Flashcards
CAPE 1720 Design Process + Mechanical Properties
Cards in this deck (25)
- 1What are the 2 areas of design that may be identified?Mechanical Design and Industrial Design
- 2What are the 3 different types of design?- Original Design
- Adaptive, developmental design
- Variant design - 3Describe a technology pushWhen new materials are discovered, engineers are posed the question - what can we make?
e.g high purity silicon --> transistor
high purity glass --> optical fibres
high. temp alloys --> gas turbine - 4Describe a Market PullWhen new materials are discovered and are developed into products engineers want to make them better
e.g gas turbines/jet engines - new alloys/composites
aerospace - new alloys/polymers/ceramics
nuclear power - new alloys - 5Describe Adaptive/Developmental dESIGNIncremental advance in performance through a refinement in working principle
- often made possible by advances in materials - 6Describe variant designChange of scale/dimension without changing function of method of achieving it
- may require change of material
e.g scaling up of boilers - 7What is a technical system?A technical system consists of assemblies and components put together in such a way as to perform a function
e.g Bike
- made up of lots of different parts (each - 8Describe the design processConceptual design - consider various ways of fulfilling market need
Embodiment design - hone in on promising ideas
Detailed design - refine the chosen design - 9What is the conceptual stage?Alternative working principles or scheme for the function which make up the system
Example - fountain pen
• Function : to write
• Subfunction : to store ink
• The implications of each scheme for the performance and cost
• Approximate material property data needed for a wide range of materials since all options are open
• Metal for one scheme
Polymer for another - 10What is the embodiment stage?• Starts with a function structure
• Seeks to analyse its operation at an approx. Level
• Sizing components
• Selecting materials to perform properly at levels of stress, temp. And environmental suggested by the analysis
• Ends with a feasible layout which is passed to the detailed design stage - 11What is the detailed stage?• Specifications for each component are drawn up
• Critical components may be subjected to precise mechanical or thermal analysis
• Finite element methods (computer modelling) is
• Optimisation methods are applied to individual components or groups of components to maximise performance
• Material and production routes chosen
Design cost - 12Which 3 points must be considered when choosing a material?Requirements imposed by the service conditions
E.g a product subject to loads probably requires a strong material
Requirements imposed by the proposed manufacturing routes
e.g if a product needs to be bent then if must be sufficiently ductile to avoid breaking
Cost
Financial and environmental - 13Describe Elastic Deformation.When a material deforms under load but returns to its orig. dimensions when the load is removed
- ALL MATERIALS HAVE AN ELASTIC LIMIT - 14What can happen to a material when it reaches its elastic limit?- The material will break
The material deforms plastically (i.e giving a permanent deformation which remain when the load is removed) - 15Define plastic deformation.Giving a permanent deformation which remains when the load is removed
- 16What is the stiffness of a material? What is the material property that determines stiffness?- Can resist elastic deformation
- Young modulus (E) (measured in Pa)
NOTE: the stiffness of a component also depends on geometry, not just material e.g a rolled up piece of paper is stiffer than just a regular sheet of paper - 17Define tensile strength- The ability of a material to withstand tensile (stretching) loads without breaking
• For the weight fastened to a beam, the rod needs sufficient tensile strength to resist the force exerted by the load - 18What is compressive strength?The ability of a material to withstand compressive (squeezing) loads without being crushed or broken
* For the component being pressed by a heavy load, the component requires sufficient compressive strength to resist the load - 19Define shear strengthThe ability of a material to withstand offset loads or transverse cutting (shearing) actions without failure
• Because the loads acting on the two bars are not exactly in line (offset) the rivet experiences shear
If the rivet material does not have sufficient shear strength, the rivet will break (shear off)
- 20What defines the hardness of a materialThe hardness of a material is a measure of its resistance to - indentation or scratching (abrasion)
- a tough material is one that resists breaking regardless of a crack being present - 21Describe the Rockwell hardness tested discuss its advantages.A hardness number is determined by the difference in depth of penetration resulting from the application of an initial minor load followed by a larger major load.
Advantages:
- simple + cheap
- non-destructive - 22Define ductilityA ductile material allows a useful amount of plastic deformation to occur in tensile loading before fracture occurs
- 23Define toughnessToughness - the work required to propagate a crack through a material/the ability of a material to withstand shock loads
(different to strength) - how damage tolerant a material is - 24Define malleabilityMalleable material : allows useful amount of plastic deformation to occur in compressive loading before fracture occurs
E.g gold is very malleable, can be hammered into a very fine sheet (gold leaf) whilst still not presenting any cracks - 25Define brittleness- shows little no plastic deformation before fracture
- materials with low toughness are generally brittle
-EXAMPLE: steel - tough, difficult to propagate a crack through steel, not brittle
Glass - easy to propagate a crack, brittle
Lead/ jelly: breaks the trend, example of brittle + tough material
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- Chemical Engineering Flashcards on CAPE 1720 Design Process + Mechanical Properties , created by Sian Hughes on 19/10/2021.
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- Sian Hughes
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