Rough Surface Normal Nanocontact Stiffness: Experimental Measurements and Rough Surface Contact Model Predictions

2017 ◽  
Vol 84 (3) ◽  
Author(s):  
Jungkyu Lee ◽  
Ali Beheshti ◽  
Andreas A. Polycarpou
Keyword(s):  
Thin Film ◽  
Rough Surface ◽  
Predictive Accuracy ◽  
Contact Stiffness ◽  
Flat Punch ◽  
Surface Contact ◽  
Contact Models ◽  
Rough Surface Contact ◽  
Contact Response ◽  
Good Agreement

This work presents experimental contact stiffness measurements for various thin films as well as homogenous materials through pressing a flat punch onto a nominally flat rough surface. These materials are typically used in micro/nano technological applications with thickness of the order of few nanometers. The experimental contact stiffness results are compared with predictions by different statistical rough surface contact models to assess their predictive accuracy for thin-film applications and, in addition, to get better insight to the physics of the contact. It is observed that rough surface contact models that account for asperity interaction show good agreement with the experimental results of the thin-layered specimens contact response. This indicates the importance of accounting for asperity interaction in surface roughness contact modeling of relatively smooth thin-film materials. It is verified that interfaces with compliant films on stiff substrates as well as homogeneous materials compare relatively well with statistical models accounting for asperity interactions.

Rough Surface Contact of Curved Conformal Surfaces: An Application to Rotor–Stator Rub

2016 ◽  
Vol 138 (4) ◽  
Author(s):  
Philip Varney ◽  
Itzhak Green
Keyword(s):  
Rough Surface ◽  
Contact Force ◽  
Contact Stiffness ◽  
Point Contact ◽  
Contact Model ◽  
Industrial Society ◽  
Real Surface ◽  
Linear Elastic ◽  
Surface Contact ◽  
Rough Surface Contact

Rotating machines and associated triboelements are ubiquitous in industrial society, playing a central role in power generation, transportation, and manufacturing. Unfortunately, these systems are susceptible to undesirable contact (i.e., rub) between the rotor and stator, which is both costly and dangerous. These adverse effects can be alleviated by properly applying accurate real-time diagnostics. The first step toward accurate diagnostics is developing rotor–stator rub models which appropriately emulate reality. Previous rotor–stator rub models disavow the contact physics by reducing the problem to a single esoteric linear contact stiffness occurring only at the point of maximum rotor radial deflection. Further, the contact stiffness is typically chosen arbitrarily, and as such provides no additional insight into the contacting surfaces. Here, a novel rotor–stator rub model is developed by treating the strongly conformal curved surfaces according to their actual nature: a collection of stochastically distributed asperities. Such an approach is advantageous in that it relies on real surface measurements to quantify the contact force rather than a heuristic choice of linear contact stiffness. Specifically, the elastoplastic Jackson–Green (JG) rough surface contact model is used to obtain the quasistatic contact force versus rotor radial deflection; differences and similarities in contact force between the linear elastic contact model (LECM) and JG model are discussed. Furthermore, the linear elastic model's point contact assumption is assessed and found to be inaccurate for systems with small clearances. Finally, to aid in computational efficiency in future rotordynamic simulation, a simple exponential curve fit is proposed to approximate the JG force–displacement relationship.

The Use of Ultrasound in the Investigation of Rough Surface Interfaces

2000 ◽  
Vol 123 (1) ◽  
pp. 8-16 ◽  
Author(s):  
R. S. Dwyer-Joyce ◽  
B. W. Drinkwater ◽  
A. M. Quinn
Keyword(s):  
Reflection Coefficient ◽  
Rough Surface ◽  
Incident Wave ◽  
Contact Stiffness ◽  
Repeated Loading ◽  
Asperity Contacts ◽  
Contact Models ◽  
Average Size ◽  
Rough Surface Contact ◽  
Effect Of Surface

The measurement of ultrasonic reflection has been used to study the contact between rough surfaces. An incomplete interface will reflect some proportion of an incident wave; this proportion is known as the reflection coefficient. If the wavelength is large compared with the width of the gaps in the plane of the interface then the reflection mechanism can be modeled by considering the interface as a spring. The proportion of the incident wave reflected (reflection coefficient) is then a function of the stiffness of the interface and the frequency of the ultrasonic wave. The sensitivity of the ultrasonic technique has been quantified using a simple model, from which the stiffness of individual gaps and contacts are calculated and their effect on the ultrasonically measured stiffness predicted. The reflection of ultrasound at a static interface between a rough, nominally flat aluminum plate and a rough, nominally flat hardened steel punch has been investigated. Plastic flow on first loading was evident, while repeated loading was largely elastic. However, subsequent cycles indicate a small amount of further plasticity and contact irreversibility. The effect of surface roughness on the resultant contact has also been investigated. A simple plastic contact model is described which allows prediction of the average size of the asperity contacts and their number. This model shows that the average size of the contacts remains constant over most of the loading whereas the number of contacts increases almost linearly. The contact stiffness has also been modeled with two well known elastic rough surface contact models. These models predicted a lower interface stiffness than was observed in the experiments. However they provide a useful way of interpreting the ultrasonically measured interface stiffness data.

Rotordynamic Analysis of Rotor–Stator Rub Using Rough Surface Contact

2016 ◽  
Vol 138 (2) ◽  
Author(s):  
Philip Varney ◽  
Itzhak Green
Keyword(s):  
Rough Surface ◽  
Contact Force ◽  
Bulk Material ◽  
Contact Stiffness ◽  
Contact Model ◽  
Real Surface ◽  
Time Step ◽  
Surface Contact ◽  
Orbit Analysis ◽  
Rough Surface Contact

Undesirable rotor–stator rub is frequently observed in rotordynamic systems, and has been the subject of many investigations. Most of these studies employ a simple piecewise-smooth linear-elastic contact model (LECM), where the rotor switches between noncontacting and contacting operation once the clearance is exceeded (various complications have been incorporated, though the essential model premises endure). Though useful as a first step, the LECM relies on an arcane contact stiffness estimate, and therefore does not emulate the actual contacting surfaces. Consequentially, the LECM fails to elucidate how real surface parameters influence contact severity and surface durability. This work develops a novel model for rotor–stator rub which is commensurate with reality by treating the surfaces as a collection of stochastically distributed asperities. Specifically, the elastoplastic Jackson–Green (JG) rough surface contact model is used to calculate the quasistatic contact force as a function of rotor displacement, where bulk material deformation and surface cumulative damage are ignored. A simple exponential fit of the contact force is proposed to reduce computational burden associated with evaluating the JG rough surface contact model at each simulation time step. The rotor's response using the LECM and JG rough surface contact model is compared via shaft speed bifurcations and orbit analysis. Significant differences are observed between the models, though some similarities exist for responses with few contacts per rotor revolution.

scholarly journals Evaluating Elastic-Plastic Wavy and Spherical Asperity-Based Statistical and Multi-Scale Rough Surface Contact Models with Deterministic Results

Materials ◽  
2021 ◽  
Vol 14 (14) ◽  
pp. 3864
Author(s):  
Nolan Ryan Chu ◽  
Robert L. Jackson ◽  
Xianzhang Wang ◽  
Arup Gangopadhyay ◽  
Hamed Ghaednia
Keyword(s):  
Contact Problem ◽  
Rough Surface ◽  
Computing Time ◽  
Multiscale Model ◽  
Deterministic Models ◽  
Elastic Plastic ◽  
Multi Scale ◽  
Surface Contact ◽  
Contact Models ◽  
Rough Surface Contact

The solution to an elastic-plastic rough surface contact problem can be applied to phenomena such as friction and contact resistance. Many different types of models have therefore been developed to solve rough surface contact. A deterministic approach may accurately describe the entire surface, but the computing time is too long for practical use. Thus, mathematically abbreviated models have been developed to describe rough surface contact. Many popular models employ a statistical methodology to solve the contact problem, and they borrow the solution for spherical or parabolic contact to represent individual asperities. However, it is believed that a sinusoidal geometry may be a more realistic asperity representation. This has been applied to a newer version of the stacked multiscale model and statistical models. While no single model can accurately describe every contact problem better than any other, this work aims to help establish guidelines that determine the best model to solve a rough surface contact problem by applying mathematical and deterministic models to two reference surfaces in contact with a rigid flat. The discrepancies and similarities form the basis of those guidelines.

An Improved Elastic Contact Model Accounting for Asperity Interaction and Bulk Substrate Deformation

2009 ◽  
Author(s):  
Jungkyu Lee ◽  
Chang-Dong Yeo ◽  
Andreas A. Polycarpou
Keyword(s):  
Rough Surface ◽  
Contact Stiffness ◽  
Elastic Half Space ◽  
Contact Model ◽  
Asperity Contact ◽  
Single Asperity ◽  
Surface Contact ◽  
In Series ◽  
Bulk Substrate ◽  
Rough Surface Contact

An improved rough surface contact model is proposed accounting for bulk substrate deformation and asperity interaction. The asperity contact stiffness is based on Hertzian solution for spherical contact, and the bulk substrate stiffness on the solution of Hertzian pressure on a circular region of the elastic half-space. The contact behavior of a single asperity composed of hemi-spherical asperity deformation as well as bulk substrate deformation is calculated by introducing the concept of spring-in-series. Based on the single asperity model, the contact stiffness for the rough surface is calculated including the effect of asperity interaction. Analytical simulation results using the proposed rough surface contact model were compared with the CEB model and experimental measurements.

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