Abstract: In this study, experimental investigations were performed to gain insights into the processing parameter effects of laser-assisted automated fibre placement (AFP) on the mechanical properties of carbon fibre (CF)/polyphenylene sulphide (PPS) composites from the perspective of void content and crystallinity. First, thermal characterisation was carried out to obtain the processing window for the PPS/CF composites. The temperature histories at the nip point during an AFP process were measured using an in-house temperature measurement system and the desired ranges of laser power and placement rate were determined based on the measured temperatures. The placement rate was ranging from 6 to 60 m/min, and the range of the used laser power was 1–6 kW. Then, the effects of tool temperature ranging from 30 to 120 °C on the interlaminar shear strength and compression strength of the CF/PPS composites were examined. It was found that the interlaminar void content dominated the mechanical properties of the composite rather than the crystallinity. Finally, the composites produced by the AFP were further treated by an autoclave. It was shown that the interlaminar shear strength of the composites was significantly improved after the autoclave post-consolidation treatment due to the reduction in void content and the improvement of crystallinity. The interlaminar shear strength of the composites after the autoclave treatment was found to be independent of the placement rate, indicating elimination of the AFP thermal history due to sufficient heating and compaction time in the autoclave.

Abstract: Heat dissipation problem is the primary factor restricting the service life of an electronic component. The thermal conductivity of materials has become a bottleneck that hinders the development of the electronic information industry (such as light-emitting diodes, 5G mobile phones). Therefore, the research on improving the thermal conductivity of materials has a very important theoretical value and a practical application value. Whether the thermally conductive filler in polymer composites can form a highly thermal conductive pathway is a key issue at this stage. The carbon fiber/carbon felt (CF/C felt) prepared in the study has a three-dimensional continuous network structure. The nickel-coated carbon fiber/carbon felt (CF/C/Ni felt) was fabricated by an electroplating deposition method. Three-dimensional CF/C/Ni/epoxy composites were manufactured by vacuum-assisted liquid-phase impregnation. By forming connection points between the adjacent carbon fibers, the thermal conduction path inside the felt can be improved so as to improve the thermal conductivity of the CF/C/Ni/epoxy composite. The thermal conductivity of the CF/C/Ni/epoxy composite (in-plane K∥) is up to 2.13 W/(m K) with 14.0 wt % CF/C and 3.70 wt % Ni particles (60 min electroplating deposition). This paper provides a theoretical basis for the development of high thermal conductivity and high-performance composite materials urgently needed in industrial production and high-tech fields.

Abstract: Selective laser melting (SLM) is one of the most promising additive manufacturing (AM) technologies in recent years. However, some sub-millimeter defects often appear accidently in SLM specimens, resulting in deterioration of mechanical properties. Therefore, the effects of these defects on the mechanical properties of the SLM materials are significantly important. In this study, the effect of a single spherical defect on the tensile properties was investigated by embedding a spherical pore inside the SLM Ti6Al4V specimens. Different combinations of pore diameters (Ф100 μm, Ф300 μm, Ф500 μm, Ф1000 μm) and locations (center, sub-surface, near-surface) were designed to mimic the sub-millimeter printing defects. The results demonstrated that these embedded pores had negligible influence on the elastic modulus and tensile strength but had a noticeable influence on the tensile elongation. With the increase of pore size, the elongation to failure of the specimens tended to be stochastic, stably high and stably low in sequence, which could be related to different fracture modes. The tensile specimens fractured at the embedded pore when the embedded pore size was increased to a critical diameter (approximately Ф1000 μm). Concurrently, the location of the embedded pore started to have an obvious influence on ductility, namely, the elongation to failure decreased as the embedded pore became closer to free surface.

Abstract: With the structure design and muscle-like actuators, soft robots have been extensively studied for various application potentials in rescue exploration, medical rehabilitation, military reconnaissance etc. It is highly desirable yet challenging to develop fast 3D-assembly, multifunctional and self-healing soft robots to adapt to rapid changing environments. Inspired by multi-bit screwdriver, we address this challenge using a self-healing light-driven shape memory polymer via photo-welding. Semicrystalline poly (ethylene-co-vinyl acetate) (EVA) involved with silver nanowires (AgNWs) exhibit reversible light-trigged morphing behavior in air or underwater. Additionally, the re-crosslinking of EVA molecular and chain mobility under photothermal effect endows the composite with self-healing property, resulting in fast assembly of soft robotics with sophisticated 3D structures via photo-welding. More importantly, to change the function, the unit could be first cleaved from the main body and then another programmed component could be photo-welded on the main body. Our work provides a facile and cost-effective strategy for creating multifunctional, self-healing soft robots.

Abstract: The microstructure, fracture mechanism and their correlation with the mechanical properties of as-cast Mg-Nd-Zn-Zr alloy were studied, in which the effect of cooling rate on the microstructure and the mechanical properties were taken into account. The results showed that the microstructure of the alloy is composed of primary phase (α-Mg) and eutectic compounds. With the increase of the cooling rate in the range of 0.4–2.4 °C/s, the grain size of the alloy decreases from 66 μm to 44 μm, while the volume fraction of the eutectic compounds increases from 3% to 6.1%. The decrease of the grain size tends to improve the yield strength, ultimate tensile strength and elongation of the alloy. The eutectic compounds have complicated effects on the mechanical properties. It is found that the increase of the volume fraction of the eutectic compounds leads to the decrease of the yield strength while the network-like eutectic compounds formed at higher cooling rates decreases the ultimate tensile strength. The fracture pattern of the alloy changes from intergranular to quasi-cleavage fracture and then to a mixed fracture of intergranular and transgranular fracture with the increase of cooling rate.

Abstract: The particular microstructure of Ti-6Al-4V fabricated by additive manufacturing (AM) makes it exhibit a different corrosion resistance compared with that of the conventional forged Ti-6Al-4V Here we utilize the electrochemical impedance (EIS) and potentiodynamic polarization (Tafel) to evaluate the electrochemical dissolution behavior in runway deicing fluids (RDF) of three kinds of Ti-6Al-4V alloy, which are respectively fabricated by forging, electron beam melting (EBM), and selective laser melting (SLM) The microstructure and electrochemical results suggest that EBM samples have a better corrosion resistance than others', which is attributed to an appropriate proportion of α-lath width and the volume fraction of β phase A higher relative proportion of TiO2 is formed on surface, resulting in the fine-lamellar structure with a higher density of grain boundaries Besides, the corrosion resistance anisotropy of AMed Ti-6Al-4V samples is ascribed to the existence of β columnar gains In addition, the acicular martensite α′ phase with metastable structure leads to the worst corrosion resistance of SLMed Ti-6Al-4V samples This work enriches the corrosion resistance of Ti-6Al-4V alloy in strong electrolyte solutions, which helps to promote the service performance of aviation titanium alloys in harsh environments

Abstract: Volatile organic compounds (VOCs) as a non-negligible aircraft cabin air quality (CAQ) factor influence the health and comfort of passengers and crew members. On-board measurements of carbonyls (short-chain (C1 -C6 )) and other volatile organic compounds (VOCs, long-chain (C6 -C16 )) with a total of 350 samples were conducted in 56 commercial airliner cabins covering 8 aircraft models in this study. The mean concentration for each individual carbonyl compound was between 0.3 and 8.3 μg/m3 (except for acrolein & acetone, average = 20.7 μg/m3 ) similar to the mean concentrations of other highly detected VOCs (long-chain (C6 -C16 ), 97% of which ranged in 0-10 μg/m3 ) in aircraft cabins. Formaldehyde concentrations in flights were significantly lower than in residential buildings, where construction materials are known formaldehyde sources. Acetone is a VOC emitted by humans, and its concentration in flights was similar to that in other high-occupant density transportation vehicles. The variation of VOC concentrations in different flight phases of long-haul flights was the same as that of CO2 concentration except for the meal phase, which indicates the importance of cabin ventilation in diluting the gaseous contaminants, while the sustained and slow growth of the VOC concentrations during the cruising phase in short-haul flights indicated that the ventilation could not adequately dilute the emission of VOCs. For the different categories of VOCs, the mean concentration during the cruising phase of benzene series, aldehydes, alkanes, other VOCs (detection rate > 50%), and carbonyls in long-haul flights was 44.2 µg/m3 , 17.9 µg/m3 , 18.6 µg/m3 , 31.5 µg/m3 , and 20.4 µg/m3 lower than those in short-haul flights, respectively. Carbonyls and d-limonene showed a significant correlation with meal service (p < 0.05). Unlike the newly decorated rooms or new vehicles, the inner materials were not the major emission sources in aircraft cabins. Practical Implications. The on-board measurements of 56 flights enrich the VOC database of cabin environment, especially for carbonyls. The literature review of carbonyls in the past 20 years contributes to the understanding the current status of cabin air quality (CAQ). The analysis of VOC concentration variation for different flight phases, flight duration, and aircraft age lays a foundation for exploring effective control methods, including ventilation and purification for cabin VOC pollution. The enriched VOC data is helpful to explore the key VOCs of aircraft cabin environment and to evaluate the acute/chronic health exposure risk of pollutants for passengers and crew members.

Abstract: As electronic devices tend to be integrated and high-powered, thermal conductivity is regarded as the crucial parameter of electronic components, which has become the main factor that limits the operating speed and service lifetime of electronic devices. However, constructing continuous thermal conductive paths for low content particle fillers and reducing interface thermal resistance between fillers and matrix are still two challenging issues for the preparation of thermally conductive composites. In this study, 3D-oriented carbon fiber (CF) thermal network structures filled with boron nitride flakes (BN) as thermal conductive bridges were successfully constructed. The epoxy composite was fabricated by thermal conductive material with a 3D oriented structure by the vacuum liquid impregnation method. This special 3D-oriented structure modified by BN (BN/CF) could efficiently broaden the heat conduction pathway and connected adjacent fibers, which leads to the reduction of thermal resistance. The thermal conductivity of the boron nitride/carbon fiber/epoxy resin composite (BN/CF/EP) with 5 vol% 10 mm CF and 40 vol% BN reaches up to 3.1 W m−1 K−1, and its conductivity is only 2.5 × 10−4 S cm−1. This facile and high-efficient method could provide some useful advice for the thermal management material in the microelectronic field and aerospace industry.

Abstract: In general, results from the birdstrike tests are employed so that they can be used to validate numerical models and promote the use of numerical tools in aircraft design and the certification proc...

Abstract: Carbon dioxide (CO2 ) is an important environmental parameter in aircraft cabins. To understand the most recent, real-time CO2 concentration levels and their key influencing factors in aircraft cabins, we conducted in-flight measurements of 52 randomly selected commercial flights with different aircraft types and durations from August 2017 to August 2019. The spatial temporal characteristics of CO2 concentrations on board were analyzed and summarized. For the flight time scale, the CO2 concentrations during the boarding phase (1680 ± 558 ppmv) were notably higher than that in other phases, whereas the condition of the cruising phase was the lowest in most flights. The flight average CO2 concentrations of the cruising phase were 1253 ± 164 ppmv, and the corresponding estimated outside airflow rates were 6.2 ± 1.3 L/s/p in the economy class across all flights. Single-aisle and twin-aisle flights did not show noticeable differences for the same phases. Relatively uniform CO2 concentrations were observed at different positions of the same class. By comparing the results of this study with those previously reported, CO2 concentrations showed a slightly decreasing trend over the last 30 years. This suggested a slightly increased ventilation rate and potentially superior air quality on board.

Abstract: In situ consolidation of thermoplastic composites can be realized through laser-assisted automated fiber placement (AFP) technology, and the properties of composites were significant affected by th...

Abstract: In this paper, the shape and material optimization problems of the curvilinearly stiffened plates are solved by using the non-uniform rational B-splines (NURBS) based isogeometric analysis (IGA) method. The analytical formulas for calculating the sensitivity of plates and stiffeners are given and applied to shape optimization problems successfully. By designing the coordinates of the control points of the stiffener, the shape of the stiffener can be determined to minimize its flexibility under a certain volume constraint. Then, functionally graded materials (FGMs) are used for curvilinearly stiffened plates. The volume fraction of the constituent materials of FGMs is expressed in the form of polynomial expansions. By designing the coefficients of these polynomial expansions to determine the material distribution, the total volume fraction of some constituent materials under certain displacement and stress constraints is minimized.

Abstract: As one of the most effective energy storage compounds, phase change materials (PCMS) play an important role in energy conservation and storage. However, the inherent poor thermal conductivity and l...

Abstract: Dynamical systems with binary-valued observations are widely used in information industry, technology of biological pharmacy and other fields. Though there have been much efforts devoted to the identification of such systems, most of the previous investigations are based on first-order gradient algorithm which usually has much slower convergence rate than the Quasi-Newton algorithm. Moreover, persistence of excitation(PE) conditions are usually required to guarantee consistent parameter estimates in the existing literature, which are hard to be verified or guaranteed for feedback control systems. In this paper, we propose an online projected Quasi-Newton type algorithm for parameter estimation of stochastic regression models with binary-valued observations and varying thresholds. By using both the stochastic Lyapunov function and martingale estimation methods, we establish the strong consistency of the estimation algorithm and provide the convergence rate, under a signal condition which is considerably weaker than the traditional PE condition and coincides with the weakest possible excitation known for the classical least square algorithm of stochastic regression models. Convergence of adaptive predictors and their applications in adaptive control are also discussed.