Finite element analysis of the impact of liner thickness and hydrodynamic limit on the penetration depth of a shaped charge warhead

In this work, an identification method for the hydrodynamic limit of shaped charge jets (SCJs) is proposed using numerical analysis. To identify the hydrodynamic limit, we consider situations where two targets of the same density but different strengths are penetrated by the same SCJ. As a result, the SCJ corresponding with the hydrodynamic theory is a jet region with a velocity larger than 4 km/s. In addition, an investigation based on the hydrodynamic limit and liner thickness indicates that the penetration capability before and after the hydrodynamic limit improves as apex thickness decreases and base thickness increases, respectively. The simple and clear identification of the hydrodynamic limit is expected to be possible using the proposed method. Accordingly, a selective and organized liner thickness design can be developed.

     

An improved thermal model for characteristics analysis of multi-link ultra-precision press system

Journal of Mechanical Science and Technology - In traditional models, only the effect of temperature change of bearings on the heat generation power and thermal contact resistance is considered....     

Lyapunov exponent of friction-induced vibration under smooth friction curve

This paper studies the nonlinear behavior of the friction-induced vibration by using spring-mass model subject to the smooth frictionvelocity curve. The nonlinearity and instability of the friction may produce the chaotic vibration depending on the friction curve. In order to show this, the Lyapunov exponents are calculated for a variety of the slope and magnitude in the smooth friction curve. In turn, the dependency of the friction curve on the chaotic attractor is illustrated.     

Effects of work hardening models on low-cycle fatigue evaluations of coiled tubing with CT-100 steel

In the present study, low-cycle fatigue life of a coiled tubing (CT) with a CT-100 steel was evaluated by using various work hardening models. Tensile and low-cycle fatigue tests were performed, and experimental results were used to calibrate material model constants. A nonlinear finite element model was constructed in the ABAQUS program by using a CT fatigue test machine. During the test cycles, bending and straightening conditions were repeated and histories of strains were collected. The multiaxial low-cycle fatigue life was calculated by using Manson–Coffin relation and Tresca criterion. The kinematic and combined hardening models can be used to evaluate the fatigue life of CT, and their results are conservative compared with the fatigue test results. Results of the present study can be used as the basic data in establishing CT fatigue analysis.     

Wear resistance characteristics of materials used in oil sands plants

The surge in demand for natural resources has shifted the focus of the international community toward the development of oil sands, shale oil, shale gas and other non-traditional energy sources. In extreme environments, materials used in petroleum gas plant modules are accompanied by various problems caused by low-temperature brittleness such as damage, corrosion and wear. Many researchers have been conducting studies to discover a suitable material whose lifespan could be improved by performing characteristics analyses and performance assessments. In this study, a material characteristics assessment was conducted based on a wear resistance test on materials that are commonly used at oil sands plants. Prior to a wear resistance test, a chemical composition analysis was performed on each of the specimens, and tensile, impact, hardness and corrosion tests were carried out to examine the correlation between their results with the results of the wear resistance test. Each test was performed according to ASTM G 105 standards, and the change in weight according to wear length was analysed for each material to determine the related tendencies. In addition, the results of the wear test were derived by analysing the change in the mass of the specimen before and after the test, and the surface roughness was assessed to analyse the performance related to wear and define the service life. The aim was to use these results to select a material that would be suitable for the abrasive environment of the key equipment and materials of plants.     

Geometric accuracy long-term continuous monitoring using strain gauges for CNC machine tools

The accuracy retentivity has become one of the most important performance index of CNC machine tools, which are affected by many complicated factors, such as stress-induced deformations, bolt preload loss, wear, and the manufacturing process itself. The long-term continuous monitoring can bridge the wide gap between the accuracy retentivity and the manufacturing processing of machine tools. In this research, a geometric accuracy monitoring approach using the discrete strain gauges is proposed. The machine basis is firstly simplified based on the structural characteristics and stress condition. And, the straightness is evaluated through the reconstructed strain field of machine tool basis. Finally, to verify the validity of our method, a vertical machining center has been monitored for 7 months using the established wireless monitoring system.     

反应精馏生产乙酸正丁酯分析与优化

使用了Aspen Plus11.1模拟正丁醇与乙酸反应精馏生成乙酸正丁酯的反应精馏过程,对进料温度、回流比和进料位置进行了优化分析,得到了最佳工艺参数:进料温度常温;回流比为1;进料位置为第六块塔板。另外,模拟得到了反应精馏塔的温度和浓度分布,为指导乙酸正丁酯的工业生产提供了理论参考。     

工程总承包质量与进度、成本的关系探讨

保证质量、控制进度和优化成本是工程总承包项目管理的重要环节,但在实施过程中,由于参建方各自所站的角度不同,不能处理好三者之间的相互关系。其结果是：质量管理效率低下,工程建设进度延误、成本增加。本文对工程总承包项目的质量、进度和成本三者之间的关系进行了探讨。     

Analyses of structurally modified quasi‐solid‐state electrolytes using electrochemical impedance spectroscopy for dye‐sensitized solar cells

Electrochemical properties of structurally modified quasi‐solid‐state electrolytes were examined using porous substrates (PSs). The PS was prepared into two categories by a phase inversion method with a brominated poly(phenylene oxide) (BPPO): the sponge and finger types. Effects of the humidification and cosolvent compositions on the morphology of the PS were analyzed by scanning electron microscopy. In all cases of the PSs, a higher V_OC was observed of about 0.1 V than that of a liquid electrolyte owing to a suppressed back electron charge transfer. In addition, the PS prepared by the polymer solution of 1 : 4 : 1 (BPPO : N‐methyl‐2‐pyrrolidone : butyl alcohol) with the humidification process showed better photovoltaic properties in terms of the current density and conversion efficiency owing to the appropriate combinations of pore size, tortuosity, and interconnectivity. Effects of the pore structures were intensively examined using electrochemical impedance spectroscopy. The impedance results revealed that large pores at the surface layers are advantageous for a lower R_S and R_TiO2. Meanwhile, the straight inner structure is beneficial for the facile I^?/I₃^? diffusion, thus lowering R_Pt. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39739.     

Electrically and thermally conductive elastomer/graphene nanocomposites by solution mixing

The greatest challenge in developing polymer/graphene nanocomposites is to prevent graphene layers stacking; in this respect, we found effective solution-mixing polymers with cost-effective graphene of hydrophobic surface. Since graphene oxide is hydrophilic and in need of reduction, highly conducing graphene platelets (GnPs) of ∼3 nm in thickness were selected to solution-mix with a commonly used elastomer – styrene–butadiene rubber (SBR). A percolation threshold of electrical conductivity was observed at 5.3 vol% of GnPs, and the SBR thermal conductivity enhanced three times at 24 vol%. Tensile strength, Young's modulus and tear strength were improved by 413%, 782% and 709%, respectively, at 16.7 vol%. Payne effect, an important design criteria for elastomers used in dynamic loading environment, was also investigated. The comparison of solution mixing with melt compounding, where the same starting materials were used, demonstrated that solution mixing is more effective in promoting the reinforcing effect of GnPs, since it provides more interlayer spacing for elastomer molecules intercalating and retains the high aspect ratio of GnPs leading to filler–filler network at a low volume fraction. We also compared the reinforcing effect of GnPs with those of carbon black and carbon nanotubes.