In endoprosthesis surgery there are typically a high percentage of implant defects, these can lead to failure of the whole prosthesis. One type of total hip replacement function loss is acetabular cup loosening from the pelvic bone. This article examines manufacture perturbations as one of the possible reasons for this kind of failure. Both dimension and geometry manufacturing perturbations of ceramic head and polyethylen cup were analyzed. We find that perturbations in the variables analysed here affect considered values of contact pressure and frictional moment. Furthermore, contact pressure and frictonal moment are quantities affecting replacement success and durability. From obtained results we can recommend to fit head and cup with a clearance of between 0 mm andd 0.05 mm. We do not recommend using interference type of fit. Roundness perturbation of ceramic head should not exceed 0.025 mm. and Obsahuje seznam literatury
This paper presents a brief review of selected approaches used for computational modelling of bimaterial failure and for evaluation of interface failure resistance. Attention is paid to the approaches that assume absence of initial interface crack. The applicability of such approaches to rubber-steel interface failure evaluation is discussed in the paper. The approach based on the so called ‘cohesive zone model‘ is preferred and demonstrated by an example of computational modelling of rubber-steel interface failure during a peel-test. The results of peel-test computational modelling are presented. The influence of cohesive zone element number on the results is also analysed. The results are consistent with experimental data. and Obsahuje seznam literatury
This article studies several aspects of problems associated with diseases of big joints. It is an introductory essay to another three articles that focus on solving various biomechanical problems in hip joint. Stress limit states on contact surfaces of the hip joint can be considered as a common denominator of all these problems. General analyses of these states are described in a separate part of this article. Other general analyses concern the complex of problems associated with diseases of big joints. As an illustration (in view of the articles that follow), this article includes a systemic conception on analysis of the applicability of biomechanics in solving therapeutic problems of big joints. As an illustrative example, the hip joint was selected. and Obsahuje seznam literatury
The paper deals with stress concentration in inclined bars and beams, where the shoulder radius is often not prescribed in the detail drawings. The commonly accepted notch definition as a stepwise change of the beam cross section, as well as a lack of
nomograms or other data on stress concentration in inclined shoulders in the available literature ([1], [2], [3]) support the assumption of negligible stress concentration in inclined shoulders. Several failures of shaft-like components with inclined shoulders made us to investigate the stress concentration in these shoulders. Computational modelling confirmed a rather high stress concentration even in shoulders with a very low inclination β angle. Even in the case of β = 30°, the stress concentration factor is only slightly lower than in a comparable perpendicular (β = 90°) shoulder. Therefore nomograms for evaluation of stress concentration factors in inclined bar and beam shoulders under basic loading types were created and published in the paper.
The paper continues the description of constitutive behaviour of matters, the overview of which was presented in the previous part of this paper (Part I - basic and simple constitutive models). The definition and systemization of constitutive models was presented there and basic and simple models were described in detail. In the same systemic approach, combined constitutive models of materials (solid matters) are presented in this paper (Part II). It analyzes the more complex types of constitutive behaviour and presents a comprehensive overview of their responses in standard tension tests (stresses as functions of strain magnitude and strain rate), as well as the simplest mathematical interpretations of viscoelastic, elastic-plastic, viscoplastic and elastic-viscoplastic matters are presented, except for various types of anisotropic materials and their constitutive models (all the models are presented as isotropic only). On the base of both of these papers, the chapter on constitutive models was published in [1]. and Obsahuje seznam literatury
The paper presents a systemic overview of constitutive models, i.e. mathematical or graphical representations of responses of a matter iniciated by its activation coming from its surroundings (especially stress- or strain-controlled loadings in mechanics). Various states of matter showing different behaviour are related with different distances among particles of the matter and their mutual movements. However, in oppostie to the previous centuries, when different approaches and methods were developed and used for description of various types of matters (in solid mechanics, hydromechanics, thermodynamics etc.), recently more and more often solid mechanics meets materials showing some features of fluids (e.g. creep, flow), and interactions of matters in different states (e.g. solid-liquid) need to be solved as well. The presented paper, together with another consequent one (Part II), creates a set of two related articles aiming at facilitating you the orientation in various types of constitutive equations. It presents graphical representations of basic mechanical resposnes (stress as a function of strain magnitude and strain rate, creep stress relaxation), as well as their simplified mathematical substantiation. Some more complex types of constitutive models will be presented in part II. On the base of these papers, the chapter on constitutive models was published in [1]. and Obsahuje seznam literatury
The contribution deals with strain-stress analysis of torsion of a non-circular bar. Mathematical model is exactly derived and solutions are introduced and visualised for cases of triangular, rectangular and some other profiles. and Obsahuje seznam literatury