View source for Tensile Test Event-related Interpretation

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<span style="font-size:1.2em;font-weight:bold;">Tensile test event-related interpretation</span>
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==Informative character of the parameters==

The [[Tensile Test|tensile test]] is primarily used to determine the stress–strain behaviour under [[Uniaxial Stress State|uniaxial]] tensile stress. The [[Material Parameter|parameters]] derived from the tensile test represent distinctive, visually recognizable points on the diagram and can be used for simple design applications, [[Material & Werkstoff|material]] selection and development, and quality assurance. These parameters are not suitable for more exacting [[Plastic Component|dimensioning tasks]] or the design of complex [[Fracture Behaviour of Plastics Components|plastic components]], e.g., using [[Continuum Mechanics|continuum mechanics]] methods or the finite element method (FEM). The tensile test can be used to classify the macroscopic [[Deformation|deformation]] behaviour of [[Plastics|plastics]] and, for example, divide them into [[Fracture Types|brittle]], [[Ductility Plastics|ductile]], and highly ductile behaviour, whereby special characteristics such as the occurrence of [[Yield Stress|yield stress]] can be highlighted.

Information about microscopic deformation processes and damage [[Deformation Mechanisms|mechanisms]], which are of interest to material developers and designers for statements on the damage mechanics of [[Plastics|plastics]] and [[Testing of Composite Materials|composites]], cannot be derived directly from the tensile test and the associated stress–strain diagram.

For such statements, the tensile test must generally be combined with [[Non-destructive Testing (NDT)|non-destructive testing]] methods, also known as [[Hybrid Methods|hybrid methods]]. These simultaneously applied testing methods can then be used to detect [[Microscopic Structure|microstructural]] deformation and damage mechanisms in the [[Polymer|polymer]] matrix, the interface between the inclusion and the matrix, and the [[Particle-filled Thermoplastics#Technically used fillers|filler]] or reinforcing material (see also: [[Fibre-reinforced Plastics|fibre-reinforced plastics]]) and to assign them to a specific point in time or to a specific load or [[Deformation|deformation]]. As a rule, these methods work selectively, so that not all defect mechanisms can be detected at the same time. If the detected damage or deformation mechanisms have been verified without error, e.g., by microstructural investigations, then they can be assigned to the deformation phases in the tensile test, and an event-related interpretation of the tensile test is available, which also allows more in-depth statements to be made about the damage kinetics.

==Coupling of the static tensile test with acoustic emission analysis==

'''Figure 1''' shows the simultaneous recording of [[Sound Emission|sound emission]] on polyamide 6 materials with different short glass fiber contents under identical test conditions in a tensile test.

[[File:Tensile_TE-rel_Interpret-1.jpg]]
{| 
|- valign="top"
|width="50px"|'''Fig. 1''': 
|width="600px" |[[Acoustic Emission|Acoustic emission]] in [[Tensile Test|tensile testing]] of polyamide 6 with 10 wt.-% GF a) and polyamide 6 with 30 m.-% GF b) ([[Plastics – Symbols and Abbreviated Terms|abbreviation]]: PA 6) [1]
|}

It is evident that the damage kinetics for both [[Material & Werkstoff|materials]] are completely different and that the relative onset of damage, in relation to the strain, occurs at different points in time. Despite the lower fiber content, the energies emitted are significantly higher for the polyamide with 10 m.-% glass fibers, which allows conclusions to be drawn about the degree of damage but also about the coupling of the fibres to the matrix (see also: [[Fibre–Matrix Adhesion|fibre–matrix adhesion]]). However, this hybrid test method does not provide any information about the [[Micro-Damage Limit|damage]] or [[Deformation|deformation]] behaviour of the plastic material.

==Volume dilatometry in tensile testing==

Volume dilatometry ('''Fig. 2''') is a [[Hybrid Methods|hybrid method]] that can be used to obtain information on damage and deformation behaviour even in [[Ductility Plastics|ductile]] materials such as unreinforced polyamide 6 ([[Plastics – Symbols and Abbreviated Terms|abbreviation]]: PA 6) [2].

[[File:Tensile_TE-rel_Interpret-2.jpg]]
{| 
|- valign="top"
|width="50px"|'''Fig. 2''': 
|width="600px" |Schematic representation of volume dilatometry in tensile testing
|}

The test [[Specimen|specimen]] is placed in a glass box and fixed with [[Specimen Clamping|clamps]]. The box can be opened to change the test [[Specimen|specimen]]. On the top, the linkage is connected to the [[Electro-Mechanical Force Transducer|load cell]], and on the bottom, the test specimen is loaded via the movable traverse. The elongation or strain is measured with an optical sensor via measuring marks on the [[Surface|surface]] of the test specimen. A fine capillary tube is attached to the side of the container as a connected vessel, which is used to record changes in volume during the [[Tensile Test|tensile test]]. These changes in volume are caused by the formation of cavitations, [[Crack|microcracks]], or an increase in [[Density|density]] as a result of increasing [[Tensile Test Residual Stresses Orientations|orientations]].

==Event-related interpretation==

For the interpretation of the [[Deformation|deformation]] phases of the tensile test, the defect density ''Q''<sub>D</sub> is therefore used as the reciprocal mean value of the density ''ρ'' of the test specimen ('''Fig. 3''').

[[File:Tensile_TE-rel_Interpret-3.jpg|550px]]
{| 
|- valign="top"
|width="50px"|'''Fig. 3''': 
|width="600px" |Event-related interpretation with volumetric dilatometry
|}

'''Figure 3''' shows that there is no change in defect density in the linear-elastic and [[Linear-viscoelastic Behaviour|linear-viscoelastic deformation]] range due to the constant volume. In the non-linear viscoelastic range (see: [[Elasticity|elasticity]]), irreversible deformations occur, resulting in microcavitations and an increase in defect density until the [[Yield Stress|yield stress]] is reached. In the necking range and in the range of steady-state flow, ''Q''<sub>D</sub> decreases again due to the increase in molecular orientation. This process continues with a further increase in the orientation state, even in the hardening range, and ends with an increase in defect density at ultimate fracture.

==See also==

* [[Tensile Test True Stress–Strain Diagram |Tensile test true stress–strain diagram ]]
* [[Micro-damage Limit|Micro-damage limits]]
* [[Bend Test and Sound Emission Analysis|Bend test and sound emission analysis]]
* [[Laser Longitudinal–Transverse Scanner|Laser longitudinal–transverse scanner]]
* [[Polymer Diagnostics|Polymer diagnostics]]


'''References'''

{|
|-valign="top"
|[1]
|[[Bierögel, Christian|Bierögel, C.]], Fahnert, T., [[Grellmann, Wolfgang|Grellmann, W.]]: Deformation Behaviour of Reinforced Polyamide Materials Evaluated by Laser Extensometry and Acoustic Emission Analysis. Strain Measurement in the 21st Century, Lancaster (UK) 5.–6. September 2001, Proceedings (2001) pp. 56–59 [https://www.polymerservice-merseburg.de/fileadmin/inhalte/psm/veroeffentlichungen/Deformation_Behaviour_of_Reinforced_Polyamide_Materials_2001.pdf Download as pdf]]
|-valign="top"
|[2]
|Bierögel, C.: Hybrid Methods of Polymer Diagnostics. In: [https://www.researchgate.net/profile/Wolfgang-Grellmann Grellmann, W.], [[Seidler, Sabine|Seidler, S.]] (Eds.): Polymer Testing. Carl Hanser, Munich (2022) 3rd Edition, pp. 497–513 (ISBN 978-1-56990-806-8; E-Book: ISBN 978-1-56990-807-5; see [[AMK-Büchersammlung|AMK-Library]] under A 22) 
|}

[[Category:Tensile Test]]