ME260 Mechanical Engineering Design IIDefinition of DesignDesign ExamplePrinciples of DesignImportant/Often Encountered Mechanical Design PrinciplesSlide 6Design GuidelinesSlide 8Slide 9Slide 10Slide 11Mechanical Properties of MaterialsSlide 13Slide 14Slide 15Material TypesME260 Mechanical Engineering Design IIInstructor notesDefinition of DesignMany available definitionsOne definition: Design is the process of inventing artifacts that display a new physical order, organization, and form in response to functionAnother definition: Design is a conscious effort directed towards the ordering of the functional, material, and visual requirements of a problemDesign ExampleProblem: Build a tool/device that is capable of opening metal cansDesign Response:Regular, manualcan openerManual safe-operation can openerElectric safecan openerPrinciples of DesignBalanceRhythmProportion/ScaleEmphasisHarmonyApply 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 viewImportant/Often Encountered Mechanical Design Principles BalanceProportion/ScalePhysical balance often involving geometric symmetryPertains 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 convenientImportant/Often Encountered Mechanical Design Principles HarmonyIntegration of components in a systemto work seamlessly togetherThis pertains toDesign for Assembly (DFA) concepts,i.e. the ease with which one can assemble and disassemble partsDesign Guidelines Functional RequirementsMaterial/Manufacturing/Cost RequirementsVisual RequirementsDesign Guidelines Functional RequirementsA can/bottle opener must be able to open cans/bottles, otherwise it is a dysfunctional can/bottle openerDesign Guidelines Material/Manufacturing/Cost RequirementsMore material used in a design means more costMore material normally means stronger design (i.e. less chance of breaking/failure)More material also normally means higher manufacturing costThe type of material also affects both cost and likelihood of failure. It affects performance in generalMore material/manufacturing also typically means more environmental pollutionFinally, the material for your part should be amenable to manufacturing techniques/processes available to youDilemmaDesign Guidelines Material/Manufacturing/Cost RequirementsExamples: 1- You can not create a perfect 2- A bigger diameter car axle is less likely to break but costs more3- A car axle made from diamond is both prohibitive in cost as well as can easily fracture/break, i.e. is not tough towithstand a hit. Steel, however, is a good choice material hereThis pertains to Design for Manufacture (DFM) concepts,i.e. the design process needs to integrate manufacturing feasibility into itAn example of CAD (Computer-Aided Design)Design Guidelines Visual RequirementsMany times you want your product to be either:1- Appealing to the human eye for marketability2- Of certain color to serve a certain purposeExample 1: Car manufacturers compete to make visually appealing carsExample 2: Protective coats/pants for firefighters are typically made of heat reflective colors, not black for example.Mechanical Properties of Materials Force is not an obje ctive measure of loadingStress =  = Force/Area (F/Ao) isWhy? 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 F F Area = Ao loF F Area = A l(left) Before deformation, and (right) after deformationMechanical Properties of Materials Deformation is simply change in dimensions or geometry/shape of a material under loadingThe change in length, l =l – lo is 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 = l / lo is. Strain sometimes is expressed as a percentage, i.e. as 100×l / 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 (l) relative/compared to their original length (lo ), i.e. depends on how much they strained. F F Area = Ao loF F Area = A l(left) Before deformation, and (right) after deformationMechanical Properties of MaterialsMechanical Properties of MaterialsMaterial Types Ferrous metals/alloysNonferrous metals/alloysPolymersCeramicsGlassDiamond, GraphiteWoodCompositesIron-based materials, e.g. steelsBoth made from pure carbonbut have different atomic structurePlastics and rubber are prime examplesCompounds of metallic & nonmetallic elements, e.g. chinawareNatural and organic materiale.g. nickel, silver, etc.A combination of two/more material typesSolid with a random atomic structure like a