Complex Contact Conditions Research Articles

Increasing the productivity and quality of flute grinding processes through the use of layered grinding wheels

Due to the increasing relevance of resource efficiency, the production of cutting tools is exposed to increasing demands in regard to productivity and quality. Flute grinding is of particular significance within the various grinding operations used in tool manufacturing. Apart from the rake face, the flute grinding process determines the quality of the cutting edges. However, the grinding wheels typically used for flute grinding are not designed to take the complex contact conditions of this process into account. This paper presents a method for designing application-oriented grinding wheels to improve the productivity and the quality of grinding processes. Firstly, a model is presented which is used to simulate the contact conditions. The results show the significance of the grinding wheel edge in flute grinding. Based on that, grinding wheels with different layers over its width were developed to compensate the varying and complex contact conditions. To verify this approach technological experiments were carried out.

Continued Experimental Study on the Friction Contact between a Labyrinth Seal Fin and a Honeycomb Stator: Slanted Position

Labyrinth seals are a state-of-the-art sealing technology to prevent and control leakage flows at rotor–stator interfaces in turbomachinery. Higher pressure ratios and the economical use of cooling air require small clearances, which lead to potential rubbing events. The use of honeycomb liners allows for minimal leakage by tolerating rub events to a certain extent. A previous study within an EU project investigated the complex contact conditions of honeycomb liners, with the idealized contact of a seal fin and a single parallel metal foil representing the honeycomb double foil section. In the present work, the results for the slanted foil position are shown and compared to the previous results. The variation of rub velocity, incursion speed, incursion rate, and seal geometry in a test rig allows for the identification of the influence on contact forces, temperatures, and wear. For the slanted position, significantly lower friction temperatures are observed, leading to a higher ratio of abrasive wear. Overall, the rub test results demonstrate strong interactions between the contact forces, friction temperatures, and wear.

Multiaxial Fatigue Life Calculation Model for Engineering Components in Rolling-Sliding Contact

Number of important engineering components and elements such as gears, rollers, bearings operate in conditions of rolling-sliding contact loading. Determination of fatigue lives of such components and elements is very important for engineering practice but remains quite chalenging task due to complex states of stress and strain in the material in the vicinity of contact (multiaxiality, non-proportionality, rotation of principal axes, mean compressive stress) as well as complex contact conditions such as loading amplitude, complex geometry of bodies in contact, type of lubrication, value of coefficient of friction, etc. Proposed fatigue life calculation model for cases of rolling-sliding contact is based on critical plane approach in the form of Fatemi-Socie crack initiation criterion. Developed model was implemented in the case of gears teeth flanks in mesh and compared with results and fatigue lives of gears reported in literature. Good agreement was determined confirming validity of developed model. Further advantage of presented approach and developed model is obtained information on critical location(s) and critical plane(s) orientation which can subsequently be used for estimation of crack shapes in initial phases of their growth and later damage type into which they can be expected to develop.

A Novel DEM Approach to Simulate Block Propagation on Forested Slopes

In order to model rockfall on forested slopes, we developed a trajectory rockfall model based on the discrete element method (DEM). This model is able to take the complex mechanical processes at work during an impact into account (large deformations, complex contact conditions) and can explicitly simulate block/soil, block/tree contacts as well as contacts between neighbouring trees. In this paper, we describe the DEM model developed and we use it to assess the protective effect of different types of forest. In addition, we compared it with a more classical rockfall simulation model. The results highlight that forests can significantly reduce rockfall hazard and that the spatial structure of coppice forests has to be taken into account in rockfall simulations in order to avoid overestimating the protective role of these forest structures against rockfall hazard. In addition, the protective role of the forests is mainly influenced by the basal area. Finally, the advantages and limitations of the DEM model were compared with classical rockfall modelling approaches.

Modeling and Analysis of Contact Conditions during NC-Form Grinding of Cutting Edges

Due to increasing demands on cutting tools, cutting edge preparation is of high priority because of its influence on the tool life. Current cutting edge preparation processes are mostly limited to generating simple roundings on the cutting edge. Multi-axis high precision form grinding processes offer great potential to generate defined cutting edge microgeometries. Knowledge about the relation between grinding strategy and material removal rate can achieve improved work results with regard to higher precision of shape and dimensional accuracy as well as enhanced cutting edge quality. Therefore, a kinematic-geometric model was developed in order to analyze the complex contact conditions during grinding cutting edge microgeometries by using a simulation approach based on the intersection of geometric bodies. The subsequent grinding tests largely validated the utilized simulation approach.

Seismic performance of Transverse Steel Damper seismic system for long span bridges

To provide seismic resistance of long span bridges in transverse direction, fixed bearings are often installed between girders and piers (or towers). Although the fixed bearings and substructures can be designed extraordinarily strong to resist the design seismic loads, they may still be vulnerable when the design seismic loads are exceeded. To address this issue, this paper proposes a novel seismic system, which combines Transverse Steel Dampers (TSDs) with conventional sliding bearings, and is named the TSD seismic system. A TSD consists of several triangular steel plates outfitted with steel hemispheres at their upper vertices. The steel hemispheres not only allow free movements of the superstructures with respect to the piers in the longitudinal direction, but also provide reliable load paths in the transverse direction. Quasi-static tests have been conducted to investigate seismic behaviors of the TSD using two scaled and two prototype specimens. Test results show that the TSD has excellent performance in energy dissipation, large displacements, and synchronization of triangular plates under complex contact conditions. The load-displacement constitutive model of the TSD has been established using a bilinear model in ABAQUS, followed by a design method for the TSD seismic system. A 620m long-span cable-stayed bridge was selected for a case study of the TSD seismic system. Ground motions recorded at various site conditions were used as seismic inputs. Numerical results show that: (1) the TSD seismic system can achieve a desired balance of transverse seismic displacements and forces, which is not the case when a sliding bearing system (without TSDs) or a fixed bearing system is used; (2) TSDs contribute to most of the energy dissipation capacity of a TSD seismic system while the contribution of sliding bearings is negligible; and (3) the proposed TSD seismic system, compared with a sliding system, tends to be less sensitive to seismic input properties, such as peak ground accelerations and site conditions.

Numerical Modelling of AlSi7 Tubular Components Flowformed at Elevated Temperature

In small batch manufacturing, flowforming may represent an optimal semi-finishing process for axisymmetric parts, due to its versatility, the reduced material waste, the good geometrical tolerances as well as the improvement of the mechanical characteristics it allows to attain. However, the main limiting factor often lies in the lack of knowledge for the process design, which implies expensive industrial trials often based on trial-and-error approaches. Due to these reasons Finite Element (FE) numerical simulation can provide a significant help in the design and management of the process, but its application is still facing relevant issues, mainly linked to: (i) the complex contact conditions between tooling and part, (ii) the high computation effort due to the 3D geometry rotating at high speed, and (iii) the complex strain paths that the material undergoes.The paper presents an optimized FE model of the flowforming process of AlSi7 alloy tubular components carried out at elevated temperature. An implicit solution scheme and an arbitrary Lagrangian-Eulerian meshing was adopted, while the constitutive parameters of the material model were calibrated on the basis of experimental compression tests carried out in the same thermo-mechanical conditions of the industrial reference process. The influence of the main process parameters, namely thickness reduction, feed rate and mandrel rotation speed were investigated and an algorithm for parametric process charts derivation was finally proposed.

Extended Calculation Model for Generating Gear Grinding Processes

Generally, hard finishing is the final step in manufacturing cylindrical gears. The most established processes for hard finishing are continuous generation grinding and discontinuous profile grinding [1]. Despite the wide industrial application of the continuous generation grinding process, only few scientific investigations exist. One possible reason for this are the complex contact conditions between tool and gear flank. Modelling the complex contact conditions between grinding worm and gear to calculate cutting forces, characteristic values as well as micro- and macroscopic gear geometry are the topics of this paper. The approaches are introduced and results for validation are presented and discussed.

Finite element analysis of spiral strands with different shapes subjected to axial loads

In this paper a new mathematical geometric model of spiral one or two-layered oval wire strands are proposed and an accurate computational two-layered oval strand 3D solid model, which is used for a finite element analysis, is presented. The three dimensional curve geometry of wires axes in the individual layers of the oval strand consists of straight linear and helical segments. The present geometric model fully considers the spatial configuration of individual wires in the right and left hand lay strand. Derived geometric equations were used for the generation of accurate 3D geometric and computational models for different types of strands. This study develops 3D finite element models of two-layer spiral round, triangular and oval strands subjected to axial loads using ABAQUS/Explicit software. Accurate modelling and understanding of their mechanical behaviour is complicated due to the complex contact interactions and conditions that exist between individual spirally wound wires. Comparisons of predicted responses for the strands with different shapes and constructions are presented. Resultant stress and/or deformation behaviours are discussed.

Approach for the Calculation of Cutting Forces in Generating Gear Grinding

One of the main challenges in generating gear grinding is the determination of cutting forces due to their significant influence on the dynamics of the grinding process. Thus, optimizing the cutting forces can lead to an increased quality of ground gears and a minimized wear behavior of the grinding worm. Currently, the knowledge of the generating grinding process is limited and research is based mostly on empirical studies. A theoretical model which help to predict the cutting forces is missing.This paper presents an initial approach for calculating the complex contact conditions in generating gear grinding as well as cutting forces and key values to characterize the process. This approach gains more and more importance especially for large module gears, to reduce manufacturing costs. By means of the calculated forces, the manufacturing process can be optimized and the quality of the manufactured gear can be increased.

A comprehensive method for joint wear prediction in planar mechanical systems with clearances considering complex contact conditions

A comprehensive method to predict wear in planar mechanical systems with clearance joints is presented and discussed in this paper. This method consists of a system dynamic analysis and a joint wear prediction. As the size and shape of the clearance are dictated by wear and evolve with the dynamic response of the system, the contact between the journal and bearing could be conformal or non-conformal, which makes the contact conditions in clearance joints quite complicated. Therefore a modified contact force model is employed to evaluate the joint reaction force in this study. As the nonlinear stiffness coefficient is related to the physical and geometrical properties of contact bodies and varies with the deformation, this contact force model is applicable to different contact conditions between the journal and bearing. Furthermore, based on the Archards wear model, the amount of wear can be quantified in the joint. And the geometry is updated to reflect the evolving contact boundary. Then, the wear process and the contact force model are integrated into the motion equations of the system to perform coupled iterative analyses between system dynamic response and joint wear prediction. In addition, a slider-crank mechanism is simulated as an example to demonstrate efficiency of the proposed method and to carry out a parametric study on mechanical systems considering joint wear. The influence of clearance size and driving power are discussed and compared respectively. The index of concordance is introduced to quantify contributions of contact pressure and sliding distance to wear rate under different types of journal motion. This study could help to predict joint wear in mechanical systems with clearances and optimize mechanisms in design.

The finite element modeling of spiral ropes

Accurate understanding the behavior of spiral rope is complicated due to their complex geometry and complex contact conditions between the wires. This study proposed the finite element models of spiral ropes subjected to tensile loads. The parametric equations developed in this paper were implemented for geometric modeling of ropes. The 3D geometric models with different twisting manner, equal diameters of wires were generated in details by using Pro/ENGINEER software. The results of the present finite element analysis were on an acceptable level of accuracy as compared with those of theoretical and experimental data. Further development is ongoing to analysis the equivalent stresses induced by twisting manner of cables. The twisting manner of wires was important to spiral ropes in the three wire layers and the outer twisting manner of wires should be contrary to that of the second layer, no matter what is the first twisting manner of wires.

Modelling the kinetics of a triple junction

The grain structure in a one phase system involves grain boundaries (surfaces), three-grain junctions (lines) and four-grain junctions (points). A certain Gibbs energy and mobility can be assigned to each object. System evolution, driven by a decrease in the total Gibbs energy, occurs by migration of objects constrained by rather complex contact conditions. A system with cylindrical symmetry is assumed, where three grain boundaries with different mobilities and different specific Gibbs energies are in contact at a triple junction line of given mobility. The equations of evolution of the system are derived by means of the thermodynamic extremal principle. New general contact conditions at the triple junction are derived, including the mobilities of all objects and the energies, contact angles and curvatures of the grain boundaries. Special contact conditions are also provided for the cases where the triple junction mobility is infinite and/or in the case of one of the grain boundaries having zero mobility. The model is demonstrated by several examples.

Full 3D finite element modelling of spiral strand cables

Spiral strand cables are widely used in lightweight cable-supported structures such as sports stadia and bridges. Accurate understanding of their mechanical behaviour is complicated by their complex geometry and the complex contact conditions that exist between the many individual spirally wound wires. This study develops full 3D elasto-plastic finite element (FE) models of the multi-layer spiral strand cables subjected to quasi-static axial loading using LS-DYNA. A novel procedure to generate their complex geometry and FE meshes was devised and two cables with different diameters and numbers of wires were modelled in detail. The predicted axial load–axial strain curves and failure loads were in good agreement with experimental data.

Semi-Lagrangian reproducing kernel particle method for fragment-impact problems

Fragment-impact problems exhibit excessive material distortion and complex contact conditions that pose considerable challenges in mesh based numerical methods such as the finite element method (FEM). A semi-Lagrangian reproducing kernel particle method (RKPM) is proposed for fragment-impact modeling to alleviate mesh distortion difficulties associated with the Lagrangian FEM and to minimize the convective transport effect in the Eulerian or Arbitrary Lagrangian Eulerian FEM. A stabilized non-conforming nodal integration with boundary correction for the semi-Lagrangian RKPM is also proposed. Under the framework of semi-Lagrangian RKPM, a kernel contact algorithm is introduced to address multi-body contact. Stability analysis shows that temporal stability of the kernel contact algorithm is related to the velocity gradient between two contacting bodies. The performance of the proposed methods is examined by numerical simulation of penetration processes.

Numerical simulation of woven fabric wrinkling

Fabric’s tendency to wrinkle is crucially important to the textile industry as it impacts on the visual appeal of apparels. Current methods of grading this characteristic are very subjective and inadequate. As such, a quantitative method for assessing fabric wrinkling is of the utmost importance for the textile community. To that end, this paper reports on a numerical study of the wrinkling behaviour of cotton‐ and polyester‐woven fabrics using the cylindre creux test. A fabric trellis shear test method was used in order to describe the viscoelastic behaviour of fabrics. Afterwards, an approach by means of continuous mechanics theory is suggested for numerical simulation of the wrinkle recovery of textile‐woven fabric. The numerical procedure used an explicit dynamic scheme for the quasi‐static problem involving complex nonlinear effects (complex contact conditions). To characterise these coined numeric wrinkles, a state analysis of the normal vectors to the fabric surface was considered.

A comparison of implicit and explicit natural element methods in large strains problems: Application to soft biological tissues modeling

The natural element method (NEM) is one of the members of the large family of meshless methods, with clear advantages over the finite element method (FEM) in problems involving large mesh distortions or complex geometries where the design of the mesh is costly. These problems are found in many applications like, for instance, simulation of biological structures involving soft tissues, such as, articular joints. One additional advantage of NEM is that it can be easily coupled with finite elements and implemented into any FE framework, including well-known commercial packages. NEM as most other spatial approximation approaches can be applied to evolution problems in two types of time (or pseudo-time) integration schemes, namely implicit and explicit. However, the NEM explicit version has neither been implemented nor sufficiently analyzed, so a comparative study of those two types of NEM time integration schemes is still missing. The main aim of this paper is to discuss issues related to NEM accuracy and stability in its explicit version, and problems related to its implementation into an explicit FE commercial code. Finally, a comparative study addressing the main properties, advantages and disadvantages of both types of NE schemes, implicit and explicit, is presented. Several examples of application are discussed including aspects where NEM is competitive with FEM including modeling of human articular joints like the knee. Explicit NEM allows achieving accurate results for high distortions and complex contact conditions although constraints on time step still are a major drawback and comparable to those known in finite elements to keep stability and accuracy despite the less NEM sensitivity to mesh distortion.

Dynamics of a Siped Tire Tread Block—Experiment and Simulation

Abstract Within the contact zone between tire and road all normal and tangential forces have to be transmitted. The tread block is the only tire component which is in direct contact to the pavement and therefore of special interest. The rolling process of a tire can be seen as a chronology of single contact events between tread block and road surface, whereas the contact situation in detail is usually unknown. The surface texture of the pavement comprises a large range of surface wavelengths which leads to a small area of real contact and to complex contact conditions. Under braking and acceleration procedures sliding friction occurs within the footprint especially at the trailing area of the contact zone. The tangential forces strongly depend on the contact conditions, e.g., surface texture, sliding velocity, normal contact pressure, temperature, tread block geometry, and existence of a lubrication film. An intermediate layer not only simply lowers the friction coefficient but also the whole contact situation changes. This effect is considerably existent for siped tire tread blocks which react in a different manner compared to nonsiped tread blocks. Within this publication the dynamics of siped tread blocks in contact are analyzed and a mechanical model will be presented to explain the observed phenomena. The simulation results are verified by experiments.

Freestanding block overturning fragilities: Numerical simulation and experimental validation

AbstractThe overturning fragilities of symmetric and asymmetric freestanding blocks, ranging in height from 0.54 to 3.6 m and with height‐to‐width ratios ranging from 2.1 to 6.6, are determined numerically. A probabilistic formulation regularizes the overturning responses when exposed to earthquake‐like random‐vibration waveforms. The peak amplitude of the forcing excitation (peak ground acceleration or PGA) is parameterized as a function of the block size, block shape, overturning probability, and either the PGA normalized peak ground velocity (PGV/PGA), spectral acceleration at 1 s (Sa(1)/PGA), or spectral acceleration at 2 s (Sa(2)/PGA). These later intensity measures are correlated with the duration of the predominant acceleration pulse. The overturning fragilities are compared with shake table experiments using blocks ranging in height from ∼0.2 to 1.2 m and with height‐to‐width ratios ranging from ∼2 to 10. Excitations utilized in the shake table experiments include recordings of the 1979 Imperial Valley, 1985 Michoacan, 1999 Duzce, 1999 Chi‐Chi, and 2002 Denali Earthquakes along with synthetic waveforms. The overturning fragilities accurately represent the overturning responses of blocks with simple basal contact conditions. Objects with multiple rocking points, such as precariously balanced rocks, are more fragile than predicted. Nondestructive tilting tests are used to account for blocks with complex basal contact conditions, demonstrating that these blocks overturn similarly to more slender blocks with simple contact conditions. Copyright © 2008 John Wiley & Sons, Ltd.

Toward large scale F.E. computation of hot forging process using iterative solvers, parallel computation and multigrid algorithms

AbstractThe industrial simulation code Forge3® is devoted to three‐dimensional metal forming applications. This finite element software is based on an implicit approach. It is able to carry out the large deformations of viscoplastic incompressible materials with unilateral contact conditions. The finite element discretization is based on a stable mixed velocity–pressure formulation and tetrahedral unstructured meshes. Central to the Newton iterations dealing with the non‐linearities, a preconditioned conjugate residual method (PCR) is used. The parallel version of the code uses an SPMD programming model and several results on complex applications have been published. In order to reduce the CPU time computation, a new solver has been developed which is based on multigrid theory. A detailed presentation of the different elements of the method is given: the geometrical approach based on embedded meshes, the direct resolution of the velocity–pressure system, the use of PCR method as an original smoother and for solving the coarse problem, the full multigrid method and the required preconditioning by an incomplete Cholesky factorization for problems with complex contact conditions. By considering different forging cases, the theoretical properties of the multigrid method are numerically verified, optimizations of the solver are presented and finally, the results obtained on several industrial problems are given, showing the efficiency of the new solver that provides speed‐up larger than 5. Copyright © 2001 John Wiley & Sons, Ltd.