Pendulum impact tests limitation

Tensile Impact Test (ASTM D1822). The tensile impact strength test was developed to overcome the deficiencies of flexural (Izod and Charpy) impact tests. The test variables, such as notch sensitivity, toss factor, and specimen thickness, are eliminated in the tensile impact test. Unlike Izod-Charpy-type pendulum impact tests, which are limited to thick specimens only, the tensile impact test allows the user to determine the impact strength of very thin and flexible specimens. Many other characteristics of polymeric materials, such as the anisotropy and the orientation effect, can be studied through the use of the tensile impact test. 

The tensile impact test is carried for un-notched samples in a test setup where one end of the specimen is mounted in the pendulum and other end is gripped by a crosshead member which travels with the pendulum until the instant of impact. The tensile force is exerted by the pendulum. The advantage of the tensile impact test over Izod or Charpy tests is that thinner and ductile samples can also be tested by the tensile impact test, whereas Charpy/Izod tests are limited to only thicker and rigid samples. 

All impact tests suffer from some weaknesses. Izod impact sums all the energy required to break the specimen, including those to bend, draw, and tear resin and fibers. Other notched specimen pendulum tests such as the Charpy test also suffer from most of the same limitations. Tensile impact tests which use unnotched specimens are considered only slightly better ... 

Impact properties-Impact behavior, especially ASTM D256 Pendulum Impact Resistance) is one of the more commonly reported "primary" physical properties. The limited data generated poses serious problems. How was the material molded, which section of the test bar specimen was tested (gate, mid-, or dead end), how was it notched (and at what cutting wheel tpm and sled feed rate), and how many hours after notching was the specimen impacted When was the last time you saw this information on a data sheet or in a product bulletin ... 

Besides strength and stiffness, impact properties of a material are of great practical relevance. Here the time scale of loading is in the order of milliseconds, while strength properties are tested in seconds or even minutes. Therefore, elongation from tensile experiments, which is often used as a measure of ductility, can oidy be of limited interest and standard impact experiments, like Izod or Charpy pendulum methods, have been developed. 

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