ABSTRACT
Using a wheelchair over uneven terrain generates vibrations of the human body. These vibrations result from mechanical energy impulses transferred from the ground through the wheelchair components to the user's body, which may negatively affect the quality of the wheelchair use and the user's health. This energy can be dissipated through the structure of the wheelchair frame, such as polymer and carbon fiber composites. This article aims to compare a wheelchair with an aluminum alloy frame and a carbon fiber frame in terms of reducing kinematic excitation acting on the user's body. Three wheelchairs were used in the study, one with an aluminum alloy frame (reference) and two innovative ones with composite frames. The user was sitting in the tested wheelchairs and had an accelerometer attached to their forehead. The vibrations were generated by applying impulses to the rear wheels of the wheelchair. The obtained results were analyzed and compared, especially regarding differences in the damping decrement. The research shows that using modern materials in the wheelchair frame has a beneficial effect on vibration damping. Although the frame structure and material did not significantly impact the reduction in the acceleration vector, the material and geometry had a beneficial effect on the short dissipation time of the mechanical energy generated by the kinematic excitation. Research has shown that modern construction materials, especially carbon fiber-reinforced composites, may be an alternative to traditional wheelchair suspension modules, effectively damping vibrations.
ABSTRACT
Thin walled cold formed structures were, and still are, very popular structural elements used in mechanical engineering. Modern technology and the progress in materials engineering allow to fabricate various shapes of thin walled cold formed components. Therefore, combinations between technology possibilities, material properties, loads and engineering requirements are wide and unlimited for thin walled components. The aim of this paper is to perform an experimental study of cold formed C-channel steel beams under four-points bending loads based on the global and the local buckling phenomena. A test rig was developed with a specially designed support system to subject thin-walled steel beams to a four-point bending load, where the support and loads were applied to the shear center of the open section steel beam. It is shown that it is not possible to completely eliminate the torque load on a thin-walled beam with an open section where load and support are applied in the shear center because investigated beams weren't ideal made. Thin walled open section beams are very sensitive for boundary conditions and geometrical accuracy. The force of gravity is also working. The presented research methodology can be improved and do test with other open section thin walled beams.
ABSTRACT
The high awareness of intensification and frequency of smog phenomenon all over the world in XXI age makes for detailed analyses of the reasons of its formation and prevention. The governments of the developed countries and conscious of real hazards, including many European countries, aim to restrict the emission of harmful gases. In literature, we can find the discussions on the influence of this phenomenon on the health and life of inhabitants of contaminated areas. Some elaborations of prognostic models, descriptions of pollution sources, the manner of their restriction, and the analysis of causal-consecutive correlation are also popular. The influence of pollutions resulting from the operation of vehicles, planes, and the industry are well described. However, every machine and device which is driven with a combustion engine has the effect on the general level of anthropogenic pollutions. These drives are subject of different regulations limiting their emission for service conditions and applications. One of the groups of such machines described in European and American regulations is non-road mobile machinery. The aim of this paper is the presentation of the problem of weak analysis and application of engineering and technological tools for machinery drive emission, despite of many publications on hazards and problems of emission. These machines have the influence on both the increase of global contamination and the machine users. The regulations of the European Union take into consideration the generated hazards and restrict the emission of machine exhaust gases by approval tests-these regulations are continually improved, and the effects of these works are new emission limits in 2019. However, these activities seem to be liberal as opposed to limits of the emission for passenger and goods vehicles where the technological development of the construction is greater and the regulations are the most rigorous. During the analysis of the development of non-road mobile machinery in the correlation with automotive vehicles, we can indicate engineering and technological solutions which are limiting the emission of non-road mobile machinery, but which are not applied. Due to liberal regulations for this group of machinery, the producers do not apply innovative solutions which can be found in road vehicles. The paper presents the synthetic review of existing EU regulations concerning limits of the emission of harmful exhaust gases which are generated by spark-ignition combustion engines of non-road mobile machinery. The authors show the divergences between the limits of the emission of harmful exhaust gases generated by road vehicles and non-road mobile machinery (boats and railway engines are not taken into account). The authors present the directions of the development of the combustion process control and systems limiting the emission of harmful exhaust gases. High innovative automotive industry was indicated as the direction of the development for limiting the influence of the emission on the environment by non-road mobile machinery.
