汽车稳定杆组织与疲劳性能研究

对28Mn6钢制造的汽车稳定杆，分别采用整体感应加热－整体淬火、连续感应加热淬火两种不同热处理工艺，并进行了台架疲劳寿命试验，采用光学显微镜和扫描电镜，分析了经两种不同热处理工艺处理的稳定杆的金相组织及其早期疲劳断裂的断口形貌，提出，获得细小的高韧性索氏体组织是保证良好疲劳寿命的关键，稳定杆喷丸表面质量，游离铁素体也是影响疲劳性能的重要因素。     

Numerical simulations of specimen size and mismatch effects in ductile crack growth - Part II: Near-tip stress fields

The effect of ductile crack growth on the near tip stress field in two different specimen geometries has been investigated. For homogeneous specimens it is observed that the peak stress level increases with ductile crack growth. The effect is most pronounced up to about 1 mm of crack growth. For low and intermediate hardening there is a significant effect of specimen size on the stress level. In case of mismatch in yield stress, the simulations show that the increase in stress level in the material with the lower yield stress is of a similar magnitude as is the case for stationary cracks. In case of ductile crack growth deviation from the original crack plane occurs, the highest stresses are still found close to the interface, and not in front of the current crack tip.     

A comparative study of numerical solutions to non-linear discrete crack modelling of concrete beams involving sharp snap-back

Numerical problems are often encountered in modelling crack propagation in concrete beams using non-linear finite element (FE) analysis, especially when sharp snap-back behaviour in load-displacement relations occurs. This paper firstly identifies 16 arc-length control based numerical strategies based on extensive literature review. They are then used to carefully model the structural behaviour of a four-point single notched shear beam using discrete crack modelling approach in which cracks are represented by interface elements with bilinear softening constitutive laws. Based on extensive FE analyses, detailed comparisons of the merits and demerits of these numerical algorithms are then made. The results indicate that the effectiveness and efficiency of different algorithms may vary considerably from one to another, with the local arc-length based procedures in conjunction with tangential stiffness strategy and reversible unloading model being the most robust.     

混凝土结构的质量通病——裂缝

从材料、结构构造、施工工艺、地基变形、温湿度变形等方面论述了混凝土裂缝产生的原因 ,提出只有真正了解裂缝产生的原因 ,才能有针对性地采取有效措施 ,确保工程质量     

高层地下室底板混凝土施工的裂缝控制

以德益花园写字公寓楼地下室底板205m厚混凝土的施工工程为例，坚持预防为主的原则，采取了一系列温控技术措施，有效地防止或控制了温度裂缝(收缩裂缝)的产生，确保了混凝土的施工质量。     

简析Ⅲ类PHC管桩的成因及加固补强处理方法

本文主要通过Ⅲ类PHC管桩的形成分析,经过各方论证采用了合适的处理方法,取得了较好的效果。     

浅析露天栈桥改造

结合工程实例，论述了露天栈桥产生裂缝和腐蚀的原因，对栈桥结构进行了评价，提出了加固方案及加固施工中应注意的事项，经使用证明，加固效果良好。     

Threshold and growth mechanism of fatigue cracks under mode II and III loadings

ABSTRACT The fatigue crack growth behaviour of 0.47% carbon steel was studied under mode II and III loadings. Mode II fatigue crack growth tests were carried out using specially designed double cantilever (DC) type specimens in order to measure the mode II threshold stress intensity factor range, ΔK_IIth. The relationship ΔK_IIth > ΔK_Ith caused crack branching from mode II to I after a crack reached the mode II threshold. Torsion fatigue tests on circumferentially cracked specimens were carried out to study the mechanisms of both mode III crack growth and of the formation of the factory‐roof crack surface morphology. A change in microstructure occurred at a crack tip during crack growth in both mode II and mode III shear cracks. It is presumed that the crack growth mechanisms in mode II and in mode III are essentially the same. Detailed fractographic investigation showed that factory‐roofs were formed by crack branching into mode I. Crack branching started from small semi‐elliptical cracks nucleated by shear at the tip of the original circumferential crack.     

Damage mechanism in weldment of 2.25Cr-1Mo steel under creep-fatigue loading

The purpose of this study is to clarify damage process of “Type IV cracking” in weldment of a 2.25Cr-1Mo steel and to propose a micro damage prediction method. From continuous observation under a creep-fatigue test, it was found that spherical shape voids initiated and grew on grain boundaries in fine grain region and these voids grow continuously by changing their shape to crack-like. Both spherical and crack-like void growth rate equations were derived from the proposed void growth model. It was indicated that measured void growth rate under the creep-fatigue loading was well predicted by the growth rate equations.     

Fatigue Behavior and Retrofit Investigation of Distortion-Induced Web Gap Cracking

This paper studies a Kansas Department of Transportation welded plate girder bridge that developed fatigue cracks at small web gaps close to the girder top flange. Repair had been previously performed by softening the connection plate end with a slot retrofit, but cracks were recently found to have reinitiated at some of the repaired details and are again propagating. A comprehensive finite-element method study was performed to investigate the cracking behavior observed in the bridge and to recommend appropriate measures for future bridge retrofit. The analytical results show that stresses developed at the top flange web gaps could exceed yielding under the loading of an HS15 fatigue truck. The current slot repair used in the bridge was found to have introduced higher magnitude fatigue stresses in the web gap. To achieve a permanent repair of the bridge, it is recommended that a welded connection plate to flange attachment be used during future bridge retrofit. The web gap details should be able to withstand unlimited number of load cycles once this additional repair is performed.