Ductile crack initiation behavior in steels with compressive prestrain

It is well known that compressive prestrain reduces ductility in steels. On the other hand, it has also been found that high stress triaxiality reduces equivalent plastic strain at the onset of ductile fracture. In this research, plate specimens and notched bar specimens, which were prestrained in compression with bending, were used in reversed bending tests, and the effect of compressive prestrain on ductile crack initiation in steels was investigated. It was found that small ductile cracks occurred from the microscopic wrinkles which were formed on the concave surface with compressive prestrain. The critical relationship between stress triaxiality and equivalent plastic strain at ductile crack initiation was investigated by finite-element analysis. It was found that ductile crack initiation in steels with compressive prestrain can be estimated qualitatively by the relationship between stress triaxiality and equivalent plastic strain.     

光纤光栅传感器在钢桥面铺装长期监测中的应用

钢桥面板在车辆荷载作用下,容易产生较大的局部变形。国内对于桥面铺装应力应变分析多采用有限元,实桥长期监测仍然处于空白阶段。该文依托桃浦路蕴藻浜大桥项目,对实桥监测过程中的传感器布设进行了研究。从不同结构、不同用途传感器选取方面入手,对传感器的埋设方案,安装方法进行详细介绍,为以后工程中传感器使用提供了借鉴。     

桩基低应变检测波型分析及桩身完整性判别

根据桩基体系中桩顶、桩身、桩端等各部位反射波的特征,分析产生离析、夹泥、缩径、断裂、扩径差异等缺陷的原因,探讨各类型缺陷的处理措施,建立同相反射波和反相反射波的判别标准。通过对大量现场检测资料的分析,验证判别标准的合理性和适用性,该方法对提高桩身完整性判别检测的精度有较大帮助。     

船体分段焊接变形仿真

船体分段在焊接过程中产生的焊接变形会使船体结构强度降低,然而精确预测和控制焊接变形是个难题.文章提供了准确预测焊接变形的固有应变等效载荷法.这种方法运用有限元法结合固有应变理论以及实验结果对焊接变形进行分析:引入简化的弹-塑性分析杆-弹簧模型,通过分析得到固有应变受焊接区域约束度及最高温度分布情况的影响;将固有应变转化为等效载荷,应用弹性有限元分析求得整个结构的焊接变形.计算结果与LEECH计算及实验结果吻合较好.     

长江口软基围堤施工的加载速率效应

针对长江口某围堤施工软土堆载过程中的稳定性问题,进行不同加载模式下的应力路径试验,分析长江口软黏土的应力-应变关系、结构损伤特性、强度及应变率发展模式,为该围堤工程的施工速率选取及施工过程中的稳定性控制提供技术依据。结果表明:在不考虑固结的前提下,土体的不排水抗剪强度几乎不受加载模式影响;最终强度与达到破坏时的应变大小无关,但与分级加载时间和分级静置时间存在相互作用关系;土体失稳时的应变率与加载速率和静置时间均有一定关系,且加载速率的影响更大;当加荷超过不排水抗剪强度的80%时,或分级最大应变率逐渐偏离加载初期的线性变化,土样濒临破坏。     

DP2自升式平台环网电站关键技术研究

本文依托某采用环网电站技术的具有世界领先水平的DP2多功能自升式海洋平台实船项目，对这种非常规的动力定位系统的设计难点和要点进行剖析，重点介绍了平台环网电站在过载、短路等故障或扰动情况下的故障隔离和故障穿越技术，并列举了相应的解决方案，最后通过实船验证对该解决方案进行了论证和总结，供类似项目借鉴。     

Potential of low viscosity oils to reduce CO2 emissions and fuel consumption of urban buses fleets

This paper shows the results of a comparative fleet test the main objective of which was to measure the influence of Low Viscosity Oils (LVO) over the fuel consumption and CO₂ emissions of urban buses. To perform this test, 39 urban buses, classified into candidate and reference groups depending on the engine oil viscosity, covered a 60,000 km mileage corresponding to two rounds of standard Oil Drain Interval (ODI). In the same way, for 9 buses of the 39 buses, the effect of differential LVO over fuel consumption and their interaction with engine LVO was assessed during the second ODI.Test results confirm that the use of LVO could reduce fuel consumption, hence CO₂ emissions. However, special attention should be taken prior to its implementation in a fleet, particularly if the vehicles are powered by engines with high mechanical and thermal stresses during vehicle operation because this could lead to friction loss increase, loss of the potential fuel consumption reduction of LVO and, in the worst scenario, higher rates of engine wear.     

Demi-flexible operating policies to promote the performance of public transit in low-demand areas

The efforts of providing attractive transport service to residents in sparse communities have previously focused on operating flexible transit services. This paper identifies a new category of transit policies, called demi-flexible operating policies, to fill the gap between flexible transit services and conventional fixed-route systems. The passenger cost function is defined as the performance measure of transit systems and the analytic work is performed based on a real-world flag-stop transit service, in which we compare its system performance with another two comparable systems, the fixed-route and flex-route services, at expected and unexpected demand levels in order to be closer to reality. In addition, the dynamic-station policy is introduced to assist the flex-route service to better deal with unexpectedly high demand. Experiments demonstrate the unique advantages of demi-flexible operating policies in providing affordable, efficient, and reliable transport service in low-demand operating environments and this work is helpful to optimize the unifying framework for designing public transit in suburban and rural areas.     

美标高桩码头抗震计算位移法的对比

从原理和适用性的角度对美标高桩码头抗震计算方法进行对比,着重研究了位移法及其中的替代结构法。对替代结构法中推覆曲线的双折线化方式、阻尼比计算、反应谱衰减等影响因素进行分析。通过推覆分析和替代结构法计算变形能力和地震位移、复核码头抗震性能。结合实际案例,采用反应谱法和替代结构法对某高桩码头结构进行抗震分析。结果表明反应谱法趋于保守,不能反映塑性后的荷载衰减,相比而言替代结构法更为准确。而对于替代结构法,不同的等效阻尼比会较大程度影响地震位移结果。     

人湿尺骨干在冲击压缩实验下的力学性能及规律

目的探讨人湿尺骨密质骨在高应变率下的力学性能及其分布规律。方法用分离式Hopkinson压杆(SHPB)技术对人湿尺骨密质骨进行了应变率在.ε=1.2×103/s条件下的冲击压缩试验。结果尺骨密质骨在高应变率下的力学性能随其纵向位置变化而呈现出中间强两端弱的分布,最强的位置约在距近端1/3处,且近端强于远端。与静态结果的比较表明,尺骨密质骨对应变率有较大的依赖性。结论在冲击压缩力作用下,尺骨的两端,尤其是远端容易骨折。