Stress Concentration Or Would that be Concentration Stress?
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Transcript of Stress Concentration Or Would that be Concentration Stress?
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Stress Concentration
Or Would that be Concentration Stress?
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Parallel Reading
Chapter 12.2
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A Look at the Big PictureStatics
Shows how stress on systemIs distributed onto the
components
Mechanics of Materials
Understanding howStress spreads
through a component
Mohr’s CircleChecking for Critical Stress Values on
Potential Failure Planes
I want a TV like thatFor my room.
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General Stress Distributions
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Shape Changes Can Become Points of Stress Concentration
Axial stress spreads evenlyAcross a Plate. But what happens if there is a hole in
The Plate?
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Stress Diverts AroundAnd None too Evenly at That
σnew = σold * K
Where K is a stressConcentration factor
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How Bad Is It?
Diameter / w
Small holes that make sharp turns can reach K = 3 That’s really bad.
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Hypothesis – Sharp Corners are Bad
We wouldn’t want to break something inA high priority application.
Smoother transitionsAllow the stress toSpread out moreEvenly.
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Looking at the Stress Concentration Diagram
One factor is how drasticThe drop in size is!
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The Other Factor is the Radius of the Fillet
As can be seen a largerRadius on the fillet givesThe stress a chance toReally smooth out.
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Illustrating the Importance of Fillets
I’m convinced already!0.4
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We Compute Our Key Measures to Read the Chart
60mm 40m
01.040
4.0
mm
mm
d
r
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Holly Cow!
K is about 5
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So How is that Significant?
60mm 40m
Because of stress concentration we areGoing to have to keep the average a lotLower to avoid triggering failure at theConcentration point.
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Adjusting for Concentration
MPaMPa
335
165
Now calculate the allowable load
0.04*0.01
= 13.2KN
Stress Concentration not good.
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Lets See if a Good Fillet Will Make Things Better
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Calculate the Magnitude of Our Stress Concentration
It’s still stress but it couldHave been a lot worse.
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Picking Off an Answer
Adjust our allowable average stress
This is a dramatic increase from 13.2 KNWith a sharp turn and small fillet.
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Do Only Normal Stresses Concentrate?
Shear stress increasesLinearly to the outsideEdge of a torsionElement. What happens if we
Change the diameter ofA rod in torsion
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We Jack Up the Forces
NormallyOur highestShear is atThe outerFibers of theshaft
With stress concentrationThis becomes
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Concentration is a Function of the Size Change and the Size of the Fillet
Which Fillet is better?
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What About Bending Forces
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Now What if We Change the Beam Size