List of Commonly used Engineering Materials

Here is a list of commonly used engineering materials: 1. Smart Materials (Or Intelligent Materials) 2. Shape Memory Alloys (SMA) 3. Functionally Graded Materials (FGMS) 4. Biomedical Materials.

1. Smart Materials (Or Intelligent Materials):

These are magical materials which are suitable to our needs. These materials can sense, process, stimulate and actuate a response.

Their functioning is somewhat similar to human brain, slow and fast muscles action.

The intelligent material have three basic components which are given as follows:

(i) Sensors:

Piezoelectric polymers (polyvinyldene), optical fibres,

(ii) Processors:

Conductive electroactive polymers, microchips, and

(iii) Actuators:

Shape memory alloys (Ni Ti i.e. nitinol), chemically responding polymers.

Piezoelectric Ceramics:

Linear and shear deformations occur along longitudinal, transverse and thickness directions,

e.g. Quartz, Pb Zr titanate

Application:

Aircraft airfoils, identifying Braille alphabet (an aid for blinds).

Viscoelastic (VE):

These relax any stress produced in it by external strain.

Application:

Damping in space-crafts, earthquake prone structures, and aircrafts.

Electro Rheological (ER) Fluids:

These are like suspended fine polarizable particles cohesive, and tend to coalesce. They form new chains even when old chains are broken, e.g. zeolite in silicone oil, starch in corn oil.

Application:

In filling of graphite-epoxy beams to provide variable stiffness in them.

Different Type of Smart Materials:

i. Dumb Materials:

These material have been pre-processed or designed to facilitate only a limited set of responses to external stimuli.

Such responses are usually non-optimal for any single set of conditions, but ‘optimised’ to best fulfill the range of scenarios to which a material or structure may be exposed, example: the wings of an aircraft should be optimised for take-off and landing, fast and slow cruise etc.

ii. Biomimetics:

These materials are similar to animals and plants exhibits the clear ability to adapt to their environment in real time. The field of biomimetics, which looks at the extraction of engineering design concepts from biological materials and structures, are helpful to human being on the design of future manmade materials.

The process of balance is a truly ‘smart’ or intelligent response, allowing in engineering terms a flexible structure to adapt its form in real time to minimise the effects of an external force, thus avoiding catastrophic collapse.

iii. Electro-rheostatic and Magneto-rheostatic:

These materials are fluids, which can experience a dramatic change in their viscosity.

These fluids can change from a thick fluid (similar to motor oil) to nearly a solid substance within millisecond when it bring in magnetic or electric field; the effect can be completely reversed just as quickly when the field is off.

MR fluids experience a viscosity change when exposed to a magnetic field, while ER fluids similar changes in an electric field.

The most common form of MR fluid consists of tiny iron particles suspended in oil, ER fluids can be as simple as milk chocolate or corn-starch and oil.

iv. Photochromic Materials:

These materials change reversibly colour with change in temperature. They can be manufactured as semi-conductor compounds, from liquid crystals or using metal compounds.

The change in colour found at a determined temperature, which can be varied by doping the material.

Used in production of paints, inks or are mixed to moulding or casting materials for different applications.

v. Electroluminescent Materials:

These materials produce a brilliant light of different colours when stimulated electronically (e.g. by AC current). During emitting light no heat is produced. Like a capacitor, the material is made from an insulating substance with electrodes on each side.

One of the electrodes is transparent and allows the light to pass. The insulating substance that emits can be made of zinc sulphide.

They can be used for making light stripes for decorating buildings, or for industrial and public vehicles safety precautions.

vi. Fluorescent Materials:

These materials give visible or invisible light as a result of incident light of a shorter wavelength (i.e. X-rays, UV-rays, etc.)

The effect disappear as soon as the source of excitement is removed. Fluorescent pigments in daylight have a white or light colour, whereas under excitation by UV radiation they irradiate an intensive fluorescent colour.

They can be used for paints, inks or mixed to moulding or casting materials for different applications.

Other Smart Materials:

a. Phosphorescent materials

b. Conducting polymers

c. Dielectric elastomers

d. Polymer gels

e. Magnetostrictive alloys

f. Electrostrictive materials

g. Piezoelectric materials

h. Sensual materials

vii. Thermoelectric materials:

Special types of semiconductors that, when coupled, behave as a “heat pump”. By applying a low voltage DC power source, heat is moved in the direction of the current positive to negative.

Generally, used in thermoelectric modules where a single couple or many couples to obtain larger cooling capacity are combined. One face of the module cools down while the other remains in heating state, and the effect is reversible.

Thermoelectric cooling allows for small size and light devices, high reliability and precise temperature control, and quiet operation.

Disadvantages:

High prices and high operating costs, due to low energy efficiency.

Smart Materials Application:

a. Fast response valves

b. High-power-density hydraulic pumps

c. Sports equipment

d. Vibration and acoustic sensors

e. Active bearings for reduction of machinery noise

f. Dampers

g. Footwear

h. Precision machining, etc.

2. Shape Memory Alloys (SMA):

Below a critical transition temperature, they can deform plastically.

e.g. Ni Ti (nitinol)

Application:

Fire alarm due to change of shape at transition temperature.

Shape Memory Alloys:

Shape memory alloys (SMAs) are metals that possess two very unique properties – (1) pseudoelasticity (2) ‘shape memory effect’. The most effective and widely used shape memory alloys include NiTi (Nickel-Titanium), CuZnAI, and CuAINi.

The two unique properties described above are possible through a solid state phase- change i.e. a molecular rearrangement, which occurs in shape memory alloy.

Applications:

a. Coffeepots

b. Thermostat

c. Hydraulic fittings for aeroplanes

d. Space shuttle

e. Vascular stents, etc.

Nano Electro-Mechanical Systems (NEMs):

Development of ultra-miniature systems e.g. nano-electromechanical systems (NEMs) will ease the maintenance, safety and updating of computers and other hardware.

Systems will provide almost trouble free services. Installations/equipment’s into a smaller chamber is possible.

Many electronic systems may be mounted-on or housed-in the watches, shirt pockets, pens, other body parts and their belongings.

The future expectations of nanotechnology can be viewed in the light of the following development:

i. Gold nanoshells are new composite nanoparticles. They consist of a dielectric core (either gold sulphide or silica), with a metal (gold) outer shell. The shell has the same surface properties as colloidal gold and can bind to a variety of biomolecules. By varying the relative thickness of the core and the shell, the optical resonance of gold nanoshell can be shifted from the visible range to the infrared range, which is the range of the highest physiological transmissivity.

ii. The lithium-ion secondary (rechargeable) batteries have a voltage of -3.5V, which is three times that of the conventional Ni-Metal hydride batteries. Here lithium cobalite (LiCoO₂) form the cathode and C or LiC₆ forms the anode. The electrolyte is an organic liquid with a dissolved lithium salt. During charging, the Li⁺ ions migrate towards the anode. During discharge, they migrate in the reverse direction towards the cathode.

Alternate electrode materials like LiFePO₄ could benefit from nanotechnology.

3. Functionally Graded Materials (FGMS):

An FGM is an inhomogeneous material in which the physical, chemical and mechanical properties change continuously from point to point. No any discontinuities inside.

Due to gradual change of material properties with position, hence, termed as ‘gradient materials’.

The property gradient is found due to position dependent parameters as written below:

a. Micro structure

b. Atomic order

c. Chemical composition

The property variation can extend over a large part of material, on to the surface of the material, or may be limited to a smaller interfacial region only.

The FGM are useful in the sense that the microstructural gradients produce optimum functional performance with minimum material use.

Example:

a. A natural example of FGM is the culm of bamboo in which the high-strength natural fibres are embedded in a matrix of ordinary cells. In that the fibre content is not homogeneous over the entire cross-section of the culm, rather decreases from outside to inside.

b. A synthetic example of FGM is case-hardened steel in which the material has a gradation i.e. the surface is hard but the interior is tough.

Types of FGMs:

Based on shape and size of gradient, different types of functionally graded materials are found:

(a) Fraction gradient type,

(b) Shape gradient type,

(c) Orientation gradient type and

(d) Size gradient type.

Application of FGMs:

I. Thermal Protection Systems:

i. Space Re-Entry Vehicles:

A nose cone with a graded SiC protection interlayer on C/C* composite exposed to high temperature supersonic gas flow provide improved thermal protection.

ii. Gas turbine blades made of superalloy and coated with a bond coat of NiCrAlY and heat-insulating layer of ZrO, considerably improves the resistance of the coating.

iii. Thermal Barrier Coating (TBC):

By using a 2mm thick graded TBC on piston crowns and cylinder heads of diesel engines, about 5% reduction in fuel consumption can be achieved.

II. Wear Protection:

Wear resistance of tools increases by hard surface layer in a compressive stress state e.g. a WC/Co (stellated) FGM with a gradual variation in Co develops a compressive stress state at the surface.

III. Medical Implants:

Cementless artificial joints: A coating of glass on a Ti-6AI-4 V (titanium-aluminium-vanadium) substrate possessing hydroxyapatite and pores close to its outer surface is an excellent material for making cementless artificial joints and dental implants. The above-mentioned material is a graded composite material.

IV. Energy Conservation:

Thermoelectric converter: Bi₂Te₃/PbTe/SiGe for improved conversion efficiency. Radiation emitter: A/N/W for improved emissivity.

V. Electronics:

Graded capacitor: BaTiO₃/SrTiO₃ for zero temperature coefficient of capacitance.

VI. Acoustics:

Acoustic coupler: CuMn/WC for acoustic impedance machine.

VII. Optics:

X-ray mirror: Si/Ge for graded lattice constant.

4. Biomedical Materials:

i. Biometals:

High strength, good toughness, and biocompatible, Generation of fine wear particles leading to implant loosening and inflammation.

Example:

(a) CoCrMo alloy, excellent wear resistance, and excellent corrosion resistance, but release harmful Co, Ni, Cr ions into the body

(b) Ti alloys, Allows bone growth at the interface, unsatisfactory wear resistance, may produce wear debris

ii. Bioceramics:

Stiff, hard, chemically stable, and very good wear resistant, Brittle and relatively difficult to process.

Example:

(i) Alumina, Excellent bio-compatibility and inertness in body.

Application of Biomaterials:

I. Pacemakers:

Sheathed wires acting as sensing and stimulating electrodes made by Polyurethane as insulation on these wires, silicone.

Metal casing to house a battery (i.e. pacemaker housing) made by Ti, Pt and Pt-Ir electrodes for providing resistance to galvanic corrosion.

II. Dental Materials:

Tooth replacement consisting of an implant that is fixed into the bone and a crown (or denture superstructure) made of Alumina, Pure Ti, and single crystal sapphire.

To promote bone growth into implant interface is made by Glass ceramic coatings, calcium phosphate ceramics.

Tooth crown is made of dental porcelains: Example borosilicate, fieldspar glass.

Crown fusing metals are- Au, Au-Pd, Ag-Pd, Cu-Pd, Ni-Cr

III. Ophthalmology Materials:

i. Hydrogel soft contact lenses made of Poly HEMA (hydroxyethylmethacrylate).

ii. Rubbery soft lenses made of Si-rubbers, flouropolymers.

iii. Rigid contact lenses made of PMMA (Polymethylmethacrylate).

IV. Orthopedics:

a. Hip and knee implants is done by Ti-6AI-4VI, stainless steel.

b. Screws, fittings and wires made of Ti-6AI-4V, stainless steels.

c. Hip replacement is done by Alumina (polycrystalline).

d. Bone repair such as maxillofacial and periodontal defects are cured by Tri-calcium phosphate Ca₃(PO₄)₂ ceramic.

e. Bone plates are made of Polyorthoesters.

f. Bone and joint replacement is done by Austenitic 316L stainless steels, Co-based alloys, PureTi, Ti-6AI-4V, Alumina, Zirconia PMMA, UHMEWPE (ultrahigh molecular- weight polyethylene).

V. Cardiovascular Devices:

(i) Kidney Dialysis Machines:

a. Blood feeding catheters are made of Polyurethane, silicone.

b. Membrane inside the dialyzer are made of Cellulosic.

(ii) Vascular grafts is made of woven fabrics of expanded PTEE, Polyesters and PET (polyester terephthalate).

(iii) Membrane in oxygenator are made of Perfluorobutyrgl ethyl cellulose.

(iv) Cardiac Valves:

a. Metal valves made by Ti-alloy, CoCrMo.

b. Non-metal valves made by Silicone elastomer.

(v) Artificial Heart:

a. Heart valves made by Polydimethyl siloxane, polyurethane.

b. Pump bladders made by Polyurethanes with layers of butyl rubbers inside.

c. Blood contacting inlet and outlet connecters made by PET.

d. Housing for devices is made by Epoxy, kevlar, polyurethane, polycarbonates, Ti.

Miscellaneous:

i. Blood bags, tubing made by PVC, polyurethanes, silicones.

ii. Soft tissue reconstruction made by Silicones.

iii. Wound closure made by Cyanoacrylates.

iv. Tendon repair made by Polylactic acid.

v. Drug delivery system made by Ferro fluids.

Chirality:

Variation of the orientation of the rolling axis relative to the hexagonal network of the grapheme sheet can produced different types of single walled tubes this property is known as chirality. Depending on chirality a nano tubes can be a semiconductor or a metallic condenser.