Deformations in Round-Profiled Threads and their Influence on the Screw Durability

Load distribution in threads of porous metal–ceramic functionally graded composite joints subjected to thermomechanical loading

To increase reliability and fatigue life of machines it is necessary to improve calculation methods of machine elements. Elaboration and make use of calculations taking into consideration the real work conditions of machines and influence of various constructive factors upon machine capacity for work is one of the most important ways of acceleration of scientific and technical progress in mechanical engineering. Threaded parts are the most important machine parts which determine reliability of machines as a whole. The prime importance problem, on threaded joints calculations, is to know, how an axial load acting on the threaded joint is distributed on bolt and nut thread portions. Having considered the problem solution in historical development the authors have given the methods of the calculations of the axial load distribution on the bolt and nut threads for four main loading schemes of the threaded joints. The influence of bolt, nut and thread geometrical dimensions and materials are taking into account.

Combined with the soft clay layer of Foshan metro, a back‐analysis method combining model test and numerical simulation is developed. First, the similitude criterion for the model used in this study was derived from similarity theory and elasticity mechanics equations. Artificial clay is prepared by mixing kaolin, bentonite, loess, and river sand in proportions of 4 : 2: 3 : 1. Gypsum, water, and borax are mixed in proportions of 1 : 0.7 : 0.015 to simulate the tunnel lining. The model tests were carried out based on four load modes: the combination of mode 1, vertical load distribution and horizontal load linear distribution, mode 2, vertical load distribution and horizontal load parabolic distribution, mode 3, vertical load parabolic distribution and horizontal load linear distribution, and mode 4, vertical and horizontal load parabolic distribution. Then, the calculation model corresponding to the four load modes is established using ABAQUS, and the measured data is back‐analyzed as the known quantity. The specific load values obtained were 359 kPa, 380 kPa, 361 kPa, and 368 kPa by the load‐internal force curve. The bending moment and axial force are calculated by substituting the back‐analysis load values back into the model and comparing the results with the measured values; it was found that the internal forces under the back‐calculation load still deviated by varying degrees. By using the comprehensive error function E to evaluate the advantages and disadvantages of the four distribution modes, the comprehensive errors are 4.3%, 1.7%, 6.5%, and 5.9%, respectively. That is, the error of load distribution of mode 2 (the combination of vertical load distribution and horizontal load parabolic distribution) is the lowest and is highly consistent with the measured value, which is the closest to the characteristics of the load pattern of the stratum.

Conventional analytical and numerical methods for the mechanical properties of helical threads are relied on many assumptions and approximations and thus hardly yield satisfied results. A parameterized 3D finite element model of bolted joints with real helical thread geometry is established and meshed with refined hexahedral elements. The Von Mises plasticity criterion, kinematic hardening rule of materials and interfacial contacts are employed to make it possible for the suggested model be able to approach real assembly conditions. Then, the mechanical properties of bolted joints with different thread pitches, thread numbers and modular ratios are investigated, including the contact pressure distribution at joint interfaces, the axial load distribution and stress concentration in screw threads during the loading and unloading process. Simulation results indicate that the load distribution in screw threads produced by the suggested model agrees well the results from CHEN’s photoelastic tests. In addition, an interesting phenomenon is found that tightening the bolt with a large preload first and then adjusting the clamping force by unloading can make the load distribution more uniform and reduce the maximum residual equivalent stress in thread roots by up to 40%. This research provides a simple and practical approach to constructing the 3D finite element model and predicting the mechanical properties of helical thread connection.

The residual load is defined by energy demand minus energy production from renewable sources (wind and solar power). High values of residual load correspond to a high energy demand that cannot be covered by renewable energies and must be compensated with fossil energies. On the opposite, low/negative values of residual load correspond to a surplus of renewable energies with a too low demand. In this case, energy must be exported, or wind turbines and solar panels curtailed.We compute the residual load using a demand model and a solar and wind power model. For the solar power model, we use the CAMS solar energy dataset interpolated to the position of all single solar panels installed in Germany and model the solar power output with the PVlib Python package. The wind power model is using ERA5 windspeed and air density interpolated to turbine location and turbine hub height to be later fed in the power curve of all single turbines in Germany. The demand model is a linear regression of 2m-temperature from ERA5, industry production index, day-of-week, public holidays and installed solar capacity. The residual load is then given by: ResLoad = Demand - (Wind + Solar)We look at both tails of the distribution of the residual load. High values of residual load are mostly observed in winter when temperatures and renewable energy production are low (mostly during blocked regimes). These events correspond to high energy prices. Negative values of residual load are mostly observed on Sundays, public holidays and in summer, where demand is low and temperatures and solar and wind power production are high. They usually correspond to negative energy prices. Both events described above are critical for the energy industry. Skillful forecasts of these events in the sub-seasonal range help to reduce stress to the energy market. The results presented herein lay the foundation for a more comprehensive, statistical analysis of the predictability characteristics of residual load extremes.

The problem of a circular plate, with a central hole, elastically constrained against rotation and deflection, acted upon by a transverse linear temperature gradient or a general axisymmetrical loading condition is considered in this paper. With the aid of presented graphs and simple algebraic equations, it is a relatively simple matter to construct the desired deflection and stress pattern for any combination of elastic constraints and load distribution.

Porous Network Concrete: a bio-inspired building component to make concrete structures self-healing

Background Strength calculation is performed on the pipeline under the different types of loads. In the strength longitudinal-transverse bending calculation trunk pipelines section is assumed as a beam under frictional constraint of horizontal displacements of the sagging plot ends. Aims and Objectives To analyze the stress-strain state of the pipeline filled with oil on the total cross section. To assess the durability of pipeline systems under complicated engineering-geological condi-tions. Methods Strength calculation of pipelines is based on methods of mathematical modeling, when loaded pipeline section is represented as an elastic beam under longitudinal and transverse bending. Results A computer analysis of the stress-strain state of the pipeline and parameters of movement of its linear part, depending on various conditions (of the length of sagging pipeline, contact with soil, temperature gradient, etc.) is comleted. Conclusion The calculation method presented in the paper allows to estimate the durability pipeline in areas with complex geological conditions.

Introduction. This study investigated the parameters of foot load, as one of the dimensions of foot biomechanics, using a new method of objectification of the measured values. The examined biomechanical parameters directly affect correct gait and posture. The aim of this research was to determine if there was a statistically significant difference in the forefoot and rearfoot load, as well as the load on the whole foot between physically active and inactive students. Material and Methods. The study included 91 students, of whom 44 were physically inactive and 47 were physically active. Measurements were performed by using a baropodometry platform (FreeMed Maxi, Sensor Medica, Rome, Italy) used for the first time in our population for objectification of the morpho-physiological parameters. All reference values were provided by the manufacturer as a part of the Freestep version 1.4.01 software. Results. Our results showed that physically active students have statistically significantly higher forefoot load values. Physically inactive students have statistically significantly higher rearfoot load values. Also, physically inactive students have statistically significantly higher deviations in most parameters from the reference values compared to physically active students. The percentage of physically inactive students with non-physiological values is higher in every parameter compared to the percentage of physically active students. However, this difference is statistically significant only for the load on the right forefoot in relation to both feet. Conclusion. Physically active students showed a physiologically better foot load distribution than physically inactive students.

The author has presented in this paper his own experimental research on the maximum value and distribution of load in transverse roof bracing caused by a planar truss girder with geometrical imperfections. The tests were performed on 7.0 m long test models of steel truss made of square hollow sections. The tests performed verify standard recommendations concerning adoption of uniformly distributed notional load of transverse roof bracing and confirm the relations indicated in the discussed literature. The experimental research results were cross-checked by relevant numerical analysis. A comparison of notional loads recommended by the standard and literature with test results was performed and conclusions were formulated.

Distribution of loads and contact stress has a great influence on fatigue life of bearings. In view of the fact that the nonload area is ubiquitous in cylindrical roller bearings, there is a method for prolonging the fatigue life design by adjusting the working clearance of cylindrical roller bearings. In this article, optimization model of fatigue life of cylindrical roller bearings is developed with a quasi-dynamic method and calculated method of bearing life based on micro-area contact, considering the effect of assembly interference, temperature rise, and high-speed centrifugation. Aiming to the different geometry parameters and operating parameters of bearings, the effects of assembly interference on bearing fatigue life are discussed. The results show that the optimum fatigue life of roller bearings is achieved at negative working clearance with the loads distributed evenly within half ring. The optimum working clearance of roller bearings is not influenced by radial load. But with the increase in pitch diameter or decrease in rolling elements, the optimum assembly interference increases, and accelerating revolution of roller bearings will increase the optimum assembly interference as well.

This study investigated the theoretical lateral design pressures, vertical frictional forces and bending stresses exerted by shelled corn on a wall configuration made of folded steel plates. Silo walls panels with trapezoidal corrugations were considered. Lateral design pressures and vertical frictional forces were calculated by using Janssen’s equations for pressures in deep bins and bending stresses exerted by ensiled corn were calculated by using principle of engineering mechanics. Inclined sections of corrugations with 135o from the horizontal plane had the highest lateral design pressures and vertical frictional forces. Corrugations with tie bars had significantly lower bending stresses than the corrugations without tie bars. Using the results of this theoretical work, further studies can be performed for a complete silo model with a roof structure and a hopper bottom and wind forces and the shear stresses can be added to the model. This may give a better interpretation of the theoretical results on real models.

The vertical dynamic interaction between a high-speed railway vehicle and slab track is simulated in the time domain using a two-dimensional track model. The transient interaction problem is solved using an extended state-space vector approach in combination with a complex-valued modal superposition technique for the track model. The presented slab track model includes two layers of concrete beams, where the panels of the upper layer are described by possibly coupled beams of finite length, while the roadbed in the lower layer is a continuous beam. Both rail and concrete layers are modelled using Rayleigh-Timoshenko beam theory. The presented model is applied to calculate the influences of foundation stiffness gradient and track design parameters on various track responses. In particular, the influences of the thickness of the roadbed on the load distribution on the foundation, and of the stiffness of the rail pad on the bending moment in the concrete panels, are investigated in two demonstration examples.

<p>This research consists in the experimental and theoretical investigation of the finite deflection and buckling of two similar structures; the low arch or slightly curved beam and the shallow spherical dome, both subjected to lateral loads. These structures are of interest because the large interaction between bending and axial forces causes their load-deflection behavior to become nonlinear at very low values of the deflection. Due to the wide difference in the methods of solution of these two problems they are separated into two parts, each having its own abstract.</p>
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\n<p>[Part I]</p>
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\n<p>When a low arch (a thin curved beam of small curvature) is subjected to a lateral loading acting toward the center of curvature, the axial thrust induced by the bending of the arch may cause the arch to buckle so that the curvature becomes suddenly reversed. The critical lateral loading depends on the dimensions and rigidity of the arch, the elasticity of the the end fixation, the type of load distribution, and the initial curvature of the arch. A general solution of the problem is given in this paper, using the classical buckling criterion which is based on the stability with respect to infinitesimal displacements about the equilibrium positions.</p>
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\n<p>For a sinusoidal arch under sinusoidal loading, the critical load can be expressed exactly as a simple function of the beam dimension parameters. For other arch shapes and load distributions, approximate values of the critical load can be obtained by summing a few terms of a rapidly converging Fourier series. The effect of initial end thrust and axial and lateral elastic support are discussed.</p>
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\n<p>The buckling load based on the energy criterion of Karman and Tsien is also calculated. The results for both the classical and the energy criteria are compared with experiments made on a series of centrally loaded, pin-ended arches. For larger values of a dimensionless parameter [gamma subscript l], which is proportional to the ratio of the arch rise to the arch thickness, the experimental critical buckling loads agreed quite well with the classical criterion, but, for smaller values of [gamma subscript l], the experimental critical loads were appreciably below those calculated from the classical criterion, although they were always above those obtained from the energy criterion.</p>
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\n<p>[Part II] The shallow spherical dome subjected to lateral pressure is a structure for which the deformation departs appreciably from the linear theory at very small values of the deflection amplitude. It is also. one for which the buckling process is characterized by a rapid decrease in the equilibrium load once the buckling load has been surpassed. For structures having this type of buckling characteristic, the question arises as to whether the proper buckling criterion to apply is the classical criterion, which considers equilibrium with respect to infinitesimal displacements or the finite displacement "energy criterion" proposed by Tsien.</p>
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\n<p>In this paper the problem of the finite displacement and buckling of a shallow spherical dome is investigated both theoretically and experimentally. In the theoretical approach the nonlinear equations are converted into a sequence of linear equations by expanding all of the variables in powers of the center deflection and then equating the coefficients of equal powers. The basic parameter for the shallow dome is proportional to the ratio of the central height of the dome, h, to its thickness, t. For small values of this ratio the expansions converge rapidly and enough terms are computed to determine the buckling load. For higher values of h/t, convergence deteriorates rapidly and the buckling, load is not computed. However, even for these higher values of h/t the deflection shapes are determined for deflection amplitudes below the amplitude at which buckling occurs. These deflection shapes are characterized by their rapid change as h/t increases and by the fact that, over most of the range of h/t studied, the maximum deflection does not occur at the center of the dome.</p>
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\n<p>The experimental program was carried out on a series of clamped-edge, eight inch base diameter shells, subjected to uniform pressure. The deflection shapes and the buckling loads agreed quite well with the values computed theoretically. It was also found that there was no significant difference between the buckling loads observed using air pressure and those observed using oil pressure. Thus it is concluded that for the shallow domes studied the classical buckling criterion holds rather than the "energy criterion" proposed by Tsien.</p>

Even under constant operating conditions, greases lubricating lead screw assemblies, as well as materials comprising their nut and screw threads, must perform over a range of contact pressures that not only varies from thread-to-thread, but also evolves with sliding distance as most-heavily loaded threads wear most rapidly. An example modeled here, consisting of a nut whose bulk body is rigid and elastic screw body having continuous elastic meshed threads, reveals the broad distribution of load along the length of the nut threads in an unworn lead screw assembly, as well as the distribution of wear depth that must accompany an eventual steady-state of uniform rate of nut thread wear. Thread load redistributions brought on by changes in operating conditions such as applied load, or even temperature in the case of a nut/screw pair of dissimilar materials, are similarly modeled. Such load redistributions in worn lead screws may cause either the top or the bottom positions of the nut thread to become most heavily loaded, depending on whether an operating condition is increased or decreased, and the extents of these redistributions using this continuous thread model can significantly exceed those predicted by a preliminary model where threads were considered as discrete turns. Operating condition changes are shown capable of causing worn threads at either extreme of the nut to become momentarily unloaded and removed from contact, and this continuous-thread model indicates that even smaller changes in operating condition can initiate such unloading, as compared to predictions from the discrete-thread model.Copyright © 2006 by ASME