Since the 1950s, plastics have become a major industry – one that affects all aspects of our lives – providing improved packaging, creating new textiles, and permitting the production of new products and cutting-edge technologies. Due in part to its unique capability to be manufactured to meet very specific, functional needs, plastic is the most used material in the world. Its versatility allows it and its composites to be used in everything from car parts to doll parts; from drink bottles to the refrigerators they are stored in.
Increased demand has resulted in the need for more demanding acceptance criteria with respect to the mechanical and chemical properties of plastic materials. 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 than 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 resins used are filled or unfilled; color additives; and forming processes all affect the strength and durability of not only the end material but the end product as well. Testing per ASTM D3763 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 Instron 9450 with optional High Energy system, instrumented with a 22 kN loas cell, a ½-inch (12.7 mm) hemispherical tup insert, Data Acquisition System (DAS) with touch screen dashboard and Bluehill Impact software, along with a pneumatic clamping fixture designed in accordance to ASTM D3763. Impact velocity was set at 3.3 m/s and 4.4 m/s. Time range for data acquisition was set to 30 milliseconds. ASTM D3763 states that the specimen shall be centered and clamped between the two plates of the support fixture in such a way as to provide uniform clamping pressure to prevent slippage during testing. The available energy used for the test should be such 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 slowdown is less than 20%.
These tests should be conducted under the standard laboratory atmosphere of 23(± 2) degrees Celsius, 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.
If the throughput and resources optimization is a concern, the Instron 9450 can also be equipped with smart solutions to test up to 30 specimens fully unmanned or up to 10 specimens with a limited user effort and up to 50% saving in term of cycle time and nitrogen liquid consumption.
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.