Bone Stress-Strain State Evaluation Using CT Based FEM

Nowadays, the use of a digital prototype in numerical modeling is one of the main approaches to calculating the elements of an inhomogeneous structure under the influence of external forces. The article considers a finite element analysis method based on computed tomography data. The calculations used a three-dimensional isoparametric finite element of a continuous medium developed by the authors with a linear approximation, based on weighted integration of the local stiffness matrix. The purpose of this study is to describe a general algorithm for constructing a numerical model that allows static calculation of objects with a porous structure according to its computed tomography data. Numerical modeling was carried out using kinematic boundary conditions. To evaluate the results obtained, computational and postprocessor grids were introduced. The qualitative assessment of the modeling data was based on the normalized error. Three-point bending of bone specimens of the pig forelimbs was considered as a model problem. The numerical simulation results were compared with the data obtained from a physical experiment. The relative error ranged from 3 to 15%, and the crack location, determined by the physical experiment, corresponded to the area where the ultimate strength values were exceeded, determined by numerical modeling. The results obtained reflect not only the effectiveness of the proposed approach, but also the agreement with experimental data. This method turned out to be relatively non-resource-intensive and time-efficient

Ob ustoichivosi tsilindricheskikh i knoicheskikh obolochek krugovogo cecheniia pri sovmestnom deistvii osevogo szhatiia i vneshnego normalnogo davleniia

"We consider in this report the determination of the upper limit of critical loads in the case of simultaneous action of a compressive force, uniformly distributed over plane cross sections, and of isotropic external normal pressure on cylindrical or conical shells of circular cross section. As a starting point we use the differential equations for neutral equilibrium of conical shells which have been used for the solution of the problem of stability of conical shells under torsion and under axial compression; upon solution of the problem it is possible to satisfy all boundary conditions, in contrast to the report where no attention is paid to the fulfillment of the boundary conditions, and to the report where only part of the boundary conditions are satisfied by solution of the problem according to Galerkin's method" (p. 1)

Stability of Cylindrical and Conical Shells of Circular Cross Section, with Simultaneous Action of Axial Compression and External Normal Pressure

We consider in this report the determination of the upper limit of critical loads in the case of simultaneous action of a compressive force, uniformly distributed over plane cross sections, and of isotropic external normal pressure on cylindrical or conical shells of circular cross section. As a starting point we use the differential equations for neutral equilibrium of conical shells which have been used for the solution of the problem of stability of conical shells under torsion and under axial compression; upon solution of the problem it is possible to satisfy all boundary conditions, in contrast to the report where no attention is paid to the fulfillment of the boundary conditions, and to the report where only part of the boundary conditions are satisfied by solution of the problem according to Galerkin's method. Approximate formulas are used for the determination of the critical external normal pressure with simultaneous action of longituninal compression. Let us note that the formulas suggested in reference 5 are not well founded and may lead, in a number of cases, to a substantial mistake in the magnitude of the critical load

Investigation of stress-strain state in the flywheel and estimation their specific energy capacity

In this paper, the specific energy intensity of the kinetic energy storage devices, including the flywheel-casing scheme in the potential field, is investigated. The possibilities of using various structural materials in the manufacture of structural elements of a mechanical accumulator are analyzed, the stress-strain state of the flywheel and the casing under quasistatic increase in the rotational speed of the rotor part of the structure is investigated. It is noted that the presence of a potential field in the flywheel-casing system makes it possible to increase the specific energy intensity of the kinetic energy storage

Automation of bone tissue histology

© 2019 Yaikova, Gerasimov, Fedyanin, Zaytsev, Baltin, Baltina and Sachenkov. In abstract methods of automation of histology, bone structure is considered. Possible inputs are snapshots from a microscope or computed tomography slices. An algorithm is proposed that differentiates objects according to their color (or grayscale) and recover morphology topology. An algorithm to separate morphological objects by their dimensions and color parameters was built. Measured parameters were bone surface, bone area, porosity, cortical thickness, canal number, canal area, and etc. Additionally, we measured the anisotropy properties of the bone tissue: distribution of porosity direction and degree of porosity elongation. A bone example was scanned by computed tomography. All data were measured by the proposed method and the results presented. An example algorithm of work on computed tomography data is shown in this work

Modeling the change in the stiffness parameters of bone tissue under the influence of external loads

© Published under licence by IOP Publishing Ltd. The paper considers the problem of restructuring trabecular bone tissue under external loads. The evolutionary relationships was used in Cowin statement, changes of orientation of the pores was described in terms of the fabric tensor and the volume fraction of solid bone. To estimate the elastic properties, the mechanical constants were recalculated according to the actual states of the fabric tensor. The process of bone remodeling of a rounded rectangular area under external loads was simulated; using the theory of lazy zone and physical relations, the initial value of the change in the proportion of solid bone volume is obtained. The initial state was given by a homogeneous porous state. The boundary-value problem was solved by the finite element method, and the initial problem was solved by the method of finite differences. As a result, fields were obtained for the distribution of the mechanical properties of bone tissue in the region

Automation of bone tissue histology

© 2019 Yaikova, Gerasimov, Fedyanin, Zaytsev, Baltin, Baltina and Sachenkov. In abstract methods of automation of histology, bone structure is considered. Possible inputs are snapshots from a microscope or computed tomography slices. An algorithm is proposed that differentiates objects according to their color (or grayscale) and recover morphology topology. An algorithm to separate morphological objects by their dimensions and color parameters was built. Measured parameters were bone surface, bone area, porosity, cortical thickness, canal number, canal area, and etc. Additionally, we measured the anisotropy properties of the bone tissue: distribution of porosity direction and degree of porosity elongation. A bone example was scanned by computed tomography. All data were measured by the proposed method and the results presented. An example algorithm of work on computed tomography data is shown in this work

Modeling the change in the stiffness parameters of bone tissue under the influence of external loads

© Published under licence by IOP Publishing Ltd. The paper considers the problem of restructuring trabecular bone tissue under external loads. The evolutionary relationships was used in Cowin statement, changes of orientation of the pores was described in terms of the fabric tensor and the volume fraction of solid bone. To estimate the elastic properties, the mechanical constants were recalculated according to the actual states of the fabric tensor. The process of bone remodeling of a rounded rectangular area under external loads was simulated; using the theory of lazy zone and physical relations, the initial value of the change in the proportion of solid bone volume is obtained. The initial state was given by a homogeneous porous state. The boundary-value problem was solved by the finite element method, and the initial problem was solved by the method of finite differences. As a result, fields were obtained for the distribution of the mechanical properties of bone tissue in the region

Three-dimensional (3D) model-based lower limb stump automatic orientation

© 2020 by the authors. Modern prosthetics largely relies upon visual data processing and implementation technologies such as 3D scanning, mathematical modeling, computer-aided design (CAD) tools, and 3D-printing during all stages from design to fabrication. Despite the intensive advancement of these technologies, once the prosthetic socket model is obtained by 3D scanning, its appropriate orientation and positioning remain largely the responsibility of an expert requiring substantial manual effort. In this paper, an automated orientation algorithm based on the adjustment of the 3D-model virtual anatomical axis of the tibia along with the vertical axis of the rectangular coordinates in three-dimensional space is proposed. The suggested algorithm is implemented, tested for performance and experimentally validated by explicit comparisons against an expert assessment