Fatigue Design Notes

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MecE 360: Engineering Design II

Section 3: Materials


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Class Notifications

Jason Carey will be providing information about graduateopportunities

B and A group meeting sign-up outside of 10-227

Quiz 1: early Feb

I posted: old A3 and soln online Class notes purchased through MECE club for $20

Many extra examples, detailed notes

Teams are notified of projects

Relaxed design specifications as long as explained

5 pages of writing: figure out story, and write

Keys success : bearing, connections, fatigue, creativity


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Objectives

Initial considerations Materials, loading, failure

Presentation on designing materials


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Material Considerations (p.3-2)

1. Availability and cost

It is very possible that the perfect material existsfor you design - but at what cost.

Titanium: high specific strength (strength/density).But costs $8.20/ kg vs. $1.50/kg for Al.

2. Strength

Critical for stress related failure (Section 5).

n

TCy

applied

,,

Produced with a Trial Version of PDF Annotator - www.PDFAnnotator.com


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3. Rigidity/stiffness

Designs are often limited by the amount of deflectionbetween mating components for alignment and propermating.

Deflection is dependent on elastic modulus (E) andgeometry.

4. Hardness and ductility

Is scratch resistance or large deformation important? Contact problems: wear

Material ConsiderationsProduced with a Trial Version of PDF Annotator - www.PDFAnnotator.com


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5. Resistance to fatigue

Steel and aluminium have different fatigue behaviour.

6. Manufacturability and machinability

How easy is it to build?

3D printing: only certain materials



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7. Resilience

The energy before yielding is important for combinedloading, temperature effects.

8. Friction coefficient Different applications require different surfaces or

mediums for proper functions, e.g. bearings low, andclutches high

9. Weight

Some designs are weight critical: consider polymers,wood, foams, aluminium or titanium.



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Uncertainty (p.3-3)

Uncertainty and variability in material properties areinherent due to microstructure variability

Assessed through experimental testing.

0

20

40

60

80

100

120

140

40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61

Sy (kpsi)

Numberoftes



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Engineering Materials

Metals: Magnesium

Ceramic: alumina

Polymer: electrospun polyethylene oxide-Garcia and Hernandez 2014

Carbon-reinforced-composite



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Metals (p.3-6)Produced with a Trial Version of PDF Annotator - www.PDFAnnotator.com


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Polymers (p.3-7)

Different behaviour based on microstructure/chain linking



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Polymers

Properties change

significantly withincreasing temperature

Modulus drops

Should not used above

glass transitiontemperature



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Composite Materials (p.3-9)

In general, composites consistof two or more materials

Fiber-reinforced polymers (FRP)

long fibers in resin matrix

fibers strength, brittle

resin toughness,rigidity, protection offibers

Lamina is transverse isotropic material

Properties proportional to fiber volume fraction



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Composite Materials

Several laminae combined form a laminate

Laminates can be quasi-isotropic

Laminate layup canbe tailored to meetspecific strength andstiffness requirements



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Ceramics (p.3-8)

Only for compressiveloading

Poor in tension,cracks propagate

catastrophically Reinforced with steel,

or fibre reinforcedpolymers

Good thermal andelectrical insulators

More later



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Comparison (p.3-10)

Material Advantages Disadvantages

SteelStrength, stiffness, ductility, strength and corrosionresistance adjustable with alloying elements

Heavy

Aluminum Lightweight, high ductility, corrosion resistant Low strength and stiffness

Brass Corrosion resistant, good wear properties Heavy, cost

TitaniumGood strength over wide temperature range,corrosion resistant, lightweight

Poor machinability, cost

Polymers

Lightweight, corrosion resistant, easy to form andmanufacture, versatile, impact resistance, shockand vibration absorbance, low friction and wear,recyclable (thermoplastics)

Low strength and stiffness, smalltemperature changes causelarge change in properties, poorrecyclability (thermosets)

FRPComposites

Lightweight, high specific strength and stiffness,corrosion resistant, flexible design and versatility

Brittle, expensive, poorlycharacterized (codes/standards),quality strongly affected by

manufacturing, poor recyclability



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Material Selection (p.3-16)

1. Decision matrix

Simple, basic design

Need specifications/requirements

Select material that best meets the specs

See previous sections for example2. Ashby charts

Advanced methodology

Allows for optimization

Need information on function, objective, constraints

examples will be presented in Seminar #3 Ive never seen this in a 460 report, attempt to incorporate here



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Material Selection:Ashby Charts

Used with permission:Materials Selection in Mechanical Design, 2nd Edition, M.F. Ashby, Elsevier, 2011.



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Three basic elements are required for the selection charts:

Materials Selection in Mechanical Design, 2nd Edition, M.F. Ashby, Elsevier, 2011.

P d d ith T i l V i f PDF A t t PDFA t t


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Performance (p) of a component based on the requirements of the design

Designs will have three requirements:

1. functional

2. geometric3. materials property

These are associated to a function (equation)(which are assumed be independent of each other)

MGFfp ,

properties

Material,

parameters

Geometric,

tsrequiremen

Functional,,

MfGfFfp321



P d d ith T i l V i f PDF A t t PDFA t t


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Comments

Example: All the materialslying on a line of constantE1/2/rperform equally wellas a light stiff beam.

Those above the line are

better, those below, worse. A material withM= 8 in

these units gives a beamwhich has one quarter theweight of one withM= 2.

Example in seminar

Materials Selection in Mechanical Design, 2nd Edition, M.F. Ashby, Elsevier, 2011.



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38

Designing Next Generation

Protection Materials

Jamie HoganAssistant ProfessorMechanical EngineeringUniversity of Alberta


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Take Away

Exposure to brittle materials

Failure depends on microstructure, stress-state and strain-rate

Talk about how to design microstructures to control failure

Example: fragmentation for body armor applications

50 um

PADB4C-Microstructure300 um

PADB4C- Fragments


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Materials in Defense Applications

bankspower.com

www.galls.com

Big question: Why is one system better than the other?

1. Requires fundamental understanding of material failure (experiments and models)

2. Manufacturing processes to produce tailored microstructures (processing)
http://bankspower.com/fridaynightnews/show/94-Hot-Rod-Humveehttp://www.galls.com/http://www.galls.com/http://bankspower.com/fridaynightnews/show/94-Hot-Rod-Humvee


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Approaches to Materials Design

Microstructures and material properties (K1c, , E, ) + identification of failure mechanisms

Material Science: alter microstructure property performance (test, test, test)

Mechanics: microstructure/properties mechanisms (models) performance

Philosophy: see it (experiments), understand it (models), control it (processing)

Twinning in Mg (Dixit)

10 um

Boron Carbide Microstructure


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Failure Mechanisms in Brittle Materials

Failure: Defects nucleate mechanisms, which lead to macro-cracks, and often to catastrophic failure

Defects: grain boundaries, secondary phases, initial cracks (we want to identify key defects)

Objective: Control failure mechanisms by designing the defect populations (microstructure design)


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Impact Failure of Brittle Materials

Failure Processes (time and space):

1. Fracture

2. Granular flow

3. Plasticity

4. Phase transformations (amorphization)

Manifest in fragmentation

Hypothesis: controlling fragmentation willlead to improved performance

Material: boron carbide

Fig. Impact into PAD B4C at 930 m/s

500 microns

Fig. Ballistic fragments for PAD B4C at 930 m/s


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1. See it:

Microstructure Characterizationand Experimentation


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Boron Carbide Material Composition: B4C (or B12C3): rhombohedral (bucky balls)

High hardness (Mohs 9.5) and low density (2.5 g/cm3)

Silicon carbide (SiC): 3.2 g/cm3

Manufacturing: grow boron crystal, ball milled, hot-presswith carbon and aluminum nitride additives

Yields defects (serve as fracture sites).

Not all defects are bad

10 um

PADB4C- Microstructure


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Boron Carbide Defect Microstructure*

Globules (ellipsoids): graphitic disks Spherical features: graphite/pores

Bright phases: aluminum nitride

Q: What processing defects initiate failure?

Hogan et al. JACS 2014

Hot Pressing Direction


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Strength and Failure


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Dynamic Compressive Failure

2.5 mm2 Mfps, exposure= 500 ns

2.5 mm5 Mfps, exposure= 110 ns

Unconfined Configuration Bi-Axial Confined Configuration

Strain rates: ~10-3 (MTS) and ~10+3 s-1 (Kolsky bar) and Stress-states: compression, confined, tension (BD)

Crack speeds set deformation time scales: 2,000 +/- 300 m/s (left) vs. 510 +/- 130 m/s (right)

Deformation mode changes with confinement: need to understand this

Hogan et al. JACS 2014


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Strength: Confinement Effects

Confined Configuration

Unconfined Configuration

HotPressingAxis

HotPressingAxis

We can use strength measurements to guide us on package design

Hogan et al. Acta 2015


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Rate-Dependent Strength

Kimberley et al. 2013 scaling relation forstrength as a function of strain rate*

Dynamic strength of brittle materialsis controlled by fracture

Governed by microstructure featuresandproperties

This example: can control strength bycontrolling fracture through design ofdefect populations


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Fractography: Failure Mechanisms


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2. Understand it:

Compressive BrittleFragmentation Model


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2. Understand It: Theoretical andComputational Modeling

Brittle Failure Model Crack Growth

Anisotropic Damage

Initial Damage

Flaw Size distribution

Flaw Orientation distribution

Flaw Density

Damage Evolution

Crack growth Kinetics

Micromechanics

Self-ConsistantScheme

IrreversibleDamage Strain

StiffnessDefinition

Evolution as afunction of Damage

Influence of BulkingFlow Behavior

Granular Flow

EOS

Visco-Plastic Flow

Porosity

Crack Coalescence

Crack Nucleation

Inputs From Experiments

Figure 9. Inclusion number/area fraction vs.inclusion size distribution.

Figure 11. Orientation of inclusions in relation tothe hot pressing axis (AR is the aspect ratio).

Flaw Density (#/m2)

and Spacing

Incorporate the physics in the model: properties and microstructure

Fig. Mind-map for brittle failure


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2. Strength and FragmentationMicro-Mechanical Models

0

0.5

1

1.5

2

2.5

0

0.5

1

1.5

2

2.5

3

0 0.002 0.004 0.006 0.008

Tr(Damage)

Stress(GPa)

Strain

Flaw Size Dependence

6 m

10 m

20 m

40 m

1000 s-1

We can use simple models to inform about materials design

10-4

10-3

10-2

10-1

100

101

102

10-2

10-1

100

101

102

103

Normalized Strain Rate

N

ormalizedSize

Grady 2006

Glenn and Chudnovsky 1986

Zhou et al. 2006

Levy and Molinari 2010

Mod. Grady (vcc)

Spinel

PAD SiC-N

PAD B4C

BasaltStony meteorite


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3. Control it:Materials Design


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Ballistic Performance Curve

Highlights power of simple model to inform design decisions

Remember: consider physics of problems (whats importantand what isnt)

Normalized Velocity

0.7 0.75 0.8 0.85 0.9 0.95 1 1.05

Pr

obability

of

Penetration

0

0.2

0.4

0.6

0.8

1PS B4C

HP B4C

Hot-pressed (PAD-B4C)

Pressureless sintered (PS)

We designed microstructures for controlled strength andfragmentation outcomes


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5. Summary


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Take Away

Exposure to brittle materials

Failure depends on microstructure, stress-state and strain-rate

Talk about how to design microstructures to control failure

Example: fragmentation for body armor applications

Fig. Impact into PAD B4C at 1000 m/sCompressive failure of boron carbide

Length: 5 mm


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Acknowledgements

Support of the Materials in Extreme Dynamic EnvironmentsCollaborative Research Alliance through Cooperative AgreementNumber W911NF-12-2-0022.

Support from ARL (ITOL 2015-2443) NSERC Engage

CFI for ultra-high-speed camera

Lukasz Farbaniec, Debjoy Mallick, Matt Shaeffer, NitinDaphalapurkar, Ravi Sastri, Jim McCauley, KT Ramesh

Undergraduate support: Will Wagers, Erez Krimsky

James Hogan email:[email protected]
mailto:[email protected]:[email protected]


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Bonus Work for ME 360

Assigned as 5%+ on quiz #1

Develop 1 ppt slide:

Choose an industrial application that interests you

Select a material within that application

Show its microstructure, material properties

Address why it is used in this application

Be creative

Due before Quiz 1- assignment box will be created


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Next Topic

Unit # 2: Initial Considerations

Section 4: Loading and deflections

Static Cyclic

Impact

Beam deflection Section 5: Failure criteria

Fatigue Design Notes

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