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, manual can opener
Manual safe-operation can opener
Electric safe can opener

4. Principles of Design Balance Rhythm Proportion/Scale Emphasis Harmony
Apply to design in general but 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 (the study of human factors in design)
Size of door and inside space must accommodate people/merchandise to be elevated. Also, location of buttons must be convenient

6. Important/Often Encountered Mechanical Design Principles
Harmony
Integration of components in a system to 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 Requirements A 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. CAD (Computer-Aided Design)
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. 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 F
Area = A l F
Area = Ao lo
(left) Before deformation, and (right) after deformation

13. Mechanical Properties of Materials
Deformation is simply change in dimensions or geometry/shape of a material under loading
The change in length, Dl =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 = Dl / lo is. 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. F
Area = A l F
Area = Ao lo
(left) Before deformation, and (right) after deformation

14. Mechanical Properties of Materials

15. Mechanical Properties of Materials

16. Material Types Ferrous metals/alloys Nonferrous metals/alloys Polymers
Ceramics
Glass
Diamond, Graphite
Wood
Composites
Iron-based materials, e.g. steels
e.g. nickel, silver, etc.
Plastics and rubber are prime examples
Compounds of metallic & nonmetallic elements, e.g. chinaware
Solid with a random atomic structure like a fluid
Both made from pure carbon but have different atomic structure
Natural and organic material
A combination of two/more material types