Applied Mechanics and Materials Vol. 455

Abstract: Serrated flow behavior of the 316LN austenitic stainless steel was investigated through tensile tests at initial strain rates of 2×10^-5 to 10^-4 s^-1 at temperatures ranging from room temperature to 1048 K. Serrated flow occurred at room temperature and 6981048K at the strain rate of 2×10^-4 s^-1, as well as at temperatures of 623673 K at the strain rate of 2×10^-5 s^-1. Type A, A+B, C and E serrations appeared. The activation energy for the occurrence of serrated flow at high temperatures was about 327 kJ/mol. The dynamic strain aging caused by the interaction between substitutional solute Cr atoms and moving dislocations is considered as the mechanism of serrated flow at the temperatures higher than 973 K.

Abstract: Forming process of TC4 titanium alloy laser weld joint during superplastic deformation is simulated. The stress and strain curve, which is obtained in the simulation, is compared with that obtained by hot tensile experiments. The simulation results provides a basis for subsequent laser welding / superplastic forming technology, and proposes outlook to the analyze problems for laser welding / superplastic forming (LBW / SPF) technology.

Abstract: The design and simulation of a polarization-independent active metamaterial terahertz modulator is presented in this work. The device incorporates an array of gold triple SRRs on an n-doped gallium arsenide layer to create an active metamaterial terahertz modulator with a high modulation depth, a high modulation speed and an especial polarization-independent performance for use in terahertz communication, imaging and sense.We established the theoretical model and simulatedthe key performances of the device with Ansoft HFSS.The results showed that the device exhibits a polarization-insensitivebehavior with a maximum amplitude modulation depth of 71% and a modulation rate of3.2Mbps at the resonance frequency of0.86 THz.

Abstract: 800MPa grade Advanced High Strength Steels (AHSS), including Complex Phase steel CP800 and Ferrite-Bainite steel FB800, were chosen to test the forming performance in different test conditions and compared with the reference traditional high strength low alloy (HSLA) steels HR700LA. Tensile test, hole expansion (HE) test, and HAT shape stamping test were taken to investigate the forming performance of the materials. Test results indicated that the studied 800MPa grade AHSS showed a better strength ductility balance compared with the reference steel. Among all the steels researched, FB800 showed the best hole expansion ratio (HER), and CP800 the worst. Springback angles of AHSS after HAT shape stamping tests were markedly smaller than those of HR700LA steels, though the springback angles of HR700LA decreased continuously with blank holding force (BHF) increasing. Steel FB800, CP800S and CP800B had much better shape stability compared with steels HR700LA. AHSS showed much smaller springback behavior under the same stamping condition, especially for steels CP800-B, FB800-2 and FB800-1. When increasing the BHF to 100KN, AHSS showed the largest springback deformation. Among the three kinds of CP800 steels researched, steel CP800-B indicated outstanding springback restrain trend in BHF further increasing attempt. So, springback behavior could be restricted obviously by using a larger BHF in AHSS CP800B forming operations.

Abstract: Effect of quenching-tempering process on microstructure and hardness of X38CrMo16 steel was investigated by means of OM, SEM, XRD and a digital hardness tester. The quenched and tempered steel consists of martensite (or its tempered structure), δ-ferrite and secondary particles. The secondary particles are identified as a FeCr intermetallic phase based on EDS and XRD analysis. Along with the increase of quenching temperature, the quantity of secondary particles gradually decreases and the prior austenite grains grow significantly, which led to the coarsening of martensite. A large number of blocky ferrite formed due to the increase of chromium level in the matrix. In addition, the hardness of the quenched steel continuously increases with quenching temperature up to 1100°C and then drop observably. Hence, the suitable quenching temperature of the steel is between 1050 and 1100°C. After tempering at 200 and 300°C, the hardness of the steel decreased due to the formation of tempered martensite and increased slightly after tempering at 400°C owing to secondary hardening, whereas this value decreased again after tempering at 500 and 600°C due to the formation of tempered sorbite.

Abstract: MODAPTS of Industrial Engineering (IE) work measurement was used for formulating welding hours. It was analyzed the program, operations and motion of production process on the arc welding production site. According to the theory of similar manufacturing principle, the auxiliary operation of the arc welding was divided into standard operation, typical operation and special operation. Their working hours were respectively analyzed and estimated. Arc welding operation time was treated as a set of the basic time and auxiliary operation sequence time. It is more scientific, rationalization and standardization for the welding hours, and improves the efficiency of formulating welding hours. A using example was given.

Abstract: This experiment collected sound signals of four different cars driving at different speeds on highway and replayed the noise samples with playback software HEAD Audio Recorder. The subjective evaluation tests were carried out with paired comparison method. Evaluating models between subjective evaluation and objective psychoacoustic parameters were established with SPSS analysis software.

Abstract: A n-order shear deformation theory is used to study the free vibration of functionally graded beams. Present theory satisfies the zero transverse shear stress boundary conditions on the top and the bottom surface of the beam. The natural frequencies computed by present theory are compared with previous published results which demonstrate the accuracy of present theory.

Abstract: Frame is the basic component of rice transplanting mechanism, which needs sufficient strength and stiffness because the frame often endures heavy loads and hits on poor working conditions. The UG geometric model of design frame was imported into the ANSYS for meshing. Reasonable constraint conditions and load were imposed, and the most significant four operating conditions of the frame were analyzed though static method. The stress-strain contours of the frame were obtained. The analyzed result provides design theory for the new type frame of rice transplanting mechanism and reference for the rebuilding and optimizing of the frame structure.

Abstract: The friction pair for bellows mechanical seal as a friction element is one of the key components for it. In this research, by based on the computational fluid dynamics (CFD) numerical theory, using the Fluent software, corresponding model and parameters, the fluid-film between the clearance of the sealing ring friction pair for the bellows mechanical seal under such the high-temperature, high-pressure, high-speed as complex working conditions is numerically simulated, the relationship between the carrying-capacity of the fluid-film and the temperature, the viscosity of the fluid-film, the relationship between friction torque of the fluid-film and the speed, viscosity of the fluid-film, the influence factor of leakage are obtained. The researching results provide the scientific basis for the optimization designing of the high parameter bellows mechanical seals.