Design Optimization of Ultra-Low Flying Head-Disk Interfaces Using an Improved Elastic-Plastic Rough Surface Model

2006 ◽  
Vol 128 (4) ◽  
pp. 801-810 ◽  
Author(s):  
Allison Y. Suh ◽  
Sung-Chang Lee ◽  
Andreas A. Polycarpou
Keyword(s):  
Rough Surface ◽  
Contact Pressure ◽  
Surface Model ◽  
Successful Implementation ◽  
Contact Conditions ◽  
Friction Forces ◽  
Interfacial Forces ◽  
Elastic Plastic ◽  
The Mean ◽  
Improved Model

Sub-5nm flying head-disk interfaces (HDIs) designed to attain extremely high areal recording densities of the order of Tbit∕in2 are susceptible to strong adhesive forces, which can lead to subsequent contact, bouncing vibration, and high friction. Accurate prediction of the relevant interfacial forces can help ensure successful implementation of ultra-low flying HDIs. In this study, an improved rough surface model is developed to estimate the adhesive, contact, and friction forces as well as the mean contact pressure relevant to sub-5nm HDIs. The improved model was applied to four different HDIs of varying roughness and contact conditions, and was compared to the sub-boundary lubrication rough surface model. It was found that the interfacial forces in HDIs undergoing primarily elastic-plastic and plastic contact are more accurately predicted with the improved model, while under predominantly elastic contact conditions, the two models give similar results. The improved model was then used to systematically investigate the effect of roughness parameters on the interfacial forces and mean contact pressure (response). The trends in the responses were investigated via a series of regression models using a full 33 factorial design. It was found that the adhesive and net normal interfacial forces increase with increasing mean radius R of asperities when the mean separation is small (≈0.5nm), i.e., pseudo-contacting interface, but it increases primarily with increasing root-mean-square (rms) surface height roughness between 2 and 4nm, i.e., pseudo-flying interface. Also, increasing rms roughness and decreasing R, increases the contact force and mean contact pressure, while the same design decreases the friction force. As the directions of optimization for minimizing the individual interfacial forces are not the same, simultaneous optimization is required for a successful ultra-low flying HDI design.

An Investigation on Elastic-Plastic Rolling Contact Over Rough Surfaces Using a 3-D Dynamic Finite Element Model

2008 ◽  
Author(s):  
Xin Zhao ◽  
Zili Li ◽  
Rolf Dollevoet
Keyword(s):  
Finite Element ◽  
Rough Surface ◽  
Rough Surfaces ◽  
Maximum Shear Stress ◽  
Rolling Contact ◽  
Fe Model ◽  
Stress Distributions ◽  
Friction Forces ◽  
Elastic Plastic ◽  
Dynamic Finite Element

A full-scale 3-D dynamic finite element (FE) model is created to solve the elastic-plastic wheel-rail rolling contact over rough surfaces under different friction forces. Both normal and tangential loads are applied properly. A bi-linear plastic material model is introduced and the real wheel and rail head geometries are simulated. The rolling of a drive wheel with full friction exploitation over a rough contact surface is analyzed in this paper. The stress distributions at the zone with rough surface are derived. From the results at a selected instant, it is found that roughness significantly increases the stress level of the surface layer. Furthermore, plasticity can greatly reduce stress peaks and change stress distributions. The maximum shear stress distribution at the rough surface is also analyzed to assess effects of roughness on fatigue crack initiation.

Acoustic estimation of deep sea floor nodule densities

Geophysics ◽  
1983 ◽  
Vol 48 (11) ◽  
pp. 1450-1452 ◽  
Author(s):  
Ivan Tolstoy
Keyword(s):  
Rough Surface ◽  
Acoustic Waves ◽  
Surface Model ◽  
Biot Theory ◽  
Simple Method ◽  
Small Bodies ◽  
Sea Floor ◽  
The Mean ◽  
Rigid Plane ◽  
Coherent Part

A particularly simple method of calculating sound scatter from planar distributions of small bodies was devised some years ago by Biot (1968) for a type of rough surface model pioneered by Twersky (1957) consisting essentially of spheroidal or hemispheroidal bumps on a rigid plane. The Biot theory has been generalized recently by Tolstoy (1979, 1980, 1981, 1982a, b) to scatterers of arbitrary shapes and impedance contrasts at interfaces between arbitrary fluids. It applies to the case [Formula: see text], (1) where k is the wavenumber, a the mean height of the scatterers, and h the spacing between their centers (Figure 1). The theory deals with the coherent part of the multiple scatter and predicts phenomena not adequately described by conventional stochastic models of rough surface scattering of acoustic waves, whose usefulness is restricted by the assumption that the slopes of the irregularities are everywhere small (Bass and Fuks, 1979; Wenzel, 1974; Kuperman, 1975).

A new elliptical microcontact model considering elastoplastic deformation

2018 ◽  
Vol 232 (11) ◽  
pp. 1352-1364 ◽  
Author(s):  
Yuqin Wen ◽  
Jinyuan Tang ◽  
Wei Zhou ◽  
Caichao Zhu
Keyword(s):  
Rough Surface ◽  
Contact Pressure ◽  
Elastoplastic Deformation ◽  
Height Distribution ◽  
New Model ◽  
Surface Contact ◽  
Calculation Results ◽  
The Mean ◽  
Rough Surface Contact ◽  
Change Curve

A new elliptical microcontact model considering elastoplastic deformation is proposed to overcome the shortcomings of the existing elastoplastic microcontact model. A new low-order interpolation function is used to describe the relationship between the normal deformation of asperity and the mean contact pressure in the elastoplastic deformation stage, and a smooth, continuous, monotonic change curve of the mean contact pressure is obtained. Then, the contact of rough surfaces is studied based on the new elastoplastic elliptical microcontact model and the height distribution of asperity. The calculated results are compared with those obtained from the existing rough surface contact models and the comparisons show that: (1) the change curve for the average contact pressure in the new model is smooth, continuous, and monotonic; (2) the calculation results of the new model are consistent with the numerical results based on the finite element method; (3) the new model is helpful to study the rough surface contact analysis of the elliptical micro-convex body.

scholarly journals Linear and Nonlinear Normal Interface Stiffness in Dry Rough Surface Contact Measured Using Longitudinal Ultrasonic Waves

2021 ◽  
Vol 11 (12) ◽  
pp. 5720
Author(s):  
Saeid Taghizadeh ◽  
Robert Sean Dwyer-Joyce
Keyword(s):  
Rough Surface ◽  
Contact Pressure ◽  
Ultrasonic Wave ◽  
Bulk Material ◽  
Nonlinear Differential Equations ◽  
Small Deformation ◽  
Ultrasonic Waves ◽  
Solid Contact ◽  
Interfacial Stiffness ◽  
Linear And Nonlinear

When two rough surfaces are loaded together contact occurs at asperity peaks. An interface of solid contact regions and air gaps is formed that is less stiff than the bulk material. The stiffness of a structure thus depends on the interface conditions; this is particularly critical when high stiffness is required, for example in precision systems such as machine tool spindles. The rough surface interface can be modelled as a distributed spring. For small deformation, the spring can be assumed to be linear; whilst for large deformations the spring gets stiffer as the amount of solid contact increases. One method to measure the spring stiffness, both the linear and nonlinear aspect, is by the reflection of ultrasound. An ultrasonic wave causes a perturbation of the contact and the reflection depends on the stiffness of the interface. In most conventional applications, the ultrasonic wave is low power, deformation is small and entirely elastic, and the linear stiffness is measured. However, if a high-powered ultrasonic wave is used, this changes the geometry of the contact and induces nonlinear response. In previous studies through transmission methods were used to measure the nonlinear interfacial stiffness. This approach is inconvenient for the study of machine elements where only one side of the interface is accessible. In this study a reflection method is undertaken, and the results are compared to existing experimental work with through transmission. The variation of both linear and nonlinear interfacial stiffnesses was measured as the nominal contact pressure was increased. In both cases interfacial stiffness was expressed as nonlinear differential equations and solved to deduce the contact pressure-relative surface approach relationships. The relationships derived from linear and nonlinear measurements were similar, indicating the validity of the presented methods.

scholarly journals Experimental Investigation of Fully Plastic Contact of a Sphere Against a Hard Flat

2005 ◽  
Vol 128 (2) ◽  
pp. 230-235 ◽  
Author(s):  
J. Jamari ◽  
D. J. Schipper
Keyword(s):  
Experimental Investigation ◽  
Contact Pressure ◽  
Contact Area ◽  
Measurement Method ◽  
Contact Load ◽  
Model Predictions ◽  
The Mean

In this paper we report the experimental investigation to evaluate the published models for the contact of a deformable sphere against a hard flat in the fully plastic contact regime. A new measurement method has been used to measure the contact area. The behavior of the mean contact pressure and the contact area as a function of the contact load are presented. Substantial differences are found between the measurements and the model predictions. A constant value of the mean contact pressure as the load increases is observed, however, the value is lower than the hardness, as often reported. The contact area is found to be a simple truncation of the sphere by a hard flat.

scholarly journals A Three-Dimensional Semianalytical Model for Elastic-Plastic Sliding Contacts

2007 ◽  
Vol 129 (4) ◽  
pp. 761-771 ◽  
Author(s):  
Daniel Nélias ◽  
Eduard Antaluca ◽  
Vincent Boucly ◽  
Spiridon Cretu
Keyword(s):  
Pressure Distribution ◽  
Contact Pressure ◽  
Computing Time ◽  
Three Dimensional ◽  
Gradient Methods ◽  
Reciprocal Theorem ◽  
Contact Pressure Distribution ◽  
Sliding Contacts ◽  
Elastic Plastic ◽  
Residual Strains

A three-dimensional numerical model based on a semianalytical method in the framework of small strains and small displacements is presented for solving an elastic-plastic contact with surface traction. A Coulomb’s law is assumed for the friction, as commonly used for sliding contacts. The effects of the contact pressure distribution and residual strain on the geometry of the contacting surfaces are derived from Betti’s reciprocal theorem with initial strain. The main advantage of this approach over the classical finite element method (FEM) is the computing time, which is reduced by several orders of magnitude. The contact problem, which is one of the most time-consuming procedures in the elastic-plastic algorithm, is obtained using a method based on the variational principle and accelerated by means of the discrete convolution fast Fourier transform (FFT) and conjugate gradient methods. The FFT technique is also involved in the calculation of internal strains and stresses. A return-mapping algorithm with an elastic predictor∕plastic corrector scheme and a von Mises criterion is used in the plasticity loop. The model is first validated by comparison with results obtained by the FEM. The effect of the friction coefficient on the contact pressure distribution, subsurface stress field, and residual strains is also presented and discussed.

Modeling Complex Contact Conditions and Their Effect on Blade Dynamics

2020 ◽  
Author(s):  
Chiara Gastaldi ◽  
Johann Gross ◽  
Maren Scheel ◽  
Teresa M. Berruti ◽  
Malte Krack
Keyword(s):  
Contact Pressure ◽  
Harmonic Balance Method ◽  
Structural Vibrations ◽  
Bladed Disks ◽  
Contact Conditions ◽  
Softening Behavior ◽  
Contact Models ◽  
Coulomb Friction Law ◽  
Fatigue Failures ◽  
Laboratory Demonstrator

Abstract Dry friction devices such as underplatform dampers are commonly included in turbine bladed disks designs to mitigate structural vibrations and avoid high cycle fatigue failures. The design of frictionally damped bladed disks requires adequate models to represent the friction contact. A widely used approach connects contact node pairs with normal and tangential springs and a Coulomb friction law. This simple model architecture is effective in capturing the softening behavior typically observed on frictionally damped structures subjected to increasing forcing levels. An unexpected hardening behavior was observed on the frequency response functions of two-blades-plus-damper system tested by the authors in a controlled laboratory environment. The reason behind this unexpected behavior will be carefully analyzed and linked to the damper kinematics and to the dependence of contact elasticity on the contact pressure. The inadequacy of contact models with constant spring values will be discussed and alternatives will be proposed. The importance of being able to represent complex contact conditions in order to effectively predict the system dynamics is shown here using a laboratory demonstrator, however its implications are relevant to any other case where large contact pressure variations are to be expected. The nonlinear steady state simulations of the blades-plus-damper system will be carried out using an in-house code exploiting the Multi-Harmonic Balance Method (MHBM) in combination with the Alternating Frequency Time (AFT) Method.

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