Design for EngineeringUnit 8 Material Scienceand Engineering Annette BeattieAugust 15, 2006

Materials ScienceETP 2006 – Annette BeattieThis material is based upon work supported by the National Science Foundation under Grant No. 0402616. Any opinions, findings and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the view of the National Science Foundation (NSF).

What are Materials?It derives from the Latin word “Materia”

which means wood.Material is anything made of matter.Our clothes are made of materials, our homes

are made of materials - mostly manufactured.Most things are made from many different

kinds of materials.

Materials ScienceDefined as the study of the properties of solid

materials and how those properties are determined by a material’s composition and structure.

Example - the dramatic role of iron throughout the ages is not really the result of it being "strong". In reality, iron has been important because we can change its properties by heating and cooling it.

The ability to change the properties and/or behavior of a material is what makes most materials useful and this is at the heart of materials science!

Materials Science and EngineeringAn interdisciplinary study that combines

metallurgy, physics, chemistry, and engineering to solve real-world problems with real-world materials in an acceptable societal and economical manner.

The following elements and their interaction define Materials Science and Engineering:PerformancePropertiesStructure and compositionSynthesis and processing

Kinds of MaterialsMetalsCeramicsPolymersCompositesSemiconductorsBiomaterials etc.

MetalsMaterials that are normally combinations

of "metallic elements". Example : Fe, Al, Cu etc.

Properties-

High DensityGood electrical and thermal conductivity (Due to presence of free electrons)Magnetic in natureResistant to fractureHighly stiff

CeramicsCompounds between metallic and

nonmetallic elements. Generally oxides, nitrides and carbides come in this category.

Example : SiC, Silicon nitride, Alumina etc.Less dense in comparison to metalsBrittle in natureEasily fractural (Griffith crakes)because the surfaces of ceramics nearly

always contain minute cracks ("Griffith cracks"), which magnify the applied stress.

How do we make ceramicsCeremics are produced by compacting

powders into a body which is then sintered at high temperatures. During sintering the body shrinks, the grains bond together and a solid material is produced. 

Dry Pressing, Isostatic Pressing, Roll Compaction, Continuous Tape Casting, Slip Casting, Extrusion, Injection Molding, Pre-Sinter Machining, Hot-Pressing, Hot Isostatic Pressing, Grinding, Lapping and Polishing.

ConductivityIn contrast to Metals, Ceramics have very low

electrical conductivity due to Ionic-Covalent Bonding which does not form free electrons.

Most of ceramic materials are dielectric (materials, having very low electric conductivity, but supporting electrostatic field).

Electrical conductivity of ceramics varies

with the frequency of field applied and also with temperature. This is due to the fact that charge transport mechanisms are frequency dependent. Further, the activation energy needed for charge migration is achieved through thermal energy and immobile charge career becomes mobile.

The activcation energy can be calculated very easily using the Arrheneous relation.

Polymers They are generally organic compounds

based upon carbon and hydrogen. They are very large molecular structures.

Ex : PE, PVC, PS etc.Low densityLow stiffnessNon magneticNon electrical conductivity

SemiconductorsThey have electrical properties intermediate

between metallic conductors and ceramic insulators.

Intrinsic semiconductor (Pure Si, Ge)Extrinsic semiconductorP-Type (B,Al doping)N-Type (P,As doping)

Composites: They consist of more than one material type.

Fiberglass, a combination of glass and a polymer, is an example. CFRP- Carbon Fiber Reinforced Polymer

Composite material is a material composed of two or more distinct phases (matrix phase and dispersed phase) and having bulk properties significantly different form those of any of the constituents.

Matrix Phase

The primary phase, having a continuous character, is called matrix.

Matrix is usually more ductile and less hard phase. It holds the dispersed phase and shares a load with it.

Dispersed (Reinforcing) PhaseThe second phase (or phases) is embedded in

the matrix in a discontinuous form. This secondary phase is called dispersed

phase. Dispersed phase is usually stronger than the

matrix, therefore it is sometimes called reinforcing phase.

TypesMetal Matrix Composites (MMC)Metal Matrix Composites are composed of a metallic matrix

(aluminum, magnesium, iron, cobalt, copper) and a dispersed ceramic (oxides,carbides) or metallic (lead, tungsten, molybdenum) phase.

Ceramic Matrix Composites (CMC)Ceramic Matrix Composites are composed of a ceramic

matrix and embedded fibers of other ceramic material (dispersed phase).

Polymer Matrix Composites (PMC)Polymer Matrix Composites are composed of a matrix

from thermoset (Unsaturated Polyester (UP), Epoxiy (EP)) or thermoplastic(Polycarbonate (PC), Polyvinylchloride, Nylon, Polysterene) and embedded glass, carbon, steel or Kevlar fibers (dispersed phase).

Density calculationRule of Mixtures- is a method of approach

to approximate estimation of composite material properties, based on an assumption that a composite property is the volume weighed average of the phases (matrix and dispersed phase) properties.

According to Rule of Mixtures properties of composite materials are estimated as follows:

Densitydc = dm*Vm + df*Vf

Wheredc,dm,df – densities of the composite, matrix

and dispersed phase respectively;Vm,Vf – volume fraction of the matrix and

dispersed phase respectively. 

Can we do welding on composites?

Hot Plate welding- In hot plate welding, the parts to be welded

are held in fixtures, which press them against either side of a heated platen. Once the parts are sufficiently molten, the platen is removed. The components are then pressed together and held until they are cooled.

Vibration welding- It is also known as linear friction welding.

in this heat is generated by the mechanical movement of the components to be joined.

The two parts to be joined are brought into contact under an applied load. One part is constrained whilst the other undergoes a rapid linear reciprocating motion in the plane of the joint. The heat generated by the friction at the two surfaces creates local melting. Subsequently, the vibration stops, the parts are aligned and the joint is cooled under pressure to consolidate the weld.

Newer Branches of Materials ScienceNanotechnology: a relatively new area

grown out of techniques used to manufacture semiconductor circuits. Machines can be produced on a microscopic level.

Example - miniature robots to do surgery inside the body or miniature chemical laboratories and instruments that will continuously analyze blood and dispense medications inside the body.

BiomaterialsBiomaterials are employed in components

implanted into the human body to replace diseased or damaged body parts.

These materials must not produce toxic substances and must be compatible with body tissues (i.e., must not cause adverse biological reactions). All of the preceding materials—metals, ceramics, polymers, composites, and semiconductors—may be used as biomaterials.

Example, some of the biomaterials that are utilized in artificial hip replacements.

In the United States, 45% of the 250,000

valve replacement procedures performed annually involve a mechanical valve implant. The most widely used valve is a bileaflet disc heart valve, or St. Jude valve.

Materials TestingMaterials testing is a much narrower field

than materials science or engineering.It is determining the strength of certain

materials.It is mostly used to determine safety. Ex.

concrete samples are tested.It is not used to design new materials to be

used in new applications. (VCSU, 2006)

Metal Ceramics Polymers Composite

s

Density High less low low

Electrical & Thermal conductivity

High low low low

Strength high High (less than metal)

low high

stiffness high high low high

Resistance to fracture

high low low high

Crystal structureBecause there are many different possible

crystal structures, it is sometimes convenient to divide them into groups according to unit cell configurations and

On this basis there are seven different possible combinations of a, b, and c, and α, β, and γ each of which represents a distinct crystal system.

Seven types of crystal systems are there-1. Cubic2. Hexagonal3. Tetragonal4. Rhombohedral (Trigonal)5. Orthorhombic6. Monoclinic7. Triclinic

Point coordinatesPoint position specified in terms of its

coordinates as fractional multiples of the unit cell edge lengths.

CRYSTALLOGRAPHIC DIRECTIONS

CRYSTALLOGRAPHIC PLANES1. If the plane passes through the selected origin,

either another parallel plane must be constructed within the unit cell by an appropriate translation, or a new origin must be established at the corner of another unit cell.

2. If the plane passes through the selected origin, either another parallel plane must be constructed within the unit cell by an appropriate translation, or a new origin must be established at the corner of another unit cell.

The reciprocals of these numbers are taken.

A plane that parallels an axis may be considered to have an infinite intercept, and, therefore, a zero index.

If necessary, these three numbers are changed to the set of smallest integers by multiplication or division by a common factor.

Finally, the integer indices, not separated by commas, are enclosed within parentheses, thus: (hkl).

ApplicationDeformation under loading (slip) occurs on

certain crystalline planes and in certain crystallographic directions.

Before we can predict how materials fail, we need to know what modes of failure are more likely to occur.

Other properties of materials (electrical conductivity,

thermal conductivity, elastic modulus) can vary in a crystal with orientation.

Diffusionthe phenomenon of material transport by atomic

motionFick’s 1st law- J =D (dC/dx)One practical example of steady-state diffusion is

found in the purification of hydrogen gas. One side of a thin sheet of palladium metal is

exposed to the impure gas composed of hydrogen and other gaseous species such as nitrogen, oxygen, and water vapor. The hydrogen selectively diffuses through the sheet to the opposite side, which is maintained at a constant and lower hydrogen pressure.

Fick’s 2nd law∂C/∂t =D (∂2C/ ∂2x)

ApplicationsA steel gear that has

been case hardened.Its outer surface

layer was selectively hardened by a high-temperature heat treatment during which carbon from the surrounding atmosphere diffused into the surface

Case-

hardened steel gears are used in automobile transmissions.

Increase in the carbon content raises the surface hardness which in turn leads to an improvement of wear resistance of the gear.

In addition, residual compressive stresses are introduced within the case region; these give rise to an enhancement of the gear’s resistance to failure by fatigue.

Bibliographywww.crc4mse.orgwww.vcsu.edu

www.britannica.com

www.subtech.com

www. global.kyocera.com

Standards Standard #2: Students will develop an understanding of the core

concepts of technology. 2.CC New technologies create new processes.

Standard #3: Students will develop an understanding of the relationships among technologies and the connections between technology and other fields of study.

3.H Technological innovation often results when ideas, knowledge, or skills are shared within a technology, among technologies, or across other fields.

3.J Technological progress promotes the advancement of science and mathematics.

Standard #7: Students will develop an understanding of the influence of technology on history.

7.H The evolution of civilization has been directly affected by, and has in turn affected, the development and use of tools and materials.

7.K The Iron Age was defined by the use of iron and steel as the primary materials for tools.