Polymers Charpy impact strength

In some cases, lack of noticeable influence of electron beam radiation on the values of tensile and Charpy impact strengths of 24-23-21-15-17 LDPE-HDPE-PP-PS-PET blends (based on recycled polymers) compatibilized with 1% trimethylol propane trimethylacrylate (TMPTMA) were found. Zenkiewicz et al. ° explained this lack of influence by the protective action of aromatic rings of PS and PET that hindered cross-linking. In the same article, the addition of 10% of styrene-ethylene/butylene-styrene elastomer grafted with maleic anhydride (SEBS-g-MA) led to the great increase of both tensile and Charpy impact strengths. 

Charpy impact strength - data Polymer Solids and Polymer Melts B. Langer, W. Grellmann Table 4.8 Charpy impact strength values (unnotched and notched) of unfilled materials (number in brackets represents the hammer energy used). ... 

Fig. 20.7 Variation of Charpy impact strength versus styrenic polymers wt% incoipraated to r-PVC (Taken from D, Garcia, R. Balart, J.E. Crespo, J. Juan Lopez, Mechanical properties of recycled PVC blends with styrenic polymers, J. Appl. Polym. Sci. 101, 2464 (2006) Fig. 7. Copyright 2000 John Wiley Sons, Inc. Reproduced with permission)...

Figure 1 Charpy impact strengths (23°C) for HOPE blends containing minor proportions of PP, LDPE, HIPS, PVC and PET. After Hope, P.S., Bonner, J.G. and Miles, A.F. (1994) Polymer Blends and Alloys, Blackie Academic and Professional.

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. 

Figure 8.20. Charpy notched impact strength of calcium carbonate filled polypropylene. [Adapted, by permission, from Jancar J, Dibenedetto A T, Dianselmo A, Polym. Engng. Sci., 33, No.9, 1993, 559-63.]...

For polymer sheets, the notched Izod impact strength is often reported (ASTM D256). In this test, as well as the Charpy impact test in the same ASTM standard, the polymer sample is subjected to an impact from a falling hammer, and the... 

The most frequently applied impact tests are shown in Fig. 24.17 A and B. A pendulum (shown as a filled arrow) falls from a certain height the loss in the potential energy of the pendulum is assumed equal (with a correction for losses such as friction) to the energy Uo absorbed by the specimen see Eq. (24.1). The Charpy test is described by the ASTM D 256 standard method B, the Izod test by the same standard method A. We see (Fig. 24.17 A) that in the Charpy test there is a symmetry with respect to the center of the specimen. By contrast, in the Izod test (Fig. 24.17 B) the bottom half of the specimen remains untouched while the top part is broken off. We—and more and more laboratories around the world— perform now both tests with a sensor installed on the pendulum and connected to a computer. Thus, not only a single value of the energy but a whole curve is obtained. For convenience single values of impact strength (IS) for a number of polymers are listed in Tables at the end of this chapter. 

Vincent [110] and others have recognized that the impact strength depends on the geometry of the notch, which led Fraser and Ward [111] to propose that for comparatively blunt notches (i.e. those not introduced by a razor blade or a sharp cutting tool) failure occurs when the stress at the root of the notch reaches a critical value. This stress, which in a glassy polymer marks the stress required to initiate a craze, can be calculated by assuming that the deformation is elastic. On this hypothesis, the Charpy test, as undertaken in... 

Janick and Kroliskowski [40] investigated the effect of Charpy notched impact strength on the flexural modulus of polyethylene and polyethylene terephthalate. Polymers with good flexural modulus include polydiallylisophthalate (11.3 GPa), phenol-formaldehyde (6.5 GPa), alkyd resins (8.6 GPa), and polyphenylene sulfide (13.8 GPa), as well as glass-filled polyester laminate (16 GPa) epoxy resins (3-3.5 GPa), sUica-fiUed epoxies (15 GPa), and acetals containing 30% carbon fiber (17.2 GPa). 

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. 

The impact performance of unreinforced polymers is very difficult to quantify. The impact strength is usually determined in an Izod or Charpy test. Different impact tests on the same material (Figure 6.2) do not give the same numerical result and the designer has to choose the test and test data most appropriate to that encountered in service. In addition results will depend on the temperature and possibly on the presence or otherwise of a notch and its radius of curvature, the moisture content of the material, the overall dimensions of the specimen, the molecular weight of the polymer, the presence of additives, etc. At room temperature some thermoplastics, e.g. polypropylene, polyamide and polysulphone, are brittle if suitably notched, while wet polyamide is not so and is said to be tough. 

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