Resumo em Inglês:

Abstract The studies on vibration frequency as well as loading capacity of slender systems are very important issues in the design process. Integration of smart materials with the host structures allows one to create constructions which are able to adjust to the different conditions. The piezo material belongs to the smart materials group. Application of voltage to the piezoparts leads to induction of forces which can cause prestressing of the host structure. The prestressing with the use of piezoceramic elements is a main subject of this paper. The investigated system constitutes a column which is loaded with the specific load. The specific load is realized by means of specially designed heads what results in divergence or divergence-pseudoflutter type of characteristic curves. The results presented in this paper are concern on comparison of the loading capacity magnitude and vibration frequency of a slender system with and without prestressing. Finally, it will be stated when to use complex system with piezopart or the simplified one without it.

Resumo em Inglês:

ABSTRACT A closed-form analytical solution to rheological phenomena is obtained based on Hoek-Brown (HB) yield criterion and the generalized Bingham model. Once the circular tunnel is excavated, an initial plastic region is formed. When the total stresses fulfil the yield condition, the initial plastic region steps into the viscoplastic region, in which the displacement develops with time. The one-dimensional constitutive equation of the generalized Bingham model is transformed into a three-dimensional expression in polar coordinates by combining the plane strain condition. With the help of equilibrium differential equation, geometric equation and boundary condition, the stress and displacement in the initial plastic region can be expressed. At the moment of t, the stresses and displacements are described similar to the solutions of the elasto-plastic state. The stresses, strains and displacements after transformation can be expressed in the viscoplastic region. The proposed solution was verified by the closed-form solution of circular tunnels in elastic-brittle-plastic rock mass.

Resumo em Inglês:

ABSTRACT This study aimed to use a simulated vehicle to asses quantitatively the head and neck injuries of the occupants, in a frontal car crash, when the driver has only one hand on the steering wheel, such as while using a cell phone when driving. First, we conducted a survey of NHTSA reports on real laboratory tests of frontal collisions involving sedans. The effects of these collisions on the neck of a Hybrid III 50th percentile male crash test dummy were measured in terms of average head acceleration and force along the X, Z, and Y-axes. These acceleration, force and torque values obtained from the NHTSA database were used to validate the simulated model. The results obtained were compared with case E, the standard dummy position used in frontal collision tests. The results obtained in the simulation of the four cases of driving with only one hand demonstrate a probability of more than 67% that the driver will sustain AIS+2 injuries during a frontal crash. In all the cases, the skull fracture percentage was the most representative, occurring between 89 and 94% of cases where the driver had only one hand on the steering wheel.

Resumo em Inglês:

Abstract One of the most important aspects in the operation of rail vehicles is the implementation of transport while ensuring safety and comfort of passengers. Technical condition of the wheel rolling surfaces has a direct impact on these factors. These elements are subject to wear and tear in a continuous and discrete form. One of the discrete wear forms is the wheel-flat on wheel rolling surfaces that generate impulse noise. This translates into a significant deterioration of vibroacoustic comfort, and in extreme cases also to a greater risk associated with e.g. derailment of the vehicle. Therefore, it is desirable in particular by the rolling stock operator to carry out cyclic diagnostics and monitoring of the condition of wheel rolling surfaces. This paper is a continuation in a series of research articles carried out by the authors related to vibroacoustic diagnostics of wheel rolling surfaces in light rail vehicles. As part of this article, acoustic measurements were carried out at a dedicated track-side system during so-called pass-by tests. Acoustic signals were analyzed in accordance with the Fourier and Hilbert transforms. Additionally, the main assumptions of vibroacoustic diagnostics and analyses of point measures were used. This allowed for the development of yet another way of monitoring the occurrence of the problem of wheel flats in rail vehicles.

Resumo em Inglês:

Abstract Logistic train is one of the recent solutions applied in the intralogistics. It bases on the concept of the “milk-run” delivery method. The main problem in the implementation of intralogistics trains is the possibility to determine whether the train is able to pass the given path without a colliding with surrounding objects. Dynamic model presented in this paper was performed for the three most common steering systems for the trolleys: double Ackermann steering system and two drawbar systems: conventional and virtual clutch. The dynamic model was developed following Lagrange’s theorem including the possibility of lateral slip. The system of differential equations was numerically solved. In order to calculate the lateral friction forces we used three different tire models: simplified, sigmoidal and Pacejka Magic formula. The results obtained for different tire models and steering systems are presented in the form of animations presenting train run in various conditions. The analyses have shown that the use of simplified tire models is justified under certain conditions.

Resumo em Inglês:

Abstract In this study, the dynamic behavior of the 3D train-bridge system subjected to different hydrodynamic loads (TBW model) is established. By taking a continuous bridge with box girders as a case study, the dynamic responses of the bridge which is under train passing and subjected to several sea hydrodynamic loads are analyzed. Hydrodynamic forces are applied on piers according to Morison’s theory and car body is modeled by a 27-DoFs dynamic system. Model validation has been performed with other research by considering vessel collision load. In continuation, the dynamic responses of the bridge and the running safety indices of the train on the bridge under several conditions are analyzed. Consequently an assessment procedure is proposed for the running safety of high-speed trains on bridges subjected to wave loads. Results of TBW’s sensitive analyzes have shown the importance of sea-states conditions for train safe and comfortable running. These outputs indicates that in stormy conditions, the speed of the train crossing the bridges should be reduced and it is possible for the train to pass at low speeds in stormy conditions.

Resumo em Inglês:

ABSTRACT The constant strain rate loading and dynamic stress equilibrium are prerequisites for ensuring the experimental data of the Split Hopkinson Pressure Bar (SHPB). In order to achieve this requirement, a proper pulse shaper dimensions were used in the experiment. For this purpose, the pulse shaper diameter, thickness and strength and the strike bar length and its velocity on the incident pulse are studied by ∅80mm SHPB apparatus. Then, the parameters affecting the two key inflection points and three loading areas of the incident pulse are discussed. In addition, the improved methods for two typical non-constant strain rate waveforms for the concrete experiments are obtained based on the regular pulse shaping. Moreover, SHPB experiments are conducted for concrete by employing different pulse shaper dimensions. The results show that more valid data can be obtained by employing the pulse shaper with large thickness when the strain rate is non-constant during the experiment. The conclusions and method provide guidance for selecting pulse shaper for concrete SHPB experiments.

Resumo em Inglês:

Abstract In this paper, we introduce a finite element mesoscale modeling of damaged concrete structures, based on nodal positions. The mesoscale modeling consists of particle and fiber finite elements embedded in matrix finite elements. While the matrix elements represent the cement matrix, particle elements are used to simulate the coarse aggregates and fiber elements are used for reinforcement rebars. The embedded theory is used to immerse the reinforcement (both particle and fiber elements) without increasing the total number of degrees of freedom. This strategy does not require nodal coincidence, allowing randomly distribute the coarse aggregates. The materials nonlinear behavior is considered by a scalar damage model for the cement matrix and coarse aggregates, and one-dimensional elastoplastic model is used for the steel rebars. Four examples are presented, with good correlation between numerical and experimental results. It is shown that structures simulated with particulate elements could endure higher loads for the same displacement, although the maximum force is obtained in models without inclusion of particle elements.

Resumo em Inglês:

Abstract Optimum safe design through numerically investigation and simulation of FSI due to seismic loading on acid tank with piping attachment is presented. A nonlinear FSI based on the FEM is performed on a full-scale 3D model. Investigations are supplemented by a CFD to simulate the fluid motion inside the tank using acceleration time history of Kocaeli earthquake, the response of the maximum stress, deformation, and displacement of rigidly restrained fixed and flexible tanks at different fill levels and thickness are evaluated. The results are compared and analyzed with design codes and the difference observed in hydrostatic pressure is less than 0.08%, and in maximum values of hydrodynamic pressure are less than 4.3%, 0.8%, and 1.5% at three fill level while the average difference in transient time history total pressure is less than 0.4%. Finally, the provision given in the design codes and response of parameters is computed and polynomial correlation is proposed with an accuracy of above 0.99 and average difference less than 5% in fixed tank and less than 2% in the flexible tank for designing a safe tank by analysis.

Resumo em Inglês:

Abstract In the present work, a thermodynamically consistent damage phase field formulation is adapted to include the effect of preferential directions in the damage evolution. A scalar damage variable is associated with each predefined preferential direction of crack propagation. Any other direction is penalized by a parameter (β≫1) that represents the degree of anisotropy of the fracture. When β=0, the isotropic case is recovered. When there is more than one preferential direction, the material is considered totally fractured when any of the damage variables reaches value one. Simulations using the developed model show that it can reproduce the expected crack propagation pattern for materials with one and two preferential directions. In particular, the model was successful in simulating a zigzag crack pattern commonly obtained in double cantilever beam of spinel MgAl2O4 crystals. The model is fully dynamic in the sense that describes the actual time evolution of the unknown variables, in particular of damage growth. Moreover, anisotropic mechanical response can be easily included in the model by modifying the elasticity tensor.