AK7

Alloy

A metallic material that is obtained by chemical combinations of different elements.

Crystalline material

A material composed of one or many crystals. In each crystal, atoms or ions show a long-range periodic arrangement.

Glass

An amorphous material derived from the molten state, typically, but not always, based on silica.

Materials engineering

An engineering oriented field that focuses on how to transform materials into a useful device or structure.

Mechanical properties

Properties of a material, such as strength that describe how well a material withstands applied forces, including tensile or compressive forces, impact forces, cyclical or fatigue forces, or forces at high temperatures.

Polymers

A group of materials normally obtained by joining organic molecules into giant molecular chains or networks. Polymers are characterized by low strengths, low melting temperatures, and poor electrical conductivity.

Thermoplastics

A special group of polymers in which molecular chains are entangled but not interconnected. They can be easily melted and formed into useful shapes. Normally, these polymers have a chainlike structure.

Microstructure

The structure of a material at the microscopic length scale.

48,100 psi

An 850-lb force is applied to a 0.15-in. diameter nickel wire having a yield strength of 45,000 psi and a tensile strength of 55,000 psi. Determine the stress acting on the wire.

Ductility

The ability of a material to be permanently deformed without breaking when a force is applied.

Elastic strain

Fully and instantaneously recoverable strain in a material.

6.44 × 106(to the power of 6) psi

A force of 20,000 N will cause a 1 cm × 1 cm bar of magnesium to stretch from 10 cm to 10.045 cm. Calculate the modulus of elasticity.

Engineering stress

The applied load, or force, divided by the original area over which the load acts.

Flexural strength

The stress required to fracture a specimen in a bend test.

Hooke’s law

The linear-relationship between stress and strain in the elastic portion of the stress-strain curve.

0.093 in

An aluminum alloy that has a plane strain fracture toughness of 25,000 fails when a stress of 42,000 psi is applied. Observation of the fracture surface indicates that fracture began at the surface of the part. Estimate the size of the flaw that initiated fracture. Assume that f = 1.1.

Impact Test

Measures the ability of a material to absorb the sudden application of a load without breaking.

Necking

Local deformation causing a reduction in the cross-sectional area of a tensile specimen.

Proportional limit

A level of stress above which the relationship between stress and strain is not linear.

Creep

A time dependent, permanent deformation at high temperatures, occurring at constant load or constant stress.

50.0543 ft

A steel cable 1.25 in. in diameter and 50 ft long is to lift a 20 ton load. What is the length of the cable during lifting? The modulus of elasticity of the steel is 30 × 106 psi.

Factor of safety

The endurance limit divided by the tensile strength of the material.

Fatigue life

The number of cycles permitted at a particular stress before a material fails by fatigue.

Fracture toughness

The resistance of a material to failure in the presence of a flaw.

Notch sensitivity

Measures the effect of a notch, scratch, or other imperfection on a material’s properties, such as toughness or fatigue life.

Stress

Force per unit area over which the force is acting.

Young’s modulus

The slope of the linear part of the stress–strain curve in the elastic region, same as modulus of elasticity.

Tensile strength

The stress that corresponds to the maximum load in a tensile test.

Shear modulus

The slope of the linear part of the shear stress-shear strain curve.

0.4 in

A 0.4-in. diameter, 12-in. long titanium bar has a yield strength of 50,000 psi, a modulus of elasticity of 16 × 106 psi, and Poisson’s ratio of 0.30. Determine the diameter of the bar when a 500-lb load is applied.

500 MPa

A force of 100,000 N is applied to a 10 mm × 20 mm iron bar having a yield strength of 400 MPa and a tensile strength of 480 MPa. Find the stress acting on the wire.

20 kips

A polymer bar’s dimensions are 1 in. × 2 in. × 15 in. The polymer has a modulus of elasticity of 600,000 psi. What force is required to stretch the bar elastically to 15.25 in.?

1100 lb

Calculate the maximum force that a 0.2-in. rod of, having a yield strength of 35,000 psi, can withstand with no plastic deformation.

4.44 GPa

A force of 20,000 N will cause a 1 cm × 1 cm bar of magnesium to stretch from 10 cm to 10.045 cm. Calculate the modulus of elasticity.

Ceramics

A group of crystalline inorganic materials characterized by good strength, especially in compression, and high melting temperatures.

Smart material

A material that can sense and respond to an external stimulus such as change in temperature, application of a stress, or change in humidity or chemical environment.

Glass-ceramics

A special class of materials obtained by forming a glass and then heat treating it to form small crystals.

Materials science and engineering

A field of science that emphasizes studies of relationships between the microstructure, synthesis and processing, and properties of materials.

Polymerization

The process by which organic molecules are joined into giant molecules, or polymers.

Semiconductors

An element that has metallic bonding and generally good ductility, strength, and electrical conductivity.

Plastic

Polymers containing other additives.

Thermosets

A special group of polymers that decompose rather than melt upon heating.

Elastomers

Natural or synthetic plastics that are composed of molecules with spring-like coils that lead to large elastic deformations.

Elastic deformation

Deformation of the material that is recovered instantaneously when the applied load is removed.

Extensometer

An instrument to measure change in length of a tensile specimen, thus allowing calculation of strain.

Impact energy

The energy required to fracture a standard specimen when the load is applied suddenly.

Strain gauge

A device used for measuring strain typically consists of a fine wire embedded in a polymer matrix bonded to the test specimen and deforms as the specimen deforms.

Impact toughness

Energy absorbed by a material, usually notched, during fracture, under the conditions of the impact test.

Strain rate

The rate at which strain develops in or is applied to a material indicated.

Non-newtonian

Materials in which the shear stress and shear strain rate are not linearly related; these materials are shear thinning or shear thickening (e.g., polymer melts, slurries, paints, etc.).

Tensile toughness

The area under the true stress–true strain tensile test curve.

Newtonian

Materials in which the shear stress and shear strain rate are linearly related (e.g., light oil or water).

Engineering strain

Elongation per unit length calculated using the instantaneous dimensions.

Strain

Elongation per unit length.

Modulus of elasticity

Young’s modulus, or the slope of the linear part of the stress–strain curve in the elastic region. It is a measure of the stiffness of the bonds of a material and is not strongly dependent upon microstructure.

Density

Mass per unit volume of a material, usually expressed in units of g/cm3 or lb/in3.

Grains

Crystals in a polycrystalline material.

Physical properties

Characteristics such as color, elasticity, electrical or thermal conductivity, magnetism, and optical behavior that generally are not significantly influenced by forces acting on a material.

Polycrystalline

A material composed of many crystals.

Semiconductor

A group of materials having electrical conductivity between metals and typical ceramics

Strength-to-weight ratio

The strength of a material divided by its density.

Elastic limit

The magnitude of stress at which plastic deformation commences.

8 cm

An aluminum plate 0.5 cm thick is to withstand a force of 50,000 N with no permanent deformation. If the aluminum has a yield strength of 125 MPa, what is the minimum width of the plate?

Hardness test

Measures the resistance of a material to penetration by a sharp object.

Flexural modulus

The modulus of elasticity calculated from the results of a bend test; it is proportional to the slope of the stress-deflection curve.

Impact loading

Application of stress at a very high strain rate.

0.99

A polymer that contains internal flaws 1 mm in length fails at a stress of 25 MPa. Determine the plane strain fracture toughness of the polymer. Assume that f = 1.

Kinematic viscosity

Ratio of viscosity and density.

Modulus of resilience

The maximum elastic energy absorbed by a material when a load is applied.

% elongation

The total percentage permanent increase in the length of a specimen due to a tensile test.

Creep test

Measures the resistance of a material to deformation and failure when subjected to a static load below the yield strength at an elevated temperature.

0.77 mm

A piece of copper originally 305 mm (12 in.) long is pulled in tension with a stress of 276 MPa (40,000 psi). If the deformation is entirely elastic, what will be the resultant elongation?

Endurance limit

An older concept that defined a stress below which a material will not fail in a fatigue test.

Fatigue test

Measures the resistance of a material to failure when a stress below the yield strength is repeatedly applied.

Poisson’s ratio

The negative of the ratio between the lateral and longitudinal strains in the elastic region.

Stiffness

A measure of a material’s resistance to elastic deformation.

Tensile test

Measures the response of a material to a slowly applied uniaxial force. The yield strength, tensile strength, modulus of elasticity, and ductility are obtained.

True stress

The load divided by the instantaneous area over which the load acts.

Yield strength

A stress value obtained graphically that describes no more than a specified amount of deformation (usually 0.002).