Study on Fracture Delay of High-Strength Bolts in Road Bridge Maintenance

In the maintenance work of highway and bridge engineering structures,the fracture delay of high-strength bolts is a content that needs to be focused on and researched.Based on this,the paper analyzes the fracture delay of high-strength bolts in highway bridge maintenance,including an overview of the fundamental research on fracture delay and related specific studies.It is hoped that this study can provide scientific reference for the reasonable maintenance of high-strength bolts,so as to ensure the overall maintenance effect of highway bridge projects.

Deformation-softening behaviors of high-strength and high-toughness steels used for rock bolts

In deep ground engineering,the use of high-strength and high-toughness steels for rock bolt can significantly improve its energy absorption capacity.However,the mechanisms and effects of rock loading conditions on this kind of high energy-absorbing steel for rock bolt remain immature.In this study,taking Muzhailing highway tunnel as the background,physically based crystal plasticity simulations were performed to understand the effect of rock loading rate and pretension on the deformation behaviors of twinning induced plasticity(TWIP)steel used for rock bolt.The material physical connecting to the underlying microscopic mechanisms of dislocation glide and deformation twinning were incorporated in numerical modeling.The rock loading conditions were mimicked by the real-time field monitoring data of the NPR bolt/cable equipment installed on the tunnel surrounding rock surface.The results indicate that the bolt rod exhibits pronounced deformation-softening behavior with decrease of the loading rate.There is also a sound deformation-relaxation phenomenon induced by the dramatic decrease of loading rate after pre-tensioning.The high pretension(>600 MPa or 224 k N)can help bolt rod steel resist deformation-softening behavior,especially at low loading rate(<10~(-1)MPa/s or 10~(-2)kN/s).The loading rate was found to be a significant factor affecting deformation-softening behavior while the pretension was found to be the major parameter accounting for the deformation-relaxation scenario.The results provide the theoretical basis and technical support for practical applications.

Numerical Model Research on Rotational Performance of Beam-Column High-Strength Bolt Extension End-Plate Connection Node

The high-strength bolted end plate connection is widely used in the construction industry with its green environmental protection and excellent seismic performance. The joints of the joints are semi-rigid, the force performance is extremely complicated, and the experimental research cost is relatively high, and the cycle is very long. Therefore, the establishment of an efficient numerical model is of great significance for evaluating the force performance of high-strength bolt end plates. In this paper, the influence of different material models on the rotation performance of the joint is studied by numerical simulation, and the bending moment-rotation curve is obtained. The numerical simulation and the experimental results are in good agreement, so as to provide a reference for the design and application of this kind of joint.

摩擦型高强螺栓连接抗剪滑移行为研究

为研究摩擦型高强螺栓抗剪连接的滑移行为,分析了钢结构全过程的受力和变形性能。采用简化的螺栓滑移数值计算方法,使用COMBIN39弹簧单元模拟了螺栓与盖板、芯板之间的摩擦行为以及螺杆与螺栓孔壁之间的接触挤压行为。通过ANSYS有限元软件模拟了单行四列螺栓连接抗剪滑移过程并采用试验加以验证。建模分析了三行六列螺栓群在摩擦阶段、滑移阶段和弹塑性变形阶段的连接抗剪滑移过程,总结出各行螺栓在各个阶段的传力比和芯板、盖板的应力分布规律。根据三阶段滑移过程,提出了螺栓群总滑移量的计算公式。以孔壁变形特点为依据,采用分段函数拟合出孔壁的变形-荷载曲线,并将拟合的曲线与芯板和盖板各螺栓孔壁变形平均值有限元结果进行了比对。结果表明:有限元计算的荷载-位移曲线与实测的荷载-位移曲线吻合良好,验证了有限元模型的正确性;拟合的变形-荷载曲线与有限元模拟值吻合良好;当外荷载为375 kN时,传力比最大的第1列螺栓首先开始松动,之后便出现微小滑移;当外荷载增加至905 kN时,第1列螺栓芯板位置处出现大面积塑性变形区并发生孔壁挤压破坏,可以认为芯板已经达到极限承载能力状态,但此时盖板的Von Mises应力仅为231.1 MPa,说明盖板没有进入屈服状态。研究结果可为摩擦型高强螺栓群的研究和设计提供参考。

Influence of anchorage length and pretension on the working resistance of rock bolt based on its tensile characteristics

In coal mining roadway support design,the working resistance of the rock bolt is the key factor affecting its maximum support load.Effective improvement of the working resistance is of great significance to roadway support.Based on the rock bolt’s tensile characteristics and the mining roadway surrounding rock deformation,a mechanical model for calculating the working resistance of the rock bolt was established and solved.Taking the mining roadway of the 17102(3)working face at the Panji No.3 Coal Mine of China as a research site,with a quadrilateral section roadway,the influence of pretension and anchorage length on the working resistance of high-strength and ordinary rock bolts in the middle and corner of the roadway is studied.The results show that when the bolt is in the elastic stage,increasing the pretension and anchorage length can effectively improve the working resistance.When the bolt is in the yield and strain-strengthening stages,increasing the pretension and anchorage length cannot effectively improve the working resistance.The influence of pretension and anchorage length on the ordinary and high-strength bolts is similar.The ordinary bolt’s working resistance is approximately 25 kN less than that of the high-strength bolt.When pretension and anchorage length are considered separately,the best pretensions of the high-strength bolt in the middle of the roadway side and the roadway corner are 41.55 and 104.26 kN,respectively,and the best anchorage lengths are 1.54 and 2.12 m,respectively.The best anchorage length of the ordinary bolt is the same as that of the high-strength bolt,and the best pretension for the ordinary bolt in the middle of the roadway side and at the roadway corner is 33.51 and 85.12 kN,respectively.The research results can provide a theoretical basis for supporting the design of quadrilateral mining roadways.

钢桥密集螺栓异常状态视觉识别方法

针对传统机器视觉方法无法从不同拍摄视角和拍摄距离的图像中较好地识别出异常螺栓的问题,依据钢桥密集螺栓区域自身视觉特点,提出基于区域异常点分析的密集螺栓异常状态视觉识别方法。该方法首先提取和比对图像蓝色和红色通道灰度,完成梁体颜色分割,并运用选定的Canny算子提取梁体区域内边缘,采用Hough线识别方法剔除杂波;其次依据密集螺栓呈现簇状分布特点,运用密度聚类分析定位螺栓簇区域,并依据密集螺栓位置呈现平行网格分布的特点,运用投影分析定位单个螺栓区域;然后依据各螺栓的阴影特征,利用切比雪夫不等式快速判定螺栓状态,完成螺栓异常识别;最后,制作钢桥节点板模型,采集不同螺栓松动或脱落图像,对该方法进行测试。结果表明:该方法对图像拍摄视角和距离的适用度高,对螺栓脱落的识别能力优于对螺栓松动的识别;不同场景下单个螺栓定位的平均交并比大于0.75,且螺栓脱落和松动识别的准确率和召回率分别在0.89和0.85以上。

菠菜种质资源耐抽薹性评价与分析

以487份菠菜材料为研究对象,对5个耐抽薹指标进行相关性分析、主成分分析、隶属函数法和聚类分析,综合评价了菠菜的耐抽薹性.研究结果表明:各指标的频数分布基本符合正态分布.菠菜在上海地区抽薹和开花启动的时间为10~13 h,越耐抽薹,抽薹开花启动的时间越长.相关性分析结果表明:抽薹期、开花期、抽薹昼长和开花昼长存在极显著正相关.主成分分析将5个指标转化为2个主成分因子,累计贡献率达到99.5%.用隶属函数法将487份材料划分为5个等级,并筛选出12份极耐抽薹材料.用聚类分析将487份菠菜材料划分为5个类群,其中第Ⅳ类群为极耐抽薹材料,说明隶属函数法和聚类分析均可以有效地评价菠菜的耐抽薹性.最后筛选出10份极耐抽薹材料US175,CS105,CS120,CS121,CS175,CS232,CS253,CS256,CS257和S14,可应用于菠菜耐抽薹材料创制或新品种选育.

Hydrogen-induced delayed fracture of Cu-containing high-strength bolt steel

The hydrogen-induced delayed fracture(HIDF)behavior of a 1300-MPa-grade high-strength bolt steel 42CrMoV containing 0.42 wt.%Cu was investigated by constant load tensile test in a pH 3.5 Walpole solution.It is shown that the addition of Cu is beneficial to enhance the HIDF resistance by~13%.The observation of the fracture surface revealed that the area fraction of brittle crack initiation zone decreased remarkably for the Cu-added steel.Both the corrosion pit depth and the corrosion rate of the Cu-added steel in the Walpole solution are notably decreased,which is primarily because of the formation of a Cu-rich protective compact rust layer and slightly higher corrosion potential.As a result,the absorbed hydrogen content in that solution was also decreased by~21%.It is concluded that the improvement in the HIDF resistance of the tested steel is primarily due to the increase in corrosion resistance and resultant decrease in the absorbed diffusible hydrogen content in the acidic condition.

An ultra-thin bolt tension sensor and online monitoring system:For application in hydropower plant unit

The condition of bolted connections significantly affects the structural safety.However,conventional bolt tension sensors fail to provide precise measurements due to their bulky size or inadequate stability.This study employs the piezoresistive effect of crystalline silicon material to fabricate an ultrathin sensor.The sensor exhibits a linear relationship between pressure and voltage,an exceptional stability at varying temperatures,and a superior resistance to corrosion,making it adaptable and user-friendly for applications of high-strength bolt tension monitoring.A monitoring system,incorporating the proposed sensor,has also been developed.This system provides real-time display of bolt tension and enables the assessment of sensor and structural conditions,including bolt loosening or component failure.The efficacy of the proposed sensor and monitoring system was validated through a project carried out at the Xiluodu Hydropower Plant.According to the results,the sensor and online monitoring system effectively gauged and proficiently conveyed and stored bolt tension data.In addition,correlations were created between bolt tensions and essential unit parameters,such as water head,active power,and pressures at vital points,facilitating anomaly detection and early warning.

高强螺栓应力锈蚀的声发射特征

高强螺栓是钢结构的重要连接构件,其在高应力服役过程中易因锈蚀而出现断裂。为了研究其在应力锈蚀下的损伤演化规律,利用声发射技术对其损伤过程进行了实时监测。结合改进的K均值算法和动态门槛,对声发射损伤信号进行聚类,并进一步对聚类的声发射信号进行锈蚀损伤阶段划分。试验结果表明,高强螺栓的损伤信号可以分为3类,进一步划分其中第三类信号的损伤阶段,最终得到应力锈蚀的4个阶段,验证了提出的声发射方法的有效性,并可使用该声发射方法实时监测高强螺栓的健康状况。

普通白菜种质资源耐抽薹性评价及耐抽薹种质的筛选

以64份普通白菜种质为试材进行露地栽培试验,通过对耐抽薹指标和主要农艺性状进行主成分分析、相关性分析以及隶属函数、聚类分析,综合评价普通白菜种质的耐抽薹性。结果表明:利用主成分分析法将普通白菜9个指标转化为抽薹时间、植株生长状态和生长量3个主成分因子,累积贡献率达79.147%。相关性分析结果表明,抽薹期、现蕾期、开花期之间呈极显著正相关,其中现蕾期的观测最为简单可靠,可快速评价普通白菜的耐抽薹性。运用隶属函数法将64份材料分为5个耐抽薹等级,并筛选出4份极耐抽薹种质和6份耐抽薹种质。聚类分析将隶属函数法筛选出的极耐抽薹种质和耐抽薹种质均划分到第Ⅱ类群,说明隶属函数法和聚类分析法均能有效鉴定普通白菜的耐抽薹性,其中隶属函数法更为简便直观。

白菜类蔬菜种质资源抽薹性状鉴定评价

为筛选耐抽薹白菜类蔬菜种质资源,以233份白菜类蔬菜种质资源为研究对象进行露地栽培,通过对现蕾期和开花期指标进行隶属函数法和系统聚类分析,综合鉴定评价白菜类蔬菜抽薹性状。现蕾期的变异幅度为39.00~181.00天,开花期的变异幅度为46.00~196.00天,变异系数分别达到24.53%和19.80%,表明白菜类蔬菜种质的抽薹性状具有丰富的遗传多样性。采用隶属函数法将233份白菜类蔬菜种质资源划分为5组,其中极耐抽薹种质80份。聚类分析结果表明,在距离系数4.5处233份白菜类蔬菜种质资源被分为5个类群,第Ⅳ类群极耐抽薹类型包括63份种质资源,均属于隶属函数法划分的极耐抽薹等级,说明隶属函数法和聚类分析法均能有效鉴定白菜类蔬菜种质的耐抽薹性。

基于神经网络聚类分析的电磁无损检测技术

将电磁无损检测原理与聚类分析相结合,利用改进的神经网络聚类学习方法,对钢铁材质进行检测,结果证明,该方法作为一种新的自适应模式识别技术,比传统的电磁检测准确度高,误判率低。

基于点云处理的机车车辆车底中心鞘螺栓故障检测方法

针对机车车辆车底中心鞘螺栓松动和缺失这一常见故障,提出了一种基于三维点云处理的检测算法。首先对目标点云进行下采样和离群点的移除,然后根据欧式距离对点云进行聚类分割,最后通过计算分割后每个点云包围盒形状系数和平均Z坐标实现螺栓点云定位,进而通过采样一致性算法拟合点云平面计算出螺栓松动程度,识别螺栓故障。将文中提出的算法与传统的基于2D图像的识别算法进行了对比,最后在地铁车辆智能巡检机器人中进行了应用,结果表明,该算法检测精度约为0.1 mm,且检测速度快,可满足实时检测的要求。

重庆朝天门长江大桥高强度螺栓群栓试验研究

针对重庆朝天门长江大桥拼装式节点板层多、板束厚度大、外形尺寸变化大及单个节点高强度螺栓数量多等特点,结合重庆地区气侯条件、该桥设计采用的抗滑移摩擦面技术参数和目前国内高强度螺栓连接副的性能,选取具有代表性的不同板厚组成的板束,通过压力传感器及静态应变系统进行了群栓模拟试验。通过群栓试验,了解了高强度螺栓预拉力随时间变化的损失情况,螺栓施拧先后顺序对栓群预拉力的影响,用终拧扭矩值的50%作为厚板的初拧扭矩时板束密贴情况,确定了高强度螺栓终拧扭矩检查时机,验证了该工程高强度螺栓施拧工艺的可操作性。该试验研究为今后类似工程的施工提供了宝贵的数据和经验。

Seismic behavior and mechanism analysis of innovative precast shear wall involving vertical joints

To study the seismic performance and load-transferring mechanism of an innovative precast shear wall(IPSW) involving vertical joints, an experimental investigation and theoretical analysis were successively conducted on two test walls. The test results confirm the feasibility of the novel joints as well as the favorable seismic performance of the walls, even though certain optimization measures should be taken to improve the ductility. The load-transferring mechanism subsequently is theoretically investigated based on the experimental study. The theoretical results show the load-transferring route of the novel joints is concise and definite. During the elastic stage, the vertical shear stress in the connecting steel frame(CSF) distributes uniformly; and each high-strength bolt(HSB)primarily delivers vertical shear force. However, the stress in the CSF redistributes when the walls develop into the elastic-plastic stage. At the ultimate state, the vertical shear stress and horizontal normal stress in the CSF distribute linearly; and the HSBs at both ends of the CSF transfer the maximum shear forces.

芥菜种质资源耐抽薹性评价及相关生理指标测定

以42份芥菜自交系为材料进行耐抽薹性状的综合鉴定,对耐抽薹相关农艺性状进行相关性、主成分、隶属函数、聚类分析,同时,检测萌动种子中的相关生理指标,综合评价芥菜自交系的耐抽薹性。试验结果表明,抽薹期、现蕾期、开花期3项指标之间两两呈现极显著相关性,且3项指标的主成分累积贡献率达到80.69%,其中,抽薹期观测简单方便;4℃低温处理下,植株的耐抽薹性更强,萌动种子中的POD活性也越强。上述研究结果为芥菜耐抽薹新品种的选育奠定了坚实基础。

基于机器视觉高空飞机螺栓松动监测仿真

高空飞机受到自身振动、气流冲击和温度瞬变等干扰时,导致飞机螺栓结构松动、断裂或者脱落等问题。飞机螺栓结构具有复杂的动态性,传统的飞机螺丝辅助视觉松动检测方法在处理飞机螺栓复杂结构时,获取的螺丝帽和螺丝杆的相对位置过程中,受到采集环境的影响,很难得到稳定特征,导致图像监测误差,无法获取准确的螺栓松动监测结果。提出聚类RBF神经网络算法的高空飞机螺栓紧固方法。根采集检测部分螺丝视觉图像序列,并对上述图像进行离散变换处理,提取高空飞机螺栓图像的可识别分离特征。针对螺栓机器视觉图像特征误差较大的缺陷,构建特征分离目标函数,并建立聚类RBF神经网络模型,对特征进行多次校验计算,完成判断。实验结果表明,利用改进算法进行机器视觉的高空飞机螺栓松动监测,能够极大的提高监测的准确性。

承受轴向压力和弯矩共同作用的螺栓群的受力分析

对受轴向压力和弯矩共同作用的螺栓群进行了受力分析,并以实例对该方法进行了验证。

Effect of Nanoscale Cu-Riched Clusters on Strength and Impact Toughness in a Tempered Cu-Bearing HSLA Steel

The effect of Cu-riched clusters on strength and impact toughness in a tempered Cu-bearing high-strength low-alloy(HSLA)steel is investigated. With increasing the tempering temperature, it is found that the yield strength increases firstly, achieving the maximum value(~ 1053 MPa) at the tempering temperature of 450 ℃, and then decreases significantly with the rise of tempering temperature. The tempering temperature-dependent yield strength is closely related to the precipitation of Cu-riched clusters. When tempering at 450 ℃, the peak strength will be reached as the nanoscale Cu-riched clusters with small size and high number density will cause a strong precipitation strengthening(~ 492 MPa) due to the dislocation shearing mechanism. However, the Cu-riched clusters will coarsen with further increasing tempering temperature, resulting in obvious decrement of yield strength owing to the dislocation bypassing mechanism. Compared with the yield strength,the variation in impact energy displays an inverse tendency and the impact energy is only 7 J for the sample tempered at 450 ℃. The fracture mode can be well explained by the competition between the cleavage fracture strength( σ F) and “yield strength”( σ Y). Although transgranular cleavage fracture can be found in samples tempered at 450 and 550 °C, the crack propagation along the lath boundaries is prevented in the sample tempered at 550 ℃. The reason is that the number density of Cu-riched clusters at lath boundaries decreases and the segregation of Mo element at the lath boundaries is induced,which will increase the bonding energy.