Search

Scientific investigations of structures characterised by auxetic properties conducted so far have led to analyses on a molecular and macroscopic scale and few studies have been concerned with descriptions of auxetic models which could find application in objects of everyday use. The aim of this paper was to carry out numerical modelling and physical verification of furniture seat quality made up of auxetic pressure springs. The authors decided to determine system stiffness and distribution of contact pressure on their surface. The performed detailed numerical analysis made it possible to evaluate the comfort of seat utilisation as well as to assess the impact of seat modification with NHE35 foam on changes of this comfort. In addition, it was demonstrated that numerical modelling may provide a useful tool for rapid prototyping of complex, multilayer systems manufactured from materials with non-linear characteristics. Results of numerical calculations were verified in the laboratory determining the scale of errors with which these results should be interpreted.

The objective of this paper is to present and compare the results of numerical solutions of contact problem for two types of seats subjected to typical sitting loadings. The first seat is made of a typical hyperelastic foam, the other is designed with an auxetic polyamid spring skeleton. Computer simulations of the seat structure under a typical static loading exerted by a human body are performed by means of ABAQUS FEA. The model provides an insight into deformation modes and stress field in relation to geometric and material parameters of the seat structure.The other type of seat, due to the fact of global auxecity and progressive springs characteristics reduces contact stress concentrations, giving an advantegous distribution of pressure and provides the sensation of physical comfort. The proper seat skeleton shape leads to an improvement of ergonomic quality.

This paper presents micromechanical approach to assessment of elastic properties of composite polyurethane-carbon foams. Analysis is based on specific choice of RVE combined with micro-macro transition. It leads to evaluation of strength and elastic constants of a composite. Foam behaviour is investigated numerically. Solid skeleton part shape is based on the tetrahedron cut out with spheres. 3D unit cell model is FE discetized. Calculations are performed for foams of selected densities using ABAQUS system. The comparison shows good agreement between the theoretical approach and experimental data. The presented method may be applied to design novel materials such as graphitized foam and nano composites and tailoring these materials for desired elastic properties.

This paper presents numerical study of deformation and stresses in seat skeleton elements subject to static and dynamic pressure loads. Elastic skeleton made of polyamide or elastomer is taken as an example of a seat material. Auxetic type of seat structure ensures the reduction of real contact stresses between human body and seat, making it more comfortable than typical. FEM analysis is performed using ABAQUS system. Numerical calculations are carried out to determine the nonlinear stiffness characteristics of seat springs. The study makes possible the selection of material and structural topology fulfilling design constraints and additional recommendations concerning structural flexibility, stability and optimal reduction of contact stresses. This paper presents an application of the problem.