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Created page with "{{Language_sel|LANG=ger|ARTIKEL=Dehnrate Applikationen}} {{PSM_Infobox}} Strain rate applications __FORCETOC__ ==General information== In many applications, e.g. in automotive engineering, aerospace technology and sports, high strain rates of up to 500 s-1 can occur in the material/component [1–3]. '''Table 1''' provides an overview of the test methods use..."

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{{Language_sel|LANG=ger|ARTIKEL=Dehnrate Applikationen}}
{{PSM_Infobox}}
Strain rate applications
__FORCETOC__

==General information==

In many applications, e.g. in automotive engineering, aerospace technology and sports, high strain rates of up to 500 s-1 can occur in the [[Material & Werkstoff|material]]/[[Plastic Component|component]] [1–3]. '''Table 1''' provides an overview of the test methods used to determine material properties under the respective stress conditions with the achievable strain rates. Since the principle was introduced in 1914, the SPLIT-HOPKINSON Pressure Bar (SHPB) test has played a leading role in determining material behaviour under strain rates > 100 s-1 due to its versatility and continuous development, in particular the feasibility of different [[Stress|types of loading]] [4].

{| border="1px" style="border-collapse:collapse"
|+ '''Table 1''': Test methods for material characterisation at high [[Strain Rate Basics|strain rates]] [3, 5, 6]
!! style="width:100px; background:#DCDCDC" | nominal strain rate (s-1)
!! style="width:80px; background:#DCDCDC" | type of loading
!!e style="width:400px; background:#DCDCDC" | testing technique
|-
|<0.1
|rowspan=5 | compression
|electromechanical [[Material Testing Machine|material testing machine]]
|-
|0.1–100
|'''[[Servo-hydraulic Testing Machine|Servo-hydraulic testing machine]]'''
|-
|0.1–500
|''Cam plastometer,'' [[Impact Loading Free-falling Dart Test|free-falling dart test]]
|-
|200–104
|''Split-HOPKINSON Bar'' (compression loading)
|-
|104–105
|ballistics, projectiles
|-
|<0.1
|rowspan=5 | tensile
|electromechanical material testing machine
|-
|0.1–100 (300)
|'''servo-hydraulic testing machine'''
|-
|100–104
|''Split-HOPKINSON Bar'' (tensile loading) explosive acceleration:
|-
|104
|plate(''flyer plate'')
|-
|>105
|ring (''expanding ring'')
|-
|<0.1
|rowspan=6 | shear
|electromechanical material testing machine
|-
|0.1–100 (300)
|'''servo-hydraulic testing machine'''
|-
|10–103
|impact test (''torsional impact'')
|-
|100–104
|''Split-HOPKINSON Bar'' (shear arrangement)
|-
|103–104
|interlaminar shear test of a double-notched test specimen (double-notch shear test)
|-
|104–107
|''pressure-shear plate impact''
|}

In addition to the [[Strain Rate Basics|strain rates]], the '''Figure''' also shows the characteristic test times and the deformation processes occurring in metals and [[Plastics|plastics]] (using the example of isotactic and impact-modified polypropylene [7]). Modern [[Servo-hydraulic Testing Machine|servo-hydraulic testing machines]] can cover a strain rate range from 10-3 to 10+3 [8], which is highlighted in grey in the '''Figure'''.

[[File:Dehnrate_1.jpg|500px]] 
{|
|- valign="top"
|width="50px"|'''Figure''':
|width="600px" |Practically relevant, characteristic test times, strain rates and [[Deformation Mechanisms|deformation mechanisms]] [9]
|}

At [[Strain Rate Basics|strain rates]] greater than 1 s-1, vibrations occur which reduce the information content of the [[Tensile Test|stress–strain curves]] and make evaluation more complicated. These oscillations are due to the [[Impact Loading Plastics|impact]] introduction of energy into the [[Specimen|test specimen]] and are significantly influenced by the entire [[Material Testing Machine|testing machine]] and the damping behaviour of the [[Material & Werkstoff|material]] [3, 10, 11] and cannot be avoided in high-speed tensile tests.

==Reflected stress waves==

These vibrations are attributable to the shock-like introduction of energy into the test specimen and are significantly influenced by the entire [[Material Testing Machine|testing machine]] and the damping behaviour of the [[Material & Werkstoff|material]] [3, 10, 11]. In [3], the number of elastically reflected vibrations ''N'' ('''Eq. 1''' and '''2''') is defined as the criterion for the evaluability of recorded curves in the average strain rate range of 1–100 s-1.

{|
|-
|width="20px"|
|width="500px" | <math>N\,=\,\frac{\varepsilon_y \cdot c}{v_T}</math>
|(1)
|}

with
{|
|-
|''ε''y
|width="15px" |
|yield strain
|-
|''c''
|
|[[Velocity|velocity]] of the elastic stress wave
|-
|''v''T
|
|[[Crosshead Speed|crosshead speed]]
|}

{|
|-
|width="20px"|
|width="500px" | <math>c\,=\,\sqrt{ \frac{E_t}{\rho}}</math>
|(2)
|}

with
{|
|-
|''E''T
|width="15px" |
|[[Elastic Modulus|elastic modulus]]
|-
|<math>\rho</math>
|
|[[Density|density]]
|}

The minimum number of oscillations for uniform stress distribution is specified as 10 in [12] and, based on the evaluation of SHPB tests (Split-HOPKINSON pressure bar) in [3], as three complete oscillations. If the number of oscillations is sufficiently high, uniform stress distribution in the [[Specimen|test specimen]] can be assumed, although this condition is not comparable to the homogeneous stress distribution in a [[Quasi-static Test Methods|quasi-static]] [[Tensile Test|tensile test]].

==Elastic modulus of plastics at high strain rates==

The trend in automotive engineering is towards [[Plastic Component|plastic components]] that are exposed to [[Impact Loading Plastics|impacts]] and [[Impact Loading High-Speed Testing|high dynamic loads]], such as airbags, bumpers, instrument panels, etc.

To simulate the behaviour of materials under highly dynamic loads, [[Material Value|characteristic values]] are required that enable the crash behaviour to be predicted. M. Keuerleber's dissertation [13] deals with a [[Material Parameter|characteristic parameter]] that is relatively easy to determine using testing methods, namely the [[Elastic Modulus|modulus of elasticity]].

To determine the [[Elastic Modulus|modulus of elasticity]], [[Uniaxial Stress State|uniaxial]] [[Tensile Test|tensile tests]] were carried out on polypropylene at speeds ranging from 0.0001 m/s to 8 m/s and temperatures ranging from -10 °C to 40 °C.

==See also==

* [[Strain Rate Basics|Strain rate basics]]
* [[Deformation Rate|Deformation rate]]
* [[Deformation Velocity|Deformation velocity]]
* [[Crosshead Speed|Crosshead speed]]
* [[Test Speed|Test speed]]

==References==

{|
|-valign="top"
|[1]
|Bardenheier, R.: Dynamic Impact Testing – VHS High Rate Testing Systems. Instron Ltd., High Wycombe, UK (2005)
|-valign="top"
|[2]
|Thoma, K.: Measurement of Mechanical Parameters in the Range of High and Highest Strain Rates – Examples of Practical Application for a Wide Spectrum of Materials. Report 17/02. Fraunhofer-Institut für Kurzzeitdynamic – Ernst-Mach-Institut EMI Freiburg (2002)
|-valign="top"
|[3]
|Xiao, X.: Dynamic Tensile Testing of Plastic Materials. Polymer Testing 27 (2008) 164–178 DOI: [https://doi.org/10.1016/j.polymertesting.2007.09.010 https://doi.org/10.1016/j.polymertesting.2007.09.010]
|-valign="top"
|[4]
|Gray-III, G. T.: Classic Split-Hopkinson Pressure Bar Testing. In: ASM Handbook, Vol. 8, Mechanical Testing and Evaluation. ASM International (2000) pp. 462–476
|-valign="top"
|[5]
|Bardenheier, R., Rogers, G.: Dynamic Impact Testing. Instron Ltd., High Wycombe, UK (2003)
|-valign="top"
|[6]
|Hamouda, A. M. S., Hashmi, M. S. J.: Testing of composite materials at high rates of strain: Advances and challenges. Journal of Materials Processing Technology 77 (1998) 327–336 DOI: [https://doi.org/10.1016/S0924-0136(97)00436-6 https://doi.org/10.1016/S0924-0136(97)00436-6]
|-valign="top"
|[7]
|Gensler, R., Plummer, C. J. G., Grein, C., [[Kausch,_Hans-Henning|Kausch, H.-H.]]: Influence of the loading rate on the fracture resistance of isotactic polypropylene and impact modified isotactic polypropylene. Polymer 41 (2000) 3809–3819 DOI: [https://doi.org/10.1016/S0032-3861(99)00593-5 https://doi.org/10.1016/S0032-3861(99)00593-5]
|-valign="top"
|[8]
|Bardenheier, R., Borsutzki, M.: Anforderungen an Hochgeschwindigkeitsprüfsysteme zur Ermittlung von Kennwerten an Blechwerkstoffen. In: Buchholz, O.W., Geisler, S. (Eds.): Herausforderung durch den industriellen Fortschritt – Tagungsband Werkstoffprüfung (2003) 78–87 (ISBN 978-3-514-00703-1; ISBN 3-514-00703-9; see [[AMK-Library]] under M 11)
|-valign="top"
|[9]
|Schoßig, M.: Schädigungsmechanismen in faserverstärkten Kunststoffen – Quasistatische und dynamische Untersuchungen. Vieweg+Teubner / GWV Fachverlage GmbH, Wiesbaden (2010), (see [[AMK-Library]] under B 1-21) [https://www.polymerservice-merseburg.de/fileadmin/inhalte/psm/veroeffentlichungen/Schossig_Promotion_Inhaltsverzeichnis.pdf Content as pdf]
|-valign="top"
|[10]
|Beguelin, P., Kausch, H. H.: The effect of the loading rate on the fracture toughness of poly(methyl methacrylate), polyacetal, polyetheretherketone and modified PVC. Journal Materials Science 29 (1994) 91–98 DOI: [https://doi.org/10.1007/BF00356577 https://doi.org/10.1007/BF00356577]
|-valign="top"
|[11]
|Karger-Kocsis, J., Benevolenski, O. I., Moskala, E. J.: Toward understanding the stress oscillation phenomenom in polymers due to tensile impact loading. Journal Materials Science 36 (2001) 3365–3371 DOI: [https://doi.org/10.1023/A:1017935323058 https://doi.org/10.1023/A:1017935323058]
|-valign="top"
|[12]
|Society of Automotive Engineers Japan (SAE J) 2749 (2008): High Strain Rate Testing of Polymers
|-valign="top"
|[13]
|Keuerleber, M.: Bestimmung des Elastizitätsmoduls von Kunststoffen bei hohen Dehnraten am Beispiel von Polypropylen (PP). Dissertation Universität Stuttgart, Institut für Kunststoffprüfung und Kunststoffkunde, Stuttgart, August (2006) (see [[AMK-Library]] under C 35), see [https://www.deutsche-digitale-bibliothek.de/item/GUWDXAPY36IG3YVL63GNFYJZC3RER3KJ?isThumbnailFiltered=true&query=Bestimmung+des+Elastizit%C3%A4tsmoduls+von+Kunststoffen+bei+hohen+Dehnraten&rows=20&offset=0&viewType=list&firstHit=GUWDXAPY36IG3YVL63GNFYJZC3RER3KJ&lastHit=lasthit&hitNumber=1 see Deutsche Digitale Bibliothek]
|}

[[Category:Deformation]]
[[Category:Velocity]]
[[Category:Tensile Test]]

Strain Rate Applications - Revision history