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Chapter 1: Introduction
BAE
417-Design of Machine Systems
Fall
2005
![](3D"master93_image002.gif")
Design
nA
design must be:
nFunctional-
fill a need or customer expectation
nSafe-
not hazardous to users or bystanders
nReliable- conditional probability that product will
perform its intended function
without failure to a certain age.
nCompetitive-
contender in the market
nUsable-
accommodates human size and strength
nManufacturable- minimal number of parts and suitab=
le for
production
<=
/div>
nMarketable-
product can be sold and serviced
n“To design is either to formulate a plan for the =
satisfaction
of a specified need or to solve a problem.”
Design Process Actions
<=
span
class=3DBB style=3D'position:absolute;left:-4.43%;top:.39em'>nConce=
ive
alternative solutions
nAnaly=
ze,
test, simulate, or predict performance of alternatives
<=
span
class=3DBB style=3D'position:absolute;left:-4.43%;top:.39em'>nChoos=
e the
“best” solution
<=
span
class=3DBB style=3D'position:absolute;left:-4.43%;top:.39em'>nImple=
ment
design
Design is…
<=
span
class=3DBB style=3D'position:absolute;left:-4.43%;top:.39em'>nAn in=
novative
and iterative process
<=
span
class=3DBB style=3D'position:absolute;left:-4.43%;top:.39em'>nA
communication intensive activity
<=
span
class=3DBB style=3D'position:absolute;left:-4.43%;top:.39em'>nSubje=
ct to
constraints
Steps to Design
![](3D"slide0006_image003.jpg")
Design Considerations
=
1.Strength
=
=
2.Stiffness
=
;
=
3.Wear
=
4.Corrosion
=
;
=
5.Safety
=
6.Reliability&#=
13;
=
7.Friction
=
=
8.Usability
=
;
=
9.Utility
<=
/span>
=
10.Cost
=
11.Processing&#=
13;
=
12.Weight
<=
/span>
=
13.Life<=
/span>
<=
span
style=3D'font-size:71%'>14.Noise
<=
span
style=3D'font-size:71%'>15.Styling
=
<=
span
style=3D'font-size:71%'>16.Shape
<=
span
style=3D'font-size:71%'>17.Size
<=
span
style=3D'font-size:71%'>18.Control
=
<=
span
style=3D'font-size:71%'>19.Thermal
Properties
<=
span
style=3D'font-size:71%'>20.Surface
=
<=
span
style=3D'font-size:71%'>21.Lubrication&=
#13;
<=
span
style=3D'font-size:71%'>22.Marketabilit=
y
<=
span
style=3D'font-size:71%'>23.Maintenance&=
#13;
<=
span
style=3D'font-size:71%'>24.Volume
<=
/span>
<=
span
style=3D'font-size:71%'>25.Liability=
3;
<=
span
style=3D'font-size:71%'>26.Recovery
=
;
Codes and Standards
nCode- a set of
specifications for the analysis, design, manufacture, and
construction of something
nStandard- a set =
of
specifications for parts, materials, or processes intended to
achieve uniformity, efficiency, and a specified quality
Organizations
nAluminum Association (AA)
nAmerican Gear Manufacturers Association (AGMA)
nAmerican Institute of Steel =
Construction (AISC)
nAmerican Iron and Steel Institute =
(AISI)
nAmerican National Standards =
Institute (ANSI)
nAmerican Society for Metals (ASM)
nAmerican Society of Mechanical =
Engineers (ASME)
nAmerican Society of Testing =
Materials (ASTM)
nAmerican Welding Society (AWS)
nAmerican Bearing Manufacturers Association (ABMA)
nBritish Standards Institute (BSI)
nIndustrial Fasteners Institute (IFI)
nInstitution of Mechanical Engineers (I. Mech. E.)
nInternational Bureau of Weights and Measures (BIPM)
nInternational Standards Organization (ISO)
nNational Institute for Standards and Technology (NIST)
nSociety of Automotive Engineers (SAE)
nAmerican Society of Agricultural =
and Biological Engineers (ASABE)
=
n
Economics
nCost plays an important role in design decision process
nNo matter how great the idea may be, if it’=
s not profitable it may never be seen
nThe use of standard sizes and large manufacturing =
tolerances reduce costs
nEvaluating design alternatives with regard to cost=
nBreakeven Points
nCost Estimates
Product Liability
n“Strict
liability” concept prevails in the U.S.
nManufacturers are liable for any damage or harm =
that
results from a defect.
Uncertainty
<=
span
class=3DHBB style=3D'position:absolute;left:-4.34%;top:.39em'>nRoman
Method- repeat designs that are proven
=
nFactor
of Safety Method of Philon- separate the loss-of-=
function
load and the impressed load using a ratio
![](3D"slide0012_image005.gif")
Uncertainty
nDesign Factor Me=
thod-
factor of safety is increased with rounding error to achieve
nominal size (5.3 mm designed bolt size is increased to =
6.0
mm)
nStochastic Design Factor Method- uncertainty in stress =
and
strength is quantified for linearly proportional loads
![](3D"slide0013_image007.gif")
Measures of Strength
<=
span
class=3DHBB style=3D'position:absolute;left:-9.7%;top:.39em'>nS =
211;
Strength
<=
span
class=3DHBB style=3D'position:absolute;left:-9.7%;top:.39em'>nSs =
–
Shear Strength
<=
span
class=3DHBB style=3D'position:absolute;left:-9.7%;top:.39em'>nSy =
–
Yield Strength
<=
span
style=3D'text-shadow:none'>nSu =
–
Ultimate Strength
<=
span
class=3DHBB style=3D'position:absolute;left:-9.7%;top:.39em'>n - Mean Strength=
![](3D"slide0014_image009.gif")
Measures of Stress
<=
span
style=3D'font-family:Symbol'>nt R=
11;
Shear Stress
<=
span
style=3D'font-family:Symbol'>ns R=
11; Normal Stress
<=
span
style=3D'font-family:Symbol'>ns1 – <=
/span>Principal
Stress
<=
span
style=3D'font-family:Symbol'>nsy<=
/span> =
–
Stress in y-direction
<=
span
style=3D'font-family:Symbol'>nsr<=
/span> =
–
Radial Stress
<=
span
style=3D'font-family:Symbol'>nst<=
/span> =
–
Tangential Stress
Stress
Allowable
(AISC)
(AISC)
<=
span
class=3DBB style=3D'position:absolute;left:-4.43%;top:.39em'>nTensi=
on: 0.45 Sy ≤ sall ≤ 0.60 Sy&=
#13;
<=
span
class=3DBB style=3D'position:absolute;left:-4.43%;top:.39em'>nShear=
: tall =3D 0.40 Sy
<=
span
class=3DBB style=3D'position:absolute;left:-4.43%;top:.39em'>nBendi=
ng: 0.60 Sy ≤ sall ≤ 0.75 Sy&=
#13;
<=
span
class=3DBB style=3D'position:absolute;left:-4.43%;top:.39em'>nBeari=
ng: sall =3D 0.90 Sy
Loads Used to Obtain Stresses
nWhere:
Wd<=
/span>-
dead loads
Wl<=
/span>-
live loads
k- service
factor
Fw<=
/span>-
wind load
Fmi=
sc-
locality effects (earthquakes)
![](3D"slide0017_image011.gif")
Service Factors
=
nApplications
Elevators
Traveling Crane Supports=
3;
Light Machinery Supports=
3;
Reciprocating Machinery =
Supports
=
Floor and Balcony =
nk
=
n2
=
n1.25
=
n1.20
=
n1.50
=
n
=
n1.33
=
n
Factor of Safety
nDesign factors (nd<=
/span>)
are defined as:
<=
/div>
n&=
#13;
=
n
=
n and
n
n
=
nwhere
n ns<=
/span>-accounts
for uncertainty of strength
n nd<=
/span>-accounts
for uncertainty of loads
![](3D"slide0019_image013.gif")
![](3D"slide0019_image015.gif")
Realized Factor of Safety
![](3D"slide0020_image017.gif")
![](3D"slide0020_image019.gif")
Reliability
n Probability that a mechanical elem=
ent
will not fail in use
n0 ≤ R ≤ 1
nReliability approac=
h to
design: judicious selection of material, processes, and geometry =
to =
achieve
reliability goal
nFactor of Safety
Method- time proven, widely accepted
nReliability Approach- new, requires data
Homework Assignment
nDo problems1-6, =
1-9,
and 1-14 for next Tuesday.
' + ENDSHOW_MESG + '
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