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Ultrasonic cutting with a disc cutter is an advanced machining method for the high-quality processing of Nomex honeycomb core. The machining quality is influenced by ultrasonic cutting parameters, as well as tool orientations, which are determined by the multi-axis machining requirements and the angle control of the cutting system. However, in existing research, the effect of the disc cutter orientation on the machining quality has not been studied in depth, and practical guidance for the use of disc cutters is lacking. In this work, the inclined ultrasonic cutting process with a disc cutter was analyzed, and cutting experiments with different inclination angles were conducted. The theoretical residual height models of the honeycomb core, as a result of the lead and tilt angles, were established and verified with the results obtained by a linear laser displacement sensor. Research shows that the residual height of the honeycomb core, as a result of the tilt angle, is much larger than that as a result of the lead angle. Furthermore, the tearing of the cell wall on the machined surface was observed, and the effects of the ultrasonic vibration, lead angle, and tilt angle on the tear rate and tear length of the cell wall were studied. Experimental results revealed that ultrasonic vibration can effectively decrease the tearing of the cell wall and improve the machining quality. Changes in the tilt angle have less effect than changes in the lead angle on the tearing of the cell wall. The determination of inclination angles should consider the actual processing requirements for the residual height and the machining quality of the cell wall. This study investigates the influence of the inclination angles of a disc cutter on the machining quality of Nomex honeycomb core in ultrasonic cutting and provides guidelines for machining.

The vertical surface is a common and typical characteristic structure among Nomex honeycomb core components. However, the conventional high-speed milling and ultrasonic cutting struggle to meet the high-quality machining requirements of a vertical surface. In this study, an ultrasonic trepanning method is proposed and a special ultrasonic trepanning tool is developed, aiming to improve the machining quality of the vertical surface. The trepanning quality of the vertical surface is further studied from the aspects of dimensional error and trepanning incision quality. Based on the kinematic characteristics of ultrasonic trepanning, a theoretical model of dimensional error in trepanning is established. Meanwhile, the influence of ultrasonic vibration on the trepanning process is analyzed, and the result shows that ultrasonic vibration significantly improves the equivalent elastic constant of the honeycomb core material. The theoretical model is proposed to predict the trepanning dimensional error, which is verified by experiment. The effectiveness of the ultrasonic vibration on the incision quality is verified by several experiments, and the quantitative analysis results demonstrate that ultrasonic vibration significantly improves the trepanning quality of the vertical surface.

Ultrasonic cutting with a straight blade is an advanced method for cutting Nomex honeycomb cores. However, crushing has generally been observed on the machining surface of the honeycomb core during ultrasonic cutting (UC). In this paper, to avoid crushing, a new blade-inclined ultrasonic cutting (BIUC) method is proposed to decrease the geometric interference between the cutting tool and the honeycomb cores. The cutting geometry systems of UC and BIUC with a straight blade are systematically established to study the effect of the cutting geometry on the machining quality. The crushing degrees caused by the major flank under different tool orientations in UC and BIUC are analyzed. The causes of crushing during the machining of the honeycomb core were revealed from the aspects of machining quality, cutting force, and geometric interference between the major flank and the material. Experiments involving the quantitative analysis of the crushing and cutting forces verify that the BIUC method is able to avoid crushing by controlling the cutting angle. This paper provides a new method for solving the crushing problem in machining honeycomb core with a straight blade.

Aluminum honeycomb, as the core part of sandwich structure, has been widely used in aeronautics and astronautics industry owing to its superior properties. Ultrasonic cutting has a great potential to reduce the machining defects relative to traditional milling. To have an insight comprehension on the ultrasonic cutting mechanism of aluminum honeycomb by disc cutter, a finite element model is developed. It is found that the widened cell wall, which is a typical phenomenon, is generated on the machined surface. A plastic deformation model for cell wall was established based on the plastic strain energy theory to study the relationship between the width of machined cell wall and ultrasonic cutting parameters. Experiments are performed to verify the developed models and study the relationship between cell wall morphologies and cutting parameters. According to that, an alternating up and down cutting process and plastic deformation of material are observed, which is confirmed to be the reason of cell wall widening; a better machining quality of cell wall can be achieved utilizing a greater ultrasonic amplitude and a lower feed speed.

Aluminum honeycomb has been widely used in many industrial fields, especially the aeronautics and aerospace industries, owing to its high strength and stiffness to weight ratio. Machining of aluminum honeycomb is usually associated with deformations and burrs. Ultrasonic cutting has been introduced as a promising method to overcome these constraints. In order to conduct in-depth research on the ultrasonic cutting for aluminum honeycomb by disc cutter, a 3D finite element model is carried out and verification tests are performed. Comparison result of simulated and experimental cutting forces indicates that the developed model agrees well with the experiment. Based on the developed model, cutting forces and contact relationship between cutter and honeycomb during the cutting process are studied. The reason for the periodic increase in cutting force is analyzed, subsequently. Moreover, the stress distribution in the cutting zone and honeycomb morphologies under different cutting conditions are compared and analyzed. Results show that the hexagonal structure of aluminum honeycomb can be protected and machining quality can be improved by using ultrasonic vibration. Therefore, high quality and efficient machining for aluminum honeycomb can be achieved.

Scanning measurement with laser displacement sensor is an effective method to measure the surface precision of honeycomb cores. Due to the special discontinuous structure of honeycomb cores, cell wall recognition plays an important role in its measurement data processing. The existing method is not stable enough in actual application because it is susceptible to burr data owing to its poor accuracy of identifying the true vertex from the detected corners. In this study, a new cell wall recognition method was proposed based on the corner type identification considering the regular structural features of the cell walls. The corner type identification method is used to distinguish the 3 types of corners according to the directions of the cell walls surrounding the given corner. By selectively determining the endpoints from the identified corners, the cell walls are recognized. One endpoint is determined once the neighbouring cell wall is recognized, and the other one is determined through detailed local analysis around the determined endpoint based on the corner type identification method. The experimental results demonstrate that the proposed method is significantly robust to burrs. Quantitatively, the recognition rate has an accuracy above 98%, and the mean position accuracy is below 0.2 mm.

Photovoltaic properties of the two polymers (named as PBQ-0F and PBQ-4F) were investigated by employing [6, 6]-phenyl-C-71-butyric acid methyl ester (PC71BM) as the acceptor and a water-alcohol-soluble polymer interlayer material (named as PFNBr) to fabricate photovoltaic devices. For the PBQ-0F:PC71BM blend, the device using Ca/Al as cathode showed very similar efficiency as the device using PFNBr/Al as cathode, while for the PBQ-0F:PC71BM blend, photovoltaic performance of the device can be distinctly improved by replacing Ca/Al with PFNBr/Al. As a result, the best PCE of the PBQ-4F:PC71BM based devices reached 9.04%, which is much higher than that of the PBQ-0F:PC71BM based devices. The results obtained from the quantum chemistry calculations and water contact angle measurements demonstrate that these two polymers are low polar materials, and also the films based on them have hydrophobic surfaces. Since PFNBr has an amphipathic structure (hydrophobic backbone and hydrophilic side chain) and the blend films of PBQ-4F:PC71BM and PBQ-4F:PC71BM have different surface energies, the PFNBr organization atop these two blend types of should be different, which will affect device photovoltaic performance. (C) 2015 Elsevier B.V. All rights reserved.

Perovskite solar cells have attracted significant attention in just the past few years in solar cell research fields, where the power conversion efficiency was beyond 22. 1%. Now, the most important challenge for perovskite solar cells in practical applications is the stability issue. In this mini-review, we will summarize the degradation mechanism of perovskite solar cells, including the perovskite material itself and also the interfaces. While we also provide our opinion on improving the stability of perovskite solar cells.