Charpy test, impact resistance testing

Methods employed to determine the impact resistance of plastics include pendulum methods (Izod, Charpy, tensile impact, falling dart, Gardner, Dynatup, etc.) and instrumented techniques. In the case of the Izod test, what is measured is the energy required to break a test specimen transversely struck (the test can be done either with the specimen notched or unnotched). The tensile impact test has a bar loaded in tension and the striking force tends to elongate the bar (Chapter 5, Impact Strength). 

Impact resistance is related to impact strength. Two of the most utilized tests are the Izod (ASTM D-256) and Charpy (ASTM D-256) tests illustrated in Figure 14.16. 

Secondary Properties of Candidate Materials. In terms of maximum and minimum use temperatures, we must simply ensure that our final candidate materials meet the use temperature requirements listed in Table 8.10. This design specification is not particularly restrictive, so we will save it for last. The most common measure of impact resistance is using an Izod impact test (cf. Figure 5.79). A similar test is called the Charpy test, a schematic diagram for which is shown in Figure 8.15. We will find relevant impact resistance data for our candidate materials, if available, and ensure that this design criterion is met as well. 

Charpy impact test—a destructive test of impact resistance, consisting of placing the specimen in a horizontal position between two supports then striking the specimen with a pendulum striker swung from a fixed height. The magnitude of the blow is increased until specimen breaks. The result is expressed in in-lb or ft-lb of energy-... 

Nakamura ct al. [68] have used the instrumented Charpy test to examine the effect of silica fillers on epoxy resins, while Wang ct al. [69] have used the same technique for examining RIM parts. An examination of fillers in polypropylene has been reported by Jancar and DiBcncdetto [70]. Trantina and Ochler [71] discuss the application of Charpy (and Izod) tests to the prediction of impact resistance for use in design calculations. Sharpe... 

Liquid chlorine is generally stored in vessels made from non-alloyed carbon steel or cast steel. Fine grain steel, stress-relieved and subjected to Charpy impact tests for low temperature impact resistance [29], is used. Erosion of the protective layer on steel... 

Charpy impact test n. A destructive test (ASTM D 256B) of impact resistance using a centrally notched test specimen 126 mm long and typically 12.7 mm... 

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. 

Standardized notched impact tests such as the Izod and Charpy tests (ASTM, ISO, DIN) are the most commonly used to characterize the impact strength of plastic materials. It is very difficult to use measured data from tests using idealized laboratory specimens to predict impact behavior of end-use polymeric material. The apparent lack of good correlation between measured impact fracture energy and end-use impact resistance is due to the extreme complexity of microscopic fracture processes. In particular, the influence of specimen geometry is sometimes poorly matched with the type of failure mechanism of defects present in the actual molded part subjected to end-use impact forces. 

Widely used impact tests are for rigid materials, hod (ASTM D256) and Charpy (ASTM D256) and for flexible structures, falling dart impact (ASTM D3029) and pendulum impact resistance (ASTM D3420). 

Charpy flexural impact testing showed that the thin section moldings that contained an oriented zone exhibit greater impact resistance than thick section moldings. 

Mechanical properties are critical for many composite applications. The properties of the composites depend on the combination of the properties of the matrix and the reinforcing agent or fiber. The properties of polymer composites reinforced with short fibers depend on such factors as the fiber/ matrix interaction, the orientation and volume fraction of the fiber, the fiber aspect ratio (defined as Lid where L and d correspond to the fiber length and diameter, respectively) (Chawla, 1998) and processing conditions (Thomas and Pothan, 2008). Different tests can be used to evaluate the mechanical properties of the composites, such as tensile, flexural or impact resistance tests (Izod or Charpy tests). 

Charpy Test. An impact test for fracture resistance. A V-notched specimen, fixed at both ends, is struck behind the notch by a pendulum. The energy lost by the pendulum in fracturing the test-piece gives a measure of the impact strength of the material. See fracture toughness... 

Charpy Impact Test n A destructive test (ASTM D 256B) of impact resistance using a centrally notched test specimen 126 mm long and typically 12.7 mm. The specimen is supported horizontally near its ends and struck on the side opposite the notch by a pendulum, having sufficient kinetic energy to break the specimen with one blow. The result is expressed as the quotient of the energy absorbed from the pendulum divided by the specimen width (J/cm or ft-lb/in). 

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