Failure Analysis of Brittle and Ductile Materials:

Raising the Surface Energy

Failure Analysis of Brittle and Ductile Materials:

Raising the Surface Energy

2007 North Carolina State Science Fair______ Middle School

6th Grade Entry

by

_____Deleted for privacy purposes_____

Science Instructor: Ms. __________

February 13, 2007

Table of ContentsTable of Contents

• Background

• Motivation

• Problem

• Hypothesis

• Material Lists

• Experimental Procedures and Variables

• Results

• Observations and Data Analysis

• Conclusions

• Acknowledgements

BackgroundBackground

• Structure is a long molecular chain

• Actually a type of plastic although clear like glass

• Material is light but very durable

• Can be laminated to make “bullet resistant glass”

• Crystal structure of silica or quartz or “glass”

• Hard, but easily broken due to symmetry of crystal and microscopic defects

• Most common particle found in sand

BackgroundBackground

• Many ductile materials are metals that have an FCC crystal structure including Aluminum and Copper

• Brass is a substitutional alloy of copper and zinc

MotivationMotivation

Failure Analysis Can . . . .

• Improve human safety– Prevent plane crashes – Bullet resistant shielding

• Improve engineering design– Cars (safety features)– Trains– Sky Scrapers

• Help criminal investigations– Forced entry

• Improve environmental protection – Prevent oil tanker spills

Video deleted for privacy purposes

Figure containing sensitive (military) information not shown

Problem and HypothesisProblem and Hypothesis

• Problem: – How and which materials fail under the conditions of

impact force and/or tensile loading and how is energy transferred to these materials under these conditions?

• Hypothesis: – Under impact testing (window glass, tile, acrylic glass,

polycarbonate), all the brittle materials will shatter or break into fragments. The window glass will break into the most fragments.

– Under ductile testing (Aluminum, Brass, Copper) the

metal sheets will bend and the aluminum foil will probably tear completely. The most ductile metal will be the copper.

Impact Testing MaterialsImpact Testing Materials

• Brittle Targets:– Window glass– Acrylic glass– Bathroom tile– Polycarbonate

• Impact Forces:– Large chrome

doorknob – Brass Caster

• Support Materials:– Large cardboard box– Large wooden box– Large foam pillow

• Tape measurer or ruler• Glass cutting kit• Saftey goggles• Leather gloves• 5lb Postal scale• Ziplock plastic bags• Optional: Digital camera

Impact Testing ProcedureImpact Testing Procedure

1) Put on saftey goggles and leather gloves

2) Cut pieces of target material to be 11 X 11cm except for polycarbonate or acrylic glass, for these mark an area of the same dimensions on the material with a marker

3) Place target material on support material and setup testing area to prevent injury.

4) Weigh each impact force material with the postal scale

5) Drop impact force material onto the target from exactly 3 ft by using the tape measure

6) Optional: Before touching anything take a picture of broken pieces or damages from targets using the ruler or tape measure as a scale in the picture

7) Carefully count the number of pieces and record the data before storing them in the Ziplock bags.

8) Impact Energy Effects: Repeat procedure using the brass caster or another spherical-like object of different weight. Using the weight value to calculate the potential energy or impact energy.

9) Support Material Effects: Repeat procedure using the different support materials

Impact TestingImpact Testing

Tension Testing MaterialsTension Testing Materials

• Tensile Specimen– Aluminum foil – Copper flashing– Brass sheet

• Scissors• Two C-clamps• 1 gallon jug• 10lb postal scale• Safety goggles and leather gloves• Level or large ruler• Caliper

Tension Testing ProcedureTension Testing Procedure

1) Cut out ~0.1 mm thick, 16X6 inch metal strips from the tension specimen using scissors. Measure thickness with Caliper. Five sheets of standard Al foil pressed together should equal a 0.1mm thickness.

2) Find two flat parallel bars suspended in air or line up two table overhangs of equal height separated by a known distance. Use these surfaces to firmly clamp down the metal strips on both ends with the length of the strip suspended in air between the two clamps

3) Mark the center of the metal strip (half the length) with a line at one of the edges to indicate the measuring point.

4) Weigh the jug on the postal scale

5) Measure the height of the metal strip with the level/ruler from the measuring point to the floor.

6) Place the empty jug in the center of the metal strip and measure the height again at the measuring point.

7) Effect of Loading: Take off the jug and repeat steps 4), 5), and 6) but while increasing the weight of jug by filling with various levels of water (make sure to close the jug tightly).

8) Calculations: Use the change in height plus some geometry to find the change in length of the tension specimen. The length during the load minus the length after load is the change in the elastic deformation length. The length after load minus the length before the load is the change in the plastic deformation length.

Tension TestingTension Testing

Impact Testing Results Impact Testing Results

Effect of Impact Energy for Impact Testing on a Cardboard Surface

0

10

20

30

40

50

60

tile window glass acrylic glass polycarbonate

# o

f F

rag

men

ts o

r C

rack

s

chrome (1.25 kg, Impact E = 11.2 J)

brass (0.30 kg,Impact E = 2.7 J)

The Effect of the Support Material on Impact Testing

0

10

20

30

40

50

60

tile window glass acrylic glass polycarbonate

# o

f c

rac

ks

an

d f

rag

me

nts

Cardboard

Wood

Foam

CracksFragments CracksFragments

•

Impact Testing Observations / Data Analysis

Impact Testing Observations / Data Analysis

• More Brittle = More Fragments

• Window glass is very brittle

• Both Impact Energies not enough to break

• Acrylic glass or polycarbonate

• Polycarbonate so ductile it doesn’t crack!!

• Foam support adsorbs a lot of impact energy (Foam support actually broke) so there is less energy to directly break the target, however the time of impact is longer.

• Wood adsorbed the least impact energy so the time of impact was shorter. Impact of tile on wood support caused many small pieces in specific area because of nail underneath, caused error in data

• Cardboard adsorbs a little less energy than foam and allows for an impact time longer than that for wood. This caused a larger # of fragments for the window glass

Forms of Energy during Impact Testing

Forms of Energy during Impact Testing

Forms of Energy during Impact Testing of Very Brittle Materials (Window glass and Tile)

0

2

4

6

8

10

12

14

Potential Energy Kinetic Energy Adsorbed StrainEnergy

New Surface Energy

Arb

itra

ry U

nit

s o

f E

ne

rgy

Before drop

During drop

Just before contact

After contact

Forms of Energy during Impact Testing on Non-Brittle Materials

0

2

4

6

8

10

12

14

Potential Energy Kinetic Energy Adsorbed StrainEnergy

New Surface Energy

Arb

itra

ry U

nit

s o

f E

ne

rgy

Before drop

During drop

Just before contact

After contact

Forms of Energy during Impact Testing of Somewhat Brittle Materials (Acrylic Glass)

0

2

4

6

8

10

12

14

Potential Energy Kinetic Energy Adsorbed StrainEnergy

New Surface Energy

Arb

itra

ry U

nit

s o

f E

ner

gy

Before drop

During drop

Just before contact

After contact

• Before dropping, impact force there is a certain potential energy.

• During drop, potential energy changes into kinetic energy

• After impact, energy is either adsorbed as strain energy or released as new surface energy

• More surface energy = more surface area = more pieces

Tension Test ResultsTension Test ResultsElastic Deformation by Tensile Load Testing of Thin Metal Sheets

0

0.2

0.4

0.6

0.8

1

1.2

0 5 10 15 20 25 30 35 40

Load Weight or Force (N)

To

tal

Ela

sti

c D

efo

rma

tio

n L

en

gth

(m

m))

Brass

Aluminum

Cardboard backed Copper

Plastic Deformation by Tensile Load Testing of Thin Metal Sheets

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

0 5 10 15 20 25 30 35 40

Load Weight or Force (N)

To

tal

Pla

sti

c D

efo

rma

tio

n L

en

gth

(m

m)

Brass

Aluminum

Cardboard backed Copper

Total Deformation by Tensile Load Testing of Thin Metal Sheets

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

0 5 10 15 20 25 30 35 40

Load Weight or Force (N)

To

tal

De

form

ati

on

Le

ng

th (

mm

)

Brass

Aluminum

Cardboard backed Copper

Stress Strain Behaviour of Thin Metal Sheets

y = 0.1848x + 1E-04

R2 = 0.9731

y = 0.3779x + 0.0002

R2 = 0.9718

y = 0.5126x + 0.0001

R2 = 0.9793

0

0.0005

0.001

0.0015

0.002

0.0025

0.003

0 0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016

Strain (unitless or m/m)

Str

es

s (

MP

a)

Brass

Aluminum

Copper

Linear (Aluminum)

Linear (Brass)

Linear (Copper)

Tension Testing Observations / Data Analysis

Tension Testing Observations / Data Analysis

• Copper had cardboard backing which may have introduced some errors in our results, esp. for the elastic deformation b/c the cardboard seemed to make it more elastic

• General trend – Aluminum is the most ductile, then Brass, then Copper

– consistent with published results

Table 1: Comparison of Elastic Moduli for Selected Thin Metal Sheets with Published Values found for Thicker Metal Specimens

Thin metal sheet (thickness ~ 0.1 mm)

Elastic or Young’s Modulus Experimental (MPa)

Elastic or Young’s Modulus Published Value (GPa)

Aluminum 0.185 69 Brass 0.380 97 Copper 0.513 110

Conclusions Conclusions

• Impact Testing Conclusions:– More surface energy = more surface area = more fragments.

– Window glass and tile are the most brittle since they adsorb less impact energy but instead release surface energy so more fragments are created under impact forces.

– Polycarbonate is the least brittle (actually ductile) as it adsorbed more impact energy without releasing surface energy so it didn’t even have cracks.

• Tensile Testing Conclusions:– Copper was not the most ductile but was actually the most stiff as it had

highest elastic modulus, so my hypothesis was wrong.

– Alloying copper and zinc (brass) allows it to become more ductile than either copper or zinc.

– Aluminum is most ductile since it had the lowest elastic modulus and did not tear under the applied load.

– Energy from tensile load is adsorbed by ductile materials and stretches elastically or plastically instead of rapidly breaking it into pieces.

AcknowledgmentsAcknowledgments

• I want to thank . . . .

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