scholarly journals A Simple Contact Mechanics Model for Highly Strained Aqueous Surface Gels

2021 ◽  
Author(s):  
A. L. Chau ◽  
M. K. Cavanaugh ◽  
Y.-T. Chen ◽  
A. A. Pitenis
Keyword(s):  
Simple Model ◽  
Contact Mechanics ◽  
Contact Lenses ◽  
Radius Of Curvature ◽  
Winkler Foundation ◽  
Surface Layers ◽  
Mechanics Model ◽  
Soft Surface ◽  
Simple Contact ◽  
Highly Strained

Abstract Background Soft, biological, and bio-inspired materials are often compositionally heterogeneous and structurally anisotropic, and they frequently feature graded or layered organizations. This design complexity enables exceptional ranges in properties and performance yet complicates a fundamental understanding of the contact mechanics. Recent studies of soft gel layers have relied on Hertzian or Winkler foundation (“bed-of-springs”) models to characterize the mechanics but have found neither satisfactory. Objective The contact mechanics of soft gel layers are not yet fully understood. The aim of this work is to develop a simple contact mechanics model tailored for compositionally-graded materials with soft surface layers under high strains and deformations. Methods Concepts from polymer physics, fluid draining, and Winkler foundation mechanics are combined to develop a simple contact mechanics model which relates the applied normal force to the probe radius of curvature, elastic modulus, and thickness of soft surface layers subjected to high strains. Results This simple model was evaluated with two examples of graded surface gel layers spanning multiple length-scales, including commercially available contact lenses and stratified hydrogels. The model captures the nonlinear contact mechanics of highly strained soft aqueous gel layers more closely than either Hertz or Winkler foundation theory while simultaneously enabling a prediction for the thickness of the surface gel layer. Conclusion These results indicate that this simple model can adequately characterize the contact mechanics of highly strained soft aqueous gel layers.

Simple contact mechanics model of the vertebrate cartilage

Soft Matter ◽  
2017 ◽  
Vol 13 (37) ◽  
pp. 6349-6362 ◽  
Author(s):  
B. N. J. Persson ◽  
A. Kovalev ◽  
S. N. Gorb
Keyword(s):  
Contact Mechanics ◽  
Mechanics Model ◽  
Simple Contact ◽  
Osmotic Effects

We study a simple contact mechanics model for the vertebrate cartilage, which includes (bulk) osmotic effects.

Friction of Aromatic Thiols in Contacts of Different Adhesive Strength

2007 ◽  
Author(s):  
M. Ruths ◽  
Y. Yang
Keyword(s):  
Contact Mechanics ◽  
Friction Force ◽  
Adhesive Strength ◽  
Boundary Friction ◽  
Friction Force Microscopy ◽  
Force Microscopy ◽  
Mechanics Model ◽  
Elastic Film ◽  
Aromatic Thiols

We have used friction force microscopy to study the boundary friction of thiophenol and 2-napthalenethiol monolayers on gold. The strength of the adhesion was altered by working in dry N2 gas or in ethanol. A contact mechanics model developed by Sridhar, Johnson and Fleck1,2 (SJF) for a thin, compliant elastic film confined between stiffer substrates was used to evaluate the data in systems with higher adhesion.

Amplification Effects of Thin Soft-Surface Layers

2016 ◽  
Vol 32 (4) ◽  
pp. 2109-2126 ◽  
Author(s):  
W. D. Liam Finn ◽  
Francisco Ruz
Keyword(s):  
Soft Soil ◽  
Soil Layer ◽  
Tohoku Earthquake ◽  
Response Spectra ◽  
Surface Layers ◽  
Soft Layer ◽  
The 2011 Tohoku Earthquake ◽  
Amplification Factors ◽  
Soft Surface ◽  
Using Data

The amplification effects of shallow soft-surface layers with respect to an underlying hard-soil layer or rock are studied using data recorded from the 2011 Tohoku earthquake. Twenty-four sites have been studied with depths to rock ranging from 4–30 m. At each site, two records were available: one in rock at the bottom of the borehole at depths of 100–500 m and one on the surface of the soft-soil layer. Analyses of the soil-rock columns were conducted using the program SHAKE. Good agreement was found between calculated and recorded surface spectra, which demonstrated the reliability of SHAKE analyses for the sites under study. Therefore, SHAKE analyses were used to determine the outcrop motions at the top of rock. Amplification factors were determined by comparing characteristics of the surface and outcrop motions such as Fourier and response spectra. Computed amplification factors were correlated with V S30, V soil, and soft layer period, T = 4 H/ V soil. The results show clearly that the most reliable correlations for estimating the amplification of soft shallow surface layers less than 30 m are those based on V S30 and soft layer period, T.

Dry Adhesion Based on Electrospun Polymer Nanofibers

2010 ◽  
Author(s):  
Qiang Shi ◽  
Shing-Chung Wong ◽  
Kai-Tak Wan ◽  
Todd A. Blackledge ◽  
John Najem
Keyword(s):  
Relative Humidity ◽  
Linear Relationship ◽  
Contact Mechanics ◽  
Adhesion Force ◽  
Van Der Waals ◽  
Polymer Nanofibers ◽  
Mechanics Model ◽  
Tensile Tester ◽  
Dry Adhesion ◽  
Fiber Radius

Dry Adhesion exists between polymer nano/microfibers. An elaborate experiment was performed to directly measure the adhesion between electrospun poly(ε-caprolactone) (PCL) microfibers using a nano force tensile tester. Electrospun nano/microfibers with radius ranging from 0.2 to 1.1 μm were investigated. It was found that the adhesion force depended on the fiber radius following a linear relationship, which complied with the classical Johnson-Kendall-Roberts (JKR) contact mechanics model. The force increased with temperature and decreased with relative humidity between two fibers positioned in orthogonal directions. Our data suggested the van der Waals’ (vdW) interactions are primarily operative between the micro-/nano-fibers.

scholarly journals A new approach for quantifying epithelial and stromal thickness changes after orthokeratology contact lens wear

2021 ◽  
Vol 8 (12) ◽  
Author(s):  
Ziying Ran ◽  
Joshua Moore ◽  
Fan Jiang ◽  
Hongmei Guo ◽  
Ashkan Eliasy ◽  
...  
Keyword(s):  
Corneal Epithelium ◽  
Contact Lenses ◽  
Automatic Segmentation ◽  
Central Area ◽  
Radius Of Curvature ◽  
Corneal Surface ◽  
Contact Lens Wear ◽  
Thickness Profile ◽  
Before And After ◽  
Lens Wear

The aim of the study was to develop an automatic segmentation approach to optical coherence tomography (OCT) images and to investigate the changes in epithelial and stromal thickness profile and radius of curvature after the use of orthokeratology (Ortho-K) contact lenses. A total of 45 right eyes from 52 participants were monitored before, and after one month of, uninterrupted overnight Ortho-K lens wear. The tomography of their right eyes was obtained using optical OCT and rotating Scheimpflug imaging (OCULUS Pentacam). A custom-built MATLAB code for automatic segmentation of corneal OCT images was created and used to assess changes in epithelial thickness, stromal thickness, corneal and stromal profiles and radii of curvature before, and after one month of, uninterrupted overnight wear of Ortho-K lenses. In the central area (0–2 mm diameter), the epithelium thinned by 12.8 ± 6.0 µm (23.8% on average, p < 0.01) after one month of Ortho-K lens wear. In the paracentral area (2–5 mm diameter), the epithelium thinned nasally and temporally (by 2.4 ± 5.9 µm, 4.5% on average, p = 0.031). The stroma thickness increased in the central area (by 4.8 ± 16.1 µm, p = 0.005). The radius of curvature of the central corneal anterior surface increased by 0.24 ± 0.26 mm (3.1%, p < 0.01) along the horizontal meridian and by 0.34 ± 0.18 mm (4.2%, p < 0.01) along the vertical meridian. There were no significant changes in the anterior and posterior stromal radius of curvature. This study introduced a new method to automatically detect the anterior corneal surface, the epithelial posterior surface and the posterior corneal surface in OCT scans. Overnight wear of Ortho-K lenses caused thinning of the central corneal epithelium. The anterior corneal surface became flattered while the anterior and posterior surfaces of the stroma did not undergo significant changes. The results are consistent with the changes reported in previous studies. The reduction in myopic refractive error caused by Ortho-K lens wear was mainly due to changes in corneal epithelium thickness profile.

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