Abstract
We present experimental results for the elastic and plastic deformation of sandblasted polymer balls resulting from contacts with flat smooth steel and silica glass surfaces. Nearly symmetric, Gaussian-like height probability distributions were observed experimentally before and remarkably, also after the polymer balls were deformed plastically. For all the polymers studied we find that the surface roughness power spectra for large wavenumbers (short length scales) are nearly unchanged after squeezing the polymer balls against flat surfaces. We attribute this to non-uniform plastic flow processes at the micrometer length scale. The experimental data are analyzed using the Persson contact mechanics theory with plasticity and with finite-element method (FEM) calculations.
Highlights
Solids have surface roughness, which tremendously affects their contact mechanics and thereby a large number of interfacial phenomena including adhesion, friction, and the leakage of seals [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15]
Using the surface roughness power spectra of the sandblasted polymer balls, and the penetration hardness obtained from the conical indenter, in Figure 24 we show the plastic contact area as a function of the logarithm of the wavenumber of the shortest wavelength roughness component included in the calculation
For the ultra-high-molecular-weight polyethylene (UHMWPE) ball squeezed against the flat steel or silica glass surfaces, we have shown in Sections 2.1 and 2.2 that the small flattened surface area formed due to plastic deformation is still curved, but with a radius of curvature which is much larger than that of the original spherical ball
Summary
Solids have surface roughness, which tremendously affects their contact mechanics and thereby a large number of interfacial phenomena including adhesion, friction, and the leakage of seals [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15]. In the elasto-plastic model, see Figure 1b, a solid deforms non-locally as a linear elastic material until the local stress reaches the penetration hardness when it starts to flow such that the contact stress is always less than or equal to the penetration hardness. In work-hardened metals, the plastic flow occurs such that the displaced material flows up around the indenter whereby it forms a raised portion close to the indenter surface. This behavior is reminiscent of that predicted by the model of rigid-plastic solids.
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