Presented paper is focused on description of algorithm for fast analysis of leveling process in detail and on verification of obtained results. The main idea is based on using Finite Element Method (FEM) and solving its fundamental equation. The algorithm is programmed using software MATLAB. The program has modular structure, so it is not complicated to modify any setting or utility. Leveling process of long semi products respecting the Eulerian approach is considered. Curved material passes through laterally offset rollers so repeated elasto-plastic bending occurs. Plastic deformation causes redistribution of residual stress. The semi product is straightened when rollers are appropriately positioned. Given problem is complicated due to high inherent nonlinearity and sensitivity, caused by cyclic plasticity. Useful setting of the leveling machine is found by iterative process, based on input measured geometrical data and material characteristics. and Obsahuje seznam literatury
This paper deals with experimental simulation of mechanical properties of transtibial prosthesis. Artificial limb allows patient standing and moving without of using others supporting devices. Therefore, patient returns back to common and active life. Design and prosthesis properties decide about comfort, safeness and reliability of prosthesis. The article summarizes a conclusion of preliminary experiment, which was performed to measurement procedure of prosthesis strain (for real loading of straight walking, downhill walking and downstairs walking) and data processing. and Obsahuje seznam literatury
The aim of this study is to perform detail experimental mapping of the lubricating film thickness of bovine serum (BS) within the contact between an artificial metal or ceramic femoral head and a glass disc and analyze effect of proteins on the film formation. Mapping of the lubricating film of various concentrations of BS solutions was carried out using an optical test rig. Chromatic interferograms were recorded with a high-speed digital camera and evaluated with thin film colorimetric interferometry. The film thickness was studied as a function of both time and mean speed. The results showed that film thickness increases with time for both the metal and ceramic heads. Films formed at the end of measurements with the metal head were found to be typically in the range of 60-100 nm for all BS solutions and were independent on the amount of proteins in tested fluids. At the beginning of the speed measurements, BS of all concentrations forms a very thin film (1-2 nm) and its thickness increases with increasing mean speed. However, when the speed was decreased, the film thickness did not reduce but increased with decreasing speeeds that supports the findings of other researchers. Moreover, it was found that BS supply is sensitive parameter. When the lubricant reservoir below tested head was used then the measured central film thicknesses achieved values only about 20 nm, whereas when the tests were realized without the reservoir, measured central film thicknesses achieved higher values about 100 nm. For both types of the experiments, distribution of the film thickness within the contact zone is not homogeneous and two different film thickness regions can be found; thicker protein film and thinner base film that both increase with time and speed. and Obsahuje seznam literatury
This work presents the procedure of a computational model of pathological hip joint allowing a simple modification of individual parts of the model according to the planned course of femoral and pelvic osteotomy. Both presented models were subjected to strain-stress analysis by a finite element method using the ANSYS program system. The obtained results are compared with physiological hip joint results and the feasibility of planned osteotomy is evaluated based on selected mechanical parameters. The conclusions are consulted with surgeons and possible corelations with clinical results are searched for. and Obsahuje seznam literatury
The paper deals with the problems of ceramic head of hip joint endoprosthesis destructions, and with assessing the impact of shape deflections of conical surfaces on the probability of this failure. Concerned are shape deflections from the ideal conical surfaces of the stem and the head of the endoprosthesis, which - when the head is put on the stem and the endoprosthesis loaded - form a contact configuration. The shape deflections may be modelled at the macro-level - this concerns model shape inaccuracies such as deflection from the nominal degree of taper, ovality, and their combination, or, possibly, at the micro-level - when the stochastic distribution of unevenness on the contact areas is respected. The problem of stress in ceramic heads was solved using the algorithm of the finite element metod for spatial contact tasks, and the Weibull probability model was used for solving the problem of head cohesion failure probability. In the paper are presented and analysed the results of solution of the micro-level shape deflections, obtained from measurements made on the cones of stems and heads.
Possibility of substituting the affected hip joint with endoprothesis is - for many people all over the world - the only way for returning to the normal life without pains and significant motion limitations. But the age limit requiring the application of replacement becomes lower and lower. The endoprothesis applied to young patients must be replaced several times during their lives and the application and repeated replacements affect the bone so that it may happen that the next application may not be possible any more. For such cases the surface replacement the propose of which is to postpone the need of the first application of the classic total endoprothesis, has been invented. So that the objective of the contribution consists in creating a computing model of the healthy hip joint and the hip joint with the classic total hip replacement and with the surface replacement, in carrying out the stress-strain analyses, and in mutually confronting the results obtained. The problem has been solved as a direct task by means of computational modelling, by the method of finite elements in the ANSYS. The computational model consists of these components: sacral, pelvic and femoral bone, muscles, cup, and femoral compponent. and Obsahuje seznam literatury