …

Plastics: thermoplastics (acrylic, nylon, polyethylene, ABS,…) thermosets (epoxies, Polymides, Phenolics, …) elastomers (rubbers, silicones, polyurethanes, …)

Ceramics, Glasses, Graphite, Diamond, Cubic Boron Nitride

Composites: reinforced plastics, metal-, ceramic matrix composites

Physical Properties

Property Application (e.g.)

Density, r = mass/volume Drop forging, hammering

Specific heat Coolant in machining

Thermal conductivity Cutting titanium

Coeff of linear thermal expansion, a = DL/(L DT) Compensation in Casting, …

Melting point Brazing, Casting, …

Electrical conductivity EDM, ECM, Plating

Magnetic properties Magnetic chucking

Chemical Properties:-• Corrosion Resistance• Oxidation• Flammability• Toxicity

The MECHANICAL PROPERTIES of a material are those properties that involve a reaction to an applied load.

• The mechanical properties of metals determine the range of usefulness of a material and establish the service life that can be expected.

• Mechanical properties are also used to help classify and identify material.

• The most common properties considered are strength, ductility, hardness, impact resistance, and fracture toughness.

Definition

Mechanical Properties:-• Strength – it is the ability of a material to resist failure under working

conditions

• Ductility – it is the ability of a material to be drawn into wires, increase in length and decrease in cross sectional area occur, tensile forces are involved

• Malleability – it is the property of a material to be hammered into thin sheets, compressive forces are involved, increase in surface area in all directions, decrease in cross sectional area

• Brittleness – absence of ductility, when the material fail without warning in working conditions

• Elasticity – the property of a material that returns to its original shape after stress (e.g. external forces) that made it deform or distort is removed

• Plasticity -- material cannot regain its original shape when the external load is removed, permanent deformation takes place

• Toughness – the ability of a material to absorb load shock etc.

• Hardness -- the ability of a material to resist scratches, chemical reaction marks, indentations etc.

• Machinability – the property of a material that can be shaped by hammering, pressing, rolling

• Stiffness-- it is the ability of a material to resist elastic deformation

• Resilience – ability to resist deformation till elastic range

Ductility

Measures how much the material can be stretched before fracture Ductility = 100 x (Lf – Lo)/Lo High ductility: platinum, steel, copperGood ductility: aluminumLow ductility (brittle): chalk, glass, graphite

Hardnessresistance to plastic deformation by indentation

Failure under impact

CharpyIzod

pendulum

scale

pointer starting position

sample placed here

CharpyIzodIzod

pendulum

scale

pointer starting position

sample placed here

Impact tests are used in studying the toughness of material. A material's toughness is a factor of its ability to absorb energy during plastic deformation. Brittle materials have low toughness as a result of the small amount of plastic deformation that they can endure. The impact value of a material can also change with temperature. Generally, at lower temperatures, the impact energy of a material is decreased. The size of the specimen may also affect the value of the Izod impact test because it may allow a different number of imperfections in the material, which can act as stress risers and lower the impact energy.

Application: Drop forging

Shear stress and Strain: the torsion test

L

g

C

C’

q

T

T

L

g

T

T

D

d

T = torque,J = polar moment of inertia J = r2 dACylindrical shell: J = (p D4-d4)/32

Angle of twist: q = TL/GJShear stress: t = Tr/JMaximum shear stress = tmax = TR/JShear strain = g = rq/L

G: Modulus of rigidity

Which properties do the following materials possess?

Material Properties

aluminium lightness ; strength

rubber elasticity ; insulation

ceramics thermal resistivity

steel strength

copper conductivity ; corrosion resistance

lead high density; ductility

nylon strength ; toughness

cast iron damping capacity

wood insulation ; environmental friendliness

Material Application

aluminium foil; aircraft; window frame

rubber tyres,; seal; gasket

ceramics furnace; brick

steel section; pipe

copper pipe; cables

lead storage battery; radiation protection ballast; bullets

nylon rope; clothing

cast iron engine block; valves

wood furniture; deck

Applications

Summary

Knowledge of materials’ properties is required to

Select appropriate material for design requirementSelect appropriate manufacturing processOptimize processing conditions for economic manufacturing…

Materials have different physical, chemical, electrical properties

Presented by—Akash Sharma