View source for Impact Loading Free-falling Dart Test

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<span style="font-size:1.2em;font-weight:bold;">Impact loading free-falling dart test</span>
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==Higher deformation rates==

Modern high-performance plastics for lightweight construction applications in mechanical engineering, the automotive and aerospace industries, and for containers and pipelines in the chemical industry require precise knowledge of how these [[Material & Werkstoff|materials]] behave under impact loads at high stress rates, especially in crash situations (see also: [[High-speed Tensile Test|high-speed tensile test]]). Such impact loads overlap with the existing static/dynamic loadings and can thus cause critical conditions that can lead to [[Component Failure|component failure]] of [[Plastic Component|plastic components]]. This is caused by locally greatly increased [[Deformation|deformation]] rates, especially in the presence of stress peaks at sharp [[Notch|notches]] or edges, [[Multiaxial Stress State|multiaxial stress states]] and/or reduced operating temperatures [1].

In [[Plastics|plastics]], the molecular [[Relaxation Plastics|relaxation]] and [[Creep Plastics|retardation mechanisms]] require a sufficient reaction time, which cannot be guaranteed at high impact speeds and/or very low temperatures. As a result, the [[Failure Analysis – Basics|damage]], [[Strength|strength]], [[Deformation|deformation]] and [[Fracture Behaviour|fracture behaviour]] of these high-performance plastics is significantly influenced by the [[Velocity|velocity]] d''ε''/d''t'' or frequency ''f'' or the exposure time ''t''<sub>B</sub> of the [[Impact Loading Plastics|impact loading]], as illustrated by the different impact loads in '''Table 1'''.

{| border="1px" style="border-collapse:collapse"
|+ '''Table 1''': Assignment of typical types of loading to test time or deformation rate
!! style="width:240px; background:#DCDCDC" | impact process
!! style="width:120px; background:#DCDCDC" | maximum velocity
!! style="width:120px; background:#DCDCDC" | typical load duration
!! 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>
|-
|automotive engineering: 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: bullet 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 technology: 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>
|}

'''Table 1''' shows that [[Notched Tensile Impact Test|conventional]] or [[Instrumented Tensile Impact Test (ITIT)|instrumented tensile impact test]] or [[Instrumented Charpy Impact Test|instrumented Charpy impact tests]] cannot be used to investigate or simulate the behaviour of [[Material & Werkstoff|materials]] at such high stress rates, as the maximum achievable [[Test Speed|test speed]] of 3.9 m/s is insufficient, even with locally excessive [[Deformation Rate|deformation rates]]. In addition, these tests, which are used industrially for the [[Toughness|toughness characterisation]] of plastics, as well as [[High-speed Tensile Test|high-speed tensile tests]], are dominated by a [[Uniaxial Stress State|uniaxial stress]] and strain state that cannot reflect the real situation of [[Plastic Component|components]] in use.

==High-speed testing equipment==

To investigate the impact behaviour of [[Component Testing|components]] under high [[Test Speed|test speeds]] and multiaxial stress, drop bolt test systems are therefore usually used, which are optionally equipped with temperature control chambers. When equipped with an additional acceleration system, test speeds of up to 20 m/s can be achieved instead of 4.4 m/s ('''Fig. 1''').

[[File:Impact loading Free-falling Dart Test_Fig-1.jpg|500px]]
{| 
|- valign="top"
|width="50px"|'''Fig. 1''': 
|width="600px"|Schematic diagram of the FRACTOVIS drop bolt testing system from Instron/Ceast
|}

In these high-speed test systems, a drop bolt with different diameters (10, 12.5 or 20 mm) is raised to the specified height and then released to fall freely. The required impact energy is determined by the drop height and the additional masses attached. When using the test facility's acceleration system, the linkage is preloaded via springs, whose energy provides additional acceleration. Shortly before the impact of the test specimen, the impact velocity of the drop bolt is determined by an optical measuring section. The load–time diagram is recorded using [[Strain Gauge|strain gauges]] or a [[Piezoelectric Force Transducer|piezoelectric force transducer]], which is usually installed close to the tip of the drop bolt. If the measuring system is optionally equipped with a three-point bending arrangement ('''Fig. 2''') (see: [[Bend Loading|bend loading]]), [[Notched Impact Test|conventional]] or [[Instrumented Charpy Impact Test|instrumented impact]] or instrumented bend tests according to [[Charpy Testing|CHARPY]] can be performed at test speeds of up to 20 m/s.

[[File:Impact loading Free-falling Dart Test_Fig-3.jpg|300px]]
{| 
|- valign="top"
|width="50px"|'''Fig. 2''': 
|width="600px"|Optional CHARPY testing device for drop bolt testing systems
|}

The load–deflection diagram is determined from the recorded load–time curve, knowing the impact velocity ''v''<sub>0</sub>, and the [[Material Value|characteristic values]] are then calculated in accordance with ISO 179-1 [2]. Problems can arise when evaluating [[Instrumented Charpy Impact Test|instrumented Charpy impact tests]] (ICIT), as the experimental conditions change with increasing [[Test Speed|test speeds]] as a result of the [[Initial Load|initial load]] and strong vibrations can interfere with the useful signal. A meaningful fracture mechanical [[Toughness|toughness]] assessment or evaluation according to ISO 179-2 [3] may then no longer be possible (see: [[Fracture Mechanical Testing|fracture mechanical testing]]).

==See also==

* [[Impact Loading Plastics|Impact loading plastics]]
* [[High-speed Tensile Test|High-speed tensile test]]
* [[Impact Loading High-Speed Testing|Impact loading high-speed testing]]
* [[Instrumented Puncture Impact Test|Instrumented puncture impact test]]
* [[Puncture Impact Test|Puncture impact test]]
* [[Compression After Impact Test (CAI)]]

==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 978-13-56990-806-8; E-Book: ISBN 978-1-56990-807-5; see [[AMK-Library]] under A 22) 
|-valign="top"
|[2]
|ISO 179-1 (2026-03): Plastics – Determination of Charpy Impact Properties – Part 1: Non Instrumented Impact Test
|-valign="top"
|[3]
|ISO 179-2 (2020-05): Plastics – Determination of Charpy Impact Properties – Part 2: Instrumented Impact Test 
|}

[[Category:Damage Analysis_Component Failure]]
[[Category:Impact Tests]]