基于XCT扫描图像的混凝土二维细观受压断裂模拟

为了研究混凝土细观层次断裂力学特性,对混凝土试件进行原位XCT扫描,基于扫描图像提出了具有真实内部结构特征的混凝土二维细观模型,并预先在水泥砂浆和骨料-水泥砂浆界面插入零厚度粘结裂缝单元用以模拟潜在的裂缝。通过对该模型进行混凝土单轴受压数值仿真模拟,讨论其裂缝的发展过程以及不同细观结构和相应参数对混凝土断裂损伤行为的影响。结果表明：数值模拟得到的混凝土二维模型抗压强度与试验测得的强度相接近;混凝土的抗压强度受到水泥砂浆和骨料-砂浆界面裂缝单元的绝对数值影响,其中水泥砂浆裂缝单元强度对材料强度起控制作用;骨料-砂浆界面裂缝单元强度与水泥砂浆裂缝单元强度的比率对裂缝衍生发展有显著影响。     

3D evaluation of the oxidation and porosity in 9Cr tubing using FIB and X-ray

Abstract

A combination of focussed ion beam milling and X-ray tomography has been used to evaluate the steam grown oxide on plant-exposed Grade 91 material, comparing the features observed with those on laboratory coupons, which have not been ground. A particular focus was the characterisation of any pre-existing oxides and features; and the effect these have on elemental segregation and the formation of porosity in the Fe–Cr spinel. In particular, X-ray computed tomography (XCT) has been used to characterise the defect structure within the magnetite layer of the scale. The results have shown that laboratory tests on as-received material replicate features seen in plant-exposed material, and that macroscopic crazing-like cracks extend from the surface of the oxide through the spinel layer, and that this provides a mechanism for oxide healing and densification around the cracks.     

基于XCT扫描的砂岩矿物颗粒微尺度变形行为

为了定量表征岩石中三维微结构在单轴压缩下的物理和力学行为,采用高精度原位计算机断层扫描技术研究砂岩矿物颗粒运动、旋转变形和主应变特性,揭示断裂带与非断裂带之间的晶粒行为.结果表明:卸载后,矿物颗粒的剪切应变在径向呈现周期性变化;断裂带和非断裂带区域内部颗粒应变分别约为试样宏观应变的30和5倍;断裂带区域附近的剪切应变大...     

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 diffusion treatment. The microstructure and mechanical properties of the composites were investigated in detail using field emission scanning electron microscopy, electron backscatter diffraction, 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 diffusion regions, was evolved in the composites due to incomplete diffusion between Ti and Ta splats. Further, Kirkendall pores were formed in the composites due to uneven diffusion 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 effect of Ta in Ti, while high tensile strength was related to the solid solution strengthening effects. The obtained results indicated that the prepared Ti-Ta composites have a great potential to become a new candidate for biomedical applications.     

Non-destructive high-resolution X-ray micro computed tomography for quantifying dry water particles

Dry water, a powder containing up to 98%wt. water and 2–6%wt. hydrophobic nanoparticles, is a novel material for novel applications like CO₂ capture, transportation and storage in the form of clathrate hydrates. In this study, novel high-resolution X-ray micro computed tomography (HRXMT) was used as an in situ, non-destructive tool to visually and quantitatively examine the inner structure of dry water that has not been accessible previously. Specifically, the HRXMT was used to study the effect of silica/water wt. ratio on the number, surface area and volume distributions of dry water. The results showed that dry water was stable under ambient condition for long time. The technique was also successful in characterizing the structure changes in dry water after exposing to low temperature, high pressure and stirring. Low temperature did not affect the structure significantly, while high pressure and slow stirring broke the structure fairly readily with separation of dry water into the primary solid and liquid phases. These findings are useful to our understanding of the role of dry water in promoting the formation of CO₂ and gas hydrates.     

XCT damage evaluation and analysis of SiC/SiC turbine guide vanes after thermal shocks

In this paper, the two-dimensional (2D) (0°/90°) plain-woven Amosic-3 SiC/SiC turbine guide vane (TGV) was fabricated using the chemical vapor infiltration method. Thermal and stress analysis of the TGV was conducted using the finite element method analysis. Multiple thermal shock tests at T = 1250, 1350, 1400, 1420, 1450, 1470, and 1480°C were conducted for N = 100, 100, 400, 300, 200, 200, and 700 cycles. After thermal shock tests, the surface damage of the TGV was observed visually, and the micro damage mechanism was analyzed using the scanning electronic microscopy. Micro X-ray computed tomography was adopted to characterize the internal damages in the SiC/SiC guide vanes. The delamination occurred at the positions approaching internal hollow, due to the weak binding force along the thickness direction and the high thermal shock stress caused by the temperature change. The diameter, area, volume, and sphericity distributions of the pores inside of the guide vanes were also obtained.     

3D evaluation of the oxidation and porosity in 9Cr tubing using FIB and X-ray

A combination of focussed ion beam milling and X-ray tomography has been used to evaluate the steam grown oxide on plant-exposed Grade 91 material, comparing the features observed with those on laboratory coupons, which have not been ground. A particular focus was the characterisation of any pre-existing oxides and features; and the effect these have on elemental segregation and the formation of porosity in the Fe–Cr spinel. In particular, X-ray computed tomography (XCT) has been used to characterise the defect structure within the magnetite layer of the scale. The results have shown that laboratory tests on as-received material replicate features seen in plant-exposed material, and that macroscopic crazing-like cracks extend from the surface of the oxide through the spinel layer, and that this provides a mechanism for oxide healing and densification around the cracks.     

含能材料密度的XCT自参照测试

运用同步测试技术和体积CT灰度值计算方法,研究含能材料的体密度与体积CT灰度值的线性关系。以密度相近的含能材料试验件组成的体系密度作为参照,利用各试验件的VCT灰度值计算CT密度值。试验结果表明,采用自参照密度测试方法可以简化含能材料局部密度均匀性的测试,CT法计算获得的试验件密度值与排水法测得密度值的相对误差0.1%。     

基于XCT的气固流化床布风板射流特征研究

构建了X光层析成像（XCT）气固流动参数测量系统,基于锥形束滤波反投影算法（FDK）开发了CT三维重建软件,并设计了射流识别及量化算法。基于以上方法获得了不同流化风速下床料粒径d_p、布风板孔口直径d₀和布风板孔口均分面积A₀对射流形态结构和几何特征的影响规律。结果表明平均射流长度L、最大直径D和体积V与床料粒径d_p成反比,与孔口直径d₀和孔口均分面积A₀成正比,最终拟合了流化床平均射流长度关联式。     

Chemical self-healing system with novel microcapsules for corrosion inhibition of rebar in concrete

Two kinds of chemically-triggered self-healing systems with novel microcapsules are designed to protect rebar from corrosion in concrete. X-ray micro-computed tomography (XCT) method is employed to non-destructively visualize the protection performance and quantitatively evaluate the efficacy of the self-healing system in a wet-dry cyclic accelerating corrosion test. Environmental scanning electron microscopy (ESEM) system equipped with texture element analysis microscopy (TEAM) is used to verify the results of XCT imaging analysis. The results reveal that the self-healing system-high efficiency is achieved by delaying the depassivation of the rebar and reducing the corrosion rate.