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1.
Quasi-static and dynamic crushing behaviors of aluminum and steel tubes with a cutout 总被引:3,自引:0,他引:3
Tubular members are commonly used as an energy absorber in engineering structures and many such members have a cutout. In this study, the crushing behaviors of tubes with a cutout are characterized and the effects of cutout on the energy absorption capabilities of these tubes are quantified. Systematic parametric studies were carried out to study the effect of material properties, including yield and ultimate strength of material, strain rate effect, location of cutout, tube length and impact speed on the crushing behaviors and energy absorption capacity of aluminum and steel tubes. First, a numerical model was constructed with a commercial explicit finite element code. It will be first proven that the numerical simulation can produce sufficiently accurate results in an economic manner. Subsequently, the crushing behavior of aluminum and steel tubes with a cutout was experimentally characterized and their energy absorption capacity was evaluated in terms of mean crushing force, peak crushing force and specific energy absorption (SEA). Tubes of various lengths with a cutout located at different locations, subject to both quasi-static and dynamic impact loadings were considered. For steel tubes, the numerical simulation investigated the influence of the strain rate effect and variation in strain hardening ratio of the material. Empirical equations describing the mean and peak crushing forces of aluminum and steel tubes with a cutout were developed using linear and nonlinear regression methods applied to the results obtained from the numerical and experimental studies. 相似文献
2.
多协议标记交换MPLS通过在传统的IP包里加入标记,使原来依赖于IP头标分析的路由转发转变为依赖于标记的转发,这不仅可以大大地提高IP包的转发速度,更可使传统IP网络具有QoS能力。本文深入分析了标记转发的思想.并指出了MPLS实现其优点所用的机制与原理。 相似文献
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The effect of Mo on the morphology, crystal structure and hydrogen sorption properties of Mg/C composites prepared by reactive milling was studied. Transmission electron microscopic(TEM) observation shows that Mg/C composites prepared with the addition of Mo are of nanoscale with particle size about 20-120 nm after 3 h of milling under 1 MPaH_2. MgH_2 of tetrahedral crystal structure predominates in the materials with the geometric shape of oblique hexagonal prism. From X-ray diffraction(XRD) and hydrogen content studies, Mo and crystallitic carbon have a synergistic effect on promoting the hydrogenation rate in the reactive milling process. From differential scanning calorimetric(DSC) studies, the dehydrogenation peak temperature of the Mg/C materials with Mo is lowered to 299-340 ℃. 相似文献
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在阐述了锁相环频率综合的工作原理、分析和设计方法的基础上,结合环路稳定性和相位噪声两方面因素对锁相环电路进行了建模及分析。采用安捷伦公司的ADS软件对锁相环进行了系统设计及仿真,并采用Cadence公司的Spectre-RF系列软件进行了锁相环具体电路设计和仿真。采用该方案设计的锁相环输出频率范围18.15 23 GHz,相位噪声-90 dBc/Hz,锁定时间小于5μs。 相似文献
6.
Zhaowu Wang Haipeng Ji Zongtao Zhang Jian Xu Deliang Chen 《Journal of the American Ceramic Society》2021,104(10):5077-5085
The cation exchange method has been demonstrated to be efficient in doping Mn4+ ions into various fluorides to synthesize the red-emitting LED phosphors. This paper, however, reports the challenge in using this method to dope Mn4+ into the Na2SiF6 single crystals, to prepare the fluoride phosphor in single-crystal form, a state-of-the-art study in the white LED lighting field. The millimeter-sized Na2SiF6 single crystals with a uniform columnar morphology (2–3 mm in length) were successfully grown in solution by a slow cooling process after optimizing the precursors. Then, the crystals were soaked in the HF solution dissolved with K2MnF6 to implement Mn4+-doping via the cation exchange process. Evaluation of the Mn4+-doping behavior reveals that the Mn4+ ↔ Si4+ cation exchange is less efficient in the case of single crystal host compared with the polycrystalline powdery ones and by-reactions also occur which generates new phases. The Na2SiF6 single crystals doped with Mn4+ exhibit a series of discrete sharp peaks with intense zero phonon line emission at 617 nm under 450 nm blue irradiation. This study may trigger the exploration of new single crystal fluoride phosphor. 相似文献
7.
西安某汽车厂客车蒙皮组焊件焊接采用CO2焊,生产效率低,焊接变形大,表面处理难度大,质量难以保证,使产品的质量和产量受到严重的制约,为此必须进行工艺改进.通过采用全自动缝焊焊接工艺及选择合理的工艺参数,在保证结构和强度的前提下,使蒙皮组焊件焊接表面质量大幅度提高,劳动强度大幅度下降,生产效率提高数倍. 相似文献
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Yanrong Lu Lixiang Li Haipeng Peng Yixian Yang 《Peer-to-Peer Networking and Applications》2016,9(2):449-459
The Session Initiation Protocol (SIP) as the core signaling protocol for multimedia services is receiving much attention. Authentication is becoming increasingly crucial issue when a user asks to use SIP services. Many authentication schemes for the SIP have been proposed. Very recently, Zhang et al. has presented an authentication scheme for SIP and claimed their scheme could overcome various attacks while maintaining efficiency. In this research, we illustrate that their scheme is susceptible to the insider attack and does not provide proper mutual authentication. We then propose a modified secure mutual authentication scheme to conquer the security flaws in Zhang et al.’s scheme. Through the informal and formal security analyses, we demonstrate that our scheme is resilient possible known attacks including the attacks found in Zhang et al.’s scheme. In addition, the performance analysis shows that our scheme has better efficiency in comparison with other related ECC-based authentication schemes for SIP. 相似文献