Fabrication of periodic nanostructures using AFM tip-based nanomachining: combining groove and material pile-Up topographies

This paper presents an atomic force microscopy (AFM) tip-based nanomachining method to fabricate periodic nanostructures. This method relies on combining the topography generated by machined grooves with the topography resulting from accumulated pile-up material on the side of these grooves. It is shown that controlling the distance between adjacent and parallel grooves is the key factor in ensuring the quality of the resulting nanostructures. The presented experimental data show that periodic patterns with good quality can be achieved when the feed value between adjacent scratching paths is equal to the width between the two peaks of material pile-up on the sides of a single groove. The quality of the periodicity of the obtained nanostructures is evaluated by applying one- and two-dimensional fast Fourier transform (FFT) algorithms. The ratio of the area of the peak part to the total area in the normalized amplitude–frequency characteristic diagram of the cross-section of the measured AFM image is employed to quantitatively analyze the periodic nanostructures. Finally, the optical effect induced by the use of machined periodic nanostructures for surface colorization is investigated for potential applications in the fields of anti-counterfeiting and metal sensing

An mechatronics coupling design approach for aerostatic bearing spindles

In this paper, a new design approach for aerostatic bearing spindles (ABS) is firstly proposed which takes into account of the interactions between the mechanical and the servo subsystems, including the integration of electromagnetic effects, static pressure characteristics, servo control and mechanical characteristics. According to the air bearing design principle, the geometry of the spindle rotor is designed. The fluid software is used to analyze the influence of the bearing capacity and stiffness on the stability of the spindle. The simulation shows when the air film thickness is 12 μm, the bearing has good load carrying capacity and rigidity. In addition, the influence of motor harmonics on the spindle shaft modes is considered to avoid the resonance of ABS, and to ensure ABS anti-interference capability, proper inertia of ABS is calculated and analyzed. Finally, ABS has a good follow-up effect on the servo control and machining performance through the experimental prototype. The electromechanical coupling design approach for ABS proposed in this paper, can achieve a peak value better than 0.8 μm (surface size: 9 mm × 9 mm) and a surface roughness better than 8 nm in end face turning experiments

Experimental and Numerical Investigations of Fretting Fatigue Behavior for Steel Q235 Single-Lap Bolted Joints

This work aims to investigate the fretting fatigue life and failure mode of steel Q235B plates in single-lap bolted joints. Ten specimens were prepared and tested to fit the S-N curve. SEM (scanning electron microscope) was then employed to observe fatigue crack surfaces and identify crack initiation, crack propagation, and transient fracture zones. Moreover, a FEM model was established to simulate the stress and displacement fields. The normal contact stress, tangential contact stress, and relative slipping displacement at the critical fretting zone were used to calculate FFD values and assess fretting fatigue crack initiation sites, which were in good agreement with SEM observations. Experimental results confirmed the fretting fatigue failure mode for these specimens. It was found that the crack initiation resulted from wear regions at the contact surfaces between plates, and fretting fatigue cracks occurred at a certain distance away from hole edges. The proposed FFD-N relationship is an alternative approach to evaluate fretting fatigue life of steel plates in bolted joints

Laser-assisted grinding of reaction-bonded SiC

The paper presents development of a novel laser-assisted grinding process to reduce surface roughness and subsurface damage in grinding reaction-bonded (RB)-SiC. A thermal control approach is proposed to facilitate the process development, in which a two-temperature model is applied to control the required laser power to thermal softening of RB-SiC prior to grinding operation without melting the workpiece or leaving undesirable microstructural alteration, while Fourier's law is adopted to obtain the thermal gradient for verification. An experimental comparison of conventional grinding and laser-assisted grinding shows significant reduction of machined surface roughness (37%-40%) and depth of subsurface damage (SSD) layer (22%-50.6%) using the thermal control approach under the same grinding conditions. It also shows high specific grinding energy 1.5 times that in conventional grinding at the same depth of cut which accounts for the reduction of subsurface damage as it provides enough energy to promote ductile-regime material removal