Journal of the Brazilian Society of Mechanical Sciences and Engineering

Fiber-reinforced polymers (FRPs) are sensitive to moisture diffusion. Deterioration caused by moisture can limit their service lives considerably. In this work, a three-dimensional finite element modeling and analysis framework is presented to investigate the moisture diffusion kinetics inside fiber-reinforced inside polymer matrix composites by considering different angle and cross-ply orientations. A small localized representative volume element considering a few fibers in the neighborhood of three-layer stacks has been analyzed. The emphasis is on the effect of different fiber orientations over moisture saturation time and diffusion-induced stresses. Stresses induced due to moisture diffusion in FRPs are evaluated on the free fiber ends. The numerical results from finite element approximations are compared with theories of composite micromechanics such as rule of mixtures, Halpin–Tsai model and concentric cylinder assemblage framework. It is observed that the orientation of fiber layers can greatly influence the moisture ingress inside the matrix and resulting stresses. At intermediate time durations of moisture progression, the cross-ply orientation had ~ 25% lower weight gain in comparison with the unidirectional ply orientations. The overall von Mises stresses at the fiber matrix interface were also lower in cross-ply orientations by ~ 40% in comparison with the other orientations with similar fiber volume fraction. The three-layered cross-ply, 90/90/90 orientation took almost 50% more time to fully saturate with moisture in comparison with the unidirectional, 0/0/0 orientation. The interpretations from the smaller local microstructural models presented in this work can be extended to study and design the structure scale composite layups for the improved moisture durability.

Wheel polygonalization is one of the most common failures of the wheelset, which can directly affect the safety and comfort of railway vehicle operation. In the actual condition, traction/braking torque continuously acts on the polygonal wheel fault can result in the modulation of its vibration representation and then influence the effect of the feature exaction of the polygonal wheel faults. Considering this phenomenon, this study aims to clarify the forming mechanism of fault signals under variable speed conditions to improve the accuracy of feature extraction and ensure the safe operation of vehicles. This paper derived the Lagrangian equations with the dissipation function of a railway vehicle model with polygonal wheel fault under traction/braking conditions. After that, the modulation representation under constant speed, linear variable speeds, and nonlinear variable speeds is investigated, respectively. Finally, the vibration evolution of polygonal faults under different working conditions is visualized using statistical features. Compared with the constant speed, the curve in the time domain has more high-frequency fluctuations under variable conditions, and the phase modulation causes the half-wave asymmetry of the waveform. In the time–frequency domain, the continuous input of torque increases the harmonics frequency and side frequency response of fault response and excites the resonance frequency of the vehicle system. The dynamic evolution of fault statistical characteristics is positively correlated with speed and fault severity, and the fluctuation is sharper under braking conditions. The results can provide the theoretical support for feature extraction, interpretable features, and intelligent diagnosis of polygon faults.

The journal bearings are one of the main components of the rotating machines and always bear considerable weight and dynamic stresses. Bearing defect may cause bending and eventually axis fracture and, in some cases, lead to an increase in the temperature of other components. One of the most important challenges of this type of bearings is the instability of the oil film layer, which appears as oil whirl and oil whip. The main objective of this research is the numerical analysis of the journal bearing of a centrifugal pump and the investigation of variations in the eccentricity and the rotation of the bearing to detect the instability resulting from the oil whirl and whip. For this purpose, assuming the steady and laminar flow, the Reynolds theory modified by the Elrod–Adams cavitation model is utilized. In addition, the finite element method is used for the numerical solution. The results indicate that the pressure on the bearing shell increases considering the effect of the oil whip phenomenon. Moreover, by increasing the eccentricity ratio, the pressure applied to the bearing increases and the mass fraction of the oil film decreases. After that, in order to improve the performance, by creating a horizontal groove in a simple bearing (without groove), the oil whirl and whip are numerically analyzed and the effect of the eccentricity as well as the rotational speed of the modified bearing is investigated. Numerical results indicate that the presence of the groove in the bearings causes the pressure on the grooved bearings to decrease dramatically. As a result, the probability of occurrence of the oil instability phenomenon in this case will be less than simple state (no groove). In addition, in this case, it could be observed that as the rotational speed of the grooved bearing increased, the pressure applied around the groove bearing from the oil film increases. However, the pressure applied to the grooved bearings is much less than the pressure applied to the simple bearings.

As the main anti-stability factor, pull-in type of instability has always been a decisive concern in design and usage of micro-electro-mechanical systems. Curved microbeams have been devised to extend the range of stability in these systems. Snap-through is another type of instability which appears as a sudden jump in beam curvature from one configuration to another counterpart state. In order to make optimal use of curvature in the structure, in this study, the performance of a more complex system consisting of a curved-microbeam and curved-electrode combination is investigated. In this regard, assuming Euler–Bernoulli beam model and using Hamilton's principle, the governing differential equation of the system is obtained. Using the Galerkin method, the governing equation is converted into a reduced-form nonlinear differential equation and its numerical solution is obtained by MATLAB software. Considering a typical system and using its characteristic amplitude–potential curve, the conditions which trigger the instabilities are uncovered. The results show that, unlike the use of a single curved member, the use of two curved members would increase both the position and the voltage of snap-through and pull-in instabilities. Also, it is shown that, in some amounts of initial gaps in which a system might be destabilized, its counterpart curved-beam/curved-electrode combination with the same dimensions could be secure from the risk of pull-in incidence. Accordingly, this curved-beam/curved-electrode system can help to benefit higher percentage of initial gaps.

The development of strategies to evaluate health of mechanical structures has been studied by the international community due to their potential application in the prevention of failures and optimization of maintenance procedures. These systems requires digital signal processing algorithms and interpretation methods, which aim to extract parameters sensitive to the rise of discontinuities in the material from measurements, to classify signal events to detect the damage onset. This paper proposes a simple and effective methodology for monitoring the integrity of mechanical structures, based on Lamb wave and pitch–catch approach, through analysis of signals generated by multisensor arrangements. These signals are processed by discrete wavelet and Hilbert transform, intended to improve peak amplitude estimation, through noise and dispersion reduction. Assessment of structure’s integrity proceeds through the joint analysis of damage indices calculated from the discrepancy of the maximum amplitude of the signal measured by each sensor of the arrangement. Experimental application of the method to an aluminum plate showed its effectiveness to detect, localize and evaluate damage severity in established regions of the monitored area, including the case of two simultaneous damages.

Side beams are among various types of structures used for reinforcing the safety of automobiles against lateral collisions which have been widely explored. In this study, it was attempted to increment the energy absorption capacity of the beam by creating a non-uniform cross-section with a cosine function at the upper part of the beam. This study was conducted both experimentally and numerically. The numerical investigations were achieved by finite element software of LS-DYNA and the simulation results were validated by experimental three-point flexural tests. By creating a non-uniform cross-section, it was tried to augment the energy absorption capacity as much as possible. NSGA-III and MOEAD algorithms were also used for optimization purposes to select the best beam with superior efficiency. Obtained results showed that non-uniform thin-walled beams can increase specific energy absorption (SEA) of a simple beam up to 71%.

This paper presents an integrated control of longitudinal, yaw and lateral vehicle dynamics using active front steering (AFS) and active braking systems. The designed active braking system based on sliding mode controller includes two kinds of working modes. It is activated as an anti-locked brake system (ABS) and an electronic stability control (ESC) with active differential braking strategy (DBS) for hard braking in straight line and unstable situation in cornering, respectively. The AFS is proposed based on fuzzy controller. In addition, a nonlinear estimator utilizing unscented Kalman filter (UKF) is applied to estimate the vehicle dynamics variables that cannot be measured in a cost-efficient way such as wheel slip, yaw rate, longitudinal and lateral velocities. According to the estimated values and Dugoff tire model, the tire-road friction coefficients are calculated. As the ABS performance for shortening the stopping distance depends on the optimal tire slip ratios, an adaptive neuro-fuzzy inference system (ANFIS) is proposed to obtain their optimum values. The tire-road friction coefficients, longitudinal velocity, and the vertical wheel load are considered as the ANFIS inputs. In the simulation part, the hard-braking action in straight line on the roads with various friction coefficients and split-μ roads is investigated. The results demonstrate high precision of the estimation of road friction coefficient and optimum wheel slip ratio, greatly reduction of the distance and stopping time, as well as improvement of the lateral and yaw stability in comparison with the vehicle without estimator.