Measuring soil compaction and soil behavior under the tractor tire using strain transducer

Soil compaction can occur due to machine traffic and is an indicator of soil physical structure degradation. For this study 3 strain transducers with a maximum displacement of 5 cm were used to measure soil compaction under the rear tire of MF285 tractor. In first series of experiments, the effect of tractor traffic was investigated using displacement transducers and cylindrical cores. For the second series, only strain transducers were used to evaluate the effect of moisture levels of 11%, 16% and 22%, tractor velocities of 1, 3 and 5 km/h, and three depths of 20, 30 and 40 cm on soil compaction, and soil behavior during the compaction process was investigated. Results showed that no significant difference was found between the two methods of measuring the bulk density. The three main factors were significant on soil compaction at a probability level of 1%. The mutual binary effect of moisture and depth was significant at 1%, and the interaction of moisture, velocity, and depth were significant at 5%. The soil was compressed in the vertical direction and elongated in the lateral direction. In the longitudinal direction, the soil was initially compressed by the approaching tractor, then elongated, and ultimately compressed again.     

金属粉末爆炸烧结界面能量沉积机制

本文用绝热摩擦机制和微爆炸焊接模型讨论了爆炸烧结过程中金属粉末颗粒边界局部升温以至熔融的机理。指出这种升温时间大致和激波前沿的上升时间相当,约10-8秒量级 升温率高达1011度/秒。其界面温度可超过常压下的金属熔点。并与McQueen等人建立的多孔隙材料的绝热压缩理论进行了比较。     

Comparisons of different procedures of pre-compaction stress determination on weakly structured soils

Compaction is an important component of soil degradation. In this regard, the pre-compaction stress (σ_pc) concept is considered useful in mechanized agriculture nowadays. When the external forces exceed the internal strength (σ_pc) of soil, soil structure and soil physical quality will deteriorate. This concept was introduced at first for confined consolidation of non-structured, homogenized and saturated subsoils in civil engineering, though it is also suitable for agricultural conditions where the topsoil and subsoil are considered and both are often structured, heterogeneous and unsaturated. The best method for predicting σ_pc is by the plate sinkage test (PST) in the field, but it is expensive and time-consuming. This study was conducted to find an alternative laboratory method besides the confined compaction test (CCT) for predicting σ_pc. The CCT may not be a good method, especially at higher water contents, and for soils with low organic matter content, because of low sharpness of the critical region on the stress–strain curves. The study was performed on five soil types with a range of soil textures and organic matter content from central Iran using three loading types and three pF (i.e. Log [soil matric suction in cm]) values of 2.3, 2.7 and 2.9 with two replicates. Loading types consisted of CCT, the semi-confined compaction test (SCCT) and the kneading compaction test (KCT) at three maximum (or pre-compaction) stresses of 200, 400 and 600 kPa. The experiment was a completely randomized factorial design. The aim was to determine how accurately each loading type test could predict σ_pc of soil pre-compacted by one of the other methods. The applied combinations of CCT–SCCT, SCCT–CCT and KCT–CCT mean that the soil was pre-compacted by the first loading type and evaluated by the second one. The results showed that σ_pc and the sharpness of the σ_pc region were significantly affected by loading types as well as the soil conditions. The sharpest σ_pc region was observed in SCCT and the least sharp in CCT with the overall order being CCT–SCCT > SCCT–CCT > KCT–CCT. The sharpness of the σ_pc region was reduced for the soil samples with higher water content and coarser texture. Regardless of the soil and loading conditions, the prediction by SCCT was consistently more accurate than by CCT. The prediction of σ_pc by SCCT was more precise in comparison with CCT especially at higher stresses and soil water contents. However, the prediction of σ_pc by SCCT was very accurate at pF values of 2.7 and 2.9, and with low σ_pc values, when compared with the actual values of the σ_pc. For the clay soil at a pF value of 2.3, no pre-compaction region (i.e. zero σ_pc) could be determined by CCT at a maximum axial stress of 600 kPa. This was because of the incompressibility of soil water at this near-saturated soil condition at high stress. However, the sharpness of the critical region in SCCT was high enough to predict σ_pc satisfactorily. There was no significant difference between the combinations of SCCT–CCT and KCT–CCT in predicting σ_pc. The SCCT is a compromise method that lies between CCT and PST. SCCT has the advantage of using a limited and definite soil volume that can be modeled as a soil element. Marginal effects of disturbance caused by coring/sampling as well as pre-test sample preparation seem to have minor effects on the stress–strain curve determined by SCCT in comparison with CCT. Moreover, the soil volume needed for this test is the same as for CCT.     

碾压混凝土振动压实的实验研究

本文通过实验室与现场的实验,对RCC 的振动压实机理进行了研究,初步弄清RCC 层的动态特性及上层碾压对下层的作用,得到:振动压实能沿层深的衰减规律,RCC的各碾压参数之间的关系,振动碾的最佳机械参数,并阐述了RCC 的结构机理与压实过程.     

合肥电子储存环基本参数的测量

为了给改造后的合肥储存环留下参考数据,同时为了找到储存环存在的物理问题,储存环特性参数首次被系统测量,它们是动量扩张因子、色散函数、自然色品、校正色品和中心频率。     

钨粉爆炸烧结对粉末初始参数依赖关系的研究

本文从粉末爆炸烧结的能量沉积概念出发,提出了粉末爆炸烧结下限概念,讨论了钨粉末的爆炸烧结密度值和硬度分布对粉末初始参数的依赖关系,给出了实验结果。从理论和实验阐述了粉末初始参数在爆炸烧结实验中的重要作用。     

可变参数磁压缩系统设计

北京大学30MeV超导加速器包含3个RF加速单元: 自主研发的1.5cell DC-SC(直流-超导)注入器, 经过升级的3.5cell DC-SC注入器, 以及1.3GHz 2×9cell Telsa型超导加速腔. 为充分利用该装置上高品质电子束, 计划压缩1.5cell注入器出口电子束用于产生相干THz光, 以及压缩2×9cell超导加速腔出口电子束产生红外自由电子激光. 通过理论计算及模拟计算相结合设计了一套可变参数磁压缩系统, 该系统可以同时满足两个RF加速单元后束团压缩的要求.     

Numerical investigation into the influence of the punch shape on the mechanical behavior of pharmaceutical powders during compaction

During the production of pharmaceutical tablets using powder compaction, certain common problems can occur, such as sticking, tearing, cutting, and lamination. In the past, the compressibility of the powder was calculated only along the axis of the device; consequently, critical areas of the material throughout the volume could not be identified. Therefore, finite element method （FEM） can be used to predict these defects in conjunction with the use of an appropriate constitutive model. This article summarizes the current research in the field of powder compaction, describes the Drucker-Prager Cap model calibration procedure and its implementation in FEM, and also examines the mechanical behavior of powder during compaction. In addition, the mechanical behavior of pharmaceutical powders in relation to changes in friction at the wall of the system is examined, and the dependence of lubrication effect on the geometry of the compaction space is also investigated. The influence of friction on the compaction process for the flat-face, fiat-face radius edge, and standard convex tablets is examined while highlighting how the effects of friction change depending on the shape of these tablets.     

The Effect of Post Hot Compaction on Crystallinity and Thermal Behavior of Ultra-High Molecular Weight Polyethylene Fiber Laminates

Thermal compacting of previously prepared ultra-high molecular weight polyethylene (UHMWPE) fiber laminates can raise its melting temperature and crystallinity. In this article, thermal shrinkage and the effect of post hot compaction on a commercial UHMWPE fiber laminate at various temperatures was investigated. The temperature range of post hot compaction was between 115 and 145°C, while other processing parameters like pressure, time, and cooling rate were kept constant during compaction. The shrinkage of the fiber laminates increased slowly up to 138°C; as soon as the temperature passed 140°C, the shrinkage increased rapidly and reached its maximum value very quickly. The crystallinity of the fiber laminates increased with rising temperature up to 135°C, then decreased at 145°C.