Effect of Resin/Hardener Ratio On The Dynamic Fracture Of Epoxy System

Thesis Supervisor : Dr. Rajesh Kitey

Special Thanks :Dr. P.Venkitanarayan

By

SURVI RAGHU GOUD

13101049

M.Tech

A Thesis Defence in Partial Fulfilment of the Requirements for the Degree of Master of Technology

OUTLINE

• MOTIVATION

• OBJECTIVES

• MATHEMATICAL FORMULATION

• MATERIAL PREPARATION AND

CHARACTERIZATION

• EXPERIMENTAL METHODS

• RESULTS AND DISCUSSION

• CONCLUSION

MOTIVATION

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Epoxy resin react with co-reactants (hardeners) and form thermosets

with desired properties.

MOTIVATION

• Tailoring the properties by controlling the factors affecting its properties –

– Composition of epoxy• Resin/hardener ratio

– Curing condition• Temperature

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OBJECTIVES • To find the elastic properties of anhydride-cured Epoxy system

for the six Resin/Hardener (R/H) Ratios.

• To investigate the Dynamic Fracture behaviour of all the epoxy variants.

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Multi parameter Representation of the Strain field

• The stresses expressed in the generalized form are

•

where

Ref: “strain gage methods for measuring the opening-mode stress intensity factor,

dzdYYdz

dZZwhere

YYyZyxy

YyZyZyy

YYyZyZxx

',',

Im'Re'Re'Im'ImRe

Re2'Im'ImRe

M

m

mZmBzY

N

n

nZnAzZ

0

)(

0

21

)(

• Plane stress-strain relations:

• Put n=0,1 and m=0,1 in the equation

YYyZyG

YYyZyZE

YYyZyZYyZyZYYyZyZ

EG

E

E

xy

yy

yyxxxx

xyxy

xxyyyy

yyxxxx

Im'Re'Re

Re2'Im)1('Im)1(Re)1(Similarly,

Re2'Im)1('Im)1(Re)1('Im'ImReRe2'Im'ImRe

1

)(1

)(1

21

123

0

21

121

0

21

21'

zAzAZ

zAzAZ

Ref: “strain gage methods for measuring

•

Ref: “strain gage methods for measuring

2sin

2cos

21

23sin

23cos

21

21

21'

2sin

2cos

2sin

2cos

21

123

0

221

12

323

0

21

121

0

221

122

1

0

irAirA

erAerAZ

and

irAirA

erAerAZ

ii

ii

YSimilarly,

)sin(cos10B irB

BdtdY

Y '

Four parameter strain field relative to a rotated coordinate system

• From the first invariant of strain,

• And the complex form of the strain transformation equation is

•

where Ref: “strain gage methods for measuring

yyxxyyxx ''''

ixyxxyyyxxxyy eii 2

'''''' )()(

2sinsin2cos)2cos(2sinsin212cos

2sin

2cos

)2cos(2sin2

3cossin212cos

23sinsin

21

2cos2

122

1

1

021

0''

krBkrA

kBkrAxx

Single gauge- Three parameter solution

• term can be eliminated if

Cos 2= k =)

• Next, set the coefficient of to zero, which gives = cot 2

• 𝟐𝛍𝝐𝒙 ′ 𝒙 ′=

𝑲 𝑰

√𝟐𝝅𝒓

−𝟏𝟐 [𝐤𝐜𝐨𝐬 𝜽𝟐−𝟏

𝟐 𝐬𝐢𝐧𝛉𝐬𝐢𝐧 𝟑𝜽𝟐 𝐜𝐨𝐬𝟐𝛂+𝟏𝟐 𝐬𝐢𝐧𝛉𝐜𝐨𝐬 𝟑𝜽𝟐 𝒔𝒊𝒏𝟐𝜶 ]

MATERIAL PREPARATIONMATERIALS-

• Epoxy Resin: DGEBA (Di-glycidyl ether of Bisphenol-A ), (LY556)

• Curing agent: MTHPA (Methyl Tetra hydrophthalic anhydride, (HY917)

• Accelerant: 2,4,5-tris[(dimethylamino)methyl]-Phenol (DMP-30)

• Cure period: 80 °C for 3 h, followed by 140 °C for 12 h

• R/H Ratios (by weight):- 100:40, 100:60, 100:80, 100:100,

100:120 and 100:140

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MATERIAL PREPARATION- TENSILE & FRACTURE SPECIMENS• Tensile specimens : ASTM D638 : Type –I configuration

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Material Preparation-Strain gauge mounting

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MATERIAL PREPARATION- FRACTURE SPECIMENS

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MATERIAL PREPARATION- FRACTURE SPECIMENS

EXPERIMENTAL METHODS- TENSILE TESTS CHARACTERIZATION OF ELASTIC PROPERTIES

Tensile Test setup for finding Young’s modulus:

• Displacement rate : 0.5 mm/min• Extensometer gauge length : 25 mm

COMPARISION OF STRESS-STRAIN BEHAVIOUR OF DIFFERENT R/H RATIOS

• Speed of Testing : 0.5

mm/min

• Overlapping initial region

COMPARISON OF YOUNG’S MODULUS

• Loading rate : 0.5 mm/min

Tensile Test setup for finding Poisson’s Ratio:

• Sampling rate : 100S/s• Half bridge-connection

COMPARISION OF LATERAL STRAIN –LONGITUDINAL STRAIN BEHAVIOUR FOR DIFFERENT R/H RATIOS

• Loading rate : 0.5 mm/min

COMPARISON OF POISSON’S RATIO

Calculation Of parameters for fracture samples :

EXPERIMENTAL METHODS- FRACTURE TESTS

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EXPERIMENTAL METHODS- FRACTURE TESTS

EXPERIMENTAL METHODS- FRACTURE TESTS

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• Pressure : 0.5 Kg/

• Sampling Frequency : 1M Hz

0 1000 2000 3000 4000 5000 6000

-0.003

-0.002

-0.001

0

0.001

0.002

0.003

Average Inc Strain SG

Time (μs)

inci

dent

, ref

lect

ed a

nd st

rain

pul

ses

Ist = 450 secRst = 2814 sec

t= d= 1540 mm= 1302.876 m/s

= 6.25 m/s

Representative Data of Strain-Time plots for different R/H ratios

0 20 40 60 80 100 120 1400

200

400

600

800

1000

1200

100:40100:60100:80100:100100:120100:140

Time (µ sec)

ε_rr

(μ s

train

)

Comparison of Fracture toughness of all the six R/H ratios

CONCLUSIONS• Elastic modulus changing slightly by R/H ratio in the tested epoxy

variants and was observed to be highest for stoichiometric ratio, 100:80

• Poisson’s ratio was observed to be least for stoichiometric ratio, 100:80.

• All R/H ratios showed the monotonically increasing strain history

variation until the crack initiation.

• The Fracture Toughness was observed to be least for the 100:40 R/H

ratio and 0.578 MPa for 100:80 R/H ratio.

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SCOPE FOR FURTHER WORK

• Dynamic Fracture properties of bimaterials prepared with epoxy variants

could be studied and the Finite Element Simulations on them could be

investigated to understand the failure criterion in these materials.

• The impact test could be done for deeply cracked specimens of the

different R/H ratios.

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THANK YOU!