scholarly journals Influence of Loading History and Soil Type on the Normal Contact Behavior of Natural Sand Grain-Elastomer Composite Interfaces

Polymers ◽  
2021 ◽  
Vol 13 (11) ◽  
pp. 1830
Author(s):  
Yu Tian ◽  
Sathwik S. Kasyap ◽  
Kostas Senetakis
Keyword(s):  
Normal Load ◽  
Contact Stiffness ◽  
Rigid Bodies ◽  
Dissipated Energy ◽  
Natural Sand ◽  
Normal Contact ◽  
Contact Behavior ◽  
Plastic Energy ◽  
Geological Materials ◽  
Soft Interfaces

Recycled rubber in granulated form is a promising geosynthetic material to be used in geotechnical/geo-environmental engineering and infrastructure projects, and it is typically mixed with natural soils/aggregates. However, the complex interactions of grains between geological materials (considered as rigid bodies) and granulated rubber (considered as soft bodies) have not been investigated systematically. These interactions are expected to have a significant influence on the bulk strength, deformation characteristics, and stiffness of binary materials. In the present study, micromechanical-based experiments are performed applying cyclic loading tests investigating the normal contact behavior of rigid–soft interfaces. Three different geological materials were used as “rigid” grains, which have different origins and surface textures. Granulated rubber was used as a “soft” grain simulant; this material has viscoelastic behavior and consists of waste automobile tires. Ten cycles of loading–unloading were applied without and with preloading (i.e., applying a greater normal load in the first cycle compared with the consecutive cycles). The data analysis showed that the composite sand–rubber interfaces had significantly reduced plastic displacements, and their behavior was more homogenized compared with that of the pure sand grain contacts. For pure sand grain contacts, their behavior was heavily dependent on the surface roughness and the presence of natural coating, leading, especially for weathered grains, to very high plastic energy fractions and significant plastic displacements. The behavior of the rigid–soft interfaces was dominated by the rubber grain, and the results showed significant differences in terms of elastic and plastic fractions of displacement and dissipated energy compared with those of rigid interfaces. Additional analysis was performed quantifying the normal contact stiffness, and the Hertz model was implemented in some of the rigid and rigid–soft interfaces.

Analysis and Research on Fractal Model of Normal Contact Stiffness of Joint Interfaces

2011 ◽  
Vol 328-330 ◽  
pp. 336-345
Author(s):  
Guo Sheng Lan ◽  
Xue Liang Zhang ◽  
Hong Qin Ding ◽  
Shu Hua Wen ◽  
Zhong Yang Zhang
Keyword(s):  
Numerical Simulation ◽  
Fractal Dimension ◽  
Normal Load ◽  
Contact Stiffness ◽  
Fractal Model ◽  
Normal Contact ◽  
Fractal Models ◽  
Normal Contact Stiffness

Through the analysis and research on three fractal models of normal contact stiffness of joint interfaces, the differences between them can be found. Furthermore, numerical simulation was carried out to obtain the complicated nonlinear relations between normal contact stiffness and the normal load. The results show that the normal contact stiffness increases with the normal load, decreases with G but complicatedly varies with D. According to different fractal dimension, we can chose an appropriate one among the three fractal models of normal contact stiffness of joint interfaces when describing normal contact stiffness of joint interfaces.

A Contact Model for Nonlinear Forced Response Prediction of Turbine Blades: Calculation Techniques and Experimental Comparison

2008 ◽  
Author(s):  
Christian M. Firrone ◽  
Marco Allara ◽  
Muzio M. Gola
Keyword(s):  
Normal Load ◽  
Contact Stiffness ◽  
Turbine Blades ◽  
Harmonic Balance Method ◽  
Forced Response ◽  
Contact Forces ◽  
Contact Model ◽  
Experimental Comparison ◽  
Normal Contact ◽  
Contact Models

Dry friction damping produced by sliding surfaces is commonly used to reduce vibration amplitude of blade arrays in turbo-machinery. The dynamic behavior of turbine components is significantly affected by the forces acting at their contact interfaces. In order to perform accurate dynamic analysis of these components, contact models must be included in the numerical solvers. This paper presents a novel approach to compute the contact stiffness of cylindrical contacts, analytical and based on the continuous contact mechanics. This is done in order to overcome the known difficulties in simultaneously adjusting the values of both tangential and normal contact stiffness experimentally. Monotonic loading curves and hysteresis cycles of contact forces vs. relative displacement are evaluated as a function of the main contact parameters (i.e. the contact geometry, the material properties and the contact normal load). The new contact model is compared with other contact models already presented in literature in order to show advantages and limitations. The contact model is integrated in a numerical solver, based on the Harmonic Balance Method (HBM), for the calculation of the forced response of turbine components with friction contacts, in particular underplatform dampers. Results from the nonlinear numerical simulations are compared with those from validation experiments.

scholarly journals Linear relationship of normal and tangential contact stiffness with load

2020 ◽  
Vol 476 (2243) ◽  
pp. 20200329
Author(s):  
K. S. Parel ◽  
R. J. Paynter ◽  
D. Nowell
Keyword(s):  
Surface Roughness ◽  
Linear Relationship ◽  
Normal Load ◽  
Contact Stiffness ◽  
Roughness Parameter ◽  
Image Correlation ◽  
Tangential Load ◽  
Normal Contact ◽  
Tangential Contact ◽  
Normal Contact Stiffness

Measurements with digital image correlation of normal and tangential contact stiffness for ground Ti-6Al-4V interfaces suggest a linear relationship between normal contact stiffness and normal load and a linear relationship between tangential contact stiffness and tangential load. The normal contact stiffness is observed approximately to be inversely proportional to an equivalent surface roughness parameter, defined for two surfaces in contact. The ratio of the tangential contact stiffness to the normal contact stiffness at the start of tangential loading is seen to be given approximately by the Mindlin ratio. A simple empirical model is proposed to estimate both the normal and tangential contact stiffness at different loads for a ground Ti-6Al-4V interface, on the basis of the equivalent surface roughness and the coefficient of friction.

Forced Response of Bladed Disks in Cyclic Symmetry With Underplatform Dampers

2006 ◽  
Author(s):  
Stefano Zucca ◽  
Juan Borrajo ◽  
Muzio M. Gola
Keyword(s):  
Contact Stiffness ◽  
Harmonic Balance Method ◽  
Rigid Bodies ◽  
Forced Response ◽  
Numerical Code ◽  
Algebraic Equations ◽  
Bladed Disks ◽  
Disk Model ◽  
Normal Contact ◽  
Linear Algebraic Equations

In this paper a methodology for forced response calculation of bladed disks with underplatform dampers is described. The FE disk model, supposed to be cyclically symmetric, is reduced by means of Component Mode Synthesis and then DOFs lying at interfaces are further reduced by means of interface modes. Underplatform dampers are modeled as rigid bodies translating both in the radial and in the tangential direction of the engine. Contacts between blade platforms and damper are simulated by means of contact elements characterized by both tangential and normal contact stiffness, allowing partial separation of contact surfaces. Differential equilibrium equations are turned in non-linear algebraic equations by means of the Harmonic Balance Method (HBM). The methodology is implemented in a numerical code for forced response calculation of frictionally damped bladed disks. Numerical calculations are performed to evaluate the effectiveness of both the reduced order model and the underplatform model in simulating the dynamic behavior of bladed disks in presence of underplatform dampers.

scholarly journals Influences of Morphology Parameters on the Contact Behavior of a Steel Interface

2020 ◽  
Vol 12 (01) ◽  
pp. 2050009
Author(s):  
L. F. Fan ◽  
L. Zhao ◽  
X. M. Liu
Keyword(s):  
Contact Stiffness ◽  
Normal Pressure ◽  
Mean Value ◽  
Mechanical Equipment ◽  
Normal Contact ◽  
Contact Behavior ◽  
Proposed Model ◽  
Normal Contact Stiffness ◽  
Rigid Smooth ◽  
Morphology Parameters

The surface roughness induced by geometric irregularities (asperities) has substantial influence on the contact stiffness, which further affects the working performance and service life of mechanical equipment. In this study, an elastic–plastic contact law between a sinusoidal asperity and a rigid smooth flat is first studied, which is then applied on a statistical model to simulate the contact behavior of a pair of 18CrMo4 steel surfaces to investigate the influences of morphology parameters on the contact stiffness. The analysis shows that smaller shape ratios [Formula: see text] and larger wavelengths [Formula: see text] induce larger normal contact stiffness [Formula: see text] for surfaces with identical roughness, wherein the roughness is defined by the mean value of asperity heights [Formula: see text] and the standard deviation of asperity heights [Formula: see text]. The normal contact stiffness increases as [Formula: see text] decreases under the same loading conditions, while the normal contact stiffness increases as [Formula: see text] decreases for surfaces with a fixed [Formula: see text]. Besides, the normal pressure and normal contact stiffness derived from the proposed contact model are validated. The results demonstrate the potential of the proposed model in contact design due to its ability of establishing the relations between the normal contact stiffness and surface morphology parameters.

Numerical Analysis of Normal Contact Stiffness of Rough Surfaces

2016 ◽  
Vol 846 ◽  
pp. 300-305
Author(s):  
Chong Pu Zhai ◽  
Yi Xiang Gan ◽  
Dorian Hanaor
Keyword(s):  
Rough Surface ◽  
Rough Surfaces ◽  
Normal Load ◽  
Contact Stiffness ◽  
Surface Characterisation ◽  
Small Surface ◽  
Normal Contact ◽  
Contact Behaviour ◽  
Normal Contact Stiffness ◽  
Stress Dependent

A numerical model was proposed to investigate the contact behaviour of a solid with a rough surface squeezed against a rigid flat plane. We considered simulated hierarchical surface structures as well as scanned surface data obtained by the profilometry of isotropically roughened specimens. The simulated and treated surfaces were characterised using statistical and fractal parameters. The evolution of contact stiffness under increasing normal compression was analysed through the total truncated area at varying heights, in order to relate contact mechanics to different surface parameters employed for surface characterisation. For a relatively small surface interference, the predicted stress-dependent normal contact stiffness of both scanned and simulated surfaces is in good agreement with experimental observation from nanoindentation tests, revealing a power-law function of the normal load, with the exponent of this relationship closely depending on the fractal dimension of rough surfaces. The numerical results show that the amplitude of a fractal rough surface mainly contributes to the magnitude of the contact stiffness at a given normal load.

scholarly journals Critical thresholds for mode-coupling instability in viscoelastic sliding contacts

2021 ◽  
Author(s):  
Antonio Papangelo ◽  
Carmine Putignano ◽  
Norbert Hoffmann
Keyword(s):  
Shear Strength ◽  
Mode Coupling ◽  
Degrees Of Freedom ◽  
Normal Load ◽  
Contact Stiffness ◽  
System Stability ◽  
Shear Stresses ◽  
Sliding Contacts ◽  
Normal Contact ◽  
Mode Coupling Instability

AbstractMode-coupling instabilities are known to trigger self-excited vibrations in sliding contacts. Here, the conditions for mode-coupling (or “flutter”) instability in the contact between a spherical oscillator and a moving viscoelastic substrate are studied. The work extends the classical 2-Degrees-Of-Freedom conveyor belt model and accounts for viscoelastic dissipation in the substrate, adhesive friction at the interface and nonlinear normal contact stiffness as derived from numerical simulations based on a boundary element method capable of accounting for linear viscoelastic effects. The linear stability boundaries are analytically estimated in the limits of very low and very high substrate velocity, while in the intermediate range of velocity the eigenvalue problem is solved numerically. It is shown how the system stability depends on externally imposed parameters, such as the substrate velocity and the normal load applied, and on contact parameters such as the interfacial shear strength $$\tau _{0}$$ τ 0 and the viscoelastic friction coefficient. In particular, for a given substrate velocity, there exist a critical shear strength $$\tau _{0,crit}$$ τ 0 , c r i t and normal load $$F_{n,crit}$$ F n , c r i t , which trigger mode-coupling instability: for shear stresses larger than $$\tau _{0,crit}$$ τ 0 , c r i t or normal load smaller than $$F_{n,crit}$$ F n , c r i t , self-excited vibrations have to be expected.

A multi-scale stiffness fractal model of joint interfaces

2021 ◽  
pp. 81-95
Author(s):  
Jingfang Shen ◽  
◽  
Sijie Cheng ◽  
Siyan Wang ◽  
Wenwei Liu ◽  
...  
Keyword(s):  
Contact Mechanics ◽  
Normal Load ◽  
Contact Stiffness ◽  
Roughness Parameter ◽  
Numerical Control ◽  
Joint Interface ◽  
Normal Contact ◽  
Multi Scale ◽  
Stiffness Model ◽  
Fractal Roughness

Stiffness characterization of mechanical interfaces is quite crucial for the analysis of several tribological behaviors. The stiffness of different machine tools varies greatly, particularly for computer numerical control machine. Therefore, this research aims at providing an assessment of influence factors for stiffness of joint interfaces theoretically. Based on fractal roughness parameters independent of scale and contact mechanics theory, the contact area of joint interface is studied, and the multi-scale normal contact stiffness model and multi-scale tangential contact stiffness model are proposed. Meanwhile, the problem of the deformation of any contact asperity is considered as three separate regimes. The laws of area-displacement and force-displacement under elastic-plastic regime are established. The transition which is in the deformation mechanism of asperity from elastic to plastic is consistent with classical contact mechanics. The analysis of numerical calculation results indicates the approximate linear relation among dimensionless normal load and key parameters. Moreover, these key parameters have been divided into two main categories for the multiscale model of joint interfaces, one is fractal parameters such as fractal dimension D and fractal roughness parameter G, and the other is interfacial parameters. In addition, tangential load and friction factor are two important factors to the tangential stiffness.

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