Puncture Impact Test
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Puncture impact test
Definition of terms
The term ‘puncture test’ is used in poymer testing for both tests with dynamic stress rates and quasi-static test methods, although the push-through test would actually be more appropriate for the latter. In testing practice, such quasi-static tests are usually referred to as push-out tests.
This article describes puncture tests with dynamic stress rates.
General
Puncture tests and fall tests (sometimes referred to as drop bolt tests) are used to characterise the behaviour of materials under sudden impact (see: impact loading free-falling dart test) and are therefore classified as dynamic stress tests.
In contrast to the (notch) impact bending test, the puncture test results in a multiaxial stress and strain state. Various standards have been developed for polymer testing that describe puncture tests. A distinction is made between instrumented and conventional methods, as well as between film tests and sheet tests.
The following sections explain the test methods from an application technology perspective.
Conventional puncture impact test for solid plastics (sheets)
When plastics are used in lightweight construction, such as in the automotive or aerospace industries, manufacturing-related damage such as thickness variations, foreign inclusions, resin enrichments, layer defects or delamination, as well as disorientation, can occur, which subsequently have a negative effect on the properties of such components (see also: failure analysis of plastic products, VDI Guideline 3822). On the other hand, operational causes (overloading, impact, high or low temperatures, and media or biochemical attack) can also cause specific damage (see also: deformation mechanisms) to plastic components, which can greatly affect the service life and functionality of these components and parts.
For the development of new polymer modifications, the reinforcement/filling and toughness optimisation of existing plastics and polymer blends, as well as for operational quality assurance, the determination of impact strength using the falling hammer method is an important test method in [Polymer Testing|polymer testing]] [1].
To characterise the multiaxial impact behaviour of solid plastics, the simplest case is to use the conventional test method with the non-instrumented puncture or impact test, which works with the so-called staircase method according to ISO 6603-1 [2].
The tests can be carried out with falling drop test systems (see: impact loading free-falling dart test).
The test method is suitable in principle for thermoplastic unfilled and filled as well as reinforced moulding and extrusion compounds, curable plastics and composites with unidirectional or non-directional reinforcement up to a test piece thickness of 4 mm.
The panel or test specimen to be tested is subjected to a puncture body with a diameter of 20 ± 0.2 or 10 ± 0.1 mm with a specified energy content. The energy of the falling bolt is varied by changing the falling height at a constant additional mass or the mass at a constant falling height in suitable increments. The support distance is 40 mm for falling bolts with a diameter of 10 mm and 100 mm for those with a diameter of 20 mm, whereby the tip of the falling bolt is usually lubricated with oil or grease of a viscosity defined in standard [2] (information must be included in the report).
Before the actual test with 30 or 40 test specimens, preliminary tests are carried out on 10 test specimens to determine the energy limits for 0 and 100 % damage. Depending on the damage that occurs, the tests are loaded with varying energy increments ΔE until approximately 50 % of the test specimens are damaged and 50 % are undamaged, whereby only damaged or undamaged test specimens can be evaluated. There are two evaluation methods (input method A and statistical method B), the results of which are generally not clearly comparable, as the measurement results are strongly influenced by the quality of the test specimens and the type of damage that occurs (Fig. 1).
| Fig. 1: | Damage characteristics of plastics with different toughness in a puncture impact test according to [2] on round specimens |
Since testing in accordance with ISO 6603-1 [2] is relatively time-consuming and material-intensive, provides little meaningful information and does not generate interpretable diagrams of the load--deformation behaviour, recording or instrumented testing techniques (see: electronic instrumentation) are now mostly used to characterise the impact behaviour of solid plastics. The article Instrumented puncture impact test describes the instrumented test for solid plastics.
Conventional puncture impact test for films
When plastic films or sheets are used in the packaging industry or for agricultural purposes, damage to these films may occur, e.g. due to manufacturing-related variations in thickness, foreign inclusions, surface variations or orientations, as well as operational causes (impact, high or low temperatures, and media or biochemical attack), which can have a significant impact on service life and functionality (see also: film testing).
For the material development of new plastic films, the modification and optimisation of the toughness of existing films, and operational quality assurance, the determination of impact strength using the falling hammer method is an important test method in polymer testing [3−6].
There is essentially one test standard available for investigating the non-instrumented impact behaviour of plastic films. This is the conventional test method using the fall hammer method, which works with the so-called boundary method (staircase method) according to ISO 7765-1 [7, 8].
This method is also known as the ‘free-falling dart method’ and ‘dart drop test’ (Fig. 2).
In this method, the film to be tested (thickness < 1 mm) is subjected to a load with a puncture body with a diameter of 38 ± 1 mm from a constant height of 0.66 ± 0.01 m with additional masses of 0.05 to 2 kg until damage occurs (method A).
In method B, the hemispherical puncture body has a diameter of 50 ± 1 mm and is also dropped from a constant height of 1.50 ± 0.01 m with additional masses of 0.3 to 2 kg onto the film test specimen.
Both test methods are carried out with a material-specific mass increment Δm until 50 % damaged and undamaged film test specimens are available at a statistically estimated puncture body mass. Methods A and B are not comparable in terms of test results, as the results of the measurement are strongly influenced by the quality of the test objects.
Since testing using the falling hammer method [7] is comparatively time-consuming and material-intensive and not very meaningful (at least 20 test specimens are required) and no interpretable diagrams of the load--deformation behaviour are generated, recording or instrumented test techniques are now mostly used to characterise the impact behaviour of plastic films (see: electronic instrumentation). The article instrumented puncture impact test describes the instrumented test for films.
ASTM D1709 [9] describes virtually the same procedure. There are minor differences in detail, particularly with regard to the permissible tolerances. In addition, this standard limits the application to films with a maximum thickness of 0.25 mm, which is described as an arbitrary specification. The ASTM standard extends the range of falling weights to up to 6 kg and describes a second, alternative test method in which ten test specimens are to be tested per weight increment.
In principle, it is therefore possible to test according to both ISO 7765-1 and ASTM D1709 using the same testing device.
| Fig. 2: | Dart Drop Tester FDI-01 of Labthink Instruments Co. Ltd, Jinan (China) |
See also
- Impact loading free-falling dart test
- High-speed tensile test
- Instrumented puncture test for solid plastics (sheets)
- Instrumented puncture impact test for films
- Film testing
References
| [1] | Grellmann, W.: Schlagartige Beanspruchung. In: Grellmann, W., Seidler, S. (Eds.): Kunststoffprüfung. Carl Hanser, Munich (2025) 4th Edition, pp. 151–163 (ISBN 978-3-446-44718-9; E-Book: ISBN 978-3-446-48105-3; see AMK-Library under A 23) |
| [2] | ISO 6603-1 (2000-05): Plastics – Determination of Puncture Behaviour of Rigid Plastics – Part 1: Non-instrumented Impact Test |
| [3] | Nentwig, J.: Kunststoff-Folien: Herstellung – Eigenschaften – Anwendung. Carl Hanser, Munich (2006) 3rd Edition, (ISBN 978-3-446-40390-1; see AMK-Library under G 7-1) |
| [4] | Maier, R.-D., Schiller, M. (Eds.): Handbuch Kunststoff Additive. Carl Hanser, Munich (2016) 4th Edition, (ISBN 978-3-446-22352-3) |
| [5] | Trempler, J.: Optische Eigenschaften. In: Grellmann, W., Seidler, S. (Eds.): Kunststoffprüfung. Carl Hanser, Munich (2025) 4th Edition, pp. 311–343 (ISBN 978-3-446-44718-9; E-Book: ISBN 978-3-446-48105-3; see AMK-Library under A 23) |
| [6] | Reincke, K., Grellmann, W., Söver, A., Frormann, L.: Verhalten von Polymeren unter stoßartiger Beanspruchung. GAK – Gummi Fasern Kunststoffe 65 (2012) 4, pp. 290–296 |
| [7] | ISO 7765-1 (1988-12): Plastic Film and Sheeting – Determination of Impact Resistance by Free-falling Dart Method – Part 1: Staircase Methods |
| [8] | Reincke, K.: Testing of Polymeric Films. In: Grellmann, W., Seidler, S. (Eds.): Polymer Testing. Carl Hanser Verlag München (2022). 3rd Edition, pp. 643–678 (ISBN 978-1-56990-806-8; E-Book: ISBN 978-1-56990-807-5; ePub ISBN 978-1-56990-808-2; see AMK-Library under A 22) |
| [9] | ASTM D 1709 (2024): Standard Test Methods for Impact Resistance of Plastic Film by the Free-falling Dart Method |