Distribution of Axial Load on Bolt and Nut Threads

An analytical solution to the buckling of cylindrical shells under arbitrarily distributed axial loads

Plastic precision cropping of metal materials

Static stability of higher order functionally graded beam under variable axial load

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.

Modern multistage axial compressors are designed for high aerodynamic loading and wide range with front stages rotor inlet relative Mach number above one over a large portion of span. Rotor shock waves propagate and reflect in the upstream stator where they provoke extra aerodynamic losses and aeromechanic risks. This paper discusses stator–rotor shock interactions using both steady and unsteady numerical simulations. The computations focus on three different stage designs with the same capacity and total pressure ratio, but different axial gaps and load distribution in stator and rotor. Speedlines from steady and unsteady computations compare the designs, and the detailed flow fields are analyzed at design and close to stall conditions. The steady and unsteady calculations predict similar stage performance, but different stator–rotor loss split. The analyses reveal how the rotor shocks orientation with respect to the upstream stator camber line controls the intensity of shocks interaction with the stator row and its propagation upstream. Finally, the paper indicates the ways to reduce the shock-driven rotor–stator interaction and suggests simple criteria to determine when to switch from steady to unsteady calculations for a reliable transonic stage performance prediction.

A model for determination and analysis of bearing external radial and axial load distributions per individual rolling elements and a model for determination of the resistance to motion of rolling friction, accounting for rolling element locations during the bearing track motion with respect to the direction the bearing radial load resultant vector acts, are presented. A dynamic angle of the rolling element location has been defined as well. The models have been developed to determine values of bearing load distribution parameters, individual rolling element loads, and resistances to rolling motion of bearings and rolling bearing systems, as well as to analyze distributions and values of the radial and axial stiffness of rolling elements, bearings, and kinematic pairs as a function of the bearing rolling element distribution and the direction along which the bearing radial load resultant vector acts. The proposed models have been built to carry out analysis of the resistance to motion of rolling kinematic pairs of industrial robot manipulators. Slow-speed and short-period motions of rolling bearings have been assumed as a characteristic type of motion of rolling kinematic pairs in manipulators. © 2000 John Wiley & Sons, Inc.

Background. The accurate fit between the dental implant and the prosthetic abutment is crucial for the stability of the entire prosthetic-implant system, providing a better distribution of the occlusal load to the surrounding bone. To improve stress distribution between the implant and bone, various types of internal connection implants have been introduced. However, few studies are available on the biomechanical behavior of these connections. This study investigated the stress distribution in screwed implant-supported prosthesis with different implant‒abutment connections using a photoelastic analysis. Methods. Eight photoelastic models were fabricated in PL-2 resin and divided according to the different types of internal connections: Morse taper (MT), internal Morse hexagon (IMH), Morse taper hexagon (MTH), and frictional Morse taper (FMT) implants (3.75×11.5 mm), and the number of crowns (single and 3-unit pieces). Models were positioned in a circular polariscope, and 100-N axial and oblique (45º) loads were applied to the occlusal surface of the crowns using a universal testing machine. The stresses were photographically recorded and qualitatively analyzed using Adobe Photoshop software. Results. Under axial loading, the number and distribution of high-intensity fringes did not differ among groups for both crown types (single and splinted 3-element). Low stress values were noted at the implant apex. The oblique loading increased the number of fringes for all groups. In conclusion, the internal connection tested in this study did not affect the number and distribution of stress.Conclusion. The different types of internal connections provided better stability for the implant‒prosthesis set, which improved stress distribution when the prosthetic pillar was loaded, with the Morse cone friction system showing less stress. Oblique loading resulted in a higher stress concentration than axial loading.

The article discusses a calculation procedure for determining deformations and load distribution in round-profiled threads under general load conditions. It is shown that on manufacturing of threaded parts with different classes of accuracy owing to a small theoretical linear contact between screw and nut threads the real contact can be moved up to rounded portions of the thread crests. In this case the contact and bending deformations of the threads will have a great influence on the screw durability. The equations for calculation both these deformations and the deformations from thread shearing are given. The load distribution in screw drive with the round-profiled thread is shown in comparison with the load distribution in the widely used screw-drive with the trapezoidal thread. The law of change of the load value on the most loaded thread depending on a screw diameter and a number of the working threads are given as well. A comparative analysis for guarantee the equal durability of the thread and the screw shank is carried out

The nut and bolt thread protector system is a patented, ultraviolet stabilized polyethylene thread protector which seals nut and bolt threads in pressurized grease to effectively prevent corrosion and provide protection against physical damage. Laboratory corrosion testing has shown no corrosion on bolting using this system in 90-day ASTM B 117 salt spray tests and in 60-day wet sour gas tests. The system has proven its effectiveness for the corrosion protection of bolting in many marine applications. The corrosion protection provided allows removing the nut from the bolt after long exposure in corrosive environments without the use of special tools, and dramatically extends the useful life of the nut and bolt. The result is the elimination change-outs required from corrosion damage and significantly easier change outs when they are required for operational reasons, providing significant time savings for maintenance personnel. The system is state-of-the-art in corrosion protection for bolting in corrosive marine environments.

Energy geostructures, particularly energy piles, are foreseen as an alternative to reduce the environmental impact of the growing energy demand for space conditioning. This environmental friendly technology is a type of closed-loop Ground Source Heat Pump (GSHP) in which foundation elements are used to extract or inject thermal energy from/to the soil. Despite their multiple benefits, energy piles have not yet been employed in Mexico, where there is a general lack of knowledge about these systems. In the present paper the feasibility, limitations and challenges of using energy piles in the Mexican context are discussed. In order to understand the geotechnical implications of their functioning, a numerical simulation of the behavior of an energy pile subjected to different combinations of thermo-mechanical loads considering Coatzacoalcos (Veracruz) subsoil conditions is presented. The fully coupled thermo-hydro-mechanical analysis are made using the finite element program PLAXIS 2D Thermal. Vertical displacement and axial load distributions are obtained. The results of the parametric studies show that the magnitude of the thermal-induced stresses is significant, but their effects on the behavior of the foundation depends on the magnitude of the applied mechanical load.

Rock-socketed drilled shafts are widely used to transfer the heavy loads from the superstructure especially in mountainous area. Extensive research has been done on the behavior of rock-socketed drilled shafts under compressive load. However, little attention has been paid to uplift behavior of drilled shaft in rock, which govern the overall behavior of the foundation system. In this paper, a series of centrifuge tests have been performed to investigate the uplift response of rock-socketed drilled shafts. The pull-out tests of drilled shafts installed in layered rocks having various strengths were conducted. The load-displacement response, axial load distributions in the shaft and the unit skin friction distribution under pull-out loads were investigated. The effects of the strength of rock socket on the initial stiffness, ultimate capacity and mobilization of friction of the foundation, were also examined. The results indicated that characteristics of rock-socket has a significant influence on the uplift behavior of drilled shaft. Most of the applied uplift load were carried by socketed rock when the drilled shaft was installed in the sand over rock layer, whereas substantial load was carried by both upper and lower rock layers when the drilled shaft was completely socketed into layered rock. The pattern of mobilized shaft friction and point where the maximum unit shaft friction occurred were also found to be affected by the socket condition surrounding the drilled shaft.

Behavior of single rammed aggregate piers considering installation effects

Crashworthiness design draws considerable attention and interest in energy absorption systems. An optimal design of circular stepped tubes based on free inversion is presented in the current work to improve and enhance the crashworthiness characteristics under axial impact loading. Circular tubes have been known to be efficient energy absorbers per unit weight, and may be considered as the main part of energy absorbing devices even for frequently impact operation like landing gear or for sudden accidents like other vehicles. The precise choice of the circular tubes' material, shape, and mechanism may save a person life or save a valuable equipment from damage. Adaptive Multiple-Objective Optimization (AMO) can obtain more light and efficient section. An optimization of variable parameters, which represent the shape of a stepped tube under axial impact, is performed using the platform of ANSYS-DESIGN-EXPLORATION linked with LSDYNA code. The analysis leads to 16% reducing in mass with corresponding 31% improving in energy absorption.

The exact stability matrix approach is used to study the internal force distribution effect on the elastic critical load and subsequently on the failure load of planar frameworks. In particular, three options are considered. The first option utilizes an assumed axial load distribution in the structure, while in the second option an iterative procedure is employed to find the exact distribution of the axial load. The third option accounts for second order effects. A parametric study is conducted to determine the elastic critical load of various rigid-jointed frames by these three options. Also, the aforementioned options are compared on the basis of accuracy and efficiency.

Centrifuge modeling of the behaviour of helical piles in cohesive soils from installation and axial loading