中文3100字,2000单词，10500英文字符出处：Sahin S, Yayla P. Effects of processing parameters on the mechanical properties of polypropylene random copolymer[J]. Polymer Testing, 2005, 24(8):1012-1021.本科生毕业设计（论文）外文译文学院专业导师学生学号Effect of testing parameters on the mechanical propertiesofpolypropylene random copolymerSenol Sahin, Pasa Yayla*Mechanical Engineering Department, Engineering Faculty, Kocaeli University, 41040 Kocaeli, Turkey Received 24 January 2005; accepted 2 March 2005 Abstract:The effects of temperature on the impact resistance and hardness of polypropylene random copolymer are studied for a wide range of temperatures. The variations in the mechanical properties with a wide range of strain rates are also evaluated. Finally, the variations in mechanical properties as a function of time after production are studied. Keywords: Polypropylene random copolymer; Mechanical properties; Storage time; Strain rate1. IntroductionThere is a vast literature on processing, morphology, testing and ultraviolet (UV) degradation of polypropylene(PP) [1–3]. However, the literature lacks results on the effects of storage time, outdoor ageing time and the addition of different master batches at different ratios on the mechanical properties. This may be connected to the fact that those investigations are very rigorous and time-consuming. For these reasons, the aim of this paper is to study the influence of testing parameters on the mechanical and thermal properties of injection moulded polypropylene random copolymer(PP-R) samples with different storage times.2. Experiments2.1. MaterialsThe polymer used in this study is a natural colour PP-R, produced by Borealis s. a, trade name RA 130E, and supplied in granular form. The properties of the polymer are given in Table 1.2.2. Specimen preparationA specially designed injection mould was used to produce test samples. The configuration of the moulded test samples is depicted in Fig. 1.All the test samples were injection moulded on a ERATFE 130/95 injection moulding machine. Table 2 shows the specification, set parameters of the machine and the moulding conditions. Unless otherwise mentioned, before testing all the samples were conditioned at room temperature for a period of 30 days.2.3. Tensile testsThe tensile test samples were dumbbell-shaped with dimensions of 156*1014 mm, complying with ISO 527-1 (1993) standard. Tensile tests at various speeds were carried out on the samples. A Z wick Z10, screw-driven universal tensile/compression testing machine equipped with a data acquisition system , was utilised to carry out the tensile tests. Unless otherwise mentioned, a 50 mm/min test speed was used. For strain rate effect investigation, a wide range of speeds from 1 to 1000 mm/min were used. An extensometer was utilised to determine the elastic modules. Tests were carried out at a temperature of 23 8C. From at least threeTable 1Typical properties of polymer used in this studyspecimens for each test series, average values for yield stress（Y）, tensile strength（Mpa）, elastic modulus（E）, strain-to yield（Y）, and strain-to-break, 3B, were deduced using the testing program of the controlling computer2.4. Charpy impact testsImpact fracture energy is an important parameter characterizing toughness of materials. Impact values represent the total ability of the material to absorb impact energy, which is composed of two parts: (a) the energy required to break bonds, and (b) the energy consumed in deforming a certain volume of the material. With conventional impact testing equipment (without instrumentation), it is practically impossible to measure separately these two parts. Instrumented impact testing provides valuable information on energies involved in the fracture process, giving individual evaluation of energy for crack initiation and energy required to propagate the crack through the material, which is not possible with the conventional Charpy impact test. In many materials, the formation of the crack at the notch root occurs just prior to or at the peak load. Therefore, it is a reasonable approximation to define the energy up to the peak load as the ‘crack initiation resistance’ [4]. Similarly, post-peak energy is also defined as the ‘crack propagation resistance’ of the material. For many industrial applications, the temperature dependence of impact strength is very interesting and has attracted considerable attention, not only from industry, but also from academic circles [5].The geometry of the Charpy impact test samples was rectangular with dimensions of 80!10!4 mm, conforming to the ISO 179/1eA (2000) standard. A single-edge 458 V-shaped notch (tip radius 0.25 mm, depth 2 mm) was milled in the bars with a fly-cutter using a milling machine.A series of Charpy impact tests were carried out for a wide range of temperatures according to ISO 179/1eU (2000). For setting the test temperature, a mixture of liquid nitrogen and acetone at different ratios was used. The test samples were kept in the cooling medium for at least 30 min before testing.The Charpy impact tests of the notched specimens were conducted at a wide range of temperatures ranging from K 75 to 85 8C, employing a creast Instrumented Charpy Impact Tester (Code 6545/000) at an impact speed of 2.93 m/s. The Charpy impact energy evaluation was based on the linear elastic fracture mechanics (LEFM) analysis to determine impact strength of materials as proposed by Plati and Williams [6]. Charpy impact energy Cv is given bywhere U is the absorbed energy by the sample, B and D are the width and thickness of the samples, respectively, and F is the sample geometry-dependent calibration factor. Bearing in mind the advantages of instrumented Charpy impact tests, both the crack initiation energy, which is consumed up to the maximum force, and the total impact energy, which is the conventional Charpy impact energy, dissipated during whole impact process, were calculated.2.5. Hardness testHardness is defined as the resistance of a material to deformation, particularly permanent deformation,Table 2Specification and set parameters of the injection moulding machine used in this studyindentation or scratching. In general, the most widely used methods to measure hardness are Rockwell and Shore. The Rockwell method is usually used for harder materials , The Shore (or Durometer) method, regulated by ISO 868 (2003), has scales for both softer rubbers and plastics.In this work, Shore D hardness tests were performed at different temperatures using a Z wick 3100 Shore D Durometer hardness tester. All results are the average of three measurements.3. Results and discussion3.1. Tensile testsThe tensile behaviour and ultimate mechanical properties are very importantcharacteristics of semi-crystalline polymers. These macroscopic properties are known to very closely depend on the strain rate, thus an understanding of strain rate dependence of their deformation behaviour is important for encouraging their wide use in engineering and structural applications [7]. Strain rate has a complicated and dramatic effect on materials deformation processes because the energy expended during plastic deformation is largely dissipated as heat. This process was observed to be more prominent at higher loading rates that are associated with adiabatic drawing than during lower loading rates where isothermal drawing occurred [8]. In general, three stages of plastic deformation were suggested in tensile tests of semicrystalline polymers [9,10]: (1) pre-neck deformation of micro-spherulitic structure that proceeds in the wholesample, (2) large deformation in the neck, which transforms the micro-spherulitic structure to fibrillar structure, and lastly (3) post-neck deformation of the fibrillar structure. In general, in the neck, the polymeric material softens drastically for a very short period, which is associated with a decrease of plastic modulus. However, as the neck develops and exceeds a limiting zone, the morphology changes to that of a fibrillar structure with increase in plastic modulus, termed as strain-hardening.Typical stress–strain curves of the PP-R samples tested at different crosshead speeds are given in Fig. 2. The test samples were not broken at 600% elongation at crosshead speeds up to 25 mm/min, but for the higher test speeds, the samples were ruptured at lower % elongation and had a value of about 38% at crosshead speed of 1000 mm/min. At lower test speeds, the PP-R samples formed a very marked and stable neck with a wide stress-whitening zone; as the test proceeded, the necked zone extended throughout the whole test gauge to the point of rupture at very large deformation values. At this stage, due to strain-hardening there was a gradual increase in the stress as the test proceeded up to rupture. As the test speed increased, the stress-whitening zone narrowed and, at very high crosshead speeds, the remainder of the gauge length was not plastically deformed.The effec ts of cross head speeds on the variations in‘yield stress’, ‘yield strain’ and ‘elastic modulus’ are given in Figs. 3–5, respectively. The behaviour of these properties with log(crosshead speed) was linear and suggested that, like other semi-crystalline polymers, the mechanical properties of PP-R is also very strain rate-sensitive. It has been pointed out that the slope in these figures might vary from one semi-crystalline material to another and could be a good indication to define the strain rate dependency of material [11].3.2. Impact testsThe effect of temperature on the variation of force–time signal obtained from instrumented Charpy impact tests were depicted in Fig. 6, showing remarkable change in nature of the force–time signal as the temperature changes. Fig. 6 shows that up to about 25℃, almost all of the energy isconsumed at crack initiation stage, and the energy consumed during crack propagation stage becomes visible for temperatures above 50℃. At temperatures above 75℃, the specimens were partly fractured, while below this temperature they were completely fractured.The variation of Charpy impact energy with temperature is given in Fig. 7, giving relatively constant impact strength between K75 and 0℃.and then the impact strength rapidly increases with increasing temperature. After 90℃, it becomes impossible to break the sample into two. The phenomenon of characteristic brittle–ductile transition starts after 0℃, indicating the fact that the impact strength deteriorates dramatically as the temperature approaches from higher values to 0℃. These results are practically important from two points of view. First, in practical applications, pipes made from PP-R could be used down to water freezing temperatures, and secondly, transportation and installation of the pipe at lower temperatures are possible. Thus, these two important points require particularattention as the pipes get rather fracture-sensitive at lower temperatures.The Charpy crack initiation and crack propagation fracture resistance evaluation are given in Fig. 8. The figure shows that up to the lower transition temperature of 0℃, about 90% of impact energy is consumed to initiate fracture, but the trend changes as the test temperature increases,implying that crack propagation energy is higher than the crack initiation energies for temperatures above 50℃. For higher temperatures, the crack initiation consumes only about 35% of the total impact energy.4. ConclusionsThis paper outlines experimental results from tensile tests at different crosshead speeds and instrumented Charpy impact tests on notched samples of polypropylene random copolymer over a wide range of temperatures. Special attention was focused on the changes in the tensile properties over a long period of storage after injection. Regarding the effects of on the mechanical properties of polypropylene random copolymer, the following conclusions could be drawn:(1) The tensile properties of the materials are fairly rate sensitive. The properties such as the yield stress, elastic modulus and yield strain of the material increase with strain rate. The variations of these properties with log (crosshead speed) were linear and it is envisaged that the slope in these figures might very from one semi-crystalline material to another and could be a good indicator to define the strain rate dependency of semi-crystalline polymeric materials.(2) The Charpy impact crack initiation and propagation resistances of the material are rather sensitive to the test temperature. For lower temperatures of up to 0℃, relativelybrittle behaviour has been observed. The effect of an increase in temperature becomes visible after 0 and above 85℃the material becomes too ductile to break.(3) The Shore D hardness of the natural PP-R material is diminished with increasing temperature. The decrease in hardness becomes more remarkable after the lower transition temperature of 0℃.5 References[1] E.P. Moore (Ed.), Polypropylene Handbook: Polymerisation, Characterisation, Properties, Applications, Hanser/Gardner, New York, 1996, p. 113.[2] J. Karger-Kocsis (Ed.), Polypropylene—An A–Z Reference, Kluwer, Dordrecht, 1999.[3] J. Karger-Kocsis, Polypropylene: Structure and Morphology, Chapman & Hall, London, 1995.[4] M.P. Manahan Sr., C.A. Cruz Jr., H.E. Yohn, Instrumented impact testing of plastics in limitation of test methods for plastics, in: J.S. Peraro (Ed.), ASTM STP 1390, American Society for Testing and Materials, West Conshohocken, PA, 2000.[5] P.S. Leevers, P. Yayla, M.A. Wheel, Charpy and dynamic fracture testing for rapid crack propagation in polyethylene pipe, Plast. Rubber Compos. Process. Appl. 17 (1992) 247–253.[6] E. Plati, J.G. Williams, Determination of the fracture parameters of polymers in impacts, Polym. Eng. Sci. 15 (1975) 470–477.[7] R. Gensler, C.J.G. Plummer, C. Grein, H.-H. Kausch, Influence of the loading rate on the fracture resistance of isotactic polypropylene and impact modified isotactic polypropylene, Polymer 41 (10) (2000) 3809–3819.[8] A. Dasari, R.D.K. Misra, On the strain rate sensitivity of high density polyethylene and polypropylene, Mater. Sci. Eng. A 358 (2003) 357–371.[9] A.J. Peterlin, Molecular model of drawing polyethylene and polypropylene, J. Mater. Sci. 6 (6) (1971) 490.[10] A. Dasari, S.J. Duncan, R.D.K. Misra, Atomic force microscopy of scratch damage in polypropylene, Mater. Sci. Technol. 18 (10) (2002) 1227–1234.[11] J. Fiebig, M. Gahleitner, C. Paulik, J. Wolfschwenger, Ageing of polypropylene: processes and consequences, Polym. Test. 18 (1999) 257–266.1无规共聚聚丙烯在不同试验参数下对其机械性能的影响Senol Sahin, Pasa Yayla*（科贾埃利大学工学系机械工程系，科贾埃利 41040 土耳其日期2005年1月24日，接受2005年3月2日）摘要：研究一定温度范围内温度对无规共聚聚丙烯（PP-R）的抗冲击性能和硬度的影响；研究了材料的拉伸性能与应变率的关系，在很宽的应变率范围内其多项力学性能受应变率的影响较大；最后研究了PP-R成型后的储存时间与其机械性能的关系。
