Investigation of differences in mechanical models obtained by processing of 2d serial scanning data in the scope of image processing procedures

In this study, differences in mechanical models which are obtained by performing two dimensional scanning data are investigated in the scope of image processing procedures.Voxel based finite elements methods (VB-FE) in which obtained data by non-damaged imaging techniques are used as main input have an increasing area of usage while solving micro and nano scaled problems in several fields as medicine, mechanical and material engineering. Voxel based finite elements models are directly effected by image quality obtained by imaging techniques as computed tomography and magnetic resonance. In this study, effects of related subjects on natural vibration analysis of structures which have micro scaled complex geometry are investigated.For this purpose, natural vibration modes of three models which have same slice thickness and whose thresholds are changed in small values by using Micro-BT imaging data of vertebral trabecular bone tissue are studied. Furthermore, natural vibration modes of models that are free from voxel based finite elements size effect by using Micro-BT imaging data of this bone tissue having four different slice thicknesses are investigated.To perform the subjected analyses, while material properties and boundary conditions of the samples which are transferred to ABAQUS® are defined for natural vibration analyses, material properties, boundary conditions, condition and direction of the load are stated for buckling analysis. However, a range of image processing, voxelization and format change processing shall be done to analyse the samples as finite element model by ABAQUS®. For this purpose, CUBOID-SI2FE MATLAB® script is advanced by ALTINTAS. CUBOID-SI2FE which is a compact software containing threshold value, reconstruction and specific floodfill algorithm in its structure and it directly makes Mikro-BT image files available for use of ABAQUS®. Performed operations by CUBOID-SI2FE are explained below.First of all, 3D voxel members are created while indicating slice thickness value in imaging data of Micro-BT data sets. Corner point numbers of voxels are given in accordance with ABAQUS® input files and assigned gray scaled values of pixels to voxels. (Scaled values of pixels are between 0 and 255. While threshold value of absolute white is 255, the value of full black is 0. Bones in Micro-BT image files are white.) A proper threshold value is used to determine the voxels belonging to bone tissue while checking with eye and bone tissue is separated from other tissues by this process. In this study, (133-255) threshold range is taken as suitable range. In this step, data is provided as processable in ABAQUS® while transferring voxel members which are signed as bone tissue to ABAQUS® files and arranging member and nodal point numbers by defining voxel members by CUBOID-SI2FE Matlab script to linear tehrahedral member type C3D4.Investigation of threshold value results shows that, natural vibration behaviors of voxel based finite element models change not only natural frequency values but also mode shape ordering. It is stated that threshold values in which tolerance range of eye is acceptable, natural frequency values change much and natural frequency value decreases while threshold value increases. As a matter of fact, it is seen that not only the regions where mode shapes in the same mode number and maximum displacement occur but also the natural frequency values are not same.Similarly, change in slice thickness effects the natural frequency values. In addition, it is seen that, slice thickness change makes different not only natural frequency values but also regions where mode shapes having same mode number and maximum displacement occur.Finite elements models effects of slice thicknesses of the same bones tissue on buckling behavior are also investigated. Anisotropic voxels are directly used in analyzed modes. For this reason, the results are not free from size effect unlike the previous vibration example.When effect of slice thickness change on buckling analysis is investigated, load range where first ten buckling modes appear becomes tight due to decrease in slice thickness. Buckling loads of all modes except the first one increases with the slice thickness increase.There are interesting results occurred after evaluating both buckling load values and mode shapes. A general mode structure is not mentioned as distinct from standard prismatic objects and mode shapes having same mode numbers belong to different mode structures. For this reason, it may be wrong to make a comment while taking only mode number and buckling load values into consideration. In other words, it indicates that an object takes extra mode which does not appear in another one. This situation shows that effect of investigated parameters that is slice thickness on buckling behavior is important not only as numerical but also as change in mode shapes.It can be said as the general result of this study that correct selection of image processing parameters in voxel based finite elements applications is significant not only numerical but also modal behaviors of natural vibration and buckling problems in which eigenvalue solution is required.Obtained results reveal that, investigated parameters have significant effect on natural vibration of trabecular bone tissue which is selected as an example of complex geometries. The results also present the importance of imaging data that shall be taken into consideration in practical applications.