The complex interactions between abrasives and workpieces across both spatial and temporal dimensions, the difficulty in quantitatively characterizing material removal under ductile–brittle coexistence, and the uncertainty in the material removal behaviors associated with internal defects pose significant challenges in dynamic force modeling involved in grinding of hard and brittle solids. To resolve the above issues, a theoretical model of the dynamic grinding force involved in the grinding of B₄C ceramics was developed by comprehensively considering the time evolution, strain rate effect, random abrasive distribution, multi-abrasive coupling effect, material removal behavior under ductile–brittle coexistence, plastic pile-up, and defect distribution. The simulation results of the model demonstrated a strong correlation with the experimental findings, with an average error of less than 10%. This model elucidated the comprehensive influence of multi-abrasive coupling in the spatial dimension and material damage accumulation in the temporal dimension on the evolution behaviors of grinding forces, thereby enabling the simultaneous capture of both the time-domain and frequency-domain characteristics of grinding force signals. A systematic analysis of the waveform features and spectral components enabled the clear characterization of transient dynamic responses during the grinding process, thereby facilitating the identification of material removal modes. The findings demonstrated that B₄C ceramics were characterized by high-frequency force signals originating from brittle fractures, with a concomitant reduction in grinding force observed as the size and density of internal defects increased. This study not only enhances the understanding of the mechanisms underlying multi-abrasive interactions and their influence on material removal behaviors but also quantitatively characterizes the effects of grinding parameters and the distribution of defects on grinding forces, thereby providing a theoretical foundation for optimizing the grinding processes of hard and brittle materials.

The application potential of tuning two-dimensional materials (2DMs) characteristics through strain engineering for wearable and flexible devices has been widely recognized. However, the challenges lie in achieving accurate deterministic positioning, spatial modulation, controllable magnitude, and permanent nanostrains. Herein, motivated by the skin swelling caused by mosquito bites, a technique utilizing the heated nanotip in atomic force microscopy for thermomechanical nanoindentation is demonstrated. This method enables precise positioning of localized nanostrain and regulation of bandgap in tungsten diselenide (WSe₂)/molybdenum disulfide (MoS₂) heterobilayer transferred onto a flexible polymethyl methacrylate film. The magnitude of strain in the WSe₂/MoS₂ heterobilayer can be controlled by adjusting the parameters of nanoindentation, leading to a spatially modulated average strain of up to 2.5% on the ring-shaped expansion structure (RES). The local bandgap of the WSe₂/MoS₂ heterobilayer is spatially regulated through three distinct regions. In particular, the RES exhibits the largest extent of bandgap modulation, accompanied by a significant change of ∼12 meV. The nanostrain significantly enhances the photoresponse speed of the photodetector device. For instance, under illumination from a 405 nm wavelength-laser, the rise time and fall time are reduced by 75% and 87.52%, respectively, compared to the device without strain. Similarly, under illumination from a 532 nm wavelength-laser, the rise time and fall time are reduced by 66.67% and 80.60%, respectively. These findings demonstrate that the proposed method serves as a versatile way for improving the photoresponse of optoelectronic devices based on 2DMs.

To understand the anisotropy dependence of the damage evolution and material removal during the machining process of MgF₂ single crystals, nanoscratch tests of MgF₂ single crystals with different crystal planes and directions were systematically performed, and surface morphologies of the scratched grooves under different conditions were analyzed. The experimental results indicated that anisotropy considerably affected the damage evolution in the machining process of MgF₂ single crystals. A stress field model induced by the scratch was developed by considering the anisotropy, which indicated that during the loading process, median cracks induced by the tensile stress initiated and propagated at the front of the indenter. Lateral cracks induced by tensile stress initiated and propagated on the subsurface during the unloading process. In addition, surface radial cracks induced by the tensile stress were easily generated during the unloading process. The stress change led to the deflection of the propagation direction of lateral cracks. Therefore, the lateral cracks propagated to the workpiece surface, resulting in brittle removal in the form of chunk chips. The plastic deformation parameter indicated that the more the slip systems were activated, the more easily the plastic deformation occurred. The cleavage fracture parameter indicated that the cracks propagated along the activated cleavage planes, and the brittle chunk removal was owing to the subsurface cleavage cracks propagating to the crystal surface. Under the same processing parameters, the scratch of the (001) crystal plane along the [100] crystal-orientation was found to be the most conducive to achieving plastic machining of MgF₂ single crystals. The theoretical results agreed well with the experimental results, which will not only enhance the understanding of the anisotropy dependence of the damage evolution and removal process during the machining of MgF₂ crystals, but also provide a theoretical foundation for achieving the high-efficiency and low-damage processing of anisotropic single crystals.