Crack Imaging in Composite Materials using High-resolution Nano-XCT

© Fraunhofer IKTS

Fig. 1: XCT based virtual cross-sections through a carbon fiber reinforced Aluminum matrix composite. 1A and 1B display the 3D reconstructed data set with the indenter tip (green) and the crack along the carbon fiber/Aluminum matrix interface (red), 1C and 1D show virtual cross-sections of the crack grown along the interfaces.

© Fraunhofer IKTS

Fig. 2: Virtual cross sections from a 3D nanoXCT data set showing micro solder bumps in a 3D stacked microchip.

High-resolution X-ray microscopy and nano X-ray computed tomography are excellent techniques for three-dimensional investigation of nanostructured materials. In combination with mechanical loading devices, e.g. an in-situ nano-indentation stage, the technique combines the advantages of high-resolution three-dimensional visualization of microstructure with the observation of microstructural changes under loading. Phenomena such as crack initiation, crack propagation and, with composite materials, also delamination can thus be studied. Therefore, the set-up can provide fundamental understanding about the deformation behavior and failure mechanism of advanced materials.

A newly designed mechanical load stage for in-situ mechanical loading was developed for the laboratory-based X-ray microscope at Fraunhofer IKTS (Xradia nanoXCT-100). The special design of the stage allows the use several types of indenters and force sensors depending on the mode and type of material. The indenter geometry and the samples are prepared to fit within the field of view of the X-ray microscope (FOV width: 65 µm or 16 µm). With an operating range of up to 1000 mN and a force resolution better than 0.25 mN, it is well suited to perform mechanical tests with various composite materials like carbon fiber composites and composites with ceramic or metal matrices while enabling the simultaneous non-destructive 3D imaging of the components/micro-structure of the composite materials with sub-100 nm resolution. This can be used, for instance, to monitor crack propagation and delamination under mechanical loading at the microscale.

The apparatus has the following properties:

  • - Experimental set-up with miniaturized micro-indentation using diamond tip with Berkovich geometry to initiate damage in composites
  • - High-resolution transmission X-ray microscopy (TXM) and nano X-ray computed tomography (nano-XCT) for nondestructive 3D imaging with sub-100 nm resolution.