Photon Factory Activity Report 2017 #35 (2018)

AR-NW2A/2016S2-001

In situ observation of crack initiation and propagation in CFRP
using a newly-developed XAFS-CT
Toshiki Watanabe1,*, Yasuo Takeichi1,2, Yasuhiro Niwa1, and Masao Kimura1,2
Institute of Materials Structure Science, Photon Factory, 1-1 Oho, Tsukuba, 305-0801, Japan
2
School of High Energy Accelerator Science, SOKENDAI, 1-1 Oho, Tsukuba, 305-0801, Japan
1

1 Introduction
Carbon fibre reinforced plastic (CFRP) composites areof growing use in aircrafts because of their high specificstrength and stiffness. Micromechanism of damages andmicroscopic chemical properties of CFRPs is a key tounderstand the mechanical properties and durability ofthese materials. Recent reports pioneered themicromechanical analysis of fractures under quasi-static
stress [1] and fatigue failures [2] in CFRPs from threedimensional dataset obtained using synchrotron X-ray
computed tomography (CT).
2 Experiment
We have developed and installed a new X-ray
microscope: Synchrotron Radiation X-ray Absorption
Fine Structures – CT (SR-XAFS-CT) at the NW2A
beamline of PF-AR in IMSS, KEK. The outline of theSR-XAFS-CT system is illustrated in Fig. 1. A
monochromatic X-ray beam is focused onto the sample
using an elliptical glass capillary and the image isprojected onto the CCD detector by means of a micro Fresnel zone plate lens. It was confirmed that the system
has a high spatial resolution less than 50 nm using astandard test pattern. The sample is mounted on an X, Y, Z, stage, and we can perform X-CT measurements byrotating the sample for a specific X-ray energy. By
repeating this measurement over an energy range near theabsorbing energy of a specific element, we can obtain 3Dmapping of chemical states of the elements. SR-XAFSCT can provide 3D-imaging information about (a)microstructure, (b) cracks, and (c) chemical states ofmaterial with the high spatial resolution.
Furthermore, we have been challenging ‘highresolution time-lapse study of in situ crack growth inCFRP’. We utilized a novel nanomechanical test stage,
which was designed specifically for the SR-XAFS-CT
system (Fig.2). The stage features a high precision piezo
actuator and an integrated load cell up to 5000 N,
enabling the load-displacement curve to be measured andrelated to the evolving microstructure observed in thecorresponding 3D tomographic reconstructions.
A CFRP specimen was indented with a diamond coneto initiate and propagate cracks in the specimen.
Snapshots of initiation and propagation of cracks weresuccessfully obtained with a high resolution less than 50nm. It was clearly observed that a crack initiates at theinterface between a fiber and the resin matrix, and that it
branches into cracks that are (a) propagating along theinterface and (b) traversing across the resin matrix to aneighboring fiber.

Fig. 1: Outline of SR-XAFS-CT microscope.

Fig. 2: Nanomechanical test stage.
3 Results and Discussion
Fig. 3 shows typical examples of cross section imagesof the three-dimensional volume data reconstructed from151 projections. Interfaces between carbon fibers andepoxy resin were clearly observed. It should be noted theimages show features not the surface but inside thespecimen and that the crack initiation and propagation isfree from surface effects. Cracks propagate along theinterface between carbon fibers and epoxy resin in XY
slice, and crack branching observed on the tip in XZ slice.
We have successfully developed the technique ofnanomechanical testing for in situ X-CT observation ofcrack propagation in CFRP with XRM using synchrotronradiation.

Photon Factory Activity Report 2017 #35 (2018)

Fig. 3: A cross section image of the volume data obtainedby X-CT after the crack propagation.
Left: XY slice and Right: XZ slice.
Acknowledgement
This work was supported by the Structural Materials forInnovation of the Cross-ministerial Strategic InnovationPromotion Program (SIP) of Japan Science andTechnology (JST). Experiments using synchrotron
radiation were performed with the approval of the Photon
Factory Program Advisory Committee (Proposal Nos.
2015S2-002 and 2016S2-001).
References[1] A. E. Scott, M. Mavrogordato, P. Wright, I. Sinclair, and S.
M. Spearing, Compos. Sci. Technol., 71, 1471 (2011).

[2] S. C. Garcea, I. Sinclair, and S. M. Spearing, Compos. Sci.
Technol., 109, 32 (2015).

* toshiki.watanabe@kek.jp