DESIGN PHASE
What kind of analysis you
need to do?
MIME Senior Design Projects - Spring 2013
Overview
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Design/Analysis Requirements
Common Design Issues
 Welds
 Fatigue
 Safety
 Quality
Design Requirements

What type of analyses do I need?
Technical Analysis
Description
Examples
1
Static Analysis
Calculate forces and moments for stationary
Lifts, supports, structures, connections.
components.
2
Dynamic Analysis
Calculate s, v, a of moving components and All moving components such as gears,
the forces and torques needed.
mechanisms, pulleys,
3
Power Analysis
Calculate the power needed to run the
machine.
Use the force and dynamic
4
Stress Analysis inclg FEA
Calculate stresses and compare with
strengths to see if failure would occur.
Components under high forces, moments or
torques such as support members.
5
Thermal Analysis
Calculate temperature, temp changes,
pressures, and possibly heat transfer.
Components including fluids where heat and
temperature are involved.
6
Fluid Flow Analysis
Calculate flow rate, speed, quantity,
pressure, and possibly temperature.
Determine pump sizes, pipe diameters, flow
measurement when you have fluids.
7
Process Analysis
8
Vibration Analysis
9
Cost Analysis
Improve business activities in order to
reduce overall costs, provide more efficient Lean manufacturing, six sigma and total quality
use of resources, and to better support and management.
add value for customers.
Determine vibration frequency, and if
vibration will be a problem.
Anything moving with a certain frequency. Also
some electrical components.
Determine the costs in the short run and
long run, as well as ROI.
Determine if it is more cost effective to produce
or to outsource a component.
Design Requirements

Measure twice, cut once
 Make
sure you do adequate calculations and analysis
 Tendency to build first, design later
 Works
if you’re right the first time
 Costs material, effort, and time if you’re wrong


Anticipate use
Anticipate misuse!
Design/Analysis

FREE BODY DIAGRAM

FEA

Approximate Design/Calculations
 Is
it a beam or a plate?
Design/Analysis - FEA


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Quality of input determines quality of output
“Magic” Black Box
Factors
 Solid
model quality
 Correct boundary conditions
 Load accuracy
 Proper material selection
 Mesh quality
 Correct Failure Criteria
Design/Analysis - FEA

Solid Model Quality
 Balance
simplicity/accuracy
 Use
your intuition to include features that will increase
stresses
 Exclude trivial features

Correct Boundary Conditions
 Make
sure your restraints accurately represent real
conditions
 Check
degrees of freedom
 Check fastener/mating conditions in assemblies
Design/Analysis - FEA

Load Accuracy
 What
type of loading? point load? distributed load?
 Am I missing loads? thermal? centripedal?
 What is the magnitude? 10lbs? 500lbs? 1,000,000lbs?
 Rationalize
with intuition
 Determine with testing

Material Selection
 Did
I select the correct material?
 Are my properties in the correct units?
FEA – What to expect?
http://machinedesign.com/article/fe-update-expecting-too-much-from-fea-0710
Design/Analysis - FEA

Mesh Quality
 Make
sure it is fine enough to
accurately depict features
 Affects processing time
Design/Analysis - FEA

Correct Failure Criteria
 Stress
based: yielding or fracture?
 Excessive displacement
 Loss of function
 Corrosion
 Thermal degradation
 Fatigue
Remember that ductile and brittle materials
fail differently and have different failure
criteria!
Design/Analysis

When in doubt, do some hand calculations
 Mathcad
and Matlab are very useful
 Shigley is very useful
 DANotes is a good resource as well:
 http://www.mech.uwa.edu.au/DANotes/
 Your
basic calculations and FEA should support each
other
 If
they don’t, you should know why
Welds

Strength of welds
 Location-
sharp corners?
 Loading- stress state of weld?
 Size
 Quality of weld!
 Fatigue
Fatigue
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Are their cyclic loads?
Do fatigue analysis
S/n approach used in Shigley
Safety
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Pinch points?
Sanitation?
Exposed wiring?
Warnings?
Quality

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Deliverables should function well
Make sure products are durable
Double-check safety
References

References:
 What
Kind of Analysis do you Need for your Project?,
Dr. Kramer, MIME Dept.
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Photo Credits:
http://www.msha.gov/Accident_Prevention/Tips/im
ages/HandTools-Jacks.jpg
http://machinedesign.com/article/fe-updateexpecting-too-much-from-fea-0710