Stress uniformity process of specimens in SHPB test under different loading conditions of rectangular and half-sine input waves

Based on the characteristics of 1D waves,the stress uniformity process in specimens under different loading conditions of rectangular and half-sine input waves was analyzed in split Hopkinson pressure bar (SHPB) test.The results show that the times of an elastic wave propa-gating from one end to the other in a specimen to attain stress equilibrium,is related to input wave-forms and relative mechanical impedance between the specimen and the input/output bars.Here-into,with the increae of the relative impedance,the times decreases under rectangular input waves loading,while it increases under half-sine input wave loading.The dimensionless stress value of specimen corresponding to the status of stress equilibrium increases with the increase of the rela-tive mechanical impedance.However,the dimensionless stress value under half-sine input wave loading is significantly lower than the value under rectangular input wave loading for specimen with low mechanical impedance,and the relative differentia of the dimensionless stress values under two loading conditions decreases with the increase of the relative mechanical impedance.In gen-eral,the forced state of specimen with relatively low mechanical impedance under half-sine input wave loading is evidently superior to the state under rectangular input wave loading in SHPB test,and the advantages of forced state under half-sine input wave loading turns weak with the increase of the relative mechanical impedance.     

基于 Fluent 的锂离子电池及模组风冷温度场数值研究

为了研究锂离子电池充（放）电过程中热性能特点,更好地进行热管理分析,基于 Fluent 软件建立锂离子电池组三维瞬态散热模型并对温度场进行仿真计算,分析不同条件对电池及模组散热性能的影响。结果表明：减小充（放）电倍率和增大表面对流换热系数可改善电池因温度过高而导致的热失控。进口风速从 0.5 m/s增至 6 m/s 且 4C 充电终止时,电池组最高温度、平均温度、温差、一致性系数降低了 33.57 K、21.23 K、9.84 K 和 2.82%,但泵功耗增加了 0.35 W。进风温度从 298.15 K 降至 283.15 K 且 4C 充电终止时,电池组最高、平均温度降低 12.8 K 和 13.92 K,温差与一致性系数升高 1.86 K 和 0.76%。即增大风速,电池组温升和温度均匀性得到改善;降低进风温度,可控制电池组温升,但温度均匀性抑制效果变差。     

短行程直线直流电机的温度场分析

介绍了温度场分析的基本原理,在已有短行程直线电机的设计基础上,运用ANSOFT软件对电机进行三维温度场建模,对电机内部线圈进行热分析,计算在不同电流下电机稳定运行后各组线圈的温度变化情况,得到电机内部温度场分布图。另外也分析了冷却水的流换热系数对温度变化的影响,这些为后续对电机内部的冷却系统设计,找出最佳的冷却水循环路线,进行电机的优化设计提供参考。     

Analysis of ice slurry production by direct contact heat transfer of air and water solution

In this paper, a novel system using direct contact heat transfer between air and water solution was proposed to generate ice slurry. The heat transfer process and the system performance were studied; energy efficiency coefficients of 0.038, 0.053, and 0.064 were obtained using different solutions. An empirical relationship between the volumetric heat transfer coefficient Uv and the main parameters was obtained by fitting the experimental data. The Uv calculated from the empirical formula agreed with the experimental Uv quite well with a relative error of less than 15%. Based on the empirical formula, a laboratory-scale direct contact ice slurry generator was then constructed, with practical application in mind. If the air flow rate is fixed at 200 m3/h, the ice production rate will be 0.091 kg/min. The experimental results also showed that the cold energy consumption of the air compressor accounted for more than half of the total amount. To improve the system energy efficiency coefficient, it is necessary to increase the air pipes insulation and the solution＇s thermal capacity, and also it is appropriate to utilize the free cold energy of liquefied natural gas （LNG）.     

SHPB虚拟仿真实验教学项目的研究与开发

高应变率下材料的动态力学性能一般采用分离式霍普金森压杆进行实验测量,但由于该类设备的操作危险性大,测试参数设置互相影响,实验经验对测试结果影响较大,学生学习和操作困难。该文所开发的虚拟仿真实验教学项目,可通过设置不同的测试参数,得到不同的实验结果和测试精度,甚至是失败的测试,从而帮助学生掌握和分析测量参数设置的规律,培养学生的实际操作能力。     

Simplification and Experimental Verification for Temperature and Humidity Field Coupling Model of Conservatory Soil

Based on the surface energy balance model which is widely used abroad, a temperature and humidity field coupling model of conservatory soil without crop vegetation in full illumination was established. Considering the relatively closed environment in conservatory, weak solar radiation and little surface evaporation of soil, the daily variation of water content in different soil layers may be neglected, then the temperature and humidity field coupling model was simplified to a one-dimensional thermal diffusion model. The simplified model and the temperature and humidity field coupling model adopted the same computational method of soil physical parameters and discrete format of heat diffusion differential equations, and were applied to the continuous simulation of temperature field in conservatory soil without crop vegetation in full illumination. Through the comparison between simulation results and experimental data, the precision of the simplified model was verified. The typical rule of soil heat flux variation in a 24 h cycle was also obtained.     

6061铝合金热变形行为与热加工图

基于Gleeble-3500热模拟试验机平台,对6061铝合金进行等温热压缩实验,研究了该合金在变形温度为350~500℃和应变速率为0.01~10s-1条件下的高温流变行为并建立了6061铝合金的Arrhenius本构方程,应用于Deform软件进行热压缩实验模拟基于动态材料模型和Murty准则,建立了6061铝合金在不同应变下的加工图,结合显微组织进行验证。结果表明,该合金材料的流变应力随应变速率增加而增大,随变形温度降低而增大建立的本构方程能较好描述该合金的高温流变行为变形温度为460~500℃,应变速率为0.1~0.5s-1的区域是该合金最佳工艺参数范围。     

高温力学试验机电加热炉炉温智能控制

针对高温力学试验机电加热炉炉温控制的复杂性、工艺特点及要求，提出采用计算机与神经元控制技术相结合，组成具有解耦能力的智能控制方法，给出了控制原理及仿真研究结果。     

混凝土环境中BFRP筋耐久性能试验研究(英文)

针对玄武岩纤维增强树脂基复合筋(BFRP)在混凝土环境中的耐碱性能进行了加速腐蚀试验研究.腐蚀试验环境包括3种,分别为自来水、盐水及室内空气环境,将包裹有混凝土保护层的BFPR筋试件分别放置在上述3种环境中,试验同时采用碱溶液直接浸泡BFRP筋作为对比,对直接碱溶液浸泡环境与混凝土包裹环境之间的加速系数进行了研究.试验采用60℃的高温进行加速.试验结果表明:自来水和盐水浸泡对于包裹有混凝土的BFRP筋试件没有明显差异.分析认为,与混凝土内部高碱性的孔隙溶液接触是BFRP筋退化的主要原因,当经受高温和高湿环境共同作用时,混凝土环境中BFRP筋的退化将明显加速;BFRP筋的退化速率在初期较快,随着龄期的增长,退化速率降低.基于试验数据分析表明,对于所采用的BFRP筋,60℃饱和吸湿混凝土环境下,BFRP筋2.18 a的退化程度与60℃碱溶液直接浸泡环境下1 a的退化程度相当.     

THE MICROSTRUCTURE AND PROPERTIES OF ALUMINA FIBER-REINFORCED ALUMINIUM ALLOY MATRIX COMPOSITE

The morphology of the microstructure of Al-alloy composite with variousfiber contents was examined under optical microscope.The fracture of tension specimenwas studied under scanning electron microscope(SEM).The mechanical properties,wearresistance and coefficient of thermal linear expansion of the composite were measured.Theexperiment shows that the composite studied is suitable for engine pistons due to its goodwear resistance,higher elevated temperature mechanical properties and lower coefficient ofthermal linear expansion.     

Numerical Simulation on Nugget Formation and Evolution in Spot Welding of Aluminum Alloy

With the squeeze of electrode tips, the oxide film on aluminum (Al) alloy surface is broken and numbers of micro-gaps are formed randomly. The micro-gaps act as conducting spots at the beginning of welding, so the contact resistance is extremely high and unstable in spot welding of Al alloy. In this paper, a new contact resistance model is adopted to simulate the nugget forming process. This model describes the random distribution characteristic of conducting spots. The simulation results indicate that, within the first 5 ms of welding current (AC, 50 Hz), the temperature distribution at the workpieces interface is seriously irregular. In addition, the nugget does not nucleate from the weld center and grow continuously, however, it nucleates randomly from several points almost instantaneously and then merges into an entity quickly. Experimental results agreed with the numerical simulation.     

Spallation mechanism of RC slabs under contact detonation

The spallation of the concrete slabs or walls resulting from contact detonation constitutes risk to the personnel and equipment inside the structures because of the high speed concrete fragments even though the overall structures or structural members are not destroyed completely.Correctly predicting the damage caused by any potential contact detonation can lead to better for-tification design to withstand the blast loadings.It is therefore of great significance to study the mechanism involved in the spallation of concrete slabs and walls.Existing studies on this topic of-ten employ simplified material models and 1D wave analysis,which cannot reproduce the realistic response in the spallation process.Numerical simulations are therefore carried out under different contact blast loadings in the free air using LS-DYNA.Sophisticated concrete and reinforcing bar material models are adopted,taking into account the strain rate effect on both tension and com-pression.The erosion technique is used to model the fracture and failure of materials under tensile stress.Full processes of the deformation and dynamic damage of reinforced concrete (RC) slabs and plain concrete slabs are thus observed realistically.It is noted that with the increase of quantity of explosive,the dimensions of damage crater increase and the slabs experience four different damage patterns,namely explosive crater,spalling,perforation,and punching.Comparison be-tween the simulation results of plain concrete slabs and those of RC slabs show that reinforcing bars can enhance the integrity and shearing resistance of the slabs to a certain extent,and mean-while attenuate the ejection velocity and decrease the size of the concrete fragments.Therefore,optimizing reinforcement arrangement can improve the anti-spallation capability of the slabs and walls to a certain extent.     

某低合金钢SHPB动态压缩试验的数值模拟

应用Perzyna材料强度模型,对应变率敏感的某低合金钢的SHPB动态压缩试验进行了数值模拟分析,获得了高应变率下的应力-应变曲线,并与实验值相比较。比较结果表明:当应变大于2%时,模拟结果与实验结果非常吻合,偏差在8%以内。     

Effects of Temperature and Strain Rate on Dynamic Properties of Concrete

To study the dynamic properties of the concrete subjected to impulsive loading,stress-time curves of concrete in different velocities were measured using split Hopkinson pressure bar (SHPB).Effects of temperature and strain rate on the dynamic yield strength and constitutive relation of the concrete were analyzed.The dynamic mechanical properties of the reinforced concrete are subjected to high strain rates when it is at a relatively low temperature.But with temperature increasing,the temperature softening effect makes the strength of the concrete weaken and the impact toughness of the concrete is saliently relative to strain rate effect.So,strain rate effect,strain hardening and temperature softening work together on the dynamic mechanical capability of concrete and the relation between them is relatively corn plex.     

Effects of Temperature and Strain Rate on Dynamic Properties of Concrete

To study the dynamic properties of the concrete subjected to impulsive loading, stress-time curves of concrete in different velocities were measured using split Hopkinson pressure bar (SHPB).Effects of temperature and strain rate on the dynamic yield strength and constitutive relation of the con-crete were analyzed. The dynamic mechanical properties of the reinforced concrete are subjected to high strain rates when it is at a relatively low temperature. But with temperature increasing, the temperature softening effect makes the strength of the concrete weaken and the impact toughness of the concrete is saliently relative to strain rate effect. So, strain rate effect, strain hardening and temperature softening work together on the dynamic mechanical capability of concrete and the relation between them is relatively complex.     

Aggregate gradation design of asphalt mixture with stone-to-stone contact based on fuller's model

Based on Fuller's model, a gradation design is presented for the load-carrying capacity of an asphalt mixture with stone-to-stone contact. The coarse aggregate gradation, fine aggregate and filler gradation are respectively designed for their different effects on an asphalt mixture with stone-to-stone contact. The equation of coarse aggregate gradation is deduced from the Fuller's model. Fine aggregate gradation is calculated by using Fuller's equation. The asphalt mixture with the 16 mm maximum size of aggregate is verified. When the coefficient of coarse aggregate gradation is 0.35 and fine aggregate gradation is 0.25, the volume parameters of asphalt mixture meet the technical specifications. Moreover, the high temperature stability and crack resistance at low temperature are all well.     

测量玻璃热膨胀系数和折射率温度系数实验

为了测量玻璃热膨胀系数和折射率温度系数,设计了基于水平光路的玻璃热膨胀系数和折射率温度系数的测量方法。运用光束在玻璃样品中发生干涉的原理,用自然降温法进行测量。实验得到干涉光斑的条纹移动数与温度呈线性关系,通过拟合实验曲线的斜率,即可计算该玻璃样品的热膨胀系数和折射率温度系数。该实验装置结构简单、调节方便、条纹移动清晰,自然降温法获得的数据线性良好,精确度高。     

Performance investigation of 2D lattice Boltzmann simulation of forces on a circular cylinder

The lattice Boltzmann method (LBM) is employed to simulate the uniform flow past a circular cylinder. The performance of the two-dimensional LBM model on the prediction of force coefficients and vortex shedding frequency is investigated. The local grid refinement technique and second-order boundary condition for curved walls are applied in the calculations. It is found that the calculated vortex shedding frequency, drag coefficient and lift coefficient are consistent with experimental results at Reynolds nu...     

Aggregate gradation design of asphalt mixture with stone-to-stone contact based on fuller＇s model

Based on Fuller＇s model, a gradation design is presented for the load-carrying capacity of an asphalt mixture with stone-to-stone contact. The coarse aggregate gradation, fine aggregate and filler gradation are respectively designed for their different effects on an asphalt mixture with stone-to-stone contact. The equation of coarse aggregate gradation is deduced from the Fuller＇s model. Fine aggregate gradation is calculated by using Fuller＇s equation. The asphalt mixture with the 16 mm maximum size of aggregate is verified. When the coefficient of coarse aggregate gradation is 0.35 and fine aggregate gradation is 0.25, the volume parameters of asphalt mixture meet the technical specifications. Moreover, the high temperature stability and crack resistance at low temperature are all well.     

铝合金压铸模具温度场数值分析

采用PROCAST对铝合金压铸用模具在压铸过程中的温度场进行了数值模拟,对压铸边界条件和传热系统的潜热采用热焓法进行了处理,分析了在不同时刻模具的温度场分布,分析了在不同的浇注温度和不同的模具预热温度情况下对模具温度场的影响,并且预测了热应力集中的位置,对压铸工艺参数的优化提出了见解,分析了冷却水管的作用,为压铸模具的热应力分析奠定基础。