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Stress rate and incremental principle of virtual work in finite deformations
Fiala, Zdeněk
Solution of finite deformation problems is sought in the space of all deformation tensor fields. Representation of a deformation process here as a trajectory makes us possible to further classify symmetric second-order tensor fields either as points, vectors, or covectors, and, as a consequence, assign them the corresponding time derivatives. However, as the space of all deformation tensor fields has proved non-euclidean, the time derivative of vector, and covector fields along the trajectory should be defined by the covariant derivative. This approach enables us coherently to formulate an incremental principle of virtual work, and propose the corresponding procedure in solving finite deformation problems.
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Stanovení kritéria poškození hlavy pomocí konečnoprvkového modelu
Jiroušek, Ondřej ; Jíra, J.
Paper presents a detailed finite element model of human head used for head injury criteria assessment. Today most used HICs are based on the history of linear acceleration only. However, the rotational acceleration plays also important role, due to the rupture of bridging veins involved in the relative motion between the skull and the brain. Presented model allows for new approach to define the HIC based on either strain energy or on combination of linear and rotational acceleration history. The model is based on a series of CT and MRI scans of a cadaver head of high resolution and is composed of three different regions: 1. skull, 2. brain and 3. subarachnoidal space. Discussion on material properties of these four distinct regions is given in the paper.
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Vliv tvaru pánevní kosti na pole napění po implantaci cerkvikokapitální endoprotézy
Kytýř, Daniel ; Jírová, Jitka ; Micka, Michal ; Jíra, J.
Migration of the implant head after hemiarthoplasty is a problem which appertain to nearly all patients. Article deals with development and utilization of parametrical FE model of the hip joint for numerical analysis of implant head migration. There are two main input parameters for the stress analysis. CE angle representing the shape of acetabulum and direction of the femoral replacement loading. To assess the influence of selected parameters on the implant migration and to enable easy comparison to patients X-Ray scanning, the analysis was carried out as axially symmetric 2D and 3D contact problem. Ultimate values of first principal stress, third principal stress and sum of displacements were used as a reference magnitude.
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Interakce acetabulární komponenty a pánevní kosti s vadou v cementové vrstvě
Vyčichl, Jan ; Jiroušek, Ondřej ; Jírová, Jitka
The article deals with contact stress analysis of pelvic bone after implantation of cemented acetabular component with imperfections of cemented layer. 3D high resolution FE model of pelvic bone was created from the sequence of CT--slices. Imperfections were created both in the cement layer and in the bone tissue by drilling fixation holes. Boolean operations were used for inserting the spherical cemented component. Two contacts were defined in the FE model. The first contact is defined between the cement layer and the pelvic bone and the second one is between the cement layer and the polyethylene cup. The model was loaded by quasi--static joint forces, representing the maximum value of stance phase of gait (Bergmann HIP98). The FE model was used to ascertain the contact stress conditions in the underlying subchondral bone.
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