Cantilever Bar Research Articles

Vibrodiagnostic Parameters of the Presence of a Semielliptic Breathing Crack in Circular Bars Under Super- and Subharmonic Resonances

UDC 620.178,620.179 The paper addresses the methods and results of approximate analytical and numerical calculation of vibrodiagnostic parameters of the presence of a closing semielliptic surface crack in a circular cantilever bar under super- and subharmonic resonances of the lower natural mode of bending vibrations at force and kinematic excitation. The dependences of vibrodiagnostic parameters on crack location and relative depth and on the point of load application are presented. The amplitudefrequency response under the strong superharmonic resonance is shown to differ from those under the weak superharmonic resonance and subharmonic resonance. The reasons why the results of the analytical solution differ from the numerical one obtained by using a finite-element model of the bar have been clarified.

Stress Transmitted To Palatless Overdenture Retained By Four Implants Splinted With and Without Cantilever Bar (Strain Gauge Evaluation) (In-Vitro Study)

Stress Transmitted To Palatless Overdenture Retained By Four Implants Splinted With and Without Cantilever Bar (Strain Gauge Evaluation) (In-Vitro Study)

РАСЧЁТ ЖЕЛЕЗОБЕТОННЫХ ДЫМОВЫХ ТРУБ НА ОСНОВЕ ДИАГРАММ ДЕФОРМИРОВАНИЯ БЕТОНА И АРМАТУРЫ

The method for calculation of reinforced concrete chimney shafts using the diagrams of concrete and steel deformation is described. The design diagram is accepted in the form of a constrained in the base cantilever bar. Moments of flection are specified on the basis of calculations according to a deformation scheme (geometrical nonlinearity) taking into consideration nonlinearity of concrete and steel deformation (physical nonlinearity). The problem formulation, traditional physical dependences fully meet the requirements of current design norms, which in its turn offers a possibility in principle to put the developed calculation method and a computer program into practice. The calculation examples compared to existing methods for calculation of chimneys, which detected significant drawbacks of the existing method and shown prospects of applying the suggested calculation method, are given. Keywords: chimneys, physical nonlinearity, geometrical nonlinearity, deformation diagrams.

Analysis of Deformation in Ni-Cr Structures with New and Recast Alloys

The present study analyzed new and recast Ni-Cr alloys, regarding the relationship between the applied force and the deformation in cantilevered bar segments, with dimensions of 4.0 mm, 3.5 mm, 3.0 mm in thickness, 4.5 mm width and 15 mm length, on a universal testing machine “EMIC”. The bars in the tests were initially obtained acrylic resin by 4.8 mm wide × 4.3 mm thick × 4 cm long. We obtained 30 bars divided into two groups, with 15 to test new alloys and 15 with alloys recast. The alloy used was Tilite. For the application of the load, the bars were attached to “EMIC” where the active tip of 200 kgf load cell was at a specific point of the bar (15 mm) with a speed of 0.5 mm per minute. The data showed statistically significant differences in relation to alloys and thickness among the bars, and all thicknesses evaluated were different. Thus, it was concluded that there was statistically significant difference between the groups and their variables, and that the alloys recast could be reused at least 1 time, without loss of properties.

Bending, torsion and asymptotic analysis of the cantilever bar

Bending, torsion and asymptotic analysis of the cantilever bar

Radio-frequency sheaths physics: Experimental characterization on Tore Supra and related self-consistent modeling

During the 2011 experimental campaign, one of the three ion cyclotron resonance heating (ICRH) antennas in the Tore Supra tokamak was equipped with a new type of Faraday screen (FS). The new design aimed at minimizing the integrated parallel electric field over long field lines as well as increasing the heat exhaust capability of the actively cooled screen. It proved to be inefficient for attenuating the radio-frequency (RF)-sheaths on the screen itself on the contrary to the heat exhaust concept that allowed operation despite higher heat fluxes on the antenna. In parallel, a new approach has been proposed to model self-consistently RF sheaths: the SSWICH (Self-consistent Sheaths and Waves for IC Heating) code. Simulations results from SSWICH coupled with the TOPICA antenna code were able to reproduce the difference between the two FS designs and part of the spatial pattern of heat loads and Langmuir probe floating potential. The poloidal pattern is a reliable result that mainly depends on the electrical design of the antenna while the radial pattern is on the contrary highly sensitive to loosely constrained parameters such as perpendicular conductivity that generates a DC current circulation from the private region inside the antenna limiters to the free scrape off layer outside these limiters. Moreover, the cantilevered bars seem to be the element in the screen design that enhanced the plasma potential.

Equivalence and dynamic analysis for jointed trusses based on improved finite elements

Deployable trusses that are widely applied in space missions utilize many hinged members to adapt to different geometrical shapes and work conditions. This paper presents two improved finite elements for a link and a bending beam to calculate dynamic characteristics of non-jointed and jointed trusses. First, the axial and transverse wave motion equations of a beam are used to get the shape functions of the link and the beading beam in their axial and transverse directions. Second, the dynamic matrices of stiffness and mass for a link and a bending beam are established on the basis of virtual work principle. The dynamic matrix and a theoretical equation are used to calculate the natural frequency of a cantilever bar. The comparison of the two results shows the effectiveness of the dynamic stiffness matrix. These improved elements are proved to be more accurate in calculating the responses of structures at high frequencies than common elements. Equivalent models of non-jointed and jointed structures are obtained on the basis of the displacement and strain energy equivalence of a truss unit. The result of the period truss confirms the accuracy of the equivalent model of the non-jointed truss expressed by dynamic matrices. The dynamic influences of cubic joints on a jointed structure are evaluated by giving the simulations of the equivalent jointed structure based on improved matrices. The results indicate that the natural frequencies of the jointed structure increase with the excitation force and the stiffness of joints. A relational function among the natural frequencies, joint stiffness, and excitation force is also presented.

Mechanical Numerical Analysis for L-Shape Traffic Signs Bar with Variable Cross-Section

L-shape traffic sign bar is composed of a stand column and a cantilever bar using bolted connection. The cross-section of stand column and a cantilever bar is closed thin wall with regular octagon and their cross sectional area is variable along axial line. The finite element simulation analysis for the bar is done under gravities and wind loads. Three-dimensional finite element model of bar is set up and stress field and displacement field is given under different load and their combination. Stress and displacement values of key parts are extracted and compared with theoretical calculation. Indicates that the theoretical calculation and finite element calculation is correct.

Mechanical Calculation Model for L-Shape Traffic Signs Bar with Variable Cross-Section

L shape traffic sign bar is composed of a stand column and a cantilever bar using bolted connection. The cross-section of stand column and a cantilever bar is closed thin wall with regular octagon and their cross sectional area is variable along axial line. The calculation formulas of stress for cantilever bar, stand column and flange bolts and calculation formulas of deformation for L rod are derived under gravities and wind loads, which provide theoretical basis for the design and use of L-shape bar. Calculation results using these formulas by comparison with finite element calculation results verify the correctness.

Mechanical Numerical Analysis for L-Shape Traffic Signs Bar with Variable Cross-Section

L-shape traffic sign bar is composed of a stand column and a cantilever bar using bolted connection. The cross-section of stand column and a cantilever bar is closed thin wall with regular octagon and their cross sectional area is variable along axial line. The finite element simulation analysis for the bar is done under gravities and wind loads. Three-dimensional finite element model of bar is set up and stress field and displacement field is given under different load and their combination. Stress and displacement values of key parts are extracted and compared with theoretical calculation. Indicates that the theoretical calculation and finite element calculation is correct.

The first frequency of cantilevered bars with geometric effect: a mathematical and experimental evaluation

In engineering, a large number of structures may be modeled as cantilevers. Due to their intrinsic characteristics, some of these structures are sensitive to dynamic actions. Gusts of wind are dynamic excitations for which the fundamental frequency of vibration is an important factor when calculating the structural response. Modeling the effects of the axial force on the natural frequencies of a structure usually results in systems of differential equations that are not solvable from a practical engineering perspective. This article develops a simple mathematical expression for calculating the fundamental frequency of cantilevered structures, within small ranges, that considers the presence of an axial demand. This expression has been validated by dynamic laboratory testing.

Переходные режимы колебаний консольного стержня с присоединенным гасителем при заданных начальных условиях

Переходные режимы колебаний консольного стержня с присоединенным гасителем при заданных начальных условиях

Experimental and Numeric Stress Analysis of Titanium and Zirconia One-Piece Dental Implants

The aim of this study was to evaluate the effect of cantilevered bar length on strain produced around two implants supporting a mandibular overdenture. Two root-form implants were placed bilaterally in the canine region of an edentulous acrylic resin mandibular cast and connected with a resilient bar/clip attachment. Four linear strain gauges were bonded to the acrylic resin at the mesial and distal surfaces of each implant. Each gauge was wired separately into a 1/4 Wheatstone bridge of a multichannel digital bridge amplifier. Strains were measured without cantilevered bar extensions (control group) and with the following lengths of cantilevered bars: 11 mm (group 1), 9 mm (group 2), and 7 mm (group 3). For each cantilevered bar length, strains were measured using clips placed on the cantilevers and attached to the overdenture (bar-clip contact) and without clips (bar-acrylic resin contact). Strain measurements were performed under central and unilateral loading using a loading device. The bar with cantilevers (either with or without clips) demonstrated a significant increase in strain compared to the bar without cantilevers. The 11-mm cantilever length generated the highest peri-implant strain values, while the 7-mm length recorded the lowest. For all cantilevered bar lengths, the strains significantly decreased with bar-clip contact compared to bar-acrylic resin contact. Under central loading, distal and mesial peri-implant strains were the highest and the lowest values, respectively, while under unilateral loading, the highest strain was recorded at distal sites of the loading side and the lowest was recorded at distal sites of the nonloading side. A positive correlation was found between the recorded strain and the cantilevered bar length. The 7-mm cantilevered bar with clips placed on the cantilevers was recommended when two implants were used to support mandibular overdentures, as it demonstrated the lowest magnitude of strains with no significant differences between peri-implant sites.

The Frequency Veering Phenomena of the Beams of Cantilever Screen

The special structure of beams of cantilever screen has the advantages comparing with the traditional screen and special dynamic characteristics, such as the dynamic characteristics of frequency veering. The traditional analysis method of vibrating screen is not applicable to its dynamic analysis because of the special structure. By analysis and decomposition of stiffness matrix of beams of cantilever screen, the frequency veering phenomenon of the beam of cantilever screen was explained from the point of view of modal energy equation and the influence of sub-stiffness matrix of beams of cantilever screen on the frequency veering was analyzed. The analysis results showed that the sub-stiffness matrix of the hollow beam and sub-stiffness matrix of cantilever bars is the main reason for the segmentation of modal natural frequencies and the coupling stiffness between hollow beam and cantilever bars is the main reason for the concentration of modal natural frequencies and the formation of the regular mode shapes for cantilever bars group.

Crack as modulator, detector and amplifier in structural health monitoring

A model of a one-dimensional cracked cantilever bar subjected to longitudinal harmonic excitation is used to analyse a nonlinear response as a way to monitor structural health. The effect of the bilinear (nonlinear) character of the crack on the dynamics of the structure is studied. Simulation and experiments were performed to analyse the nonlinear behaviour of the cracked bar. In simulation the nonlinear information is obtained based on a combination of the analytical technique and the Matlab–Simulink computation. From analysis and experiment, it is found that the crack-induced nonlinearity leads to the generation of higher harmonics, whose intensity is a function of a distance from the crack. Side band frequencies were clearly revealed as well. The latter indicate modulation of exciting frequency due to systematic interaction of crack faces. The nonlinear transformation of modulated vibration by crack leads to generation of a low frequency periodic component. Its intensity is proportional to the forced response of the cracked bar at the exciting frequency. The phenomenology revealed can be effective for Structural Health Monitoring.

Single-Port-Access Surgery with a Novel Magnet Camera System

In this paper, we designed, built, and tested a novel single-port access laparoscopic surgery (SPA) specific camera system. This device (magnet camera) integrates a light source and video camera into a small, inexpensive, portable package that does not compete for space with the surgical tools during SPA. The device is inserted through a 26-mm incision in the umbilicus, followed by the SPA port, which is used to maintain an insufflation seal and support the insertion of additional tools. The camera, now in vivo, remains separate from the SPA port, thereby removing the need for a dedicated laparoscope, and, thus, allowing for an overall reduction in SPA port size or the use of a third tool through the insertion port regularly reserved for the traditional laparoscope. The SPA camera is mounted to the abdominal ceiling using one of the two methods: fixation to the SPA port through the use of a rigid ring and cantilever bar, or by an external magnetic handle. The purpose of the magnet camera system is to improve SPA by: 1) eliminating the laparoscope SPA channel; 2) increasing the field of view through enhanced camera system mobility; and 3) reducing interference between the camera system and the surgical tools at the port, both in vivo and ex vivo.

Flexural Characteristics of Tapered Bar in Relation to Taper Angle Measurements

Flexural motion of a cantilever bar can be used to monitor the taper angle measurements of the bar without incorporating any geometric measurement. This provides non-destructive taper measurement with fast processing in manufacturing line. The laser ablation of a free end of the cantilever bar enables to generate a recoil pressure at the irradiated surface while resulting in external forcing function for the initiation of the flexural motion. Consequently, in the present study, laser induced ablation of free end tapered cantilever bar and resulting displacement and frequency of the flexural motion is examined. The study is extended to include influence of positive and negative bar taper angles on the flexural characteristics. In addition, deviation of displacement and frequency of the flexural motion due to tapered bar from the parallel bar is examined. It is found that the flexural characteristics of the tapered bar enable to determine taper angle of the bar with high accuracy.

Flexural Characteristics of Tapered Bar in Relation to Taper Angle Measurements

Flexural motion of a cantilever bar can be used to monitor the taper angle measurements of the bar without incorporating any geometric measurement. This provides non-destructive taper measurement with fast processing in manufacturing line. The laser ablation of a free end of the cantilever bar enables to generate a recoil pressure at the irradiated surface while resulting in external forcing function for the initiation of the flexural motion. Consequently, in the present study, laser induced ablation of free end tapered cantilever bar and resulting displacement and frequency of the flexural motion is examined. The study is extended to include influence of positive and negative bar taper angles on the flexural characteristics. In addition, deviation of displacement and frequency of the flexural motion due to tapered bar from the parallel bar is examined. It is found that the flexural characteristics of the tapered bar enable to determine taper angle of the bar with high accuracy.

A simple mathematical model for free vibration analysis of combined system consisting of framed tube, shear core, belt truss and outrigger system with geometrical discontinuities

Dynamic analysis of beam-like structure is significantly important in modeling real cases such as tall buildings, aircraft wings, spacecraft antennas and many other applications. This paper tries to determine the first natural frequency of tall buildings including framed tube, shear core, belt truss and outrigger system with multiple jumped discontinuities in the cross section of framed tube and shear core. In this regard, the entire length of the tall building is partitioned into uniform segments between each two successive discontinuity points. The effect of belt truss and outrigger system is modeled as a concentrated rotational spring applied at the belt truss and outrigger system location. Many cantilevered tall structures can be treated as cantilever bars with multiple jumped discontinuities in the cross section for the analysis of their free vibration. In this paper, the continuous approach was accepted and by using the Hamilton’s variational principle, the general form of governing equation for free vibration of tall building can be obtained. By applying the separation of variable method on time and space, the governing Partial Differential Equation (PDE) of motion is reduced to an Ordinary Differential Equation (ODE) with one variable coefficient while the other coefficients are constant based on the assumption that the transverse displacement is a harmonic vibration. To find exact solution of ODE, we must have exact distribution of EI(x), AG(x), N(x) and m(x) in the height of the structure. Some of these parameters such as EI(x), AG(x) and m(x), are constant throughout the height of each segment. These parameters can be expressed exactly by using of multi criteria function, while N(x) is variable in the height of each segment. Therefore, the ODE by using the method of variable separation and partitioned method can be expressed for each segment. We must apply the continuity conditions in conjunction with different segments for obtaining unique mode shape for mentioned system. Tall building characteristics matrix can be derived based on the boundary conditions and the continuity conditions applied at the partitioned points. This matrix is particularly used to find combined system first natural frequency and mode shape. Three numerical examples with different stepped discontinuities in their cross sections are studied to demonstrate the reliability of this method. The results of the proposed mathematical model give a good understanding of the structure’s dynamic characteristics; it is easy to use, yet reasonably accurate and suitable for quick evaluations during the preliminary design stages which require less time.

Reduced Modeling for Turbine Rotor-Blade Coupled Bending Vibration Analysis

In a traditional turbine-generator set, rotor shaft designers and blade designers have their own models and design process which neglects the coupled effect. Since longer blade systems have recently been employed (Saito et al. 1998, “Development of a 3000 rpm 43-in. last stage blade with high efficiency and reliability,” International Joint Power Generation Conference, pp. 89–96.) for advanced turbine sets to get higher output and efficiency, additional consideration is required concerning rotor bending vibrations coupled with a one-nodal (k = 1) blade system. Rotor-blade coupled bending conditions generally include two types so that the parallel and tilting modes of the shaft vibrations are respectively coupled with in-plane and out-of-plane modes of blade vibrations with a one-nodal diameter (k = 1). This paper proposes a method to calculate the natural frequency of a shaft blade coupled system. According to this modeling technique, a certain blade mode is reduced to a single mass system, which is connected to the displacement and angle motions of the shaft. The former motion is modeled by the m-k system to be equivalent to the blade on the rotating coordinate. The latter motion is commonly modeled in discrete form using the beam FEM on an inertia coordinate. Eigenvalues of the hybrid system covering both coordinates provide the natural frequency of the coupled system. In order to solve the eigenfrequencies of the coupled system, a tracking solver method based on sliding mode control concept is used. An eight-blade system attached to a cantilever bar is used for an example to calculate a coupled vibration with a one-nodal diameter between the blade and shaft.