What is a Tensile pendulum impact test?

A test method for determining energy required to fracture a specimen under shock tensile loading. Typically executed on a pendulum testing machine, the tensile impact strength test was originally developed to overcome the deficiencies of flexural (both Izod and Charpy) impact test. All the test variables that have a high effect on the results, such as notch sensitivity, toss factor and specimen thickness, are eliminated in the tensile impact test. This test, on the contrary of Izod and Charpy types, which are limited to thick specimen only, allows to determine the impact strength of very thin and flexible specimens.

How is a Tensile pendulum impact test performed?

There are two different test configurations. One consists in a specimen-in-head kind of setup (ISO 8256 method B), where the specimen is attached directly to the pendulum hammer. The energy to break by impact is determined by the kinetic energy value extracted by the pendulum in the process of breaking the specimen. The test setup requires to mount one end of the specimen on the hammer and the other end has to be gripped inside a crosshead member, which travels together with the pendulum until the impact instant. As long as the machine bas is rigid enough to prevent vibrations, the energy lost by the bounce of the crosshead in the opposite direction can be easily calculated.

The second test configuration is a specimen-in-base setup (ISO 8256 method A). The specimen is clamped in a specimen vice supported by the frame of the pendulum and it is broken by the impact between pendulum and crosshead member, which is always clamped on the other extremity of the specimen.

The following figure illustrates the most common specimen-in-base impact configuration.
Hammer energies are available from 0.5 - 50 J (0.37 - 36.9 ft-lbs) depending on the type of the test and impact velocities of 2.9 m/s and 3.8 m/s. The tensile impact test introduces strain rate as an important test variable and many researchers have demonstrated that the tensile impact test results correlate better with the actual field failures than Izod or Charpy impact test analysis.