Impact testing of polymers

The ability of a component to withstand a sudden impact is obviously of great importance for any practical application of the material. The impact testing of polymers is therefore equally important. By using standardised techniques it is fairly straightforward to obtain results that allow the comparison of one type of polymer with another, but it is less easy to obtain fundamental data. 

1 flexed-beam impact tests 1 falling weight impact tests 

Charpy impact test r 1 Izod impact test 1 falling dart impact test 

1 blunt notdi test 1 sharp notch test  

In the falling-dart test a circular sample of polymer is supported horizontally and a pointed steel dart is allowed to fall so that it strikes the centre of the disc. The standard dimensions for this test are radius of test disc 6 cm, thickness of disc 2 mm and radius of dart tip 1 mm. The disc is supported horizontally by an annulus of 4 cm aperture to which it is clamped by a second annulus. The behaviour of the sample can be studied under a variety of dilferent degrees of severity of impact simply by varying the height from which the dart is allowed to fall. 

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Inverse Methodfor the Analysis of Instrumented Impact Tests of Polymers... 

The ability of a structural part to maintain its integrity and to absorb a sudden impact is often a relevant issue when selecting a suitable material. Impact testing of polymers is thus a subject of some importance and is extensively employed, although many of the results obtained are of an empirical and hence comparative... 

In view of the technical relevance the impact resistance of polymers has been intensively investigated. The cited references [88—103] may serve as an introduction into the large body of literature. Vincent [88] and Bucknall et al. [89] give a general survey of the impact testing of polymers. Other references concern the molecular aspects [88-96], instrumentation [97—100], and particle impact [101—103]. The extensive literature on the fracture mechanical analysis of impact bending tests will be referenced in Chapter 9. 

We test the impact resistance of polymer plaques using the configuration shown in Fig. 8.8. We subject circular injection molded plaques to the shock of a falling weight with a hemispherical impacter. This test is also known as the Dart Drop Test . Samples can fail in a brittle or a ductile manner. Brittle samples often shatter. Ductile samples can split or a small disk may be punched out of their center. This test provides results that are analogous to those obtained from un-notched impact beam testing. 

Impact strength (impact resistance), 10 177 of polycarbonates, 19 810-811 of styrene-based plastics, 23 362-363 Impact testing, 19 580 Impact tests, for polymer blends, 20 352... 

Since several different wear characteristics were noted for the materials tested (e.g.y charring, flow, and brittle behavior), it can be inferred that there is no unique mechanism associated with impact wear of polymer thin films. Further, because of this aspect and the probability that the same mechanisms do not occur under impact testing conditions (Charpy and Izod), it is reasonable to infer that there is little correlation between impact wear resistance and impact strength. This latter point may be illustrated by considering polycarbonate. Even though it has the highest impact strength of any unfilled polymer (4), it exhibits the poorest wear behavior in this study. 

Method of test for impact resistance of polymer-modified mortar... 

Aretxabaleta L., Aurrekoetxea J., Urrutibeascoa I. Sanchez-Soto M. (2005) Characterisation of the impact behaviour of polymer thermoplastics. Polymer Testing, Vol.24, pp.l45-151. 

Nak Nakamura, Y., Yamaguchi, M., Okubo, M. Instrumented Charpy impact test of epoxy resin filled with irregular-shaped silica particles. Polym. Eng. Sci. 33 (1993) 279-284. 

Dijkstra, K., Laak, J., and Caymans, R. J. 1994. Nylon-6/rubber blends 6. Notched tensile impact testing of nylon-6/(ethylene- propylene rubber) blends. Polymer 35 315-322. 

J Jancar, A DLAnsehno, AT DiBenedetto, J Kucera. Polymer 34 1684-1694, 1993. SK Gaggar. Instrumented Impact Testing of Plastics and Composite Materials. S Kessler, GC Adams, SB DriscoU, DR Ireland, eds., ASTM STP 936, Philadelphia American Society for Metals, 1987. 

Manufacturers handbooks give data on tensile and flexural yield or fracture stress, tensile elongation at break, notched Charpy or Izod impact strength, and fatigue life. Whilst these data are useful for materials selection, they are not always sufficient for quantitative design. To date, fracture mechanics has been used to only a limited extent in design with plastics, and data are not provided in data books. The lack of approved standards for testing of polymers is currently a major obstacle to the wider use of fracture mechanics. 

Kozlov, G. V., Novikov, V. U. (1997). The Physical Significance of Dissipation Processes in Impact Tests of Semicrystalline Polymers Prikladnaya Fizika, 7,77-84. 

FIGURE 7.1 The dependence of local overloading coefficient (the Eq. (7.3)) on fractal dimension of chain part between clusters for 10 pol5aners, pointed out in Table 7.1. 1 - results of impact tests of HOPE samples with sharp notch, where figures indicated notch length in mm. In insertion the dependence is shown for the same 10 polymers [9]... 

Kozlov, G. V., Novikov, V. U. (1997). The Physical Significance of Dissipation Processes in Impact Tests of Semicrystalline Polymers. Prikladnaya Fizika, 1,77-84. Kozlov, G. V., Serdyuk, V. D., Beloshenko, V. A. (1994). Plastic Constraint Factor and Mechanical Properties of High Density Polyethylene at Impact Loading. Mekhanika... 

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