Structural Strength and Service Life of the Extrusion Forming Die for Agricultural Engine Piston Heads

Three-tier high-strength prestressed combination concave dies are designed to manifacture highpower corn combine harvester engine piston heads. This design integrates the advantages of traditional casting or hot die forging and warm extrusion. The following key parameters, viz radial dimensions of each mating layer, axial bonding and radial contact interaction, are obtained by theoretical calculation. Nonlinear analysis of the contact interaction was carried out, and the die contact condition was studied at no-load and full-load. Based on the Archard wear theory, thermomechanical bonding was studied in operation of the die. Through numerical simulation of the die wear in each operation cycle, the univariate linear regression equation of the die service life was derived, and the reliability of this equation was verified. The results show that the die contact is both stable and reliable if the radial contact interaction of the inner and outer layers is δ₂= 1.9716 mm and δ₃= 1.3870 mm, respectively. With the nitriding layer thickness of 0.24 mm, the extrusion die service life in the production of piston heads corresponds to 6357 pieces.Разработаны трехъярусные высокопрочные предварительно-напряженные многоместные вогнутые головки для изготовления днищ поршня двигателя мощного кукурузоуборочного комбайна. Конструкция соединяет в себе преимущества литья или горячей ковки и горячей экструзии. Радиальные размеры каждого соединяемого слоя, осевое сцепление и радиальное контактное взаимодействие рассчитаны теоретически. Выполнен нелинейный анализ контактного взаимодействия, изучены условия контактирования в головке при нулевой и полной нагрузке. На основании теории износа Арчарда выполнена оценка термомеханического сцепления в процессе эксплуатации головки. Путем численного моделирования износа головки в каждом рабочем цикле получено однопараметрическое уравнение линейной регрессии для срока ее службы; проверена достоверность данного уравнения. Показано, что контакт в головке устойчив и надежен, при радиальном контактном взаимодействии внутреннего и наружного слоев δ₂= 1.9716 мм и δ₃= 1.3870 мм соответственно. При толщине нитридного слоя 0,24 мм срок службы экструзионной головки в производстве днищ поршня соответствует 6357 изделиям

The superconductivity at 18 K in LiFeAs system

A new iron arsenide superconducting system LiFeAs was found that crystallizes into a tetragonal structure with space group P4/nmm. The superconductivity with Tc up to 18 K was observed in the compounds. This simple 111 type layered iron arsenide superconductor can be viewed as an analogue of the infinite layer structure of copper oxides.Comment: 11 pages 3 Figure

The photosynthetic function analysis for leaf photooxidation in rice

Photooxidative damage causes early leaf senescence and plant cell death. In this study, a light-sensitive rice cultivar, 812HS, and a non-light-sensitive cultivar, 812S, were used to investigate early leaf photooxidation. Leaf tips of 812HS exhibited yellowing under a light intensity of 720 µmol(photon) m-2 s-1, accompanied by a decrease in chlorophyll and carotenoids, but 812S was unaffected. The photosynthetic performance of 812HS was also poorer than that of 812S. The H2O2, O2*-, and malondialdehyde content increased sharply in 812HS, and associated antioxidant enzymes were inhibited. The degradation of core proteins in both PSI and PSII, as well as other photosynthesis-related proteins, was accelerated in 812HS. When shaded [180 µmol(photon) m-2 s-1], 812HS recovered to normal. Therefore, our findings suggested excess light disturbed the balance of ROS metabolism, leading to the destruction of the antioxidant system and photosynthetic organs, and thus triggering the senescence of rice leaves