Acoustic emission test

from Wikipedia, the free encyclopedia

The acoustic emission testing ( English Acoustic Emission Testing ) and acoustic emission analysis is a test method, often referred to as non-destructive testing method is called. These methods take advantage of the fact that sudden changes in the structure of a material, which are triggered by chemical or thermal processes or under mechanical stress, lead to the emission of sound . Strictly speaking, the acoustic emission test is therefore not a non-destructive test method, as changes such as plastic deformation or crack propagation in the material are commonly defined as damage. The analysis of measured noise emissions allows conclusions to be drawn about the structural integrity of the material or the component.

Advantages and disadvantages

General advantages of the acoustic emission test are:

  • The acoustic emission test is an integral test method, damage can be identified within the entire volume of the test body even with a few sensors
  • Structures can be checked under operating conditions and thus in real time, which is why the acoustic emission test is used particularly for applications in structural health monitoring
  • often the nucleation of damage can already be identified and larger consequential damage can be predicted
  • Location methods allow the source of an acoustic emission signal to be located
  • further signal analysis allows different types of sources to be distinguished (e.g. different types of damage)

The advantages of acoustic emission testing when testing pressure vessels are that:

  • the operating medium does not have to be drained.
  • no pressure sample water is required and this has to be emptied again.
  • the supporting structures of the container did not have to be designed for the weight of the pressure sample water, which is particularly important for large pressure air vessels.
  • there are low overall testing costs.
  • no bladder expansion is necessary with hydraulic accumulators.

The limits of acoustic emission analysis are:

  • Sources of interference (e.g. machine noise, electromagnetic noise or friction between cracks and rivers) can also generate sound emissions; appropriate filter criteria are required in the data analysis
  • static defects cannot be identified
  • Sensors must be suitable for the application, so broadband sensors can be advantageous over resonant sensors

functionality

If a component is exposed to critical mechanical or thermal loads, structural changes occur in the material. The elastic energy stored in the material is suddenly released and spreads out as a transient, elastic stress wave. These sound waves contain information about the underlying mechanical processes. The waves generally propagate as longitudinal and transverse waves as well as Rayleigh waves . In thin-walled structures, the waves can also propagate in Lamb wave mode due to the additional boundary condition that the plate thickness is smaller than the wavelength of certain frequency components of the broadband sound emission signal. Piezoelectric sensors can convert the transient deflections in the material when the wave passes through it into a voltage signal, which can be digitized and further evaluated using software for data analysis. The entire waveform (time-based recording) or only certain parameters (parameter-based recording) of the measured signal (e.g. maximum amplitude, signal duration, energy) can be recorded. The latter method is characterized by a higher recording speed and a reduced data volume, while the time-based recording allows further frequency-based analysis options (e.g. FFT ).

Examples of areas of application

With the acoustic emission test, materials such as metals, ceramics, glasses, rocks, concrete, exclusively brittle polymer materials, wood and composite materials can be tested, whereby the following incipient failure mechanisms of components and devices such as crack formation, crack progression, delamination , crack edge friction, dislocation movement, phase change, corrosion processes, turbulent Currents in leaks, high-voltage partial discharges in large transformers, breaks in mines, etc. can be detected.

The following devices and machines were tested by means of acoustic emission testing: Storage bottles, breathing air filling points, breathing air storage bottles, storage bundles, pressure vessels, compressed air tanks, expansion vessels, hydrogen tanks, tanks, hydraulic accumulators, pulsation dampers, autoclaves , heat exchangers, natural gas preheaters and water-water heat exchangers.

Norms

  • DIN EN 1330-9, Non-destructive testing - Terminology - Part 9: Terms of acoustic emission testing
  • DIN EN 13554, non-destructive testing - noise emission - general principles
  • DIN EN 13477-1, Non-destructive testing - Acoustic emission testing - Device characterization - Part 1: Device description
  • DIN EN 13477-2, Non-destructive testing - Acoustic emission testing - Device characterization - Part 2: Checking the operating parameters
  • DIN EN 14584, Non-destructive testing - Acoustic emission testing - Testing of metallic pressure equipment during the acceptance test - Planar location of noise emission sources
  • DIN EN 15856, non-destructive testing - acoustic emission testing - general principles of acoustic emission testing for the detection of corrosion within metallic enclosures filled with liquid
  • DIN EN 15857, non-destructive testing - acoustic emission testing - testing of fiber-reinforced plastics - specific procedure and general evaluation criteria
  • ISO 12713, Non-destructive testing - Acoustic emission testing - Primary calibration of transducers
  • ISO 12714, Non-destructive testing - Acoustic emission testing - Secondary calibration of acoustic emission transducers
  • ISO 12716, Non-destructive testing - Acoustic emission testing - Terms
  • ISO / DIS 16148, Gas cylinders - refillable seamless gas cylinders - Acoustic emission testing for periodic inspection
  • ASTM Designation E 750: Standard Practice for Characterizing Acoustic Emission Instrumentation, 1992 ASME Boiler & Pressure Vessel Code, Section V, Article 11, pp.159 - 181, Acoustic Emission Examination of Fiber-Reinforced Plastic Vessels
  • ASTM Designation E 1067: Standard Practice for Acoustic Emission Examination of Fiberglass Reinforced Plastic Resin (FRP) Tanks / Vessels
  • ASTM Designation E 1118: Standard Practice for Acoustic Emission Examination of Reinforced Thermosetting Resin Pipe (RTRP)

Individual evidence

  • Nondestructive Testing Handbook, 2nd Edition, Volume 5, Acoustic Emission Testing, American Society For Nondestructive Testing, 1987
  • LM Rogers: Structural and Engineering Monitoring by Acoustic Emission Methods - Fundamentals and Applications, Lloyd's Register Technical Investigation Department, September 2001
  1. ↑ Peter TSCHELIESNIG: Acoustic emission test - The modern alternative
  2. ↑ DIN EN 1330-9, Non-Destructive Testing - Terminology - Part 9: Terms used in acoustic emission testing
  3. ↑ Examples of acoustic emission testing