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With the development of lightweight technology, advanced high strength steel (AHSS) had been widely used in automotive and construction industry. However, twist defect restricts the application of thin-walled components with asymmetric section. In this work, AHSS MS1500 was taken to investigate the complex non-linear elastoplastic behaviors and twist defect in roll forming process. Finite element analysis (FEA) model was established by COPRA software and the material model considered Young’s modulus variation with plastic deformation and material anisotropy was selected. With the developed model, the mechanism of twist defect was discussed and the effect of forming strategy on twist defect was analyzed. For asymmetric hat channel steel, the asymmetric residual longitudinal stress is the principal reason for twist defect. Loading patterns have a significant effect on twist defect and the developed UDT-type (USTB-Durable-type) method can control twist defect effectively. This study has provided theoretical and technical support on large-scale application of AHSS.

In order to obtain the pure shear deformation characteristics along the circumferential direction of tubes, a circumferential shear test for thin-walled tubes is proposed in this paper. The experimental device consists of a tubular sample and two cylindrical mandrels with shear plates. The torque along the circumferential direction was applied to the tubular sample by the two shear plates to make the pre-set shearing zone of the sample under a circumferential pure shear stress state. The two cylindrical mandrels support the inner wall of the tube to avoid buckling so that the pure shear stress state can be maintained during the whole deformation process. A 5052 aluminum alloy tube with an outer diameter of 50 mm and a wall thickness of 1.2 mm was used in the test. It is shown through simulation and experiment that shear deformation is concentrated in the pre-set shearing zone. This test can be used to obtain the circumferential pure shear stress-strain relationship.

In recent years, there has been development of several significant pipeline projects for the transmission of oil and gas from deep water environments. The production of gas transmission pipelines for application demands heavy wall, high strength, good lower temperature fracture toughness, low yield ratio and good corrosion resistance. To overcome the difficulties of producing excellent performance in heavy wall X65MOS pipe Shougang Steel Research in cooperation with the Shougang Steel Qinhuangdao China (Shouqin) 4.3m heavy wide plate mill research was conducted. This paper describes the background, composition design, key process strategy to produce excellent performance in heavy wall X65MOS plate. The importance of recrystallized rolling process, the tensile property change during pipe making and the corrosion resistance change by “pre-stretching + bend” deformation simulate pipe making in the lab will be discussed. The results showed the per pass reductions during recrystallized rough rolling should be increased in a steady fashion, with special emphasis on the reduction of the final two roughing pass prior to the intermediate hold (transfer thickness for finishing) should be more than 20%. The tensile properties change rule and the reasonable pipe expansion process should be determine during pipe making. The crack length ratio(CLR) internal control criteria of the plate should be less than 6%, it helps to ensure the HIC performance of the pipe can meet the technical specification(CLR≤15%).

With the increase of wind power capacity incorporated into the grid, the permeability of wind power increases continuously, which leads to the reduction of the equivalent inertia of the system. A new strategy of recovering rotor speed that increases the output power by modifying the variable power curve is proposed in this paper, which decreases the drop of the active power. So as to reduce the secondary frequency dips caused by the sudden drop of the active power when the speed restores. The paper optimizes the secondary frequency dips by modifying the variable power curve continuously. This article simulates this strategy through setting up a system by Simulink. Compared with the traditional recovery strategy, validity of the proposed strategy is demonstrated through simulation and analysis.

A 2319 aluminum alloy is deposited by the Wire+Arc Additive Manufacturing technology with Cold Metal Transfer process. Porosity that are both existing in the as-deposited and as-heat treated state metal are revealed by optical microscopy and quantitatively analyzed. It explains the reason why the newly initiated pores are easily tend to gather between each layer around the fusion line zone for the WAAM metal after heat treatment. The inner morphology of the pores are demonstrated by Scanning Electron Microscopy. Porosity evolution and distribution during high temperature exposure are demonstrated. Thus two porosity growth and number increase mechanisms are proposed eventually, providing theoretical basis for related material design and process optimization.

Grassland ecosystem is important for climatic regulation, maintaining the soil and water. Research on the grassland monitoring method could provide effective reference for grassland resource investigation. In this study, we used the vegetation index method for grassland classification. There are several types of climate in China. Therefore, we need to use China's Main Climate Zone Maps and divide the study region into four climate zones. Based on grassland classification system of the first nation-wide grass resource survey in China, we established a new grassland classification system which is only suitable for this research. We used MODIS images as the basic data resources, and use the expert classifier method to perform grassland classification. Based on the 1:1,000,000 Grassland Resource Map of China, we obtained the basic distribution of all the grassland types and selected 20 samples evenly distributed in each type, then used NDVI/EVI product to summarize different spectral features of different grassland types. Finally, we introduced other classification auxiliary data, such as elevation, accumulate temperature (AT), humidity index (HI) and rainfall. China's nation-wide grassland classification map is resulted by merging the grassland in different climate zone. The overall classification accuracy is 60.4%. The result indicated that expert classifier is proper for national wide grassland classification, but the classification accuracy need to be improved.