Conditions Of Stress-strain State Research Articles

NUMERICAL INVESTIGATION OF THE VALVE MODEL FOR PRIMARY SUTURELESS IMPLANTATION

HighlightsThe presented numerical model of the bioprosthesis support frame for sutureless fixation needs to be optimized to reduce the amplitude of the von Mises stresses.The presented setup of numerical modeling has been validated using the study of commercial analogs. AbstractAim. To assess the stress-strain state of three computer models of TAVI prosthesis support frames during crimping and shaping to the delivery configuration.Methods. The study included three models of stent-like support frames for balloon-expandable devices, which are intended to serve as a foundation for the subsequent development of a domestic aortic valve prosthesis: two models of commercial bioprostheses and one experimental. The objects were evaluated numerically under the conditions of stress-strain state that arises in the stent support frames, simulating two loads: crimping and shaping to the delivery configuration. The study was conducted using the numerical modeling complex Abaqus/CAE (“Dassault Systemes”, France). The key indicators for evaluation were the von Mises stress, as a strength criterion, and its distribution over the frame; the presence and proportion of elastic recoil.Results. It was shown that all samples are capable of reaching the required diameter without excessive material. A quantitative investigation of the Von Mises stress showed that commercial models display amplitudes below the material`s strength limit (892.4 and 916.8 MPa), whereas the proprietary model exceeds this limit, reaching 991.4 MPa, requiring geometry optimization. Shaping to the delivery configuration indicates that all models provide safe expansion up to 26 mm, with a Von Mises stress level in the range of 882.4–914.1 MPa, which is below the strength limit of the cobalt-chrome alloy. Moreover, we have noted heterogeneous stress distribution, with concentration in the lamella junction areas.Conclusion. Thus, it has been demonstrated that numerical modeling and the finite element method can be effectively applied to assess the stress-strain state of sutureless prostheses. Geometry optimization and further development of this project – the development of a Russian minimally invasive aortic valve prosthetic system, may contribute towards increasing the accessibility of this treatment method.

Mathematical modeling of overhead crane under conditions of stress-strain state of metal structure as a control object

The article considers an example of the application of the existing mathematical model of an overhead crane to equipment with irreversible structural defects. The course of the solution of the problem is considered: obtaining primary data, finding the existing mathematical model of the crane, adapting it to the problem in question, building a computational model, modeling and analyzing the results obtained. The peculiarity of a crane as a control object is the non-typical state of the metal structure. The overhead crane is in this state after prolonged operation of the equipment with incorrect loading and control modes. As a result of such operating modes, significant wear of the wheels and the rail track take place. Worn elements must be replaced. The frequency of wheel replacement is very intensive, and is about twice a year. The process of replacing wheels with corner boxes is a very expensive procedure – it is necessary to buy equipment, stop the warehouse for a few days and attract staff. To eliminate such costs, it is proposed to conduct a simulation of the crane in order to identify methods of controlling it. The result of the first stage of modeling is the answer to the question: is it possible to operate the crane that is deformed using the correctly selected control mode.

Optimization of the Structures at Shakedown and Rosen’s Optimality Criterion

Paper focuses on the problems of application of extreme energy principles and nonlinear mathematical programing in the theory of structural shakedown. By means of energy principles, which describes the true stress-strain state conditions of the structure, the dual mathematical models of analysis problems are formed (static and kinematic formulations). It is shown how common mathematical model of the structures optimization at shakedown with safety and serviceability constraints (according to the ultimate limit state (ULS) and serviceability limit state (SLS) requirements) on the basis of previously mentioned mathematical models is formed. The possibilities of optimization problem solution in the context of physical interpretation of optimality criterion of Rosen’s algorithm are analyzed.

Deformation of an elastic anisotropic micro-inhomogeneous half-space

There is considered the problem of deformation of a transversally-isotropic microinhomogeneous half-space under macro-homogeneous stress-strain state conditions. It is assumed that the half-space boundary is parallel to the plane of isotropy of the medium, filling it, and the elastic parameters governing the medium are independent of the coordinate normal to the boundary, and are random functions of two coordinates. The problem is solved by the method of perturbations. Dispersions of the deformation are constructed by this method in a first approximation. The behavior of the deformation dispersion is investigated as a function of the coordinate normal to the plane of isotropy.