When a material is subjected to a sudde, intense blow, in which the strain rate is extremely rapid, it may behave in a much more brittle manner than is observed in the tensile test. An iimpact test is often used to evaluate the brittleness of a material under these conditions. Many test procedures have been devised, including the Charpy test and the Izod test. Izod test is often used for nonmetalic materials. The test specimen may be either notched or unnotched; V-notched specimens better measure the resistance of the material to crack propagation. In the test, a heavy pendelum, starting as an elevation h0, swinging through its arc, strikes and breaks the specimen, and reaches a lower final elevation hf. If we know the initial and final elevations of the pendelum, we can calculate the difference in potencial energy. This difference is the impact energy absorbed by the specimen during failure. The ability of a material to withstand an impact blow is often referred to as the roughness of the material. The material properties obtained from a serşes of impact tests are transition temperature, notch sensitivity an relationship to the stress-strain diagram.
(Askeland D.R., The Science and Engineering of Materials, 3rd Ed., Pg. 149-150, Kayra Ermutlu)
Wankel Engine
The Wankel Engine is a rotary combustion engine, developed from the work of Felix Wankel. The triangular rotor has a centrally placed internalgear that meshes with as un gear that is part of the engine casing. An eccentric that is an integral part of the output shaft constrains the rotor to follow a planetary motion about the output shaft. the gear ratios are such that the output shaft rotates at three times the speed of the rotor and the tips of the rotor trace out the two-lobe epitrochoidal shape of the casing. the compression ratio is dictated geometrically by the eccentricity of the rotor and the shape of its curved surfaces. The convex surfaces miximise and minimise the sealed volumes, to give the highest compression ratio and optimum gas exchange. A recess in the combustion chamber provides a better-shaped combustion chamber.
The advantages of the Wankel engine are its compactness, the apparent simplicit, the ease of balance and the potential for high outputs by running at high speeds. The major disadvantages of the Wankel engine are its low efficiency (caused by limited compression ratios) and the high exhaust emissions resulting from the poor combustion chamber shape.
(Stone R., Introduction to Internal Combusiton Engines, 2nd Ed., pg.17-18, Kayra Ermutlu)
Optimized Production Technology
Optimized production technology (OPT) is an approach to scheduling, which places the primary focus upon the "bottleneck" process or processes. Bottlenecks are an everyday concept. Motorway roasworks and super market chechouts are bottlenecks at busy times of the day. They restrict the flow of work through the operation. Processes may be bottlenecks because either their capacity is less than the level of demand or because their capacity is used in an inefficient manner. Once bottleneck processes are identifiedi supplying processes are backward scheduled from the bottleneck. At all of the bottleneck processes, therefore, operations are activated on the basis of delivering products just in time for their linked downstream processes. OPT is a computer-based scheduling system. The more bottlenecks a system contains, the more complex the scheduling task becomes and a computer is essential.
OPT is based on the view that the goal of the operation is to make money. It was developed for manufacturing, however some of the principles of OPT are applicable to all organizations.
(Azhashemi M., Galloway L., Rowbotham F.,Operations Management in Context, 2nd Ed., pg.259, Kayra Ermutlu)
Tool Allocation
The operational capabilities of an advanced CNC machine are determined and/or constrained to a great degree by the set of cutting-tools assigned to the machine. Maximizing the operational flexibility of a machining center would be easy is each machine had a tool magazine of infinite (or very large) size. This would enable each machine to be loaded with all the different types of tools available in the tool crib. However, this option is not economically viable, since it would require a very high investment in cutting tools. In addition, the average utilization of cutting-tools in the system would be poor. In practice, therefore, cutting-tool magazines at machines are of limited size, typically having capacity of 20 to 60 tools.
(Josh S.B., Computer Control of Flexible Manufacturing Systems: Research and Development, pg.415, Kayra Ermutlu)
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