Search results

The purpose of this paper is to provide a static friction coefficient prediction model of rough contact surfaces based on the contact mechanics analysis of elastic-plastic fractal surfaces.

In this paper, the continuous deformation stage of the multi-scale asperity is considered, i.e. asperities on joint surfaces go through three deformation stages in succession, the elastic deformation, the elastic-plastic deformation (the first elastic-plastic region and the second elastic-plastic region) and the plastic deformation, rather than the direct transition from the elastic deformation to the plastic deformation. In addition, the contact between rough metal surfaces should be the contact of three-dimensional topography, which corresponds to the fractal dimension D (2 < D < 3), not two-dimensional curves. So, in consideration of the elastic-plastic deformation mechanism of asperities and the three-dimensional topography, the contact mechanics of the elastic-plastic fractal surface is analyzed, and the static friction coefficient nonlinear prediction model of the surface is further established.

There is a boundary value between the normal load and the fractal dimension. In the range smaller than the boundary value, the normal load decreases with fractal dimension; in the range larger than the boundary value, the normal load increases with fractal dimension. Considering the elastic-plastic deformation of the asperity on the contact surface, the total normal contact load is larger than that of ignoring the elastic-plastic deformation of the asperity. There is a proper fractal dimension, which can make the static friction of the contact surface maximum; there is a negative correlation between the static friction coefficient and the fractal scale coefficient.

In the mechanical structure, the research and prediction of the static friction coefficient characteristics of the interface will lay a foundation for the understanding of the mechanism of friction and wear and the interaction relationship between contact surfaces from the micro asperity-scale level, which has an important engineering application value.

This paper aims to study the contact between rough cylindrical surfaces considering the elastic-plastic deformation of asperities.

The elastic deformation of the nominal surface of the curved surface is considered, the contact area is discretized by the calculus thought and then the nominal distance between two surfaces is obtained by iteration after the pressure distribution is assumed. On the basis of the Zhao, Maietta and Chang elastic-plastic model, the contact area and the contact pressure of the rough cylindrical surfaces are calculated by the integral method, and then the solution for the contact between rough cylindrical surfaces is obtained.

The contact characteristic parameters of smooth surface Hertz contact, elastic contact and elastic-plastic contact between rough cylindrical surfaces are calculated under different plastic indexes and loads, and the calculation results are compared and analyzed. The analysis shows that the solution considering the elastic-plastic deformation of asperities for the contact between rough cylindrical surfaces is scientific and rational.

This paper provides a new effective method for the calculation of the contact between rough cylindrical surfaces.

An algorithm is described for the incremental solution of elastic—plastic finite element analysis using a piecewise holonomic constitutive law based on a von Mises yield condition. The holonomic assumption effectively converts each incremental problem into a non‐linear elastic—plastic problem. The algorithm is iterative, substituting the non‐linear strain potential by a quadratic potential at each iteration, and convergence is proved. The algorithm has been implemented into a finite element program as a series of secant modulus approximations, and results for a variety of problems are given. The rate of convergence is fairly slow, but the algorithm can be very easily programmed as an extension of an elastic program, and may have value as an independent method of determining incremental elastic—plastic solutions.

This paper considers the classical problem of the deformation of an elastic‐plastic body subjected to a prescribed history of loading. Attention is focused on the basis for the time discretization of the problem for numerical solution. It is suggested that this discretization can be achieved consistently by conceiving of the problem as a sequence of holonomic, or non‐linear elastic, problems. Complementary work bounds can be given, in special circumstances, for increasing numbers of time steps. The holonomic problem for a single time step is a non‐linear mathematical programming problem: it is shown that the conventional Newton‐Raphson algorithm used in elastic‐plastic finite element analysis can be interpreted as an iterative procedure for finding the least value of the holonomic potential work functional.

A review is made of methods for calculating parameters characterizing crack tip behaviour in non‐linear materials. Convenient methods of calculating J‐integral type quantities are reviewed, classified broadly into two groups, as domain integrals and virtual crack extension techniques. In addition to considerations of how such quantities may be calculated by finite elements, assessment methods of conducting the actual incremental analyses are described.

Crack tip stresses are used to relate the ability of structures to perform under the influence of cracks and defects. One of the methods to determine three-dimensional crack tip stresses is through the J-T_z method. The J-T_z method has been used extensively to characterize the stresses of cracked geometries that demonstrate positive T-stress but limited in characterizing negative T-stresses. The purpose of this paper is to apply the J-T_z method to characterize a three-dimensional crack tip stress field in a changing crack length from positive to negative T-stress geometries.

Elastic-plastic crack border fields of deep and shallow cracks in tension and bending loads were investigated through a series of three-dimensional finite element (FE) and analytical J-T_z solutions for a range of crack lengths ranging from 0.1⩽a/W⩽0.5 for two thickness extremes of B/(W − a)=1 and 0.05.

Both the FE and the J-T_z approaches showed that the combined in-plane and the out-of-plane constraint loss were differently affected by the T-stress and the out-of-plane size effects when the crack length changed from deep to shallow cracks. The conditions of the J-T_z dominance on the three-dimensional crack front tip were shown to be limited to positive T-stress geometries, and the J-T_z-Q^2D approach can extend the crack border dominance of the three-dimensional deep and shallow bend models along the crack front tip until perturbed by an elastic-plastic corner field.

The paper reports the limitation of the J-T_z approach, which is used to calculate the state of three-dimensional crack tip stresses in power law hardening materials. The results from this paper suggest that the characterization of the three-dimensional crack tip stress in power law hardening materials is still an open issue and requires other suitable solutions to solve the problem.

This paper demonstrates a thorough analysis of a three-dimensional elastic-plastic crack tip fields for geometries that are initially either fully constrained (positive T-stress) or unconstrained (negative T-stress) crack tip fields but, subsequently, the T-stress sign changes due to crack length reduction and specimen thickness increase. The J-T_z stress-based method has been tested and its dominance over the crack tip field is shown to be affected by the combined in-plane and the out-of-plane constraints and the corner field effects.

The purpose of this paper is to present the characteristics of elastic-plastic deformation and stress fields at the intersection of a crack front and the free surface of a three-dimensional body, referred to as corner fields.

The structures of elastic-plastic corner deformation field were assessed experimentally by looking at the corner border displacement and strain fields on the surface of a compact tension (CT) specimen using digital image correlation method. For assessment and verification purposes, the results were compared with the fields predicted through finite element analysis. The latter method was used further to assess the corner stress field.

The characteristics of displacement, strain and stress fields in the vicinity of a corner vertex in a finite geometry CT specimen in a strain hardening condition are independent of load and geometry. One of the distinctive features that becomes evident in this study is that the stress state at the corner vertex at θ=0° is a simple uniaxial tension.

This paper provides some insights on the structure of elastic-plastic corner fields that could optimistically be served as a fundamental framework towards the development of analytical solutions for elastic-plastic corner fields.

Recent publications have highlighted the effectiveness of using a consistent tangent modulus when solving elastic‐plastic problems. The formulation of a consistent tangent modulus is closely related to the scheme used to integrate the constitutive equations. Recent work has shown how many of these schemes currently in use can be derived from certain broad classes of algorithms. In this paper these procedures are examined for a number of commonly used yield/failure criteria. For certain cases a remarkably simple formulation results which can lead to considerable savings in computational time.

The purpose of this paper is to expound the relationship among microstructure, mechanical property, tribological behavior and deformation mechanism of carburized layer deposited on Ti-6Al-4V alloy by double-glow plasma hydrogen-free carburizing surface technology.

Morphologies and phase compositions of the carburized layer were observed by scanning electron microscope and X-ray diffraction. The micro-hardness tests were used to evaluate the surface and cross-sectional hardness of carburized layer. The reciprocating friction and wear experiments under various load conditions were implemented to investigate the tribological behavior of carburized layer. Moreover, scratch test with ramped loading pattern was carried out to illuminate the deformation mechanism of carburized layer.

Compared to substrate, the hardness of surface improved to ∼1,100 HV_0.1, while the hardness profile of carburized layer presented gradual decrease from ∼1,100 to ∼300 HV_0.1 within the distance of the total carburizing-affected region about 30 µm. The coefficient of friction, wear rate and wear morphology of carburized layer were analyzed. Scratch test indicated that the deformation process of carburized layer could be classified into three mechanisms (elastic, changing elastic–plastic and stable elastic–plastic mechanisms), and the deformation transition of the carburizing-affected region was from changing elastic–plastic to elastic mechanisms. Both the elastic and changing elastic–plastic mechanisms are conducive to the wearing course.

Using this technology, hydrogen embrittlement was avoided and wear resistance property of titanium alloy was greatly improved. Simultaneously, the constitutive relation during the whole loading process was deduced in terms of scratch approach, and the deformation mechanism of carburized layer was discussed from a novel viewpoint.

The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-11-2019-0489/

This paper aims to propose a semi-analytical model to investigate the elastic-plastic contact between fractal rough surfaces. Parametric studies have been performed to analyze the dependencies between the contact properties and the scale-independent fractal parameters.

A modified two-variable Weierstrass-Mandelbrot function has been used to build the geometrical model of rough surfaces. The computation program was developed using software MATLAB R2015a. The results have been qualitatively validated by the existing theoretical and experimental results in the literature.

In most cases, a nonlinear relation between the load and the displacement of the rigid plane is found. Only under the condition of larger loads, an approximate linear relation can be seen for great D and small G values. (D: fractal dimension and G: fractal roughness).

The contact model of the cylindrical joints (conformal contact) with radial clearance is constructed by using the fractal theory and the Kogut-Etsion elastic-plastic contact model, which includes purely elastic, elastic-plastic and fully plastic contacts. The present method can generate a more reliable calculation result as compared with the Hertz contact model and a higher calculation efficiency as compared with the finite element method for the conformal contact problem.