MDP 1 Lecture 1 Design Methods Revised

8/3/2019 MDP 1 Lecture 1 Design Methods Revised

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Mechanical Design Practice

Topic 1, ,

failure mechanisms and balanced design

(Shigley’s Mechanical Engineering Design - Chapter 1)

John Fielke

Associate Professor

School of Advanced Manufacturing and Mechanical Engineering



Copyright Notice

MD – Week 1, Slide No. 2

Do not remove this notice.

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This material has been produced and communicated to you by or onbehalf of the University of South Australia pursuant to Part VB of the

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The material in this communication may be subject to copyright under theAct. Any further reproduction or communication of this material by you

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,• BEn Mechanical BESc A En PhD Soil Science

• CPEng, SMIEAust

•

• Dried grape processing

a. Research

. onsu ng

c. Expert Witness




,Other courses

• Computer Techniques

• CADD CAM Principles and Practice

• Product Design Communication

• Final ear ro ects

• PhD supervision ( x 5)




,Other interests

• Family, gardening

•

• Learning rock and roll dancing




,Learnin ex ectations

• Attend lectures, interact and ask questions.

•

• Use the weekly quizzes to revise lecture material.

lecture).

• Work on assi nment as rou meetin both at tutorials and in own time during the week.

• Use discussion forum to ask course related questions.

• Try to grasp topics weekly and seek help early. If you are havingdifficulties/issues please let me know.

• Provide feedback where you can see improvements can be made• Make this best course in program.




e en o e course s u en s s ou e a e o:-

a. apply an appropriate design methodology and appreciate thelegal implications of the design process.

b. select appropriate materials to satisfy design requirements.

c. explain material behaviour and simple failure mechanisms anddesign for these situations.

. es gn mec an ca componen s or s reng andeflection with regard to safety standards.

.manufacturer's catalogues.

DO NOT REMOVE THIS NOTICE. Reproduced and communicated on behalf of the University of South Australia pursuant to Part VB of the copyright Act 1968 (the Act) or with permission of thecopyright owner on (24/709) Any further reproduction or communication of this material by you may be the subject of copyright protection under the Act. DO NOT REMOVE THIS NOTICE.

http://www.ntn.co.jp/english/products/pdf/ball/pdf/Bearing_en_all.pdf



Course Teaching & LearningMD – Week 1, Slide No. 8

Arrangements

Course website (LearnOnline)

Weekly lectures and tutorials

Weekly quiz (10% grade)

Two assi nments 20% rade each

Three hour exam (50% grade)

Must achieve at least 40% in exam and an overall pass grade topass the course.

There will be no supplementary assessment.



Course Teaching & LearningMD – Week 1, Slide No. 9

Arrangements

Any questions?




At the end of this lecture, students will be able to:-

• Explain the engineering design process and the importance of an

appropriate design.

• List the requirements to document a design in a professional andresponsible manner.

• Recall the range of static failure modes.• Explain the difference between

.

• Select an appropriate design factor

factor of safet .

• Undertake a balanced design.

DO NOT REMOVE THIS NOTICE. Reproduced and communicated on behalf of the University of South Australia pursuant to Part VB of the copyright Act 1968 (the Act) or with permission of thecopyright owner on (22/6/10) Any further reproduction or communication of this material by you may be the subject of copyright protection under the Act. DO NOT REMOVE THIS NOTICE.

http://takemeiamyours.files.wordpress.com/2008/02/roller

coaster.jpg




1. Functional. a e

3. Reliable4. Competitive

5. Usable6. Manufacturable7. Marketable

Design is an innovative and highly iterative process

Decisions must sometimes be made with:1. Too little information.

3. Excessive and often contradictory information





Mechanical Engineering Design, 9 th

Edition. (2011) Budynas, R.G. and Nisbett, J.K. Page 6




.

en n ury, a ure or poor per ormance occurs:-- Legal proceedings will examine design reports, notes and

calculations.

- Your work will be presented in court.

Courts will be lookin for rofessional ne li ence and a ortioninblame for payment of damages/prosecution.




“Ride owners also had to pay

out some $3 million last year

collapsed when 44 of its' ,

injuring 42 at the Royal AdelaideShow in southern Australia in2000. Victims received up to$400,000 each as part of the

”.

http://goliath.ecnext.com/coms2/gi_0199-- - - -

DO NOT REMOVE THIS NOTICE. Reproduced and communicated on behalf of the University of South Australia pursuant to Part VB of the copyright Act 1968 (the Act) or with permission of thecopyright owner on (24/709) Any further reproduction or communication of this material by you may be the subject of copyright protection under the Act. DO NOT REMOVE THIS NOTICE.

http://news.bbc.co.uk/2/hi/asia-pacific/908310.stm

- - - - .




When desi n oes wron

,

http://media.photobucket.com/image/southern%20


http://business.theage.com.au/business/design-fault-to-keep-ailing-wheel-shut-20090301-8lh8.html

star%20observation%20wheel/rustyhawkbf/TheWheel2171008.jpg




When desi n oes wron

650,000 occupational injuries and illnesses

Costs at least $20 billion a year

n us ra a an o une :> 77 workplace deaths can be attributed to poor design,

- - ,NOHSC July 2004)




-

• Assumptions• a cu a ons• Decision reasoning• Calculations

• Drawings and sketches• Design history

Manufacturers are governed by product liability laws




-

oo ou or mec an ca a ures

Upload an image/URL to the course FAILURES DATABASE

Have a look at what others have uploaded and place a comment




-

oo ou or pro uc reca no ces ue o mec an ca es gn ssues

Upload an image/URL to the course RECALL DATABASE

Have a look at what others have uploaded and place a comment




– .

– .

Often the real need is not always evident to all.

Decide with confidence what is the problem.




– .

-

1. Performance (force, power, speed, volumes)

. mens ons s ze an we g

3. Shape/layout

4. Strength5. Manufacturing process

6. Environment

7. Safety8. Costs




– .

-

1. Strength and dimensions

. ro uc on me o s

3. Standard size availability

4. Weldability and machinability5. Corrosion, heat and wear resistance

6. Reliability (e.g. castings and welds may have porosity or inclusions which can lead to premature failure)




Desi n Procedure – 4. Preliminar Desi ns

Rarely is there only 1 “correct” solution

Some solutions will be better than others, but you will need to developthem to see their potential.

Select 3 to 6 preliminary designs and- Make a roximate calculations for sizes/selections- Create sketches or CAD models- Develop a workable solution for each design

-- Maybe undertake tests of the design using a proto-type/simulation




– .

“ ” .

Use a structured decision making process to choose the best design.

e.g. weighted scoring method

5A. Develop criteria for assessment (excluding cost as cost will be thefinal determinant after the weighting process)

For example:Reliability - since it is to be used on remote sites

– Uses standard components – easy to get spare parts




– .

. justification

or examp e

Reliability has a weight of 10 as it so important the machine will notbreak down when needed as the whole production line dependsupon it.

Low maintenance has a weight of 7 as it is expensive to stop the lineand undertake maintenance and it can only be done on routine shut

.

Uses standard components has a weight of 6 as it is easier to get a local.




– .

.the criteria

Criteria Wei ht Desi n 1 Desi n 2 Desi n 3

Score Score Score

Reliability 10 6 8 10

Low Maintenance 7 10 6 2Standard components 6 3 7 10

Performance 5 10 6 1

Low Energy consumption 4 2 8 10

Corrosion resistance 1 10 4 1




– .

. .


Score Total Score Total Score Total

Reliability 10 6 60 8 80 10 100

Low Maintenance 7 10 70 6 42 2 14Standard components 6 3 18 7 42 10 60

Performance 5 10 50 6 30 1 5

Low Energy consumption 4 2 8 8 32 10 40

Corrosion resistance 1 10 10 4 4 1 1

Totals 218 250 230




– .

. .


Score Total Score Total Score Total

Reliability 10 6 60 8 80 10 100

Low Maintenance 7 10 70 6 42 2 14

Standard components 6 3 18 7 42 10 60

Performance 5 10 50 6 30 1 5

Low Energy consumption 4 2 8 8 32 10 40

Corrosion resistance 1 10 10 4 4 1 1

Totals 218 250 230

Design ranking 3 1 2

Estimated cost $150,000 $170,000 $120,000

MD W k 1 Slid N 29




– .

.that includes:

-

- Justification of selection scores (weights and scores)

-

- Sketches

-

- Costs

- A discussion on why the preferred design is recommended

MD Week 1 Slide No 30




– .

-

- A statement of the design brief

- summary o e na ou comes, nc u ng a raw ng

- A step-by-step record of the design evolution, including-

- Diagrams, sketches etc of all alternative designs- Selection procedure for final design-- Results of all calculations

- Material selection criteria and data- Reference used, especially Standards- Standard product or component drawings- Final design details and drawings

- Recommendations for proving or testing the design, includingtest procedures.

MD Week 1 Slide No 31




– .

, -should be carried out

e resu s o pro o- ype es ng mus e a e o e es gn epor .

Kverneland (ploughmanufacturer), Norway – notehydraulic cylinders used tocrea e a cyc c oa o es or

fatigue

MD – Week 1 Slide No 32




– .

The timber block was 45 kg dropped from 1.5 metres.

The Timber bundle was 1600 kg dropped from 1.4 metres.




MD Week 1, Slide No. 33

How have you seen companies test proto-types?




MD Week 1, Slide No. 34

Design Procedure – 8. Release for

pro uc onFurther detailed design work

Specifications are written

Production drawings are created

Bills of materials finalised and structuring of assemblies

Details for manufacturin /toolin , urchasin and roduction lannin

Required quality checks

Operators Manuals

The above is done for medium to large projects, but smaller projects ma not need full ustification.

All projects will need assumptions and calculations to bedocumented.




,

Getting the design right early saves

me an money




At time of preliminary design $1

Checking $10Process planning $100

o ow ng oo ng an gs ave een ma e ,

Once production has commenced $10,000

,




Break




Maximum stress (shock and start up loads)

Component strength (yield or UTS)

Design Factor (Factor of Safety)




Stress is a state property at a specific point

Shear stress (τ)

Only by knowing the actual forces acting on the.

Loads may be maximum on stopping, startingor jamming.

s oc ac or sh s app e o e s a c oa .




–

Source : unknown




.

Yield Stren th SUltimate tensile strength (Sut)Shear Strength (Ss)

within a component of the same

material due to work hardeninheat treatment, surface finish,inclusions etc.




In order to have a safe design the ComponentStrength must be greater than the Actual

.

In man cases there is a reat deal of uncertaint

on both the values for the strength and thestress and these are accounted for using aDesign Factor or Factor of Safety




,

Accounts for uncertainties concerning stress and strength:• Composition of materials

• Effect of local processing on properties• Effect of nearb welds shrink fits

• Effect of heat treatment• Intensity and distribution of loading• Validity of loading model to represent reality• Intensity of stress concentration

• Effect of corrosion• Effect of wear • Uncertainty of other factors




,

Design Factors (Uncertainty) must be managed byengineers

For example – aircraft use• Materials with hi h certaint of ro erties certified

• Known loads from study and measurement• Testing to verify all assumptions• High quality control• Routine testing to detect signs of failure

Hence they can use small design factors of 1.05 to 1.15otherwise the lane will be too heav to fl




-,

The uncertainties can be broken down into:-

m

Workshop Accuracy (Nw)Desi n load accurac N

Consequence of Failure (Ncf )

The design factor N = Nm x Nw x Na x Ncf

-uncertainties.

Calculating Design Factor NMD – Week 1, Slide No. 46



Calculating Design Factor, N

N = Nm x Nw x Na x Ncf

Material Reliability Nm = 1.0 Certified Sut or Sy

Nm = 1.1 Ductile materials

Nm = 1.5 to 2.0 Brittle material using Suc

Nm = 3.0 Brittle material using Sut

Workshop andinspection accuracy

Nw = 1.0 Machined surfaces

Nw = 1.05 to 1.1 Forged and die cast surfaces

Nw = 1.15 to 1.2 Sand cast surfaces

Design accuracy Na = 1.05 For precise, well defined situations

N = 1.2 to 1.5 If theor uses un roved assum tions

Na = 2.0 to 3.0 Rough, preliminary calculations

Consequence of failure Ncf = 1.2 If no danger to persons and replacement is no problem

Ncf = 1.4 to 2.0 For general applications

Ncf = 2.0 to 3.0 When replacement means material losses

cf .

Ncf = 4.0 When failure is disastrousSource : unknown




-,

1.25 < N < 1.5 low weight is necessary and exceptional certainty exists.

1.5 < N < 2.5 ductile materials, known constant load

2.5 < N < 3.0 brittle materials, known loads

3.0 < N < 4.0 uncertain loads

4.0 < N < 6.0 dangerous or disastrous consequence of failure




–

,Failure is based on permanent deformation i.e. yield (Sy)

For tension/compression

For bending,




–

,Failure is based on permanent deformation i.e. yield (SS)However, torsion tests show for ductile materials S

s= 0.6S

y

For direct shear

or tors on




–

,

There is no yield prior to ultimate failure (strain at failure < 5%)

Hence Suc or Sut is used for material strength




-

. y .

2. Calculate the Design Factor for each component

N = Nm x Nw x Na x Ncf

3. Determine the allowable stress for each component= Sy/N (for normal stresses)= . y

4. Trace the force through the assembly, splitting the force wherethere is more than one path (e.g. if the load is carried by 5 rivets,orce per r ve = orce .

5. Explode the assembly and show forces acting on each part.

. ,compression/bearing, shear, bending, torsion).

7. Write the equation for each mode of failure as followsAllowable stress ≥ Actual Stress

Sy/N or 0.6Sy/N ≥ F/A or Mc/I or Tr/J




-

.equation per failure mode).

9. Solve the equations (look for equations with least no. of unknowns)10. Round up the sizes to preferred sizes (see next slide).

.

11. Consider reducing the size of the part you desire to have fail first ine even o an over oa . oose e eas es par o rep ace or e

cheapest so as to provide protections to the other parts fromfailure.

A balanced design minimises the use of material and will look

.




0.05, 0.06, 0.08,

0.1, 0.12, 0.16, 0.2, 0.25, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9,1.0, 1.1, 1.2, 1.4, 1.5, 1.6, 1.8, 2.0, 2.2, 2.5, 2.8, 3.0, 3.5, 4.0, 4.5,

5.0, 5.5, 6.0, 6.5, 7.0, 8.0, 9.0,

10, 11, 12, 14, 16, 18, 20, 22, 25, 28, 30, 32, 35, 40, 45, 50, 60, 80,

100, 120, 140, 160, 180, 200, 250, 300

Source: Shigley Table A-17, pp 1035.




ne o e suppor co umnsof a 50 tonne (500kN) press is

shown in the diagram.Each column is attached to thepress platen (B) by split rings (C)

tension due to the 250kN downforce from the press (B) through to.

Determine the dimensions shownfor the following materials:

A:Sut = 780 MPa, Syt = 590 MPa

B:Sut = 340 MPa, Syt = 240 MP.

C:Sut = 950 MPa, Syt = 810 MP

Use a design factor of N = 4




-




-

Preferred Size = 50 mm




-

50

.

Preferred size = 80 mm




-

802)

108 mm

Preferred Size = 120 mm




-

8.2 mm

Preferred size = 9 mm




D2 D3 D4 t

Pref. Size 50 mm 80 mm 120 mm 9 mm

Design Factors

• Column Tension = 4.6• Bearing on column = 7.2

.

• Shear of ring = 4.4


Reference: Safe Design for



ng neer ng u en s

http://www.safeworkaustralia.gov.au/NR/rdonlyres/DD7E1- - - -


39F13A8A50ED/0/SafeDesignEngineering.pdf




Due last Frida before Teachin Break










an you

MDP 1 Lecture 1 Design Methods Revised

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