Chapter 1 Introduction to materials and

family of materials

Chapter 1 and 2 (Ashby)+Chapter 1 (Callister)

Study outcomes: •Appreciate the development and increase in diversity of materials.•Know and define material properties•Know the five family of materials•Understand the classification system for a material .•Know the three families of processing of a material•Understand the classification system of the process.•Process property interaction•Specify a material and /or process for manufacturing of a given component

1.1 Materials , process and choice.

• Why do we need materials???

• To make something out of material you need a process.

• Process has to be compatible with the material you plan to use.

Figure 1.1 The development of materials over time. The materials of pre-history, on the left, all occur naturally; the challenge for the engineers of that era was one of shaping them. The development of thermochemistry and (later) of

polymer chemistry enabled man-made materials, shown in the colored zones. Three—stone, bronze and iron—were of such importance that the era of their dominance is named after them.

1.2 Material properties

• Mechanical properties• Thermal properties• Electrical, magnetic and optical properties• Chemical properties

1.2.1 Mechanical PropertiesSome of the important mechanical property terms:1)E: Elastic Modulus indicates the stiffness of material.

For example steel has E of 207Gpa and polyethylene has1.08Gpa

2) Yield strength Strength at which permanent deformation start to occur. Examples Al alloys has 107Mpa Lead has 5.5 Mpa

3) Tensile strength :is defined as the highest value of engineering stressexamples High strength steel 3000 MPa , Al-500 MPa

4) Fracture toughness: measure of resistance to crack and fracture. Glass epitomizes brittleness;it has low K1c0.77Mpa*(m)1/2 and steel has 54Mpa *(m)1/2.

1.2.1 Mechanical Properties

5) Ductility : It is the maximum deformation to fracture

6) Hardness : It is the resistance to plastic deformation when object under load penetrates the material.

7) Resilience :It is the measure of the amount of energy that can be absorbed under elastic loading conditions and which is released completely when loads are removed.

Fig shows consequences of various mechanical properties mentioned above.

1.2.2 Thermal propertiesProperties of material change with temperature. With

increasing temperature it starts to creep, it may oxidize or degrade and there is loss of strength.

1) There is a limiting temperature called the maximum service temperature Tmax for use of material.

2) Thermal expansion coefficient __. Materials expand when heated but by differing amount which depend on this factor. Its unit is (C-1)

Thermal conductivity and heat capacity are the two factors responsible for the feel of the material.

Thermal conductivity λλλλ measures the rate at which heat flows through the material . Unit is W/m K.

Heat capacity Cp is the measure of the amount of heat that it takes to make temperature of material rise by a given amount .Unit is J/KUses of materials with high and low thermal conductivity and heat capacity

Thermal diffusivity : The property governing transient heat flow (when temperature varies with time) is the thermal diffusivity, a (units : m2/sec)

Various aspects of thermal properties

1.2.3.Electrical, magnetic and chemical properties

• Electrical conduction• Resistivity. It is the inverse of electrical conductivity.

The materials for conductors and insulators. • Dielectric properties

• Electric current induce magnetic fields.• Hard magnets and soft magnets and their uses• Optical properties• Products often have to function in hostile environment.

Design- limiting properties

The performance of a component is limited by certain properties of material of which it is made. Materials are chosen by identifying design limiting properties and applying limits to them.

1.3 Classifying materials

• Conventionally materials are classified into five broad families.

1. Metals2. Polymers3. Ceramic / Glasses4. Composites5. Advanced materials

Examples of each material family

• Members of each family have certain characteristics in common:

1. Metals : Have high stiffness, they are tough with usefully high fracture toughness. They are made strong by alloying ,mechanical process and heat treatment. They are reactive and so most of them corrode if not protected.the key feature that distinguishes metal from non metals is their bonding. Metallic materials have free electrons that are free to move easily from one atom to next

• Metals are mainly grouped into two categories

• Ferrous metals and alloys examples are irons , carbon steel, alloy steels , stainless steel , tool steel and die steels

• Non ferrous metals and alloysExamples are Aluminum, copper, nickel, titanium precious metals, super alloys and others alloys

Typical examples of metals and its family

2 Ceramics : They are non metallic inorganic solids. They are typically crystalline in nature and are compounds formed between metallic and non metallic elements ex Alumina, silicon nitrideThe two most common chemical bonds in ceramic materials are covalent and ionic bondThey are stiff hard abrasion resistant and retain their strength to high temperatures. Most of them are good insulators. They have low K1c value.

• Typical examples of ceramics are• Structural clay products (bricks, roofing ,

wall tile etc)• Refractories, cements, abrasives, cutting

tools• Graphite , sand

3 Glasses : Are noncrystalline solids. Commonest are borosilicate glasses and sodalime. Lack of crystal structure suppresses plasticity. They are hard and remarkably corrosion resistant . They are excellent insulators and transparent to light. But like ceramics they are brittle .

• Uses : flat glass for windows, container glass (bottles) pressed and blown glass (Dinnerware), glass fibers (home insulation)

4 Polymers : are organic solids based on long chain of carbon atoms. They are characterized by low density and low moduli E. They are easy to shape. Few polymers have useful strength above 1500C the polymer is a long chain of covalent bonded atoms and secondary bonds then hold group of polymer chains togetherIndustrially important polymeric materials are plastics plastics can be subdivided into two groups thermoplastics and thermosetting plasticsExamples of thermoplastics are polyethylene, polypropylene, polystyrene and polyvinyl chlorideExamples of thermosetting polymers include alkyds, phenolic resins, epoxies, polyurethanes and unsaturated polyesters

5 Composites (Hybrids): a composite is usually defined as a combination of two or more distinct materials, each of which retains its own distinctive properties, to create a new material with properties that cannot be achieved by any of the components alone Ex concrete is mixture of Portland cement and aggregate

• Composites are said to have two phases. The reinforcing phase is the fibers, sheets or particles that are embedded in the matrix phase.

• Typically reinforcing materials are strong with low densities while matrix is usually ductile or tough material.

• Typical examples are reinforced plastics. Metal matrix composites, ceramic matrix composites etc

• Advanced materials:They are members of the above families but

with specific applications e.g electronic, bio materials and nanomaterials

The taxonomy of the kingdom of materials and their attributes. Computer-based selection software stores

data in a hierarchical structure like this.

MemberSub-Class

ClassFamilyKingdom

Material

Ceramics

Metals

Polymers

Hybrids

Advanced

SteelCu alloysAl alloysTi alloysNi alloysZn alloys

1000

2000

3000

4000

5000

6000

7000

6013

6060

6061

6063

6151

1.4Process and its classification� A process is the method of joining, shaping or finishing a

material. The choice of material limits the choice of process.

The first row contains primary shaping process below it secondary process, followed by family of joining and finishing

• Primary process creates shapes. The six primary process are listed :like casting , molding, deformation methods , powder methods, methods for forming composites, special methods.

• Secondary process: modifies the shapes and properties. Like machining which add features to already shaped body, heat treatment which enhances surface or bulk properties.

• After secondary process comes joining and surface treatment

� in a broad manner the process universe can be classified as three families : shaping , joining and surface treatment.

The taxonomy of the kingdom of process with part of the shaping family expanded. Each member is characterized by a set of attributes. Process selection involves matching these to the requirements of the design.

Process property interaction

� Processing change properties. • If you hammer a metal it gets harder; if you heat it

softens.• Plastic bags when drawn to fibers , its strength increases

by a factor 5• Soft stretchy rubber is made hard and brittle by

vulcanizing