基于ABAQUS的金属板料激光冲击成形数值模拟

在激光冲击波加载转换模型的基础上,以有限元分析软件ABAQUS／CAE为平台,对圆形板料进行了直线形轨迹和圆形轨迹多点冲击成形的数值模拟,探索了冲击轨迹、应力分布和板料变形之间的相互关系。数值模拟分析表明,对圆形板料进行多点冲击成形时,选择圆形轨迹是最佳的。根据模拟结果对铝合金板料试样进行了无间隔冲击成形的实验,获得了和数值模拟相同的成形结果,模拟和实验结果一致性较好。     

History, origin and extent of soil erosion on Easter Island (Rapa Nui)

The isolated Easter Island (Rapa Nui) is an outstanding example of land degradation caused by land use in a sensitive ecosystem. The focus of the investigation was placed on Poike peninsula, the most eastern part of Rapa Nui. While Poike peninsula was once supplied with fertile soils, in large areas desertification takes place today. Detailed analysis of soil profiles allowed the reconstruction of the history and of causes and effects of soil erosion and gullying in the context of land use history and cultural evolution. The results of the stratigraphic analysis prove that from the beginning of human settlement around AD 300/600 until AD 1280 the agriculture on Poike peninsula was characterised by sustainable land use and a traditional type of agro-forestry. Soil erosion was not significant. At around AD 1280 the woodland on Poike, dominated by the endemic palm Jubaea sp., was cleared by slashing and burning. Intensive farming on the upper slopes of the volcanic peninsula resulted in sheet erosion lasting until the 20th century. Settlements and ceremonial places which were built around AD 1300 on downslope areas were buried soon by sediments. Agriculture ceased around AD 1400 on downslope areas as the fertile soils were completely eroded. From AD 1400 until the late 19th century sheet erosion and the accumulation of fine-layered sediments migrated upslope. On average 8.6 Mg of soil per hectare and per year were reworked by erosion (eroded and accumulated within the catchment). Gullying began on Rapa Nui with the sudden increase in the number of sheep during the early 20th century. Gullies are still developing on the island and their ongoing enlargement created extended badlands on Poike which pose a significant problem for ecological and archaeological conservation strategies. Gullying rates exceed 190 Mg ha^{− 1} y^{− 1}.     

Modelling sediment transport from bare rilled hillslopes by areally averaged transport equations

Treating the dynamics of sediment transport as two-dimensional on interrill-areas and as one-dimensional in rill sections, areally averaged sheet sediment transport equations are developed. The two-dimensional sheet sediment transport equation is averaged over an individual interrill-area width and then along the interrill-area length to obtain local-scale areally averaged interrill-area sheet sediment transport equation (local-scale areal averaging). Similarly, the cross-sectionally-averaged rill sediment transport equation is averaged along an individual rill length to obtain local-scale areally averaged rill sediment transport equation (local-scale areal averaging). In order to minimize computational effort and economize on the number of model parameters, the local-scale areally averaged equations are then averaged over a whole hillslope section (large-scale areal averaging). These equations constitute the areally averaged model. The expectations of the terms containing more than one variable are obtained by the method of regular perturbation. In the large-scale areal averaging it is assumed that all the randomness in the state variable is due to the randomness in the parameters of the process. Comparison of the results obtained from the areally averaged model with those of the point-scale model indicates that the areally averaged model uses far less data and yet it performs as well as the point-scale model. The results of the developed model indicate that on a rilled-surface most of the sediment loads comes from rill sections. The developed model is successfully tested against experimental data obtained from a bare rilled hillslope. It predicted measured runoff and sediment rates with mean absolute errors of 11.07 l/min and 0.382 kg/s, respectively.     

不同烘丝方式对烟丝外加香料持留率的影响

[目的]了解不同烘丝方式对烟丝外加香料持留率的影响。[方法]将10种外加香料加入到烟丝中,分别经薄板烘丝与HXD烘丝后,进行同时蒸馏萃取,并用气相色谱仪与气质联用仪测定外加香料的持留率。[结果]薄板烘丝与HXD烘丝后的外加香料持留率相差不大,可能与所用香料沸点均在128℃以上有关。[结论]薄板烘丝后的外加香料持留率比HXD烘丝后的要高一些。     

基于连续多点成形原理的旋压成形技术

介绍了传统的旋压工艺,提出了基于连续多点成形原理的旋压成形工艺,对工作旋轮的布置和驱动方式进行了探讨,研制出高效旋压成形装置,在所研制的旋压成形装置上成形了大量的实验件,实现了圆形板料件的高效旋压成形,为建立新型高效旋压成形的基本理论,解决柔性旋轮结构设计与控制点设置、自动控制系统的控制模式及探索技术参数作必要的准备工作.     

板料深冲成形过程的静态隐式有限元模拟

采用有限元对板料冲压过程进行模具设计,可以降低设计成本,缩短设计周期。综述了板料深冲成形过程数值模拟平台和静态隐式算法的基本理论,并基于此建立了四节点的有限元模型。采用此模型对油底壳和水槽的深冲成形过程和起皱进行了模拟,模拟结果验证了该分析技术的正确性、可行性和高效性。     

激光冲击波技术在金属表面改性和成形中的应用

在对激光冲击强化技术的原理、特点及工程应用须解决的关键问题进行系统分析的基础上,介绍了激光冲击波技术在金属板材成形方面的最新研究进展：激光冲击成形和激光喷丸成形,对激光冲击成形和激光喷丸成形的机理、技术特点及国内外的研究现状进行了综述,并对今后的应用前景和发展趋势作了分析.     

Fine structure and physical properties of poly(buthylene terephthalate) sheets prepared by roller drawing method

Poly(butylene terephthalate) sheets were prepared by roller-drawing method with various draw ratio. The drawing temperature is 100 °C and draw ratios were varied 2, 2.5, 3, 3.5 and 4. The effect of draw ratio on the crystal structure, the molecular orientation, dynamic viscoelastic properties, sonic modulus and tensile properties of the roller-drawn PBT sheets were investigated. In WAXD results, with increasing of the draw ratio, (010) and (100) planes of preferred orientation have the strongest intensity on the equator. In the meridional scans, it was confirmed that α and β crystal co-existed in the roller drawn PBT sheets with various draw ratio. Uniaxially roller-drawn PBT sheets clearly increased orientation along the stretched direction at high draw ratio. And the four-methylene groups of PBT orient along the surface of the sheet. The mechanical properties of PBT sheets were improved by orientation-induced crystallization during roller drawing process at 100 °C.     

汽车底盘弹簧支架冲压成形的数值模拟研究

基于大变形非线性有限元理论，建立了三维Ｈｕｇｈｅｓ－Ｌｉｕ壳单元有限元模型，模拟了轻型汽车底盘金属薄板弹簧支架冲压成形过程，给出了板料在成形过程中厚度、法向应变等结果。结果表明本文提出孤力学模型是可靠的。模拟结果为确定冲压工艺参数提供重要的理论依据。     

冲压成形极限图虚拟试验

基于非线性有限元软件系统平台进行虚拟FLD试验,即通过数字建模虚化FLD试验装置及其试样,在不使用塑性失稳准则或断裂准则的情况下,利用数值模拟运算求解板材发生塑性失稳时的极限应变,并把这些应变拟合成相应的成形极限曲线(FLC)。虚拟FLC不仅与实测FLC之间具有比较接近的几何图形,而且彼此间的最大应变误差(Δε1、Δε2)仅为4%,因此从工程上讲,虚拟FLD试验具有替代或部分替代实测FLD试验的可能性。