Purpose: We investigate the dependence of the kinematics of the human knee on its anatomy. The idea of describing the kinematics of the knee in the sagittal plane using four-bar linkage is almost as old as kinematics as an independent discipline. We start with a comparison of known four-bar linkage constructions. We then focus on the model by H. Nägerl which is applicable under form closure. Methods: We use geometry and analysis as the mathematical methods. The relevant geometrical parameters of the knee will be determined on the basis of the dimensions of the four-bar linkage. This leads to a system of nonlinear equations. Results: The four-bar linkage will be calculated from the limits of the constructively accessible parameters by means of a quadratic approximation. Conclusions: By adapting these requirements to the dimensions of the human knee, it will be possible to obtain valuable indications for the design of an endoprosthesis which imitates the kinematics of the natural knee.
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Purpose: The aim of this paper is to outline the mechanical conditions when sheet metals are tested by hydraulic bulging as a research background for analysis of the experimental results. Design/methodology/approach: The methodology adopted for this investigation consists in application of the engineering plasticity to a general description of the sheet bulge deformation under lateral hydraulic pressure. Findings: Governing differential equations of hydraulic sheet bulging are found and the current thickness over the bulged dome of the deformed diaphragm is expressed in terms of loading and geometric parameters. Research limitations/implications: The mathematical treatment is limited here to the cases of axial symmetry which assumes that planar isottropic sheet metals are bulged into circular die apertures. Practical implications: Experimental results and other computational models can be analysed in more details comparing them with the derived general mathematical expression. Originality/value: The mechanical state of the sheet bulging is analysed in more general way without any restrictions to the loading rate and to the hydraulic pressure distribution.
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