View source for Impact Loading High-Speed Testing

{{Language_sel|LANG=ger|ARTIKEL=Schlagbeanspruchung Hochgeschwindigkeitsprüfung}}
{{PSM_Infobox}}
<span style="font-size:1.2em;font-weight:bold;">Impact loading, plastics, high-speed testing</span>
__FORCETOC__

==General==

When using [[Plastics|plastics]] or [[Composite Materials Testing|composite materials]] for lightweight construction in machines, vehicles or aircraft, in the event of explosions in containers or pipelines, in crash situations or even when processing these materials, sudden [[Impact Loading Plastics|impact]] [[Stress|stresses]] can occur which superimpose themselves on the static/dynamic load collective. These usually cause locally greatly increased [[Deformation Rate|deformation rates]] and are further intensified by the presence of stress peaks at sharp [[Notch|notches]] or edges, [[Multiaxial Stress States|multiaxial stress states]] and low temperatures [1].

==Effects of high deformation rates==

Since the molecular [[Relaxation Plastics|relaxation]] and [[Creep Plastics|retardation mechanisms]] of plastics require sufficient reaction time, high impact speeds or very low temperatures significantly influence [[Deformation Mechanisms|damage]], [[Strength|strength]], [[Deformation|deformation]] and [[Fracture Behaviour|fracture behaviour]], as the time required for the material to react to the [[Impact Loading Plastics|impact loading]] is no longer available. The decisive factor for the effect of the sudden stress on the plastic is the generated [[Strain Rate|strain rate]] d''ε''/d''t'' or the characteristic exposure time, as shown by different impact loadings ('''Table 1''').

{| border="1px" style="border-collapse:collapse"
|+ '''Table 1''': Assignment of typical types of stress to the test time or deformation rate
!! style="width:240px; background:#DCDCDC" | impact-process
!! style="width:120px; background:#DCDCDC" | maximum speed
!! style="width:120px; background:#DCDCDC" | typical load
!! style="width:120px; background:#DCDCDC" | maximum strain rate
|-
|building construction: jackhammer
|style="text-align:center"|5 m/s
|style="text-align:center"|5 &middot; 10<sup>-3</sup> s
|style="text-align:center"|1 s<sup>-1</sup>
|-
|Automobilbau: crash
|style="text-align:center"|20 m/s
|style="text-align:center"|5 &middot; 10<sup>-2</sup> s
|style="text-align:center"|500 s<sup>-1</sup>
|-
|ballistics: projectile penetration
|style="text-align:center"|2.000 m/s
|style="text-align:center"|1 &middot; 10<sup>-4</sup> s
|style="text-align:center"|1,000,000 s<sup>-1</sup>
|-
|manufacturing: machining
|style="text-align:center"|-
|style="text-align:center"|-
|style="text-align:center"|1,000,000 s<sup>-1</sup>
|-
|astronomy: meteorite impact
|style="text-align:center"|10,000 m/s
|style="text-align:center"|1 &middot; 10<sup>-6</sup> s
|style="text-align:center"|10,000,000 s<sup>-1</sup>
|}

With the increase in the [[Deformation Rate|deformation rate]] or the decrease in the test or examination time, a transition from isothermal to adiabatic testing occurs, as the heat generated can no longer be dissipated to the environment within the short test duration. As a result of this, the [[Material Value|material values]] of the [[Impact Loading Plastics#Dependence of the dynamic yield strength on the deformation rate|dynamic yield strength]], the [[Tensile Strength|tensile strength]] and the [[Elastic Modulus|modulus of elasticity]] increase, whereas the deformation characteristics show a decrease. Of particular significance here is the reduction in [[Impact Test|impact strength]], which promotes deformation-free critical [[Fracture Types|brittle fracture]]. Of interest here is not only the [[Bend Loading|bend loading]], as in the impact bending test, but often also the tensile loading at high test speeds or strain rates.

==Schematic structure of a high-speed testing machine==

For such tests, [[Impact Loading Free-Falling Dart Test|drop bolt testing systems]] with a so-called reverse suspension or specially equipped high-speed testing machines ('''Fig. 1''') can be used, which allow a maximum [[Test Speed|test speed]] of 80 m/s (see: [[High-Speed Tensile Test|high-speed tensile test]] and [[Servo-hydraulic Testing Machine|servo-hydraulic testing machine]]).

However, most of these testing systems can only be operated at [[Test Speed|test speeds]] of up to 20 m/s, as evaluation problems arise in this test range due to the superposition of vibrations and the [[Inertial Load|inertial load]].

[[file:ImpLoadHighSpeed_Fig1.jpg|550px]]
{| 
|- valign="top"
|width="50px"|'''Fig. 1''': 
|width="600px"|Schematic diagram of a high-speed testing machine for rapid tear tests
|}

In these high-speed testing systems, the test specimen, including the holder, is pre-accelerated over a specified run-up distance and then loaded by the moving cylinder piston until [[Fracture|fracture]] occurs.

In some cases, even in this speed range, it is possible to control the [[Strain Rate|strain rate]] in order to maintain constant test conditions.

As with the [[Impact Loading Pendulum Impact Tester|pendulum impact testers]] or [[Impact Loading Free-falling Dart Test|drop bolt test systems]], optional equipment with a temperature control or media chamber is also available here.

==Device systems==

Technical implementation variants of these test systems are shown in '''Fig. 2'''.

[[file:Schlagbeanspruchung_Hochgeschwindigkeitspruefung-3.JPG|500px]]
{| 
|- valign="top"
|width="50px"|'''Fig. 2''': 
|width="600px"|High-speed tensile testing machines from (a) Instron GmbH, Darmstadt, and (b) [https://www.zwick.de Fa. ZwickRoell GmbH & Co. KG, Ulm]]
|}

During the test, the test software records the force-strain diagram in high resolution, which can then be evaluated offline using the available evaluation routines or special software for graphical and mathematical analysis.

Experimental results for determining the strength of PP-GF composites are presented in the article [[High-Speed Tensile Test|High-speed tensile test]].

==See also==

* [[Impact Loading Free-falling Dart Test]]
* [[High-Speed Tensile Test]]
* [[Impact Loading Plastics]]
* [[Instrumented Puncture Impact Test]]
* [[Compression After Impact Test]]


'''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 978-1-56990-807-5; see [[AMK-Büchersammlung|AMK-Library]] under A 22) 
|}

[[category:Velocity]]
[[category:Impact Tests]]