Machine Design Finals

Hard-Drawn Spring Wire

A low-cost material available in sizes from 0.028 in to about 3/8 in; suitable for applications where service conditions are not severe and high dimensional precision is not required; cold-drawn; contains 0.45–0.75% carbon; not used for applications requiring indefinite life; surface quality is lower compared to other grades; cost index 1.

Music Wire

A high-quality hard-drawn steel wire with approximately 80% reduction during processing; excellent surface finish and strength comparable to valve-spring quality steel; contains 0.7–1.0% carbon; cold-drawn; available in sizes from 0.004 to 0.156 in; best material for small spring sizes (below ~1/8 in); cost index 3.5.

Oil-Tempered Spring Wire

Cold-drawn wire that is hardened and tempered after forming (50–70% reduction); typically contains 0.55–0.75% carbon; stress-relieved at low temperatures (~450°F); available in sizes from 0.225 to 0.5 in; surface quality better than hard-drawn wire but not as good as music wire; cost index 1.5.

Valve-Spring-Quality

A high-quality oil-tempered wire containing 0.60–0.75% carbon; excellent surface finish and highly reliable for fatigue resistance; used in severe service applications such as valve springs; available in sizes from 0.093 to 0.375 in.

Chromium-Vanadium Steel

An alloy steel that is oil-tempered; contains 0.45–0.55% carbon; available in sizes from 0.28 to 0.375 in; performs better than carbon steels at temperatures above 250°F; cost index 4.

Valve-Spring-Quality Chromium-Vanadium Steel

A refined chromium-vanadium steel with superior commercial surface quality; available in sizes from 0.032 to 0.437 in.

Chromium-Silicon Steel

A high-quality alloy steel suitable for impact loading and moderately high temperatures (up to ~450°F depending on allowable relaxation); cost index 4.

Stainless Steel Type 302

A chromium-nickel alloy steel with excellent corrosion resistance and good availability; sizes range from 0.009 to 0.375 in; cold-drawn; exhibits low relaxation at elevated temperatures compared to other materials; strength comparable to or better than music wire; cost index 8.5.

Ultimate Stress or Tensile Strength

Highest point on the stress-strain curve. It is the maximum load divided by the original area before straining occurs.

Yield Strength

The stress for a specified deviation from the straight part of the stress-strain curve.

Elastic Limit

The maximum stress to which a standardized test specimen may be subjected without a permanent deformation.

Proportional Limit

Is coincident with the elastic limit, but is precisely defined as the stress at which the stress-strain curve deviates from a straight line.

Modulus of Elasticity

A measurement of stiffness.

Factor of Safety

A number that is divided into a criterion of strength in order to obtain a design criterion. Also called Design Factor.

Strain

Deformation per unit gage length.

Plain Carbon

In AISI number system, 10XX means.

Free Cutting

In AISI number system, 11XX means.

Manganese

In AISI number system, 13XX means.

Boron

In AISI number system, 14XX means.

Nickel

In AISI number system, 2XXX means.

Nickel-Chromium

In AISI number system, 3XXX means.

Heat and Corrosion Resistant

In AISI number system, 303XX means.

Molybdenum

In AISI number system, 4XXX means.

Molybdenum-Chromium

In AISI number system, 41XX means.

Molybdenum-Chromium-Nickel

In AISI number system, 43XX means.

Molybdenum-Nickel

In AISI number system, 46XX means.

Silicon-Manganese

In AISI number system, 92XX means.

Chromium

In AISI number system, 5XXX means.

Chromium-Vanadium

In AISI number system, 6XXX means.

Nickel-Chromium-Molybdenum

In AISI number system, 8XXX means.

Age Hardening (Precipitation Hardening)

Occurs in some metals, notably certain stainless steel, aluminum, and copper alloys, at ambient temperature after solution heat treatment, the process being one of the constituent precipitating from solid solution. Where used, the consequences include increased strength and hardness, decreased ductility.

Artificial Aging

Aging at moderately elevated temperature expedites the process.

Alloy

A substance with metallic properties, composed of two or more elements of which at least one is metal.

Alloy

They are used to improve hardenability of steel, to reduce distortion from heat treatment, to increase toughness, ductility, and tensile strength, and to improve low-temperature or high-temperature properties.

Alloying Elements

In steel, are usually considered to be the metallic elements added for the purpose of modifying the properties.

Anisotropy

The characteristic of exhibiting different properties when tested in different directions.

Brittleness

A tendency to fracture without appreciable deformation.

Charpy Test

One in which a specimen, supported at both ends as simple beam, is broken by the impact of a falling pendulum.

Cold Shortness

Brittleness of metals at ordinary or low temperatures.

Cold Working

The process of deforming a metal plastically at a temperature below the recrystallization temperature and at a rate to produce strain hardening.

Damping Capacity

The ability of a material to absorb or damp vibrations, which is a process of absorbing kinetic energy of vibration owing to hysteresis. The absorbed energy is eventually dissipated to the surroundings as heat.

Decarburization

A loss of carbon from the surface of steel, occurring during hot rolling, forging, and heat treating, when the surrounding medium reacts with the carbon (as oxygen and carbon combining).

Ductility

That property that permits permanent deformation before fracture in tension. It is the opposite of brittleness. It is frequently a valuable property because, by virtue of it, a member may take an occasional exceptionally-high load without breaking.

Elasticity

The ability of a material to be deformed and to return to the original shape. Stress is proportional to the strain only during an elastic deformation.

Embrittlement

Involves the loss of ductility because of a physical or chemical change of the material.

Free Carbon

That part of the carbon content of steel or iron that is in free form of graphite or temper carbon.

Hard Drawn

A temper produced in wire, rod, or tube by cold drawing.

Homogeneous Materials

Have the same structure at all points.

Isotropic Materials

Have the same properties in all directions.

Izod Test

A test in which a specimen, supported at one end as a cantilever beam, is broken by the impact of a falling pendulum.

Killed Steel

Steel that has been deoxidized with a strong deoxidizing agent, such as silicon or aluminum, in order to eliminate a reaction between the carbon and oxygen during solidification.

Ingots of Killed Steel

Are sounder, containing fewer gas holes, and more homogeneous than non-killed or rimmed steel; these are desirable characteristics for forgings and heavy rolled sections.

Machinability

A somewhat indefinite property that refers to the relative ease with which a material can be cut.

Malleability

A material’s susceptibility to extreme deformation in rolling or hammering.

Mechanical Properties

Those that have to do with stress and strain: ultimate strength, and percentage elongation, for example.

Percentage Elongation

The extension in the vicinity of the fracture of a tensile specimen, expressed as percentage of the original gage length, as 20% in 2 in.

Percentage Reduction of Area

The smallest area at the point of rupture of a tensile specimen divided by the original area.

Physical Properties

Exclude mechanical properties, and are other physical properties such as density, conductivity, coefficient of thermal expansion.

Plasticity

The ability of a metal to be deformed considerably without rupture. In a plastic deformation, the material does not return to its original shape.

Poisson’s Ratio

The ratio of the lateral strain (contraction) to the longitudinal strain (extension) when the element is loaded with a longitudinal tensile force.

Precipitation Heat Treatment

Brings about the precipitation of a constituent from a supersaturated solid solution by holding the body at an elevated temperature, also called artificial aging.

Aging

In some alloys, precipitation may also occur at ambient temperatures, a process called.

Proof Stress

Stress which causes a specified permanent deformation of a material, usually 0.01% or less.

Red Shortness

A brittleness in steel when it is red hot.

Relaxation

Associated with creep, is the decreasing stress at a constant strain; important for metals in high-temperature service.

Residual Stresses

Those not due to applied loads or temperature gradients; they exist for various reasons, as unequal cooling rates, cold working, etc.

Rimmed Steel

Incompletely deoxidized steel.

Ingots of Rimmed Steel

Have a surface layer quite free of slag inclusions and gas pockets, which results in the optimum surface on rolled sheets.

Solution Heat Treatment

The process of holding an alloy at a suitably high temperature long enough to permit one or more constituents to pass into solid solution and then cooling fast enough to hold the constituents as a supersaturated solution. (Precipitation may occur with time).

Stiffness

The ability to resist deformation. It is measured by the modulus of elasticity in the elastic range, the higher the modulus, the stiffer the material.

Strain Hardening

Increasing the hardness and strength by plastic deformation at temperatures lower than the recrystallization range.

Temper

A condition produced in a non-ferrous metal by mechanical or thermal treatment; for example, annealed temper (soft), hard temper, spring temper.

Toughness

The capacity of material to withstand a shock load without breaking.

Transverse Strength

Refers to the results of a transverse bend test, the specimen being mounted as a simple beam.

Transverse Strength

Also called rupture modulus. It is frequently applied to brittle materials, especially cast iron.

Work Hardening

The same as strain hardening.

Wrought Steel

Steel that has been hammered, rolled, or drawn in the process of manufacture; it may be plain carbon or alloy steel.

Heat Treatment

An operation or combination of operations involving heating and cooling of metal or an alloy in the solid state for the purpose of altering the properties of the material.

Aging and Age Hardening

A change in a metal by which its structure recovers from an unstable or metastable condition that has been produced by quenching or cold working.

Aging and Age Hardening

The result is a change of mechanical and physical properties, a process that may be accelerated by using a temperature slightly higher than room temperature.

Annealing

A comprehensive term, is a heating and slow cooling of a solid metal, usually done to soften it.

Annealing

Other purposes of annealing include those of altering the mechanical and physical properties, producing a particular microstructure, removing internal stresses (stress relieving), and removing gases.

Critical Range

Has the same meaning as transformation range.

Drawing

Often used to mean tempering, but this usage conflicts with the meaning of the drawing of a material through a die and is to be avoided.

Graphitizing and Annealing Process

Causes the combined carbon to transform wholly or in part into a graphitic or free carbon; it is applied to cast iron, sometimes to high-carbon steel.

Hardening

The heating of certain steels above the transformation range and then quenching, for the purpose of increasing the hardness. In the general case, hardening is any process of increasing the hardness of a metal.

Malleablizing

Is an annealing process whereby combined carbon in white cast iron is transformed wholly or in part to temper carbon. Temper carbon is free (graphitic) carbon in the form of rounded nodules, characteristic forms in graphitizing and malleablizing.

Normalizing

The heating of an iron-base alloy to some 100°F above the transformation range with subsequent cooling below that range in still air at room temperature. The purpose is to produce a uniform structure.

Spheroidizing

Any heating and cooling of steel that produces a rounded or globular form of carbide.

Stress Relieving

The heating of a metal body to a suitable temperature and holding it at that temperature for a suitable time for the purpose of reducing internal residual stresses.

Tempering

A reheating of hardened or normalized steel to a temperature below the transformation range, followed by any desired rate of cooling.

Transformation Range

The temperature interval during which austenite is formed during heating; it is also the temperature interval during which austenite disappears during cooling.

Hardness

A measure of its resistance to indentation, and is one of the most significant properties because, properly interpreted, it says much about the condition of the metal.

Brinell Hardness Number (BHN)

Determined by a standard pressure applied to a 10 mm ball which presses for 10 sec or more on the surface of the material being tested. This hardness number is closely related to the ultimate tensile stress of steel.

Rockwell Tester

Faster than the Brinell and widely used commercially, utilizes several different indenters and, in effect, measures the depth of penetration by the indenters.

Rockwell Superficial Tester

A different machine, is used for a piece of material too thin for the standard tester.

Vickers Tester

Has a square-base, diamond pyramid indenter, and the Vickers number is the load in kilograms divided by the impressed area in square millimeters.

Shore Scleroscope Number

Obtained by letting a freely falling hammer with a diamond point strike the object to be tested and measuring the height of rebound. This height is the Shore Number; the higher the rebound, the harder is the material.

Shore Machine

Can be used on large parts and is often used as a quick inspection aid, but it is less accurate than the other tests.

ASTM

American Society for Testing Materials.