İbrahim İLGÜZ 030040113 (9th week)

Weathering

Weathering is a degradation process in which the material is damaged by exposure to atmospheric effects such as sunlight, rain, heat or cold. Sometimes the effect is physical. For example, if water is absorbed into brick or stone, it will expand as it freezes and split the brick or stone into fragments. Wind and rain will also erode (wear away) the surface of softer materials. Sometimes sunlight (ultraviolet rays) will break down the chemical structure of the material. Certain polymers may become brittle, and will craze and crack when exposed to sunlight, heat or immersion in water over a long period of time.
Pigments are added to some polymers to act as stabilizers to absorb the ultraviolet (UV) rays in sunlight. For example, window frames are made from an ultraviolet resistant grade of polyvinyl chloride (UPVC). In the case of polyethylene (polythene) sheet, carbon black is added to retard ultraviolet degradation. In another case, polyethylene detergent bottles are stabilized with polyisobutylene to protect the polymer against the effects of the detergent.
On the other hand, some polymers are deliberately made to degrade. At one time, polymers buried in land-fill sites did not break down. Nowadays many polymers are biodegradable. They will break down as the result of bacterial attack when buried and therefore will not pollute the ground.
(Basic Manufacturing (Third edition),Roger Timings,p 81)

Overshoot

If the system is underdamped, the response of the transducer or measuring system overshoots the step-input magnitude and the corresponding oscillation occurs with a first-order decay. This type of response leads to additional response specifications which may be used by transducer manufacturers. These specifications include overshoot OS, peak time Tp, settling time T5, rise time Tn and delay time Td. If the viscous damping is at the critical value, the measuring system responds up to the step-input magnitude only after a very long period of time. If the damping is more than critical, the response of the measuring system never reaches a magnitude equivalent to the step input. Measuring-system components following a second-order behavior are normally designed and/or selected such that the damping is less than critical. With underdamping the second-order system responds with some time delay and a characteristic phase shift.
(Standard Handbook of Machine Design (3rd Edition), Edited by: Shigley, Joseph E.; Mischke, Charles R.; Brown, Thomas H. Jr., p3-18)

Compliance

The exact method of conducting a risk assessment may be specified by procurement specifications, industry standards, or government regulations. The design objective may be only compliance with the assessment requirement. However, in the process of performing a written risk assessment and classifying the risk into some severity level, it may result in a benefcial safety audit of the product. Where there is “residual risk,” the design of specific warnings and instructions may be required.
(Mechanical Engineering Handbook, Ed. Frank Kreith, p20-12)


EGR

EGR is shorthand for exhaust gas recirculation. EGR is a means of lowering combustion temperature so oxides of nitrogen pollutants that develop in a high-temperature enviroment, are kept in check. This is done by recirculating metered amount of exhaust back into the combustion process and lowers the combustion temperature. The EGR has become a forgotten soldier in the fight to contain airport pollution. According to a report issued by the Enviromental Protection Agency, malfunctioning EGR systems ranked third, behind carburetor of emission control-related equipment in new cars.
(Mort Schultz, Popular Mechanics, pg:88)