Impact Loading Pendulum Impact Tester
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Impact loading, plastics, pendulum impact tester
General information
Plastics or composite plastics are increasingly being used in machines, vehicles and aircraft for lightweight construction purposes. In the event of crash loads and explosions of containers or pipelines in the chemical industry, impact loads can occur which superimpose themselves on the existing static/dynamic load collective. These impact loading conditions usually cause locally greatly increased deformation rates and are further intensified by the presence of stress peaks at sharp notches, internal cavities (gas bubbles, vacuoles, micropores) or edges, multiaxial stress states and low temperatures [1].
Since the molecular relaxation and creep mechanisms in plastics require sufficient reaction time, high impact speeds and/or very low temperatures significantly influence the damage, strength, deformation and failure behaviour, as the time required for the material to react to the impact loading is no longer available. The local strain rate dε/dt or the characteristic exposure time of the impact load is decisive for the effect of the impact load on the plastic.
Conventional characterisation of toughness
In addition to knowledge of strength, deformation behaviour under static and dynamic loaded conditions, and stiffness behaviour, determining the toughness of the materials used is also very important. In industrial research and development, pendulum impact testers (Fig. 1) are usually used for this purpose, as they allow conventional characterisation of toughness behaviour, including as a function of test temperature.
| Fig. 1: | A schematic diagram of a conventional pendulum impact tester |
With such pendulum impact testers, the energy consumed by the test specimen during the impact is determined based on the potential energy of the pendulum hammer in the starting position α or h1, which is expressed in the lower height h2 or angle β. If the quotient of the energy consumed and the cross-sectional area is calculated, the impact or notch impact strength of the material under investigation is obtained, depending on the type of test specimen used.
Test arrangements
In testing practice, in addition to the tensile impact test for impact bending loads, the test arrangements according to CHARPY, IZOD or Dynstat are used, whereby the test methods do not produce comparable results due to different test speeds (2.9 to 3.9 m/s).
In Germany and other European countries, the test arrangement according to CHARPY in accordance with ISO 179-1 [2] is preferred, whereby unnotched and notched test specimens can be tested in an edgewise or flatwise arrangement (Fig. 2).
| Fig. 2: | Test arrangement according to CHARPY (a) edgewise or e and (b) flatwise or f |
However, the results of the edgewise or flatwise test are not comparable for the unreinforced or short-fibre reinforced and filled plastics tested. In the case of laminates or highly oriented test specimens made of plates, the test direction is also varied depending on the direction of removal. If the pendulum impact tester is equipped with a temperature control device, temperature-dependent toughness values can also be determined to characterise brittle-tough transitions. These transition areas are of particular importance when using these plastics, as they have a significant influence on the dominant failure mechanism (deformationless brittle fracture or ductile fracture).
Device systems
Depending on their age and level of equipment, these testing systems can be equipped with analogue measurement recording (trailing pointer with manual reading), digital measurement processing or incremental measurement technology (angle encoder) (Fig. 3).
| Fig. 3: | Analogue pendulum impact testing device (a), analogue pendulum with digital measurement evaluation (b) and incremental pendulum impact testing device (c) from Fa. ZwickRoell GmbH & Co. KG, Ulm |
See also
- Impact loading plastics
- Impact test
- Instrumented Charpy impact test
- MPK-Procedure MPK-ICIT
- Instrumented tensile impact test (ITIT)
References
| [1] | Grellmann, W.: Impact Loading. In: Grellmann, W., Seidler, S. (Eds.): Polymer Testing. Carl Hanser, Munich (2022) 3rd Edition, pp. 143–156 (ISBN 978-1-56990-806-8; E-Book: ISBN 978-1-56990-807-5; see AMK-Library under A 22) |
| [2] | ISO 179-1 (2026-03): Plastics – Determination of Charpy Impact Properties – Part 1: Non-instrumented Impact Test |