Charpy tester

Impact resistance n. ( ) Ability of a coating to resist a sudden blow. Ability to resist deformation from impact. (2) The relative durability of plastics article to fracture under stresses apphed at high speeds. A widely used ASTM impact test, www.astm.org, employs the Izod pendulum striker swung from a fixed height to strike a specimen in the form of a notched bar mounted vertically as a cantilever beam. The Charpy tester, an alternative in D 256, uses a specimen in the form of a horizontal beam supported at both ends. ASTM lists some several different impact tests for plastics and plastics products. 

ASTM E 23-66 was applied for the dimensions of standard specimens except that the mat reinforced specimen (GC 33 wt % ) used ASTM D 256-56. Specimens were taken from a molded plate along the longitudinal fiber direction, and V notches were cut edgewise, perpendicular to both fiber direction and molding surface. Occasionally a specimen notched on the molding surface (flatwise) was used. Tests were performed with an instrumented Charpy impact tester (10) with a 30 kg-m or 150 kg-cm capacity. Test temperatures were varied from — 196°-250°C. 

Figure 8.12 shows the principal types of test. In the Charpy test a beam of the polymer is held at each end and is struck at its centre by a hammer with one or two knife edges, giving a three- or four-point impulsive bending stress, respectively. Figure 8.13 shows a diagram of a standard Charpy impact tester. In the Izod test the specimen is held at one end and struck at the other. For either test a notch is cut in the sample at the point where it is to break and the sample is placed in the tester with the notch pointing away... 

Fig. 8.13 The Charpy impact test (a) the pendulum tester, ASTM 256 and (b) the sample and striking hammer tip. ((a) Reprinted and (b) adapted, with permission from the American Society for Testing and Materials.)...

This section will examine some of the characteristic features of IPN s from a physical and mechanical point of view. Emphasis will be on relating the glass transition behavior to corresponding aspects of morphology. The principal instrumentation employed in the studies discussed here includes a torsional tester for creep-type studies (Section 8.3.1) and a fixed-frequency vibrating unit for dynamic mechanical spectroscopy (see Section 8.3.2). In addition, stress-strain, tensile, and Charpy impact strength values will be briefly discussed. 

Notch sensitivity n. The extent to which a material s tendency to fracture under load, particularly an impact load, is increased by the presence of a surface in homogeneity such as a notch or sharp inside corner, a sudden change in section thickness, a crack, or a scratch. Low notch sensitivity is usually associated with ductility, while brittle materials exhibit higher notch sensitivity. Most engineers and physical testers consider the notched Izod and Charpy impact tests to be as much measures of notch sensitivity as they are of pure impact strength. 

Figure6.3 Photographs of impact test equipment, (a) JMI Monitor/ImpactTester (Courtesy Thermofil, Inc.), (b) Mitsubishi Kasei Auto Impact Tester (Courtesy Thermofil, Inc.), (c) Dynatup Instrumented Multiaxial Tester (Courtesy Thermofil, Inc.), (d) Manual Charpy Impact Tester (Courtesy Thermofil Polymers, Havant, UK).

Flexural experiments were carried out in three-point loading geometry with inner span being 20 mm, and crosshead speed 1 mm/min. The impact fracture tests were conducted in a Zwick impact tester using Charpy specimens 4x10x50 mm. They contained razor-sharp initial cracks of 1,2,3,4 and 5 mm in the depth direction. The impact fracture toughness (G ) was obtained using the equation of Plati and Williams [7]. 

In the Charpy impact tester the specimen is mounted on a span support and struck centrally with a swinging pendulum (see Fig. 2). The results are expressed in terms of breaking energy per nnit of cross-sectional area. 

Figure 12.33 (a) Schematic drawing of a Charpy impact tester, (b) The notched Charpy... 

Figure 3-78. A schematic of a Charpy impact tester. The specimen is supported as a horizontal simple beam, per ASTM D 256. 

The phase morphology of the blends was characterized by the optical (Zeiss Amplival pol) and scanning electron microscopy (SEM JEOL JSM 35C). The mechanical properties were measured using tensile (Zwick tensile tester 1464) and Charpy impact testers (Zwick impact tester 5102). 

The most common impact tester is a pendulum. A pendulum tester is divided into a beam (Charpy) type and a cantilever beam (Izod) type according to the way the sample sets. Samples either can have a gap or be without a gap. 

A Physmet SB-750 tester was used for slow-bend tests with crosshead speed of 2.5 mm/min (0.1 inTmin) and load deflection curves were recorded along with energy veilues. Precracked Charpy specimens with notch roots approximately 1.5 mm (0.060 in.) de were used. 

Figure 13.38 (a) Schematic drawing of a Charpy impact tester, (b) The notched Charpy impact specimen. (Reproduced with permission from Fasce, L, Bernal, C., Frontini, R et al. (2001) On the impact essential work of fracture of ductile polymers. Polym. Eng. Sci., 41, 1. Copyright (2001) John Wiley Sons, Ltd.)... 

The bulk fracture surface may come from one of three general sources deformation of the sample in a standard mechanical testing device, such as a tensile tester (e.g., Instron, Norwood MA), an impact testing machine (e.g., Charpy or Izod), or a tear tester deformation by frac-... 

The mechanical properties of the composite sheets made in laboratory are tested according to ASTM methods. The impact strength, however, was measured at -20 C using Charpy impact tester. All these test results simulate the properties of end product. Besides physical and mechanical properties the chemical characteristics of modified and unmodified composites can be very well correlated from Infrared spectroscopy and ESCA analyses data. 

Impact strength is usually only determined for plastics and hard elastomer compounds (i.e., those in the D durometer hardness range), where the impact resistance of the material in actual service is important. Soft elastomer compounds will bend, not break, on impact unless they have been cooled below their brittleness temperature. Several types of impact testers and test methods are available. Basically, they all measure the energy required to break a test specimen in a single sharp blow, and can be performed over a temperature range from -70 to +120°C (-94 to +248°F). The most widely used tests are Izod Impact and Charpy Impact both procedures are given in ASTM D-256. 

Ultimate strength Yielding Toughness Weibull distribution Stress concentration Trousers tear Simple shear test Energy to cause rupture Impact tester Izod test Charpy test... 

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