Pendulum Test According to ASTM D256
Written by Francesca Pinto
Written by Francesca Pinto
ASTM D256 is a common pendulum impact testing standard for determining the impact resistance and the notch sensitivity in plastics.
In Test Methods A, C and D, the notch produces a stress concentration that increases the probability of a brittle, rather than a ductile, fracture.
With the increasing use of high performance engineered plastics, PEEK is likely to be the key alternative material to glass, steel, aluminum, and other polymers. Its strength and durability make it highly accepted for a wide range of applications (automotive, biomedical and more) that require a resistance to relatively high temperatures and aggressive environments while keeping excellent mechanical properties.
3D-printed PEEK materials are nowadays of great interests to the additive manufacturing research community for their flexibility in making parts especially for complex structures and for low-volume production or special designs.
There are many factors to consider in 3D printing: there can be a wide variance of mechanical properties including impact strength (after annealing).
3D printing PEEK presents an apparent thermal deformation during the printing process and the layer bonding is not as good as other 3D printing plastics.
There are few researches about the impact strength evaluation aimed to understand the ability of the material to withstand against impact load. Extensive testing and heat treatment process deserve further studies to confirm the properties of the material and ensure that print parts are optimized.
Instron testing equipment can help validate the testing results. A 9050 pendulum can perform a range of accurate Izod and Charpy impact tests to measure the impact strength of 3D-printed PEEK.
In addition to this the linear knife cutting technique of Instron notching machines ensures that notched specimens do not overheat and do not develop internal stresses affecting subsequent testing results. This solution allows users to compare results between 3D-printed PEEK specimens and specimens notched after molding.
The testing procedure complies with ASTM standards so the operator can easily master it. The Instron pendulum impact test is well designed and convenient for testing. The 9050 pendulum consists of a monolithic metal structure of remarkable rigidity. Testing components are readily interchangeable with different sizes of hammer and specimen supports. The operation is simple and the machine interface is intuitive: the on-board touch-screen is used to insert and select test parameters, view results, and, in the motorized version, control and automate the pendulum.
Thanks to Dr. Gong and Georgia Southern University for having shared their testing experience: Impact Strength of 3D Printed Polyether-ether-ketone (PEEK)
Impact resilience is one of the most important properties and cost-effective evaluations for material producers, both with respect to product development and quality control. As components could fail at stress levels well below the critical fracture stress, accurate determination of impact damage propagation is necessary. With the combined experience of CEAST, Instron® has more than 50 years experience in designing pendulum impact testing systems.