The University of Manchester runs static and dynamic inspection using a large Computed Tomography (CT) bay. Source: Nikon Metrology

Paleontologists rub shoulders with aircraft designers at the Henry Moseley X-ray Imaging Facility. Academic and industrial users gather instant scientific proof regarding otherwise hidden information using radiography and Computed Tomography (CT). Projects run on Nikon Metrology systems have shed new light on power plant metal corrosion, damage propagation in composite aerospace structures, Velociraptor behavior, and animal organ vascular networks.

Located at the School of Materials at the University of Manchester, the Henry Moseley X-ray Imaging Facility houses a suite of six computed tomography (CT) systems. “Worldwide academic and industry researchers have access to top-class equipment that offers full resolution and length scale capabilities for samples ranging from heavy engineering items to micron-sized biological specimens,” says Professor Phil Withers, founder and director of the X-ray imaging facility. “Evaluating stunning 3-D models reconstructed from a series of x-ray images revolutionizes many research fields, including materials science, biology, mineralogy, paleontology, entomology, medicine and life science.”

CT slices of a Velociraptor manus claw served as input for FE modeling to predict claw capability. Source: Nikon Metrology

Dinosaurs and Other Animal Specimens

The Henry Moseley X-ray Imaging Facility is shedding light on a diverse range of natural samples. Recently, fossilized portions of ungual claws of a Velociraptor dinosaur were inspected to generate an accurate 3-D finite element (FE) microstructurally faithful model. Analog material from a similar dinosaur as well as the pedal digit and claw of an eagle owl, were analyzed to provide input data for the Velociraptor claw FE model. Strength and strain simulations confirmed that the claws were resistant to extreme forces in the longitudinal direction and therefore well adapted for climbing.

“Medicine is undoubtedly a growth area in high resolution X-ray micro tomography,” says Chris Martin, senior experimental officer managing the operation of the Henry Moseley Imaging Facility. “A nice example is a research project for investigating the action of cancer treatments. It encompasses ex-vivo studies of the vascular system of blood vessels in animal brains, livers, kidneys and lungs.”

When evaluating these remarkable 3-D images on powerful workstations, the software determines the volumetric fraction of the blood vessels. This project illustrates that ex-vivo CT inspection offers much higher resolution than in-vivo magnetic resonance imaging (MRI), which typically falls short on detailed visualization of the smaller vessels.

Unlike metals, cracks in composites often remain largely invisible until very late in the testing process. Source: Nikon Metrology

CT Critical for Studying Composites Failure Mechanisms

According to Chris Martin, another growing research activity concerns new lightweight materials gaining popularity, particularly for aerospace applications. He mentions current research projects to develop and exploit in-situ rigs to enable multi-mode stressing of composite samples – a keen interest of the international aerospace companies the School of Materials collaborates with. “Identifying failure mechanisms in composites is a tricky business, knowing that the damage often remains largely invisible externally until late in the testing process. X-ray and CT technology help gain a better understanding of the failure mechanisms and develop mathematical formulae describing the degrading performance characteristics.”

At various stages throughout the fatigue process, the composite samples are investigated in the walk-in radiation bay of the unique Nikon Metrology 320kV microfocus X-ray system. Such voluminous parts easily fit in the large cabinet bay, which is equipped with a fully programmable 5-axis manipulator designed for samples up to 100 kilograms.

The X-ray source is a proprietary 225/320-kilvolt microfocus source with a spot size that is considerably smaller than competitors’ mini-focus sources, providing image resolution up to 3 microns.

A premium 2,000 x 2,000 pixel Perkin Elmer flat panel detector accurately digitizes cracks and fractions formed in the composite material, within a 400 by 400 millimeters field of view. “Superior X-ray technology is needed to get sufficient contrast, as composite parts are low-density by nature and absorb different energies in different directions,” Chris Martin concludes.

A similar approach is applied to study metal corrosion mechanisms that occur in nuclear reactors or chemical plants. CT observations provided insight into the development of corrosion pits, stress corrosion cracks and their geometries, to improve system design and deduce mathematical formulae. When dealing with metal and other dense materials, the system can be equipped with a rotating target source. Such a source generates an X-ray flux that is up to 5 times higher without risking permanent source damage, providing faster data acquisition and/or higher image accuracy.

Chris Martin says that the Nikon Metrology 225/320-kilovolt inspection system also supports dynamic investigations. Its walk-in radiation bay provides sufficient space to install instrumentation to study how specimens evolve over time, either naturally or under a range of loads, temperatures or other stimuli. A triaxial loading cell, for example, can be used to monitor the evolution of voids, inclusions, fractions and disturbances in large rock and soil samples. For the inspection of smaller parts, researchers at the imaging facility use a similar, yet more compact 225-kilovolt CT inspection system from Nikon Metrology.

Pitting corrosion in stainless steel usually initiates through local breakdown of the passive surface film. Source: Nikon Metrology

Increasing Productivity and Pushing the Limits of CT Technology

“To maximize CT infrastructure availability for fundamental research and commercial projects, we decided to operate the facility 24/7,” says Professor Phil Withers. “To free up CT equipment after data capture, the X-ray data is automatically transferred to a central cluster of computers, which handles the reconstruction of the 3-D models from a series of X-ray images. This guarantees maximum productivity, while local reconstruction resources remain available in case of failure.”

“Equally important is that we try to push the limits of CT technology by focusing on the optimization of the reconstruction software. We benefit from strong programming expertise present at the University of Manchester, and have active academic links with Nikon Metrology and other CT specialists. Detailed insight into our own reconstruction software allows us to optimize data acquisition and precisely figure out how to interpret 3-D Computed Tomography models.”

“Both our micro-CT systems from Nikon Metrology respond to a broad range of academic and industrial applications. The systems’ high accuracy, large field of view and fast image acquisition are well appreciated. Our experience with these systems is that parties applying CT for a specific purpose generally discover more purposes for this enabling technology. We are currently expanding the imaging facility to further explore the nano length scale, in order to provide an even wider range of possibilities.”
Nikon Metrology
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