| 1. |
- Lindblom, David, et al.
(author)
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In-situ neutron imaging of delayed hydrogen cracking in highstrength steel - experiments and modeling
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Review (other academic/artistic)abstract
- Hydrogen delayed fracture, also known as hydrogen-induced cracking, is a type of brittle fracture that occurs due to the slow diffusion and accumulation of hydrogen atoms, leading todecreased ductility and eventual cracking under constant load. This paper presents an in-situobservation, using neutron imaging, of delayed crack propagation caused by hydrogen embrittlement in a high strength martensitic steel specimen. The experiments involved mechanicalloading of a single-edge-notch bend specimen while submerged in an electrolyte solution (H2O+ 3.5% NaCl) under cathodic polarization to facilitate hydrogen ingress. Neutron transmission images were obtained in-situ and used to monitor intermittent crack propagation wasrecorded over a period of 12 hours. The stress state at each crack configuration was extracted from a three-dimensional elastic-plastic finite element simulation, which was tailoredto match the quantitative information acquired from the neutron radiographs of the fractureprocess. To gain insight into the evolution of hydrogen concentration with crack propagation,a modeling scheme for stress-assisted hydrogen diffusion was employed. These simulationsprovided qualitative information on the relation between intermittent crack propagation andthe subsequent supply of hydrogen to the crack tip. Finally, a failure locus was constructedbased on the calculated hydrogen concentration levels and the experimentally determinedcrack growth resistance.
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| 2. |
- Martell, Josefin, et al.
(author)
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The scale of a martian hydrothermal system explored using combined neutron and x-ray tomography
- 2022
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In: Science Advances. - : American Association for the Advancement of Science (AAAS). - 2375-2548. ; 8:19
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Journal article (peer-reviewed)abstract
- Nakhlite meteorites are igneous rocks from Mars that were aqueously altered ~630 million years ago. Hydrothermal systems on Earth are known to provide microhabitats; knowledge of the extent and duration of these systems is crucial to establish whether they could sustain life elsewhere in the Solar System. Here, we explore the three-dimensional distribution of hydrous phases within the Miller Range 03346 nakhlite meteorite using nondestructive neutron and x-ray tomography to determine whether alteration is interconnected and pervasive. The results reveal discrete clusters of hydrous phases within and surrounding olivine grains, with limited interconnectivity between clusters. This implies that the fluid was localized and originated from the melting of local subsurface ice following an impact event. Consequently, the duration of the hydrous alteration was likely short, meaning that the martian crust sampled by the nakhlites could not have provided habitable environments that could harbor any life on Mars during the Amazonian.
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| 3. |
- Törnquist, Elin, et al.
(author)
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The Hydration State of Bone Tissue Affects Contrast in Neutron Tomographic Images
- 2022
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In: Frontiers in Bioengineering and Biotechnology. - : Frontiers Media SA. - 2296-4185. ; 10
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Journal article (peer-reviewed)abstract
- Neutron tomography has emerged as a promising imaging technique for specific applications in bone research. Neutrons have a strong interaction with hydrogen, which is abundant in biological tissues, and they can penetrate through dense materials such as metallic implants. However, in addition to long imaging times, two factors have led to challenges in running in situ mechanical characterization experiments on bone tissue using neutron tomography: 1) the high water content in specimens reduces the visibility of internal trabecular structures; 2) the mechanical properties of bone are dependent on the hydration state of the tissue, with drying being reported to cause increased stiffness and brittleness. This study investigates the possibility of improving image quality in terms of neutron transmission and contrast between material phases by drying and rehydrating in heavy water. Rat tibiae and trabecular bovine bone plugs were imaged with neutron tomography at different hydration states and mechanical testing of the bone plugs was carried out to assess effects of drying and rehydration on the mechanical properties of bone. From analysis of image histograms, it was found that drying reduced the contrast between bone and soft tissue, but the contrast was restored with rehydration. Contrast-to-noise ratios and line profiles revealed that the contrast between bone tissue and background was reduced with increasing rehydration duration but remained sufficient for identifying internal structures as long as no free liquid was present inside the specimen. The mechanical analysis indicated that the proposed fluid exchange protocol had no adverse effects on the mechanical properties.
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