Oluschinski: Created page with "{{Language_sel|LANG=ger|ARTIKEL=Fäden, Zipfel und Folien}} {{PSM_Infobox}} Threads, tips and films or filaments, ears and films FORCETOC ==General information== Component failure is usually initiated by microscopic crack formation processes. Depending on the material behaviour of the plastics, stable Crack Propagation|crack pr..."

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Created page with "{{Language_sel|LANG=ger|ARTIKEL=Fäden, Zipfel und Folien}} {{PSM_Infobox}} <span style="font-size:1.2em;font-weight:bold;">Threads, tips and films</span> or filaments, ears and films __FORCETOC__ ==General information== Component failure is usually initiated by microscopic crack formation processes. Depending on the material behaviour of the plastics, stable Crack Propagation|crack pr..."

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{{Language_sel|LANG=ger|ARTIKEL=Fäden, Zipfel und Folien}}
{{PSM_Infobox}}
<span style="font-size:1.2em;font-weight:bold;">Threads, tips and films</span> or filaments, ears and films
__FORCETOC__

==General information==

[[Component Failure|Component failure]] is usually initiated by microscopic [[Fracture Formation|crack formation]] processes. Depending on the [[Material & Werkstoff|material]] behaviour of the [[Plastics|plastics]], stable [[Crack Propagation|crack propagation]] then occurs, usually culminating in unstable crack propagation, also known as [[Fracture Types|brittle fracture]] or ultimate fracture [1].

In the subsequent [[Failure Analysis – Basics|failure analysis]], it is essential to determine the location where the [[Crack Initiation|crack originated]] and the direction of crack propagation in order to draw conclusions about the failure mechanism and [[Stress|stress]] parameters [2, 3].

Microscopic examination of the [[Fracture Surface|fracture surfaces]] provides additional information on the type and magnitude of stress, as well as on the influence of temperature and media, the [[Test Speed|loading speed]] application, and on [[Ageing|ageing]] effects or manufacturing defects.

The main objective of the failure analysis is to determine the location where the crack originated, the course of the [[Fracture|fracture]] and the direction in which it propagated, as well as the crack propagation velocity, the [[Fracture Types|fracture type]] ([[Ductility Plastics|ductile]] or brittle) and any factors that may have [[Brittle Fracture Promoting Factors|promoted the fracture]].

The [[Failure Analysis Plastics Products, VDI Guideline 3822|VDI Guideline VDI 3822, sheet 2.1.4]] [3], summarises and explains the [[Fracture Types|typical features]] observable on plastic fracture surfaces; however, only a few specific fracture surface features can provide information about the direction of crack propagation and the location of crack initiation. These are the so-called [[Fracture Parables|fracture parabolas or hyperbolas]], also known as U- or V-ramps, and the [[Ramps, Bars and Steps|ramps, bars or steps]], which are used as synonymous terms [2–6].

==Fracture surface features: threads, tips and films==

Threads, tips and films are only observed in [[Ductility Plastics|ductile]] [[Material & Werkstoff|materials]] and result from severe local [[Deformation#Plastic deformation|plastic deformation]], which typically appears on the fracture surface in combination with fracture parabolic curves, as well as ramps, clods or steps. These secondary fracture features do not normally allow conclusions to be drawn regarding the location of crack initiation or the direction of crack propagation and are characterised in the VDI guideline VDI 3822 using the symbols shown in '''Fig. 1''' [3].

[[File:Threads,_Tips_and_Films_Fig-1.jpg|500px]]
{|
|- valign="top"
|width="50px"|'''Fig. 1''':
|width="600px"|Symbolic fracture surface features for (a) a tip, (b) a film and (c) threads according to [3]
|}

Tips, which occur specifically at the edges of ramps as a result of [[Deformation#Plastic deformation|plastic deformation]], are three-dimensional local bulge-like deformations ('''Fig. 1a'''). These are significantly thicker and more compact than, for example, threads or foils, and the tip generally points against the direction of the principal tensile stress ('''Fig. 2a'''). Tips are often observed symmetrically at the edges of ramps.

[[File:Faeden_Zipfel_Folien2.JPG|500px]]
{|
|- valign="top"
|width="50px"|'''Fig. 2''':
|width="600px"|Fracture surface features: tips and films for ductile material behaviour for (a) polyethylene ([[Plastics – Symbols and Abbreviated Terms|abbreviation]]: PE) tips at ''T'' = –20 °C and (b) polyethylene films at 23 °C according to [3]
|}

Films are local two-dimensional deformations ('''Fig. 1b''') that can result from biaxial stretching processes. Their thickness is significantly smaller than their other dimensions, which is why the films can fold over and buckle ('''Fig. 2b'''). Threads ('''Fig. 1c''') are one-dimensional plastic deformations resulting from [[Craze-Types|fibrillation processes]] and are usually very clearly visible on the fracture surface ('''Fig. 3'''). The films often serve as the starting point for branching thread structures ('''Fig. 3b''').

Given the localised nature of the tips, films and threads, these [[Fracture Surface|fracture surface]] features can be regarded as secondary fracture surface characteristics, which allow only limited conclusions to be drawn. The fracture features of threads, tips and films therefore do not provide any significant information regarding the location of [[Crack Initiation|crack initiation]] and rarely indicate the direction of [[Crack Propagation|crack propagation]].

[[File:Faeden_Zipfel_Folien3.JPG|500px]]
{|
|- valign="top"
|width="50px"|'''Fig. 3''':
|width="600px"|Fracture surface features of threads in ductile materials for (a) polyethylene at 23 °C in the near-notch region and (b) polyethylene at ''T'' = 23 °C under [[Impact Loading Plastics|impact loading]] [3]
|}

==See also==

* [[Fracture]]
* [[Fracture Types|Fracture types]]
* [[Fracture Parables|Fracture parables]]
* [[Ramps, Bars and Steps|Ramps, bars and steps]]
* [[Vibration Fracture|Vibration fracture]]
* [[Brittle Fracture Promoting Factors|Brittle fracture promoting factors]]
* [[Waves and Arrest Lines|Waves and arrest lines]]

==References==

{|
|-valign="top"
|[1]
|[[Grellmann,_Wolfgang|Grellmann, W.]]: Beurteilung der Zähigkeitseigenschaften von Polymerwerkstoffen durch bruchmechanische Kennwerte. Habilitation (1986), [https://de.wikipedia.org/wiki/Technische_Hochschule_Leuna-Merseburg Technische Hochschule Leuna-Merseburg], Wiss. Zeitschrift TH Merseburg 28 (1986), No. 6, pp. 787–788 ([https://www.polymerservice-merseburg.de/fileadmin/inhalte/psm/veroeffentlichungen/Habil_Grellmann_Inhaltsverzeichnis.pdf Content], [https://www.polymerservice-merseburg.de/fileadmin/inhalte/psm/veroeffentlichungen/Habil_Grellmann_Kurzfassung.pdf Summary])
|-valign="top"
|[2]
|Kotter, I., [https://www.researchgate.net/profile/Wolfgang-Grellmann Grellmann, W.]: Die Fraktografie als Hilfsmittel in der Schadensanalyse an Kunststoffprodukten. 24th Internationale Fachtagung Technomer an der Technischen Universität Chemnitz, (2015), Proceedings V 8.6
|-valign="top"
|[3]
|VDI 3822 Blatt 2.1.4 (2024-06): Failure Analysis – Defects of Thermoplastic Products Made of Plastics Causedd by Mechanical Stress
|-valign="top"
|[4]
|VDI 3822 Blatt 2.1.2 (2024-06): Failure Analysis – Defects of Thermoplastic Products Made of Plastics Caused by Faulty Processing
|-valign="top"
|[5]
|[[Ehrenstein,_Gottfried_W.|Ehrenstein, G. W.]]: Schadensanalyse an Kunststoff-Formteilen. VDI Public House Düsseldorf, (1981), (ISBN 3-18-404068-2; see [[AMK-Library]] under D 3)
|-valign="top"
|[6]
|[https://de.wikipedia.org/wiki/Gottfried_W._Ehrenstein Ehrenstein, G. W.], Engel, K., Klingele, H., Schaper, H.: Scanning Electron Microscopy of Plastics Failure / REM von Kunststoffschäden. Carl Hanser, Munich (2011), (ISBN 978-3-446-42242-1; see [[AMK-Library]] under D 5)
|}

[[Category:Damage Analysis_Component Failure]]

Threads, Tips and Films - Revision history