Tensile Properties of Polypropylene

Tensile Properties of PolypropyleneIntroductionIf an engineer wanted to design a bridge to span a river, it would be absurd to consider building it out of papier-mch or rubber. We know this because we know something about the demands that will be put on the bridge and we know that these textiles do non satisfy the requirements. After considering early(a) materials, perhaps titanium or high tech alu bitium alloys, we may discount them on the grounds of damage even if they do have suitable mechanical properties to make a good bridge. Eventually we may decide on steel but which unmatched? There are thousands to choose from. Which has the best properties at an affordable price? The cost effectiveness of any material is a matter not to be dealt with here but we mustiness ask which steel has the most appropriate physical properties. In order to answer this question, we must conduct screen outs on opposite steels and compare the results when samples of the steel are streamleted to destruction.Polypropylene has the ability to crystallise which was a very exciting prospect as it is also an economical material so the popularity of it grew and production began all across most of Europe its use. Lots of distinct types of polypropylene have been under production since the early 1950s principally because of its insulating properties. it is apply in many different fields, bumpers and some of the interior in a car is developed using polypropylene its also widely used in electrical components because of its great electrical resistance at high temperatures. It has similar properties to polyethylene.Because of its use in many different fields its necessary to test the material in a variety of ways. In this test the elastic properties will be examined at different testing runs. This test is done becauseThe test process involves placing the test prototype in the testing machine and slowly extending it until it conk outs. During this process, the elongation of the g auge section is recorded against the applied force. The data is manipulated so that it is not specific to the geometry of the test sample.Theory Polypropylene, like other plastics, typically starts with the distillation of hydrocarbon fuels into lighter groups called fractions some of which are combined with other catalysts to produce plastics (typically via polymerisation or poly-condensation)For example, the polymerisation of propylene, which is identical to ethylene except that one hydrogen substituent has been replaced by a methyl (CH3) group, tax returns polypropylene. This material has a higher(prenominal) melting point (160-170 oC), higher fictile strength, and greater rigidity than polyethylene.Figure 1-Propylene monomers polymerisation to polypropyleneDepending on how they are linked or joined (chemical bonds or intermolecular forces) and on the arrangement of the different chains that forms the polymer, the resulting polymeric materials stinkpot be classified asThermopl asticsElastomersThermosetsDepending on the chemical composition, polymers can be inorganic such as glass, or they can be organic, such as adhesives of epoxy resin. Organic polymers can be also divided into natural polymers such as proteins and synthetic substance polymers as thermosets materials.Description of apparatusThe apparatus used the most for the testing part of the experiment was the zwick tensile testing machine this is a highly unblemished piece of equipment as it has high resolution angle measurement which allows excellent repeat accuracy.This type of machine has two crossheads one is adjusted for the length of the specimen and the other is driven to apply tension to the test specimenhe machine must be able to generate enough force to destroy the specimen. The machine must be able to apply the force quickly or slowly enough to properly mimic the actual application. Finally, the machine must be able to accurately and precisely measure the gauge length and forces applie dFigure 2-Tensile testing machine (diagrammatic sketch form)Test function The test will be carried out using the Zwick tensile testing machine, with 3 different specimens each of them will be all-embracing at different vivifys sample 1 Extension speed= 100 mm/minSpecimen 2 Extension speed= 50 mm/minSpecimen 3 Extension speed= 12.5 mm/minBefore testing the specimens, they must be measured before and after the test to see what affect the test had on the specimensAfter the measurement, have been taken its required to make a table to compare the clog to the multiplication this graph will be required to estimate relevant values that will be needed to complete the calculations.For all the specimens you are required to obtain a verity of tensile properties includingNominal yield markYoungs modulusFracture stress (nominal and true)Tensile ductilityResultsSpecimen (mm)Average (mm)Av.CSA = tw (1T2.132.182.202.1710.20W4.684.734.704.702T2.132.152.162.1410.10W4.684.724.714.703T2.142.152.1 62.1510.11W4.704.724.694.70Specimen 1 calculated results when extended at speed of 100 mm/min Gauge Length (mm)33.00 sign cross-sectional domain of a function ()10.21Fracture length (mm)(55-33) 22.00Thickness at relegate (mm)0.91Width at fracture (mm)2.50Cross-sectional field of honor at Fracture ()2.28 make full at yield (N)270.00Load at fracture (N)170.00Nominal yield stress ()26.45Extension at high yield (mm)1.54Young modulus ()566.79Nominal fracture stress ()16.65True fracture stress ()74.56Tensile Ductility (mm)0.66Specimen 2 calculated results when extended at speed of 50 mm/min Gauge Length (mm)33.00Initial cross-sectional flying field ()10.10Fracture length (mm)(123-33) 90.00Thickness at fracture (mm)0.93Width at fracture (mm)2.61Cross-sectional area at Fracture ()2.43Load at yield (N)262.50Load at fracture (N)172.50Nominal yield stress ()25.99Extension at high yield (mm)1.54Young modulus ()556.93Nominal fracture stress ()17.08True fracture stress ()70.98Tensile Ductilit y2.72Specimen 3 calculated results when extended at speed of 12.5 mm/min Gauge Length (mm)33.00Initial cross-sectional area ()10.11Fracture length (mm)(242-33) 209.00Thickness at fracture (mm)0.88Width at fracture (mm)2.01Cross-sectional area at Fracture ()1.77Load at yield (N)273.75Load at fracture (N)267.50Nominal yield stress ()27.08Extension at high yield (mm)110.26Young modulus ()8.08Nominal fracture stress ()26.46True fracture stress ()151.13Tensile Ductility6.33Calculations of average cross sectional area specimen 1 Average cross sectional area = Average thickness x Average widthAverage cross sectional area = 2.17 mm x 4.70 mm = 10.20 Calculations of specimen 1 Nominal yield = Nominal yield = = 26.45 Youngs modulus= Youngs modulus= = 566.79 Nominal fracture stress = Nominal fracture stress = = 16.65 True fracture stress = True fracture stress = = 74.56 Tensile ductility = Tensile ductility = = 0.66 mmGraphs Figure 3-Graph of load vs flank for specimen 1- Figure 4-Graph of load vs extension for specimen2- Figure 5- Graph of load vs extension for specimen 3- DiscussionUnsurprisingly when you inspect between the three graphs you can see a slight pattern occur which is that the faster you extend the Polypropylene the quicker it breaks. The graph readings are used to find how overmuch it was extended when broken so that the tensile ductility can be worked out. There have been errors in the graphs because in the laboratory the measured extension of the break was 22mm whereas the zwick tensile testing machine made a graph that showed it to be a lot less around 8mm which is surprising to have such a wide-ranging result. Retrieving most of the results from the graph required a lot of estimation because specimens one and two had scales of 20 and specimen 3 had a scale of 50 these two arent precise enough to get an accurate reading of the graph so a lot of estimation was required.As it can be seen in the results the extension at high yield point was very different for specimen 3 compared to the other specimens, this at first glance could be considered as an unusual person even though this was expected because the less stress that is put on the specimen meant that the extension of the yield would be higher but such a big gap wasnt expected. However, looking at the results of the other groups in the lab it shows that the result is acceptable. The other result that differed in specimen 3 when compared to the other specimens was the load at fracture this is because specimen 3 extended for a much longer distance then the other two so there was much more load at fracture which meant that the fracture stress was much greater too as shown in the results.Also, glass transition temperature had to be controlled so that the polypropylene wasnt too brittle, as temperature is hard to get accurate most of the readings might have differed because of it.Conclusion It can be seen in this test how speed effects the tensile properties of polypropylene , as the results and graphs show that when tension is applied quicker as its done in the first specimen it can take a lot less stress to break the polypropylene compared to the 3rd specimen which took a lot more tension because it expanded much more than the other 2 specimens as seen in figure 6.The results of the test are reliable but improvements could have been made the graph could have a much littler scale which would have made the readings off the graph much easier to obtain. Also, there were assumptions that were made while doing this for example when working out the youngs modulus we had to assume that the line between the origin and the high yield point is linear.Figure- 6Photos of the 3 specimens before and after the test.References Informationhttps//www.creativemechanisms.com/blog/all-about-polypropylene-pp-plastichttp//www.bpf.co.uk/plastipedia/polymers/pp.aspxhttps//en.wikipedia.org/wiki/Tensile_testingImageshttp//www.chemistry.wustl.edu/edudev/Designer/session4.html