Modelling shear behaviors of 2D C/SiC z-pinned joint prepared by chemical vapor infiltration

Progressive failure model is developed to investigate shear behaviors of 2D C/SiC z-pinned joint prepared by chemical vapor infiltration (CVI). It includes progressive failure model of 2D C/SiC composites and cohesive model of faying plane, in order to describe joint nonlinear shear behaviors and z-pin shear-off failure mode, respectively. All cohesive parameters are directly obtained from mechanical properties of 2D C/SiC composites. Results show that the model can almost reproduce joint shear behaviors and z-pin shear-off failure process. Joint failure results from coupled fiber tensile and fiber–matrix shearing damages at faying plane. The model also successfully demonstrates that joint shear properties can be effectively improved by changing z-pin density and diameter. The relationship between joint properties and mechanical properties of 2D C/SiC composites are subsequently obtained with the model. In this sense, joint shear strength increases with cohesive or in-plane shear strengths of 2D C/SiC composites.     

Micro-CT Imaging of MEMS Components

Micro-Electromechanical Systems (MEMS) have become increasingly commonplace in varied uses such as miniature pumps, motors, and sensors. As MEMS size continues to decrease, the intricacy of their construction has increased. With this increase in complexity comes a need to evaluate the assembly and functionality of these devices in a nondestructive manner. We proposed the utilization of micro-CT imaging as a method of such evaluation for MEMS devices. Computational simulations were performed in order to determine optimal source materials and imaging parameters for micro-CT scans. Multiple MEMS components of various architecture, fabricated by Sandia National Labs, were then imaged in order to verify the simulations, as well as to prove the feasibility of micro-CT imaging of such devices. The raw data from these scans was run through computational simulations to verify the best choice of filter and interpolation method when reconstructing micro-CT images. The results of the simulations, as well as the level of detail present in the three dimensional reconstructed images of various MEMS devices proved the feasibility of micro-CT as an effective tool for the evaluation of such devices.     

利用Micro-CT建立蝙蝠发声器官的三维数字模型

研究蝙蝠的超声定位特性对智能设备的性能提高具有重要的借鉴意义，精确的生物模型是此类研究的前提. 简述Micro-CT的重构原理，并应用该设备与计算机相结合制作了中国大菊头蝙蝠超声波发声器官的数字三维立体模型. 该数字模型精确度高，并可根据研究需要变化模型矩阵的大小. 该方法及中国大菊头蝠鼻叶数字模型此前国内未见报道.     

Microstructure,thermal conductivity and simulation of elastic modulus of MAX-phase (Ti2AlC) gel-cast foams

MAX-phase (Ti₂AlC) gel-cast foams manufactured using agarose as gelling agent were investigated in terms of their microstructural, mechanical and thermal properties. The microstructural analysis of Ti₂AlC foams made using SEM were compared with those using X-ray micro tomography. The Young’s Modulus of Ti₂AlC foams was determined using the impulse excitation technique. This experimental data was correlated with the Gibson-Ashby, Spriggs and Cross-property relation models. The thermal conductivity measurements were carried out by Laser-Flash analysis correlating to the pore network in the Ti₂AlC foam structure derived from μCT measurement. FEM-simulations of the mechanical behaviour were carried out on real structure models to determine a strut wise stress distribution under load.     

Microstructural characterization and robust comparison of ceramic porous orbital implants

This research work tackles the challenge of developing an objective and reliable criterion to score porous bioceramic orbital implants with different microstructural characteristics. We produced porous glass-ceramics by the foam replica method and characterized their 3D micro-architecture through non-destructive X-ray micro-computed tomography. Six key features were estimated influencing their clinical performance, i.e. total porosity, pore interconnectivity, pore size distribution, surface-to-volume ratio, connectivity density and degree of anisotropy. Surface roughness was also characterized by profilometry. A multiparametric score accounting for all the estimated features was developed and used to evaluate the similarity between the produced porous bioceramics and commercial orbital implants. The clinical use of such a global score could make the selection of orbital implants less arbitrary and less dependent on the skills and personal experience of the ophthalmic surgeon. The approach presented in this study could be extended to other areas of ceramics science and technology.     

Comparison of micro-CT and conventional dye penetration for microleakage assessment after different aging conditions

AimThe aim of this study was to compare microleakage assessment by micro-tomography (micro-CT) and conventional microscopy in class V restorations after different aging treatments.MethodsClass V cavities were prepared in sound human molars and restored with composite (Filtek Supreme XTE) after application of a self-etch adhesive (Clearfil SE Bond). Sealing ability was evaluated by assessing silver nitrate penetration along enamel and dentin margins either by micro-CT or by conventional stereomicroscopy. Class V cavities were divided in three groups (each n = 5): control: no aging, thermocycling: 10,000 cycles, 5–55 °C; thermo-erosive cycling: thermocycling with concomitant storage in HCl (pH 2.1, 5 min, 6×/day, 8 days). Penetration of silver nitrate was quantified by micro-CT and stereomicroscopy (25-fold magnification). Data for silver penetration assessed by stereomicroscopy and micro-CT were checked for normality and analyzed by Pearson or Spearman correlations. Differences between the aging effects were analyzed by one-way ANOVA (enamel) or Kruskal-Wallis tests (dentin) (p< 0.05).ResultsFor enamel, the correlations between stereomicroscopy and micro-CT data were not significant. For dentin, silver penetration depths obtained by stereomicroscopy and by micro-CT were moderately correlated (r=0.54, p=0.039), while volume of silver penetration (micro-CT) was not significantly correlated with penetration depth of silver (stereomicroscopy). Thermo-erosive cycling mostly increased microleakage compared with the control group and restorations submitted to thermocycling.ConclusionsThermo-erosive aging increased the microleakage at enamel and dentin. The micro-CT analysis resulted in lower values of microleakage compared with the conventional stereomicroscope.Clinical significanceMicroleakage is often used to evaluate the interfacial integrity of adhesives with dental hard tissues. The micro-CT analysis underestimated the dye penetration compared with the assessments made by the conventional stereomicroscopy, leading to lower microleakage values.     

Investigation of water and CO2 (carbon dioxide) flooding using micro-CT (micro-computed tomography) images of Berea sandstone core using finite element simulations

The present study reports a numerical investigation of water and CO₂ (carbon dioxide) flooding at the pore scale of a porous medium. We use high resolution micro-computed tomography (micro-CT) images of Berea sandstone core to obtain the pore geometry. The numerical solution used for the simulation was carried out by a finite element based software package. Level Set method is used to determine the position of the interface between two immiscible fluids when oil is displaced by water and CO₂, respectively. The present formulation is validated against single-phase flow through the porous structure. It is found that, fluid flow inside the pore space takes place through preferential inlet and outlet pores. For two-phase flow, it is observed that continuous displacement of oil occurs during water flooding but CO₂ is able to displace oil at certain locations in the pores. Also, the separation of flow front is observed in the case of CO₂ flooding. A quantitative comparison of the results obtained in two types of flooding simulations suggests that water displaces a higher volume of oil than CO₂ in the time period for which the simulations are performed.     

致密砂岩微米级孔隙网络系统石油驱替实验三维在线模拟

致密油储层孔隙度和渗透率均较低,其微米级孔隙网络系统内石油赋存状态是致密油成藏地质研究中亟待解决的核心问题之一。采用油气驱替系统与X射线微米CT扫描系统联用,通过对3 mm和5 mm直径致密砂岩干岩心、饱和碘化钾（KI）溶液及油驱替KI溶液后致密砂岩岩心在线CT扫描及数据重构,三维展示了致密砂岩微米级孔隙网络系统中石油的赋存状态。研究发现孔隙半径10 μm以上孔隙的连通性较好,是石油聚集的优势孔隙网络系统,致密砂岩62.9%~84.1%的石油聚集于半径在10~60 μm之间的孔隙内;孔隙半径小于10 μm的孔隙数量多,但其在空间上多呈孤立状分布,该部分孔隙的石油充满度较低,只聚集了致密砂岩内6.8%~20.0%的石油。致密砂岩含油饱和度随孔径呈阶梯状增长,半径小于10 μm、10~60 μm和60~80 μm的孔隙的含油饱和度分别为10%~40%,30%~75%,40%~75%。致密砂岩微米级孔隙网络系统石油的赋存与孔隙的尺寸、成因类型及空间分布特征有关。     

用Micro—CT测量ICFT型源靶柱腔诊断孔轴线与靶杆夹角的研究

用微CT测量ICF（惯性约束聚变）T型源靶柱腔诊断孔轴线与靶杆夹角（下文以θ代替）可以有效的排除柱腔外壁所镀金层厚度的不均匀对测量结果的影响。将微CT测量的两种方法与金层厚度均匀条件下用显微镜测量的结果进行比较,得出划定诊断孔上下边界点找中心的微CT测量方法具有更高的可信度。