Oluschinski: Created page with "{{Language_sel|LANG=ger|ARTIKEL=Schlagbeanspruchung Kunststoffe}} {{PSM_Infobox}} Impact loading plastics FORCETOC ==Significance of high deformation rates== When plastics or composite materials are used in machines or vehicles, in explosions, in crash situations or even during high-speed machining of these materials, sudden impact forces can..."

2026-09-04T07:35:48Z

Created page with "{{Language_sel|LANG=ger|ARTIKEL=Schlagbeanspruchung Kunststoffe}} {{PSM_Infobox}} Impact loading plastics __FORCETOC__ ==Significance of high deformation rates== When plastics or composite materials are used in machines or vehicles, in explosions, in crash situations or even during high-speed machining of these materials, sudden impact forces can..."

New page

{{Language_sel|LANG=ger|ARTIKEL=Schlagbeanspruchung Kunststoffe}}
{{PSM_Infobox}}
Impact loading plastics
__FORCETOC__

==Significance of high deformation rates==

When [[Plastics|plastics]] or [[Composite Materials Testing|composite materials]] are used in machines or vehicles, in explosions, in crash situations or even during high-speed machining of these [[Material & Werkstoff|materials]], sudden impact forces can occur, which usually cause locally greatly increased [[Deformation Rate|deformation rates]] and are further intensified by the presence of [[Stress|stress]] peaks at sharp [[Notch|notches]] and/or low temperatures [1].

Since the molecular relaxation mechanisms in plastics require sufficient reaction time, the [[Strength|strength]], [[Deformation|deformation]] and [[Fracture Behaviour|fracture behaviour]] are significantly altered at high impact speeds or very low temperatures, as the [[Material & Werkstoff|material]] does not have the time required to react to the impact loading. The decisive factor for the effect of impact loading on the material is therefore the generated [[Strain Rate Basics|strain rate]] d''ε''/d''t'' or the characteristic exposure time.

==Classification of test methods according to test duration and deformation rate==

In principle, impact test methods are classified according to the impact frequency or test duration or strain rate as follows (see '''Fig. 1'''):

* 10-1 – 10 s-1 or Hz – impact [[Stress|loading]]
* > 102 – elastic or elastic-plastic stress waves with [[Sound Velocity|sound propagation velocity]]

[[File:Schlagbeanspruchung_Kunststoffe-1.JPG|450px]]
{|
|- valign="top"
|width="50px"|'''Fig. 1''':
|width="600px"|Classification of test methods according to test duration and deformation rate
|}

==Dependence of dynamic yield strength on deformation rate==

With the increase in the deformation rate or the decrease in the test or inspection time, a transition from isothermal to adiabatic testing occurs, as the heat generated cannot be dissipated to the environment within the short test duration. As a result of this, the [[Material Value|characteristic values]] of the dynamic yield strength (see also: static [[Yield Stress|yield stress]]), the [[Tensile Strength|tensile strength]] and the [[Elastic Modulus|modulus of elasticity]] increase ('''Fig. 2'''), whereas the deformation characteristics show a decrease. Of particular significance here is the reduction in impact strength (see: [[Impact Test|impact test]]), which promotes deformation-free critical [[Fracture Types|brittle fracture]].

[[File:Schlagbeanspruchung_Kunststoffe-2.JPG|350px]]
{|
|- valign="top"
|width="50px"|'''Fig. 2''':
|width="600px"|Dependence of the dynamic yield strength of a polymer blend consisting of polycarbonate ([[Plastics – Symbols and Abbreviated Terms|abbreviation]]: PC) and acrylonitrile butadiene styrene ([[Plastics – Symbols and Abbreviated Terms|abbreviation]]: ABS) on the deformation rate
|}

==Factors promoting brittle fracture==

[[Plastics]] in particular are subject to a multitude of testing, manufacturing, stress-related and material-related factors that [[Brittle Fracture Promoting Factors|promote brittle fracture]] in the respective [[Polymer|polymer]] [[Material & Werkstoff|material]]. These testing and geometry-related influencing factors are essentially (see Fig. 3):

* low testing or operating temperatures,
* stress crack-promoting environmental media,
* [[Multiaxial Stress State|multiaxial stress states]] and stress concentrations (see: [[Fracture Mechanics|fracture mechanics]]),
* [[Tensile Test Residual Stresses Orientations|residual stresses]] in the [[Specimen|test specimen]] or [[Plastic Component|component]],
* [[Notch|notches]] and sharp edges, and
* internal cavities ([[Gas Bubbles|gas bubbles]], [[Shrink Voids|vacuoles]], [[Micropores|micropores]]), porosities and [[Crack|cracks]].

[[File:Impact_Loading_Plastics_Fig-3.jpg|600px]]
{|
|- valign="top"
|width="50px"|'''Fig. 3''':
|width="600px"|Geometric influencing factors (a), stress concentrations and [[Multiaxial Stress State|multiaxial stress state]] (b) and [[Tensile Test Residual Stresses Orientations|residual stresses]] in a motorcycle helmet visor (c)
|}

Due to these influencing factors, testing under sudden loading is often carried out on notched or cracked [[Specimen|test specimens]], varying the [[Test Speed|test speed]] and test temperature. Material-related influencing factors include, for example:

* the [[Microscopic Structure|morphology]] and [[Polymers & Structure|structure]] of the [[Material & Werkstoff|materials]],
* frozen [[Tensile Test Residual Stresses Orientations|orientations]] or orientations of [[Particle-filled Thermoplastics#Technically used fillers|fillers]],
* the [[Crystallinity|degree of crystallinity]] and
* the [[Spherulitic Structure|spheroidal size]] in semi-crystalline [[Plastics|plastics]].

High orientations can lead to higher impact strength in amorphous plastics and reduced impact strength in semi-crystalline materials.

==Test methods for characterizing toughness under impact loading==

The test methods commonly used to characterise the [[Impact Test|impact strength]] of [[Plastics|plastics]] range from 1 to 10 m s-1 and are carried out using the following methods, although various technical variants exist:

* [[Impact Test|Impact test]] and [[Notched Impact Test|notched impact test]],
* [[Tensile Impact Test|tensile impact test]] and [[Notched Tensile Impact Test|notched tensile impact test]],
* [[Instrumented Charpy Impact Test|instrumented Charpy impact test]],
* [[Instrumented Tensile Impact Test|instrumented tensile impact test]] and
* [[Instrumented Puncture Impact Test|instrumented puncture impact test]] (free-falling dart test).

If higher test speeds are required, as shown in '''Fig. 4''', more technically sophisticated test methods are used (see '''Fig. 1''').

[[File:Impact_Loading_Plastics_Fig-4.jpg|550px]]
{|
|- valign="top"
|width="50px"|'''Fig. 4''':
|width="600px"|Overview of achievable test speeds for impact loading depending on the test speed
|}

==See also==

* [[Impact Loading Free-falling Dart Test|Impact loading free-falling dart test]]
* [[Impact Loading High-Speed Testing|Impact loading high-speed testing]]
* [[Impact Loading Pendulum Impact Tester|Impact loading pendulum impact tester]]
* [[Instrumented Puncture impact Test|Instrumented puncture impact test]]
* [[Instrumented Charpy Impact Test (ICIT)|Instrumented Charpy impact test (ICIT)]]
* [[Instrumented Tensile Impact Test (ITIT)|Instrumented tensile impact test (ITIT)]]

==References==

{|
|-valign="top"
|[1]
|[[Grellmann,_Wolfgang|Grellmann, W.]]: Impact Loading. In: [https://www.researchgate.net/profile/Wolfgang-Grellmann Grellmann, W.], [[Seidler,_Sabine|Seidler, S.]] (Eds.): Polymer Testing. Carl Hanser, Munich (2022) 3rd Edition, pp. 143–156 (ISBN 978-1-56990-806-8; E-Book: ISBN 978-1-56690-807-5; see [[AMK-Library]] under A 22)
|}

[[Category:Velocity]]
[[Category:Impact Tests]]

Impact Loading Plastics - Revision history