碳钢表面碳—氮共渗层在高速干摩擦条件下的摩擦学性能研究

对 2 0 # 钢试样进行碳 -氮共渗热处理 ,考察了共渗层在高速干摩擦条件下的摩擦学性能 ,并用扫描电子显微镜和X射线光电子能谱仪对其磨损表面形貌和元素化学状态进行了分析 .结果表明 :随着滑动速度的增加 ,2 0 # 钢表面碳 -氮共渗层的磨损率逐渐降低 ,当滑动速度达到 35m/s左右时 ,磨损率显著增大 .扫描电子显微镜和X射线光电子能谱分析结果表明 ,高速轻载干摩擦条件下 2 0 # 钢表面碳 -氮共渗层的摩擦学性能同磨损表面氧化物的形成和剥落密切相关 ,而磨损率的显著增加是由于磨损表面氧化物类型发生从Fe2 O3 到FeO的转变所致 .     

超静定型钢桁架优化设计的面积比法

满应力准则是对超静定型钢桁架进行优化设计的有效方法．但这种方法的主要缺点在于收敛速度很慢甚至不收敛,这给设计工作带来很大的不便．对问题进行了研究,在“型钢压杆稳定设计直接法”的基础上,提出了满应力优化设计的一种新方法——面积比法,有效地提高了设计过程的收敛速度,降低了设计成本,供有关结构设计人员参考．     

常速度拉伸实验惯性效应的实验研究

本文统计了１５０根Ａ３低碳钢比例拉伸试件的断口位置，并测定了常速度拉伸（４００ｍｍ／ｍｉｎ，０．５ｍｍ／ｍｉｎ）时应变随时间和沿杆长的分布以及应力应变关系；发现７２％试件的断口靠近不动端内。同一时刻在设定速度为４００ｍｍ／ｍｉｎ时杆中最大工程应变差１８％．     

不同水介质润滑下GCr15钢的微动磨损特性

采用液压高精度材料试验机考察了平面-球面接触GCr15钢摩擦副在海水、酸性水和洁净水等3种不同水介质润滑下的微动磨损性能．用激光扫描显微镜(LSM)观察了磨痕表面形貌．结果表明：3种水介质对钢-钢摩擦副具有明显的润滑作用，其中酸性水的润滑作用最明显；磨损体积损失同介质的润滑作用和腐蚀作用相关，在洁净水和海水介质润滑下的磨损体积损失较小，在酸性水介质润滑下的磨损体积损失较大；在海水润滑下的GCr15钢磨损表面呈现明显的点蚀特征．     

预应力钢梁体外索的张力增量分析

将预应力钢梁看作梁与索的组合结构,充分考虑了二者之间的相互作用．利用变分原理推导出在外荷载作用下,体外索张力增量的计算公式,并通过预应力钢梁模型试验对计算结果进行了验证．     

Deformation and failure mechanism in AISI 4340 steel under ballistic impact

Deformation and failure mechanism in quench-hardened AISI 4340 steel under ballistic impact is investigated. The influence of microstructure on damage evolution is also evaluated. Strain localization and shear failure along adiabatic shear bands are the dominant deformation and failure mechanisms. The time and critical strain for the commencement of strain localization is influenced by strain rate and microstructure. The microstructure of the steel sample also influenced the type of adiabatic shear bands formed during impact. Failure mechanism involves nucleation of micro-voids, which clusters to form bigger pores. Extremely fine micro-cracks are initiated adjacent to the pores and in shear flow direction along the shear bands. These micro-cracks become interconnected and grow to macro-cracks, which cause fracture of some of the investigated cylindrical steel samples under impact. The susceptibility of the adiabatic shear bands to cracking increases with decreasing tempering temperature of the steel.     

Fatigue criteria for integrity assessment of long-span steel bridge with health monitoring

A structural health assessment (SHA) methodology is developed using data acquired from structural health monitoring (SHM) system installed on long-span bridges. A set of fatigue criteria has been proposed for pre-determining the global state of the bridge structure failure due to fatigue. This involves finding the threshold of fatigue initiation, below which the rate of fatigue damage may be undetectable under current technology or it is economically unfeasible. The state-of-art for large structures corresponds to the initiation of macro-cracks caused by the accumulation of damage generated by actual service loads for the case of bridges. In what follows, consideration is given to developing fatigue crack growth criterion based on the concept of the continuum damage mechanics (CDM). Fatigue accumulative is included in the model where a fatigue limit for multi-axial stress state is considered. The proposed criterion advocates the evolution of micro-crack growth up to the stage of macro-crack formulation. Considered are the loading histories that correspond to normal traffic loading for highways and railways, incidental or accident loadings such as those caused by typhoons and effective environmental loadings. The potential sites of damage are determined are discussed. The proposed criterion is applied to analyze the fatigue damage of the Tsing Ma Bridge with online strain history data acquired by the SHM system that is permanently installed in the bridge.     

回火温度对40Cr钢疲劳裂纹萌生寿命的影响

用系统分析的方法，通过三点弯曲疲劳试验，以数值描述的方式，在线跟踪了40Cr钢及其在三种回火温度下疲劳裂纹萌生过程的疲劳损伤，实验结果表明：随着回火处理温度的提高，40Cr钢的疲劳裂纹萌生寿命都有不同程度的提高．但裂纹萌生寿命在低于450℃的温度范围里，随着回火温度的提高，裂纹萌生寿命有明显的提高，在450℃至580℃范围内，随回火温度的上升，裂纹萌生寿命则没有明显的增加．     

半刚性钢框架的内力分析

采用二阶非线性分析方法分析和设计半刚性钢框架，包括连接的柔性以及构件的几何非线性的影响，提出了半刚性钢框架中梁柱单元刚度矩阵和半刚性梁的单元刚度矩阵；推导了半刚性梁在集中荷载，均布荷载，线性荷载作用下的固端弯矩的求解公式；连接的柔性对无支撑框架的侧移有很大的影响，设计时通过变化连接的刚度以平衡梁的跨中和端弯矩。     

钢丝帘线泊松比的实验研究

本文对钢丝帘线／橡胶复合材料中的钢丝帘线泊松比的定义提出了新的见解，建议用钢丝帘线横截面变化率代替其横向应变，并提出了利用扫描电子显微镜测定截面变化率的实验方法