Influence of strain rate on the mechanical properties of thermoplastic materials.

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Influence of strain rate on the mechanical properties of thermoplastic materials.

Influenceof strain rate on the mechanical properties of thermoplasticmaterials.

Declarationof Originality

&quotThiswork or any part thereof has not previously been presented in anyform to the University or to any other institutional body whether forassessment or other purposes. Save for any express acknowledgements,references and / or bibliographies cited in the work, I confirm thatthe intellectual content of the work is a result of my own effortsand no other person&quot.

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Impactresistance and Strain rate are known to extensively influence themechanical behaviour of thermoplastic materials.Thermoplastic&nbspmaterialsalso known as polymers are those components that are made of polymerslinked by Van der Waal forces or intermolecular interactions, formingbranched or linear structures. A polymer material can be matched upto of a set of mixed strings on a table, the strings which have astrong degree of mixing they will require greater effort to separatethem from each other. The friction present between each of thestrings offers resistance to separate in this example the frictionbetween the strings represents the Van der Waal forces orintermolecular forces that hold the polymer together.

Polymerscan have two different types of structures crystalline or amorphousstructures, some polymers have both the structures depending on thedegree of intermolecular interaction that occurs between the chainsof the polymer. In a crystal structure the polymer chains have acompacted and an ordered structure it can be distinguished mainly asmicellar form and lamellar structures. This crystal structure isdirectly conscientious for the mechanical properties of temperatureresistance and resistance to stresses or loads of thermoplasticmaterials. Amorphous structure have a bundled structure, similar to aball of thread tangled, amorphous structure in polymers is directlyresponsible for the elastic properties. If the polymer material hasmore of amorphous structure quantity they end up having poorresistance to loads but excellent elasticity. But when thethermoplastic has a high concentration of crystalline structure, thematerial will be very strong and even stronger than thermosetmaterials, but with less elasticity that provides the distinctivefragility of these materials.

Tensiletest is used to find out and evaluate mechanical propertiesparameters such as yield strength%, % elongation, ultimate strength,area of reduction and Young`s modulus. Impact test is also used toevaluate mechanical properties of polymer. Caring out impact test ona polymer allows you to determine the materials impact resistance.

  1. Experimental Procedure

    1. Materials used

Thefollowing thermoplastic materials were used for both the tensile testand impact test High-density polyethylene (HDPE),Low-densitypolyethylene (LDPE), Polycarbonate (PC), Polyvinylchloride (PVC),Nylon 66 and Acetal. For tensile test Zwick-Roell Z020 machine isused while for impact test Zwick Roell B5113 machine is used.

    1. Tensile Test procedure

Firstthe polymer specimen is prepared by making both ends have allowancesfor gripping on the machine. The specimen width and thickness areprecisely measured using vernier calliper and a dial gauge. The nextstep is putting the specimen in the tensile testing machine(Zwick-Roell Z020) and switching it on. The specimen is slowlyelongated until it reaches its breaking point. During this process,the extension of the gauge readings is recorded against the appliedforces.

Zwick-RoellZ020 gives the best solutions for the different tensile tests, withtesting forces from 200 N to 2,500 kN available. A broad range ofpolymer specimen grips is available to fit the material being testand the specifications in the standard, while various systems areavailable for extension measurement, including both contact andnon-contact extensometers. During the test the force on the specimenand the elongations are measured by extensometers.&nbspThe followingcharacteristic data are tabulated strain, tensile modulus, point ityield point, failure or breaking point and Poisson`s ratio.

    1. Impact Test procedure

Thefirst step here is to prepare the polymer specimen then it is placedin the machine with the notch facing opposite pendulum on the impacttester machine (Zwick Roell B5113). Zwick Roell B5113 has two typesof Impact test The Izod test and Charpy test. Charpy test has alarger range of function and is better suited to tests on materialsdisplaying interlaminar surface effects or shear fractures. This testmethod also offers advantages when testing at low temperatures as thespecimen support is farther away from the notch, so that rapid heattransfer to the critical areas of the specimen is avoided. Charpytest is normally performed on unnotched specimens with edgewiseimpact (1eU). During the testing process, if the specimen does notbreak as per the given configuration, the test is usually performedwith notched specimens, although the notched test results are notdirectly comparable to the unnotched test. If specimen break is stillnot achieved the impact tensile method is employed.

  1. Results

Table1:Tensilestrength (MPa)

Materials /Strain Rate

500 mm/min

50 mm/min

10 mm/min

Acetal

69.42

67.05

64.12

PVC

62.49

59.54

58.64

Nylon 66

47.63

43.91

46.97

LDPE

9.81

10.35

HDPE

27.58

25.20

PC

86.16

64.61

63.00

Figure1: Graph of Tensile Strength against Strain rates

Table2: ∑Break

Materials/Strain Rates

500 mm/min

50 mm/min

10 mm/min

Acetal

15.69

40.58

35.13

PVC

12.15

5.51

86.17

Nylon 66

91.63

121.44

140.27

LDPE

204.17

173.08

HDPE

44.77

+480%

PC

5.31

6.90

25.08

Figure2: Graph of ∑Break against Strain rates

Table3: E-Modulus

Materials/Strain rates

500 mm/min

50 mm/min

10 mm/min

Acetal

3150.17

2645.92

333.35

PVC

3559.05

3632.55

3662.48

Nylon 66

877.22

965.01

917.60

LDPE

0.05

0.06

HDPE

0.38

0.35

PC

2309.18

2279.43

2215.93

Figure3: Graph of E-modulus against Strain Rate

Table4: Impact resistance

Materials

Mean, x

Coefficient of variation v

Acetal

15.48

13.28

PVC

7.26

33.97

Nylon 66

101.75

1.97

NYLON

90.90

34.46

HDPE

48.96

21.46

Polycarbonate

26.55

8.90

  1. Discussion

Fromthe six polymer specimen that we conducted the experiment, we can seethat there is a big difference on their mechanical properties. Thisdifference is because every tested specimen has their own specificchain structure which is different from one another. LDPE is apolymer with a branch-chain structure. It has a lesser degree ofcrystalinity also it has very low density contrasted to HDPE. Thebranched-chain configuration in LDPE reduces the Van der Waal orintermolecular bonding forces, therefore lowering its strength. Fromthe graph of tensile strength we see that LDPE is characterized asweak and soft polymer. HDPE is also a polymer with a straight linestructure or linear structure. This linear or straight line structuregives HDPE a stronger strength hence it has high UTS. PVC has also alinear or straight line structure which makes it strong.

Acetalis a thermoplastic material with high crystalline composition henceit is characterized by its hardness, high strength and rigidity.However Acetal has a very low coefficient of friction. Thesecharacteristic makes Acetal suitable for application in areas wherehigh abrasion resistance is required. From the graph of tensilestrength against strain rate we can see that Polycarbonates (PC) arethe second strongest material as per the tested specimen. This isbecause they contain carbonate groups in their chemical structure.Nylon 66 is has a high mechanical strength, rigidity, good stabilityunder heat.

  1. Conclusion

Inconclusion, the impact test and tensile tests carried out gaveimportant information concerning the mechanical properties of thepolymer, such as impact energy, elongation, Modulus elasticity,impact resistance and yield strength. The thermoplastic arecategorized into two types semi-crystalline and amorphous whereHDPE, LDPE, Acetal and PC are semi-crystalline and Nylon, and PVC arecategorized as amorphous material.

  1. References

IanWidi Perrdana 2015: Ploymer Tensile Test Analysis. Retrieved from:http://www.academia.edu/11566153/POLYMER_TENSILE_TEST_ANALYSIS

P.-Y.Ben Jar*&nbspandJie Xu, 2011: Analysisof tensile test results for poly(acrylonitrile-butadiene-styrene)based on Weibull distribution.Retrievedfrom:

http://eng.sut.ac.th/metal/images/stories/pdf/Lab_3Tensile_Eng.pdf

JamesShedden June, 2013: Simplifying the Testing and Calculation ofFracture Toughness of Thermoplastic and Thermoset Matrix CompositeMaterials. Retrieved from:

http://digitalcommons.calpoly.edu/cgi/viewcontent.cgi?article=1092&ampcontext=matesp

TimOsswald, 2002: UnderstandingPolymer ProcessingProcesses and Governing Equations. Retrieved from:

http://www.hanserpublications.com/SampleChapters/9781569904725_9781569904725_Understanding%20Polymer%20Processing_Osswald.pdf

Zwick/Roell,2015: Impact test on plastics -ISO 179, ISO 180, ASTM D256. Retrievedfromhttp://www.zwick.co.uk/en/applications/plastics/thermosetting-thermoplastic-materials/impact-test.html

Zwick/Roell,2015: Tensile(tension) test on plastics – ISO 527-1, ISO 527-2, ASTM D 638.Retrievedfromhttp://www.zwickroell.co.za/en/applications/plastics/thermosetting-thermoplastic-materials/tensile-test-for-plastics.html

Influence of strain rate on the mechanical properties of thermoplastic materials.

  • Uncategorized

Influenceof strain rate on the mechanical properties of thermoplasticmaterials.

Declarationof Originality

&quotThiswork or any part thereof has not previously been presented in anyform to the University, or to any other institutional body whetherfor assessment or other purposes. Save for any expressacknowledgements, references and / or bibliographies cited in thework, I confirm that the intellectual content of the work is a resultof my own efforts and no other person&quot.

Studentname:

Studentsignature:

  1. Introduction.

Themechanical properties of thermoplastic materials are mainly dominatedby its visco-elasticity. This is revealed by the time-dependency ofthe thermoplastic materials mechanical response during loading.Hence, a thermoplastic material behaves in a different way ifsubjected to long term or short term loads.

Oneway of finding mechanical properties of a thermoplastic material iscaring out a tensile test. Tensile test is used to find out andevaluate parameters such as yield strength%, ultimate strength, %elongation, area of reduction and Young`s modulus. By definition,Tensile testing is referred to as the measurement of a material’sability to overcome forces pulling it apart and the extents itextends before breaking (W. F. Smith &amp J. Hashemi, 2011). Thetensile testing is done by applying axial load or longitudinal at aspecific extension rate to a standard tensile specimen with knowndimensions (gauge length and cross sectional area perpendicular tothe load direction) till failure. The applied tensile load andextension are recorded during the test for the calculation of stressand strain.

Therate of loading for a polymer material is an important component ofhow we determine its performance. High rates of strain occurrenceover a short period of time usually favour the elastic properties ofmaterials. Elasticity of thermoplastic materials is linked withload-bearing performance as according to properties such as stiffnessand strength. However, low rates of strain occurrences over a longertime usually favour the energy-damping or viscous aspects of materialbehaviour. Viscous flow is linked management of energy, oftenreferred to as impact resistance or toughness.

Anotherway of finding mechanical properties of thermoplastic (polymer)materials is by caring out impact test. Impact testing is used todetermine the impact energy that is absorbed by a test material andthe behaviour of the specimen at higher deformation speeds. Themeasure of how a material resists damage is called impact resistance.The safety of a product is usually determined by their ability toresist breaking therefore making this test very important.

  1. Experimental procedure

    1. Materials

Thethermoplastic samples used in the tensile test were Polyvinylchloride&nbsp(PVC),Polycarbonate&nbsp(PC),High-density polyethylene (HDPE), Acetal,Nylon66 and Low-density polyethylene (LDPE). For impact test the samepolymer samples were used. The test machine used for tensile test wasa Zwick-Roell Z020 while Zwick Roell Pendulum Impact tester typeB5113.300 machine was used for impact testing.

    1. Tensile Test procedure on the thermoplastic samples

Thepolymer samples to be tested were prepared by using a dumbbellcutter. Both ends of the specimens were prepared to have sufficientlength and a surface condition such that they are firmly grippedduring testing. Thickness and width of the specimens were measuredusing a dial thickness gauge and vernier calliper. The test processinvolved placing the specimen in the Zwick-Roell Z020 testing machineand slowly extending the specimen until it fractures. Zwick-RoellZ020 machinegivesthe best solutions for the various tensile tests, since it has widerange of specimen grips to suit the material under test and it alsoallows testing forces from 200N to 2,500KN. Extension are measuredusing extensometers and the following characteristic values arerecorded tensile modulus, strain, yield point, point of failure andPoisson`s ratio.

    1. Impact Test procedure on the thermoplastic samples

Thepolymer samples to be tested were prepared. The pendulum is locked inits position to ensure it is locked in place. The sample is placed inposition that is the sample should lie against the stops supported onboth sides, with the notch facing away from the direction thependulum will come. After ensuring the path of the pendulum is clear,the pendulum is released using the two hand release mechanism. Theequipment used for these test was a Zwick Roell Pendulum ImpactTester, Type B5113.300. While using this particular machine there twotypes of impact test procedures Charpy test and Izod test. Charpytest is considered to be the best since it has a range ofapplications and it can better test the materials by displaying theirshear fracture or interlaminar surface. Charpy test is usually doneon unnotched polymer specimens.

  1. Results:

Table1:Tensilestrength (MPa)

Materials /Strain Rate

500 mm/min

50 mm/min

10 mm/min

Acetal

69.42

67.05

64.12

PVC

62.49

59.54

58.64

Nylon 66

47.63

43.91

46.97

LDPE

9.81

10.35

HDPE

27.58

25.20

PC

86.16

64.61

63.00

Figure1: Graph of Tensile Strength against Strain rates

Table2: ∑Break

Materials/Strain Rates

500 mm/min

50 mm/min

10 mm/min

Acetal

15.69

40.58

35.13

PVC

12.15

5.51

86.17

Nylon 66

91.63

121.44

140.27

LDPE

204.17

173.08

HDPE

44.77

+480%

PC

5.31

6.90

25.08

Figure2: Graph of ∑Break against Strain rates

Table3: E-Modulus

Materials/Strain rates

500 mm/min

50 mm/min

10 mm/min

Acetal

3150.17

2645.92

333.35

PVC

3559.05

3632.55

3662.48

Nylon 66

877.22

965.01

917.60

LDPE

0.05

0.06

HDPE

0.38

0.35

PC

2309.18

2279.43

2215.93

Figure3: Graph of E-modulus against Strain Rate

Table4: Impact resistance

Materials

Mean, x

Coefficient of variation v

Acetal

15.48

13.28

PVC

7.26

33.97

Nylon 66

101.75

1.97

NYLON

90.90

34.46

HDPE

48.96

21.46

Polycarbonate

26.55

8.90

  1. Discussion

Fromdata obtained after caring out both tensile and impact test onthermoplastic materials, we see that each of the six tested polymerspecimens have different mechanical properties. From the comparisongraph drawn, this difference is more vivid and this is because eachpolymer specimen has its own chain structure holding it together. Inthe graph of tensile strength against strain rate (figure1) we seethat Acetal and PC have the highest tensile strength this is becauseAcetal has high crystalline concentration hence strong intermolecularforces. PC has carbonate groups in its chemical structure that makesit strong. HDPE has linear or straight line structure that makes ithave stronger strength hence high UTS. LDPE has a lowerconcentration of crystalline hence low density compared to HDPE.LDPE has branched-chain structure which reduces the intermolecularbonding forces, therefore reducing its strength. LDPE under categoryof polymers it is categorized as a soft and weak polymer. PVC is athermoplastic material with a linear structure which makes it to be astrong polymer. Finally Nylon 66 is also seen to have high mechanicalstrength, good stability, rigidity.

PVCpolymerhas an amorphous structure which contains polar chlorine atoms in itsmolecular structures. The crystalline part in PVC polymer is fixedand the amorphous piece is flexible. PVC is stable chemically withlittle change in its molecular structure, and also it shows littlechange in its mechanical strength. However, visco-elastic materials(long chain polymers) can be deformed by application of constantexterior force, even when the force applied is well under their yieldpoint. This is known as creeping point. Although PVC polymer is avisco-elastic material or a long chain polymer, it has a low creepdeformation compared to other plastic such as PC due to limitedmolecular motion at normal temperature. PVC has Crystalline densityof 1.52 g/cm3at 25oC,molecular weight of repeat unit: 62.50 g/mol and amorphous density at25oC:1.385 g/cm3.Polyvinyl chloride has the simplest repeat unit which is-[CH2-CHCl]-.

Nylon66 (PA66)is a semi-crystalline polyamide normally used in making engineeringmaterial such as gears and bearings due to its good abrasionresistance and self-lubricating properties. Nylon 66 is often usedwhen high rigidity, mechanical strength, and good stability underheat are required. It has amorphous density of 1.07 g/cm3at 25oC,crystalline density of 1.24 g/cm3at 25o,and molecular weight of repeat unit: 226.32 g/mol. Nylon C12H22O2N2

LDPE(Low Density Polyethylene) polymerhas the most extreme branching. This causes LDPE to have a lesscompact molecular structure, this results to less density. It has adensity of 0.910-0.925 g/cm3.HDPE(High Density Polyethylene)polymer has the least branching of its polymer chain. Since it isdenser it is less permeable and more rigid than the LDPE. Itcrystalline density is 0.941-0.965 g/cm3and it has a molecular weight of repeat unit: 28.05 g/mol. Both theLDPE and HDPE mer unit/repeat unit is C2H4

Acetalischaracterized by its hardness, high strength and rigidity to −40&nbsp°C.It has a crystalline composition which makes it intrinsically opaquewhite, but it is obtainable in all colours. Acetal has a crystallinedensity of ρ = 1.410–1.420 g/cm3and a molecular weight of repeat unit: 30.03 g/mol. It merunit/repeat unit is CH2O

Polycarbonate(PC)is a long-lasting material with low scratch-resistance and highimpact-resistance.&nbspThe toughest grades of polycarbonates (PC)have the highest molecular mass. Unlike most polymers, PC canexperience large plastic deformations with no cracking or breaking.It has amorphous density of 1.20 g/cm3at25oC,molecular weight of repeat unit: 254.3 g/mol and its mer unit/repeatunit isC16H14O3.

Ingeneral, all of our test components were polymer or thermoplasticmaterials, and polymers have no cross linking on their structure.Polymers are grouped into two types amorphous and semi-crystallinewhere Acetal, HDPE, LDPE and PC are semi-crystalline and Nylon, andPVC are categorized as amorphous polymer.

  1. Conclusions

Inbrief, the tensile tests and the impact test that we conducted gaveimportant reading of mechanical properties of the thermoplastictested such as Modulus elasticity, elongation, yield strength, impactenergy and impact resistance, and so on. In design and manufacturingwe can conclude that Acetal is a good thermoplastic material to usewhere frequent tensile force occurs since it can withstand moretensile force before it yield than the other polymers tested.

  1. References

IanWidi Perrdana 2015: Ploymer Tensile Test Analysis. Retrieved from:http://www.academia.edu/11566153/POLYMER_TENSILE_TEST_ANALYSIS

P.-Y.Ben Jar*&nbspandJie Xu, 2011: Analysisof tensile test results for poly(acrylonitrile-butadiene-styrene)based on Weibull distribution.Retrievedfrom:

http://eng.sut.ac.th/metal/images/stories/pdf/Lab_3Tensile_Eng.pdf

Zwick/Roell,2015: Testing Systems TestingMachines and System for Texture Material.Retrieved from:

file:///C:/Users/Simon/Downloads/Textiles.pdf

JamesShedden June, 2013: Simplifying the Testing and Calculation ofFracture Toughness of Thermoplastic and Thermoset Matrix CompositeMaterials. Retrieved from:

http://digitalcommons.calpoly.edu/cgi/viewcontent.cgi?article=1092&ampcontext=matesp

TimOsswald, 2002: UnderstandingPolymer ProcessingProcesses and Governing Equations. Retrieved from:

http://www.hanserpublications.com/SampleChapters/9781569904725_9781569904725_Understanding%20Polymer%20Processing_Osswald.pdf

M02_KALP1681_06_SE_C02.QXD, 2009:MechanicalBehaviour, Testing, and Manufacturing Properties of 2 Materials.Retrieved from:

http://www.pearsonhighered.com/samplechapter/0136081681.pdf

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