Journal of Engineering and Thermal Sciences
Not a member yet
1200 research outputs found
Sort by
Research on wood gluing factors by a resonant oscillations method
No full textThis paper presents the methodology and equipment that is applied for experimental investigation of glued wood articles and their components by means of resonant vibrations. It is demonstrated that beam and plate, which form wood assortments along and across grain, may be studied by using theoretical calculations based on deformed beam vibrations. In addition, research data of oak glued-up panels of varying width as well as adhesive and scantlings are included. It was determined that the increase of width of the panels (the number of scantlings) practically does not change the shape of their first vibration mode. However, the research revealed slight changes in the amplitude-frequency characteristic, i.e., the first natural frequency increased up to 5 %, and the bandwidth decreased by 30 %. Irrespective of additional factors, the modulus of elasticity of the glued-up panels was higher by 10 % in comparison to average modulus of elasticity of the used scantlings, whereas damping coefficient was lower by 40 %. Obtained results may be used to evaluate the behavior of glued-up panels in the zone of dynamical loads and to produce glued-up panels with proper parameter
New intelligent regulators for mechatronic systems
Get PDFThe paper considers new intelligent regulators combining accuracy and speed without overshoot as well as controls providing adaptability at guaranteed stability of controlled system in non-stationary conditions. The developed regulators connect target and actual values of output variables of the controlled system and criteria, enabling variation of properties of the criteria in an accessible form. The proposed adaptive regulators are capable to implement control near the capability limits and consequently provide solutions of known and new control tasks at a qualitatively new leve
Control of friction forces with stationary wave piezoelectric actuator
Get PDF"In the field of the research on piezoelectric motors, the control of friction forces by ultrasonic waves was studied mainly from an experimental point of view [1]. The principle of friction force reduction by imposed mechanical vibrations in unlubricated contacts was recently studied in order to reduce the friction losses in an internal combustion engine with Langevin type actuators [2]. This article deals with the advantages of flexural stationary wave piezoelectric actuators in the control of the friction forces thanks to their high pressures generated at high frequencies (>10 Khz). The use of specific contact geometry which is defined by the Hertz theory associated with partial slip contact conditions, allows optimizing the lubrication effect. In the case of piezoelectric torque limiter application, the design and the numerical simulation of dedicated piezoelectric actuator are compared. In agreement with the contact modeling, the characterization of the complete actuator on mechanical test bench validates the ""torque limiter"" function and the optimization of lubrication principle with dedicated contact geometry
Investigation of actuators with smart links
Get PDFPrincipal schemes of actuators with smart links have been designed. Equations are presented for describing motion of a pneumatic actuator with viscous magnetorheological liquid and the vibration actuator with a smart link with shape memory. Amplitude-frequency characteristics of the vibration actuator and the pressure developed by the magnetorheological liquid vane have been determined. Application areas of the devices are propose
Vibration based research into temperature influence on circular saw parameters
Get PDFThe study presents the research results of transverse sawing circular saws in conjunction with the oscillatory research of a non-rotating circular saw. It reveals that amplitude-frequency characteristics, resonance frequencies and modes were established and operative heating regimes of the saws were modelled. It was determined that the form of the main modes insignificantly changes when the saw is heated. At the same time heating temperature considerably influences the value of both high and low resonance frequencies, as well as the size of amplitude. During the examination damping coefficient within temperature interval was estimated and both surface and deep hardness of the saw were determined. The study shows that the temperature of the saw significantly changes its surface hardness, but its deep hardness remains less changed. The research results allow forecasting the behaviour of saws during operatio
Experimental researches of a flexible waveguide of ultrasound vibrations
No full textIn this paper we report the results of experimental research of a new flexible and variable-rigidity waveguide, which operation is based on ultrasound vibrations. The tested waveguide is a combination of conical-stepped-cylindrical waveguides, which enables significant improvement of dynamic characteristics with respect to various existing static loads. The resonant frequency for excitation of the waveguide is in the range of 24-26 kHz. The measurements presented in this paper were performed on a STANDA vibration-isolation honeycomb-type table by means of the POLYTEC laser Doppler vibrometer system MSV-400 consisting of a laser interferometer OFV-512, vibrometer controller OFV-5000 and analog-to-digital converter ADC-2424 (PICO,GB) as well as by using HYTEC holographic interferometry system PRIS
Investigation of vibrations of line scale calibration systems
Get PDFThe paper treats the issue of embedding the traceable length metrology directly into technological process by performing precise dynamic measurements of line scale in real industrial environment. It addresses the error-related problems specific to line scale calibration in dynamic mode of operation that are caused primarily by static and dynamic loads as well as geometrical deviations of the calibration system components. Introducing the dynamic regime of calibration leads to the dynamic calibration error originating due to vibration sources in the structure. This term should be considered and implicated in the measurement uncertainty budget. A new 3D finite element model has been developed in order to both investigate the influence of dynamical excitations of a long stroke comparator structure and evaluate possible influence of vibrations on geometrical dimensions of the line scale. The experiments have been conducted on the new interferometer-controlled comparator setup with a moving microscope in order to evaluate the performance of the precision scale calibration proces
Vibratory stress relieving – it’s advantages as an alternative to thermal treatment
Get PDFThe aim of this study was to investigate the use of vibration to reduce the residual stress resulting from the welding process. Butt weld joints were subjected to vibration immediately after welding. The existing methods for relieving residual stress from welds are: mechanical, heat and electromagnetic. The mechanical method may be performed by hammering or vibration. The heat method consists of heating the whole welded piece or each weld, one by one. The electromagnetic method uses the electromagnetic hammer technique. In the heat treatment the part is heated until the yield point is reduced to less than the residual stress, which in turn causes local plastic distortion, decrease of the residual stress intensity and reduction of hardness. The vibration method introduces energy into the part by means of vibrations. For the stressed atomic structure there is no difference between the energy introduced through heat and the energy introduced through vibrations. The applied energy reorganizes the crystalline structure, relieving stress and stabilizing the piece, without distortion [1]. The article deals with reducement of welding stresses with the help of vibration treatment and to compare it with the classical heat treatment. The experiments were performed by a welding of structural low-alloy steel 16GS plates. Therefore the result is submitted by the mechanical tests and metal magnetic memory control. Several specimens, after welding and vibrotreatment, were cut off the welded plates and submitted for tensile, impact, hardness tests and metallographic analysis. The specimens, which were treated by vibration treatment, had strength and elasticity properties changed similarly as after the heat treatment. The metal magnetic memory test shows that this control method is suitable for evaluation of residual welding stresses variations after the weldment’s treatmen
Tool edge geometry’ and wear’ recognition by using contact method
No full textThe aim of this paper is to present a device to measure non-destructively the geometry of cutting edges as well as to detect the wear. This might sound easy. One might propose a usual optical way where an edge is illuminated by an inclined beam and observed from the top. Another might try to use a surface roughness measurement device. However, those were all tested in the past and ended up with a total failure or severe limitation in application. The major reason consists in the size of roundness. For the case of a lancet or shaving knife the roundness is of the order of 2 – 5 µm and varies along the periphery covering over 300 degrees. This paper presents a non-destructive method, which consists of a mechanical device and software package for performing reading and mathematical calculations as well as obtaining practical knowledge on the relationship between the sharpness and performance of various sharp edges according to their purpose
Dynamic synchronization of the unbalanced rotors for the excitation of longitudinal traveling waves
Get PDFThe problem about the synchronization of the unbalanced rotors for the excitation of the longitudinal traveling waves in the elastic system of a bar type is examined. The steady-state regimes of motion are investigated, the conditions of their existence and stability are obtaine