数控机床串联刚度场及其应用研究

根据数控机床整体上各装配部件之间具有串联结构这一特点,提出了数控机床串联刚度场的概念,并通过串联弹簧单自由度系统进行了理论分析,最后通过1个具体实例,阐述了数控机床串联刚度场的实际应用情况。为揭示机床的性能及刚度分布以及机床的优化分析提供了1种全新的解决方案和途径。

复杂曲面模具加工系统综合刚度场建模与分析

在加工汽车覆盖件模具复杂曲面时,机床-刀具刚度、刀具位姿变化、模具型面变化都会影响加工系统综合刚度,进而影响模具加工精度。以四轴数控加工中心为例,针对模具曲面特征设置相应采样点,依据多体小变形理论,通过点传递矩阵、雅可比矩阵等完成该采样点的加工系统综合刚度建模,并引入了力椭球。在刀具不同的空间姿态下,通过力椭球分析了机床横梁、刀柄、刀具、模具曲面特征等对加工系统综合刚度性能的影响,揭示了曲面模具加工系统综合刚度的分布规律。最后通过试验证明,该理论模型可以有效地优化复杂型面模具加工工艺,减小模具的加工误差。

数控机床静刚度有限元分析

首先进行了整机的有限元分析,然后通过试验进行了结果验证。在确定了有限元分析结果的有效性后,利用数控机床串联刚度场理论进行了部件级的详细分析,绘制了串联刚度场图谱,分析了机床的刚度分布情况及存在的薄弱环节。

基于广义加工空间及工件效应的超重型机床动态特性分析

针对超重型卧式镗车床广义加工空间的动态响应,建立了基于结合面特性的整机有限元模型,分析了整机在广义加工空间的模态及刚度场特性,并考虑到大型工件本身对整机动态特性的影响,对比分析了考虑大型工件效应的整机动态特性。为优化机床的加工工艺,提高机床加工精度提供了理论支持。

Design and evaluation of UHPP steel bridge deck pavement for high-temperature and rainy regions

To enhance the serviceability of steel bridge deck pavement(SBDP)in high-temperature and rainy regions,a concept of rigid bottom and flexible top was summarized using engineering practices,which led to the proposal of a three-layer ultra-high-performance pavement(UHPP).The high-temperature rutting resistance and wet-weather skid resistance of UHPP were evaluated through composite structure tests.The internal temperature distribution within the pavement under typical high-temperature conditions was analyzed using a temperature field model.Additionally,a temperature-stress coupling model was employed to investigate the key load positions and stress response characteristics of the UHPP.The results indicate that compared with the traditional guss asphalt+stone mastic asphalt structure,the dynamic stability of the UHPP composite structure can be improved by up to 20.4%.Even under cyclic loading,UHPP still exhibits superior surface skid resistance compared to two traditional SBDPs.The thickness composition of UHPP significantly impacts its rutting resistance and skid resistance.UHPP exhibits relatively low tensile stress but higher shear stress levels,with the highest shear stress occurring between the UHPP and the steel plate.This suggests that the potential risk of damage for UHPP primarily lies within the interlayer of the pavement.Based on engineering examples,introducing interlayer gravel and optimizing the amount of bonding layer are advised to ensure that UHPP possesses sufficient interlayer shear resistance.

Wind Vibration Study of Long-span Steel Arch Structure of Beijing Capital International Airport

The wind-induced dynamic response of long-span light-weight steel arch structure of the global transportation center (GTC) of Beijing Capital International Airport was studied. A composite technique with combination of WAWS(Weighted Amplitude Wavelet Superposition) and FFT(Fast Fourier Transformation) was introduced to simulate wind velocity time series of hundreds of spatial points simultaneously. The structural shape factors of wind load was obtained from wind tunnel model test. The wind vibration factor based on structural displacement response was investigated. After comparing the computational results with wind tunnel model test data, it was found out that the two results accord with each other if wind comes from 0° direction angle, but are quite different if wind comes from 180° direction angle in the area blocked off by airport terminals. The possible reasons of this difference were analyzed. Haar wavelet was used to transform and analyze wind velocity time series and structural wind-induced dynamic responses. The relationship between exciting wind loads and structural responses was studied in time and frequency domains.

Experimental and simulation investigation into the cause and treatment of rail corrugation for metro

The cause and treatment of rail corrugation for the metro have always been a popular and challenging issue. In this work, the field measurements were carried out on rail corrugation, track stiffness, and the track dynamic response. A three-dimensional finite element model was developed to investigate the cause of rail corrugation. The constraints on rail vibration from two wheelsets and adjacent wheel-rail interactions were taken into account in the model. According to experimental and simulation results, the suppression measure for rail corrugation was proposed and the suppression mechanism was discussed. It was found that the cause of rail corrugation is related to vertical and lateral vibration of the rails outside the two wheelsets at around 380 Hz. The increased stiffness of the fasteners reduces the vibration energy of the rail and the wheel-rail force. However, simply increasing the stiffness of the fasteners may not be effective in the suppression of rail corrugation. If necessary, the rails need to be grinded to reduce the roughness to a certain level, so that increasing the fastener stiffness can effectively suppress the rail corrugation.

On the Use of FWD Impact-Stiffness Moduli for Determining PCN in Various Pavement Structures

Various technical studies have shown that impact-stiffness modulus values, defined as the ratio of the FWD （falling-weight deflectometer） impact load to its consequent central deflection, can be used to evaluate the PCN （pavement classification number） of a particular flexible or rigid airport pavement, fn a previous study, use was made of the old dynamic stiffness modulus procedure developed by the USCOE （US Army Corps of Engineers）, this procedure was correlated with various FWD measurements conducted on several runways and taxiways in Israel, together with in-situ borings and the use of the new COMFAA-3.0 software. The results, obtained only for flexible pavements, were checked against the relevant results of full-scale trafficking tests conducted by the FAA （Federal Administration Aviation） at its National Airport Pavement Test Facility. The present study analyzes new FWD measurements and in-situ borings conducted on additional rigid and all-asphaltic runways and taxiways in Israel in order to formulate an updated correlative equation for these types of pavements. The paper concludes with an updated recommendation for the use of impact-stiffness modulus outputs from FWD measurements in order to determine the PCN of any type of pavement directly on the basis of local experience.

Motion and Deformation State of the Tancheng-Lujiang Fault Zone Derived from GPS Data

Based on the rotation in the entire block and homogeneous strain model ( REHSM) ,we firstly analyze the motion and deformation features across the southern part of Tancheng- Lujiang fault zone from GPS velocity fields in period of 1999 ～ 2001,2001 ～ 2004,2004 ～ 2007 and 2007 ～ 2009. The results show a dextral strike-slip feature in the Weifang- Tancheng segment and sinistral strike-slip in the Tancheng-Lujiang segment. And the deformation perpendicular to the Tancheng-Lujiang fault zone alternates between tension and compression in different time-intervals. Then we resolve the relative rigid motion of blocks around Bohai Bay to the Circum-Bohai Sea area by deducting the entire rigid motion of the Circum-Bohai Sea area. We find that the Yanshan-Bohai seismic belt split this area into two parts,the northern part moving NW,and the other SE.

Electrical control of antiferromagnetic metal up to 15 nm

Manipulation of antiferromagnetic(AFM) spins by electrical means is on great demand to develop the AFM spintronics with low power consumption. Here we report a reversible electrical control of antiferromagnetic moments of FeMn up to 15 nm, using an ionic liquid to exert a substantial electric-field effect. The manipulation is demonstrated by the modulation of exchange spring in[Co/Pt]/FeMn system, where AFM moments in FeMn pin the magnetization rotation of Co/Pt. By carrier injection or extraction,the magnetic anisotropy of the top layer in FeMn is modulated to influence the whole exchange spring and then passes its influence to the [Co/Pt]/FeMn interface, through a distance up to the length of exchange spring that fully screens electric field. Comparing FeMn to IrMn, despite the opposite dependence of exchange bias on gate voltages, the same correlation between carrier density and exchange spring stiffness is demonstrated. Besides the fundamental significance of modulating the spin structures in metallic AFM via all-electrical fashion, the present finding would advance the development of low-power-consumption AFM spintronics.