Wedge Contact Research Articles

Experimental investigation of fatigue for one way power transmission clutches using accelerated life tests

One way clutch (OWC) has emerged as one of the most vital devices used in heavy industries to safeguard the machines running with prime movers. It acts as a safety device to restrict the motion in the reverse direction. OWC also transmits the torque in one direction using wedge contact developed at the highly localized stress regions. The work presented consists of the development of a test bench specifically designed to simulate one way torque transmission of OWC for estimating the fatigue life based on the accelerated load tests. Accelerated load tests are performed to increase the severity within a short testing period. The microstructure disorder of the material is one the prime reasons for scattering in fatigue lives of identical batches of specimens. Therefore, several experimental tests are performed at distinct elevated load levels for different sizes of OWC. The effect of contact pressure and contact angle on fatigue lives are investigated. The fatigue life results obtained using accelerated testing correlate well with the Lundberg-Palmgren model. The load-life relationship follows the Weibull distribution. The failed ramp geometries are studied using a scanning electron microscope (SEM) to understand the governing failure mechanism for OWC.

Irreducible representation of surface distributions and Piola transformation of external loads sustainable by third gradient continua

In this paper Piola transformations are found that relate the Eulerian and Lagrangian external loads which third gradient continua can sustain. As shown by Gabrio Piola and Paul Germain, the most effective postulation scheme in mechanics is based on the principle of virtual work and therefore continuum mechanics must be mathematically founded based on the theory of distributions and on differential geometry. Using the principle of virtual work, the set of admissible external loads sustainable by third gradient continua is seen to include: i) volume force density, ii) surface density of contact force, iii) surface density of contact double force, iv) surface density of contact triple force, v) line density of edge contact forces, vi) line density of contact edge double forces and vii) contact forces concentrated on wedge points. Following the nomenclature introduced by Paul Germain, forces are dual in virtual work of virtual displacements, surface and line double forces are dual of the derivatives of virtual displacements in the normal direction(s) of the surfaces and edges constituting the boundary of the continuum, and surface triple forces are dual of the second normal derivatives of virtual displacements. Volume and surface forces transform as in first gradient Cauchy continua. Moreover we find that: a) the virtual work expended by Eulerian surface triple force, when transformed into the Lagrangian description, must be represented as the work expended by all the kinds of external Lagrangian loads listed in i)-vii); b) Eulerian surface double force transforms into Lagrangian surface double force, surface contact force and edge contact line force; c) Eulerian edge contact line double force transforms into Lagrangian edge contact line double forces, edge line forces and point concentrated wedge forces; d) Eulerian edge and wedge contact line forces transforms into their Lagrangian counterpart only. The Piola transformation formulas deduced in this paper depend on the first, second and third gradients of placement. The presented results allow for the formulation of well-posed boundary condition problems for third gradient continua in the Lagrangian description, and are relevant in computational mechanics. In view of the obtained Piola transformation formulas, the concept of dead loads needs to be modified. We believe to have given an example of how the Mechanics in the French Style, as developed on the ideas by D’Alembert and Lagrange, is still a fertile tool of invention.

Tolerance analysis of wedge assembly considering impact force

This paper proposes a dynamic theory based tolerance analysis method for wedge assembly. Wedge is a class of contact features with a small contact angle such as cone and triangle. The impact usually applied in wedge assembly to tighten the structure. The force and times of the impact could affect the assembly dimension and must be considered in tolerance analysis. The wedge contact is formulated as the dynamic model, which the model could be solved to obtain the variation length. Then the variation could be compensated to the tolerance model or dimension chain. The proposed method is used in a case of wedge belt assembly for verification.

Correlation between Properties of Oxide Compounds Formed on Contact Surfaces of Cutting Tools and Cutting Tool Wear Resistance

The article describes the influence of the acidity degree of oxide compounds formed on contact surfaces of carbide cutting tools type P on their wear resistance when cutting materials causing intensive diffusion wear. It was found out that when the acidity degree of surface film oxides formed on the cutting wedge contact surfaces decreases, wear resistance of cutting tools tends to grow.

Edge effect factor affecting the tribological properties in water of protrusion surface textures on stainless steel

Surface textures have been demonstrated to have a positive effect on the friction reduction. However, sharp edges of the normally textured patterns usually cause stress concentration and severe wear during sliding, especially for non-conformal contacting pairs. In this study, protrusion-type textures were fabricated at different area ratios on stainless steel discs and edge profiling was performed for the protrusions, and friction tests were conducted in water to investigate the tribological properties. The results show that the friction was reduced markedly by edge profiling due to the formation of wedge contact and improvement of lubricant supply to the contact interfaces under low load. Under high load, severe wear destroyed the wedge contact resulting in high friction as those of the normally textured pairs. High area ratio exhibited better friction reduction effect. The stress analysis via ANSYS indicated that much high stress concentrated at the edges of the protrusions and could be reduced significantly by edge profiling.

A simplified approach to solve quasi-statically moving load problems of elastica using end loaded elastica solution

Elastica problems with non-conservative moving forces are more complicated as compared to end loaded elastica problems. Established methods exist to solve an end loaded elastica problem. For solving a moving boundary problem , such methods need considerable modification or re-formulation. In this article, results of an end loaded elastica problem which is readily obtainable are used to solve two relatively involved moving boundary cases. The solution methodology involves a unique normalization procedure for the available elastic solution followed by few simple steps. One of the problems considered is three point bending of elastica with finite roller dimension. The other one being cantilever elastica under the action of wedge contact. Structural stiffening is observed in both the cases as a result of moving boundary condition as compared to when roller dimension is negligible or wedge makes only point contact. A structured approach may potentially originate from this kind of procedure to tackle more complicated moving boundary problems of elastica.

배관용 탄성접촉시일의 응력 및 변형거동에 관한 유한요소해석

본 논문에서는 배관을 연결하기 위해 사용한 탄성접촉시일의 밀봉접촉응력과 변형거동 특성을 다루고 있다. 본 연구에서 배관을 연결하기 위해 체결너트와 탄성접촉시일 사이에 가해진 밀봉압축 간섭량은 0.2~0.5mm이다. 탄성접촉시일을 압축하기 위한 밀봉 간섭량은 두 개의 배관을 하나의 너트로 체결하는 과정에 발생한다. FEM 해석결과에 의하면, 경사진 밀봉표면을 갖는 접촉모델 1의 접촉수직응력은 평행한 밀봉표면을 갖는 접촉모델 2의 접촉수직응력에 비해 1.5~1.75배나 높게 나타났다. 이것은 배관과 배관을 연결하는 밀봉접촉표면이 높은 밀봉압축응력을 얻을 수 있도록 하기 위해 쇄기형상의 접촉모드를 형성하는 것이 바람직함을 알 수 있다. This paper presents sealing contact stress and deformation behaviors of an elastomeric contact seal for a pipe connection. In this study, a pipe connection is used by a joint nut and an elastomeric contact seal with a sealing interference of 0.2~0.5mm. A sealing interference in which compresses an elastomeric contact seal is generated by fastening a joint nut between two pipes. The FEM computed results show that the contact normal stress of contact model 1 with an inclined sealing surface is 1.5~1.75 times high in compared with that of contact model 2 with a parallel sealing surface. This indicates that the sealing contact surface recommends a wedge contact mode between two pipe connections for a high sealing compression stress.

On the Use of a Driven Wedge Test to Acquire Dynamic Fracture Energies of Bonded Beam Specimens

A driven wedge test is used to characterize the mode I fracture resistance of adhesively bonded composite beam specimens over a range of crosshead rates up to 1 m/s. The shorter moment arms (between wedge contact and crack tip) significantly reduce inertial effects and stored energy in the debonded adherends, when compared with conventional means of testing double cantilever beam (DCB) specimens. This permitted collecting an order of magnitude more crack initiation events per specimen than could be obtained with end-loaded DCB specimens bonded with an epoxy exhibiting significant stick-slip behavior. The localized contact of the wedge with the adherends limits the amount of both elastic and kinetic energy, significantly reduces crack advance during slip events, and facilitates higher resolution imaging of the fracture zone with high speed imaging. The method appears to work well under both quasi-static and high rate loading, consistently providing substantially more discrete fracture events for specimens exhibiting pronounced stick-slip failures. Deflections associated with beam transverse shear and root rotation for the shorter beams were not negligible, so simple beam theory was inadequate for obtaining qualitative fracture energies. Finite element analysis of the specimens, however, showed that fracture energies were in good agreement with values obtained from traditional DCB tests. The method holds promise for use in dynamic testing and for characterizing bonded or laminated materials exhibiting significant stick slip behavior, reducing the number of specimens required to characterize a sufficient number of fracture events.

Finite Element Modeling and Analysis of Friction Wedge Damping During Suspension Bounce Modes

A two-dimensional finite element model (2D FEM) has been developed to improve the modeling and understanding of the friction damping characteristics of freight bogie suspensions. The specific suspension considered utilizes friction dampers with constant preload force as are widely used in three-piece bogie wagons in Australia. Unlike simpler models commonly used in rail vehicle dynamics, the FE model developed can accommodate distributed normal forces across the wedge surfaces. The model was tested in bounce modes and compared with the normal equations used to model wedge friction forces, which treat the forces on the wedge as a static problem. The simulation results using the 2D FEM model showed that the friction damping force is not constant and changes when the suspension is in motion. It was also shown that the force changes magnitude during the loading and unloading situations. The factors, which affect the change in friction force, are the friction characteristics on wedge contact surfaces, the direction and change in tangent force on wedge angular surface, the elastic deformation of the wedge, the wedge relative movement, and the wedge structure arrangement. The FE model assumptions are investigated and insights on wedge friction and creepage discussed.

Finite Element Modeling and Analysis of Friction-Wedge Dampers During Suspension Pitch Modes

A two-dimensional finite element model has been developed to investigate the friction damping characteristics of suspensions with so-called “constant-damping” friction wedges widely used in three-piece bogie wagons in Australia. The model was used to simulate the suspension during pitch modes. The simulation results show that the friction damping force in the suspension pitch modes is dependent on the friction conditions on the wedge contact surfaces, wagon speed, and the wedge shape and elasticity effects including the stuck state. The suspension pitch movements of a three-piece bogie with dry friction wedges can cause wedge rotation and partial separation of wedge contacting surfaces, which seriously affects the wedge friction damping effectiveness. The curved shape of wedge angular surface can significantly improve the friction damping characteristics of three-piece bogie suspensions.

Dislocation Nucleation and Pileup under a Wedge Contact at Nanoscale

Indentation responses of crystalline materials have been found to be radically different at micrometer and nanometer scales. The latter is usually thought to be controlled by the nucleation of dislocations. To explore this physical process, a dislocation mechanics study is performed to determine the conditions for the nucleation of a finite number of dislocations under a two‐dimensional wedge indenter, using the Rice‐Thomson nucleation criterion. The configurational force on the dislocation consists of the applied force, the image force, and the interaction force between dislocations. Dislocations reach equilibrium positions when the total driving force equals the effective Peierls stress, giving a set of nonlinear equations that can be solved using the Newton‐Raphson method. When the apex angle of the wedge indenter increases, the critical contact size for dislocation nucleation increases rapidly, indicating that dislocation multiplication near a blunt wedge tip is extremely difficult. This geometric dependence agrees well with experimental findings.

Mechanics of edge effects on frictionlesscontacts

This paper investigates edge effects on frictionless contacts. Edge phenomena are simulated by considering elastic contact near the edge of a wedge with varying wedge angle. Previous two-dimensional analysis is first reviewed and discussed to develop an understanding of the mechics when edges are in contact. Three-dimensional wedge contact is then considered. The integral equation for rigid indentation of an incompressible wedge derived by the authors is presently modified to study indentation by a dissimilar elastic body. The analysis will focus on evaluating the effect of proximity to the wedge apex on contact stress, contact area geometry and contact compliance. The effect of varying wedge angles and elastic mismatch (encompassed by the Dundurs constant α) will also be quantified. The conditions under which elastic mismatch results in a singular contact stress when contact extends to the wedge apex, derived by Dundurs and Lee, will be discussed and used to interpret the present numerical results.

A Surface Layer Model for Thin Film Lubrication

A rheological model has been developed which can be applied to thin film lubrication. It is known that great differences are seen between behavior in thin (molecular scale) films and in bulk (macroscopic) rheological measurements. There appear to be layers near the surface in which viscosity is increased by many orders of magnitude. The model contains three material property parameters, i.e., the conventional viscosity, the thickness of the surface layer, and a surface layer viscosity. A modified Reynolds equation is developed. Behavior of correction factors to Reynolds' equation and to the shear stress are shown. Results are computed for a one-dimensional converging wedge contact. The effect of increasing the layer thickness parameter is to increase the load and reduce the friction coefficient. Increasing the surface layer vicosity also tends to increase the load and reduce the friction coefficient.

A Porous Media Model for Thin Film Lubrication

A rheological model has been developed which can be applied to boundary lubrication. The model is applicable to thin films in which the molecular length scale is the same order as the film thickness. The micro structure is simulated by porous layers attached to the contact surfaces. The model contains three material properties: (1) viscosity, (2) the thickness of the porous layer, and (3) a porosity parameter. A modified Reynolds equation is developed. Behavior in two types of contacts is calculated: squeezing flow between crossed cylinders (Chan and Horn’s, 1985 drainage experiment) and a one-dimensional converging wedge contact. The effect of the layer thickness parameter is to increase the load and reduce the friction coefficient. Increasing the porosity parameter value tends to reduce the magnitude of the load increase.

Supersonic cleavage of an elastic strip

The problem of the longitudinal cleavage of an infinite elastic strip by a thin smooth rigid wedge is examined. The wedge moves symmetrically with respect to the faces of the strip at a constant supersonic velocity. Formulas are obtained that govern the stresses in the domain of wedge contact with the elastic medium and the displacements of points of the slit edge outside the contact domain for certain relationships between the parameters of the problem. Conditions are set up for which separation of the medium from the wedge surface occurs. Unlike the case of wedge motion at a speed less than the Rayleigh velocity /1, 2/, when a crack is formed ahead of the wedge, no crack is formed when the wedge moves at supersonic speed. The contact problem of the motion of a rigid stamp with a flat smooth base at a supersonic speed over the surface of an elastic strip was investigated /3/ in a similar formulation.

Enrichment of trace elements in garnet amphibolites from a paleo-subduction zone: Catalina Schist, southern California

The abundance, P- T stability, solubility, and element-partitioning behavior of minerals such as rutile, garnet, sphene, apatite, zircon, zoisite, and allanite are critical variables in models for mass transfer from the slab to the mantle wedge in deep regions of subduction zones. The influence of these minerals on the composition of subduction-related magmas has been inferred (and disputed) from inverse modelling of the geochemistry of island-arc basalt, or by experiment. Although direct samples of the dehydration + partial-melting region of a mature subduction zone have not been reported from subduction complexes, garnet amphibolites from melanges of circumpacific and Caribbean blueschist terranes reflect high T (>600°C) conditions in shallower regions. Such rocks record geochemical processes that affected deep-seated, high- T portions of paleo-subduction zones. In the Catalina Schist, a subduction-zone metamorphic terrane of southern California, metasomatized and migmatitic garnet amphibolites occur as blocks in a matrix of meta-ultramafic rocks. This mafic and ultramafic complex may represent either slab-derived material accreted to the mantle wedge of a nascent subduction zone or a portion of a shear zone closely related to the slab-mantle wedge contact, or both. The trace-element geochemistry of the complex and the distribution of trace elements among the minerals of garnet amphibolites were studied by INAA, XRF, electron microprobe, and SEM. In order of increasing alteration from a probable metabasalt protolith, three common types of garnet amphibolite blocks in the Catalina Schist are: (1) non-migmatitic, clinopyroxene-bearing blocks, which are compositionally similar to MORB that has lost an albite component; (2) garnet-amphibolite blocks, which have rinds that reflect local interaction between metabasite, metaperidotite, and fluid; and (3) migmatites that are extremely enriched in Th, HFSE, LREE, and other trace elements. These trace-element enrichments are mineralogically controlled by rutile, garnet, sphene, apatite, zircon, zoisite, and allanite. Alkali and alkaline earth elements are much less enriched in the solid assemblage, and thus appear to be decoupled from the other elements in the inferred metasomatic process(es). The compositions of migmatitic garnet amphibolite blocks seem to complement that of “average” island-arc tholeiite. Trace-element metasomatism reflects fluid-solid, rather than melt-solid, interaction. The metasomatic effects indicate that H 2O-rich fluid, perhaps with a significant component of Na-Al silicate and alkalis, carried Th, U, Sr, REE, and HFSE. Fractionations of LREE in migmatites resemble those of migmatitic metasedimentary rocks underlying the mafic and ultramafic complex. “Exotic” LREE deposited in allanite in migmatites could have been derived from fluids in equilibrium with subducted sediment. If the paleo-subduction zone represented by the mafic and ultramafic complex of the Catalina Schist had continued its thermal and fluid evolution, a selvage of similarly enriched rocks might have been generated along the slab-mantle wedge contact between ~30 and 85 km depth. Rocks affected by “subduction-zone metasomatism,” although rarely recognized at the surface, could be volumetrically significant products of the initiation of subduction and may prove to be geochemical probes of convergent margins that approach the significance of xenoliths in the study of other magmatic environments.