Yasushi Ikeda

3D modeling of porous ceramics by high-resolution X-ray CT for stress analyses

Porous ceramic materials are in widespread use and continue to be developed as the key materials for many industrial fields. The mechanical properties of these porous materials are very sensitive to their 3-dimensional structures. It is very important to analyze such materials taking into account their 3-dimensional morphology of the pore structure. An image-based modeling method using high resolution 3-dimensional computed tomography (CT) was developed, which makes it possible to reconstruct the complicated porous structures of porous ceramics nondestructively. From the 3-dimensional CT data, binary-processed images can be obtained and a voxel mesh computational analysis was carried out with a homogenization method, from which macroscopic and microscopic stress distribution for porous ceramics were possible to be calculated and visualized. From the 3-D CT image, a local microscopic model of the porous alumina was analyzed using voxel mesh method of mathematical homogenization method. Using the data the microscopic local stress distribution of the model was obtained. Introduction 3-dimensional X-ray CT is now available to reconstruct solid materials and samples in computing systems. It is very convenient to built a model of complicated 3-D structure of a sample. For the purpose, a high-resolution CT using a micro-focus X-ray and a corn beam one is employed. The high-resolution of the CT enables to reconstruct a model with a few μm of resolution [1, 2]. Although the sample must be smaller than conventional industrial or medical CT systems, material investigation is possible with such 3-D high-resolution. The purpose of this work is to develop an image-based modeling method for computing simulation of local stress distribution in complicated porous structures of ceramic materials [3]. Porous ceramic materials are now in widespread use and continue to be developed as the key materials for many industrial fields, e.g., filters for environmental purification systems, food manufacturing, and high temperature fuel cells. The mechanical properties of these porous materials are very sensitive to their 3-dimensional structures. Therefore, it is very important to analyze such materials taking into account their 3-dimensional morphology of the pore structure [4]. From the 3-dimensional CT data, binary-processed images can be obtained and a voxel mesh computational calculation is carried out by mathematical simulation method called as homogenization method [5, 6]. After calculating homogenized elastic matrixes and homogenized elastic constants, macroscopic finite element method (FEM) analyses and microscopic voxel mesh analyses of stress concentration are carried out. Method and Procedures Principle of the method. The outline of this study is shown in Fig.1 in the form of a flow chart. Our final purpose is to analyze macroscopic and microscopic stress concentrations in porous ceramic materials, which will be an origin of fracture of the materials. In this work, we prepared Key Engineering Materials Online: 2004-08-15 ISSN: 1662-9795, Vols. 270-273, pp 28-34 doi:10.4028/www.scientific.net/KEM.270-273.28

Analysis of the Resorption of Calcium Phosphate Cement by Using High-Resolution X-Ray 3-D CT

High resolution X-ray CT is a powerful means for analyzing comprehensive ceramic biomaterials in a living body. The benefit of this method is that morphological and volume changes of implant materials can be evaluated without retrieve of the implant in an animal body, resulting in no killing of the animals and long term evaluation even more than one year. In this study, in situ techniques for observation of calcium phosphate cement is developed. Calcium phosphate cement (CPC) was implanted into a femur and under skin of a rat. The volume and morphology change of the CPC were repeatedly measured using the same rat for more than 12 months. The 3-dimentional (3-D) structures of the CPC were imaged and reconstructed from hundreds of 2-D cross sectional CT images, which were obtained at one time by a 360 degree rotation of the sample. The structure of the CPC was visualized with 3-D, and the volume were numerically analyzed by using a 3-D structure analyzing computer software, which enabled two-value processing and estimation of the quantities of the CPC. Moreover some of the CPC samples were retrieved and were observed by SEM. In the results, the surface of the calcium phosphate cement changed from smooth to jagged with increasing implanted period. The CPC volume implanted into bone was gradually decreased with increasing implanted period. The volume loss was 8 % after 12 months. The CPC volume under skin after 1 month increased by 7 %. After that the volume gradually decreased in next 3 months. Absorption process of CPC in a rat will be discussed.

Application of 3D X-Ray CT to Stress Simulation Analysis of Porous Materials With Homogenization Method

A 3D X-ray CT method was developed using a combination of a micro-focus X-ray generator and an image intensifier camera. An image processor used produced 2D projection data for CT imaging. The channel number of the data was 1024, and the slicing number was up to 200. A micro-focus X-ray generator was used and image-magnifying method was carried out to imaging porous ceramic materials. Using obtained 3D CT images, voxel mesh method was carried out with mathematical homogenization method. Complicated structures of porous materials were taken into the simulation process as an image-based modeling. Equivalent homogenized elastic constants were calculated for the microscopic porous models, and global macroscopic stress and local stress distribution in porous materials were calculated with the simulation method. This simulation method was considered to be applicable to much larger porous materials of piping and construction.Copyright

Measurement of Internal Stress of Ceramics by Neutron Diffraction Method.

The neutron diffraction method is a useful nondestructive technique to measure the internal stress distributed within a ceramic component because the neutron penetration depth for ceramics is more than one millimeter. The diffraction from the Si3N4 (321) plane by monochromatic neutrons (wavelength λ=1.99A) was used for stress measurement. The linear absorption coefficient for Si3N4 was 0.69 cm-1, so that the internal stress distributed within specimens less than 5.4 mm thick could be measured by the neutron diffraction method. In order to generate a linear internal stress distribution, a bending moment was applied to a silicon nitride specimen, the thickness of which was 4mm. The incident beam angle and the widths of the incident and diffracted beam slits were adjusted to limit the diffracting area. The distribution of internal stress was measured by scanning the diffracting area from the tensile side to the compressive side. The stress in the diffracting area was determined from the change in the diffraction angle. The measured stress distribution was almost identical to the applied stress distribution. It is concluded that the internal stress of ceramic components can be measured by the neutron diffraction method.