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Bildgebende Verfahren und optische Analytik

Computed Tomography

Wandstärkenanalyse an einem Kunststoff-Spritzgießbauteil, Foto: Fraunhofer WKI, HOFZET
Faservolumengehalt und Faserorientierung in einem holzfaserverstärk­ten Spritzgießbauteil, Foto: Fraunhofer WKI, HOFZET

Computed Tomography (CT) is a fast and non-destructive method for material and component inspection. It provides a three-dimensional representation of the inner and outer structure of objects with detail recognition down to the micrometer range. CT evaluation involves a number of qualitative and quantitative analyzes, such as the characterization of materials with regard to defects such as cracks, voids and pores or dimensional investigations.

It should be emphasized that the method is in principle suitable for any material or combination of materials.

Computed Tomography Procon X-Ray CT-Alpha Duo

Technical details:

  • 240 kV microfocus and 225 kV high-power x-ray tube
  • 4MP detectors
  • Samples: Diameter max. 500 mm, height max. 400 mm, weight max. 25 kg
  • Z-shaft for further in situ structures (e.g. fluids, pressure, etc.)
  • Scan volume depending on recording mode:
  • 500 mm diameter, 250 mm height
  • 250 mm diameter, 400 mm height
  • Minimum voxel size: <1 μm

In cooperation with the HOFZET application center of Fraunhofer WKI matters regarding CT measurements can be worked on.

Optische Materialanalysen

Some thermoplastics crystallize because their macromolecules or side chains of macromolecules form an ordered system while solidifying from melt. The macromolecules of the polymers can form crystalline and amorphous (disordered) structures within the matrix. Crystalline structures with a radial arrangement are called spherulites.
The formation and the size of these spherulites have a significant influence on the material properties of the respective plastics.

Additives influence the crystallization of plastics. For example, the bacterial count of the spherulites increases with the addition of talc or natural fibers in semi-crystalline plastics. These spherulitic systems are examined with the aid of a hot stage microscope. It is possible to visually examine plastics and their melting behavior.

Hot stage microscope

Areas of application:

  • Examination of non-isothermal and isothermal crystallization (Spherolite systems)
  • Examination of the phase distribution of polymer blends
  • Examination of melting points in thermoplastics
  • Transmitted light up to 650 x magnification
  • Various surveying possibilities

Scanning Electron Microscopy incl. EDX for elemental analysis, line scans and mapping

Scanning Electron Microscopy Type Zeiss EVO 60 EP, Source: IfBB
Scanning Electron Microscopy Type Zeiss EVO 60 EP, Source: IfBB

A scanning electron microscope (SEM) is an electron microscope in which a primary electron beam is guided (scanned) over a sample. This creates interactions between the electrons and the sample and thus creates an image. The entire process normally takes place in a high vacuum in order to avoid interactions with atoms and molecules in the air. The main areas of application of a SEM are material and damage analysis.

Scanning electron microscopy has several advantages over traditional light microscopy:

  • High depth of field
  • Increased resolution
  • Low effort during sample preparation
  • Easy adaptation of additional
  • Measuring instruments for microanalysis

The bombardment of the sample with the electron beam produces secondary products that can be used for visualization and material analysis. The secondary electrons (SE) and the backscattered electrons (RSE) are the signals used for imaging. For the characterization of materials X-rays are used, which are analyzed with an energy-dispersive (EDX) spectrometer. Another development of the REM is the use of VP-diaphragms (Variable Pressure). This makes it possible to microscopy highly gaseous, moist and non-conductive samples and to realize non-destructive examinations.

3D digital microscope VHX 5000 Keyence

3D digital microscope VHX 5000 Keyence, Source: IfBB
3D digital microscope VHX 5000 Keyence, Source: IfBB

The 3D digital microscope enables three-dimensional surface examinations of plastics and other materials. Compared to classical two-dimensional microscopy it is possible to measure elevations and depressions on plastic samples. The three-dimensional image is created by the motorized Z-axis and software that calculates image information. Furthermore, the lens can be adjusted up to 90 °. Other options include the motorized table and various lighting options.

  • Scratch resistance of plastics (width and depth measurement)
  • Examination of fracture surfaces and fiber matrix systems
  • Three-dimensional display options quality assurance
  • Fiber distribution on surfaces
  • Volume and surface calculations of 3D bodies
  • Incident and transmitted light options up to 5000x magnification
  • Lens in adjustable angle
  • Various surveying possibilities

Particle, fiber analysis and characterization by Fibershape

Beispiel einer Fibershape-Double-Auswertung, Foto: IfBB
Beispiel einer Fibershape-Double-Auswertung, Foto: IfBB

The morphology of fibers can be determined using an optical measurement method called Powdershape or Fibershape.

The software for this system was developed by the company Innovative Sintering Technologies AG (short: IST AG). For the Powdershape analysis a KONICA MINOLTA slide scanner, the Dimage Scan Elite 5400 ΙΙ, is used. It achieves a maximum resolution of 5400 dpi. To examine a sample the material is trapped between two glass plates that are attached to each other with a transparent adhesive tape. The material is inserted into the sample holder of the scanner and scanned. The Fibershape analysis is done with the flatbed scanner Perfection 4990 Photo from the manufacturer EPSON, which has a maximum resolution of 1200 dpi. At a resolution of 5400 dpi, particles and fibers from 7 μm are clearly visible, at 1200 dpi all particles and fibers from 40 μm are visible.

The software evaluates the results and creates a test report of the material. Various measurement masks are available for this, which are selected according to the type of material and use special calculation algorithms. There is a difference between fibers and particles. As a rule, the length-to-width ratio (l / d ratio) is used to distinguish between these two states. For an examiner a statement of manufacturer as to whether the sample material is a fiber or a particle is very helpful. Other variables that influence the choice of measurement mask and the measurement are the curvature, the squareness and the orientation as well as the optical properties, transparency and color of the material studied. The example of such a measurement can be seen in the figure above.

Advantages:

  • very fast measuring method
  • very large measuring range over several powers of ten
  • Measurement of complex structures
  • easy and fast sample preparation
  • Minimization of user errors
  • reliable and fast industrial quality control
  • very comprehensive parametrizable

Color and gloss measurement

Type: "spectro-guide sphere gloss" from BYK-Gardner GmbH

  • Measurement of color values ​​according to DIN 5033
  • Determining the L * a * b * color values
  • Determination of the ΔE value
  • Determination of gloss level

FTIR spectrometer TENSOR II

Technical details:

  • Model: TENSOR II (Brucker Optik GmbH)
  • Spectral range: 11,000 to 350 cm-1
  • Resolution: better than 0.4cm-1
  • Measurement modes: ATR, transmission, reflection with the angles of incidence of 30 ° and 80 °
  • Sample space: 25 x 27 x 16 cm (W x D x H)
  • Polymer library with over 10,000 entries