A study of biomechanical model of seated human body exposed to vertical vibrations

Abstract This paper presents a human biomechanical model with 4 degrees of freedom of a human body in a car seat with backrest exposed to vertical vibrations. The proposed model has been analysed for five various values of radian frequency as numerical input data, and the results were compared with the results obtained for similar models in the published literature. In the biodynamic analyses the model was simplified to linear system to reduce the complexity of analytical and numerical simulations.</jats:p

Researches regarding the static and dynamic behaviour of composites with natural reinforcements

Abstract In this paper, some composite materials were built in this way: the reinforcement is made with natural fibers (there were used two types of natural fibers in this way: hemp and cotton) and the matrix is made from epoxy resin. The Resoltech 1050 epoxy resin is used, with its Resoltech 1050 hardener. The casting was made at room temperature and the matrix was applied using the brush. The static experimental conditions are characterized by tensile loading of the build specimens and the determination of statically Young modulus. There was used an Instron Universal testing machine and the force-extension curves were obtained. The dynamic parameters were determined from the bars free vibrations. The next experimental montage was used: the bars were clamped at one end and were left free at the other end. At the free end, a Bruel&amp;Kjaer accelerometer with 0.04 pC/ms−2 sensitivity was placed in order to record the beams dynamic response. A force was applied at the free end to bend the beams and after bending, the force was cancelled and the beams were left to freely vibrate. The accelerometer was connected to a signal conditioner Nexus and the signal conditioner was connected to a data acquisition system SPIDER 8 made by Hottinger Baldwin Messtec. The acquisition system was connected to a notebook and the experimental parameters were obtained through CATMAN EASY software. From the free vibrations recording, the next mechanical parameters were determined: the eigenfrequency of the first eigenmode, the damping factors per unit mass and per unit length, the loss factor and the dynamic Young modulus.</jats:p

Experimental research regarding some dynamic parameters determination for sandwich bars reinforced with carbon fiber

Abstract For this study, we have built some composite sandwich bars with polypropylene honeycomb core reinforced with carbon fiber. We have clamped the bars at one end and we left them to vibrate freely. From the free vibrations we have determined the damping factors per unit mass and length, loss factor, dynamic Young modulus, dynamic stiffness and the frequency of the first eigenmode. The general conclusions obtained from the vibrations results show tat the sample width can influence the damping coefficient, by the fact that it determines the surface in which the air friction acts on the sample. The sample mass or specific linear mass influence the damping factor by the fact that the samples with higher mass and width, the deformation energy which is stored in the sample through the initial deformation, is dissipated in a larger quantity of material. An influence may occur due to the sample rigidity, explained by the fact that a force initially applied to the sample produces a smaller deformation if the stiffness is higher.</jats:p