基于Fluent的高压水射流喷嘴优化模拟研究

为了提高高压水射流技术的破煤效率,采用Fluent软件对高压水射流的喷嘴结构和几何参数进行了优化模拟。通过分析水射流的轴向速度和壁面静压分布,选择了最佳的喷嘴结构和几何参数。结果表明:圆柱形喷嘴的最大射流速度发生在喷嘴内部,而锥形和锥直形喷嘴的最大射流速度发生在喷嘴外部,且锥形和锥直形喷嘴的最大射流速度和最大压力均明显大于圆柱形喷嘴,考虑到水射流的附壁效应,锥形喷嘴为最佳选择。锥形喷嘴的最优几何参数为:喷嘴出口直径3 mm,喷嘴锥角7°,喷嘴长度9 mm。高压水射流喷嘴的优化对提高煤层瓦斯抽采效率具有重要意义。     

高速激光热丝钎焊表面成形质量的控制

高速激光钎焊会引起熔池流动紊乱导致焊缝成形质量恶化,从而限制了其在汽车制造领域的应用。通过正交试验研究了高速下激光功率、送丝角度等工艺参数对焊缝成形质量的影响,发现焊缝成形质量随激光功率增加和送丝角度减小而提升。激光功率是通过影响熔池获得的热输入,从而影响熔池表面扰动的铺展来影响焊缝成形质量的。送丝角度是通过影响焊丝送入熔池的位置,从而影响焊丝对熔池的扰动强度和扰动的铺展速度来影响焊缝成形质量的。采用正交试验获得的最优工艺参数组合进行试验,获得了表面光滑平整无缺陷的高质量焊缝,为激光钎焊在高速下的应用发展奠定了基础。     

新型微坑车刀切削AISI4140残余应力影响因素分析研究

为了探究切削用量对新型微坑车刀切削工件表面残余应力的影响规律,应用AdvantEdge切削仿真软件,结合单因素和正交实验,通过微坑车刀和原车刀切削AISI_4140仿真及实验验证。结果表明,原车刀和微坑车刀残余拉应力随切削速度增大,先增大后减小,随进给量的增大而减小,总体上,微坑车刀切削工件残余拉应力更小。残余压应力随切削速度增大,微坑车刀切削工件先增大后减小,随进给量增大先增大后减小。原车刀几乎不变。切削用量对微坑车刀切削工件残余应力影响,进给量最大,切削速度次之,切削深度最小。通过实验验证,相同切削条件下,微坑车刀降低了加工工件表面残余拉应力,提高了加工工件表面质量,一定程度提高了工件的服役寿命。     

用于阀芯类零件去毛刺的磁极板优化设计与实验研究

目的 为解决阀芯类零件节流边毛刺去除不均匀和效率低下的问题，对磁极板尺寸和曲率进行规律性研究和实验验证。方法 首先，用Maxwell仿真软件对磁极板的各个参数进行规律性仿真，得出合适的磁极板尺寸;其次，为提高加工区域的磁感应强度值，设计了曲面磁极板，并对其相关参数进行仿真;最后对优化后的装置进行磁感应强度测试，并使用液体磁性磨具对45钢和阀芯棱边毛刺进行去除实验。结果 根据仿真结果发现，磁极板长度比工件大20 mm时，工件轴向磁场分布最均匀，磁极板厚度对磁场影响较小，磁极板宽度应根据加工间隙进行选择。曲面磁极板可以加强加工区域的磁感应强度值，曲率半径越小，加工区域获得的磁感应强度值越大，其中半圆形磁极板效果最佳。对装置的磁感应强度测试也表明，将工件置于磁场中后，其表面磁感应强度值最高达600 mT左右，满足加工需求。最后通过加工实验发现，在转速为500 r/min的条件下，阀芯节流边的毛刺去除效果理想，且轴向加工均匀。结论 该装置可以对阀芯这类导磁性回转类零件产生良好的加工效果。     

Effects of welding parameters and welding sequence on residual stress and distortion in Al6061-T6 aluminum alloy for T-shaped welded joint

The distribution of temperature and then the distribution of residual stress and distortion in the stiffened aluminum alloy Al6061-T6 plates under the metal inert gas (MIG) welding process were investigated by three dimensional thermo-mechanical coupled finite element model using Ansys software. The properties of materials were considered temperature-dependent and the filler metal was added to the workpiece by the element birth and death technique. In three modes of current, two different speeds and two various sequences, the distribution of residual stress and distortion were calculated and analyzed. The results showed that increase in welding speed decreased the vertical deflection in the plate, transverse shrinkage and angular distortion of plate and the lateral deflection of stiffener, but increased the maximum longitudinal tensile stress in the plate and stiffener. Furthermore, increase in current increased the residual stress and deformation in the plate and stiffener, and the change in the welding sequence changed the distribution of the distortion in the plate and the stiffener without significant change in the distribution of the longitudinal residual stress.     

Microstructure and mechanical properties of TiC0.7N0.3-HfC cermet tool materials

TiC_0.7N_0.3-HfC cermet tool materials were fabricated by hot-press sintering. Effects of different metal additives (Ni, Co, Ni-Co and Ni-Mo), sintering temperature and holding time on the microstructures and mechanical properties of TiC_0.7N_0.3-HfC cermets were investigated. Results showed that Ni-Mo or Ni-Co as metal additives was better for the mechanical properties of TiC_0.7N_0.3-HfC cermets than only Ni or only Co as the metal additives and Ni-Mo better than Ni-Co. HfC particle dispersion existed in these four cermets and only in the TiC_0.7N_0.3-HfC-Ni-Mo cermet the core-rim structure obviously existed. TiC_0.7N_0.3-HfC-Ni-Mo cermet had significantly smaller grains than the other three cermets because Ni-Mo can significantly refine the grain. With the sintering temperature increasing from 1450?°C to 1650?°C, grains grew gradually; Vickers hardness and flexural strength decreased gradually and the fracture toughness increased firstly and then decreased. With the holding time increasing from 15?min to 60?min, grains grew gradually; Vickers hardness, flexural strength and the fracture toughness increased firstly and then decreased. TiC_0.7N_0.3-HfC-Ni-Mo cermets sintered at 1450?°C with 30?min holding time had the better comprehensive mechanical properties with flexural strength of 1346.41?±?31?MPa, fracture toughness of 8.46?±?0.23?MPa?m^1/2 and Vickers hardness of 22.91?±?0.22?GPa.     

Effects of ionic radius on phase evolution in Ln-Al co-doped Ca1-xLnxZrTi2-xAlxO7 (Ln = La,Nd, Gd,Ho, Yb) solid solutions

Zirconolite ceramic has been considered as a promising matrix to dispose high-level radioactive waste due to its excellent performance in immobilizing radionuclides. In this work, a series of zirconate solid solutions with stoichiometric Ca_1-xLn_xZrTi_2-xAl_xO₇ (Ln = La, Nd, Gd, Ho, Yb; x?=?0.1–1) were systematically studied to investigate the radius effect on their phase evolution. Powder X-ray diffraction (XRD) and scanning electron microscopy with energy dispersive X-Ray spectrometry (SEM-EDX) were used to characterize the products. XRD and SEM results show that complete solid solutions of Ln and Al in zirconolite phase for Ca_1-xLn_xZrTi_2-xAl_xO₇ cannot found. In the Ca_1-xLa_xZrTi_2-xAl_xO₇ ceramics, single zirconolite phase cannot form, instead of multiple phases, such as zirconolite-2M, zirconia, perovskite and LaTi₂Al₉O₁₉. In the Nd-Al co-doping ceramics, nearly single zirconolite-2M and zirconolite-3O were found at x?≤?0.6 and 0.8?≤?x?≤?0.9, respectively. The miscibility gap between zirconolite-2M and 3O was found at x?=?0.7. Single zirconolite-2M formed in the Gd-Al, Ho-Al and Yb-Al co-doped ceramics can only be detected in a compositional range of 0.1?≤?x?≤?0.8. Higher incorporation contents in these three series can form an additional phase cubic zirconia which is usually a ceramic waste form for radionuclides. Based on the XRD data, lattice parameters of zirconolite-2M and zirconolite-3O were calculated by Pawley refinement method. The evolution of lattice parameters of zirconolite-2M shows great difference between different lanthanide ions, indicating different substitution mechanisms in the Ln-Al co-doped zirconolite-2M.     

Thermal stability of nanometric TiC-carbon composites: effects of carbon allotropes and Zr milling impurities

In the ISOL (Isotope Separator OnLine) method a target at high temperatures (up to 2300?°C), is bombarded with high energy protons in order to produce isotopes through nuclear reactions which are simultaneously extracted from the target, ionized and delivered to physics experiments. Due to the enhanced isotope release properties of nanosized porous materials, titanium carbide-carbon porous nanocomposites have been developed at CERN and tested up to 1500?°C. In the interest of the ISOL application, in this study we extended the range of temperatures up to 1800?°C, to test the sintering hindering capabilities of different carbon allotropes. Carbon black was the most effective with the smallest TiC crystallite size: <80?nm at 1800?°C. Additionally, using thermodynamic modelling, ex-situ X-ray powder diffraction and in-situ gas phase analysis, we show that there are interesting additional phase and lattice parameter changes due to the ZrO₂ impurities from the attrition milling.