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Creep Rupture Strength

Creep is that phenomenon associated with a material in which the material elongates with time under constant applied stress, usually at elevated temperatures. A material such as tar will creep on a hot day under its own weight. For steels, creep becomes evident at temperatures above 650F. The term creep was derived because, at the time it was first recognized, the deformation which occured at the design conditions occured at a relatively slow rate. Depending upon the stress load, time, and temperature, the extention of a metal associated with creep finally ends in failure.

Creep-rupture or stress-rupture are the terms used to indicate the stress level to produce failure in a material at a given temperature for a particular period of time. For example, the stress to produce rupture for carbon steel in 10,000 hours(1.4 years) at a temperature of 900F is substantially less than the ultimate tensile strength of the steel at the corresponding temperature. The tensile strength of carbon steel at 900F is 54,000 psi, whereas the stress to cause rupture in 10,000 hours only 11,500 psi.

(Rules of thumb for chemical engineers, Yazar: Carl Branan, page 288)

Diecast Alloys

The four major types of alloys that are die cast are zinc, aluminum, magnesium, and copper-based alloys. The die casting process was developed in the nineteenth century for the manufacture of lead/tin alloy parts. However, lead and tin are now very rarely die cast because of their poor mechanical properties.

The most common die-casting alloys are the aluminum alloys. They have low density, have good corrosion resistance, are relatively easy to cast, and have good mechanical properties and dimensional stability. Aluminum alloys have the disadvantage of requiring the use of cold-chamber machines, used for zinc alloys, owing to the need for a seperate molten metal ladling operation.

(Product Design for Manufacture and Assembly, Third Edition, Yazar Geoffrey Boothroyd, Peter Dewhurst, Winston A. Knight, Page 424)

Electrostatic Fluid Bed

As the name implies, this, this process combines elements of both fluidized-bed and the electrostatic-spray processes. Standard fluidized-bed equipment is used, but in addition, the plastic particles are given a negative charge by applying a high-voltage(approximately 90,000 volts) direct current. The part to be coated is electrically grounded and suspended above the fluidized bed, so that the charged particles can be attracted to the part. The process has several advantages over the straight fluidized-bed process, among which are:

-The part to be coated does not need to be immersed.
-Preheating the part is not necessary for particle adhesion.
-Large fluidized beds are not needed to coat large parts.
-The process can be used to coat thin, low-mass parts such as wires that cannot be coated by the straight fluidized-bed process due to their poor heat retention.

The process has been found most useful in coating large complex parts and thin-gauge wire.

(Coating materials for electronic applications,Yazar: James J. Licari, Page 239)

Energy Release Rate

When a flaw in an infinite plate is approximated by a line crack, the so-called flaw energy, i.e. the part of the stored energy attributed to the presence of the flaw, can be calculated exactly. The derivatie of the flaw energy with respect to the crack length is the so-called energy-release rate, a quantity of singular importance in the theory of fracture mechanics.

When a flaw is approximated by a cavity other than a line crack or when a line crack does not extend co-linearly, the energy release rate can-not be obtained by differentiating the flaw energy, even if the latter can be obtained exactly.

(Asymptotic methods and singular perturbations, Yazar: Robert E. O'Malley,American Mathematical Society,Society for Industrial and Applied , Page 153)