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National Repository of Grey Literature 2 records found  Search took 0.00 seconds. 
Sensitivity Analysis of the Material Parameters Obtained from the Measurements
 Fuis, Vladimír
The paper deals with sensitivity analysis of the material parameters of the ceramic material on the dispersion of the measured data from the sensors. Material parameters of ceramic material are calculated from a set of destruction tests of ceramic heads of total hip joint replacements. The standard way of calculation of the ceramic material parameters consists in carrying out a set of 3 (or 4) point bending tests of specimens which were cut out from parts of the ceramic material to be analysed. In case of ceramic heads of the prosthesis, it is not possible to cut out specimens of required dimensions because the heads are too small. On that score, a special testing jig was made, in which 40 heads were destructed. From the measured values of circumferential strains of the head’s external spherical surface under destruction (by the sensors – strain gauges), the state of stress in the head under destruction was established using the finite elements method. From the obtained values the material parameters of the ceramic material were calculated using Weibull’s weakest-link theory. The calculated material parameters (Weibull modulus m and normalized volume strength σo, the last material parameter – stress σu is assumed to be equal 0 and corresponds to the conservative approach) has the dispersion and the influence of this dispersion (in our case the dispersion ± 5 % is assumed) is analysed in detail.
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Comparing the Results of Probability of Ceramic Head Fracture According to Weibull's Theory with Inclusion of One or Three Principal Stresses
 Kovář, J. ; Fuis, Vladimír
This paper focuses on the assessment of probability of ceramic head hip joint endoprothesis fracture.\nThe Weibull's weakest link theory with inclusion of one or all three principal stresses was used for calculations of probability of failure and the results were compared. The test of head of the hip joint endoprothesis according to ISO 7206 was modelled. Three variants were considered. In the first variant, the head of hip joint endoprothesis ended up without any imperfections from ideal geometry. In other two variants, the ceramic head had shape imperfection from nominal conicity. Principal stresses needed for the calculation of probability of failure were calculated by finite element method. The results with the use of linear and quadratic solid elements were compared and better option was chosen for the next calculations. The influence of allowed penetration, density of the mesh on the results of stresses and probability of failure was assessed. The Gaussian quadrature of 13th order was used for integration over the surface of unit hemisphere in space of principal stresses which was needed for computation of probability of failure with inclusion of all principal stresses. The influence of imperfection from nominal conicity on probability of failure of the head hip joint endoprothesis was calculated and the relative difference between the results of Weibull's weakest link theory with the inclusion of one or all three principal stressed was analyzed.
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