Failure Analysis of a Pan HandleGroup 10

Meet BhatiPrateek DeshmukhAman TakshakAmruth raj

Introduction• Plastic handle used for holding a frying pan

Tests PerformedBurn Test Hardness test Density TestThermoset 29.4 HRA

1209 Kg/m3

What’s the Material ?• Burn test proves that our material is Thermoset• Most Common type of thermoset are• Polyurethane• Bakelite• Polyester Resins• polyamides

• Polyurethane or Bakelite ?

It’s not Polyurethane because..

• Density of Solid Polyurethane is about 1200 Kg/ but this is not used for thermal application• Type of polyurethane that is used for

thermal application are polyurethane foam whose density lies between 10-100 Kg/• Hardness value of polyurethane is also

lower than Bakelite• These are used at low temperature below

1200C

So its Bakelite but how?• Thermoset by burn test• Hardness test shows 29.4 HRA• Density test shows density of material is 1209 Kg/m3

• Also confirmed it from Manufacture Catalogue

Properties of BakeliteProperties Values Units

Density 1240-1320 Kg/m3

Yield Strength 27.6-49.7 MpaCompressive Strength 30.4-54.6 MpaElongation 1.5-2 %Hardness Rockwell A 23-37Fracture Toughness 0.787-1.21 Mpa.m1/2

Thermal Conductivity 0.14-0.15 W/m.KMaximum service Temperature

200-230 0C

Thermal Conductor or Insulator

Good Insulator

Why Bakelite is Used For Handles?• Bakelite is a good insulator of heat and of electricity,

so the handles do not get hot to touch.• Bakelite is a plastic (thermosetting, which is why it

doesn't melt), so it can be mounded to any desired shape.• Bakelite can handle high temperatures• Bakelite chars with excessive temperature and

releases a very characteristic smell, so it gives some warning of danger of fire.

Manufacturing Process

Failure Analysis

Vague Chevron Markings

Radial Markings

• Rectangular cross section

• Stress concentration

Area

Failure Modes

Ground

OR

Solidworks

SOLIDWORKS ANALYSIS

case 1 case 2

So what’s happening on impact?• When a handle is hit impact energy is transferred to plastic

matrix.• If the energy is below peak force then plastics absorbs energy

by forming crazes• These craze structure represents micro voids and fine cracks• If the impact energy exceeds, then these crazes cannot absorb

more energy and fast crack occurs• In our case the material fell from the height of about 2.5 m• So the potential energy that material bears when hitting the

ground is 19.135 N-m which is suffiently large to break the material

CalculationEdge Vs• Failure at edge caused due

Semicircular flaw

• K = 2.48 > 0.707(Kc)

Bolt hole Crack From round hole

K = 12.99 > 0.707 (Kc)

Elliptical corner Crack

K = 8.63 > 0.707 (Kc)

So finally …• Crack initiation may occur from any of the two parts

edge and the hole• Its unclear which might be dominant among two • Both are playing pivotal role in fracture• But after seeing calculation and observing the stress

intensity at hole ,it was appearing to be greater even after application of same load• So we conclude that bolt might be dominating factor

Impact Tests• These test shows how much energy is needed to break

the material• So improvements can be made to increase its strength Charpy Izod Falling dart

Improvements for handle• To reduce stress concentration round handles can be

used • Introducing impact modifier• Reducing internal defects and contaminants which

acts as stress reducers• Modifying molecular structure

Future work•Microscopic Analysis•Look for clear crazing markings•Look for clear understanding of crack initiation

•Check for other modes that might cause failure such as environmental effects.•More Detailed Calculation for Kic

References• http://www.impact-solutions.co.uk/impact-failure-in-pla

stics/• https://

books.google.com/books?id=RJWiilJLdxYC&pg=PA24&lpg=PA24&dq=how+to+analyze+a+failure+in+bakelite&source=bl&ots=L2O0kPCxjR&sig=b8twTT5XnJuKIUvWkLrkQrSwWr4&hl=en&sa=X&ved=0ahUKEwih3amQha_JAhWK2SYKHXUlBcEQ6AEIIjAB#v=onepage&q=how%20to%20analyze%20a%20failure%20in%20bakelite&f=false• http://

www.plascocorp.com/plasco/html/tech_topics/materials_archive/hardness.mat_archive.html• http://www.carbidedepot.com/formulas-hardness.htm• http://

polyurethane.americanchemistry.com/Introduction-to-Polyurethanes/Applications