Gökhan Malakçı-030070802-8th Week

Feedback Control 02.04.2011 21:26

A feedback control system is a control system that tends to maintain a prescribed relationship of one system variable to anohter by comparing functions of these variables and usig the difference as a means of control.With an accurate sensor, the measured output is a good approximation of the actual output of the system.

A feedback control system often uses a function of a prescribed relationship between the output ans reference input to control the process.

(Richard C.dorf and robert H.Bishop,Modern Control Systems, 11th edition page 3)

Epoxy 02-04-2011 23:35

Epoxy resins are based on a chemical group called the epoxides. The sim­plest formulation of epoxide is ethylene oxide (C₂H₃0). Epichlorohydrin (C3H5OCI) is a much more widely used epoxide for producing epoxy resins. Uncured, epoxides have a low degree of polymerization. Toincrease molecular weight and to cross-link the epoxide, a curing agent must be used. Possible curing agents include polyamines and acid anhydrides. Cured epoxies are noted for strength, adhesion, and heat and chemical re­sistance. Applications include surface coatings, industrial flooring, glass fiber-reinforced composites, and adhesives. Insulating properties of epoxy thermosets make them use­ful in various electronic applications, such as encapsulation of integrated circuits and lamination of printed circuit boards.

(Mikell P.Groover, Fundamentals of Modern Manufacturing , materials,processes, and systems third edition page 164-165)

Elastomers 02.04.2011 23:42

Elastomers are polymers capable of large elastic deformation when subjected to relatively low stresses. Some elastomers can withstand extensions of 500% or more and still return to their original shape. The more popular term for elastomer is, of course, rubber. We can divide rubbers into two categories: (1) natural rubber, derived from certain biological plants; and (2) synthetic elastomers, produced by polymerization processes similar to those used for thermoplastic and thermosetting polymers.

(Mikell P.Groover, Fundamentals of Modern Manufacturing , materials,processes, and systems third edition page 167)

Composite 02.04.2011 23:47

Composites do not really constitute a separate category of materials; they are mixtures of the other three types. A composite is a material consisting of two or more phases that are processed separately and then bonded together to achieve properties superior to those of its constituents. The term phase refers to a homogeneous mass of material, such as an aggregation of grains of identical unit cell structure in a solid metal. The usual structure of a composite consists of particles or fibers of one phase mixed in a second phase, called thematrix.

Composites are found innature (e.g., wood), and they can be produced synthetically. The synthesized type is of greater interest here, and it includes glass fibers in a polymer matrix, such as fiber-reinforced plastic; polymer fibers of one type in a matrix of a second polymer, such as an epoxy-Kevlar composite; and ceramic in a metal matrix, such as a tungsten carbide in a cobalt binder to form a cemented carbide cutting tool.

Properties of a composite depend on its components, the physical shapes of the components, and the way they are combined to form the final material. Some composites combine high strength with light weight and are suited to applications such as aircraft components, car bodies, boat hulls, tennis rackets, and fishing rods. Other composites are strong, hard, and capable of maintaining these properties at elevated temperatures, for example, cemented carbide cutting tools.

(Mikell P.Groover, Fundamentals of Modern Manufacturing , materials,processes, and systems third edition page 10)