|
|
Failure probability of the ceramics part using Weibull weakest link theory
Kovář, Jaroslav ; Návrat, Tomáš (referee) ; Fuis, Vladimír (advisor)
This thesis compares Weibull weakest link theory with inclusion of one and all three principal stresses. Principal stresses needed for this theory were calculated with finite element method. The informational research is in the introduction of this thesis. It includes ceramic materials, Weibull weakest link theory, Gaussian quadrature over spherical surface and ceramic head of hip joint endoprothesis. Theoretical part is used for next calculations of probability of failure. The probability of failure of ceramic rod loaded by four-point bending is calculated in first calculations. This task is solved as contact in the next step. Next part of this thesis is about selection of suitable method of numerical integration. This method will be used in the calculation with all three principal stresses. The results of calculation with all three principal stresses are compared with the results of the calculation which includes only first principal stress. Firstly, this is done for cylindrical body and then used on head of hip joint endoprothesis. In the last part of this thesis, probability of fracture of head hip joint endoprothesis with shape deviation of nominal conicity is calculated.
|
|
|
Calculation of the probability of the endoprosthesis ceramic head with shape deviation
Kučerková, Miroslava ; Fuis, Vladimír (referee) ; Kovář, Jaroslav (advisor)
The main content of the diploma thesis is to determine the probability of failure of the hip joint endoprosthesis ceramic head. The assumption is the three-axis state of stress. To calculate the probability of failure three principal stresses, which are determined numerically using finite element method, are needed. Ceramic materials, hip joint endoprosthesis and Weibull weakest link theory, which describes the calculation of the probability of failure of ceramic components, are described in the first part of the thesis, after that, the second part with calculations follows. The first model, for which the stress and probability of failure were calculated, is a cylindrical body. The stress distribution in it was determined numerically as well as analytically. Its primary goal is to verify the developed algorithm of calculating the probability of failure. This algorithm is also used in calculations of probability of failure of ceramic femoral head. The suitability of using averaged principal stress values was also verified here. In the next part of the thesis, a model of an ideal ceramic head was created and its probability of failure was calculated. The impact of friction, penetration and the size of elements used for discretization of the model on the value of probability of failure were all analysed. The evaluated findings were subsequently used in the calculations of the model of ceramic head with an deviation from the ideal ovality. The impact of this change on the resulting probability of failure in comparison with the ideal state was evaluated in the conclusion.
|
|
|
Calculation of the probability of the ceramic component failure according to the Weibull’s weakest link theory
Kučerková, Miroslava ; Fuis, Vladimír (referee) ; Kovář, Jaroslav (advisor)
Weibull weakest link theory is used to determine the probability of failure of ceramic components. This bachelor thesis examines the cylindrical body, beams and rotating circular and intercircular disc. In these bodies it is possible to identify course of the stress in an analytical way. The research part of the work approaches ceramic materials in terms of their structure, composition, method of production or mechanical properties. From a theoretical point of view, Weibull weakest link theory for uniaxial and triaxial stress in the body is described and required relations for further calculations are given here. In the second part, the probability of failure of previously mentioned models is calculated. Beams are stressed by a simple and four - point bending. The impact of the body size on the probability of failure is also analyzed. The cylindrical body is solved for different variants, which are compared afterwards. At last, the effect of operating speed on the probability of failure of the rotating circular and intercircular disc is investigated.
|
|
|
Calculation of the probability of the endoprosthesis ceramic head with shape deviation
Kučerková, Miroslava ; Fuis, Vladimír (referee) ; Kovář, Jaroslav (advisor)
The main content of the diploma thesis is to determine the probability of failure of the hip joint endoprosthesis ceramic head. The assumption is the three-axis state of stress. To calculate the probability of failure three principal stresses, which are determined numerically using finite element method, are needed. Ceramic materials, hip joint endoprosthesis and Weibull weakest link theory, which describes the calculation of the probability of failure of ceramic components, are described in the first part of the thesis, after that, the second part with calculations follows. The first model, for which the stress and probability of failure were calculated, is a cylindrical body. The stress distribution in it was determined numerically as well as analytically. Its primary goal is to verify the developed algorithm of calculating the probability of failure. This algorithm is also used in calculations of probability of failure of ceramic femoral head. The suitability of using averaged principal stress values was also verified here. In the next part of the thesis, a model of an ideal ceramic head was created and its probability of failure was calculated. The impact of friction, penetration and the size of elements used for discretization of the model on the value of probability of failure were all analysed. The evaluated findings were subsequently used in the calculations of the model of ceramic head with an deviation from the ideal ovality. The impact of this change on the resulting probability of failure in comparison with the ideal state was evaluated in the conclusion.
|
|
|
Calculation of the probability of the ceramic component failure according to the Weibull’s weakest link theory
Kučerková, Miroslava ; Fuis, Vladimír (referee) ; Kovář, Jaroslav (advisor)
Weibull weakest link theory is used to determine the probability of failure of ceramic components. This bachelor thesis examines the cylindrical body, beams and rotating circular and intercircular disc. In these bodies it is possible to identify course of the stress in an analytical way. The research part of the work approaches ceramic materials in terms of their structure, composition, method of production or mechanical properties. From a theoretical point of view, Weibull weakest link theory for uniaxial and triaxial stress in the body is described and required relations for further calculations are given here. In the second part, the probability of failure of previously mentioned models is calculated. Beams are stressed by a simple and four - point bending. The impact of the body size on the probability of failure is also analyzed. The cylindrical body is solved for different variants, which are compared afterwards. At last, the effect of operating speed on the probability of failure of the rotating circular and intercircular disc is investigated.
|
|
|
Failure probability of the ceramics part using Weibull weakest link theory
Kovář, Jaroslav ; Návrat, Tomáš (referee) ; Fuis, Vladimír (advisor)
This thesis compares Weibull weakest link theory with inclusion of one and all three principal stresses. Principal stresses needed for this theory were calculated with finite element method. The informational research is in the introduction of this thesis. It includes ceramic materials, Weibull weakest link theory, Gaussian quadrature over spherical surface and ceramic head of hip joint endoprothesis. Theoretical part is used for next calculations of probability of failure. The probability of failure of ceramic rod loaded by four-point bending is calculated in first calculations. This task is solved as contact in the next step. Next part of this thesis is about selection of suitable method of numerical integration. This method will be used in the calculation with all three principal stresses. The results of calculation with all three principal stresses are compared with the results of the calculation which includes only first principal stress. Firstly, this is done for cylindrical body and then used on head of hip joint endoprothesis. In the last part of this thesis, probability of fracture of head hip joint endoprothesis with shape deviation of nominal conicity is calculated.
|
|
|
Stress-strain analysis of ceramic heads in the destruction device
Janíček, Přemysl
This article deals with the issues of modification of destructive device for ceramic heads of total hip replacement based on the analysis of tensile stress state in the head. The goal of device modification is a shift of the location with extreme value of sigma-1max from the region of head’s hole bottom to its opening. This modification will increase the credibility of the obtained material properties of bioceramics, which will be determined from a set of head destructions using the Weibull weakest link theory.
|
|
| |
|
|
Reliability analyses of the hip joint ceramic head under oblique loading production inaccuracies
Fuis, Vladimír
Paper presents the analysis on the stress in the ceramic head and its reliability for different loading angle, which simulates the physiological loading. The analysed system consists of the testing stem and ceramic head of the hip joint endoprosthesis thout the production inaccuracies in the region of the cone contact area between the head and the stem. The stress is calculated by FEM - system ANSYS, head's reliability is based on Weibull weakest link theory
|
|
|
Experimental evaluation of the weibull paramaters of the bioceramics strength
Fuis, Vladimír
The solution to the problem of ceramic head reliability requires realization of two computational models: one for determination of stress states and another one for evaluation of the fracture probability. Material characteristics of ceramics used in fracture probability evaluation have been determined by a 3-point-bending test till now. Within the framework of this paper is that the characteristics will be determined by destruction tests of ceramic heads.
|
guest ::
