Computed Laminography of CFRP Using an X-Ray Cone-Beam and Robotic Sample Manipulator Systems

Abstract

Carbon fibre reinforced polymers (CFRPs) are of interest to the aerospace sector for meeting future CO2 emission targets due to their weight reduction potential. However, the detection of structural and matrix defects is crucial for determining the performance and suitability of CFRPs in current and future generations of aircraft. Computed laminography (CL), a well-established nondestructive testing method, is well-suited to the scanning of CFRP components with large aspect ratios, for which conventional computed tomography is less suitable. Utilising an existing Nikon Metrology custom build X-ray CT scanner, two lift-in lift-out robotic sample manipulator systems are used to extend the capability of the system and allow the exploration of atypical scanning geometries. Implementing raster and limited angle trajectories, reconstructions using the ASTRA Tomography Toolbox and the SIRT algorithm are able to show structural defects in CFRPs, despite the reduced information inherent with CL systems. This paper reports on the system design and initial experiments that demonstrate benefits and drawbacks of different design options and scanning trajectory choices.

Spatial resolution of a laboratory based X-Ray cone-beam laminography scanning system for various trajectories

“…Prior to filtering, the projections were padded to 2048 pixels by repeating the edge values. This reduced line artefacts common in raster laminographic scans [29]. CGLS was used due to its fast convergence.…”

“…Traditional CT scanning is best suited to approximately cylindrical objects, but the technique is less well suited to the inspection of plate-like components/structures especially for high resolution imaging with cone-beam systems. There is now an increasing demand for three dimensional inspection of such components/structures including ball grid arrays [21], paintings [22,23], printing circuit boards [24][25][26], fossils [27], and composite panels in the aerospace industry [18,28,29]. For instance, many aerospace composite panels are potentially very large but extremely flat structures, such as aircraft wings and tails and therefore have extremely high aspect ratios which are extended beyond the field of view of the detector.…”

“…The former requires additional scanning time, and both solutions still require a full rotation of the object, and are thus limited to smaller components or lower resolution scans. An alternative is computed laminography (CL) which has recently received increasing attention [28,29,[34][35][36][37][38].…”

“…In laminographic scanning, relative motion between the source and the test object generates a range of scan trajectories [26,28,38,40,[43][44][45][46]. Many of these scan trajectories allow laterally extended samples to be imaged at high-resolutions.…”

“…The implementation of certain trajectories requires the relative movement of source and detector [28,46]. As calibrated motion of X-ray source and/or detector are often challenging, limited angle and rotary laminography are gaining more attention in industrial applications as they can be implemented on standard CT scanners by moving the sample only, Fig.…”