两级低-高加载下拉剪点焊试样的疲劳损伤研究

对拉剪点焊试样进行了两组不同载荷水平的两级低-高循环加载试验,得到随第一级载荷下循环数变化,点焊试样的剩余寿命和总疲劳寿命变化规律。使用Miner线性累积损伤理论计算得到两种不同载荷水平下试样总的疲劳损伤。结果表明:对于低-高加载,随着低载水平下循环数的增多,高载荷水平下的剩余寿命以及损伤值呈逐渐减小趋势,总疲劳寿命逐渐增大。当低载水平载荷幅值较小时,点焊试样破坏时的累计损伤值普遍存在小于1的现象,且这种现象可能对疲劳寿命估算存在一定的影响。

高加载MPS磨煤机磨损期运行特性

对高加载MPS磨煤机在磨辊磨损不同时期的磨煤机运行特性进行试验研究,分析了该类型磨煤机在不同磨辊磨损程度下主要运行参数的调节特性及影响规律,并对实际操作提出建议。结果表明:高加载MPS磨煤机在碾磨试验煤质下,磨辊磨损早、中、后期的风量特性、分离器挡板特性、加载力特性基本相同;磨辊磨损早期,石子煤排放量均处在较低的水平;磨损中期,高出力下的石子煤排放量比低出力下有所降低;磨损后期,石子煤量有所增加,且高出力下的石子煤排放量增大较多;在磨辊磨损的中、后期,磨煤单耗有所增加,且随着磨煤机出力增加,磨辊磨损对磨煤单耗的影响有所减少。

高加载速率工况下履带板与可变形地面附着力测量实验系统

针对履带车辆机动性实验教学要求,设计了测量履带板与可变形地面的动态加载附着力的实验系统。实验系统包含动态垂向加载系统、水平牵引系统和数据采集装置,利用电液伺服激振台的垂向加载特性设计了可实现高加载速率、重载荷的垂向加载系统,采用蜗轮丝杠升降机和减速机设计了可调速率的水平牵引系统。实验表明,该系统操作简单,实验工况真实有效,可以满足高频重载工况下履带板与可变形地面之间的附着力测量需求。

不同应变率加载下硅的高压相变行为

高压相变是凝聚态物理、地球与行星科学、材料科学等领域关注的核心问题之一,而加载应变率是相变动力学过程的重要影响因素。由于动态加载下物质相结构原位诊断技术的不足以及宽广加载应变率下物质高压相变系统实验研究的缺失,难以开展基于原子尺度物理机制的相变动力学过程建模和数值模拟研究。由于硅的高压相极其丰富,且拥有大量亚稳相,动力学因素在其高压相变过程中发挥着至关重要的作用,因此,硅是研究高压相变动力学的理想材料,对普适相变动力学过程的理论建模具有重要意义。以硅为例,介绍其在准静态、中等应变率和高应变率加载下的相变行为,探讨加载应变率对其高压相变行为的影响。

焊接接头高应变率下的动态断裂韧度分析

对采用Hopkinson气炮加载—CharpyV形冲击试样试验方法对焊接接头高应变率下的动态断裂韧度数据进行了分析研究 ,通过对试样断口形貌、冲击吸收功、断裂韧度及其影响因素进行分析 ,表明在高应变率加载条件下 ,焊接接头冲击试样断口形貌有特殊的表现 ,延伸带或钝化区的尺寸大小反映了裂纹萌生前的塑性变形大小 ,也反映了裂纹萌生功的变化趋势。同时说明焊接接头在高速动态冲击载荷作用下 ,其断裂韧度参量受组配强度、冲击速度及环境温度等因素影响显著 。

低温和高载荷速率对某船用结构钢断口形貌的影响--对动载荷促进材料脆性断裂本质的探讨

研究了低温和高载荷速率条件下结构钢断口形貌变化规律,讨论了沿晶断裂的本质.研究指出降低温度和提高载荷速率都使沿晶断裂倾向增加,结构钢沿晶断裂倾向决定于晶界协调相邻晶粒塑性变形的能力.

结构钢焊缝金属在低温和动载条件下的脆断本质

研究了结构钢焊缝金属在低温和高加载速率条件下的断裂韧度与断口形貌变化规律,讨论了沿晶脆性断裂的本质。研究指出,降低温度和提高加载速率都导致断裂韧度降低和沿晶脆性断裂倾向增加,表现出一定的低温效应和高加载速率效应,降低试验温度和提高加载速率的作用是相互促进的。焊缝金属沿晶脆性断裂是特定的材料因素、结构因素和环境因素共同作用的结果,沿晶脆性断裂倾向决定于晶界协调相邻晶粒塑性变形的能力,在晶界不足以协调其两侧晶粒的变形时便出现沿晶断裂。

A model of continuum damage mechanics for high cycle fatigue of metallic materials

A non-linear continuum damage model was presented based on the irreversible thermodynamics framework developed by LEMAITRE and CHABOCHE. The proposed model was formulated by taking into account the influence of loading frequency on fatigue life. The parameters H and c are constants for frequency-independent materials, but functions of cyclic frequency for frequency-dependent materials. In addition, the expression of the model was discussed in detail at different stress ratios （R）. Fatigue test data of AlZnMgCu1.5 aluminium alloy and AMg6N alloy were used to verify the proposed model. The results showed that the model possesses a good ability of predicting fatigue life at different loading frequencies and stress ratios.

Failure characteristics of high stress rock induced by impact disturbance under confining pressure unloading

The failure characteristics under coupled static and dynamic loading were investigated by the improved split Hopkinson pressure bar （SHPB） with axial pre-pressure and confining pressure. The results show that the stress—strain curve of the rock under static-dynamic coupled loading is a typical class I curve when the dynamic load is comparatively high; With the decrease of the dynamic load, the stress—strain curve transforms to a typical class II curve. The dynamic failure process was recorded by high-speed photography. Analyses of fracture surface morphology show that the failure modes of specimens are tensile failure or combined shear failure when the impact load energy is low, but the failure modes of specimens become tensile failure when the impact load energy is high. The results of fractal dimension show that the elastic potential energy release leads to increase in the degree of crushing of samples when the energy of impact load is low under coupled static and dynamic loads with high stress.

Experimental study on energy storage and dissipation characteristics of granite under two-dimensional compression with constant confining pressure

To study the energy storage and dissipation characteristics of deep rock under two-dimensional compression with constant confining pressure,the single cyclic loading-unloading two-dimensional compression tests were performed on granite specimens with two height-to-width(H/W)ratios under five confining pressures.Three energy density parameters(input energy density,elastic energy density and dissipated energy density)in the axial and lateral directions of granite specimens under different confining pressures were calculated using the area integral method.The experimental results show that,for the specimens with a specific H/W ratio,these three energy density parameters in the axial and lateral directions increase nonlinearly with the confining pressure as quadratic polynomial functions.Under constant confining pressure compression,the linear energy storage law of granite specimens in the axial and lateral directions was founded.Using the linear energy storage law in different directions,the elastic energy density in various directions(axial elastic energy density,lateral elastic energy density and total elastic energy density)of granite under any specific confining pressures can be calculated.When the H/W ratio varies from 1:1 to 2:1,the lateral compression energy storage coefficient increases and the corresponding axial compression energy storage coefficient decreases,while the total compression energy storage coefficient is almost independent of the H/W ratio.

Coefficients of earth pressure at rest in thick and deep soils

The effect of test methods and stress paths on the experimental value of the coefficient of earth pressure at rest, K0, was investigated under high pressures. The results indicate that the rigid pressure chamber and flexible lateral confining pressure medium method gives a stress ratio at the initial stage that is not the real K0. Moreover, K0 increases during the loading process becoming greater at high pressures. In the unloading process, however, K0 increases only at the initial stage but decreases thereafter. In addition, the incremental magnitude definition, K0=dσ3/dσ1, gives higher values than the total magnitude definition, K0=σ3/σ1, under loading. This is also true during initial stages of unloading. The experiment results also indicate that earth pressure at rest in deep and thick soils can be estimated by a power function of axial and confining pressures. It is necessary to choose the appropriate Kn to avoid some accidents.

LTAG Technology Passed Appraisal

Recently the LTAG technology combining selective hydro-saturation of LCO with selective catalytic cracking technology for producing high-octane gasoline or light aromatic hydrocarbons has passed technical appraisal.

Shear Behavior of Novel Prestressed Concrete Beam Subjected to Monotonic and Cyclic Loading

Prestressed steel ultrahigh-strength reinforced concrete(PSURC) beam is a new type of prestressed concrete beam, which not only has a considerable compressive strength attributed to the ultrahigh strength concrete, but also ensures a certain degree of ductility at failure due to the existence of structural steel. Five of these beams were monotonically tested until shear failure to investigate the static shear performance including the failure pattern, loaddeflection behavior, shear capacity, shear crack width and shear ductility. The experimental results show that these beams have superior shear capacity, crack control ability and shear ductility. To study the shear performance under repeated overloading, seven PSURC beams were loaded in cyclic test simultaneously. The overall shear performance of cycled beams is similar to that of uncycled beams at low load level but different at high load level. The shear capacity and crack control ability of cycled beams at high load level are reduced, whereas the shear ductility is improved. In addition, the influences of variables including the degree of prestress, stirrup ratio and load level on the shear performance of both uncycled and cycled beams were also discussed and compared, respectively.

Progress of XHV Technology at Particle Accelerators

Recent vacuum system development with an XHV condition for the particle accelerators is briefly described. The progress of selecting and treatment of the materials used in XHV systems is introduced,and the choice of the main pump for an XHV system and some new pumping method are presented.Some leak detection experiences both for the superconducting and warm vacuum systems are recommended and the status of XHV measurement and the gauge calibration are introduced.

Geoid Deformation and Elevation Influence Caused by Building Loading

The paper studies the ground vertical deformation and the geoid undulation caused by loading of neighboring buildings, based on the loading tides theory. The influence on elevation is also considered. The results show that the ground vertical deformation and the geoid undulation both reach millimeter magnitude. Therefore, it is obvious that the building loading significantly affects the precise engineering surveying, and it must be seriously considered in application.

Aeroelastic stability analysis of heated panel with aerodynamic loading on both surfaces

Focusing on the aeroelastic stability of thin panel structure of airframe component such as engine nozzle of high-speed flight vehicles,a nonlinear aeroelastic model for a two-dimensional heated panel exposing both surfaces to the airflow with different aerodynamic pressures is established.The von Karman large deflection plate theory and the first-order piston theory are used in the formulation of aeroelastic motion.The critical conditions for aeroelastic stability and the stability boundaries are obtained using theoretical analysis and numerical computations,respectively.The results show that the panel is more prone to become unstable when its two surfaces are subject to aerodynamic loading simultaneously;only if the sum of the aerodynamic pressures on both surfaces of the panel satisfies flutter stability condition,can the panel be likely aeroelastically stable;compared with the general panel flutter problem that only one surface is exposed to the airflows,the present condition makes the panel become aeroelastically unstable at relatively small flight aerodynamic pressure.