Resumo em Inglês:

Abstract In this work, a vibration-based method for damage detection at welded beams and rods is presented. The model of the structural element includes the effect of the added inertia due to the welding process. Two methods of solution, analytically and by means of the Finite Element Method (FEM), are presented. From the results obtained it can be asseverated that the method can be a useful tool to detect degradation of welded structures. In contrast to other existing methods for cracks detection, it is shown that several frequencies have to be taken into consideration to determine the wear characteristics of the welded elements, since depending on the location of welding, some frequencies can be very little sensitive to the reduction of rigidity at the welded section. The results presented show similar tendency to those obtained by other investigations for cracks detection when added inertia was not included.

Resumo em Inglês:

Abstract Surface treatment of the adherends prior to adhesive bonding plays an important role in the enhancing of strength and durability of bonded joints. In this work, an investigation on effect of adherend surface roughness on adhesive bond strength was performed. Single strap joints with different adherends (mild steel and aluminium) bonded with an epoxy resin (Araldite(r) 2015) were tested. The adherend surface was treated by mechanical abrasion process using an emery paper. Contact angle measurement and SEM analysis to understand the wettability and the failure mechanism of the joints were performed. It was found that an optimum surface roughness exists for a maximum bonding strength and the roughness range depends on the adherend material. The joint strength changes are associated not only simply by the increased bonding area, surface texture or mechanical interlocking, but also by the chemical characteristics of the surface and the chemical bond between them.

Resumo em Inglês:

Abstract The estimation of the ship hull girder ultimate strength under vertical bending moments as close to real behavior is vital both for design stage or seagoing life. The maximum load carrying capacity of ship hulls called ultimate strength depends on a number of factors including the strength of the structural material, initial distortions, dimensions and layout of the structural components, the component discretization (idealization) of hull girder section. In this study, the main target is to evaluate the effects of hull girder section component discretization, initial deflection of plates and residual welding stress and 50% corrosion margin for individual structural components on the ultimate hull girder strength. Within this context, hull girder ultimate strength calculations are carried out for ten benchmark ships' cross sections for validation of HULT developed by authors, firstly. Next, to reflect the effect of diverse key factors, selected ships among ten are analysed for different scenarios using progressive collapse analysis based method HULT and with IACS-CSR formulations. Critical collapse moment values of ten mid-ship cross sections are calculated and shown to agree well with the results of previous studies. As a result, both the accuracy of HULT, as well as the effects of diverse key factors on ultimate strength are shown clearly by case studies.

Resumo em Inglês:

Abstract To study the influence of a foundation structure on the ground, the finite layer method of composite ground is derived based on the finite layer method (FLM) theory of the semi-analytic numerical method and the force method principle of elastic material, which is used to analyze a layered ground including multiple internal constraint planes. By simplifying a pile body as a solid constraint composed of four side plane constraints, the composite ground FLM is applied to solve the displacement and stress field of the ground. The change of the ground displacement and stress caused by the addition of a single pile constraint are then discussed, and the influence rules of a pile position on the ground displacement are also determined. Finally, the necessity, rationality and validity of the composite ground FLM are demonstrated by the model test examples of a single pile and pile raft foundation.

Resumo em Inglês:

Abstract The effects of distinctive parameters such as revolute joint angle or spherical joint location of mobile platform in a 6-DOF 6-RUS parallel manipulators on workspace, kinematic, and dynamic indices are investigated in this study to select proper structure commensurate with performance. Intelligent multi-objective optimization method is used to design the manipulator. Considering distinctive parameters, relevant relations for developing inverse kinematic and Jacobin matrix are obtained. In order to study dynamic properties, mass matrix is obtained from calculating the total kinetic energy of the manipulator. After modifying multi-objective Bees algorithm, it used to optimize the manipulator structure considering all geometrical parameters with proper constraints. In addition of comparison of three well known 6-RUS manipulators' types, variation diagram of workspace, local and global dynamics and kinematics performance indices have been drawn with respect to structural parameters variation and limitation of these parameters with proper value are determined. Moreover, considering all dimensional parameters, Pareto front line of multi objective optimization of structure is presented based on dynamic and kinematic performance in pre-determined workspace. Based on the results, a fairly comparison among various types of 6-RUS manipulators can be conducted and the most appropriate set of dimensional parameters are selected based on specific demand.

Resumo em Inglês:

Abstract Residual stresses are present in materials or structural component in the absence of external loads or changes in temperatures. The most common causes of residual stresses being present are the manufacturing or assembling processes. All manufacturing processes, such as casting, welding, machining, moulding, heat treatment, etc, introduces residual stresses into the manufactured object. The residual stresses effects could be beneficial or detrimental, depending on its distribution related to the component or structure, its load service and if they are compressive or tensile. In order to do the studies of residual stresses inside pipes, where the fatigue cracks normally initiate, an equipment that allows applying the Hole-Drilling Method was developed. The equipment efficacy was confirmed in this work by using it to detect residual strains inside a Mock-up that simulates the relief and security nozzle of Angra 1 Nuclear Power Plant (NPP) pressuriser.

Resumo em Inglês:

Abstract Here goes the abstract. For instance, one can write that this work The experimental research of thin circular plate of pseudo-elastic TiNi alloy under fixed supports and transversal impact loading was conducted through using the modified apparatus of Split Hopkinson Pressure Bar. The experiment results of pseudo-elastic TiNi alloy was compared with that of A3 steel. The nature of dynamic mechanical response of the structure in spatio-temporal scale, including the propagation of flexible wave in the plate, evolution of transformation zones and full-field out of plane displacement were derived. The results show that transformation zones and transformation hinge may generate near the center of the plate (about 5mm) because of two-dimensional diffusion effect of the circular plate under impact loading. The transformation hinge disappears after unloading; however, the A3 steel plate has residual deformation obviously. The impact response of TiNi alloy thin circular plate is dominated by the thermo-elastic martensite phase transformation and inverse transformation, which differs from the conventional elastic-plastic transformation mechanism.

Resumo em Inglês:

Abstract The main goal of this article is to study the oscillatory motion of a spherical gas bubble immersed in a Newtonian liquid subjected to a harmonic pressure excitation. We use the classical Rayleigh-Plesset equation to study the radial motion of the bubble undergoing a forcing acoustic pressure field. The second order nonlinear ordinary differential equation that governs the bubble motion is solved through a robust fifth order Runge-Kutta scheme with adaptive time-step. Several interesting patterns are identified. First we develop an asymptotic solution for low amplitudes of excitation pressure to validate our numerical code. Then we develop a bifurcation diagram in order to show how the parameters of the flow modify the vibrational patterns of the bubble. We also train a neural network to identify the vibrational pattern through its FFT data. The combination of neural networks with a bifurcation diagram could be useful for the identification of the flow physical parameters in practical applications. For each pattern we also provide an analysis of the motion of the bubble on the phase-space and interpret physically the system behavior with its FFT. In addition, we analyze nonlinear patterns using standard tools of dynamical systems such as Poincaré sections and calculate the Lyapunov exponents of the system. Based on that, we have identified topological transitions in phase plane using for instance the analysis of Poincaré sections and the solution in the frequency spectrum. We have seen that the mechanisms that dominate the dynamics of the oscillating bubble is the competition of the acoustic field excitation with surface tension forces and momentum diffusion by the action of the surrounding fluid viscosity.

Resumo em Inglês:

Abstract A three-dimensional rail-bridge coupling element of unequal lengths in which the length of the rail element is shorter than that of the bridge element is presented in this paper to investigate the spatial dynamic responses of a train-track-bridge interaction system. Formulation of stiffness and damping matrices for the fastener, ballast, and bearing, as well as the three-dimensional equations of motion in matrix form for a train-track-bridge interaction system using the proposed element are derived in detail using the energy principle. The accuracy of the proposed three-dimensional rail-bridge coupling element is verified using the existing two-dimensional element. Three examples of a seven-span continuous beam bridge are shown: the first investigates the influence of the efficiency and accuracy of the lengths of the rail and bridge elements on the spatial dynamic responses of the train-track-bridge interaction system, and the other two illustrate the influence of two types of track models and two types of wheel-rail interaction models on the dynamic responses of the system. Results show that (1) the proposed rail-bridge coupling element is not only able to help conserve calculation time, but it also gives satisfactory results when investigating the spatial dynamic responses of a train-track-bridge interaction system; (2) the double-layer track model is more accurate in comparison with the single-layer track model, particularly in relation to vibrations of bridge and rail; and (3) the no-jump wheel-rail interaction model is generally reliable and efficient in predicting the dynamic responses of a train-track-bridge interaction system.

Resumo em Inglês:

Abstract This paper shows and discusses a generic implementation of the global-local analysis toward generalized finite element method (GFEMgl). This implementation, performed into an academic computational platform, follows the object-oriented approach presented by the authors in a previous work for the standard version of GFEM in which the shape functions of finite elements are hierarchically enriched by analytical functions, according to the problem behavior. In global-local GFEM, however, the enrichment functions are constructed numerically from the solution of a local problem. This strategy allows the use of a coarse mesh even when the problem produces complex stress distributions. On the other hand, a local problem is defined where the stress field presents high gradients and it is discretized using a large number of elements. The results of the local problem are used to enrich the global problem which improves the approximate solution. The great advantage is allowing a well-refined description of the local problem, when necessary, avoiding an overburden for the computation of the global solution. Details of the implementation are presented and important aspects of using this strategy are highlighted in the numerical examples.