Archive of Mechanical Engineering

Thermal buckling behavior of a functionally graded material (FGM) Timoshenko beam is studied based on the transformed-section method. The material and thermal properties of the FGM beam are assumed to vary across the beam thickness according to a power-law function, a sigmoid function and an exponential function. The results of buckling temperature for the FGM beams with respective temperature-dependent and temperature-independent properties under uniform and non-linear temperature rises are presented. Some results are compared with those in the published literature to verify the accuracy of the present work. The effects of the material distributions, temperature fields, temperature-dependent properties and slenderness ratios on the thermal buckling behaviors of FGM beams are discussed. It is believed that the present model provides engineers with a simple and effective method to study the effects of various parameters of the FGM beam on its thermal buckling behavior.

A nanoscale beam model containing defect under the piezoelectricity considering the surface effects and flexoelectricity is established on the framework of Euler-Bernoulli theory. The governing equations of motion and related boundary conditions are derived by using Hamilton’s principle. The imperfect nanobeam is modeled by dividing the beam into two separate parts that are connected by a rotational and a longitude spring at the defect location. Analytical results on the free vibration response of the imperfect piezoelectric nanobeam exhibit that the flexoelectricity and the surface effects are sensitive to the boundary conditions, defect position, and geometry of the nanobeam. Numerical results are provided to predict the mechanical behavior of a weakened piezoelectric nanobeam considering the flexoelectric and surface effects. It is also revealed that the voltage, defect severity, and piezoelectric material have a critical role on the resonance frequency. The work is envisaged to underline the influence of surface effects and flexoelectricity on the free vibration of a cracked piezoelectric nanobeam for diverse boundary conditions. It should be mentioned, despite our R. Sourkiprevious works, an important class of piezoelectric materials used nowadays and called piezoelectric ceramics is considered in the current study.

In the paper, the authors present the solution aimed at increasing reliability of the conveyor units. The analysis of technological and operational defects of conveyor rollers is presented. The changes in manufacturing technology have been proposed, which allowed for avoiding welding and provided the required level of tightness.

Computer simulation of the motion of air in the labyrinth seal of the roller was conducted to determine the numerical parameters of possible airflows. It is proved that the airflow is present in the gap of the labyrinth seal due to the roller rotation. It is shown that the reason for the penetration of abrasive particles through the labyrinth seal after stopping is decompression, which occurred as a result of temperature change and push out of airflows during rotation. It is also suggested that the number of stops during the operation should be taken into account when determining the durability of rollers. Practical recommendations are given for preventing the penetration of abrasive particles during conveyor stops and the need for combined seals. The results can be used for the construction of roller conveyor belts in any industry.

In the rotor system, depending upon the ratio of rotating (internal) damping and stationary (external) damping, above the critical speed may develop instability regions. The crack adds to the rotating damping due to the rubbing action between two faces of a breathing crack. Therefore, there is a need to estimate the rotating damping and other system parameters based on experimental investigation. This paper deals with a physical model based an experimental identification of the rotating and stationary damping, unbalance, and crack additive stiffness in a cracked rotor system. The model of the breathing crack is considered as of a switching force function, which gives an excitation in multiple harmonics and leads to rotor whirls in the forward and backward directions. According to the rotor system model considered, equations of motion have been derived, and it is converted into the frequency domain for developing the estimation equation. To validate the methodology in an experimental setup, the measured time domain responses are converted into frequency domain and are utilized in the developed identification algorithm to estimate the rotor parameters. The identified parameters through the experimental data are used in the analytical rotor model to generate responses and to compare them with experimental responses.

Simulation studies of the hobbing process kinematics can effectively improve the accuracy of the machined gears. The parameters of the cut-off layers constitute the basis for predicting the cutting forces and the workpiece stress-strain state. Usually applied methods for simulation of the hobbing process are based on simplified cutting schemes. Therefore, there are significant differences between the simulated parameters and the real ones. A new method of hobbing process modeling is described in the article. The proposed method is more appropriate, since the algorithm for the momentary transition surfaces formation and computer simulation of the 3D chip cutting sections are based on the results of hobbing cutting processes kinematics and on rheological analysis of the hob cutting process formation. The hobbing process is nonstationary due to the changes in the intensity of plastic strain of the material. The total cutting force is represented as a function of two time-variable parameters, such as the chip’s 3D parameters and the chip thickness ratio depending on the parameters of the machined layer.

Nowadays, self-climbing formworks are commonly used in the construction of concrete buildings with a great height, such as high-rise buildings, silos, and bridge piers. A regular formwork can be improved to have more functions, e.g., the formwork itself can climb to the desired construction site. Climbing characteristics of the formwork as well as opening and closing characteristics of the formwork shell are essential criteria for evaluating the performance of a self-climbing formwork. The effective ones were mentioned in different studies, where most of them were published in patents of countries, e.g., the United States and China. Dissimilar from these studies, this paper presents several improvements for some certain groups to enhance the features of a hydraulic self-climbing formwork. Based on the analysis of the composition and the working principle of the actual climbing formwork types, a new opening and closing method of the formwork shells and a new rail clamping device are suggested. They are applied to design a self-climbing formwork with the shell’s working size of 4 m x 3 m. Their load capacity, as well as the flatness of the concrete surface after casting, are assessed. The proposed solutions can result in various advantages, e.g., the shorter initial alignment time, the increase of the quality concrete surface, and the maximal automation for construction operations.