Polymer Properties:Experiment 3 Impact Test

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Polymer Properties (EBT 326) Exp. 3: Impact Test

EXPERIMENT 3

Impact Test

1.0 OBJECTIVE

1.1 To apply the Charphy method in measuring impact strength of polymer materials.

2.0 INTRODUCTION

The stresses that are applied by subjecting the test sample to a sudden blow are the basic

characteristics of an impact test. Impact is something that can happen in service and the test

methods that have been developed seek to stimulate this and to provide a relatively simple meansof achieving high strain rates. Impact strength can be defined as energy required to break the

samples per original cross sectional area, since impact load had been applied to the samples.

There are two main forms of impact test, the Iod and the Charpy test, both involve striking a

standard specimen with a controlled weight pendulum travelling at a set speed. The amount of

energy absorbed in fracturing the test piece is measured. !or this e"periment, we using the

Charphy test for measuring impact strength of each polymer samples prepared.

Charpy impact test is practical for the assessment of brittle fracture of metals and is also used

as an indicator to determine suitable service temperatures. The Charpy test sample has

10x10x55mm3

in dimensions and a #$ % notch. To perform the test, the pendulum set at a

certain height is released and impact the specimen at the opposite end of the notch to produce a

fractured sample. &y calculating the energy lost in propagating a crack through the specimen, we

can learn about the toughness of a specimen, as well as its tensile strength. 'dditionally, by

inspecting the breakage plane of the specimen, we can also gain some insight into the ductility ofthe material.

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!igure 1( Charphy Impact Testing )achine

!igure *( +orking principle of pendulum impact test machine

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3.0 COMPONENTS AND EQUIPMENT

.1 -endulum Impact Tester

!igure ( -endulum Impact Tester )achine

.* %ernier caliper

!igure #( %ernier caliper

. amples

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..1 -olystyrene /-0

!igure $( -- /black0

..* -olypropylene /--0

!igure ( -- /yellowish0

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.. 2ow 3ensity -olyethylene /23-40

!igure 5( 23-4 /opaque0

..# -olycarbonate /-C0

!igure 6( -C /white0

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.0 PROCEDURES

#.1 The sample sheets were prepared into bars at dimension $$mm " 17mm " 17mm.

#.* 8sing vernier caliper, the width, length and thickness of every sample were measured.#. The -endulum Impact Tester had to make sure in good conditioned, clean and safe to

use.#.# The sample was clamper into the pendulum impact test fi"ture.

#.$ The pendulum was released and was allowed to strike through the sample.

#. The pendulum was stopped and the impact reading was written.#.5 teps #.#9#. for another samples.

#.6 3 117 /Charphy0 was referred for more details.

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!.0 RESU"TS AND DISCUSSION

To calculate the impact strength of the sample, we used this formula(

Impact strength (J/m2)=

impact energy (J/m)

cross section area(m)

The cross sectional area of each sample is $$mm : 17mm ; $$7 mm* or 7.777$$m*

Table 1( Table of data of impact energy of every un9notched sample.

Type of samples

/unnotched0$2.95

0.00055=5363.64

23-4 7.$$

0.55

0.00055=100.00

-C #.74.0

0.00055=7272.73

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$.1 3iscuss on ductile and brittle failure of the sample used.

P! PP "#PE P$

%

%.5

1

1.5

2

2.5

3

3.5

4

4.5

The Graph of Average Impact Energy vs. Samples

Type of samples

Average impact energy (J/m)

!igure >( The graph of average impact energy vs. type of samples.

&ased on !igure >, it shows the graph of average impact energy gained from

pendulum impact tester vs. type of samples. The graph shows ig9agged pattern as the

average of impact energy of samples up and down. The highest value of average impact

energy is #.7 =?m which is belongs to polycarbonate /-C0. 's the highest energy

absorbed, it make the sample in conformity with a ductile fracture. &oth 23-4 and -

mostly have same value which it have 7.$ j?m in difference. &ut the lowest energy

absorbed is 7.$$ =?m which is belong to 23-4 thus make it brittle fracture. The ductile

material will give higher impact reading test thus the energy value will indicate biggerthan the brittle material.

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P! PP "#PE P$

%

1%%%

2%%%

3%%%

4%%%

5%%%

6%%%

%%%

&%%%

The Graph of Impact Strength vs. Samples

Type of samples

Impact Strength (J/m2)

!igure 17( The graph of impact strength vs. type of samples.

The graph of average impact strength calculated from gained impact energy using

respectively sample vs. type of samples is shown at !igure 17. This graph also shows up

and down value which we can say it as fluctuated. 's the calculations had done, the

highest value of impact strength is 5*5*.5 =?m* determined belongs to polycarbonate

/-C0 as it has highest average impact energy. +ith value 1777 =?m*, the 23-4 sample

has been determined as the sample that has lowest impact strength as its impact energy

also the lowest. 23-4 sample has seen as brittle material as it needed the less energy to

break compared to -C which required more energy to make it break.

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$.* 3iscuss effect of notched on properties of impact craing.

The Charpy specimen may be used with one of three different types of notch, a

@keyhole@, a @8@ and a @%@. The keyhole and 89notch are used for the testing of brittle

materials such as cast iron and for the testing of plastics. The %9notch specimen is thespecimen of choice for weld testing.

!igure 11( tandard Charpy9% notch specimen

The %9notch specimen acted as the point of stress concentration. 's most

materials might go for the weakness point during impact craing, it very sensitive on the

notch. ' %9notch specimen is relatively weaker than the specimen un9notched. Thus, it is

very important for some materials as it will give more understanding for calculating the

factor of safety on their applications. The %9notch specimen tends to give accurate

fracture surface reading for determining their properties.

$. 3iscuss factors that can effect impact properties. +hat is the important of impact

properties in plastics material selection for certain applicationA

There are many factors that can effect impact properties. The first is yield strength

and ductility. !or a given material the impact energy will be seen to decrease if the yield

strength is increased. !or e"ample, if the material undergoes some process that makes it

more brittle and less able to undergo plastic deformation. uch processes may include

cold working or precipitation hardening. The ne"t factor is notches. The notch serves as a

stress concentration one and some materials are more sensitive towards notches than

others. The notch depth and tip radius are therefore very important.

Temperature and strain rate also can be the factor that affects the result of the test.

)ost of the impact energy is absorbed by means of plastic deformation during the

yielding of the specimen. Therefore, factors that affect the yield behavior and hence

ductility of the material such as temperature and strain rate will affect the impact energy.

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This type of behavior is more prominent in materials with a body centered cubic

structure, where lowering the temperature reduces ductility more markedly than face

centred cubic materials.

Be"t, ductile to brittle transition . ome materials such as carbon steels undergo

what is known as a ductile to brittle transitionD. This behavior is obvious when impact

energy is plotted as a function of temperature. The resultant curve will show a rapid

dropping off of impact energy as the temperature decreases. If the impact energy drops

off very sharply, a transition temperature can be determined. This is often a good

indicator of the minimum recommended service temperature for a material.

The property of a material relating to work required to cause rupture is toughness,

which depends on the ductility and ultimate strength. It is known that a high9rate of

loading results in an increase in strength, but a reduction in ductility. +hen forces are

applied suddenly for very short time intervals, another effect of such forces is to produce

stress waves.

It is important of all impact properties in plastic material selection for certain

application because not all materials respond in the same way to variations in strain rate.

!or instance, a slowly applied point load shatters the glass while a high9speed bullet

punctures a fairly clean hole. imilarly, sealing wa" behaves in a ductile manner at low

strain rate, but snaps into two under a sharp blow.

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#.0 CONC"USIONS

&ased on the e"periment conducted, we can see from the Charphy test using the pendulum,

impact tester, polycarbonate /-C0 undergoes ductile fracture while the 23-4 undergoes brittle

fracture compared to other samples. -C absorbed more energy which will show that it is suitable

to use in electrical or electronic application. It also suitable to use in automotive application. It

because the amount of energy required to break a ductile material is greater than for brittle

material, so it will make the equipment not easy to broke.

$.0 RE%ERENCES

E1F +. !. mith, =. Gashemi -h.3. !oundation of )aterials cience and 4ngineering $th

edition. /-age *69*66 and $19$1#0

E*F =ournal of 'pplied -olymer cience, %ol. 6>, 11$91*1 /*770. +iley -eriodicals, Inc.

*77

EF 3.

Polymer Properties:Experiment 3 Impact Test

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