Normal contact stiffness model considering 3D surface topography and actual contact status

A normal contact stiffness model considering 3D topography and elastic–plastic contact of rough surfaces is presented in this paper. The asperities are generated from the measured surfaces using the watershed segmentation and a modified nine-point rectangle. The topography parameters, including the asperity locations, heights, and radii of the summit, are obtained. Asperity shoulder–shoulder contact is considered. The relationship of the contact parameters, such as the contact force, the deformation, and the mean separation of two surfaces, is modelled in the three different contact regimes, namely elastic, elastic–plastic and fully plastic. The asperity contact state is determined, and if the contact occurs, the stiffness of the single asperity pair is calculated and summed as the total normal stiffness of two contact surfaces. The developed model is validated using experimental tests conducted on two types of specimens and is compared with published theoretical models.

Influence of Multi-Step Heating Methods on Properties of Al–Si Coating Boron Steel Sheet

In this study, the influence of the multi-step heating methods, such as two-step heating methods and three-step heating methods, on the properties of Al–Si coating boron steel sheet were evaluated by using the Gleeble-3500 thermal simulator. The evolution of microstructure and 3D surface topography of the Al–Si coating were also investigated. The results showed that the heating rates of 50 °C/s, named rapid heating, at the stage of 20–500 °C did not significantly influence the microstructure and 3D surface topography of the Al–Si coating in the two-step heating methods. The results also indicated that the volume fractions of Fe3Al2Si3 intermetallic compound, FeAl intermetallic compound and a-Fe phase in the Al–Si coating reduced by rapid heating at the stage of 700–930 °C in the three-step heating methods. The roughness of 3D surface topography of the Al–Si coating increased by rapid heating at the stage of 700–930 °C. Rapid heating at the stage of 700–930 °C had little influence on the porosity of the Al–Si coating. The results provided a theoretical basis for the popularization and application of rapid heating in the Al–Si coating boron steel sheet.

The Potential of ICESat-2 to Identify Carbon-Rich Peatlands in Indonesia

Peatlands in Indonesia are one of the primary global storages for terrestrial organic carbon. Poor land management, drainage, and recurrent fires lead to the release of huge amounts of carbon dioxide. Accurate information about the extent of the peatlands and its 3D surface topography is crucial for assessing and quantifying this globally relevant carbon store. To identify the most carbon-rich peatlands—dome-shaped ombrogenous peat—by collecting GPS-based terrain data is almost impossible, as these peatlands are often located in remote areas, frequently flooded, and usually covered by dense tropical forest vegetation. The detection by airborne LiDAR or spaceborne remote sensing in Indonesia is costly and laborious. This study investigated the potential of the ICESat-2/ATLAS LiDAR satellite data to identify and map carbon-rich peatlands. The spaceborne ICESat-2 LiDAR data were compared and correlated with highly accurate field validated digital terrain models (DTM) generated from airborne LiDAR as well as the commercial global WorldDEM DTM dataset. Compared to the airborne DTM, the ICESat-2 LiDAR data produced an R2 of 0.89 and an RMSE of 0.83 m. For the comparison with the WorldDEM DTM, the resulting R2 lay at 0.94 and the RMSE at 0.86 m. We model the peat dome surface from individual peat hydrological units by performing ordinary kriging on ICESat-2 DTM-footprint data. These ICESat-2 based peatland models, compared to a WorldDEM DTM and airborne DTM, produced an R2 of 0.78, 0.84, and 0.94 in Kalimantan and an R2 of 0.69, 0.72, and 0.85 in Sumatra. The RMSE ranged from 0.68 m to 2.68 m. These results demonstrate the potential of ICESat-2 in assessing peat surface topography. Since ICESat-2 will collect more data worldwide in the years to come, it can be used to survey and map carbon-rich tropical peatlands globally and free of charge.