The properties of fiber reinforced composites are highly determined by fiber distribution and fiber orientation. We measure these characteristics non-destructively.

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Image Analysis for Fiber-Reinforced Polymers

The geometry of the fiber system of fiber-reinforced polymers has a strong impact on mechanical properties of composite parts. The mechanical properties of fiber-reinforced polymers are determined by their geometry to a large extent. Examples for important parameters include the spatial fiber arrangement and the fiber direction distribution. These and other characteristics can be computed from image data using specialized image analyses algorithms. Micro-computer tomography (µCT) is well-suited for a three dimensional characterization, but two dimensional imaging methods such as scanning acoustic microscopy (SAM) can also be used.

The software package MAVI includes a number of specialized, efficient algorithms for characterizing glass (GRP) or carbon fiber-reinforced polymers (CRP):

  • Local fiber volume density
  • Local and global orientation tensors
  • Mean fiber direction
  • Degree of anisotropy
  • Specific fiber length (total fiber length per unit volume)
  • Mean fiber diameter
  • Visualization of local fiber densities and directions
Analyse einer UUltraschall-Mikroskopie-Aufnahme einer SMC-Zugprobe
© Photo Visualization IVW Kaiserslautern

Analyse einer Ultraschall-Mikroskopie-Aufnahme einer SMC-Zugprobe, mit einem Glasfaseranteil von 30%, wobei sich die Glasfasern 0.07 mm unter der Oberfläche in einer Kunststoffmatrix befinden (a). Das Fasersystem wird binarisiert (b) und an jedem Faserpunkt die Faserrichtung berechnet (c).

Räumliche Darstellung der quantitativen Ergebnisse mit dazugehörigem Plot der Diagonalelemente der lokalen Orientierungstensoren
© Photo ITWM

The measurements can be visualized by super-imposing the results onto the fiber system. Here, the central elements of the local orientation tensors were used (Sample and image source: IVW Kaiserslautern). A plot of the diagonal elements of the local fiber orientation tensors through the thickness of the specimen reveals a rearrangement of the fiber directions in the inner area due to rheological effects.

Analyseergebnisse nach einem Region-Of-Interest-Scan an einem Bremsleitungshalter.
© Photo ITWM

Analysis results for a region of interest CT data set of a break pipe clip. 3D visualization of local deviation fiber direction from global mean fiber direction. Yellow marks deviations larger than 20°.

These geometric parameters are suitable for verification homogeneity and desired fiber directions in specimens. Furthermore, they enable the fitting of stochastic geometric models. These can be provided either on regular voxel grids or in the form of surface meshes and are suitable for the computation and prediction of structural mechanical properties of composite specimens.

Ultra high performance concrete (UHPC) is the high-end material in modern civil engineering. Embedded fibers improve the mechanical properties, in particular the tensile strength after cracking. In this project, fiber distribution and fiber orientation are analyzed using MAVI. Moreover, the behavior of the fibers during cracking is studied based on µCT image data of in-situ tensile tests.

 

Publications

Schuler, F.; Breit, W.; Schnell, J.; Rösch, R.:
Möglichkeiten des Einsatzes der Computer-Tomographie bei der Untersuchung von Stahlfaserbetonen.
Betonwerk International, Heft 4, S. 70-72, (2013).

O. Wirjadi, K. Schladitz, P. Easwaran, J. Ohser:
Estimating Fibre Direction Distributions of Reinforced Composites from Tomographic Images.
Image Analysis and Stereology 35, 167-179, (2016).

K. Schladitz, A. Büter, M. Godehardt, O. Wirjadi, J. Fleckenstein, T. Gerster, U. Hassler, K. Jaschek, M. Maisl, U. Maisl, S. Mohr, U. Netzelmann, T. Potyra, M. Steinhauser:
Non-Destructive Characterization of Fiber Orientation in Reinforced SMC as Input for Simulation Based Design.
Composite Structures 160, 195-203, (2017).