Impact testing may be classified according to the energy imparted to the impactor prior to contact with the material. Low energy studies are performed using a pendulum geometry, whereas higher energy failures are evaluated using falling weight apparatus. The impact properties of a material are strongly dependent on test geometry (notch radius and position), temperature, impact speed and the condition of the sample (surface defects). Therefore, in an attempt to unify these variables, measurements are often made in accordance with one of the testing standards.

The impact strength of PEEK polymer materials was evaluated using the Charpy test protocol (ISO 179, 0.25 mm notch radius) and is shown at various temperatures in Figure 15.

The data in Figure 15 show that there is little reduction in the impact properties of these materials at sub-ambient temperatures. All PEEK polymer samples tested above 212°F (100°C) could not be broken using the forces and pendulum distances specified in the test standard.

Comparative studies of the impact strengths of some high performance materials are shown in Figures 16 and 17 (ASTM D256).

The bar chart shown in Figure 16 allows comparisons to be made between PEEK polymer materials and other high performance compounds. Natural 450G polymer has the highest unnotched impact strength and remains unbroken under the Izod test conditions.

Figure 17 shows the effects on the impact strength of notching various materials. The geometry of the notch has been shown to be critical to the measured impact strength. Therefore, in component design, molded notches or acute angles should be avoided.

Instrumented falling weight techniques are used to evaluate higher energy impacts by monitoring the forces and displacements required to destructively test a sample.

Figure 18 shows the energy to failure of PEEK polymer and compound versus temperature to failure.

Information reprinted with permission from Victrex PLC