Seeing through Materials:X-Ray Imaging Using Computed Tomography

X-ray computed tomography(XCT)has recently emerged as a powerful tool for characterizing the evolution of microstructure during phase transformation in three dimensional(3D)such as dendritic solidification of alloys.This paper briefly reviews the recent advances in the in-situ observation of aluminium alloys,magnesium alloys and nickel-based superalloys during solidification using laboratory XCT and synchrotron X-ray sources.The focus is on the growth kinetics of dendrites,porosity and secondary phases.In addition,in-situ characterization during the loading and corrosion process is also discussed.

Three-dimensional finite element simulation and reconstruction of jointed rock models using CT scanning and photogrammetry

The geometry of joints has a significant influence on the mechanical properties of rocks.To simplify the curved joint shapes in rocks,the joint shape is usually treated as straight lines or planes in most laboratory experiments and numerical simulations.In this study,the computerized tomography (CT) scanning and photogrammetry were employed to obtain the internal and surface joint structures of a limestone sample,respectively.To describe the joint geometry,the edge detection algorithms and a three-dimensional (3D) matrix mapping method were applied to reconstruct CT-based and photogrammetry-based jointed rock models.For comparison tests,the numerical uniaxial compression tests were conducted on an intact rock sample and a sample with a joint simplified to a plane using the parallel computing method.The results indicate that the mechanical characteristics and failure process of jointed rocks are significantly affected by the geometry of joints.The presence of joints reduces the uniaxial compressive strength (UCS),elastic modulus,and released acoustic emission (AE) energy of rocks by 37%–67%,21%–24%,and 52%–90%,respectively.Compared to the simplified joint sample,the proposed photogrammetry-based numerical model makes the most of the limited geometry information of joints.The UCS,accumulative released AE energy,and elastic modulus of the photogrammetry-based sample were found to be very close to those of the CT-based sample.The UCS value of the simplified joint sample (i.e.38.5 MPa) is much lower than that of the CT-based sample (i.e.72.3 MPa).Additionally,the accumulative released AE energy observed in the simplified joint sample is 3.899 times lower than that observed in the CT-based sample.CT scanning provides a reliable means to visualize the joints in rocks,which can be used to verify the reliability of photogrammetry techniques.The application of the photogrammetry-based sample enables detailed analysis for estimating the mechanical properties of jointed rocks.

Effects of Carbon Nanotubes on Mechanical and 2D-3D Microstructure Properties of Cement Mortar

To study the influence of multi-wall carbon nanotubes （MWCNTs） on the mechanical and microstructural properties of cementitious composites, 0.00, 0.02, 0.08, 0.10, and 0.20 wt% of multi-wall carbon nanotubes were added into cement mortar, in which the cement-sand ratio was 1：1.5. The flexural and compressive strengths of cement mortar at the age of 3, 7, 28 and 90 d and the fracture performance at the age of 28 d were determined, its 2D micrograph was tested by means of SEM, and the 3D defects distribution was firstly determined with or without CNTs by means of XCT （X-ray computerized tomography）. The results showed that 0.08 wt% of CNTs improved the compressive strength and flexural strength by 18% and 19~A, respectively, and a significant improvement of its fracture property was observed. Moreover lower addition of carbon nanotubes to cement mortars can improve its microstructure and decrease the defects significantly compared to the cement mortar without CNTs. With the increase of the content of CNTs, the mechanical properties of cement mortars presented to be declined largely due to the agglomeration of CNTs.

COMPARISON OF EFFECTS OF ACUPUNCTURE ON CEREBRAL INFARCTION IN DIFFERENT PARTS

92 cases of acute cerebral infarction confirmed by CT were assigned to cerebral hemi sphere surface infarction group and cerebral hemisphere deep infarction gioup according to infarction parts. The two groups were further divided randomly into acupuncture groups and simp1e drug control groups, respectively, i. e, surface infarction acupuncture group, surface infarction control group, deep infarction acupuncture group and deep infarction control group. Changes of nervous function be fore and after treatment were investigated in the 4 groups. Results indicated that acupuncture treatment had a definite therapeutic effect on acute cerebral infarction, but it had different effects on cereral infarction of different parts, that is, the therapeutic effect of acupuncture on cerebral surface infarction was superi or to that on deep infarction. It is suggested that effects of acupuncture are related closely with the in farction part.

Open-porous magnesium-based scaffolds withstand in vitro corrosion under cyclic loading:A mechanistic study

The successful application of magnesium(Mg)alloys as biodegradable bone substitutes for critical-sized defects may be comprised by their high degradation rate resulting in a loss of mechanical integrity.This study investigates the degradation pattern of an open-porous fluoride-coated Mg-based scaffold immersed in circulating Hanks’Balanced Salt Solution(HBSS)with and without in situ cyclic compression(30 N/1 Hz).The changes in morphological and mechanical properties have been studied by combining in situ high-resolution X-ray computed tomography mechanics and digital volume correlation.Although in situ cyclic compression induced acceleration of the corrosion rate,probably due to local disruption of the coating layer where fatigue microcracks were formed,no critical failures in the overall scaffold were observed,indicating that the mechanical integrity of the Mg scaffolds was preserved.Structural changes,due to the accumulation of corrosion debris between the scaffold fibres,resulted in a significant increase(p<0.05)in the material volume fraction from 0.52±0.07 to 0.47±0.03 after 14 days of corrosion.However,despite an increase in fibre material loss,the accumulated corrosion products appear to have led to an increase in Young’s modulus after 14 days as well as lower third principal strain(εp3)accumulation(-91000±6361μεand-60093±2414μεafter 2 and 14 days,respectively).Therefore,this innovative Mg scaffold design and composition provide a bone replacement,capable of sustaining mechanical loads in situ during the postoperative phase allowing new bone formation to be initially supported as the scaffold resorbs.

Preliminary study on CT perfusion imaging in guiding biopsy of pulmonary lumps

Background CT perfusion imaging （CTP） has been proved to be a powerful functional imaging technique. This study aimed to evaluate the value of CTP in guiding biopsy of pulmonary lumps. Methods A total of 147 patients with pulmonary lumps who had CT guided biopsies were enrolled in this study from February 2005 to June 2007. The patients were assigned to 3 groups： 33 cases guided by CTP as group 1, 45 cases guided by contrast-enhanced scan of CT as group Ⅱ, and 69 cases guided by plain scan of CT as group Ⅲ. Each group was subdivided into central and peripheral types according to the location of the lumps. The achievement ratio of biopsy, the accuracy in grouping, and grading of lung cancer, and the incidence of complication were compared. Results The total achievement ratios of biopsy from group Ⅰ to Ⅲ were 100% （33/33）, 91% （41/45）, and 80% （55/69） respectively, and the difference was statistically significant between group Ⅰ and Ⅲ （P 〈0.05）. For the central type, they were 100% （18/18）, 88% （15/17）, and 79% （11/14） respectively, and the difference was also statistically significant between group Ⅰand Ⅲ （P 〈0.05）. For the peripheral type, they were 100% （15/15）, 93% （26/28）, and 80% （44/55） respectivelies, and the difference was not statistically significant among the three groups. The total accuracies in grouping and grading of lung cancer from group Ⅰ to Ⅲ were 100% （27/27）, 91% （31/34）, and 72% （33/46） respectively, and the difference was statistically significant between group Ⅰ and Ⅲ and between group Ⅱ and Ⅲ （P 〈0.05）. For the central type, they were 100% （16/16）, 94% （16/17）, and 70% （8/12） respectively, and the difference was statistically significant between group Ⅰ and Ⅲ （P〈0.05）. For the peripheral type, they were 100% （11/11）, 88% （15/17）, and 72% （26/36） respectively, and the difference was statistically significant between group Ⅰ and Ⅲ （P 〈0.05）. The total incidence of complication from group Ⅰ to Ⅲ were 15% （5/33）, 27% （12/45）, and 43% （30/69） respectively, and the difference was statistically significant between group Ⅰ and Ⅲ （P 〈0.01）. For the central type, they were 11% （2/18）, 24% （4/17）, and 57% （8/14） respectively, and the difference was statistically significant between group Ⅰ and Ⅲ （P 〈0.01）. For the peripheral type, they were 20% （3/15）, 29% （8/28）, and 40% （22/55） respectively, and no statistically significant difference was found among the three groups. Conclusions CTP guided biopsy of pulmonary lumps using multi-detector row CT has the potential to improve the accuracy of histopathological diagnosis with a lower risk and higher achievement ratio. More research and technical improvements are needed before it is widelv used.

Microstructure and mechanical properties of 3D Cf/SiBCN composites fabricated by polymer infiltration and pyrolysis

In this work,three-dimensional(3D)Cf/SiBCN composites were fabricated by polymer infiltration and pyrolysis(PIP)with poly(methylvinyl)borosilazane as SiBCN precursor.The 3D microstructure evolution process of the composites was investigated by an advanced X-ray computed tomography(XCT).The effect of dicumyl peroxide(DCP)initiator addition on the crosslinking process,microstructure evolution,and mechanical properties of the composites were uncovered.With the addition of a DCP initiator,the liquid precursor can cross-linking to solid-state at 120℃.Moreover,DCP addition decreases the release of small molecule gas during pyrolysis,leading to an improved ceramic yield 4.67 times higher than that without DCP addition.After 7 PIP cycles,density and open porosity of the final Cf/SiBCN composite with DCP addition are 1.73 g.cm^(-3)and〜10%,respectively,which are 143.0%higher and 30.3%lower compared with the composites without DCP addition.As a result,the flexural strength and elastic modulus of Cf/SiBCN composites with DCP addition(371 MPa and 31 GPa)are 1.74 and 1.60 times higher than that without DCP addition(213 MPa and 19.4 GPa),respectively.

Image-based numerical study of three-dimensional meso-structure effects on damage and failure of heterogeneous coal-rock under dynamic impact loads

This paper proposes a numerical three-dimensional(3D)mesoscopic approach based on the discrete element method combined with X-ray computed tomography(XCT)images to characterize the dynamic impact behavior of heterogeneous coal-rock(HCR).The dynamic impact loading in three directions was modelled to investigate the effects of the 3D meso-structure on the failure patterns and fracture mechanism,with different impact velocities.The XCT image-based discrete element model of HCR was calibrated through appropriate standard uniaxial compression tests.Numerical simulations were carried out to investigate how the breakage behaviors are affected by different loading directions with different impact velocities.The loading direction,input energy,and spatial distribution of the mineral phase had a remarkable influence on the failure patterns and load-carrying capacities.The shape of the gangue phase and the approximate location of the gangue interfaces are key parameters to consider when investigating the failure patterns and fracture mechanism of heterogeneous rock materials.The damage and fracture tended to propagate from the surfaces to the HCR interior.The gangue phase area contacting the loading wall,growth direction of the strong gangue interfaces,and loading directions greatly influenced the failure patterns of the heterogeneous rock materials.

Microstructure and Mechanical Properties of Ti–Ta Composites Prepared Through Cold Spray Additive Manufacturing

In this study, an innovative approach was used to fabricate Ti–Ta composite biomaterials through cold spray additive manufacturing followed by a diff usion treatment. The microstructure and mechanical properties of the composites were investigated in detail using field emission scanning electron microscopy, electron backscatter diff raction, 3D X-ray computed tomography, tensile test, nanohardness test and resonance vibration test. The obtained results indicated that the prepared composites have inhomogeneity in their microstructure and composition. A unique microstructure, composed of Ti-rich, Ta-rich and diff usion regions, was evolved in the composites due to incomplete diff usion between Ti and Ta splats. Further, Kirkendall pores were formed in the composites due to uneven diff usion of the two phases(of Ti and Ta) during high-temperature heat treatment. The prepared composites simultaneously showed low elastic modulus and high tensile strength which is required for a good biomaterial. Low elastic modulus was associated with the residual pores and the alloying eff ect of Ta in Ti, while high tensile strength was related to the solid solution strengthening eff ects. The obtained results indicated that the prepared Ti–Ta composites have a great potential to become a new candidate for biomedical applications.