The wind turbine gearbox is a critical equipment transforming the speed of the rotor hub to the generator, the condition of which is the reflection of operational efficiency and reliability of wind turbines. As the initial stage of the wind turbine gearbox, the fault feature extraction of the planetary gear set is challenging since it is prone to be affected by complicated structure, vibration from other high-speed stages and background noise. In this paper, a double Q factor wavelet-based sparse decomposition is applied to the fault feature extraction of the wind turbine planetary gearbox. Considering the sparsest wavelet coefficients, the vibration signal is iteratively decomposed into high Q and low Q components. The fault feature is generally hidden in the low Q component. With further demodulation, the fault information of planetary gears can be easily detected.

The paper presents the simulations of texture evolution of the AZ31B Mg alloy subjected to equal channel angular pressing (ECAP) and rotary swaging (RS) processes. It is shown that using the crystal plasticity (CP) parameters obtained by curve fitting conducted on simple mechanical tests with the aid of the evolutionary algorithm, it is possible to correctly predict the texture evolution in both processes. The influence of the initial texture as well as the CP parameters is discussed.

Structures, constructions and bridges in coastal areas are greatly affected by the corrosive attack of chlorides. This reduces their lifetime and leads to losses due to their maintenance. This study aims to improve the lifetime and corrosion-proof behavior of steel rebars in the saline environment (3.5% NaCl) by applying electroless Ni-Cu-P coatings with high corrosion resistance. Ni-Cu-P coating was deposited on Fe-600 steel rebars. The coating was deposited by varying bath condition parameters, such as concentration of nickel sulphate, sodium hypophosphite and copper sulphate. This led to a variation in Ni, P and Cu content, and finally, the optimal bath combination was obtained using the Taguchi-based grey relational analysis. For concentrations of 25, 10 and 0.3 g/l nickel sulphate, sodium hypophosphite and copper sulphate, enhanced corrosion resistance of the coated rebars could be achieved with 350 mV E corr and 0.4 μA/cm 2 I corr . At the same time, the bare rebars had E corr of -653 mV and I corr of 11.7 μA/cm 2 .

An analytical study of a two-dimensional boundary layer flow of an upper-convected Maxwell fluid is examined. In addition, an aligned magnetic field over the inclined shrinking/stretching stratified sheet in a non-Darcian porous medium is considered. The heat transfer effects are employed through nonlinear convection and variable thermal conductivity. The associated higher-order nonlinear equations are transformed to ordinary first-order differential equations by using similarity transformation. The resulting ordinary first-order differential equations are then solved numerically by the shooting method. This paper aims to investigate the special effects of parameters on velocity and temperature profiles. The results are also discussed, graphically and numerically for the skin friction and Nusselt number.

In this paper, the mathematical analysis of the robot effective mass is presented. The calculation of this effective mass and its ellipsoid are included. The relationship between the robot effective mass and the external force (collision) affecting the robot end-effector is investigated. The effective mass is analyzed using different robot configurations and different end-effector positions. This analysis is conducted using 2-DOF and 3-DOF planar robots and executed using MATLAB. The results from this analysis prove that the robot effective mass depends on the its configurations and end-effector position. Effective mass can thus be considered as one of the criteria in optimizing robot kinematics and configuration.

The large quantity of waste or by-product materials (such as waste glass and steel slag) released to landfills is considered to be a real problem. The use of these materials as cement replacements makes it possible to solve this problem and reduce the quantity of carbon dioxide emitted from the cement manufacturing process. This paper presents the effect of waste glass powder (GP) and steel slag powder (SSP) on the properties of blended cement mortar. The flow, compressive strength, direct tensile strength and dry density of cement mortar containing GP and SSP as cement replacements with and without superplasticizer (SP) are studied and compared with the control mix. The results show that the glass and steel slag powders, once they are simultaneously added as a ternary blended cement mortar, reduce the water binder ratio required to achieve flowability. Additionally, the compressive strength results of such blended mortar showed that the increased GP content exhibits better performance than that of slag powder for the same level of waste materials replacements.

The present paper concerns the study of geometrically non-linear forced vibrations of beams resting on two different types of springs: rotational and translational. Assuming that the motion is harmonic, the displacement is extended as a series of spatial functions determined by solving the linear problem. Hamilton’s principle and spectral analysis are used to reduce the problem to a non-linear algebraic system solved using a previously developed approximate method. The effects of the nature of the added springs and their location on the non-linear behaviour of the beam are examined. A multimode approach is used in the forced case to obtain results over a wide range of vibration amplitudes. This leads to examining the non-linear forced dynamic response for different positions of each spring and different levels of excitations. Following a parametric study, the non-linear forced mode shapes and their associated bending moments are presented for different levels of excitations and for different vibration amplitudes to give an estimation of the stress distribution over the beam length.

In this paper, two inequality relations are proven for the torsional rigidity of orthotropic elastic solid cross sections. By using the derived inequality relations, lower and upper bounds can be obtained for the torsional rigidity. All results of the paper follow from the Saint-Venant theory of uniform torsion. The presented bounding formulae are based on the mean value theorem of integral calculus.

The minimum sample size for a good estimation of the parameters in both three-parameter Weibull KJc distribution (3P-W) and ASTM E1921 methods was analyzed. Additionally, the estimations provided by maximum likelihood (ML) and linear regression (LR) were compared. Fracture toughness sets with different sample sizes were randomly generated following a 3P-W with parameters corresponding to experimental datasets from the Euro round robin fracture toughness test. Then, LR and ML were applied to the sets and the parameters were estimated. Standard deviation (SD) and interquartile range (IQR) were employed to analyze the goodness of fit. The results of this paper were consistent with the necessity of large sample sizes (over 30) to find a representative value of the threshold and shape parameters. However, the scale parameter showed a lower scatter and can be estimated with a smaller sample size (around six samples), as used in the standard ASTM E1921-19b.

The present work focuses on nonlinear dynamics models of multi-walled carbon nanotubes with initial curvature resting on Winkler-Pasternak elastic foundations in a nonlinear thermomagnetic environment using nonlocal elasticity theory. The derived systems of nonlinear vibration models are solved with the aid of the Galerkin decomposition and the homotopy perturbation method. Effects of temperature, magnetic field, multi-layer, and other thermomechanical parameters on the dynamic responses of the slightly curved multi-walled carbon nanotubes are investigated and discussed. As the temperature increases, the frequency ratio decreases as the linear natural frequency of the system increases. The results reveal that the frequency ratios decrease as the number of nanotube walls, temperature, spring constants, magnetic field strength, and the ratio of the radius of curvature to the length of the slightly curved nanotubes increase. These trends are the same for all the boundary conditions considered. However, clamped-simple and clamped-clamped supported multi-walled nanotube have the highest and lowest frequency ratio, respectively. Also, from the parametric studies to control nonlinear vibration of the carbon nanotubes, it is shown that quadruple-walled carbon nanotubes can be taken as pure linear vibration even at any value of linear Winkler and Pasternak constants. Therefore, this can be used for the restraining of the chaos vibration in the objective structure. These research findings will assist the designers and manufacturers in developing multi-walled carbon nanotubes for various structural, electrical, mechanical, and biological applications, especially in the areas of designing nanoelectronics, nanodevices, nanomechanical systems, nanobiological devices, and nanocomposites, and particularly when they are subjected to thermal loads, magnetic fields and elastic foundations.