Mejora de los elementos de transición en XFEM aplicado a Mecánica de la Fractura Elástica Lineal

El Método de los Elementos Finitos (MEF) es una herramienta numérica muy empleadas para la resolución de problemas de contorno. Uno de los fundamentos de la aproximación numérica en MEF es la interpolación polinómica, lo cual hace especialmente óptima su aplicación a problemas con solución suave. Desde el enfoque de Mecánica de la Fractura Elástica Lineal (MFEL), se tiene en consideración la posible presencia de grietas en el material. El comportamiento de la solución analítica no es suave en las cercanías de estas imperfecciones. El carácter local que aquí presenta la solución se ve gobernado por la singularidad, cuya intensidad, depende de la fuente que la produzca. El MEF se ha aplicado a problemas de MFEL con el objeto fundamental de obtener los Factores de Intensidad de Tensiones (FIT), parámetros que caracterizan el comportamiento de la solución cerca de la singularidad. El refinamiento adaptativo de la malla en el contorno y frente de la grieta así como el empleo de elementos especiales para el caso del extremo de grieta, han sido las principales estrategias para mejorar la solución. El Método de los Elementos Finitos Extendidos (XFEM), surge en aplicación a problemas con diversos tipos de singularidad. El método XFEM hace innecesaria la adaptación de la malla a la geometría de la singularidad. La interpolación polinómica y el enriquecimiento local de la solución basado en el cumplimiento de la partición de la unidad son sus principales características. En la aplicación de XFEM a problemas de MFEL, se emplean dos tipos de funciones de enriquecimiento capaces de representar el comportamiento discontinuo de la solución en el plano de la grieta y el comportamiento asintótico de la misma en el frente de grieta. En la Tesis se ha implementado el método XFEM incluyendo las diferentes mejoras que, en los últimos años, han sido desarrolladas con el objetivo de perfeccionar el planteamieto básico de esta herramienta numérica.Vercher Martínez, A. (2010). Mejora de los elementos de transición en XFEM aplicado a Mecánica de la Fractura Elástica Lineal [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/8506Palanci

Thermal control of a spacecraft: Backward-implicit scheme programming and coating materials analysis

[EN] The passive thermal control of a satellite consists of establishing the necessary thermal parameters involved in the process of heat transfer by radiation and conduction in order to delimit the range of temperatures to which the different components will be exposed. If the obtained range implies temperatures that the elements of the satellite are unable to cope with, therefore, an external control is demanded. This work deals with the programming of the equilibrium thermal problem taken into consideration a backward-implicit scheme. The algebraic mathematical approach for steady-state and transient analysis are implemented in Matlab scripts. In addition, the work analyzes the influence of different coating materials on the passive thermal control of a benchmark spacecraft reported in the literature. The problem under scope considers the characteristics of a low Earth Orbit: the solar, albedo and planetary radiation, the radiation coming from other isotherm surfaces of the same satellite, the heat conduction and, finally, the radiation of these isotherm surfaces to the outer space. The procedure implemented is based on a feasible matrix formulation and results avoid the numerical instabilities prevalent in the forward-explicit approach, moreover, it enables further parametric and sensitivity analysis. Regarding the coating materials influence on the thermal response, the most relevant results evidence that thermal surfaces can guarantee the desirable range of temperature in a spacecraft. We confirm that certain material properties like the absorptance, emittance and its relation (absorption coefficient) are essential in the thermal response of the system. Nevertheless, these thermal properties do not influence in the same way. It is shown that the effect of the emittance is lower than the absorptance.The authors acknowledge the Agencia Estatal de Investigaci6n for the financial support received through the project DPI2017-89197-C2-2-R and the Generalitat Valenciana for the Programme PROMETEO 2016/007. The authors declare that they have no conflict of interest.Alcayde, V.; Vercher Martínez, A.; Fuenmayor Fernández, F. (2021). Thermal control of a spacecraft: Backward-implicit scheme programming and coating materials analysis. Advances in Space Research. 68(4):1975-1988. https://doi.org/10.1016/j.asr.2021.03.041S1975198868

Explicit expressions for elastic constants of osteoporotic lamellar tissue and damage assessment using Hashin failure criterion

[EN] In this work, we have derived explicit expressions to estimate the orthotropic elastic constants of lamellar tissue as a function of the porosity at tissue level (microporosity) and the bone mineral density. Our results reveal that the terms of the main diagonal of the stiffness matrix fit an exponential equation, while the cross terms of the matrix fit a polynomial expression. Regarding to bone damage, failure onset assessed by Hashin criterion is mainly due to matrix elements failure. Finally, a linear relationship was found between bone mineral density (BMD) and cancellous bone stiffness at the macro scale.The authors acknowledge the Generalitat Valenciana for the financial support received through Plan FDGENT 2018. The authors also ackowledge the Ministerio de Ciencia e Innovacin and the ERDF-FEDER programme through the project DPI2017-89197-C2-2-R.Megías Díaz, R.; Belda González, R.; Vercher Martínez, A.; Giner Maravilla, E. (2022). Explicit expressions for elastic constants of osteoporotic lamellar tissue and damage assessment using Hashin failure criterion. En Proceedings of the YIC 2021 - VI ECCOMAS Young Investigators Conference. Editorial Universitat Politècnica de València. 150-158. https://doi.org/10.4995/YIC2021.2021.12442OCS15015

Influence of the mineral staggering on the elastic properties of the mineralized collagen fibril in lamellar bone

In this work, a three-dimensional finite element model of the staggered distribution of the mineral within the mineralized collagen fibril has been developed to characterize the lamellar bone elastic behavior at the sub-micro length scale. Minerals have been assumed to be embedded in a collagen matrix, and different degrees of mineralization have been considered allowing the growth of platelet-shaped minerals both in the axial and the transverse directions of the fibril, through the variation of the lateral space between platelets. We provide numerical values and trends for all the elastic constants of the mineralized collagen fibril as a function of the volume fraction of mineral. In our results, we verify the high influence of the mineral overlapping on the mechanical response of the fibril and we highlight that the lateral distance between crystals is relevant to the mechanical behavior of the fibril and not only the mineral overlapping in the axial direction.The authors acknowledge the Ministerio de Economia y Competitividad the financial support given through the project DPI2013-46641-R and to the Programme Prometeo 2012/023.Vercher Martínez, A.; Giner Maravilla, E.; Arango Villegas, C.; Fuenmayor Fernández, FJ. (2015). Influence of the mineral staggering on the elastic properties of the mineralized collagen fibril in lamellar bone. Journal of the Mechanical Behavior of Biomedical Materials. 42:243-256. https://doi.org/10.1016/j.jmbbm.2014.11.022S2432564

Some Practical Considerations for Compression Failure Characterization of Open-Cell Polyurethane Foams Using Digital Image Correlation

[EN] (1) Background: Open-cell polyurethane foam mechanical behavior is highly influenced by microstructure. The determination of the failure mechanisms and the characterization of the deformation modes involved at the micro scale is relevant for accurate failure modeling. (2) Methods: We use digital image correlation (DIC) to investigate strain fields of open-cell polyurethane foams of three different densities submitted to compression testing. We analyze the effect of some DIC parameters on the failure pattern definition and the equivalent strain magnification at the apparent ultimate point. Moreover, we explore speckle versus non-speckle approaches and discuss the importance of determining the pattern quality to perform the displacement correlation. (3) Results: DIC accurately characterizes the failure patterns. A variation in the subset size has a relevant effect on the strain magnification values. Step size effect magnitude depends on the subset size. The pattern matching criterion presented little influence (3.5%) on the strain magnification. (4) Conclusion: The current work provides a comprehensive analysis of the influence of some DIC parameters on compression failure characterization of foamed structures. It highlights that changes of subset and step sizes have a significant effect on the failure pattern definition and the strain magnification values, while the pattern matching criterion and the use of speckle have a minor influence on the results. Moreover, this work stands out that the determination of the pattern quality has a major importance for texture analysis. The in-depth, detailed study carried out with samples of three different apparent densities is a useful guide for DIC users as regards texture correlation and foamed structures.This research was funded by the Spanish Ministerio de Ciencia, Innovacion y Universidades grant numbers DPI2013-46641-R and DPI2017-89197-C2-2-R and the Generalitat Valenciana, Programme PROMETEO 2016/007 and Plan FDGENT 2018 GVA.Belda, R.; Megías-Díaz, R.; Feito-Sánchez, N.; Vercher Martínez, A.; Giner Maravilla, E. (2020). Some Practical Considerations for Compression Failure Characterization of Open-Cell Polyurethane Foams Using Digital Image Correlation. Sensors. 20(15):1-21. https://doi.org/10.3390/s20154141S121201

Compression failure characterization of cancellous bone combining experimental testing, digital image correlation and finite element modeling

[EN] Cancellous bone yield strain has been reported in the literature to be relatively constant and independent from microstructure and apparent density, while fracture strain shows higher scattering. The objective of this work is to assess this hypothesis, characterizing the compression fracture in cancellous bone from a numerical approach and relating it to morphological parameters. Quasi-static compression fractures of cancellous bone samples are modeled using high-resolution image-based finite elements, correlating the numerical models and experimental results. The yield strain and the strain at fracture are inferred from the micro-CT-based finite element models by inverse analysis. The validation of the fracture models is carried out through digital image correlation (DIC). To develop this work, cancellous bone parallelepiped-shaped specimens were prepared and micro-CT scanned at 22 mu m spatial resolution. A morphometric analysis was carried out for each specimen in order to characterize its microstructure. Quasi-static compression tests were conducted, recording the force-displacement response and a sequence of images during testing for the application of the DIC technique. This was applied without the need of a speckle pattern benefiting from the irregular microstructure of cancellous bone. The finite element models are also used to simulate the local fracture of trabeculae at the micro level using a combination of continuum damage mechanics and the element deletion technique. Equivalent strain, computed both from DIC and micro-FE, was the best predictor of the compression fracture pattern. The procedure followed in this work permits the estimation of failure parameters that are difficult to measure experimentally, which can be used in numerical models.This work was supported by the Spanish Ministerio de Ciencia, Innovacion y Universidades grant numbers DPI2013-46641-R and DPI2017-89197-C2-2-R and the Generalitat Valenciana (Programme PROMETEO 2016/007). The micro-CT acquisitions were performed at CENIEH facilities with the collaboration of CENIEH staff. The authors also gratefully acknowledge the collaboration of Ms. Lucia Gomez.Belda, R.; Palomar-Toledano, M.; Peris Serra, JL.; Vercher Martínez, A.; Giner Maravilla, E. (2020). Compression failure characterization of cancellous bone combining experimental testing, digital image correlation and finite element modeling. International Journal of Mechanical Sciences. 165:1-12. https://doi.org/10.1016/j.ijmecsci.2019.105213S112165Gold, D. T. (2001). The Nonskeletal Consequences of Osteoporotic Fractures. Rheumatic Disease Clinics of North America, 27(1), 255-262. doi:10.1016/s0889-857x(05)70197-6Keaveny, T. M., Morgan, E. F., Niebur, G. L., & Yeh, O. C. (2001). Biomechanics of Trabecular Bone. Annual Review of Biomedical Engineering, 3(1), 307-333. doi:10.1146/annurev.bioeng.3.1.307Rho, J.-Y., Kuhn-Spearing, L., & Zioupos, P. (1998). Mechanical properties and the hierarchical structure of bone. Medical Engineering & Physics, 20(2), 92-102. doi:10.1016/s1350-4533(98)00007-1Currey, J. D. (2011). The structure and mechanics of bone. Journal of Materials Science, 47(1), 41-54. doi:10.1007/s10853-011-5914-9Gupta, H. S., & Zioupos, P. (2008). Fracture of bone tissue: The ‘hows’ and the ‘whys’. Medical Engineering & Physics, 30(10), 1209-1226. doi:10.1016/j.medengphy.2008.09.007Nagaraja, S., Couse, T. L., & Guldberg, R. E. (2005). Trabecular bone microdamage and microstructural stresses under uniaxial compression. Journal of Biomechanics, 38(4), 707-716. doi:10.1016/j.jbiomech.2004.05.013Garcia, D., Zysset, P. K., Charlebois, M., & Curnier, A. (2008). A three-dimensional elastic plastic damage constitutive law for bone tissue. Biomechanics and Modeling in Mechanobiology, 8(2), 149-165. doi:10.1007/s10237-008-0125-2Ridha, H., & Thurner, P. J. (2013). Finite element prediction with experimental validation of damage distribution in single trabeculae during three-point bending tests. Journal of the Mechanical Behavior of Biomedical Materials, 27, 94-106. doi:10.1016/j.jmbbm.2013.07.005Hambli, R. (2012). A quasi-brittle continuum damage finite element model of the human proximal femur based on element deletion. Medical & Biological Engineering & Computing, 51(1-2), 219-231. doi:10.1007/s11517-012-0986-5Fan, R., Gong, H., Zhang, X., Liu, J., Jia, Z., & Zhu, D. (2016). Modeling the Mechanical Consequences of Age-Related Trabecular Bone Loss by XFEM Simulation. Computational and Mathematical Methods in Medicine, 2016, 1-12. doi:10.1155/2016/3495152Vellwock, A. E., Vergani, L., & Libonati, F. (2018). A multiscale XFEM approach to investigate the fracture behavior of bio-inspired composite materials. Composites Part B: Engineering, 141, 258-264. doi:10.1016/j.compositesb.2017.12.062Hambli, R. (2010). Multiscale prediction of crack density and crack length accumulation in trabecular bone based on neural networks and finite element simulation. International Journal for Numerical Methods in Biomedical Engineering, 27(4), 461-475. doi:10.1002/cnm.1413Hambli, R. (2011). Apparent damage accumulation in cancellous bone using neural networks. Journal of the Mechanical Behavior of Biomedical Materials, 4(6), 868-878. doi:10.1016/j.jmbbm.2011.03.002Lemaitre, J. (1985). A Continuous Damage Mechanics Model for Ductile Fracture. Journal of Engineering Materials and Technology, 107(1), 83-89. doi:10.1115/1.3225775Turner, C. H., & Burr, D. B. (1993). Basic biomechanical measurements of bone: A tutorial. Bone, 14(4), 595-608. doi:10.1016/8756-3282(93)90081-kBay, B. K. (1995). Texture correlation: A method for the measurement of detailed strain distributions within trabecular bone. Journal of Orthopaedic Research, 13(2), 258-267. doi:10.1002/jor.1100130214Peters, W. H., & Ranson, W. F. (1982). Digital Imaging Techniques In Experimental Stress Analysis. Optical Engineering, 21(3). doi:10.1117/12.7972925Sutton, M., Wolters, W., Peters, W., Ranson, W., & McNeill, S. (1983). Determination of displacements using an improved digital correlation method. Image and Vision Computing, 1(3), 133-139. doi:10.1016/0262-8856(83)90064-1Pan, B., Qian, K., Xie, H., & Asundi, A. (2009). Two-dimensional digital image correlation for in-plane displacement and strain measurement: a review. Measurement Science and Technology, 20(6), 062001. doi:10.1088/0957-0233/20/6/062001Khoo, S.-W., Karuppanan, S., & Tan, C.-S. (2016). A Review of Surface Deformation and Strain Measurement Using Two-Dimensional Digital Image Correlation. Metrology and Measurement Systems, 23(3), 461-480. doi:10.1515/mms-2016-0028Palanca, M., Tozzi, G., & Cristofolini, L. (2015). The use of digital image correlation in the biomechanical area: a review. International Biomechanics, 3(1), 1-21. doi:10.1080/23335432.2015.1117395Grassi, L., & Isaksson, H. (2015). Extracting accurate strain measurements in bone mechanics: A critical review of current methods. Journal of the Mechanical Behavior of Biomedical Materials, 50, 43-54. doi:10.1016/j.jmbbm.2015.06.006Bayraktar, H. H., Morgan, E. F., Niebur, G. L., Morris, G. E., Wong, E. K., & Keaveny, T. M. (2004). Comparison of the elastic and yield properties of human femoral trabecular and cortical bone tissue. Journal of Biomechanics, 37(1), 27-35. doi:10.1016/s0021-9290(03)00257-4Carretta, R., Stüssi, E., Müller, R., & Lorenzetti, S. (2013). Within subject heterogeneity in tissue-level post-yield mechanical and material properties in human trabecular bone. Journal of the Mechanical Behavior of Biomedical Materials, 24, 64-73. doi:10.1016/j.jmbbm.2013.04.014Linde, F., & Sørensen, H. C. F. (1993). The effect of different storage methods on the mechanical properties of trabecular bone. Journal of Biomechanics, 26(10), 1249-1252. doi:10.1016/0021-9290(93)90072-mLinde, F., & Hvid, I. (1987). Stiffness behaviour of trabecular bone specimens. Journal of Biomechanics, 20(1), 83-89. doi:10.1016/0021-9290(87)90270-3Keaveny, T. M., Borchers, R. E., Gibson, L. J., & Hayes, W. C. (1993). Theoretical analysis of the experimental artifact in trabecular bone compressive modulus. Journal of Biomechanics, 26(4-5), 599-607. doi:10.1016/0021-9290(93)90021-6Keaveny, T. M., Guo, X. E., Wachtel, E. F., McMahon, T. A., & Hayes, W. C. (1994). Trabecular bone exhibits fully linear elastic behavior and yields at low strains. Journal of Biomechanics, 27(9), 1127-1136. doi:10.1016/0021-9290(94)90053-1Keaveny, T. M., Pinilla, T. P., Crawford, R. P., Kopperdahl, D. L., & Lou, A. (1997). Systematic and random errors in compression testing of trabecular bone. Journal of Orthopaedic Research, 15(1), 101-110. doi:10.1002/jor.1100150115Correlated Solutions. VIC-2d v6 reference manual. 2016. http://www.correlatedsolutions.com/supportcontent/Vic-2D-v6-Manual.pdf.Whitehouse, W. J. (1974). The quantitative morphology of anisotropic trabecular bone. Journal of Microscopy, 101(2), 153-168. doi:10.1111/j.1365-2818.1974.tb03878.xKabel, J., van Rietbergen, B., Dalstra, M., Odgaard, A., & Huiskes, R. (1999). The role of an effective isotropic tissue modulus in the elastic properties of cancellous bone. Journal of Biomechanics, 32(7), 673-680. doi:10.1016/s0021-9290(99)00045-7Nalla, R. K., Kinney, J. H., & Ritchie, R. O. (2003). Mechanistic fracture criteria for the failure of human cortical bone. Nature Materials, 2(3), 164-168. doi:10.1038/nmat832Taylor, D. (2003). A crack growth model for the simulation of fatigue in bone. International Journal of Fatigue, 25(5), 387-395. doi:10.1016/s0142-1123(02)00165-2Burr, D. B., & Stafford, T. (1990). Validity of the Bulk-Staining Technique to Separate Artifactual From In Vivo Bone Microdamage. Clinical Orthopaedics and Related Research, 260, 305-308. doi:10.1097/00003086-199011000-00047Keaveny, T. M., & Hayes, W. C. (1993). A 20-Year Perspective on the Mechanical Properties of Trabecular Bone. Journal of Biomechanical Engineering, 115(4B), 534-542. doi:10.1115/1.2895536Wolfram, U., Wilke, H.-J., & Zysset, P. K. (2011). Damage accumulation in vertebral trabecular bone depends on loading mode and direction. Journal of Biomechanics, 44(6), 1164-1169. doi:10.1016/j.jbiomech.2011.01.018Kopperdahl, D. L., & Keaveny, T. M. (1998). Yield strain behavior of trabecular bone. Journal of Biomechanics, 31(7), 601-608. doi:10.1016/s0021-9290(98)00057-8Hara, T., Tanck, E., Homminga, J., & Huiskes, R. (2002). The influence of microcomputed tomography threshold variations on the assessment of structural and mechanical trabecular bone properties. Bone, 31(1), 107-109. doi:10.1016/s8756-3282(02)00782-2Parkinson, I. H., Badiei, A., & Fazzalari, N. L. (2008). Variation in segmentation of bone from micro-CT imaging: implications for quantitative morphometric analysis. Australasian Physics & Engineering Sciences in Medicine, 31(2), 160-164. doi:10.1007/bf03178592Wachtel, E. F., & Keaveny, T. M. (1997). Dependence of trabecular damage on mechanical strain. Journal of Orthopaedic Research, 15(5), 781-787. doi:10.1002/jor.1100150522Nazarian, A., Meier, D., Müller, R., & Snyder, B. D. (2009). Functional dependence of cancellous bone shear properties on trabecular microstructure evaluated using time-lapsed micro-computed tomographic imaging and torsion testing. Journal of Orthopaedic Research, 27(12), 1667-1674. doi:10.1002/jor.20931Schwiedrzik, J., Taylor, A., Casari, D., Wolfram, U., Zysset, P., & Michler, J. (2017). Nanoscale deformation mechanisms and yield properties of hydrated bone extracellular matrix. Acta Biomaterialia, 60, 302-314. doi:10.1016/j.actbio.2017.07.030Bevill, G., Eswaran, S. K., Gupta, A., Papadopoulos, P., & Keaveny, T. M. (2006). Influence of bone volume fraction and architecture on computed large-deformation failure mechanisms in human trabecular bone. Bone, 39(6), 1218-1225. doi:10.1016/j.bone.2006.06.016Althouse, A. D. (2016). Adjust for Multiple Comparisons? It’s Not That Simple. The Annals of Thoracic Surgery, 101(5), 1644-1645. doi:10.1016/j.athoracsur.2015.11.02

Numerical modelling of the mechanical behaviour of an osteon with microcracks

In this work, we present two strategies for the numerical modelling of microcracks and damage within an osteon. A numerical model of a single osteon under compressive diametral load is developed, including lamellae organized concentrically around the haversian canal and the presence of lacunae. Elastic properties have been estimated from micromechanical models that consider the mineralized collagen fibrils reinforced with hydroxyapatite crystals and the dominating orientation of the fibrils in each lamella. Microcracks are simulated through the node release technique, enabling propagation along the lamellae interfaces by application of failure criteria initially conceived for composite materials, in particular the Brewer and Lagace criterion for delamination. A second approach is also presented, which is based on the progressive degradation of the stiffness at the element level as the damage increases. Both strategies are discussed, showing a good agreement with experimental evidence reported by other authors. It is concluded that interlaminar shear stresses are the main cause of failure of an osteon under compressive diametral load.The authors wish to thank the Ministerio de Economia y Competitividad for the support received in the framework of the projects DPI2010-20990 and DPI2013-46641-R and to the Generalitat Valenciana, Programme PROMETEO 2012/023. The authors also thank Mr. Carlos Pons Gomez for his help in the development of some of the numerical models.Giner Maravilla, E.; Arango Villegas, C.; Vercher Martínez, A.; Fuenmayor Fernández, FJ. (2014). Numerical modelling of the mechanical behaviour of an osteon with microcracks. Journal of the Mechanical Behavior of Biomedical Materials. 37:109-124. https://doi.org/10.1016/j.jmbbm.2014.05.006S1091243

Calculation of the critical energy release rate Gc of the cement line in cortical bone combining experimental tests and finite element models

[EN] In this work, a procedure is proposed to estimate the critical energy release rate Gc of the so-called cement line in cortical bone tissue. Due to the difficulty of direct experimental estimations, relevant elastic and toughness material properties at bone microscale have been inferred by correlating experimental tests and finite element simulations. In particular, three-point bending tests of ovine cortical bone samples have been performed and modeled by finite elements. The initiation and growth of microcracks in the tested samples are simulated through finite elements using a damage model based on a maximum principal strain criterion, showing a good correlation with the experimental results. It is observed that microcracks evolve mainly along the cement lines and through the interstitial material but without crossing osteons. The numerical model allows the calculation of the cement line critical energy release rate Gc by approximating its definition by finite differences. This way, it is possible to estimate this property poorly documented in the literature.The authors wish to thank the Ministerio de Economia y Competitividad for the support received in the framework of the project DPI2013-46641-R and to the Generalitat Valenciana, Programme PROMETEO 2016/007. The authors also thank Dr. Jose Luis Peris, from Instituto de Biomecanica de Valencia (IBV) and Carlos Tudela Desantes for their collaboration within the context of the project.Giner Maravilla, E.; Belda, R.; Arango-Villegas, C.; Vercher Martínez, A.; Tarancón Caro, JE.; Fuenmayor Fernández, FJ. (2017). Calculation of the critical energy release rate Gc of the cement line in cortical bone combining experimental tests and finite element models. Engineering Fracture Mechanics. 184:168-182. https://doi.org/10.1016/j.engfracmech.2017.08.026S16818218

A multiscale modelling of bone ultrastructure elastic properties using finite elements simulation and neural network method

Bone is a living material with a complex hierarchical structure which entails exceptional mechanical properties, including high fracture toughness, specific stiffness and strength. Bone tissue is essentially composed by two phases distributed in approximately 30 70%: an organic phase (mainly type I collagen and cells) and an inorganic phase (hydroxyapatite-HA-and water). The nanostructure of bone can be represented throughout three scale levels where different repetitive structural units or building blocks are found: at the first level, col-lagen molecules are arranged in a pentameric structure where mineral crystals grow in specific sites. This primary bone structure constitutes the mineralized collagen microfibril. A struc-tural organization of inter-digitating microfibrils forms the mineralized collagen fibril which represents the second scale level. The third scale level corresponds to the mineralized col-lagen fibre which is composed by the binding of fibrils. The hierarchical nature of the bone tissue is largely responsible of their significant mechanical properties; consequently, this is a current outstanding research topic. Scarce works in literature correlates the elastic prop-erties in the three scale levels at the bone nanoscale. The main goal of this work is to estimate the elastic properties of the bone tissue in a multiscale approach including a sensitivity analy-sis of the elastic behaviour at each length scale. This proposal is achieved by means of a novel hybrid multiscale modelling that involves neural network (NN) computations and finite elements method (FEM) analysis. The elastic properties are estimated using a neural network simulation that previously has been trained with the database results of the finite element models. In the results of this work, parametric analysis and averaged elastic constants for each length scale are provided. Likewise, the influence of the elastic constants of the tissue constituents is also depicted. Results highlight that intelligent numerical methods are pow-erful and accurate procedures to deal with the complex multiscale problem in the bone tissue with results in agreement with values found in literature for specific scale levels.Barkaoui, A.; Tlili, B.; Vercher Martínez, A.; Hambli, R. (2016). A multiscale modelling of bone ultrastructure elastic properties using finite elements simulation and neural network method. Computer Methods and Programs in Biomedicine. 134:69-78. doi:10.1016/j.cmpb.2016.07.005S697813