Oluschinski at 05:55, 15 December 2025

2025-12-15T05:55:40Z

← Older revision		Revision as of 07:55, 15 December 2025
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	Residual stresses in [[Moulding Compound\|plastic moulded]] or [[Plastic Component\|components]] tend to occur when these parts are manufactured from molten granulate, e.g. by extrusion, injection moulding or rotational moulding, with this effect being particularly pronounced in the injection moulding process. The reason for this is that after melting, homogenising and degassing, the melt is injected under high pressure into a closed mould, where it cools and is then ejected from the tool. The influence increases with the thickness of the moulded parts (see: [[Moulding Compound\|moulding compound]]), whereby similar effects can also occur when welding plastics (see: [[Heterogeneity\|heterogeneity]] and [[Laser Heterogeneity of Strain Distribution\|laser heterogeneity of strain distribution]]).		Residual stresses in [[Moulding Compound\|plastic moulded]] or [[Plastic Component\|components]] tend to occur when these parts are manufactured from molten granulate, e.g. by extrusion, injection moulding or rotational moulding, with this effect being particularly pronounced in the injection moulding process. The reason for this is that after melting, homogenising and degassing, the melt is injected under high pressure into a closed mould, where it cools and is then ejected from the tool. The influence increases with the thickness of the moulded parts (see: [[Moulding Compound\|moulding compound]]), whereby similar effects can also occur when welding plastics (see: [[Heterogeneity\|heterogeneity]] and [[Laser Heterogeneity of Strain Distribution\|laser heterogeneity of strain distribution]]).

	[[file:~~Z_eigenspannung_o_1~~.jpg]]		[[file:Residual_Stresses_Orientations_Fig_1.jpg]]
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	The residual stresses in test [[Specimen\|specimens]] have a particular effect on the determination of elastic characteristics such as the [[Elastic Modulus\|modulus of elasticity]] and [[Poisson's Ratio\|Poisson's ratio]], as small load stresses cause the stress components to overlap (Fig. 3), which is not taken into account in the calculation of the [[Material Value\|characteristics]]. In the [[Tensile Test\|tensile test]] ('''Fig. 3a'''), this superposition causes a higher tensile stress in the core of the test specimen, while a slight compressive stress occurs in the outer area. In the [[Bend Test\|bend test]] ('''Fig. 3b'''), the distribution of the load stress and the residual stresses results in a complex stress distribution that changes with increasing [[Stress\|stress]]. A clear assignment of a neutral fibre is no longer possible in the initial stage of this test. With increasing load stress, the influence of residual stresses decreases, provided that certain limit values for [[Environmental Stress Cracking Resistance\|environmental stress cracking formation]] are not exceeded.		The residual stresses in test [[Specimen\|specimens]] have a particular effect on the determination of elastic characteristics such as the [[Elastic Modulus\|modulus of elasticity]] and [[Poisson's Ratio\|Poisson's ratio]], as small load stresses cause the stress components to overlap (Fig. 3), which is not taken into account in the calculation of the [[Material Value\|characteristics]]. In the [[Tensile Test\|tensile test]] ('''Fig. 3a'''), this superposition causes a higher tensile stress in the core of the test specimen, while a slight compressive stress occurs in the outer area. In the [[Bend Test\|bend test]] ('''Fig. 3b'''), the distribution of the load stress and the residual stresses results in a complex stress distribution that changes with increasing [[Stress\|stress]]. A clear assignment of a neutral fibre is no longer possible in the initial stage of this test. With increasing load stress, the influence of residual stresses decreases, provided that certain limit values for [[Environmental Stress Cracking Resistance\|environmental stress cracking formation]] are not exceeded.

	[[file:~~Z_eigenspannung_o_3~~.jpg]]		[[file:Residual_Stresses_Orientations_Fig_3.jpg]]
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Oluschinski: Created page with "{{Language_sel|LANG=ger|ARTIKEL=Zugversuch Eigenspannungen Orientierungen}} {{PSM_Infobox}} Tensile test residual stresses orientations FORCETOC ==Influence of residual stresses and orientations== The material value level of plastics depends to a large extent on external factors such as the test speed and temperature, as well as the test climate and test specimen..."

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Created page with "{{Language_sel|LANG=ger|ARTIKEL=Zugversuch Eigenspannungen Orientierungen}} {{PSM_Infobox}} <span style="font-size:1.2em;font-weight:bold;">Tensile test residual stresses orientations</span> __FORCETOC__ ==Influence of residual stresses and orientations== The material value level of plastics depends to a large extent on external factors such as the test speed and temperature, as well as the test climate and test specimen..."

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{{Language_sel|LANG=ger|ARTIKEL=Zugversuch Eigenspannungen Orientierungen}}
{{PSM_Infobox}}
<span style="font-size:1.2em;font-weight:bold;">Tensile test residual stresses orientations</span>
__FORCETOC__

==Influence of residual stresses and orientations==

The [[Material Value|material value]] level of [[Plastics|plastics]] depends to a large extent on external factors such as the test speed and temperature, as well as the [[Test Climate|test climate]] and test specimen geometry, which are generally summarised under the term test conditions.

On the other hand, the internal state of the [[Specimen|test specimen]] also influences the level of the [[Material Value|characteristic values]], with residual stress and orientation being particularly noteworthy here, which in turn depend on the manufacturing or processing method and its process conditions [1].

===Residual stress===

Residual stresses in [[Moulding Compound|plastic moulded]] or [[Plastic Component|components]] tend to occur when these parts are manufactured from molten granulate, e.g. by extrusion, injection moulding or rotational moulding, with this effect being particularly pronounced in the injection moulding process. The reason for this is that after melting, homogenising and degassing, the melt is injected under high pressure into a closed mould, where it cools and is then ejected from the tool. The influence increases with the thickness of the moulded parts (see: [[Moulding Compound|moulding compound]]), whereby similar effects can also occur when welding plastics (see: [[Heterogeneity|heterogeneity]] and [[Laser Heterogeneity of Strain Distribution|laser heterogeneity of strain distribution]]).

[[file:Z_eigenspannung_o_1.jpg]]
{|
|- valign="top"
|width="50px"|'''Fig. 1''':
|width="600px" |Diagram showing the formation of residual stresses during the injection moulding process
|}

Once the injection process and the holding pressure phase are complete, the melt freezes on the comparatively cold wall of the tool and in the sprue ('''Fig. 1a'''), resulting in a constant volume in the finished mould. Since the volume in the molten state is greater than in the cooled '''moulded part''' (see: [[Moulding Compound|moulding compound]]), more or less strong tensile stresses form inside the moulded part as it cools, while the outer part of the moulded part wall exhibits compressive stress ('''Fig. 1b'''). Normally, these internal stresses are in equilibrium and dissipate over time, especially at higher temperatures (tempering) ('''Fig. 1c'''). However, if they exceed material-specific limits, [[Crazing|crazing]], [[Micropores|micropores]] or [[Crack|microcracks]] ('''Fig. 1d''') may form, which ultimately create macroscopic cavities inside the moulded part that are relevant to failure ('''Fig. 1e'''). If the moulded part is thin, warping (see: [[Processing Shrinkage|Shrinkage]]) may also occur ('''Fig. 1f''').

===Orientations===

Orientation can be roughly divided into macromolecule orientation and the orientation of additives such as [[Fibre-reinforced Plastics#Types of reinforcing plastics|short fibres]] ([[Glass Fibre Orientation|glass fibre]], carbon fibre or mineral fibre) or [[Particle-filled Thermoplastics#Technically used fillers|particles]] (talc, chalk or mica), whereby the orientation effects are rather low in organic and inorganic fillers.

The orientation of macromolecules can occur during the manufacturing process through injection moulding, extrusion or blow moulding, whereby this process can take place in the molten state or in the solidified state. This means that the orientation of macromolecules can also be induced mechanically, by uniaxial stretching in the calendering or extrusion process, as well as biaxial stretching during film blowing. Orientation can also be increased, for example, in [[Tensile Test|tensile tests]] on [[Ductility Plastics|ductile]], stretchable [[Plastics|plastics]] at comparatively slow [[Test Speed|test speeds]] (cold flow).

In the case of fillers or reinforcing materials with a fibrous or platelet-like geometry (GF, CF or MF as well as mica), the orientation is also created during the manufacturing process. In the extrusion process and especially in the injection moulding of [[Fibre-reinforced Plastics|reinforced plastics]], the flow conditions in the tool result in an orientation gradient in the longitudinal, width and thickness directions (see: layer model of [[Fibre Orientation|fibre orientation]]), which depends on the thickness and geometry of the component, the injection conditions (temperature and pressure), the fibre volume fraction ([[Viscosity|viscosity]]) and the flow path length of the melt. If we consider the production of [[Multipurpose Test Specimen|multipurpose test specimens]] in the injection moulding process ('''Fig. 2'''), we see differing orientations when comparing a 1- nest and a 5-nest tool, as well as depending on the position in the multi-nest tool, since the flow path length and thus the shear (see: [[Shear Viscosity|shear viscosity]]) of the melt show significant differences. The [[Material Value|characteristic values]] of the [[Tensile Test|tensile test]] can only be compared for identical positions in the mould.

[[file:Z_eigenspannung_o_2.jpg]]
{|
|- valign="top"
|width="50px"|'''Fig. 2''':
|width="600px" |Orientation of fillers depending on the flow path length for a single-nest mould (a) and a multi-nest mould (b)
|}

The [[Fibre Orientation|fibre orientation]] of injection-moulded plates and [[Multipurpose Test Specimen|multipurpose test specimens]] cannot be compared with each other due to the geometry of the sprue channel. The plates exhibit clearer orientation states, but these show greater [[Anisotropy|anisotropy]] in the longitudinal and transverse directions [2].

===Influence on material values of the tensile test===

The residual stresses in test [[Specimen|specimens]] have a particular effect on the determination of elastic characteristics such as the [[Elastic Modulus|modulus of elasticity]] and [[Poisson's Ratio|Poisson's ratio]], as small load stresses cause the stress components to overlap (Fig. 3), which is not taken into account in the calculation of the [[Material Value|characteristics]]. In the [[Tensile Test|tensile test]] ('''Fig. 3a'''), this superposition causes a higher tensile stress in the core of the test specimen, while a slight compressive stress occurs in the outer area. In the [[Bend Test|bend test]] ('''Fig. 3b'''), the distribution of the load stress and the residual stresses results in a complex stress distribution that changes with increasing [[Stress|stress]]. A clear assignment of a neutral fibre is no longer possible in the initial stage of this test. With increasing load stress, the influence of residual stresses decreases, provided that certain limit values for [[Environmental Stress Cracking Resistance|environmental stress cracking formation]] are not exceeded.

[[file:Z_eigenspannung_o_3.jpg]]
{|
|- valign="top"
|width="50px"|'''Fig. 3''':
|width="600px" |Influence of the residual stress distribution in the [[Multipurpose Test Specimen|multipurpose test specimen]] on the resulting stress in the [[Tensile Test|tensile test]] (a) and in the [[Bend Test|bend test]] (b)
|}

In contrast to the residual stresses, the orientations of the macromolecules and additives affect the elastic constants as well as the [[Strength|strength]] and [[Deformation|deformation]] behaviour. In '''Fig. 4''', this influence is shown for polyamide 6 with 30 M.% short glass fibres ([[Plastics – Symbols and Abbreviated Terms|abbreviation]]: PA 6) using averaged '''stress–strain diagrams''' (see: [[Tensile Test|tensile test]]) for the longitudinal (red in '''Fig. 4''') and transverse (blue in '''Fig. 4''') directions. The 1.5 mm thick plates were injection moulded, and the test [[Specimen|specimens]] were then produced by sawing and milling. It is clear to see that the [[Tensile Strength|tensile strength]] in the longitudinal direction of the short glass fibres is almost twice as high as in the transverse direction. In terms of elongation at break, the ratios for the [[Material Value|characteristic values]] are the reverse of those for [[Strength|strength]].

[[file:Residual Stresses Orientations Fig_4.jpg|500px]]
{|
|- valign="top"
|width="50px"|'''Fig. 4''':
|width="600px" |Influence of orientation on [[Tensile Strength|tensile strength]] and elongation at break [3]
|}

==See also==

# [[KNOOP Hardness|KNOOP hardness]]
# [[Thermal Expansion Coefficient|Thermal expansion coefficient]]
# [[Tensile Test Event-related Interpretation|Tensile test event-related interpretation]]
# [[Processing Shrinkage|Shrinkage]]
# [[Shrinkage Test|Shrinkage test]]

'''Referecnces'''

{|
|-valign="top"
|[1]
|Bartnig, K.: Probekörperherstellung und Probekörpervorbereitung. In: Schmiedel, H. (Eds.): Handbuch der Kunststoffprüfung. Carl Hanser, Munich Vienna (1992) (ISBN 978-3-446-16336-2; see AMK-Library under A 3)
|-valign="top"
|[2]
|[[Bierögel, Christian|Bierögel, C.]]: Prüfkörperherstellung. In: [[Grellmann, Wolfgang|Grellmann, W.]], [[Seidler, Sabine|Seidler, S.]] (Eds.): Polymer Testing. Carl Hanser, Munich (2022) 3rd Edition, pp. 15–38 (ISBN 978-56990-806-8; E-Book: ISBN 978-1-56990-807-5; see [[AMK-Büchersammlung|AMK-Library]] under A 22)
|-valign="top"
|[3]
|Illing, R.: Bewertung von mechanischen und thermischen Eigenschaften glasfaserverstärkter Polyamid-Werkstoffe unter besonderer Berücksichtigung des Alterungsverhaltens von Bauteilen in der Automobilindustrie. Martin-Luther-Universität Halle-Wittenberg, Dissertation (2015) Shaker Verlag GmbH Aachen, (ISBN 978-3-8440-4212-2, 198 Seiten, 128 Abbildungen; see [[AMK-Büchersammlung|AMK-Library]] under B 1-27)
|}

[[category:Tensile Test|Tensile Test]]

Tensile Test Residual Stresses Orientations - Revision history

Oluschinski at 05:55, 15 December 2025