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ME260 Mechanical Engineering Design II

ME260 Mechanical Engineering Design II. Instructor notes. Definition of Design. Many available definitions One definition: Design is the process of inventing artifacts that display a new physical order, organization, and form in response to function

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ME260 Mechanical Engineering Design II

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  1. ME260 Mechanical Engineering Design II • Instructor notes

  2. Definition of Design • Many available definitions • One definition: Design is the process of inventing artifacts that display a new physical order, organization, and form in response to function • Another definition: Design is a conscious effort directed towards the ordering of the functional, material, and visual requirements of a problem

  3. Design Example • Problem: Build a tool/device that is capable of opening metal cans • Design Response: Regular, manualcan opener Manual safe-operation can opener Electric safecan opener

  4. Principles of Design Apply to design in generalbut not necessarily all important to “mechanical design” Also, some of these involve aesthetics which may or may not be important from a mechanical point of view • Balance • Rhythm • Proportion/Scale • Emphasis • Harmony

  5. Important/Often Encountered Mechanical Design Principles • Balance • Proportion/Scale Physical balance often involving geometric symmetry Pertains to ergonomics (thestudy of human factors in design) Size of door and inside space must accommodate people/merchandise to be elevated. Also, location of buttonsmust be convenient

  6. Important/Often Encountered Mechanical Design Principles • Harmony Integration of components in a systemto work seamlessly together This pertains to Design for Assembly (DFA) concepts,i.e. the ease with which one can assemble and disassemble parts

  7. Design Guidelines • Functional Requirements • Material/Manufacturing/Cost Requirements • Visual Requirements

  8. Design Guidelines • Functional RequirementsA can/bottle opener must be able to open cans/bottles, otherwise it is a dysfunctional can/bottle opener

  9. Design Guidelines • Material/Manufacturing/Cost Requirements More material used in a design means more cost More material normally means stronger design (i.e. less chance of breaking/failure) More material also normally means higher manufacturing cost The type of material also affects both cost and likelihood of failure. It affects performance in general More material/manufacturing also typically means more environmental pollution Finally, the material for your part should be amenable to manufacturing techniques/processes available to you Dilemma

  10. Design Guidelines • Material/Manufacturing/Cost Requirements Examples: 1- You can not create a perfect 2- A bigger diameter car axle is less likely to break but costs more 3- A car axle made from diamond is both prohibitive in cost as well as can easily fracture/break, i.e. is not tough to withstand a hit. Steel, however, is a good choice material here This pertains to Design for Manufacture (DFM) concepts,i.e. the design process needs to integrate manufacturing feasibility into it An example of CAD (Computer-Aided Design)

  11. Design Guidelines • Visual Requirements Many times you want your product to be either:1- Appealing to the human eye for marketability 2- Of certain color to serve a certain purpose Example 1: Car manufacturers compete to make visually appealing cars Example 2: Protective coats/pants for firefighters are typically made of heat reflective colors, not black for example.

  12. F Area = Ao F Area = A lo l F F Mechanical Properties of Materials Force is not an objective measure of loading Stress = s = Force/Area (F/Ao) is Why? To answer this answer first:If a force of 1 lb is applied to a rubber band and a force of 100 lb is applied to another, which rubber band will break first?Answer: depends on their cross-sectional area, i.e. the stress that they are subjected to (left) Before deformation, and (right) after deformation

  13. F Area = Ao F Area = A lo l F F Mechanical Properties of Materials Deformation is simply change in dimensions or geometry/shape of a material under loading The change in length, Dl =l – lois not an objective measure of deformation. This is positive change if material is loaded in tension and negative change if loaded in compression. Strain (the relative change in length) = e = Dl / lois. Strain sometimes is expressed as a percentage, i.e. as 100×Dl / lo. If a rubber band is extended by 1 cm and another by 1 m, which one will break first?Answer: depends on how much they stretched (Dl) relative/compared to their original length (lo), i.e. depends on how much they strained. (left) Before deformation, and (right) after deformation

  14. Mechanical Properties of Materials

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