Applied Mechanics and Materials Vols. 66-68

Abstract: Based on 2.0L spark ignition direct-injection(SIDI) turbo charged gasoline engine with variable valve timing(VVT), the spark timing effects on combustion process, fuel consumption, knock limitation and emissions were studied with external exhaust gas recirculation(EGR) on different loads and speeds. For the purpose of easily comparing data results, the location of 50% mass fraction burned(CA50) was widely used in this paper. The study results show that CA50 is changing linearly with spark timing. To reach the same combustion phase, spark timing need to be further advanced with external EGR. Combustion variability of IMEP(COV) increase sharply with retarding of CA50 with external EGR. The external EGR can greatly improve knock limitation and knock intensity(KI). To reach the best fuel consumption, CA50 need to be advanced to 6 °CA to 8 °CA for both with external EGR and without external EGR. NOx emissions increase with advancing of spark timing. HC show different trends when retarding spark timing with and without external EGR.

Abstract: By using a thermal simulator this work investigated grain growth behaviour of a Ti+Nb stabilized 12%Cr ferritic stainless steel at high temperature. The results showed that the grain growth rate was less than 1.8μm/s at the temperature of 1200°C, but it suddenly became very high and reached about 50μm/s when the temperature was 1250°C. Analysis results indicate that grain growth of this steel is affected by the small particles on the grain boundaries, and grain growth exponent is about 3.3. Moreover, the activation energy of the grain growth is when the temperature is above 1250°C. Compared with a 27Cr ferritic stainless steel containing only 0.14%Nb, the grain growth exponent of this steel is greater, and grain initial rapid growth temperature is higher.

Abstract: This paper describes that in high-speed flight of the projectile, temperature of fuze changes due to aerodynamic heating caused by the projectile surface layer, thus likely to impact fuze mechanical structure and internal circuit performance, even worse it can affect work of the fuze. So this paper studies the projectile surface aero-dynamic with the Supersonic flight of projectile based on Fluent software, then it can get the displacement of fuze component which caused by thermal stress using transient thermal analysis based on Ansys software. Therefore it can provide effective technical support for the design of fuze.

Abstract: A mechanics model of vertical impact damping system was founded based on the experimental device introduced in [1], and interrelated theory research was made on the mechanics model. The analytical solution of system dynamical response was gained using transfer function combining with the system’s neighboring boundary compatibility conditions in the fact of the piecewise linear characteristics of the system.

Abstract: The simulation research of vertical impact damping system was made in the paper, taking the experimental parameters of [1] as input of simulation program, and the comparison between the result of simulation and that of experiment was drawn, which brought some conclusions in the aspect of non-linear of system.

Abstract: In order to understand the quasi-static and dynamic compressive mechanical properties of carbon/epoxy composite laminates consisting of unidirectional carbon fiber plies and carbon fabric plies, several quasi-static and dynamic compression experiments were performed along three principal material axes. Dynamic compress experiments were conducted using the compression split Hopkinson’s pressure bar (SHPB) and MTS machine respectively. The experimental results showed that the materials had obvious strain rate effect. The performance of the composites in each of the three principal directions had unique characteristics. In the vertical direction of the carbon cloth, the materials had an obvious linear constitutive relationship. In-plane along the 0° carbon fiber direction, the carbon fiber controlled the mechanical properties and the strain rate effect. Specimens were also equipped with various failure modes. Failures were due to shear fractures in the normal direction and due to delamination and splitting failures in the in-plane direction. Identical tests were conducted for the unidirectional laminate. The results show that the static compressive strength and the dynamic peak stress values of fabric laminates were higher than those of unidirectional laminates under the same conditions.

Abstract: Adiabatic shearing is a typical response of materials under high strain rate loading. Based on the instability analysis for the thermo-viscoplastic constitutive model, a new rate-dependent failure criterion is proposed, where the failure strain decreases with the increment in strain rate. Using the finite element simulation of the Mode-II impact problem for the titanium alloy Ti-6Al-4V, we verified the damage mechanism induced by adiabatic shear band (ASB) under this rate-dependent failure criterion. Also the ASB propagation path and the width of localized shear band are predicted, which is in a good agreement with experimental observation.

Abstract: The application of automation to industries brings revolution for manufacturing techniques and allows more sophisticated, flexible, reliable, and cost-effective manufacturing process control. Automation is to use control system to reduce human labor intervention during manufacturing processes and production. It plays very important role and puts strong impact in industries. Automation is not only significantly increasing the production speed but also more accurately controlling product quality. The automated manufacturing can maintain consistent quality, shorten lead time, simplify material handling, optimize work flow, and meet the product demand for flexibility and convertibility in production. The current economic globalization requires significant labor cost reduction through industry automation, better machine tools, and efficient production process. This paper is to design and develop a new automated and high speed machinery system for filling high viscous liquids. It includes the design of automated and high speed machinery, computer aided modeling and simulation of automated mechanical system, and prototype testing. The major advantages of this new automated and high speed liquid filling system include reliable function, high volume filling rates, good sealing capacity, and cost-effective manufacturing process. This new automated and high speed manufacturing systems has been analyzed by computer aided modeling and simulation, and verified through prototype testing. Both results indicate that this automated and high speed manufacturing systems can keep high product quantity and reliable product quality.

Abstract: The microstructures of FeCoNiCrCu high entropy alloy were investigated under directional solidification. The results showed that only diffraction peak corresponding to a FCC crystal structure was observed in the directionally solidified FeCoNiCrCu alloy. With increasing solidification rate, the interface morphology would grows in planar, cellular and dendrite. Comparing the potentiodynamic polarization of as-cast and directionally solidified FeCoNiCrCu high entropy alloy in a 3.5%NaCl solution, it is clearly reveals that the corrosion resistance of directionally solidified FeCoNiCrCu alloy is superior to that of the as-cast FeCoNiCrCu alloy.

Abstract: Wear behaviors of MoSi₂ against Al₂O₃ or SiC under 30N at 1000°C in air have been investigated by using an XP-5 type High Temperature Friction and Wear Tester. The worn surfaces and phases of samples were characterized by scanning electron microscope (SEM) and X-ray diffractometer, respectively. Result shows the wear rate and friction coefficient of MoSi₂ decreases with the increase of sliding speed. SiC is superior to Al₂O₃ as the counter-face materials of MoSi₂. Serious adhesion leads to very high wear rate of Al₂O₃ in this experiment. SiC shows a surprising mass weighing phenomenon, which is caused by oxidation. The main wear mechanism of MoSi₂ against Al₂O₃ is oxidation and adhesion. However when against SiC, it is chiefly controlled by grinding.