The cyclic indentation effect is widespread in vibration-assisted grinding processes. The understanding of the material removal mechanism during cyclic indentation is scientifically important for the improvement of the quality of vibratory grinding. Therefore, in this paper, the cyclic indentation damage and crack extension mechanisms of quartz glass are investigated by experiments and finite element simulations. The evolution of surface cracks under cyclic loading from 0.203 N to 1.81 N is observed by scanning electron microscopy. The distribution of the maximum principal stress during cyclic indentation is simulated on the basis of a modified Drucker-Prager-Cap material ontology model. A combination of experiments and simulations reveals the crack evolution mechanism during cyclic indentation.

An on-machine measuring (OMM) system with a laser displacement sensor (LDS) is designed for measuring free-form surfaces of hypersonic aircraft’s radomes. To improve the measurement accuracy of the OMM system, a novel Iteratively Automatic machine learning Boosted hand-eye Calibration (IABC) method is proposed. Both the hand-eye relationship and LDS measurement errors can be calibrated in one calibration process without any hardware changes via IABC. Firstly, a new objective function is derived, containing analytical parameters of the hand-eye relationship and LDS errors. Then, a hybrid calibration model composed of two kernels is proposed to solve the objective function. One kernel is the analytical kernel designed for solving analytical parameters. Another kernel is the automatic machine learning (AutoML) kernel designed to model LDS errors. The two kernels are connected with stepwise iterations to find the best calibration results. Compared with traditional methods, hand-eye experiments show that IABC reduces the calibration RMSE by about 50%. Verification experiments show that IABC reduces the measurement deviations by about 25%-50% and RMSEs within 40%. Even when the training data are obviously less than the test data, IABC performs well. Experiments demonstrate that IABC is more accurate than traditional hand-eye methods.

Excellent wear resistance is an important feature of orthopedic implants. However, although pure polyetheretherketone (PEEK) is outperformed by carbon fiber-reinforced PEEK (CF-PEEK) for stability and durability under laboratory conditions, it is not clear whether CF-PEEK should be preferred in all real-world applications. Results indicate that, under dipalmitoylphosphatidylcholine (DPPC) lubrication, the wear rates of PEEK are 35%–80% lower than the wear rates of CF-PEEK for different implant materials, speeds, loadings, and DPPC concentrations. Molecular dynamics calculations confirm that DPPC self-assembles on the PEEK surface to form an easily adsorbed continuous phospholipid lubricating film. In contrast, the carbon fibers on the CF-PEEK surface hinder the formation of the protective DPPC film and the CF-PEEK surface is thus subject to faster wear.

Polyether-ether-ketone (PEEK) and polyimide (PI) are two kinds of engineering polymer materials widely used as roller bearing cages and rings under extreme environment because of their noise reduction and corrosion resistance properties. The Si₃N₄ ceramic is the most common ball bearing material. Many current engineering applications of ball bearings require aqueous lubrication. Therefore, this study presents the aqueous lubrication of tribopairs formed by PEEK and PI material sliding against Si₃N₄ ceramic. Experimental results show that two tribopairs exhibited the similar tribological properties under the dry condition. Water as a lubricant for the PI–Si₃N₄ tribopair pairs effectively reduces both friction coefficients by 35.5% and wear rates by 32%. The water absorption of PI induces better tribological properties by changing the tribopair surface properties. In addition, the dimples appearing on the PI tribopair surface under water generate additional hydrodynamic lubrication and further improve the friction properties of surface. The PEEK–Si₃N₄ tribopair shows similar friction coefficients under two kinds of environments. The wear rates under water are approximately more than two times of that under dry sliding. However, water inhibits the appearance of the crush phenomenon and enhances the carrying capacity of the tribopair. Energy dispersive spectroscopy and X-ray diffraction spectra demonstrate no chemical corrosion. The 3D profiler and SEM morphologies illustrate that the transfer film would be formed from the surface of PEEK under water but hindered under dry friction. Overall, the PI–Si₃N₄ tribopair exhibits better properties than PEEK under water and is promising for future applications in the bearing industry.