Resumo em Inglês:

Abstract This research paper is concerned with the disc brake squeal problem for passenger cars. The aim of the present research is developing a finite element model of the disc brake assembly in order to improve understanding of the influence of Young's modulus on squeal generation. A detailed finite element model of the whole disc brake assembly that integrates the wheel hub and steering knuckle is eveloped and validated using experimental modal analysis. Stability analysis of the disc brake assembly is accomplished to find unstable frequencies. A parametric study is carried to look into the effect of changing Young's modulus of each brake components on squeal generation. The results of simulation indicated that Young's modulus of disc brake components play a substantial role in generating the squeal noise.

Resumo em Inglês:

Abstract Wheel force transducer (WFT) is a tool which can measure the three-axis forces and three-axis torques applied to the wheel in vehicle testing applications. However, the transducer is generally mounted on the wheel of a moving vehicle, when abruptly accelerating or braking, the mass/inertia of the transducer itself has extra effects on the sensor response so that inertia/mass loads will be detected and coupled into the signal outputs. This is the inertia coupling effect that decreases the sensor accuracy and should be avoided. In this paper, the inertia coupling problem induced by six dimensional accelerations is investigated for a universal WFT. Inertia load distribution of the WFT is solved based on the principle of equivalent mass and rotary inertia firstly, thus then its impact can be identified with the theoretical derivation. FEM simulation and experimental verification are performed as well. Results show that strains in simulation agree well with the theoretical derivation. The relationship between the applied acceleration and inertia load for both wheel force and moment is the approximate linear respectively. The relative errors are acceptable within less than 5% and the maximum impact of inertia loads on the signal output is about 1.5% in the measuring range.

Resumo em Inglês:

Abstract In this study, the dynamic interaction between a 120 mm smoothbore tank barrel modeled as an Euler-Bernoulli cantilever beam and an accelerating projectile during firing is presented. The interaction was modelled using a new FEM approach that took into account the projectile's inertia, Coriolis, and centripetal forces and the horizontal and inclined positions of the barrel. The mass, exit velocity and acceleration effects of the projectile on the dynamics of the barrel were investigated. The effects of the projectile's inertia, and Coriolis and centripetal forces were evaluated as well. Furthermore, the tip displacements at different firing angles were determined by transferring the mass, stiffness and damping matrices of the barrel with the addition of the instantaneous property matrices of the projectile from a local coordinate to the global Cartesian coordinate with the aid of transformation matrices. Finally, the barrel vibrations caused by the successive firings were evaluated under different firing scenarios. To demonstrate the validity of the current study, comparisons were made with the results of previous studies and a good agreement was achieved. By using the method recommended in this study, it is possible to determine the accurate dynamic behavior of any barrel with sufficient sensitivity, without any costly or time-consuming tests being necessary.

Resumo em Inglês:

Abstract This paper is dedicated to the analyses of the effect of uncertain parameters on the dynamic behavior of a flexible rotor containing two rigid discs and supported by two fluid film bearings. A stochastic method has been extensively used to model uncertain parameters, i.e., the so-called Monte Carlo simulation. However, in the present contribution, the inherent uncertainties of the bearings' parameters (i.e. the oil viscosity as a function of the oil temperature, and the radial clearance) are modeled by using a fuzzy dynamic analysis. This alternative methodology seems to be more appropriated when the stochastic process that models the uncertainties is unknown. The analysis procedure is confined to the time domain, being generated by the envelopes of the rotor orbits and the unbalance responses obtained from a run-down operating condition. The hydrodynamic supporting forces are determined by considering a nonlinear model, which is based on the solution of the dimensionless Reynolds' equation for cylindrical and short journal bearings. This numerical study illustrates the versatility and convenience of the mentioned fuzzy approach for uncertainty analysis. The results from the stochastic analysis are also presented for comparison purposes.

Resumo em Inglês:

Abstract In this paper, modelling and simulation of a multi-body system for its vibration control using sensors and actuators is presented. The model developed on MSC ADAMS consists of six legs connecting moving and base plates using spherical joints with axial rotation of legs constrained. It contains linear actuator collocated with force sensor. Mathematical model of the mechanism representing the Kinematic and Dynamic analysis of model is presented. The Leg Length variation obtained using MATLAB is obtained in order to validate the model developed in MSC ADAMS. Natural frequencies for six different mode shapes are obtained from vibration excitation analysis. A decentralized force feedback controller which uses PID control law with single gain is used for actively attenuating the vibration, which is coming from base platform. The transfer function, defined as the ratio of Laplace transformation of the acceleration of moving plate and base plate, is considered as a measure of isolation. Effect of proportional, derivative and integral feedback is studied separately and together as well. A significant isolation in the resonance transmissibility and natural frequency of the mechanism is demonstrated.

Resumo em Inglês:

Abstract Pneumatic isolators are promising candidates for increasing the quality of accurate instruments. For this purpose, higher performance of such isolators is a prerequisite. In particular, the time-delay due to the air transmission is an inherent issue with pneumatic systems, which needs to be overcome using modern control methods. In this paper an adaptive fuzzy sliding mode controller is proposed to improve the performance of a pneumatic isolator in the low frequency range, i.e., where the passive techniques have obvious shortcomings. The main idea is to combine the adaptive fuzzy controller with adaptive predictor as a new time delay control technique. The adaptive fuzzy sliding mode control and the adaptive fuzzy predictor help to circumvent the input delay and nonlinearities in such isolators. The main advantage of the proposed method is that the closed-loop system stability is guaranteed under certain conditions. Simulation results reveal the effectiveness of the proposed method, compared with other existing time -delay control methods.

Resumo em Inglês:

Abstract This paper addresses the Caughey Absorbing Layer Method (CALM) performance in the one-dimensional problem and its implementation in commercial software, with possibility of direct extension to two-dimensions. The adequacy and numerical efficiency is evaluated using three different error measures and five different variations of the damping profile. Other parameters that are subjected to evaluation are the length of the absorbing layer in relation to the wavelength to absorb, the value of the loss factor at the end of the absorbing layer, and the ratio of the load to layer frequency. The problem is firstly analysed theoretically, resulting in estimates for the wave reflection due to transition and truncation of the model. In order to confirm that no spurious waves will be present in the finite element solution, the numerical implementation is validated by comparison with the analytical solution. The analysis of the error measures on the numerical results obtained for various combinations of the model's parameters lead to the conclusion that CALM is effective at mitigating waves reflected from the boundaries. The optimum loss factor as a function of the ratio of the length of the absorbing layer to the wavelength to absorb is determined through parametric analyses. Although the optimal damping is frequency dependent, it was shown that the CALM's effectiveness can be extended to a wider range of frequencies by increasing the smoothness of the damping profile.

Resumo em Inglês:

Abstract Structural damages are often associated with under- performance of an engineering system. Hence localisation of such damages, followed by remedial measures, is the key to ensure proper functioning of the structures during their design lives. Acoustic emission (AE) technique is one of the effective non destructive evaluation (NDE) techniques for damage localisation. The present study makes an effort to review the existing literature on this technique under a few broad categories and discuss chronological advancements in each such category. The advantages and drawbacks of each method are deliberated and further scopes of research are pointed out.

Resumo em Inglês:

Abstract This paper is focused on experimental evaluation and comparison of progressive damage behaviors in adhesively bonded single lap and double butt lap joints between aluminum and glass fiber reinforced plastic (GFRP). The effect of joint design and dissimilarity of adherents on damage evolution of adhesive bonding under tensile quasi static loading is analyzed. Bonding was created by toughened epoxy adhesive as one of the most important and widely used structural adhesives in aerospace, automobile and marine industries. Due to structural behaviour complexity of adherents and adhesive, the fracture takes place under mixed mode and the failure mechanism is characterized by the de-bonding area for the proposed joints. The results show that single lap joint could carry up to 30% more tensile load than the double butt lap joint with the same material properties while a combined failure mechanism could be observed and the most dominant ones were yielding of aluminum substrates, adhesive failure at bond-line on aluminum surface and cohesive failure of upper mat layers of composite material.

Resumo em Inglês:

Abstract The objective of the present study is to develop a numerical formulation to predict the behavior of highly deformable elastoplastic thin beams. Following the Euler-Bernoulli bending, the axial and shear effects are neglected, and the nonlinear second-order differential equation regarding the angle of rotation is defined based on the specific moment-curvature relationship. Although the formulation can be used for general materials, three constitutive models are employed: linear-elastic, bilinear elastoplastic, and linear-elastic with Swift isotropic hardening. The resultant boundary value problem is solved by means of the fourth-order Runge-Kutta integration procedure and the one-parameter nonlinear shooting method. The performance of the present formulation is investigated via three numerical problems involving finite bending of slender beams composed of elastoplastic materials. For these problems, numerical solutions regarding rotations, displacements and strains for the loading, unloading and reloading phases are provided. Finally, it is shown that the present methodology can also be used to determine the post-buckling behavior of elastoplastic thin beams.