Applied Mechanics and Materials Vols. 66-68

Abstract: Mesh-insensitive structural stress approach is a robust method for fatigue characteristic analysis of welded structures and has been validated in correlating a large amount of published fatigue test of steel welded joints in the literature. Regarding Titanium welded joints, the combination of stress states and geometric shape can also lead to stress concentration that can result in fatigue crack initiation around the welded joints. This paper aims to analyze well-documented fatigue data of transverse and longitudinal fillet welded joints of Titanium using mesh-insensitive structural stress approach. This study is the first time using the approach for titanium fatigue data analysis. The results show that the employed method can correlate fatigue data of Titanium welded joints noticeably and make sense to understand the effect of thickness on fatigue life of the joints better than conventional methods.

Abstract: Al-3Ti-0.5B master alloy was prepared by reaction of Ti sponge, KBF₄ with aluminum melt. The morphology and distribution of the second phases effected by the feeding methods have been discussed. And the grain refining performance and the resistance to fading of the master alloy were investigated. The result shows that the Al-3Ti-0.5B master alloy which was prepared by adding mixture of Ti sponge and KBF₄ power into molten aluminum contains a large number of granular TiB₂ phase and blocky TiAl₃ phase. The average grain size of commercial purity aluminum was refined from 920μm to 120μm by adding 0.5wt.% of the master alloy. And the refining performance of the master alloy shows no obviously fading phenomenon when the holding time up to 30min.

Abstract: High-speed trains are easily got overturned in strong crosswind. This paper aims to analyze the fluid field of high-speed train under different distortion angles by using computational fluid dynamics (CFD), hybrid grid method and finite volume method. The results shows that the vortexes roll by the separated airflow are alternating occur and develop along the body from the top and bottom. It causes a strong affect to the lateral stability of the train.

Abstract: A hydro-pneumatic balanced suspension is proposed based on the structural features of general hydro-pneumatic suspension and balanced suspension. Two types of suspensions mathematics models are built and differential equations of motion are derived with Lagrange-Equation. Performance of the two suspensions is simulated with the software of MATLAB. The results show that ride performance of vehicles is improved using hydro-pneumatic balanced suspension. Therefore, hydro-pneumatic balanced suspension is more suitable for multi-spindled vehicles.

Abstract: Kevlar pulps were employed as reinforcement for polyetherimide(PEI)composite. All filled and unfilled polyetherimide composites were tested against CGr15 ball and representative testing was performed. The effects of Kevlar content on tribological properties of the PEI composites were investigated. The worn surface morphologies of pure PEI and its composites were examined by scanning electron microscopy (SEM) and the wear mechanisms were discussed. Results show that all filled polyetherimides have superior tribological characteristics to unfilled ones.

Abstract: The effect of fiber surface modification on the fatigue strength of a glass fiber reinforced polyamide-6 has been investigated. Tension axial fatigue tests were conducted with specimens extracted from injection moulded plates. Results show the variation of the fatigue strength as a function of the fiber concentration. The experimental data, the tensile tests have shown the effective improvement of interfacial adhesion between the fiber surface and the matrix.

Abstract: To solve the multi-objective flexible job shop scheduling problem, an improved non-dominated sorting genetic algorithm is proposed. Multi-objective mathematical model is established, four objectives, makespan, maximal workload, total workload and total tardiness are considered together. In this paper a dual coding method is employed, and infeasible solutions were avoided by new crossover and mutation methods. Pareto optimal set was taken to deal with multi-objective optimization problem, in order to reduce computational complexity, the non-dominated sorting method was improved. The niche technology is adopted to increase the diversity of solutions, and a new self adaptive mutation rate computing method is designed. The proposed algorithm is tested on some instances, and the computation results demonstrate the superiority of the algorithm.

Abstract: Based on the establishment of a two-dimensional model, a numerical simulation was conducted in this paper to study the flow boiling and heat transfer characteristics of ethanol in a corrugated mini-channel. User defined functions were employed to describe the key processes of heat and mass exchange at the phase interface. Bubble growth profile was monitored over time and its influence on system pressure drop and heat transfer coefficient was also analyzed. The simulation result shows that the nucleation sites tend to distribute near the internal peaks of the heating wall due to the enhanced local turbulence. The system pressure drop increases over the heating time and fluctuates within a certain range. The heat transfer coefficient decreases with increasing quality, and this trend is consistent with the result of similar experimental studies.

Abstract: Shape memory alloys (SMAs) thin films have attracted much attention in recent years as intelligent and functional materials because of their unique characteristics. The sputtering thin films have been attracted great interest as powerful actuators in microelectromechanical systems (MEMS) such as microvalves, microfluid pumps, and microgrippers. Amongst SMAs, the equiatomic TiNi compound is the most widely used. In this paper, TiNi films prepared by magnetron sputtering are reviewed. The influence of parameters including thickness, target, substrate temperature and work pressure on the microstructure and properties of TiNi films are analysised. In additionally, several TiNi based ternary alloys films such as TiNiCu films, TiNiPd films and TiNiPt films are introduced. At last, the research direction of SMAs thin films is presented.

Abstract: A numerical computation and theoretical model are presented on spreading of a single droplet impacting on a solid surface at low Weber number. The numerical simulation uses combined Level Set-VOF method and a precise wetting model. The singularity at the moving contact line was analyzed and removed by present wetting model. A theoretical model based on the energy balance was developed to predict the maximum spreading ratio, accounting for wetting effect by a correction factor. The droplets shapes, the dimensionless spreading radius and the dimensionless height of droplet calculated by present numerical method were compared with the experimental data. The theoretical model is used to predict the maximum spreading ratio. The numerical and theoretical results agree well with the experimental data. Present theoretical model indicates that capillary effects may be neglected if 6We(We/3+4)>>Re.