冲压弯头压制过程应力分析及压力值的确定

本文应用弯曲应力的分析及机械自销原理，分析了弯头在冲压变形过程的应力，为压制不同规格的弯头应选用多大压力机及采用多大压力提供了初步的理论依据。

浅谈汽车新材料的发展和冲压成形技术

节能减排是当下汽车行业的重大需求,而轻量化是节能减排重要途径。轻量化材料的使用,是减轻车辆重量、降低排放、提高安全性的最有效方法。汽车新材料的发展,主要针对高强钢/超高强钢以及铝/镁合金冲压成形技术工艺和冲压生产线的研发。

Verson 焊机牵引小车伺服马达故障分析与修复改进

本文详细分析了Ｖｅｒｓｏｎ焊机牵引小车伺服马达产生故障的主要原因，针对液压冲击的危害采取了具体措施，对缸孔的修复提出了独特方案。

DEEP COLLIERY PRESSURE BUMPS AND ITS PREVENTIONS UNDER THE ACTION OF ABUTMENT PRESSURE

Based on field measurement, the relations was introduced between mining bepth and the peak value places of abutment pressures in long wall face of the deep colliery with caving method to handle goaf, and the reasons aod kinds of pressure bumps are analysed under the action of tbe moving and constant abutment pressures formed by the method of long wall caving or room and pillar mining, and the relative precautions were put foward to prevent the pressure bumps in deep mining.

Pressure impact characteristic of vane type continuous rotary motor under different buffer structures

In order to solve the problem of pressure shock on the continuous rotary electro-hydraulic servo motor,the mathematical models of pressure gradient under the structure of pre-compressed chamber and U-shaped groove were established.The optimal structure dimensions of the pre-compressed chamber and the U-shaped groove were determined.The fluid models were established by Solidworks under the four structures of triangular groove,triangular groove with pre-compression chamber,U-shaped groove and U-shaped groove with pre-compression chamber.Simulation analysis of depressurization process of fluid models was performed based on FLUENT.The pressure nephograms of different buffer structures were compared and analyzed,and the pressure change curves and pressure gradient change curves in the process of depressurization were obtained.The results show that the optimal edge length of the pre-compressed chamber of continuous rotary electro-hydraulic servo motor is 20 mm in the process of decompression.The pressure reduction effect is the best when the width of the U-shaped groove is 1.5 mm and the depth is 1.65 mm.The U-shaped groove structure with pre-compression chamber is more conducive to alleviate the pressure shock phenomenon of the motor compared with different combine buffer structures.

Asymmetric vibration characteristics of two-cylinder four-stroke single-piston hydraulic free piston engine

The structure and working principle of a two-cylinder four-stroke single-piston hydraulic free piston engine(HFPE) were introduced. The basic vibration equation of free piston assembly(FPA) was established based upon the energy conversion between the injected fuel and the friction together with the load. Both the theoretical and numerical results show that the vibration system of FPA is a nonlinear conservative autonomous system in one cycle. The FPA vibration is symmetric with constant amplitude when FPA is only driven by the compression pressure in the compression accumulator and that in the combustion chamber. When considering the friction and load, FPA could still achieve a stable vibration after a few cycles' adjustment whether the input energy is equal to the consumed energy or not. The vibration characteristics are different when FPA vibrates in the compression stroke and the expansion stroke, which is the unique feature of the single-piston HFPE.

Characteristics of wind pressure pulse on large-span flat roofs

The wind pressure pulse events, among the most important characteristics of wind pressure fluctuations on large-span flat roofs, were investigated by wind tunnel tests in this paper. Incorporating the formation mechanism of wind pressure pulse events, the peak over threshold method was employed to study properties of this kind of events. The event duration time, the energy contribution, the number of the pulse events, and the distribution of average peak pressure were calculated. Probability density functions of some typical samples in separation region were also given. Results show that the non-Gaussian roof pressure is strong in the flow separation region owing to the wind pressure pulse events. Evaluations of the extreme peak pressures, which can be determined by the peak over threshold method effectively, are important to the design of building cladding.

Theoretical analysis of effects of boundary layer bleed on scramjet thrust

The effects of boundary layer bleed on the scramjet thrust are studied in the present paper.A theoretical model is developed to evaluate the thrust increment and influencing factors.The thrust increment resulting from the bleed is dominated by the rise in total pressure recovery and bleed mass flow rate.The bleed mass flow rate exerts stronger impact on the engine thrust than the total pressure.According to current bleed design,it is a severe challenge for the engine to enhance its total pressure to maintain the original thrust when there is no bleeding.Furthermore,the initial total pressure recovery,fuel mass addition,combustion efficiency and area ratio of engine exit to entrance can affect the contributions of the bleeding to the thrust increment.The scramjet needs a higher rise in total pressure recovery to counteract the negative effect of bleed mass loss at higher initial total pressure recovery or larger area ratio of engine exit/entrance.More heat release results in a little lower demand on the rise in total pressure recovery for maintaining the scramjet thrust.These results will aid in understanding the fundamental mechanism of bleeding on engine thrust.

Drag force investigation of cavities with different geometric configurations in supersonic flow

In order to prolong the residence time of the flow retaining in the supersonic flow, wall cavity has been widely applied in the scramjet combustor, and this affects the aerodynamic surface and imposes additional drag force on the hypersonic propulsion system. The two-dimensional coupled implicit Reynolds Averaged Navier-Stokes (RANS) equations and the RNG k?ε turbulent model were employed to investigate the flow fields of cavities with different geometric configurations, namely the classical rectangular, triangular and semi-circular, and the cavities with the fixed depth and length-to-depth ratio. At the same time, the drag force performances of the cavities were estimated and compared. The obtained results show that the numerical results are in very good agreement with the experimental data, and the different scales of grid make only a slight difference from the numerical results. The intensity of the trailing shock wave is much stronger than that of the leading one, and the area around the trailing edge of the cavities plays an important role in the chemical reaction in the scramjet combustor. With the fixed depth and length-to-depth ratio, the triangular cavity can strengthen the turbulent combustion in the scramjet combustor further, but impose the most additional drag force on the scramjet engine. The classical rectangular one can impose the least additional drag force on the engine, but the function of strengthening the combustion is the weakest. The influence of the semi-circular one is the moderate, but the machining process is more complex than the other two configurations.