Introduction. Machine Element Design Walid Khraisat

Transcription

1 Introduction Machine Element Design Walid Khraisat

2 What Is Design? Engineering design is a systematic process by which solutions to the needs of humankind are obtained Examples Lightweight,compact wireless communication devices High-temperature resistance material for reentry vehicle

3 Machine Design Machine Design is a process of selecting the proper machine components for a predetermined function. To clarify this definition, machine is defined as a system of machine elements selected or designed for a specific function.

4 What Is Design?; cont Teamwork with engineers, scientists, environmentalists, economists, sociologists, legal personnel, marketing personnel, etc Public sentiments as executed through government regulations and political influence (e.g. new transportation vehicle banned in downtown, etc) Engineers must be beware of the impact of our actions on society and the environment

5 What Is Design? Object s aesthetic appearance; Like clothes The process of applying the various techniques and scientific principles for the purpose of designing a device, a process or a system in sufficient detail to permit its realization Define, calculate motions, forces, and changes in energy sizes, shapes, materials Failure stress and deflection analysis needed Applied, inertial loads; Parts geometry; Analysis of the forces, moments, and torques; Dynamics of the system

6 Engineering Design Designare; To designate, mark out To outline, plan or plot, as action or work; To conceive, invent, contrive Mechanism A device which transforms motion to some desirable pattern and typically develops low forces and transmits little power Machine Contains mechanism which are designed to provide significant forces and transmit power

7 Machine Elements MACHINE ELEMENTS Gears, Springs, Bolts,... Electric motors, Electric switches,... Optical sensors, Sonic sensors,... Control circuits,... Microprocessors,...

8 Creativity Among the many factors which effect creativity in design are; designer s experience, designer s ability, economic factors, and designer s own preference.

9 A product should be designed to function under all of the possible severe environmental conditions.

10 *10-step Design Process. 1. Identification of a need 2. Problem definition 3. Search 4. Constraints 5. Criteria 6. Alternative solutions 7. Analysis 8. Decision 9. Specification 10. Communication

11 10. communication 1.Identify the need 2. Define problem 9. Specification 3. search Iterative Design Process 8. Decision 4. Constraints 7. Analysis 6. Alternative solutions 5. criteria

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15 Factor of Safety Method Two distinct and separate approaches 1. The deterministic, or factor-of-safety approach. In this method, the maximum stress or stresses in a part are kept below the minimum strength by a suitable design factor or margin of safety, to ensure that the part will not fail. 2. The stochastic, or reliability approach. This method involves the selection of materials, processing and dimensions such that the probability of failure is always less than a pre selected value

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18 Probability-Based Design The stochastic method doesnot use a design factor at all rather attention is focused on the probability of survival Reliability- Probability Density Function For any Normally distributed variable: 68.3% of all values will lie between μ σ and μ + σ (i.e. μ ± σ ) 95.45% of all values will lie within μ ± 2 σ 99.73% of all values will lie within μ ± 3 σ

19 Reliability Method of Design Reliability R 0 R 1 R 1 P f P f Probability of Failure

20 2-2 Statistical Parameters 2-3 Probability Density Function and Cumulative Distribution Function

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24 R(z) is the integral of the standardized normal distribution from - to z 0 (in other words, the area under the curve to the left of z 0 ) P f (z) =1-R ( the area under the curve to the right of z 0 )

25 Probability of failure is reliability is

26 Answer: FOS is equivalent to 1.33 gives a reliability of 84.13%. Which is lower than 100% Reliability needed so it is insufficient for the present design, therefore there is a need to increase this factor

27 Ex:A round 1018 steel rod having yield strength (540, 40) Mpa is subjected to tensile load (220, 18) kn. Determine the diameter of rod that results in a reliability of (z = -3.09). Table A

28 Readings: