Fig. 2

The real contact area measured and simulated at increasing loads. a Fluorescence intensity images of the contact geometry. The average contact pressure rises from roughly 100 MPa at the beginning of the experiment to 250 MPa at the highest loads. Scale bar, 10 μm. b Elastic Greenwood & Tripp (GT) bearing area calculation. c Purely elastic simulation. d Elasto-plastic contact hardening simulation. Experiments and simulations were carried out on the sphere whose roughness is shown in Supplementary Fig. 9. Simulated contact geometries are convoluted with the point spread function of the microscope (Supplementary Fig. 3). Green lines indicate contact edges in the experimental images. The simulated intensity scale is adjusted such that average colors look like the experimental images. The maximum intensity in the simulated images is 3