PSI - Issue 43

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Apolena Šustková et al. / Procedia Structural Integrity 43 (2023) 276–281 Author name / Structural Integrity Procedia 00 (2022) 000 – 000

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Figure 4: Values of E app in all directions (x,y,z – same as in Figure 2c)) for the homogeneous (on the left) and nonhomogeneous (on the right) model variants.

Figure 5: Strain intensity in considered trabeculae (on the left) and along the path which was created based on the same start and end point (on the right). 4. Discussion Thresholding is a basic image processing tool for creating computational models from μ -CT images. The choice of the threshold fundamentally affects the results of stress-strain stages. As confirmed by the results of this study, the difference in the estimation of apparent mechanical properties is 74 % for homogeneous material and up to 59% for nonhomogeneous material when comparing the variants of models of geometry with minimum and maximum threshold values (0.25 and 0.65). In the case of a homogeneous material, the decrease in E app is linear and corresponds to the decrease in bone volume, which has the same value of E = 5000 MPa everywhere. When considering nonhomogeneous material, the decrease in E app with the decreasing volume for variants 0.25 N , 0.30 N and 0.35 N is not so significant. This is due to the fact that the bone tissue at the edges does not have such a high density and its E, given by relation (1), is not so high, so there will be no significant decrease in E app as in the case of a homogeneous material. For other variants of nonhomogeneous material, the decrease in E app is more pronounced. E app values are relatively low for both variants of material, as it is a bone tissue sample with high porosity (83% to 90%). This corresponds to very low-density bone tissue (classification D4 according to Misch 2008). Nevertheless, values of E app obtained in this work correspond to the observations of the literature (van Eijden et al. 200 ; Marcián et al. 201 . From the comparison of the local stress of observed trabeculae, it is evident that the choice of the threshold has a more significant effect on the character of strain intensity distribution than the used material model. Character of the distribution for both selected material models is approximately the same. From the course of the strain intensity in the graph in Fig. 5 it can be seen that due to the change of the threshold value there is a substantial redistribution of strain. The difference of strain intensity between the models 0.25 H and 0.65 H is 55% and between the models 0.25 N and 0.65 N is 43%.