Ultrasonic vibration cutting has been successfully applied in many manufacturing fields due to its superior performances, such as low cutting force, high surface quality and long tool life. However, ...few studies have applied ultrasonic vibration cutting in the field of anti-fatigue manufacturing. In this work, ultrasonic peening cutting is developed to achieve precision-strengthening integrated processing of machined surfaces, which vibration direction is always along with cutting depth direction. Meanwhile, based on analyzing the theoretical motion model of cutting edge, the cutting experiments on Ti-6Al-4V specimens are carried out utilizing ultrasonic peening cutting and conventional cutting respectively. Experimental results show that the average fatigue life of specimens machined by ultrasonic peening cutting with a vibration amplitude of 8 μm is 10.4 times higher than that processed utilizing conventional cutting, and the machined surface roughness of ultrasonic peening cutting increases from Ra0.49μm to Ra0.50μm compared to that machined by conventional cutting.
A novel unidirectional liquid spreading surface with an inclined arc pitted groove, inspired by the continuous unidirectional liquid spreading mechanism on the peristome surface of N. alata, is ...explored and fabricated by two‐step UV lithography. Its superior unidirectional liquid spreading capability to that of other surface patterns is demonstrated, and its unidirectional liquid spreading mechanism is investigated.
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•A strengthening-machining integrated ultrasonic peening drilling (UPD) was proposed.•The strengthening mechanism for UPD for Ti-6Al-4V was revealed.•The depth of subsurface plastic ...deformation is increased by 4 times by UPD.•The residual stress and the micro-hardness were greatly increased by UPD.•Smoother machined surface and narrower dimensional tolerance were obtained by UPD.
In aircraft assembly filed, introducing compressive residual stress by cold expansion around the fastening hole is considered as a common method to enhance hole fatigue resistance. However, the conventional cold expansion technology inevitably extends the processing cycle of fastening hole. Therefore, this study proposes a strengthening and machining integrated ultrasonic peening drilling (UPD) to solve this problem by introducing ultrasonic vibration perpendicular to the hole surface during drilling. Both the strengthening principle and dimension accuracy improvement mechanism in UPD were analyzed to better understand the cutting mechanism. The feasibility experiments of UPD of Ti-6Al-4V were conducted to evaluate surface integrity and machining accuracy. The results show that compared to conventional drilling (CD), smoother machined surface and narrower dimensional tolerance were obtained with UPD. Moreover, the subsurface plastic deformation was increased by as high as 4 times with severer deformation degree. Accordingly, the surface residual stress and the depth of circumferential residual stress in the subsurface was increased by 115.7% and 125% respectively. In addition, surface micro-hardness and subsurface hardening layer depth were also significantly increased. The results demonstrated that UPD achieved the integration of strengthening and precision-machining and could be a promising method for finish drilling of aircraft fastening holes.
Piezoelectric polymers with good flexibility have attracted tremendous attention in wearable sensors and energy harvesters. As the piezoelectricity of polymers such as polyvinylidene fluoride (PVDF) ...and polyvinylidene fluoride–trifluoroethylene P(VDF–TrFE) is lower than that of their ceramic counterparts, various approaches have been employed to improve the piezoelectric output of PVDF-based sensors, such as electrospinning, heat annealing, nanoconfinement, polymer blending, and nanoparticle addition. Here, we report two strategies to improve the piezoelectric sensing performance of polymer-based piezoelectric nanofibers, which include the formation of barium titanate (BTO)/P(VDF–TrFE) composite nanofibers and fabrication of penetrated electrodes to enlarge the interfacial area. BTO/P(VDF–TrFE) nanofibers with a BTO weight fraction of 5 wt % exhibit the maximum β-phase crystallinity and piezoelectricity. The piezoelectric output of the BTO/P(VDF–TrFE) nanofiber mat is significantly improved compared with that of pristine P(VDF–TrFE), which is confirmed by piezoresponse force microscopy (PFM) and compression loading tests. In order to form the penetrated electrodes, oxygen (O2) plasma treatment is employed, followed by an electroless plating process. The BTO/P(VDF–TrFE) nanofibers with penetrated electrodes demonstrate increased dielectric constants and enhanced piezoelectric outputs. A BTO/P(VDF–TrFE) nanofiber-based sensor with penetrated electrodes is capable of discerning the energy of a free-falling ball as low as 0.6 μJ and sensing the movement of a walking ant.
Fish are able to perceive the surrounding weak flow and pressure variations with their mechanosensory lateral line system, which consists of a superficial lateral line for flow velocity detection and ...a canal lateral line for flow pressure gradient perception. Achieving a better understanding of the flow field perception algorithms of the lateral line can contribute not only to the design of highly sensitive flow sensors, but also to the development of underwater smart skin with good hydrodynamic imaging properties. In this review, we discuss highly sensitive flow-sensing mechanisms for superficial and canal neuromasts and flow field perception algorithms. Artificial lateral line systems with different transduction mechanisms are then described with special emphasis on the recent innovations in the field of polymer-based artificial flow sensors. Finally, we discuss our perspective of the technological challenges faced while improving flow sensitivity, durability, and sensing fusion schemes.
For a series of unique properties, titanium alloy has been widely applied in aviation and aerospace fields. However, the poor machinability makes high-speed machining titanium alloy hardly perform as ...expected even with advanced tool materials due to the high cutting temperature. Intermittent cutting could be an effective method to decrease the cutting temperature and improve the cutting performance. As typical intermittent cutting methods, traditional ultrasonic vibration cutting (UVC) and elliptical ultrasonic vibration cutting (EUVC) have achieved significant advancements. However, the critical cutting speed confines them to the field of low speed machining. This article proposed a new type of ultrasonic vibration cutting, i.e. high-speed ultrasonic vibration cutting (HUVC), in which the vibration is always along with the feed direction. The separation of the tool and workpiece can be realized under some certain conditions although the cutting speed exceeds far away from the critical speed of the traditional UVC and EUVC methods. As a consequence, it realized high speed cutting on a macro level and intermittent cutting in the micro, and improved the machinability of titanium alloy. Firstly, a theoretical model of HUVC process was established and both of the separation criteria and the duty cycle of HUVC were fully analyzed. Then the feasibility of HUVC method for cutting Ti-6Al-4V was verified experimentally compared with conventional cutting (CC) and traditional ultrasonic vibration cutting (UVC). The results demonstrated that tool life in HUVC were extended by 300% in an optimal situation due to the significantly tool wear reduction. Besides, the cutting efficiency increased by 90% compared with CC method obviously. Furthermore, significant cutting force reduction about 50% and better surface roughness improvement in a successive cutting process were also achieved.
Superior wet attachment and friction performance without the need of special external or preloaded normal force, similar to the tree frog's toe pad, is highly essential for biomedical engineering, ...wearable flexible electronics, etc. Although various pillar surfaces are proposed to enhance wet adhesion or friction, their mechanisms remain on micropillar arrays to extrude interfacial liquid via an external force. Here, two‐level micropillar arrays with nanocavities on top are discovered on the toe pads of a tree frog, and they exhibit strong boundary friction ≈20 times higher than dry and wet friction without the need of a special external or preloaded normal force. Microscale in situ observations show that the specific micro–nano hierarchical pillars in turn trigger three‐level liquid adjusting phenomena, including two‐level liquid self‐splitting and liquid self‐sucking effects. Under these effects, uniform nanometer‐thick liquid bridges form spontaneously on all pillars to generate strong boundary friction, which can be ≈2 times higher than for single‐level pillar surfaces and ≈3.5 times higher than for smooth surfaces. Finally, theoretical models of boundary friction in terms of self‐splitting and self‐sucking are built to reveal the importance of liquid behavior induced by micro–nano hierarchical structure.
A strong wet attachment bioinspired surface with hierarchical pillars and nanocavities is introduced based on the unique interfacial liquid adjusting effects on the tree frog toe pad, where robust interfacial capillarity from nanometer‐thick liquid film generates a boundary friction ≈20 times its wet and dry friction. Such bioinspired surfaces demonstrate potential applications in fields including medical devices and wearable sensors.
Single-crystal silicon carbide (SiC)-based pressure sensors can be used in harsh environments, as they exhibit stable mechanical and electrical properties at elevated temperatures. A fiber-optic ...pressure sensor with an all-SiC sensor head was fabricated and is herein proposed. SiC sensor diaphragms were fabricated via an ultrasonic vibration mill-grinding (UVMG) method, which resulted in a small grinding force and low surface roughness. The sensor head was formed by hermetically bonding two layers of SiC using a nickel diffusion bonding method. The pressure sensor illustrated a good linearity in the range of 0.1-0.9 MPa, with a resolution of 0.27% F.S. (full scale) at room temperature.
Ultrasonic vibration has received widespread attention for its dramatic effect on grain refinement and microstructure modification during casting, additive manufacturing, cold rolling, and cutting, ...changes which can significantly improve the mechanical and physical properties of components. As a novel ultrasonic vibration cutting method, rotary ultrasonic elliptical milling (RUEM) has been introduced to mill the alloy Ti-6Al-4V. However, the effects of ultrasonic elliptical vibration on the microstructures of machined surfaces in end milling of Ti-6Al-4V are still unclear. A comprehensive study on the surface characteristics and sub-surface microstructure in RUEM of Ti-6Al-4V was conducted. The results show that the uniform textures, in the form of ridges mapped on the machined surface in RUEM, varied with the cutting speed. Compared with conventional milling, microchip debris adhesion on the machined surface was significantly reduced by using RUEM. Moreover, intense plastic deformation in the sub-surface was obtained, and nanocrystalline layers, with grain dimensions of 10 nm to 100 nm, were fabricated on the processed surfaces of RUEM. Additionally, the improvement in sub-surface microstructure increased the surface micro-hardness from 21.22% to 33.84%. This study allows an in-depth understanding of sub-surface deformation and surface nanocrystallization in RUEM of Ti–6Al–4V.
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•The effects of RUEM on machined surface morphology and surface defects are obtained.•The mechanism of microstructure evolution in the machined surface of RUEM is investigated.•The influence of RUEM on the surface nanocrystallization of Ti-6Al-4V is analyzed.
As a superior hole manufacturing process, rotary ultrasonic elliptical machining (RUEM) has been successfully employed for drilling carbon fiber reinforced plastics (CFRPs) recently. The delamination ...of CFRP during drilling is generally considered as the most undesirable form of damage and the most challenging failure mode. In order to reduce the delamination in this novel process, it is important to understand the formation and suppression mechanisms during RUEM of CFRP. In this study, the delamination formation in both core drilling (CD) and RUEM was observed and analyzed. The variation trend of delamination factor with feed speed as well as cutting speed was obtained. The experimental results show that, compared with CD, RUEM method can effectively reduce hole exit delamination by 5.4%–19.3% between 1/2 plies and 0.7%–8.4% between 2/3 plies at the feed rates from 50 to 100 μm/rev. Moreover, the delamination suppression mechanism in RUEM was fully analyzed and verified. In a word, in the industry practice, RUEM can be considered as a competitive and promising technique to drill CFRP compared to other delamination suppression techniques.
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