Contact Stress Distribution Research Articles

Simplified analysis of cantilever diaphragm walls in cohesive soils

In this paper, a method is presented for a simplified analysis of cantilever diaphragm walls in cohesive soils under undrained and drained conditions. A rectilinear distribution of the net contact stresses that are not completely predetermined by the limit state is assumed at the soil-wall interface, consistently with the mechanism usually experienced by these structures. Simple equations are derived to readily calculate the contact stress distribution on the wall and the associated internal forces in the ultimate and service conditions. Moreover, these equations require few parameters as input data. Comparisons are carried out with a limit equilibrium method commonly used in design to show the usefulness of the proposed method for practical purposes.

Mechanical performance of hexagonal multi-cell concrete-filled steel tubular (CFST) stub columns under axial compression

Multi-cell concrete-filled steel tubular (CFST) column is a type of composite members developing from conventional CFST columns. Featuring greater cross-sectional dimensions and the use of internal webs to separate inner concrete into smaller isolated cells, multi-cell CFST columns have been used in super high-rise buildings recently as the main vertical load bearing members. However, existing research on CFST members is mainly focused on conventional single-cell CFST members. To fill this research gap, this paper numerically investigates the mechanical performance of hexagonal multi-cell CFST stub columns under axial compression. A finite element analysis (FEA) model was initially established to simulate the mechanical performance of hexagonal multi-cell CFST columns. The FEA model was validated against existing experimental data. The mechanical performance of the multi-cell CFST columns were analysed, including the full-range load versus deformation relationships, the stress distributions of the main components and the distribution of contact stress on each concrete cell. A parametric study was then conducted to investigate the sensitivity of various geometric and material parameters on the compressive behaviour of multi-cell CFST columns. Finally, analytical formulae were derived to predict the axial compressive ultimate strength of hexagonal multi-cell CFST columns. The methods were found to be acceptable with reasonably good accuracy.

Continuous and discontinuous contact problem of a functionally graded layer pressed by a rigid cylindrical punch

In this study, the fundamental formulation for the continuous and discontinuous contact problems of a functionally graded (FG) layer lying on a rigid substrate are obtained without using superposition technique. The general expressions for the stresses and the displacements are derived in the presence of body forces using elasticity theory and Fourier integral transforms. As an application, the continuous and discontinuous contact problems of FG layer indented by a rigid cylindrical punch are considered. The contact problems are solved under the boundary conditions and the plane contact problems are reduced to the singular integral equations both in the case of continuous and discontinuous contact. The singular integral equations are solved numerically using Gauss-Chebychev integration formula and an iterative scheme is employed to obtain the correct contact width and critical load that satisfy the related conditions. Numerical results for critical load Pcr, initial separation distance, the separation region in the discontinuous contact, contact width under the punch, contact stress distributions between the layer-punch and the layer-substrate are given.

Indentation of a plastically deforming metal crystal with a self-affine rigid surface: A dislocation dynamics study

Although indentation of elastic bodies by self-affine rough indenters has been studied extensively, little attention has so far been devoted to plasticity. This is mostly because modeling plasticity as well as contact with a self-affine rough surface is computationally quite challenging. Here, we succeed in achieving this goal by using Green's function dislocation dynamics, which allows to describe the self-affine rough surface using wavelengths spanning from 5 nm to 100μm. The aim of this work is to gain understanding in how plastic deformation affects the contact area, contact pressure and hardness, gap profile and subsurface stresses, while the roughness of the indenter is changed. Plastic deformation is found to be more pronounced for indenters with larger root-mean-square height and/or Hurst exponent, and to be size dependent. The latter means that it is not possible to scale observables, as typically done in elastic contact problems. Also, at a given indentation depth (interference) the contact area is smaller than for the corresponding elastic contact problem, but gap closure is more pronounced. Contact hardness is found to be much larger than what reported by classical plasticity studies. Primarily, this is caused by limited dislocation availability, for which the stiffness of the deforming crystal is in between that of a linear elastic and an elastic-perfectly plastic material. When calculating hardness and nominal contact pressure, including very small wavelength in the description of the surface is not necessary, because below a given wavelength the subsurface stresses become invariant to a further decrease in true contact area. This is true for both elastic and plastic materials. Considering small wavelengths is instead required to capture accurately roughening and contact stress distribution.

Theoretical calculation of the instantaneous friction-induced energy losses in arbitrarily excited axisymmetric mechanical contact systems

In this paper, we present the theoretical formula for calculating a friction-induced energy loss in a mechanical contact system consisting of two convex axisymmetric bodies subject to arbitrarily varying oblique loading. Non-flat contact geometry engenders a particular regime, partial slip, in which weakly compressed areas of the contact zone slip, while strongly compressed ones stick. Mechanical energy is transformed into heat only in the slip area in which two field characteristics should be calculated: the local infinitesimal slip distance distribution and shear stress. Their product equals the spatial distribution of the energy loss or heat source density, while the integration over the slip zone produces the global energy loss. The energetic characteristics are obtained in a general situation. In the proposed method, energy losses can be calculated at any time during a loading protocol, in the general case of an arbitrary load expressed in terms of normal and tangential displacements. This is a step forward in comparison to more traditional approaches in contact mechanics allowing to calculate the energy loss per period in the case where the contact is excited by a single periodic input. In this work, the loading is limited to two dimensions: one normal and one tangential. Therefore, the tangential loading is colinear with the tangential displacement. All required contact characteristics, including displacement and stress distributions, are provided by the semi-analytical Method of Memory Diagrams (MMD) that has initially been developed to obtain memory-dependent solutions to the problem of frictional contact between axisymmetric profiles and has later been generalized for rough surfaces. Correspondingly, the proposed solution is exact for axisymmetric bodies and is approximately valid in the case of rough surfaces for which the energy loss per unit nominal area is calculated. The obtained theoretical results for energy dissipation are compared to analytical and numerical calculations for periodic and non-periodic loading situations, illustrating the potential of this method in realistic contact settings.

The sensitivity of contact stresses in the mandibular premolar region to the shape of Zirconia dental implant: A 3D finite element study

Abstract Background: Implant thread profile plays a vital role in magnitude and distribution of contact stresses at the implant-bone interface. The main goal of this study was to evaluate the biomechanical effects of four distinct thread profiles of a dental implant in the mandibular premolar region. Methods: The dental implant represented the biocompatible Zirconia material and the bone block was modelled as transversely isotropic and elastic material. Three-dimensional finite element simulations were conducted for four distinct thread profiles of a dental implant at 50%, 75%, and 100% osseointegration. An axial static load of 500 N was applied on the abutment surface to estimate the stresses acting within the bones surrounding the implant. Results: Regions of stress concentration were seen mostly along the mesiodistal direction compared to that in the buccolingual direction. The cortical bone close to the cervical region of the implant and the cortical bone next to the first thread of the implant experienced peak stress concentration. Increasing the degree of osseointegration resulted in increased von-Mises stresses on the implant-cortical transition region, the implant-cancellous transition region, the cortical bone, and the cancellous bone. Conclusion: The results show that the application of distinct thread profiles at different degrees of osseointegration had significant effect on the stresses distribution contours in the surrounding bony structure. Comparing all four thread profiles, a dental implant with V-thread profile induced lower values of von-Mises stresses and shear stresses on the implant-cortical transition region, implant-cancellous transition region, cortical bone, and cancellous bone.

Tyre–pavement contact stress distribution considering tyre types

Tyre–pavement contact stress distribution has a significant effect on mechanical responses in thin asphalt pavements and responses at near-surface of thick asphalt pavements. To achieve a more accurate tyre–pavement contact stress distribution considering tyre types, tyre loads and tyre inflation pressures for pavement design and analysis, three-dimensional (3D) finite element (FE) tyre–pavement models were developed. Two common tyre types (bias ply tyre and radial tyre) were considered in the models. Then, models were verified through the comparison between the predicted and measured tyre contact stresses. Excellent agreement between predicted and measured contact stresses was achieved. Then, the contact stress distributions between different tyres and pavement were analysed under different tyre loads and tyre inflation pressures combinations (nine working conditions). Results indicated that with the increase of vertical load, the location of maximum contact stress between bias ply tyre and pavement changed from inside to outside of tread while the maximum contact stress between radial tyre and pavement always appeared in the centre of tread. And under a same working condition, the maximum contact stress between radial tyre and pavement was larger than that between bias ply tyre and pavement. Besides, in the lateral direction, the variation range of the contact stresses under different ribs of a bias ply tyre was less than that of a radial tyre.

Smooth Contact of a Semiinfinite Punch with Rounded Edge and an Elastic Strip

We consider a problem of contact of an elastic strip with a semiinfinite punch with rounded edge indented into one face of the strip, while the other face of the strip is fixed. Friction forces in the contact zone are neglected. By the Wiener–Hopf method, we obtain the exact analytic solution of the problem. The distributions of contact stresses, the stresses inside the strip and along its fixed face, and the normal displacements of points of a part of the load-free face of the strip are determined. We construct the isochores and determine the position of the point at which the maximum values of the principal shear stresses are attained.

Transient behaviour of grouted connections of offshore wind turbines subject to ship impact

Grouted connections are a critical structural element of monopile-supported offshore wind turbines (OWTs), connecting turbine towers with foundation piles. Due to engineering requirements, they are normally installed at the mean water level (MWL), leading to high risk of ship collisions. In this study, transient response and damage analysis were performed on the grouted connections of monopile OWT when subjected to ship impacts. Taking into account the sandwich construction of the grouted connection of the OWT and the non-linear behaviour of the structure materials, a finite element model of a vessel of 2000-ton displacement collision with a 5 MW monopile OWT was developed using explicit finite element code LS-DYNA. The ship was assumed to strike head-on and at the middle of the grouted connection. Characteristics of the collision system in terms of energy, velocity, impact force and the response of the ship and the grouted connection were analysed. Internal contact forces, stress and effective plastic strain distribution of the grouted connection were discussed. Four phases of the collision process were identified: initial collision, motion towards maximum OWT deflection, towards vessel-OWT separation, and after separation. The ship collision response and damage of the grouted connection were considerably influenced by the strain rate effect of the structure materials. Collided by a ship, even at a low velocity of 2 m/s, the grouted connection for monopile OWT could suffer heavy or major damage. The current analysis sheds light on the dynamic response of grouted connections of monopile OWTs to ship impact. It lays a solid foundation for future analysis on the design of grouted connections of OWTs.

Study and Application of Structure Failure Simulation of Fracture Tracing by Manifold Method

By improving the simulation method of contact and contact forces, the function of tracing the propagation of Multi-cracks, the Numerical Manifold Method proposed by Genhua- Shi is developed which can simulate the discontinuity of block system, the tensile or shear failure, and the crack propagation. The least-square method to calculate SIF is presented in this paper for broken cracks. Also the calculation method of contact stiffness matrix is modified. For edge- to-edge contact, correct distribution of contact stress is guaranteed, namely the contact stiffness and contact length make direct proportion. The structure failure problems inducing by crack propagation in different engineering domains are simulated. It shows that the method put forward and the program developed in this paper can effectively simulate the structure failure and can give scientific suggestion for engineering supporting.

Thermomechanical capacity of wheel treads at stop braking: A parametric study

During tread braking, the treads of railway wheels are subjected to a complex loading due to combined rolling contact and thermally induced stresses. In revenue traffic the running mode of the train varies and the operational parameters will influence the life of the wheels. To prevent excessive damage, it is therefore important to understand at which operational conditions wheel damage becomes unacceptable. The current study aims to find limits for tread braking with respect to the influence of thermal stresses on rolling contact fatigue (RCF) of the wheel tread when subjected to repeated stop braking. A parametric study, using 3D FE simulations and involving operational parameters such as axle load, maximum vehicle speed, deceleration, brake block material and initial wheel temperature, is carried out for a new wheel with an S-shaped web. Additional analyses investigate impact from wheel geometry by studying a wheel with a straight web and a wheel with a thin (worn) rim. The effects of simultaneous thermal loading from wheel–block frictional contact during braking and mechanical loading, due to the traversing wheel–rail rolling contact, are studied in an uncoupled thermomechanical analysis. In the wheel–rail contact simulations, frictional rolling contact stress distributions induced by braking are accounted for. Interfacial shear stresses and partial slip are also included in the model. A temperature-dependent elastoplastic model is utilised to characterise changes in material behaviour during braking. In the vicinity of the wheel tread, damage evolutions for the studied brake load cases are evaluated. The results show that high tread temperatures, in particular temperatures above 450 °C, have a strong detrimental influence on the RCF formation and, hence, also on the thermomechanical capacity of the wheel. On the other hand, it is found that for braking temperatures between 300 °C and 375 °C, the fatigue resistance is increased due to strain hardening effects. In addition, the parametric study points towards actual braking load cases that can give such temperatures in terms of initial speeds, axle loads, etcetera. Specifically, the study shows that the train axle load, that controls the normal wheel–rail contact force, has a substantial impact on the life of the wheel treads. Wheels having straight webs and S-shaped wheel web exhibit the same fatigue life of their treads, whereas a reduction in wheel rim thickness promotes ratchetting due to increased flexural stresses from the mechanical wheel–rail contact loading.

Sealant behavior of gasketed segmental joints in shield tunnels: An experimental and numerical study

Segmental joints are vulnerable parts of the lining structure in precast shield tunnels, both from the structural (lower stiffness compared to main segments) and non-structural (potential water leakage points) perspectives. Previous works have focused on the structural behavior of segmental joints rather than the sealant behavior. This paper presents a combined experimental and computational study to investigate the sealant and mechanical behavior of the gasketed joints used for a tunnel prototype, i.e., Nanjing Weisan Road Tunnel, which was recently built using a tunnel-boring machine below the Yangtze River, whose 72-m water table head is the highest in China. A total of 7 gasket profiles were tested using a testing apparatus developed in-house. The objective of the joint waterproof tests was to quantify the water leakage pressure (or joint waterproof capacity) versus the joint opening relationships under various joint offset scenarios. The objective of the gasket-in-groove mechanical tests was to quantify the force versus deformation relationships. Finite element models of the gaskets were developed and verified against the test results. A supplementary parametric study was conducted to investigate the effect of joint opening, joint offset and gasket hardness on the detailed distribution of contact stress of the gasket interface. Combining the experimentally recorded and the numerically computed data presented in this paper, a simplified design formula that quantifies the relationship between the contact stress of the gasket and the water pressure was proposed, and its rationality was validated against the available test data in the literature.

Calculation of Contact Stresses during Titanium Alloy Cutting

The paper presents data about distribution of contact stresses on a rake surface and flank-land of a cutter in free orthogonal turning of a disk made from a titanium alloy (Ti-6Al-2Mo-2Cr). On the cutting edge of the bar blade, there is a normal force Nρ, directed perpendicularly to a transient surface, with a large magnitude of specific linear force qN r= 182.6 N/mm, but the tangential force on the cutting edge Fρis equal to zero. On the rake surface, there are uniformly distributed shear contact stresses with very small magnitude of τ ≈ const ≈ 25 MPa, irrespective of feed rate, which speaks about plastic character of the contact on the rake surface. The greatest normal contact stress on the rake surface σmax≈ 1009 MPa, irrespective of feed rate. The greatest magnitude of normal contact stresses on the flank surface chamfer near the cutting edge σh max= 3400-2200 MPa confirms the hypothesis about recovery of a transient surface sag after separation of a formed element of a chip, and explains increased wear of the cutting tool on the flank surface at initial time. Normal σhand shear τhcontact stresses on the flank surface chamfer are essentially diminish with a distance from the cutting edge. It explains working ability of the cutting tool even at very large wear on the flank surface (hf> 3 mm). Our experimental data allows calculating the components of cutting force and contact stresses on the rake and flank surfaces of cutting tools during titanium alloy (Ti-6Al-2Mo-2Cr) machining.

Passive Intermodulation of Contact Nonlinearity on Microwave Connectors

For the passive intermodulation (PIM) problem of nonlinear contact on microwave connectors, an effective method is presented to improve the computational accuracy of PIM. First of all, the contact stress distribution on contact surface is analyzed by finite-element method based on the Weierstrass-Mandelbrot model. The contact stress and real area of contact are evaluated under different loading conditions. Then, the electrical parameters of physical effects of nonlinear contact are derived based on the electric contact theory and the physical effects of metal-metal microcontact. Finally, the nonlinear I-V relation is established from the microcontact equivalent circuit, and the third-order PIM power level generated by contact nonlinearity is revealed in analytic form. The analytic results are verified by the PIM test experiments. This work provides a novel way for PIM calculation of rough surface contact.

Research of Contact Stresses Distribution on Plunge-Cutting into a Steel Workpiece

The paper presents the distribution of contact stresses on the flank land of a cutter during steel turning (Fe-0.4C-1Cr) at the initial time of cutting. Plunge-cutting into a steel workpiece by the whole length of the cutting tool edge features almost twofold short-term increase of in cutting force components in comparison with stable cutting. Such increase is absent, if the feed rate exceeds 0.34 mm/rev and the cut depth exceeds 2 mm. This is explained by sagging of the cutting surface under the influence of the dead zone in the area of the cutting edge, which moves before the cutting tool and reduces the contact interaction of the flank surface chamfer with the workpiece. The contact stresses on the flank surface chamfer increase with the distance from the cutting edge, which is explained by recovered cutting surface sag, conditioned by the action of the dead zone in the cutting edge area. This increase accelerates with the reduction in the feed rate. Normal contact stresses increase more quickly on a flank-land at a distance from the cutting edge of more than 0.8 mm, which is explained by recovering of a transient surface sag, and explains the increase in the probability of cutting wedge destruction when the length of flank-land wear exceeds 1.2 mm.

Effect of contact path on the mixed lubrication performance, friction and contact fatigue in spiral bevel gears

Abstract The contact path in spiral bevel gears may have significant effect on the lubrication breakdown and surface failure. However, available study mainly focus on the influence of contact path on the contact stress distribution with the assumptions of dry contact and smooth surface. In reality, these gears are lubricated and the surfaces are quite rough with three-dimensional (3D) topography. The present study aims to systematically investigate the effect of contact path on the mixed lubrication characteristics, friction and contact fatigue in spiral bevel gears with the consideration of surface roughness. A comprehensive analysis for gearing geometry, kinematics, and contact load with different contact path affected by assembling parameters is executed based on the loaded tooth contact analysis (LTCA). The corresponding lubrication characteristics, friction coefficient and flash temperature, as well as the fatigue life are conducted in a wide range of operating condition based on a recently developed mixed EHL model for spiral bevel gears. Obtained results reveal that the contact path is vital to lubrication performance, efficiency improvements and fatigue prevention. In particular, the contact path nearby toe of gear flank appears to be a weak path due to the smaller film thickness, larger friction coefficient, higher flash temperature and lower relative fatigue life.

Study on the Leakage Mechanism of Cone Sealing Structure in Metal Tube

Cone seal structure is widely used in metal tube connection of industrial equipment and ground vehicle. In vibration environment, the leakage failure of cone seal occur frequently, which will affect the function and reliability of the product directly. In this paper, the contact stress for typical cone sealing structure in low pressure metal tube under vibration loading is analyzed and the mechanism of liquid leakage failure is discussed using the finite element numerical method. Results show that the circumferential contact stress distribution is uneven on the interface of cone sealing structure under the cyclic load introduced by local vibration. The contact stress is significantly lower than the initial pretension stress in some areas, which will result in the leakage failure of cone sealing structure.

THE ANALYSIS OF THE INFLUENCE OF STRESS DISTRIBUTION ON WEAR PROFILE IN LUBRICATED SLIDING CONTACT OF UHMW-PE VS TITANIUM Ti-13Nb-13Zr ALLOY

Metal – polymer sliding contacts are a typical combination in industry and medicine. For decades such a set of materials has been the primary choice in human joints endoprosthetic technology. In this paper tribological issues of are presented from a research on the potential for practical use of Ti-13Nb-13Zr/UHMW-PE couple for orthopedic endoprosthesis. In tests on simplified models it is critically important to carefully select geometry of contact, load and velocity magnitudes and profiles to the later interpretation of results. In case of organic polymers interacting with metallic components the problem is even more prominent, than in the case of all metal systems because of great differences in the modulus of elasticity between the specimens in contact. High local loading can cause excessive heat generation and accelerated loss in polymer’s strength induced by thermal plastification. The process may not be manifested in the course of the experiment in any way detectable and might compromise the accuracy of wear measurement. In the case of the presented research an analysis has been performed to evaluate the observed wear profile of UHMW-PE with respect to non-uniform distribution of contact stress. A simulation was run with the use of FEM to evaluate the contact conditions between the titanium alloy and UHMW-PE specimens and the results were confronted with the wear profiles. Interesting similarities were discovered yielding useful information on the fundamentals of the wear in and for future research on similar systems.

Improvement of dynamical and tribological properties of friction systems by introducing parallel-grooved structures in elastic damping components

This paper presents the influence of introducing elastic damping components having different parallel-grooved structures in friction systems. Experimental and numerical studies are conducted to evaluate the effects on the friction-induced vibration, and friction and wear. A number of parallel-grooves structures are designed and manufactured on damping components. The experiments are performed using a purpose-built experimental test bench. The effects of different damping components on the dynamical and tribological properties are estimated by comparing the dynamic vibration performance, and friction and wear characteristics of the contact interface. The experimental results show that the system with damping components could effectively suppress the friction-induced vibrations, and improve the wear characteristics. Consequently, this helps stabilize system, especially for the damping components having the structure of two parallel grooves. The contact stress distribution of pad surface and the deformations of different damping components are evaluated through numerical studies. The observations and explanations are supported by experimental results.

Taking into Account the Effect of Dual Wheels on the Behavior of Lateritic Gravelly Pavements

The representation in the three-dimensional space of the physical model symbolized by the application of the pairing of the wheels described by 2 disks with a radius of 0.125 m and a 0.375 m spacing has the advantage of more accurately simulating the loading. In most cases, the assumption of a uniform distribution of loading on the circular surface is considered. In order to determine the effect of dual wheels, this research proposes a new approach to the distribution of vertical contact stress in three-dimensional space with loading on the circular surface. This allowed evaluating the maximum deformation on the space described by the dual wheels. The results showed that vertical deformation is maximum at the center of each circular surface. The distribution of the vertical contact stress is non-uniform on the circular footprint and has a significant influence on the deformation of the pavement at the level of the bituminous layer. The impact assessment of the twinning reveals that the dual wheels load causes less damage than that of a single wheel. These results are obtained by means of a numerical simulation under Cast3M with a gravitational lateritic pavement.