DK CHING (MATERIALS)

Materials

Matter having unique qualities by which it may be categorized.

Matter

That which occupies space, can be perceived by the senses and constitutes the substance of a physical body.

Atom

The smallest unit of an element that can exist either alone or in combination, consisting of a nucleus of neutrons and protons surrounded by one or more electrons bound to the nucleus by electrical attraction.

Shell

Any of up to seven spherical surfaces containing the orbits of electrons of approximately equal energy about the nucleus of an atom.

Electron

A fundamental particle of matter having a negative charge.

Neutron

A fundamental particle having no charge.

Proton

A positively charged particle that is a fundamental constituent of all atomic nuclei.

Element

One of a class of substances that cannot be separated into simpler substances by chemical means, composed of atoms having an identical number of protons in each nucleus.

Atomic number

The number of protons in the nucleus of an atom of a given element, which equals the number of electrons normally surrounding the nucleus. Also called proton number.

Atomic weight

The average weight of an atom of an element based on ½ the weight of the carbon atom.

Periodic table

A tabular arrangement of the chemical elements in related groups, formerly in the order of their atomic weights and now according to their atomic numbers.

Bond

The attractive force by which atoms, ions, or groups of atoms are bound together in a molecule or crystalline structure. Also called chemical bond.

Ionic bond

A chemical bond characteristic of salts and ceramic materials, formed by the complete transfer of one or more electrons from one kind of ion to another. Also called electrovalent bond.

Positive ion

A positively charged ion created by electron loss. Also called cation.

Ion

An electrically charged atom or group of atoms formed by the loss or gain of one or more electrons.

Negative ion

A negatively charged ion created by electro gain. Also called anion.

Valence

A measure of the capacity of an atom or group to combine with other atoms or groups, equal to the number of chemical bonds the atom or group can form.

Valence electron

An electron located in the outer shell of an atom that can be transferred or shared in forming a chemical bond with another atom.

Covalent bond

A chemical bond formed by the sharing of pairs of electrons between two atoms.

Hydrogen bond

An electrostatic bond between an electronegative atom and hydrogen atom already linked to another electronegative atom by a covalent bond.

Molecule

The smallest particle of a substance that displays all of the characteristic physical and chemical properties of the substance, consisting of one or more like atoms in a compound.

Molecular weight

The average weight of a molecule of an element or compound calculated as the sum of the atomic weights of the molecule's constituent atoms. Also called formula weight.

Mole

The molecular weight of a substance expressed in grams; grams molecule. Also mol.

Inert gas configuration

The stable configuration of an element in which the outer shells of its atoms or ions are filled with the maximum number of electron pairs. Nature moves atoms and ions toward this configuration by capturing, surrendering, or sharing electrons with neighboring atoms or ions in an effort to achieve a relatively inert state of low energy.

Noble gas

Any of the chemically inter gaseous elements: helium, neon, argon, krypton, xenon, and radon. Also called inert gas.

Gas

Matter having neither independent nor volume, possessing perfect molecular mobility and the tendency to expand indefinitely.

Fluid

A substance, as a gas or liquid, that is capable of flowing, yields easily to pressure, and conforms to the shape of its container.

Evaporate

To change or convert from a liquid or solid into a vapor.

Liquid

Matter distinguished from the solid gaseous states by characteristic readiness to flow, little or no tendency to disperse and relatively high incompressibility.

Condense

To reduce to a denser form as a gas or vapor to a liquid or solid state.

Heat of condensation

The heat liberated by a unit mass of a gas at its boiling point as it condenses to a liquid.

Heat of vaporization

The quantity of heat required to convert a unit mass of liquid at its boiling point into vapor at the same temperature equal to the heat of condensation.

Solid

Matter having relative firmness, coherence of particles, or persistence of form.

Solidify

To change or convert from a liquid or gas into a solid

Heat of solidification

The heat liberated by a unit mass of liquid at its freezing point as it solidifies.

Heat of fusion

The quantity of heat required to convert a unit mass of a solid at its melting point into a liquid at the same temperature; equal to the heat of solidification.

Metallic bond

A chemical bond characteristic of metals, produced by the sharing of valence electrons which move freely through the lattice of a usually stable crystalline structure.

Lattice

A regular pattern of isolated points in space showing the location of atoms, ions, or molecules in a crystalline solid.

Crystal

A solid having a regularly repeating internal structure of atoms, ions, or molecules and enclosed by symmetrically arranged plane surface.

Amorphous

Not crystalline in structure.

Property

An essential or distinctive attribute or quality belonging specifically in the constitution of, or found in, the behavior of a thing.

Mechanical property

Any of the physical properties of a material that exhibit a response to applied forces.

Strength

The capability of a material to resist the force imposed on it, esp. the ability to sustain a high stress without yielding or rupturing.

Strength of materials

The study of the relationship between applied external forces and the internal effects produced by these forces in a body.

Isotropic

Exhibiting the same physical properties along all axes.

Anisotropic

Having different physical properties along different axes, as wood and other fibrous materials.

Stress

The internal resistance or reaction of an elastic body to external forces applied to it, equal to the ratio of force to area and expressed in units of force per unit of cross-sectional area. Also called unit stress.

Strain

The deformation of a body under the action of an applied force. Strain is a dimensionless quantity, equal to the ratio of the change in size or shape to the original size or shape of a stressed element.

Young's modulus

A coefficient of elasticity of a material, expressing the ratio of longitudinal stress to the corresponding longitudinal strain caused by the stress.

Poisson's ratio

The ratio of lateral strain to the corresponding longitudinal strain in an elastic body under longitudinal stress.

Tension

The act of stretching or state of being pulled apart, resulting in the elongation of an elastic body.

Tensile force

An applied force producing or tending to produce tension in an elastic body.

Tensile stress

The axial stress that develops at the cross section of an elastic body to resist the collinear tensile forces tending to elongate it.

Tensile strain

The elongation of material produced by a tensile stress.

Tensile test

A test for determining the behavior of a material under axial tension, in which a specimen in gripped at both end and pulled apart until rupture occurs.

Tensile strength

The resistance of a material to longitudinal stress, measured by the minimum amount of longitudinal stress required to rupture the material.

Axial force

A tensile or compressive force acting along the longitudinal axis of a structural member and at the centroid of the cross section, producing axial stress without bending, torsion, or shear. Also called axial load.

Axial stress

The tensile or compressive stress that develops to resist an axial force, assumed to be normal to and uniformly distributed over the area of the cross section.

Eccentric force

A force applied parallel to the longitudinal axis of a structural member but not to the centroid of the cross section, producing bending and an uneven distribution of stresses in the section. Also called eccentric load.

Compression

The act of shortening or state of being pushed together, resulting in a reduction in size or volume of an elastic body.

Compressive force

An applied force producing or tending to produce compression in an elastic body.

Compressive stress

The axial stress that develops at the cross section of an elastic body to resist the collinear compressive forces tending to shorten it.

Compressive strain

The shortening of a unit length of material produced by a compressive stress.

Compression test

A test for determining the behavior of a material under axial compression. In which a specimen is crushed until fracture or disintegration occurs. The compression test is used for brittle materials since their low tensile strength is difficult to measure accurately.

Strain gauge

An instrument for measuring minute deformations in a test specimen caused by tension, compression, bending or twisting. Also called extensometer.

Elongation

A measure of ductility of a material, expressed as the percentage increase in length of a test specimen after failure in a tensile test.

Reduction of area

A measure of the ductility of a material, expressed as the percentage decrease in cross-sectional area of a test specimen after rupturing in a tensile test.

Bulk modulus

A coefficient of elasticity of a material, expressing the ratio between a pressure and the corresponding fractional change in volume produced.

Compressibility

The reciprocal of bulk modulus, equal to the ratio of the fractional change in volume to the pressure applied to a substance.

Shear

The lateral deformation produced in a body by an external force that causes one part of the body to slide relative to an adjacent part in a direction parallel to their plane of contact.

Shearing force

An internal force tangential to the surface on which it acts, developed by a body in response to a shear force. For equilibrium of a rectangular element subject to shear, shearing in a vertical plane necessarily involves shearing in a horizontal lane, and vice versa.

Shear force

An applied force producing or tending to produce shear in a body.

Shear modulus

A coefficient of elasticity of a material, expressing the ratio between shearing stress and the corresponding shearing strain produced by the stress. Also called modulus of rigidity, modulus of torsion.

Shearing stress

The force per unit area developed along section of an elastic body to resist a shear force. Also called shear stress, tangential stress.

Shearing strain

The lateral deformation developed in a body in response to shearing stresses, defined as the tangent of the skew of the deformation. Since this skew angle is always very small, shearing strain is a pure number very nearly equal to the skew angle in radians. Also called shear strain.

Bending

The bowling of an elastic body as an external force is applied transversely to its length, Bending is the structural mechanism that enables a load to be channeled in a direction perpendicular to its application.

Transverse force

A force applied perpendicular to the length of a structural member, producing bending and shear. Also called transverse load.

Combined stress

A set of tensile and compressive stresses resulting from the superposition of axial and bending stresses in the cross section of a structural member, acting in the same direction and equal at any point to their algebraic sum.

Torque

The moment of a force system that causes or tends to cause rotation or torsion

Torsion

The twisting of an elastic body about its longitudinal axis caused by two equal and opposite torques, producing shearing stresses in a body.

Stress concentration

An increase in stress that develops discontinuities or flaws in a material. Stress concentrations in brittle materials develop cracks which propagate until failure. In ductile materials, stress concentrations develop local deformations which serve to redistribute and relieve the stresses.

Stress-strain diagram

A graphic representation of the relationship between unit stress values and the corresponding unit strains for a specific material.

Proportional limit

The stress beyond which the ratio of stress to strain for a material no longer remains constant.

Elastic limit

The maximum stress that can be applied to a material without causing permanent deformation.

Yield point

The stress beyond which a marked increase in strain occurs in a material without a concurrent increase in stress. Many materials do not have clearly defined yield points. For these materials a theoretically yield strength is calculated from the stress-strain curve.

Ultimate strength

The maximum tensile, compressive, or shearing stress a material can be expected to bear without rupturing or fracturing. Also called ultimate stress.

Fracture

The breaking of a material resulting from the rupture of its atomic bonds when stressed beyond its ultimate strength.

Elastic range

The range of unit stresses for which a material exhibits elastic deformation.

Deformation

A change in the shape or dimensions of a body or structure resulting from stress.

Elastic deformation

A temporary change in the dimensions or shape of a body produced by a stress less than the elastic limit of the material.

Plastic range

The range of unit stresses for which a material exhibits plastic deformation.

Plastic deformation

A permanent change in the dimensions or shape of a body produced by a stress greater than the elastic limit of the material, remaining rigid under stresses of less than a certain intensity. The molecular bonds in a material that exhibits plastic behavior reform after being stressed beyond the elastic limit, the material thus retains a measure of reserve strength. Also called plastic flow.

Strain-hardening range

The range of unit stresses for which a material exhibits increased strength with some loss of ductility.

Brittleness

The property of a material that causes it to rupture suddenly under stress with little evident deformation. Since brittle materials lack the plastic behavior of ductile materials, the can give no advance warning of impending failure.

Stiffness

A measure of a material's resistance to deformation when stressed within its elastic range.

Ductility

The property of a material that enables it to undergo plastic deformation after being stressed beyond the elastic limit and before rupturing. Ductility is a desirable property of a structural material since plastic behavior is an indicator of reserve strength and can serve as a visual warming of impending failure.

Elasticity

The property of a material that enables it to deform in response to an applied force and to recover its original size and shape upon removal of the force.

Modulus of elasticity

A coefficient of elasticity of a material, expressing the ratio between a unit stress and the corresponding unit strain caused by the stress, as derived from Hooke's law and represented by the slope of the straight-line portion of the stress-strain diagram. Also called coefficient of elasticity, elastic modulus.

Hooke's Law

The law stating that the stress on a body is directly proportional to the strain produced, provided the stress does not exceed the elastic limit of the material.

Allowable stress

The maximum unit stress permitted for a

material in the design of a structural member, usually a fraction of the material's elastic limit, yield strength, or ultimate strength, The allowable stresses for various materials are specified by building codes, engineering societies, and trade associations, based on specifications and methods of testing established by the American Society for Testing and Materials. Also called allowable unit stress, working stress.