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During the autoclave manufacturing of sandwich components, several defects may arise. A typical defect in the use of honeycombs is core crush. The occurrence of this defect depends, among other things, on the angle of the honeycomb chamfer. To design this angle, the friction between honeycomb and prepreg must be known. Due to the low rigidity of Nomex® honeycomb in lateral direction, the determination of the frictional behavior between face sheets and honeycomb is a particular challenge. This paper shows the development of a test device for measuring the friction between honeycomb with film adhesive and carbon/epoxy prepreg for different temperatures and compressions corresponding to realistic manufacturing conditions. The device is also suitable for the evaluation of interlaminar friction between prepreg plies and tool-part-interaction. The requirements for the device are shown in detail. Advantages and disadvantages of various concepts for the individual modules are discussed in order to select the most promising design. As proof of concept, friction measurements between honeycomb and prepreg as well as prepreg to prepreg measurements are carried out. In the case of interlaminar measurements, the friction coefficient determined at 1 mm deformation deviates by 5.3% from already published values obtained with another device and is within the stated scatter range. The measurement results for honeycomb against prepreg are in direct correlation with manufacturing trials performed. Using the lowest coefficient of friction established, a critical angle of the honeycomb chamfer was determined. Subsequently, component samples were manufactured with an inclination angle of 7.5° above and 7.5° below the critical angle. The specimens with larger angle showed a strong core crush, whereas those with smaller angle exhibited no core crush. This demonstrates that with this device the honeycomb chamfer of sandwich components can be dimensioned based on the lowest friction coefficient determined between honeycomb and prepreg. [ABSTRACT FROM AUTHOR]

Fe–Ni-based composites with Ni-coated reduced grapheme oxide (RGO)–MoS2 were fabricated by powder metallurgy technique, and their morphology, phase composition, and tribological properties at different temperatures were investigated systematically. Results showed that Fe–Ni-based composite with Ni-coated RGO–MoS2 possessed much more uniform and denser microstructure, and higher hardness than that with RGO–MoS2. Furthermore, Ni-coated RGO–MoS2 additive greatly allowed increasing the friction-reducing and wear-resistant properties, due to the reinforcing and lubricating effect new phase (Fe3W3C, CrxS1+x, etc.) and the improvement on interfacial compatibility between Ni-coated RGO–MoS2 and Fe–Ni matrix. In particular, as the content of Ni-coated RGO–MoS2 was 5 wt%, the friction coefficient and wear rate of the corresponding composite was decreased nearly 50% and 75%, respectively. More importantly, Ni-coated RGO–MoS2 reinforced composite kept excellent tribological properties at elevated temperature. Its friction coefficient decreased firstly with the increased temperature from 25℃ to 400℃, then increased slightly when the temperature increased to 600℃. Besides, the wear rate was only 0.73–0.9 × 10−4 mm3/Nm during the whole temperature range. This suggested that Ni-coated RGO–MoS2 was a promising additive of metallic-based composites suitable for high-temperature sliding condition. [ABSTRACT FROM AUTHOR]

During the preforming stage of woven reinforcement, in the first step of the resin transfer moulding process, the phenomenon of friction occurring at the tool–reinforcement interfaces and the reinforcement–reinforcement interfaces is one of the key parameters of the forming process. This behaviour must be correctly taken into account when modelling the process and a better understanding of the contact and friction phenomena occurring during the woven fabric preforming process is necessary for realistic simulation of the preforming process. Although some existing studies concerning friction of reinforcement have been published, the complex frictional behaviour of fabrics is still not completely clear. The experimental characterization of the frictional behaviour of a specific carbon woven reinforcement (G1151) used for aeronautical applications is the aim of this article and three interfaces have been studied (G1151/G1151, G1151/Plexiglas, G1151/aluminium). The Coulomb coefficients of friction occurring during contact between two layers of fabric and between the fabric and other materials have been determined. The effect of the variation of normal pressure and temperature on the frictional behaviour of this reinforcement has also been analysed. Comparisons between several frictional models, described in the literature, are also conducted in associated with these experimental results. This study highlights a significant tribological anisotropy of the G1151 reinforcement and a dependence of the frictional characteristics on the applied pressure and the temperature. [ABSTRACT FROM AUTHOR]

Advanced fiber-reinforced polymers have emerged as an important class of engineering materials for load-bearing applications with all-round properties for many engineering and social applications. A designer can use the anisotropy produced by building up a laminate from plies with a properly selected fiber—resin combination and orientation to meet the performance requirements. The design procedure of nongeodesic filament-wound composite pressure vessels requires well determined available surface friction values between the applied fiber and the supporting surface. In this article, the variations in available surface friction with respect to time on a hoop substrate of cylindrical mandrels are presented. A correlation between the surface friction and the tackiness is also developed. Several experiments are conducted corresponding to different dimensions of mandrels by varying initial angles of winding. In addition, the machine-related process parameters like fiber speed, roving tension, roving dimensions, and wet versus dry (different substrates) winding are considered in this study. Experiments are conducted to determine tackiness of the material and its variation with respect to time. The results indicate that available surface friction on the hoop substrate and the tackiness varies along with the time. On the other hand, the influence of fiber speed, roving tension, and fiber material is negligible. Based on the experimental investigations, a composite pressure vessel is designed and developed. Hydraulic test is performed on the composite pressure vessel till the burst pressure. [ABSTRACT FROM PUBLISHER]

The design procedure of nongeodesic filament wound products requires well-determined values for the available friction situated between the applied roving and the supporting surface. In this paper, we propose a mandrel shape with a specially designed meridian profile that enables a linearly proportional relation between the feed eye carriage translation and the measured values for the coefficients of friction. As a result of this property, the optically or chronometrically obtained measurements can directly be translated into coefficients of friction. Additional features of this approach are the high accuracy, repeatability, low experimental costs, and simple machine control strategies. With the proposed mandrel, we performed several experiments corresponding to the variation of typical filament winding-related process parameters: fiber speed, roving tension, roving dimensions, wet versus dry winding, and surface quality of the mandrel. The results indicate that the surface quality of the mandrel and the type of winding process (wet vs. dry fibers) have a considerable influence on the obtained data. The influence of the fiber speed, roving tension, and fiber material on the other hand, is negligible. [ABSTRACT FROM AUTHOR]