Search

The integrity and regularity of pore morphology play an important role in determining the mechanical properties of the metallic foam materials. The conventional methods on refining pore morphology are mainly focused on the optimization of fabrication techniques, however, they are usually inconvenient and complicated. Recently, incorporating nano reinforcement is considered to be a suitable way to fabricate metallic composite foams accompanied by optimized pore morphology and enhanced mechanical properties. In this work, through a facile and rapid powder metallurgy foaming method, the aluminum-silicon (Al-Si) alloy composite foams reinforced by graphene nanosheets (GNSs) are successfully fabricated. The microstructure analyses reveal that, for the Al-Si alloy foams incorporating the GNSs (GNSs/Al-Si composite foams), the pore size is transformed to be smaller, the pore size distributions become more homogeneous and the pore shape is also refined to a regular and roundish state. Meanwhile, the shape of Si precipitates is found transforming from an irregular long strip (length of ~20 μm, width of ~5 μm) to a fine particle state (diameter of ~5 μm). Moreover, the compressive testing results show that, the 0.4 wt% GNSs/Al-Si composite foams own the optimal compression stress of 11.7 ± 0.5 MPa, plateau stress of 10.0 ± 1.0 MPa and energy absorption capacity of 6.8 ± 0.7 MJ/m3, which have improvement of 58.1%, 53.8% and 51.1% in comparison with the Al-Si alloy foams counterpart, respectively. The present findings may pave a new way for developing new generation of metallic composite foams that with stable microstructure and excellent mechanical performance.

Performance of a mechanical buffer can be significantly improved by strengthening the materials and optimizing its structure. Manufacturing of high-strength and light-weight foam-filled tubes (FFTs) has been proved to be an ingenious strategy. In this work, the in situ grown carbon nanotubes (CNTs) were used to reinforce aluminum (Al) foams. The FFTs were prepared by inserting CNT/Al composite foams (CFs) into 6061 Al alloy empty tubes (ETs). The crushing behavior and energy absorption property of the as-prepared CNT/Al FFTs (C-FFTs) were evaluated using uniaxial compressive tests. The results show that the adopted CFs can effectively interact with outside tubes in C-FFTs. The C-FFTs significantly improve the compressive performance and energy absorption property, but only slightly increase the structure weight compared to single ETs. The plateau stress and energy absorption capacity of C-FFTs are nearly 3.5 and 3.7 times higher than those of ETs, respectively. This phenomenon is ascribed to the stable support of CFs and the excellent load transfer ability of CNTs.

In this paper, high strain rate dynamic compressive properties of the CNT/Al composite foams reinforced by in-situ grown carbon nanotubes (CNTs) have been investigated. The results show that the compressive strength and energy absorption capacity of the CNT/Al composite foams not only increase with the increment of CNT content but also increase with the strain rate increasing, revealing a typical strain rate sensitivity. For the 3.0 wt%-CNT/Al composite foams, the peak stress at 2130 s −1 is 52.5 MPa, which is ~86% higher than that at 0.001 s −1 (28.2 MPa). Besides, the deformation behavior of the pure Al foam matrix can be significantly affected by the CNT addition and the strain rate. As the strain rate increases from 0.001 to 800 s −1 , the macro deformation way of the pure Al foam transits from the local failure to layers of collapsing, while the micro failure modes in both cases belong to a “Tension mode”. Whereas, whether under quasi-static or dynamic conditions, the macro failure characteristics of the CNT/Al composite foams mainly manifest as the shear deformation and correspond to a “Shear mode” in the micro scale. Moreover, the pore fracture, collapsing and friction, as well as the crack propagation during the compressive processes are all beneficial to the energy absorption enhancement of the CNT/Al composite foams.

Carbon nanotube (CNT) reinforced Al composite foams were successfully fabricated by the combination of an in-situ chemical vapor deposition (CVD), short-time ball-milling and space-holder method. The CNTs are homogeneously dispersed and embedded in the Al foam matrix after 90 min ball-milling while maintaining the structural integrity. Both compressive properties and energy absorption capacity of the composite foams increase with the increment of CNT content but decrease with the temperature rising between 25 and 250 °C. The compressive yield strength and the plateau stress of 3.0 wt%-CNT/Al composite foams maintain 16.8 and 20.2 MPa at 150 °C, respectively, which are much higher than the corresponding yield stress (5.7 MPa) and plateau stress (8.6 MPa) of the pure Al foam. Especially, the energy absorption capacity of the 3.0 wt%-CNT/Al composite foams reaches 19.8 MJ/m3 at 150 °C, which is ~2.5 times higher than that of pure Al foam. Fracture analysis shows that the failure mode of the Al foam changes from ductile type to brittle type combined with ductile type, as a result of the CNT addition in the matrix.

The damping properties of Al matrix composite foams reinforced by in-situ grown carbon nanotubes (CNTs) have been investigated. The results show that the damping capacity of the CNT/Al composite foams is visibly enhanced with the CNT addition. The loss factors of the composite foams are found not only increase with the increment of CNT content but also increase with the porosity raising. For the 3.0 wt%-CNT/Al composite foams, the loss factor keeps the level of ∼0.26 at 25–200 °C and further increases to 0.36 when the temperature is elevated to 390 °C, which is ∼2.71 and 1.77 times higher than that of the pure Al foam, respectively. The damping improvement of CNT/Al composite foams is mainly due to the high inherent damping of CNTs and the formation of large numbers of well-bonded CNT-Al interfaces.

As an effective way to reduce the heat leakage, High Temperature Superconducting (HTS) current leads were widely used in the superconducting magnets system. In this paper, the structure and materials of HTS current leads for large scale superconducting magnets were presented. Furthermore, the thermal characteristics of HTS current leads were described. To reveal the influence of insulating structure on the electrical strength of HTS current lead under normal operating condition and fault operating condition, the electrical analysis of a 16 kA HTS current lead were performed based on finite element technology. The simulating results indicate the dielectric strength of the HTS current lead is enough.

The reactor with adjustable reactive value plays an important role in improving the stability of power system and power quality. In this paper, the structural design and materials selection of a high temperature superconducting (HTS) controllable reactor were presented. Then, investigation on the thermal characteristics were performed. Furthermore, the key issues of development the HTS controllable reactor were summarized.

To improve the quality and efficiency of road roller, Vibratory Roller online monitoring test system of machinery based on LabVIEW is designed. The integrated structure and function of the system are introduced briefly, and the discussion of LabVIEW software design is focused on. The compaction is corresponding to the specific GPS position, and be displayed in graphic. The practice demonstrates that the system is reliable and real time, which provides a reference for the compaction and improves the efficiency of compaction.

Carbon nanotube (CNT) reinforced Al composite foams with different CNT contents are fabricated through an improved powder metallurgy approach by combining in-situ chemical vapor deposition (CVD), short time ball-milling, and space-holder method. The CNTs are uniformly dispersed on the surface of Al particles by in-situ CVD process, followed by a short time ball-milling process enabling an excellent interfacial bonding between CNTs and the Al matrix. The pore size and microstructures of the composite foams can be well tailored by the carbamide particle templates. The yield strength and energy absorption capacity of composite foams reach 18.1 MPa and 15.8 MJ m−3 with 3.0 wt% CNT addition, which are ≈1.3 and ≈3.6 times higher than those of pure Al foam, respectively. The energy absorption efficiency of the CNT/Al composite foams achieves a maximum of ≈0.86, when the CNT content is up to 3.0 wt%. Additionally, compressive and energy absorption properties of the CNT/Al composite foams increase with the increment of relative density. The failure mode of the Al foam changes from plastic mode to brittle mode combined with ductile mode, as a result of CNT addition.

This paper introduces the structure configuration and realization method of upper monitoring system of a medium and small substation and mainly completes selection and control of communication settings and real-time refreshing and display of field data collected, etc. Due to the requirement for real time performance of monitoring system, how to ensure stable serial communication has become the core problem of the whole software, and meanwhile considering that a lot of real-time data needs to be collected and a mass of historical data needs to be kept in power system, and therefore local database is also an important component of this monitoring system.

We propose a blind decoding algorithm for space-time block codes (STBC) tailored for ultra-wideband (UWB) transmissions. An orthogonality between signal and noise subspaces is exploited to build some quadratic form whose minimization yields the desired estimation of transmitted symbols. Simulations in lognormal fading channels show that, compared to the coherent decoding algorithm, the proposed method can achieve the same diversity; with the increment of channel coherent time, its performance approaches those of the coherent receiver.