Search

Friction is a fundamental force that impacts almost all interface-related applications. Over the past decade, there is a revival in our basic understanding and practical applications of the friction. In this review, we discuss the recent progress on solid-liquid interfacial friction from the perspective of interfaces. We first discuss the fundamentals and theoretical evolution of solid-liquid interfacial friction based on both bulk interactions and molecular interactions. Then, we summarize the interfacial friction regulation strategies manifested in both natural surfaces and artificial systems, focusing on how liquid, solid, gas, and hydrodynamic coupling actions mediate interfacial friction. Next, we discuss some practical applications that are inhibited or reinforced by interfacial friction. At last, we present the challenges to further understand and regulate interfacial friction.

This study investigates how uncertainty (economic policy uncertainty, market-based uncertainty, firm-specific uncertainty, and CAPM-based uncertainty) impacts the Chinese listed firms’ capital structure for the period 1999–2016, and further tests whether this relationship varies for state-owned enterprises (SOEs) and non-SOEs. In addition, we examine the moderating effect of a non-formal financing channel (trade credit) on the relationship between leverage and uncertainty. The findings show that firms decrease the level of leverage with an increase in uncertainty, and this impact is less prominent for firms owned by the state. Furthermore, the results reveal that trade credit decreases the negative association between uncertainty and leverage, suggesting that firms (especially non-SOEs) adjust their financing demands by using trade credit under high uncertainty. The findings provide implications for corporations and policymakers about how capital structure decisions are influenced by different types of uncertainties in a firm’s environment.

The tensile properties and deformation behavior of several cast Ni-based superalloys, respectively, in the equiaxed, columnar-crystal and single-crystal styles are comparatively studied. The effects of solidification way, heat treatment and strain rate on the tensile properties are discussed in detail. It is found that the reduction of grain boundaries by the feasible solidification ways offers cast Ni-based superalloys the potential capability of improving the mechanical properties, the ultimate achievement of which is also confirmed to lie on the appropriate modifications of chemical composition and heat treatment. The prolongation of solid solution facilitates the precipitation of fine secondary γ′ phase, whereas the extension of high-temperature aging leads to the coarsening of secondary γ′ phase. The combination of these two aspects has a crucial influence on the tensile properties. Under tensile applied stress, the surface grains of DZ-A alloy deform slightly, while the inner grains deform heavily. This deformation inhomogeneity is ascribed to the occurrence of cracks or oblique grains near the surface of specimens and the sliding or decohesion of grain boundaries between the surface and inner grains. Regardless of strain rate, the ILTDM (intermediate-low-temperature ductility minimum) phenomenon always happens in the temperature range from 400 to 600 °C in all the investigated alloys, the occurrence of which is closely related to the strong strain-hardening behavior in the deformation process. Finally, the interaction of slip bands which are the main deformation mode below 600 °C is established to be the essential reason for the strain hardening.

Based on the mixed control strategy (regular control and impulse dividend control strategy), we formulate a proportional reinsurance model with transaction costs. For getting the maximal return function and associated mixed control strategy, using Ito calculus and classical mixed control theory, we derive the quasi-variational inequality solution to this optimal problem. Furthermore, we obtain its closed forms under some assumptions.

SiC short fibers, with an average diameter of 13 μm, length of 300–1,000 μm and chopped from SiC continuous fibers, were surface modified by the semi-solid mechanical stirring method to produce a discrete coating of aluminum particles. Then the starting mixtures, which consist of SiC short composite fibers, aluminum powder less than 50 μm and α-SiC powder of an average diameter of 0.6 μm, were mechanically mixed in ethanol for about 3 h, dried at 80 °C in air, and hot pressed under 30 MPa pressure at 1,650, 1,750 and 1,850 °C with 1 h holding time to prepare SiCf/SiC composites. Volume fraction of SiC short fibers in the starting powder for SiCf/SiC composites was about 25 vol.%. The composites were characterized in terms of bulk density, phase composition, and mechanical properties at room temperature. In addition, the distribution of SiC short fibers in the matrix and the cracking pattern in the composites were examined by optical microscope. Fracture surface of the composites were performed by a scanning electron microscope (SEM). The effect of hot-pressing temperature on bulk density and mechanical properties was investigated. The results indicated that SiC short fibers were uniformly and randomly distributed in the matrix, bending strength and bulk density of the composites increased with increasing sintering temperature. The composite, hot-pressed at 1,850 °C, exhibited the maximum bulk density and bending strength at room temperature, about 3.01 g/cm3 and 366 MPa, respectively. SEM analyses showed that there were a few of fiber pullout on the fracture surface of samples sintered at 1,650 °C and 1,750 °C, which was mainly attributed to lower densities. But few of fiber pullout was observed on the fracture surface of sample sintered at 1,850 °C, the combined effects of high temperature and a long sintering time were considered as a source of too severe fiber degradation because of the large amount of oxygen in the fibers.