Papers by Keyword: X-Ray Microtomography

Abstract: We have studied spallation in single crystal of metals under shock at very high strain rate. Our work has been devoted to understanding, and predicting the dynamic ductile damage processes of nucleation, growth and coalescence of voids in these extreme conditions of impact. Recovered sample only indicates final state of damage. Molecular Dynamics calculations are predicting the phenomenon over time. However we need experimental results to validate and improve simulations and models. X-ray tomography analyses are appropriate to extract pore volume distributions. Our study on ductile materials allowed us to conclude that experimental analyses exhibit two power laws attributed to growth and coalescence regimes. Moreover power law is scale invariance so it is possible to compare experiment (macroscopic) to calculation (microscopic). We show that there are good correlations between experimental and Molecular Dynamics pore volume distribution. Thanks X-ray microtomographies findings we progress in understanding the phenomenon of dynamic damage.

Abstract: This paper deals with the use of X-ray microtomography in evaluating the porosity of barrage lock concrete. The main parts of the lock were built in the years 1914-1917. Its high and low heads were founded on 2.70 m thick concrete slabs. Samples for laboratory tests were taken by core drilling at half of the slab thickness. The compressive strength of the concrete was determined and the porosity of the concrete was evaluated using X-ray microtomography. The compressive strength values ranged from 17.3 to 37.3 MPa. The porosity examination results are compared with the destructively determined concrete compressive strength values.

Abstract: Several studies about porous biomaterials indicate that surgical implants success is directly linked to its surface morphology and structural characteristics. Porous implants improve osseointegration at the implant-bone interface, since they induce new bone tissue formation inside the pores providing a better mechanical stability. One of the most important parameters is the size of the pores. However, if the connectivity among the pores is not large enough for good blood irrigation, the osteocytes cells cannot reach the pores, no matter its size. The aim of this work is to analyze the porous structure of titanium samples fabricated by powder metallurgy, by characterizing pores and connections separately. This kind of structure characterization is important to improve the design of porous biomaterials. To accomplish it, a numerical code which converts 3D images into a pore-throat network structure was adopted. With this code, parameters such as size, frequency and quantity of pores and their connections can be determined. To acquire the 3D images of the samples, X-ray microtomography was used. Two samples were analyzed with distinct pore morphological types. The main result showed marked differences between the structures related to the connections radius, which suggests the one with better blood permeability.

Abstract: This review paper mainly consists of from two aspects: (a) the evolution of the cavitation damage equation from Dyson to current application in high Cr steels by traditional techniques; (b) quantitation analyses of cavitation behavior in brass, copper, dual phase steel from X-ray microtomtograph. Though there is a lack of experimental data for high Cr steels by X-ray microtomography currently, but (b) has provided reference value for studying creep cavitation behavior in high Cr steels. This paper will be the fundamental of development new creep damage constitutive equation through quantitation analyses of X-ray tomography.

Abstract: We used corrosion casts and micro-CT for quantitative description of microvascular network in porcine liver. Using stereological methods, manual tracing of microvessels and analysis of orientation in 3D, we quantified the volume fraction, the surface density, the numerical density, the length density and the tortuosity of microvessels in series of images with 1.875 μm pixel resolution. Biodur E 20 resin was more suitable for preparing and quantifying microvascular tree corrosion casts when compared to Mercox II resin. Quantified data could be applicable for correlating 3D models with 2D liver histopathology, for enhancing the interpretation of routine medical CT and for providing data for computer models of tissue perfusion and angiogenesis.

Abstract: Our aim was to use stereology to quantify the volume fraction of osteocyte lacunes, volume fraction of large blood vessels, numerical density of osteocyte lacunes, volume of osteocyte lacunae and bone surface in series of micro-CT images representing samples of spongy and compact bone of human tibia. The spongy bone had a smaller volume fraction of osteocyte lacunes, a greater numerical density of bone lacunes, a smaller volume of the lacunes within the same bone volume and a greater bone surface density when compared to the compact bone. Stereology provided us with data on hierarchical organization of bone structural heterogeneity with reasonable time costs.

Abstract: Thixoforging, one variant of semi-solid metal processing in which the metallic alloys are processed at low liquid fraction (0.1< Fl < 0.3), is used to produce complex parts with high mechanical properties. Steel thixoforging faces more challenges as compared to that of low melting point materials due to high processing temperature and lack of understanding of the thermomechanical behavior of materials in the given conditions. It is crucial to study the microstructure at the semi-solid state to improve the understanding of the thixoforging process since the material behavior strongly depends on main parameters: the liquid fraction, its distribution as well as the coherence of the solid skeleton. The microstructure has a great influence on the viscosity of the material, on the flows and finally on the final shape and mechanical properties of the thixoforged parts. Here, the characterization of the volume percentage and distribution of liquid fraction at the semi-solid state with high energy 3D X-ray microtomography was investigated on M2 steel grade as a ‘model’ alloy. The obtained results have been compared to 2D observations using EDS technique in SEM on heated and quenched specimens. They showed a good correlation making both approaches very efficient for the study of the liquid zones at the semi-solid state.

Abstract: The distribution of liquid at the semi solid state is one of the most important parameters for steel thixoforging. It has a great influence on the viscosity of the material, on the flows and finally on the final shape and mechanical properties of the thixoforged parts. Both ex situ and in situ 3D X-ray microtomography characterizations have been carried out to determine the quantity and localization of liquid at high temperature of M2 steel slugs. Microtomography was first performed ex situ at room temperature on samples heated and quenched from semi-solid state. The specimens were also scanned in situ directly at high temperature. The obtained results have been compared to 2D observations using EDS technique in SEM on heated and quenched specimens. They showed a good correlation making both approaches very efficient for the study of the liquid zones at the semi-solid state

Abstract: Hydroentangling (bonding of fabrics by means of high velocity water jets), is utilised to entangle polyethylene terephthalate (PET) and glass fibre layers which are industrially applied as high performance carriers for bitumen roofing products. Conventionally, a resin post-treatment is frequently applied to strengthen pre-entangled PET/glass fabrics whereas in the current study promising mechanical properties were obtained without the need for resin treatment. Non-destructive characterisation using x-ray microtomography reveals the transverse structure of these mechanically bonded fabrics. Normal procedures for measuring delamination cannot be applied to the evaluation of hydroentangled fibrous composites.

Abstract: The performance of biomaterial scaffolds for bone tissue engineering, as porous titanium implants, is strongly dependent of its structural features. A reliable structural characterization of this kind of implant is very important. The most of image analysis techniques just supplies 2D information about the structure of specimens. X-ray microtomography is imaging technique that can produce 3D images of samples, however, stochastic models can also estimate properties of porous materials in 3D. This work presents the evaluation of a 3D model (using a truncated Gaussian method) in comparison to 3D microtomography volume, both from a titanium scaffold sample. In order to compare, geometrical parameters were measured for both 3D volumes. By the results, the truncated Gaussian 3D method reproduced a model with similar values to the microtomography volume, showing a good agreement among data, which suggests the use of this technique to estimate physical parameters of titanium scaffolds