Increased demand has resulted in the need for more demanding acceptance criteria with respect to the mechanical and chemical properties of plastics. Due to some of the new structural uses of these materials, it is essential to know how they will behave when subjected to dynamic conditions – i.e. impacts. Dynamic failures of materials are different then those found when testing at slower, steadier speeds. This is especially true of plastics where many variables can affect the material – the way the polymers are used to make a specific material form/lie in the material; whether the resins used are filled or unfilled; addition of color additives; forming processes all affect the strength and durability of not only the end material but the end product as well. Testing per ISO 6603-2 allows both the material engineer and the design engineer to test materials for desired properties such as strength, ductility, toughness and energy absorption.
For this test, we used a CEAST 9350 with High Energy option, instrumented with a 15.6kN tup, 20 mm hemispherical tup insert, DAS (Data Acquisition system) and Visual Impact software were used to perform this testing. We also used our pneumatic clamping system with 40 mm diameter adapter plates designed in accordance to this standard. Impact mass was 20 kg and the velocity was set at 4.4 m/s, time range for data acquisition was set to 30 milliseconds.
ISO 6603-2 states that the specimens may be left unclamped. However, it is noted that the test results obtained for clamped and unclamped specimens may be different due to the freedom of movement that the specimen has away from the impact point. The free movement of the edges may cause vibrations with higher amplitudes in the data. To minimize the adverse effects of friction that occurs between the tup insert and the specimen, the standard calls for the application of a lubricant, such as Vaseline, on the striker tip. The test values obtained with the lubricated striker are lower than the unequivocal lower limits of the tested mechanical properties of the material. The available energy used for the test shall be such so that the velocity slowdown is no more than 20% from the beginning of the test to the point of peak (maximum) load. It has been noted that when the available impact energy is at least three times more than the energy at peak load, the velocity slow down is less than 20%.
Tests are to be conducted under the standard laboratory atmosphere of 23 ± 2 degrees C, and 50% relative humidity. By changing the conditioning and testing temperature, and testing in a controlled manner at any given impact velocity, the temperature at which the material transitions from a ductile to brittle failure mode can be established for most plastics.
This test configuration is well suited for determining the performance characteristics of plastic materials under impact conditions. Both plastic suppliers and their customers may use test results to verify product performance. Environmental chamber use allows both parties to get an understanding of how the material may perform in colder or warmer applications.