scholarly journals Determination of anisotropic elastic parameters from morphological parameters of cancellous bone for osteoporotic lumbar spine

2021 ◽  
Author(s):  
Christoph Oefner ◽  
Elena Riemer ◽  
Kerstin Funke ◽  
Michael Werner ◽  
Christoph-Eckhard Heyde ◽  
...  
Keyword(s):  
Finite Element ◽  
Lumbar Spine ◽  
Cancellous Bone ◽  
Elastic Constants ◽  
Bone Volume ◽  
Human Bone ◽  
Homogenization Theory ◽  
Elastic Parameters ◽  
Anisotropic Elastic

AbstractIn biomechanics, large finite element models with macroscopic representation of several bones or joints are necessary to analyze implant failure mechanisms. In order to handle large simulation models of human bone, it is crucial to homogenize the trabecular structure regarding the mechanical behavior without losing information about the realistic material properties. Accordingly, morphology and fabric measurements of 60 vertebral cancellous bone samples from three osteoporotic lumbar spines were performed on the basis of X-ray microtomography (μCT) images to determine anisotropic elastic parameters as a function of bone density in the area of pedicle screw anchorage. The fabric tensor was mapped in cubic bone volumes by a 3D mean-intercept-length method. Fabric measurements resulted in a high degree of anisotropy (DA = 0.554). For the Young’s and shear moduli as a function of bone volume fraction (BV/TV, bone volume/total volume), an individually fit function was determined and high correlations were found (97.3 ≤ R2 ≤ 99.1,p < 0.005). The results suggest that the mathematical formulation for the relationship between anisotropic elastic constants and BV/TV is applicable to current μCT data of cancellous bone in the osteoporotic lumbar spine. In combination with the obtained results and findings, the developed routine allows determination of elastic constants of osteoporotic lumbar spine. Based on this, the elastic constants determined using homogenization theory can enable efficient investigation of human bone using finite element analysis (FEA).

Effect of Microcomputed Tomography Voxel Size on the Finite Element Model Accuracy for Human Cancellous Bone

2005 ◽  
Vol 127 (1) ◽  
pp. 1-8 ◽  
Author(s):  
Yener N. Yeni ◽  
Gregory T. Christopherson ◽  
X. Neil Dong ◽  
Do-Gyoon Kim ◽  
David P. Fyhrie
Keyword(s):  
Finite Element ◽  
Shear Stress ◽  
Boundary Conditions ◽  
Cancellous Bone ◽  
Coefficient Of Variation ◽  
Volume Fraction ◽  
Bone Volume ◽  
Bone Volume Fraction ◽  
Voxel Size ◽  
Fixed End

The level of structural detail that can be acquired and incorporated in a finite element (FE) analysis might greatly influence the results of microcomputed tomography (μCT)-based FE simulations, especially when relatively large bones, such as whole vertebrae, are of concern. We evaluated the effect of scanning and reconstruction voxel size on the μCT-based FE analyses of human cancellous tissue samples for fixed- and free-end boundary conditions using different combinations of scan/reconstruction voxel size. We found that the bone volume fraction (BV/TV) did not differ considerably between images scanned at 21 and 50 μm and reconstructed at 21, 50, or 110 μm (−0.5% to 7.8% change from the 21/21 μm case). For the images scanned and reconstructed at 110 μm, however, there was a large increase in BV/TV compared to the 21/21 μm case (58.7%). Fixed-end boundary conditions resulted in 1.8% [coefficient of variation (COV)] to 14.6% (E) difference from the free-end case. Dependence of model output parameters on scanning and reconstruction voxel size was similar between free- and fixed-end simulations. Up to 26%, 30%, 17.8%, and 32.3% difference in modulus (E), and average (VMExp), standard deviation (VMSD) and coefficient of variation (COV) of von Mises stresses, respectively, was observed between the 21/21 μm case and other scan/reconstruction combinations within the same (free or fixed) simulation group. Observed differences were largely attributable to scanning resolution, although reconstruction resolution also contributed significantly at the largest voxel sizes. All 21/21 μm results (taken as the gold standard) could be predicted from the 21/50 radj2=0.91-0.99;p<0.001, 21/110 radj2=0.58-0.99;p<0.02 and 50/50 results radj2=0.61-0.97;p<0.02. While BV/TV, VMSD, and VMExp/σz from the 21/21 could be predicted by those from the 50/110 radj2=0.63-0.93;p<0.02 and 110/110 radj2=0.41-0.77;p<0.05 simulations as well, prediction of E, VMExp, and COV became marginally significant 0.04<p<0.13 at 50/110 and nonsignificant at 110/110 0.21<p<0.70. In conclusion, calculation of cancellous bone modulus, mean trabecular stress, and other parameters are subject to large errors at 110/110 μm voxel size. However, enough microstructural details for studying bone volume fraction, trabecular shear stress scatter, and trabecular shear stress amplification VMExp/σz can be resolved using a 21/110 μm, 50/110 μm, and 110/110 μm voxels for both free- and fixed-end constraints.

scholarly journals Identification of the Anisotropic Elastic Parameters of NiCrAlY Coating by Combining Nanoindentation and Finite Element Method

2019 ◽  
Vol 2019 ◽  
pp. 1-13
Author(s):  
Jingyu Zhai ◽  
Yugang Chen ◽  
Xinyuan Song ◽  
Hongchun Wu ◽  
Qingkai Han
Keyword(s):  
Finite Element ◽  
Composite Structure ◽  
Composite Structures ◽  
Optimization Design ◽  
Hard Coatings ◽  
Hard Coating ◽  
Small Scale ◽  
Elastic Parameters ◽  
Accurate Identification ◽  
Anisotropic Elastic

For vibration damping, coatings are prepared on surface of the structures (substrates), which constitute the coating-substrate composite structures. Elastic parameters of the coating are indispensable for the vibration and damping analysis of the composite structure. Due to the small scale of coating thickness and elastic difference compared with the substrate, the identification results are inevitably influenced by the existence of substrate. Moreover, resulting from the preparation process, elastic properties of hard coating often exhibit anisotropic properties. All the above factors bring about the difficulties of accurate identification. In this study, a method for identifying anisotropic elastic parameters of hard coatings considering substrate effect is proposed, by combining nanoindentation and finite element analysis. Based on the identification results, finite element models are established to analyze the vibration characteristics of the coating-substrate composite structure, which verify the rationality of the anisotropic elastic parameters for vibration analysis. The studies in this paper are significant to more accurately identify the mechanical parameters for establishing the dynamic model. Moreover, they lay the foundation for further optimization design of hard coating damping.

scholarly journals Concentration of Insulin-Like Growth Factor (IGF)-I and -II in Iliac Crest Bone Matrix from Pre- and Postmenopausal Women: Relationship to Age, Menopause, Bone Turnover, Bone Volume, and Circulating IGFs1

1998 ◽  
Vol 83 (7) ◽  
pp. 2331-2337 ◽  
Author(s):  
Thomas Seck ◽  
Beate Scheppach ◽  
Stefan Scharla ◽  
Ingo Diel ◽  
Werner F. Blum ◽  
...  
Keyword(s):  
Growth Factor ◽  
Bone Turnover ◽  
Cancellous Bone ◽  
Iliac Crest ◽  
Bone Matrix ◽  
Bone Volume ◽  
Human Bone ◽  
Age Related ◽  
Igf I ◽  
The Mean

Insulin-like growth factor-I (IGF-I) and -II are important local regulators of bone metabolism, but their role as determinants of human bone mass is still unclear. In the present study, we analyzed the concentration of IGF-I and -II in the bone matrix of 533 human biopsies from the iliac crest that were obtained during surgery for early breast cancer. There was an inverse association of bone matrix IGF-I concentration with age that was unaffected by menopause. Bone matrix IGF-I was positively associated with histomorphometric and biochemical parameters of bone formation and bone resorption and with cancellous bone volume. Based on the estimates of the linear regression analysis, women with a bone matrix IGF-I concentration 2 sd above the mean had a 20% higher bone volume than women with a bone matrix IGF-I concentration 2 sd below the mean. In contrast, serum IGF-I was neither correlated with bone turnover nor with bone volume and was only weakly associated with bone matrix IGF-I when adjusted for the serum concentration of IGF binding protein-3. Bone matrix IGF-II was positively associated with the osteoblast surface, but in contrast to IGF-I, tended to be positively associated with age and was unrelated to cancellous bone volume. In summary, our study suggests the following. 1) The concentration of IGF-I in cancellous bone undergoes age-related decreases that are similar to those of circulating IGF-I. 2) Menopause has no effect on this age-related decline. 3) Physiological differences in bone matrix IGF-I are associated with differences in iliac crest cancellous bone volume. 4) Bone matrix IGF-I is a better predictor of cancellous bone volume than circulating IGF-I. 5) The role of IGF-II in human bone tissue is clearly distinct from that of IGF-I.

Determination of Full Set Elastic Constants for Composite Materials on Basis of Frequency Response Analysis, FEA, and GA

2008 ◽  
Author(s):  
Arcady Soloviev ◽  
Anton Bychkov ◽  
Maria Shevtsova
Keyword(s):  
Finite Element ◽  
Frequency Response ◽  
Elastic Constants ◽  
Orthotropic Materials ◽  
Vibration Modes ◽  
Dynamic Tests ◽  
Good Efficiency ◽  
Static Tests ◽  
Orthotropic Composite

The number of engineering problems includes the identification of anisotropic composite elastic constants determination. We developed an experimentally - analytical technique for identification of all elastic constants of orthotropic materials. The offered technique is substantially based on measurement of eigenfrequencies and semi quantitative analysis of natural vibration modes, instead of wave propagation speed and fields of vibrational displacement used by other acoustic methods. The developed method of the elastic composite and piezoelectric materials properties identification is implemented in linked MATLAB – Comsol Multiphysics combining the finite element analysis (FEA) of oscillations dynamics and minimization of some functional, which type is determined by particularity of a solved problem. These techniques complement the early designed by authors’ FEM-based methods for orthotropic composite static tests. The offered dynamic tests include an evaluation of specimen’s frequency response, determination of natural frequencies and vibration modes of specimens both in natural experiments and numerical finite element simulations. The identification process consists of several stages. In series of static tests are determined all allowable modules. Further a complete matrix of elastic constant is constructed, but some modules specified by approximated values (in particular, interlaminar shear modules). A series of dynamic tests executed in which the periodical excitation of samples and the frequency response is recorded by means of piezoelectric actuators and sensors. Then on basis of early defined (in static tests and with use of mix rule) modules of composite and experimentally founded eigenfrequencies by means of FEM the vibration natural modes are identified. By combination of FEM, genetic algorithm (GA) and Levenberg-Marquardt minimization method the specification of composite mechanical properties is evaluated. Application of developed technique to orthotropic composite used in aviation structures (polymeric composite spar of the helicopter main rotor blade) is explicitly illustrated. The obtained results have shown a good efficiency of proposed identification methods. We demonstrate that proposed approach provides best reliability and shows small dependence on metering equipment precision.

Improved Prediction of Local Trabecular Strain Enhances Non-Invasive Assessment of Micro Bone Strength Using a Surface Smoothing Technique in FEA

2007 ◽  
Author(s):  
Suzanne L. Ferreri ◽  
Yi-Xian Qin
Keyword(s):  
Finite Element ◽  
Nondestructive Evaluation ◽  
Bone Quality ◽  
Peak Stress ◽  
Bone Volume ◽  
Micro Ct ◽  
Smoothing Technique ◽  
Surface Smoothing ◽  
Non Invasive

One key issue in clinical, non-invasive assessment of bone quality and fracture risk is the accurate prediction of localized trabecular strength through the determination of peak stress values and locations. Additionally, it has been suggested that peak stress/strain concentrations may play an important role in driving the bone remodeling process. Micro-CT based voxel finite element (FE) meshes have been widely used in nondestructive evaluation of global stiffness. Subsequently, this technique has been advantageous in studies addressing changes in bone volume and microstructure.

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