Oluschinski at 05:30, 15 December 2025

2025-12-15T05:30:53Z

← Older revision		Revision as of 07:30, 15 December 2025
Line 43:		Line 43:
	\|}		\|}

	When [[Fibre-reinforced Plastics\|reinforced plastics]] or [[Particle-filled Thermoplastics\|particle-filled plastics]] are tested with ultrasound, strong scattering also occurs at internal heterogeneities such as fibres, mats or particles. The energy losses cause a significant reduction in the penetration capability of the ultrasound. The conventional [[A-Scan\|A-scan]] is therefore overlaid by many scattering and reflection signals (gras), which often makes reliable detection of the back wall echo impossible [4, 6].		When [[Fibre-reinforced Plastics\|reinforced plastics]] or [[Particle-filled Thermoplastics\|particle-filled plastics]] are tested with ultrasound, strong scattering also occurs at internal heterogeneities such as fibres, mats or particles. The energy losses cause a significant reduction in the penetration capability of the ultrasound. The conventional [[A-Scan Technique\|A-scan]] is therefore overlaid by many scattering and reflection signals (gras), which often makes reliable detection of the back wall echo impossible [4, 6].

	==See alao==		==See alao==

Oluschinski: Created page with "{{Language_sel|LANG=ger|ARTIKEL=Absorption Schallwellen}} {{PSM_Infobox}} Absorption sound waves FORCETOC ==Physical fundamentals== When a sound wave hits an external or internal interface (see also: phase boundary surface), it will partially penetrate this material (transmission sound waves), but will also be partially reflected b..."

2025-11-28T12:02:57Z

Created page with "{{Language_sel|LANG=ger|ARTIKEL=Absorption Schallwellen}} {{PSM_Infobox}} Absorption sound waves __FORCETOC__ ==Physical fundamentals== When a sound wave hits an external or internal interface (see also: phase boundary surface), it will partially penetrate this material (transmission sound waves), but will also be partially reflected b..."

New page

{{Language_sel|LANG=ger|ARTIKEL=Absorption Schallwellen}}
{{PSM_Infobox}}
Absorption sound waves
__FORCETOC__

==Physical fundamentals==

When a sound wave hits an external or internal interface (see also: [[Phase Boundary Surface|phase boundary surface]]), it will partially penetrate this [[Material & Werkstoff|material]] ([[Transmission Sound Waves|transmission sound waves]]), but will also be partially reflected back at the [[Surface|surface]] or interface (see also: [[Ultrasonic Waves Reflection|ultrasonic waves reflection]]). In the material behind the interface, the wave is subject to material-specific absorption or dissipation, whereby the intensity ''I''0 of the incident wave is reduced. At the same time, especially in polycrystalline materials (grain boundaries in metals) and in heterogeneously structured [[Composite Materials Testing|composite plastics]] ([[Particle-filled Thermoplastics|particles]] and [[Fibre-reinforced Plastics|fibres in fibre-reinforced plastics]] (FRP)), the ultrasonic wave is scattered ('''Fig. 1''').

[[File:Absorption Sound-1.jpg]]
{|
|- valign="top"
|width="50px"|'''Fig. 1''':
|width="600px"|Scattering at internal interfaces a) in polycrystalline metals and b) in [[Short-fibre Reinforced Plastics|filled and reinforced plastics]] with perpendicular sound incidence
|}

This effect becomes clear when comparing sound attenuation, i.e. the decrease in [[Sound Pressure|sound pressure]] due to the geometric divergence of the sound wave, with the actual reduction in [[Sound Pressure|sound pressure]] [1–5]. Absorption refers to the partial conversion of sound energy into thermal energy, whereby the structure is excited to vibrate. Strictly speaking, the dissipation of sound energy refers not only to its conversion into thermal energy, but also into other forms of energy, making absorption a special case of dissipation. This thermal effect can be utilised in a non-destructive manner (see also: [[Non-destructive Polymer Testing|non-destructive polymer testing]]) by exciting internal defects, such as [[Crack|cracks]] or delaminations, using [[Ultrasound Testing|ultrasound]] and recording the thermal emission, e.g. by means of video [[Thermography|thermography]] (ultrasonic lock-in thermography). In the case of scattering, the ratio of the size of the inhomogeneity (grain size, particles or fibres) to the incident wavelength ''λ'' has a decisive influence on the extent and type of scattering, which is why this influencing factor also depends on the frequency of the ultrasound [5]. In contrast to scattering, sound absorption also depends on the type of wave and the frequency, with absorption increasing proportionally with the ultrasonic frequency.

==Sound absorption coefficient ''α''==

In isotropic [[Material & Werkstoff|materials]] without internal heterogeneities, only absorption occurs, but no scattering (see: [[Ultrasonic Waves Reflection|ultrasonic waves reflection]] and [[Refraction Sound Waves|refraction sound waves]]) [4]. In [[Ultrasound Testing|ultrasonic testing technology]], scattering and absorption, generally referred to as sound attenuation, cause a reduction in the registered sound waves in the [[Ultrasonic Transmission Technique|transmission]] or [[Pulse-Echo Ultrasonic Technique|pulse-echo method]]. The parameters absorption coefficient and absorption degree are used for the quantitative representation of sound absorption, whereby the sum of the transmitted and dissipated portions is referred to as absorbed sound energy (sound absorption). The absorption coefficient ''α'' or linear attenuation coefficient ''μ'' (also known as the damping constant) describes the reduction in intensity ''I''0 of a plane ultrasonic wave in a medium, whereby geometric losses due to divergence are not taken into account here. This [[Material Value|value]] is therefore a material-specific constant for sound attenuation.

The frequency-dependent sound absorption coefficient α is a measure of the intensity of sound ''I''0 lost in a medium due to sound transmission ''τ'' and sound dissipation ''δ'' ('''Eq. 1'''), which thus describes the absorption capacity of a [[Material & Werkstoff|material]].

{|
|-
|width="20px"|
|width="500px"|''α'' = ''τ'' + ''δ''
|(1)
|}

An absorption degree ''α'' of ''α'' = 0 means that no absorption takes place and all incident sound is reflected. Conversely, ''α'' = 1 means that the incident sound is completely absorbed, and no reflection takes place.

==Example of sound absorption in plastics==

The practical effects of absorption losses in [[Ultrasound Testing|ultrasound testing]] can be illustrated by comparing metallic materials with [[Plastics|plastics]]. Since even unfilled plastics exhibit significantly higher sound attenuation due to absorption, the penetration depth of these materials is lower, especially at higher test frequencies ('''Fig. 2''').

[[File:Absorption Sound-2.jpg|350px]]
{|
|- valign="top"
|width="50px"|'''Fig. 2''':
|width="600px"|Influence of the lead-in distance on the signal response (A-scan) for an UP resin DERAKANE 411 with whirling fibre (WF) at a thickness ''d'' = 34.4 mm
|}

When [[Fibre-reinforced Plastics|reinforced plastics]] or [[Particle-filled Thermoplastics|particle-filled plastics]] are tested with ultrasound, strong scattering also occurs at internal heterogeneities such as fibres, mats or particles. The energy losses cause a significant reduction in the penetration capability of the ultrasound. The conventional [[A-Scan|A-scan]] is therefore overlaid by many scattering and reflection signals (gras), which often makes reliable detection of the back wall echo impossible [4, 6].

==See alao==

* [[Transmission Sound Waves|Transmission sound waves]]
* [[Phase Boundary Surface|Phase boundary surface]]
* [[Ultrasonic Wave Reflection|Ultrasonic wave reflection]]
* [[Ultrasonic Weld Inspection|Ultrasonic weld inspection]]

'''Reference'''

{|
|-valign="top"
|[1]
|Krautkrämer, J., Krautkrämer, H.: Ultrasonic Testing of Materials. Springer, Berlin (1990) 4th Edition, (ISBN 978-3-540-51231-8)
|-valign="top"
|[2]
|Lerch, R., Sessler, G., Wolf, D.: Technische Akustik – Grundlagen und Anwendung. Springer, Berlin (2009) (ISBN 978-3-540-49833-9)
|-valign="top"
|[3]
|Möser, M.: Technische Akustik. Springer, Berlin (2015) (ISBN 978-3-662-47704-5)
|-valign="top"
|[4]
|Matthies, K. u. a.: Dickenmessung mit Ultraschall. DVS Media Publishing, Berlin (1998) 2nd Edition (ISBN 3-87155-940-7; see [[AMK-Büchersammlung|AMK-Library]] under M 44)
|-valign="top"
|[5]
|Deutsch, M.; Platte, V.; Vogt, M.: Ultraschallprüfung. Grundlagen und industrielle Anwendungen. Springer, Berlin (1997) (ISBN 3-540-62072-9; see [[AMK-Büchersammlung|AMK-Library]] under M 45)
|-valign="top"
|[6]
|Busse, G.: Non-destructive Polymer Testing. In: [[Grellmann, Wolfgang|Grellmann, W.]], [[Seidler, Sabine|Seidler, S.]] (Eds.): Polymer Testing. Carl Hanser, Munich (2022) 3rd Edition, pp. 431–495 (ISBN 978-1-56990-806-8; E-Book: ISBN 978-1-56990-807-5; see [[AMK-Büchersammlung|AMK-Library]] under A 22)
|}

[[Category:Acoustic Test Methods_Ultrasonics]]

Absorption Sound Waves - Revision history

Oluschinski at 05:30, 15 December 2025