Modeling of fatigue damage accumulation in multiple contact of pre-stressed bodies in the presence of wear

Рассматривается влияние остаточных напряжений, формирующихся при различных видах поверхностной обработки элементов пар трения, на скорость накопления контактно-усталостных повреждений, возникающих при циклическом нагружении поверхностей взаимодействующих тел в условиях трения качения при наличии поверхностного изнашивания. Исследовано влияние относительного проскальзывания, коэффициента трения скольжения, величины остаточных напряжений на распределение амплитудных значений максимальных касательных напряжений. Полученные результаты использованы для анализа влияния поля остаточных напряжений и скорости поверхностного изнашивания на процесс накопления контактно-усталостных повреждений. Residual stresses are formed during various types of surface treatment of elements of friction pairs. The effect of the residual stresses on the rate of fatigue damage accumulation is considered for the case of cyclic rolling contact in the presence of surface wear. The effect of relative slippage, friction coefficient, and residual stresses on the distribution of the amplitude values of the principal shear stress is studied. The results are used to analyze the effect of the residual stresses and the surface wear rate on the fatigue damage accumulation.

Approaches to modeling occurrence of rolling contact fatigue damages in rails

Rolling contact-fatigue damages of rails along with their wear are the most common types of rail defects. In recent years, there have been significant changes in the distribution of rolling contact fatigue damages of rails especially on railways operating under heavy haul conditions.This paper is devoted to the overview of approaches to modeling of the occurrence of rolling contact fatigue (RCF) damages on working surfaces of rails. Four types of such approaches to modeling are considered. The first is based on the methods of contact mechanics. To realize it, the vehicle movement on the characteristic sections of the track is modeled, the forces acting in contact are determined, the contact problem is solved, and the values of the linear criterion of contact fatigue damage are determined. The required characteristics of rolling contact fatigue of the rail material are established on the basis of laboratory tests. The second approach uses the diagram of the adaptability of rail material to cyclic loads, proposed by K. Johnson, established on the basis of laboratory tests. The third approach uses criteria that have the physical meaning of the energy released at the contact as an index of the product of the tangential force in contact and relative slippage. In the fourth approach predicting the accumulation of plastic deformation under conditions of cyclic loading is performed on the basis of a series of standard tests of rail steels, including in the welded joint zone, and finite element modeling. In addition, there is also a probabilistic model, based on the assumption that it is possible to transfer the results of the RCF damage of rails on the experimental section of the road to any other site.As the conclusion the authors formulated directions for further studies on the formation and development of surface rolling contact fatigue defects in rails.

Зернограничное проскальзывание и миграция специальных границ зерен в бикристаллах Al. Атомистическое моделирование

The energy of grain boundary shears is calculated for symmetric grain boundaries (GBs) using ab initio methods and molecular-dynamic modeling in order to elucidate mechanisms that control GB shear-migration coupling in typical symmetric GBs, such as Σ3 (111), Σ5 (012), Σ5 (013) and Σ11 (113) tilt GBs, in Al bicrystal. The energy of generalized grain-boundary stacking faults (GB–SF) is determined, and the preferred directions and the energy barrier are established for grain-boundary slippage. It is shown that the relative slippage of neighboring grains at certain directions of particle shears is accompanied by conservative migration of GB in the direction perpendicular to its plain. The modeling data are comparative to known grain-boundary shear-migration coupling mechanisms in Al.

Effect of Friction Coefficient on Relative Slippage of Fuel Cell Stack under Mechanical Impact Condition

A simplified finite element model for large polymer electrolyte membrane fuel cell (PEMFC) stack consisting of ten cells is established in order to investigate the internal structure deformation. It is found that the interface slippage occurs when the bipolar plate (BP) and membrane electrode assembly (MEA) are subjected to vertical impact acceleration. Based on this three-dimensional model, the influence of the friction coefficient between BP and MEA on the relative slippage can be analyzed efficiently. The division layer of relative slippage is found and its vibration rule is discussed. It is observed that increasing the magnitude of impact vibration has most significant effect on the movement of the division layer, and the two variables are linearly related when impact acceleration is greater than 5 g. This work provides important insight into the choice of the friction coefficient.

The generation principle, mathematical models of variable involute, and its application

A novel generation method of tooth profile curve is presented in this paper. It introduces the concept of a variable involute whose curve is generated by the generating line rolling and slipping on the base circle simultaneously. The generation principle of variable involute is described and the equation of variable involute is deduced. Then, equations are established to synthesize a conjugate profile for the gear teeth, which include some restrictions to keep the involute meshing properties. With a selectable and arbitrary relative slippage which is defined as a slipping function, the variable involute has desirable properties of controllability and flexibility. By constructing different slipping functions, involute, cycloid and circular-arc gears can be expressed into one unified form. The freedom and unified form of variable involute suggests the possibility of optimal conjugation design. An application example of gear pair with a few teeth is presented, aiming at overcoming the shortcomings of involute gear pair in load-carrying capacity and meshing performance, and its simulation analysis is conducted. Through comparative analysis with the involute gear, the results demonstrate that the variable involute gear pair with a few teeth has larger contact ratio as well as load-carrying capacity, and engagement performance has been effectively improved.

Analysis of Time Effects in Steel and Concrete Composite Beams Considering Relative Slippage

The effects of creep and shrinkage of concrete is non-ignorable to strength of steel and concrete composite beams under sustained load, and the relative slippage should be considered for internal force. Time-dependent modulus method is presented, formulas of the stress and strain at any time are deduced considering creep, shrinkage and the relative slippage. The variational stress is analysed of the steel and concrete composite beams under sustained load.

Theoretical Analysis of Shearing Capacity of U-Section Steel-Encased Concrete Composite Beams with the Full Connection Design

In this article, by studying the horizontal and vertical shear performance, the calculation formula for the fully shear connection is proposed. In order to avoid the overall vertical relative slippage between the steel and concrete, the vertical slippage formula is proposed to calculate the required number of the shear connectors for the first weak plane and second weak plane.

Theoretical Analysis on the Bond-Slip Constitutive Relationship between FRP Bars and Concrete under High Temperature

The primary objective of this study is to develop equations of the bond stress and relative slippage between fiber-reinforced polymer (FRP) bars and concrete exposed to different temperature ranging from 20°C to 190°C. Equations were established through theoretical analysis and simulation of the bond-slip constitutive relationship between FRP bars and concrete. According to the expressions, the variations of the bond stress and relative slippage between the two diffident materials can be evaluated at different locations. This paper made the analysis based on the theory of elasticity, using a bilinear model. An example to compare the results between experiment and theory had been proposed. It is indicated that the theoretical analysis here is in good agreement with the experimental data in related literature. The results can be applied to fire resistance design of FRP reinforced concrete structures.