Ultrasonic-assisted Surface Research Articles

Study on the impact of ultrasonic vibration-assisted grinding of glass-ceramics on surface/subsurface damage mechanism

PurposeAn investigation was conducted into the impact of various process parameters on the surface and subsurface quality of glass-ceramic materials, as well as the mechanism of material removal and crack formation, through the use of ultrasonic-assisted grinding.Design/methodology/approachA mathematical model of crack propagation in ultrasonic-assisted grinding was established, and the mechanism of crack formation was described through the model. A series of simulations and experiments were conducted to investigate the impact of process parameters on crack depth, surface roughness, and surface topography during ultrasonic-assisted surface and axial grinding. Additionally, the mechanism of crack formation was explored.FindingsDuring ultrasonic-assisted grinding, the average grinding forces are between 0.4–1.0 N, which is much smaller than that of ordinary grinding (1.0–3.5 N). In surface grinding, the maximum surface stresses between the workpiece and the tool gradually decrease with the tool speed. The surface stresses of the workpiece increase with the grinding depth, and the depth of subsurface cracks increases with the grinding depth. With the increase of the axial grinding speed, the subsurface damage depth increases. The roughness increases from 0.780um/1.433um.Originality/valueA mathematical model of crack propagation in ultrasonic-assisted grinding was established, and the mechanism of crack formation was described through the model. The deformation involved in the grinding process is large, and the FEM-SPH modeling method is used to solve the problem that the results of the traditional finite element method are not convergent and the calculation efficiency is low.

Characterization of microstructure and mechanical properties for Ti-6Al-4 V processed by rotary ultrasonic roller burnishing

Ultrasonic assisted surface plastic deformation can significantly improve the mechanical properties of metal material by grain refinement and crystallographic texture. This paper investigated the effect of microstructure evolution on the microhardness and residual stress for Ti-6Al-4 V treated by rotary ultrasonic roller burnishing. The microstructure evolution of α and β phases was explained from grain size, crystallographic texture, misorientation, grain boundary and recrystallization. Crystallite rotation caused by ultrasonic vibration introduced strong crystallographic textures on the cross-sections of Ti-6Al-4 V samples. When ultrasonic amplitude was 7 μm, a strong {0001} <112¯0> texture appeared on the cross-section. The strength of α grain with {0001} texture orientation was larger than that of α grains with other texture orientations. The mean grain size of Ti-6Al-4 V cross-sectional sample was 7.39 μm at an ultrasonic amplitude of 7 μm. The corresponding maximum microhardness value 392.4 HV was larger than that measured at other ultrasonic amplitudes. However, the maximum compressive residual stress affected depth was obtained at an ultrasonic amplitude of 10 μm. The high microhardness of Ti-6Al-4 V was attributed to the grain refinement and crystallographic texture distribution of α and β phases in RURB. The high compressive residual stress affected depth was related to the fraction of deformed grain for α and β phases in RURB.

Effects of the Ultrasonic Assisted Surface Rolling Process on the Fatigue Crack Initiation Position Distribution and Fatigue Life of 51CrV4 Spring Steel.

In this paper, the effects of the fatigue crack initiation position (FCIP) on fatigue life are discussed. Different modified gradient fields (MGFs) are prepared on the surface of 51CrV4 spring steel components by an ultrasonic assisted surface rolling process (USRP). Subsequently, the fatigue behaviour of steels with different FCIPs is systematically studied. The results show that the fatigue life of steels first exhibits an increasing tendency and then a decreasing tendency with increasing distance between an FCIP and the surface. When an FCIP shifts from the surface of the sample to the interior, the fatigue crack initiation resistance on the interior is greater than that on the surface, which leads to an increase in fatigue life. However, when the FCIP further shifts towards the centre of the specimen, the stress triaxiality experienced by the fatigue source gradually increases, which results in a peak in the curve of FCIP versus fatigue life. The magnitude of this peak fatigue life is related to the change in the stress triaxiality. Moreover, according to focused ion beam-high-resolution transmission electron microscopy (FIB-HRTEM) microstructural analysis near FCIPs, under a higher stress triaxiality, the crack tip area is subject to greater stress constraints, making the multiplication and movement of dislocations in this area more difficult, resulting in the decrease in movable dislocation density. This decrease in dislocation density leads to an increase in the stress concentration and accelerates the crack growth rate, decreasing the fatigue life. Therefore, the significant change in fatigue life is controlled by the MGF and stress triaxiality.

Analysis of free and forced vibrations of ultrasonic vibrating tools, case study: ultrasonic assisted surface rolling process

In this study, the mechanism design and analysis of free and forced vibrations of vibrating tool in ultrasonic assisted surface rolling process (UASR) were taken into consideration. In this regard, three free vibrations problems are studied: first, a simple five-element horn with cylindrical-conical geometry; second, an UASR horn with complex geometrical shape; and third, an integrated UASR system, including transducer and booster (made earlier) associated with UASR horn. Moreover, their natural frequency, mode shape, and amplification factor were achieved individually. UASR system is experimentally manufactured and its oscillations amplitudes are extracted for different forced excitation frequencies. It was observed that the empirical resonance frequency was more consistent with the numerical results of UASR system than UASR horn, while the latter has been used for ultrasonic analyses and designing till now. Considering appropriate damping, numerical harmonic analysis of UASR horn was performed to extract the vibrational behavior of its end involved and not involved with the workpiece, whereas an external oscillatory force excites the primary section of the UASR horn. The loading history on the workpiece surface and fluctuations amplitude of the involved horn end were extracted, where their experimental measurement was impossible. In both cases, maximum mechanical oscillations of the horn end were observed at forced excitation with the same natural frequency obtained in numerical modal analysis, which is due to resonance occurrence and standing wave formation at the horn.

Immobilizing LaFeO3 nanoparticles on carbon spheres for enhanced heterogeneous photo-Fenton like performance

LaFeO3 nanoparticles immobilized on the surface of monodisperse carbon spheres have been obtained through a facile and environmentally friendly ultrasonic assisted surface ions adsorption method. The LaFeO3/C nanocomposite was evaluated as photo-Fenton like catalyst for the degradation of Rhodamine B (RhB) under visible light irradiation (λ>420nm). The LaFeO3/C nanocomposite possesses high specific surface area compared with pure LaFeO3 and significantly enhanced photo-Fenton like catalytic performance. The possible formation process of the LaFeO3/C nanocomposite and the mechanism for photo-Fenton like reaction were discussed. The superior property was attributed to the synergistic effects from the photo-Fenton like process and the presence of carbon spheres. In addition, the heterogeneous process led to better recyclability of this type of catalyst.

Flotation separation of polyvinyl chloride and polyethylene terephthalate plastics combined with surface modification for recycling

Surface modification with potassium permanganate (KMnO4) solution was developed for separation of polyvinyl chloride (PVC) and polyethylene terephthalate (PET) waste plastics. The floatability of PVC decreases with increasing of KMnO4 concentration, treatment time, temperature and stirring rate, while that of PET is unaffected. Fourier transform infrared (FT-IR) analysis confirms that mechanism of surface modification may be due to oxidization reactions occurred on PVC surface. The optimum conditions are KMnO4 concentration 1.25mM/L, treatment time 50min, temperature 60°C, stirring rate 300r/min, frother concentration 17.5g/L and flotation time 1min. PVC and PET with different particle sizes were separated efficiently through two-stage flotation. Additionally, after ultrasonic assisted surface modification, separation of PVC and PET with different mass ratios was obtained efficiently through one-stage flotation. The purity and the recovery of the obtained products after flotation separation are up to 99.30% and 99.73%, respectively. A flotation process was designed for flotation separation of PVC and PET plastics combined with surface modification. This study provides technical insights into physical separation of plastic wastes for recycling industry.

High Efficiency Abrasive Waterjet Dressing of Diamond Grinding Wheel

A grinding wheel wears rapidly during ultrasonic assisted surface generation of a large aperture aspherical RB-SiC mirror, which leads to an increase of grinding force and profile error. In this paper, different types of resinoid bonded diamond grinding wheel with a same grit size were dressed with high-pressure abrasive water jet. The dressing effects of abrasive water jet were assessed through comparing the 3D roughness of the grinding wheel topographies before and after dressing. The experimental results show that diamond grits of a worn grinding wheel are protruding from bond after dressing. The feed rate of nozzle and the bond materials have significant impact on the 3D surface roughness of the wheel and dressing efficient. The softer binder and the decrease of the feed rates and lead to deeper grooves during dressing of grinding wheel. However, too low feed rate will make a large number of abrasive particles drop from binder, which worsens the wheel topography. Therefore, to dress grinding wheel well and efficiently, optimized feed rate must be chosen.

Synthesis and characterisation of metastable phase Bi20TiO32 nanosheets

Bi20TiO32 was synthesised successfully by sol–gel and ultrasonic assisted surface impregnation methods using tetrabutyl titanate as titanium source and bismuth nitrate as bismuth source. The samples were characterised by X-ray diffraction (XRD), scanning electron microscope (SEM), UV-vis diffuse reflectance spectrocopy (DRS) and so on. In order to evaluate its photocatalytic denitrogenation performance, simulate oil containing a certain concentration of pyridine was used as the target. The results showed that the synthesized Bi20TiO32 was a kind of tetragonal crystal system of Bi–Ti oxide in metastable phase, with nanosheet size of about 16 nm and band gap of 2·9 eV, which can absorb the light ranging from the UV to 500 nm wavelength. The activity of photocatalytic degradation of 0·05 mg photocatalyst on 50 mL simulated oil (pyridine containing 100 ug g−1) was up to 86·0% under the irradiation of visible light above 420 nm wavelength for 150 min.

Ultrasonic-Assisted Surface- Modification of Nanosilica Chloride and its Use for Synthesis of 3,4- Dihydropyrimidinones

Nanosilica chloride was prepared with modification of the surface by applying ultrasonic irradiation and has been employed as an efficient, heterogeneous and effective catalyst in the preparation of 3,4- dihydropyrimidinones (DHPMs) under solvent-free conditions. Simple workup procedure, short reaction time, and good to excellent yield of the product, are other advantages of this catalyst.