Thermomechanical Buckling Analysis of the E&P-FGM Beams Integrated by Nanocomposite Supports Immersed in a Hygrothermal Environment

Due to the widespread use of sandwich structures in many industries and the importance of understanding their mechanical behavior, this paper studies the thermomechanical buckling behavior of sandwich beams with a functionally graded material (FGM) middle layer and two composite external layers. Both composite skins are made of Poly(methyl methacrylate) (PMMA) reinforced by carbon-nano-tubes (CNTs). The properties of the FGM core are predicted through an exponential-law and power-law theory (E&P), whereas an Eshelby–Mori–Tanaka (EMT) formulation is applied to capture the mechanical properties of the external layers. Moreover, different high-order displacement fields are combined with a virtual displacement approach to derive the governing equations of the problem, here solved analytically based on a Navier-type approximation. A parametric study is performed to check for the impact of different core materials and CNT concentrations inside the PMMA on the overall response of beams resting on a Pasternak substrate and subjected to a hygrothermal loading. This means that the sensitivity analysis accounts for different displacement fields, hygrothermal environments, and FGM theories, as a novel aspect of the present work. Our results could be replicated in a computational sense, and could be useful for design purposes in aerospace industries to increase the tolerance of target productions, such as aircraft bodies.

A New Method to Verify the Measurement Speed and Accuracy of Frequency Modulated Interferometers

The measurement speed and measurement accuracy of a displacement measuring interferometer are key parameters. To verify these parameters, a fast and high-accuracy motion is required. However, the displacement induced by a mechanical actuator generates disadvantageous features, such as slow motion, hysteresis, distortion, and vibration. This paper proposes a new method for a nonmechanical high-speed motion using an electro-optic modulator (EOM). The method is based on the principle that all displacement measuring interferometers measure the phase change to calculate the displacement. This means that the EOM can be used to accurately generate phase change rather than a mechanical actuator. The proposed method is then validated by placing the EOM into an arm of a frequency modulation interferometer. By using two lock-in amplifiers, the phase change in an EOM and, hence, the corresponding virtual displacement could be measured by the interferometer. The measurement showed that the system could achieve a displacement at 20 kHz, a speed of 6.08 mm/s, and a displacement noise level < 100 pm//√Hz above 2 kHz. The proposed virtual displacement can be applied to determine both the measurement speed and accuracy of displacement measuring interferometers, such as homodyne interferometers, heterodyne interferometers, and frequency modulated interferometers.

On the Stability of the Plane Movement of Mobile Robots with Walking Propulsion Devices Working in "Pulling" Mode

Mobile robots with walking propulsion devices operating in a "pulling" mode, which, as a rule, are unstable, are considered. It is explained to the jamming of propulsion device due to the orthogonality of the acting force to the virtual displacement of the point of application. The task is to develop such an algorithm for controlling the robot, which consists in purposefully changing the geometric orientation of the propulsion devices controlled by the swing drive, which will ensure stable motion. A method for controlling the orientation of the walking plane with its initial deviation from the programmed position is proposed, based on the implementation of a discrete control algorithm, which provides for the introduction of such a piecewise constant function at each step of the mover, which has received an initial perturbation, which will provide a stable motion mode in a finite number of steps. The change in the orientation of the walking planes of the propellers connected with the steering is controlled, and thereby the direction of movement of the robot body changes in the first step, as in the subsequent ones. The described algorithm assumes the fulfillment of two necessary conditions: the presence of an information-measuring system that controls the orientation of the walking planes and ensuring that the interaction forces of the feet controlled by the steering of the propulsion devices with the supporting surface are sufficient for the absence of slippage. An algorithm for controlling "dependent" propulsion devices (working out the programmed translational motion of the body) is presented, taking into account the fact that their orientation depends on the orientation of the controlled ones, which consists in changing the step length, which should also be determined to ensure movement stability. The main task of controlling "dependent" propulsion devices, which do not change the orientation of their walking plane at the initial moment of time, is to determine the points for setting the feet by changing the step length, in accordance with the established criteria and design constraints, in particular, energy efficiency, maximum efforts in drives, maximum and minimum stride length. The propulsion device will start to work in a stable "pushing" mode at the final stage of motion correction, by performing a sequence of actions. It has been established that the "pulling" mode of the walking propulsion device can be stable, with appropriate control.

Hygrothermal environment effect on the critical buckling load of FGP microbeams with initial curvature integrated by CNT-reinforced skins considering the influence of thickness stretching

Due to the need for structures with refined properties to bear against different loading conditions, recently, carbon nanotubes (CNTs) have been used widely to reinforce them. The extremely high stiffness of CNTs makes them significant as one of the best reinforcements to improve the mechanical behaviors of structures. This work focuses on microbeam buckling response with an initial curvature that includes three layers. The mid-layer that is known as the core is constituted of functionally graded porous (FGP) materials and two CNT-reinforced composite skins are bonded to the core to integrate it. The whole structure is affected by the hygrothermal environment and springs and shear layers are put below it. For the first time, for such a structure, a refined shear deformation theory (RSDT) as a higher-order theory that considers thickness stretching effect in polar coordinates is used that presents more accurate results, especially for deeply curved beams. Modified couple stress theory (MCST) in combination with the virtual displacement principle is utilized to establish the governing equations. The obtained results demonstrate the significance of porosity percentage and CNTs’ addition to the skins on the critical nanotubes buckling load. Also, the different behaviors of the microstructure at various temperatures are analyzed and discussed in detail.

A Thermodynamics-Based Nonlocal Bar-Elastic Substrate Model with Inclusion of Surface-Energy Effect

This paper presents a bar-elastic substrate model to investigate the axial responses of nanowire-elastic substrate systems considering the effects of nonlocality and surface energy. The thermodynamics-based strain gradient model is adopted to capture the nonlocality of the bar-bulk material while the Gurtin-Murdoch surface theory is utilized to consider the surface energy. To characterize the bar-surrounding substrate interaction, the Winkler foundation model is employed. In a direct manner, system compatibility conditions are obtained while within the framework of the virtual displacement principle, the system equilibrium condition and the corresponding natural boundary conditions are consistently obtained. Three numerical simulations are conducted to investigate the characteristics and behaviors of the nanowire-elastic substrate system: the first is conducted to reveal the capability of the proposed model to eliminate the paradoxical behavior inherent to the Eringen nonlocal differential model; the second is employed to characterize responses of the nanowire-elastic substrate system; and the third is aimed at demonstrating the dependence of the system effective Young’s modulus on several system parameters.

An improved inverse method for multirow blades of turbomachinery

A three-dimensional viscous inverse design method is improved and extended to multirow blades environment. The inverse method takes load distribution as optimization objective and is implemented into the time-marching finite-volume Reynolds-averaged Navier–Stokes solver. The camber line of rotor blade is updated by virtual displacement, which is calculated by characteristic compatibility relations according to the difference between target and actual load so as to control the location and intensity of shock wave, and realize the optimization of flow structure and reduction flow separation. The inlet and outlet geometry angles of stator blade are adjusted in real time according to the inlet and outlet flow angles. Thus, it is computationally ensured that the blade row interactions are accounted and optimization process is carried out under the design condition. To preserve the robustness of calculation, the maximum virtual displacement is limited by Y+ <10 and the camber line is smoothed via cubic B-spline interpolation. The complete blade profile is then generated by adding the prescribed blade thickness distribution to the camber line. The effectiveness of the method is demonstrated in the optimization of Stage35 compressor stage. Numerical results showed that this inverse method can effectively improve the internal flow structure and optimize the matching between blade rows, and this method is robust, efficient, and flexible.

CAD SIMULATOR MODEL OF A CUTTER

When caring for forest crops, it is necessary to prune the branches. Cutting of top branches is carried out in nurseries, removal of shrubs - on clearings, the formation of crowns - in forest shelterbelts. It is difficult for the operator to simultaneously control several hydraulic cylinders and maintain the required position of the working body. It becomes possible to automate the process of pruning branches with the development of digital means of visual and automatic control. It is necessary to determine the control actions on the hydraulic cylinders of the branch cutter to automate the work of the operator. Modern technological equipment is designed in computer-aided design (CAD) systems. It enables using a numerical method to conduct a computer experiment on a simulation model. The design of the cutter in Solidworks have been made. A simulation model has been compiled. The simulation model takes into account geometric, kinematic and inertial parameters of the cutter chains. The movement of the cutter working body from the transport position to the working one has been studied. Virtual displacement sensors have been installed on the chains in the Motion Solidworks module, and cutter paths have been obtained. The resulting control actions can be used as an input parameter for simulation models in other mathematical environments, and when creating prototypes of cutting control mechanisms

Linear theory for the mechanics of third-gradient continua reinforced with fibers resistance to flexure

A linear model, framed in the setting of the second strain gradient theory, is presented for the mechanics of an elastic solid reinforced with fibers resistant to flexure. The kinematics and bending resistance of the fibers are formulated via the second and third gradient of the continuum deformation. The corresponding Euler equations and admissible boundary conditions are then obtained by means of iterated integration by parts and variational principles arising in the third gradient of virtual displacement. In particular, within the prescription of superposed incremental deformations, we derive a compatible linear model from which a complete analytical solution describing the deformations of fiber composites is obtained. The proposed linear model predicts smooth and dilatational shear angle distributions over the domain of interest, which are also aligned with the results obtained from the corresponding nonlinear theory.