Numerical Analysis of Cold-Formed Thin-Walled Steel Short Columns with Pitting Corrosion during Bridge Construction

Pitting corrosion is harmful during bridge construction,which will lead to uneven roughness of steel surfaces and reduce the thickness of steel.Hence,the effect of pitting corrosion on the mechanical properties of cold-formed thin-walled steel stub columns is studied,and the empirical formulas are established through regression fitting to predict the ultimate load of web and flange under pitting corrosion.In detail,the failure modes and load-displacement curves of specimens with different locations,area ratios,and depths are obtained through a large number of non-linear finite element analysis.As for the specimens with pitting corrosion on the web,all the specimens are subject to local buckling failure,and the failure mode will not change with pitting corrosion,but the failure location will change with pitting corrosion location;the size,location,and area ratio of pitting corrosion have little influence on the ultimate load of cold-formed thin-walled steel short columns,but the loss rate of pitting corrosion section area has a greater impact on the ultimate bearing capacity.As for the specimen with flange pitting corrosion,the location and area ratio of pitting corrosion have less influence on the ultimate load of cold-formed thin-walled steel short columns,and the section area loss rate has greater influence on the ultimate bearing capacity;the impact of web pitting corrosion on the ultimate load is greater than that of flange pitting corrosion under the same condition of pitting corrosion section area.The prediction formulas of limit load which are suitable for pitting corrosion of web and flange are established,which can provide a reference for performance evaluation of corroded cold-formed thin-walled steel.

Microstructures and Properties of 550 MPa Grade High Strength Thin-walled H-beam Steel

The microstructures and mechanical properties of 550 MPa grade lightweight high strength thin-walled H-beam steel were experimentally studied. The experimental results show that the microstructure of the air-cooled H-beam steel sample is consisted of ferrite, pearlite and a small amount of granular bainites as well as fine and dispersive V（C,N） precipitates. The microstructure of the water-cooled steel sample is consisted of ferrite and bainite as well as a small amount of fine pearlites. The microstructure of the water-cooled sample is finer than that of the air-cooled sample with the average intercept size of the surface grains reaching to 3.5 gna. The finish rolling temperature of the thin-walled high strength H-beam steel is in the range of 750 ~C-850 ~C. The lower the finish rolling temperature and the faster the cooling rate, the finer the ferrite grains, the volume fraction of bainite is increased through water cooling process. Grain refinement strengthening and precipitation strengthening are used as major strengthening means to develop 550 MPa grade lightweight high strength thin- walled H-beam steel. Vanadium partially soluted in the matrix and contributes to the solution strengthening. The 550 MPa grade high-strength thin-walled H-beam steel could be developed by direct air cooling after hot rolling to fully meet the requirements of the target properties.

A nonlinear explicit dynamic GBT formulation for modeling impact response of thin-walled steel members

A nonlinear explicit dynamic finite element formulation based on the generalized beam theory(GBT)is proposed and developed to simulate the dynamic responses of prismatic thin-walled steel members under transverse impulsive loads.Considering the rate strengthening and thermal softening effects on member impact behavior,a modified Cowper-Symonds model for constructional steels is utilized.The element displacement field is built upon the superposition of GBT cross-section deformation modes,so arbitrary deformations such as cross-section distortions,local buckling and warping shear can all be involved by the proposed model.The amplitude function of each cross-section deformation mode is approximated by the cubic non-uniform B-spline basis functions.The Kirchhoff s thin-plate assumption is utilized in the construction of the bending related displacements.The Green-Lagrange strain tensor and the second Piola-Kirchhoff(PK2)stress tensor are employed to measure deformations and stresses at any material point,where stresses are assumed to be in plane-stress state.In order to verify the effectiveness of the proposed GBT model,three numerical cases involving impulsive loading of the thin-walled parts are given.The GBT results are compared with those of the Ls-Dyna shell finite element.It is shown that the proposed model and the shell finite element analysis has equivalent accuracy in displacement and stress.Moreover,the proposed model is much more computationally efficient and structurally clearer than the shell finite elements.

Bond Performance of Adhesively Bonding Interface of Steel-Bamboo Composite Structure

The steel-bamboo composite structure is a newly developed structure,combining phyllostachys pubescens(also called Moso bamboo)plywood and cold-formed thin-walled steel with structural adhesive.The reliability of steelbamboo interface is the premise of composite effect.13 specimens were prepared to investigate the failure modes and mechanism of the steel-bamboo interface on the basis of push-out test,and the strain difference analysis method was proposed to study the distribution of shear stress.The results show that the main failure modes of steel-bamboo interface are adhesion failure and splitting of bamboo plywood.The shear stress is not evenly distributed along the longitudinal direction of the interface,showing a shape of“larger at two ends and smaller in the middle”.The lower end of the interface is the initial location of the interface failure and the shear stress concentration degree is positively correlated with the thickness of the externally bonded bamboo plate.The shear resistance of steel-bamboo interface can be enhanced by improving the adhesion between steel and structural adhesive and ameliorating the quality of bamboo products.

Feasibility of developing composite action between concrete and cold-formed steel beam

Cold-formed steel structures are steel structure products constructed from sheets or coils using cold rolling, press brake or bending brake method. These structures are extensively employed in building construction industry due to their light mass, ductility by economic cold forming operations, favorable strength-to-mass ratio and other factors. The utilization of cold formed steel sections with concrete as composite can hugely reduce the construction cost. However, the use of cold formed steel members in composite concrete beams has been very limited. A comprehensive review of developments in composite beam with cold formed steel sections was introduced. It was revealed that employing cold-formed steel channel section to replace reinforcement bars in conventional reinforced concrete beam results in a significant cost reduction without reducing strength capacity. The use of composite beam consisting of cold-formed steel open or close box and filled concrete could also reduce construction cost. Lighter composite girder for bridges with cold-formed steel of U section was introduced. Moreover, types of shear connectors to provide composite action between cold-formed steel beam and concrete slab were presented. However, further studies to investigate the effects of metal decking on the behavior of composite beam with cold-formed steel section and introduction of ductile shear connectors were recommended.

GCr15钢轴套断裂原因

采用宏观观察、化学成分分析、扫描电镜和能谱分析、金相检验、显微硬度测试等方法对某GCr15钢轴套断裂原因进行分析。结果表明:轴套的断口呈脆性断裂特征,断口的起始位置存在早期裂纹;磨削工艺不当使轴套端面产生磨削烧伤,并导致轴套表面硬度下降。

小边距孔的压合衬套强化工艺研究

针对某型机研制中遇到钛合金耳片结构小边距孔的强化问题,以Forcemate压合衬套为强化方法,研究其对小边距孔的强化效果。结合有限元方法分析干涉量分别为0.5%、1.0%、1.5%、2.0%、2.5%对孔周应力应变的影响,并将小边距孔与常规边距孔的应力结果进行对比。对强化后的耳片施加循环外载,获得干涉量与疲劳寿命之间的关系,最终为最佳工艺参数的选取提供理论依据。

橡胶-钢球支座在扭转载荷作用下的断裂分析

通过非线性有限元方法对橡胶-钢球支座的橡胶层与钢球粘结界面上及橡胶中间层在扭转载荷作用下存在中心裂纹和环形边缘裂纹的情况进行了数值模拟,给出撕裂能与裂纹尺寸、载荷和橡胶层厚度的关系曲线。结果表明,撕裂能随载荷的增加而增加,随橡胶层厚度的增加而减小。对于界面中心裂纹和橡胶层环形边缘裂纹,撕裂能都随着裂纹深度的增加先增加后减小;对于界面环形边缘裂纹和橡胶层中间钱币形裂纹,撕裂能随裂纹深度的增加而增加。

热处理工艺对机械轴套性能的影响

采用不同正火温度、淬火温度和回火温度对含0.25%V和0.15%Sr的45钢机械轴套进行了热处理,并测试与分析了45钢机械轴套的力学性能。结果表明:随正火温度从830℃上升至930℃,淬火温度从800℃上升至880℃,回火温度从550℃上升至650℃,轴套的力学性能均先提高后下降。轴套的正火温度、淬火温度和回火温度分别优选为890、860和610℃。

小变形悬架衬套全刚度力学模型的建立与验证

鉴于衬套对悬架及整车性能影响较大,以扭力梁后悬架的橡胶-钢衬套为研究对象,先通过有限元分析结合响应面优化算法对相应Yeoh本构模型的多系数寻优,拟合出逼近试验曲线的沿x/y/z三向刚度仿真曲线,为优化后的衬套模型建立新的边界条件,求解拟合出绕x/y/z三向扭转刚度仿真曲线;进一步以扭力梁后悬架的极限扭转为工况,分别对含全6向刚度衬套力学模型和含刚柔耦合预紧衬套模型的扭力梁后悬架进行结构强度分析,两种分析结果均满足材料强度要求,最大应力和最大位移出现位置相同,各自相对误差分别是6.58%和1.27%,工程中属可接受范围。研究表明,在开展小变形范围内的悬架橡胶-钢衬套相关研究时,为达到减小建模工作量、缩短计算时间、不降低计算精度等目的,可以使用简单的全6向刚度衬套力学模型代替其他较复杂衬套模型。

一种转臂定位节点的结构改进

针对一种钢簧侧置式转臂定位节点结构复杂、使用寿命短的问题进行分析,提出了一种结构更简单、使用寿命更长的结构。样机试制、型式试验和运用结果表明,该种新结构确实能更好地满足使用要求。

橡胶-钢球支座刚度的有限元分析

通过非线性有限元方法对橡胶-钢球支座在轴向拉伸、扭转和弯曲的大变形载荷作用下的力学行为进行分析,得出支座的轴向刚度、扭转刚度和弯曲刚度与变形的关系。轴向刚度和弯曲刚度随着变形的增大而减小,扭转刚度随着变形的增大而增大,但总的来说,变化很小。

发动机轴瓦钢背用低Si冷轧带钢性能稳定性分析

介绍了过程能力指数Cpk的计算方法,低Si冷轧带钢的抗拉强度的Cpk为1.28,伸长率的Cpk为2.12,两者均高于过程能力指数下限1.0,Cpk的高低反映了一个钢种在某一段时期生产的性能稳定性,Cpk值越大,表明其性能越稳定。

浅谈几种典型螺纹连接元件的应用

电子设备中常用的铝、镁、塑料等低强度工程材料上直接生成的螺纹强度及承载能力都不高,不易满足设计需要,本文介绍几种典型螺纹连接元件的应用,以期能为设计师提供一定的参考。

全套管大直径高频振动取土灌注桩施工技术

本文介绍了全套管大直径高频振动取土灌注桩的成桩工艺及其技术特点,与其他成桩工艺对比,该成桩工艺是一种先进的具推广应用价值的新型成孔技术。

退火工艺对轴瓦钢背用冷轧带钢的性能影响

分析了退火工艺对轴瓦钢背用冷轧带钢性能的影响,结果表明,延长退火保温时间、提高退火温度有利于改善渗碳体分布,并增加延伸率。在保温时间为4小时、退火温度为700℃的退火工艺条件下,试验钢的延伸率达到43%的最高值,其屈服强度为220MPa,抗拉强度为355MPa,金相组织为铁素体+渗碳体,渗碳体分布均匀。

金属射出成型过程中黑痕与熔接线现象建模与实验分析

以医疗用17-4PH不锈钢导引衬套的射出成型加工过程为例,探讨了金属在射出成型过程中所产生的黑痕与熔接线现象;建立数学模组分析了射出成型阶段的射出速度、保压压力、料温、模温等工艺参数对黑痕与熔接线的影响。并运用反应曲面法(RSM)并结合连续近似最佳法(SAO)来获取17-4PH不锈钢最佳化生产品质之工艺参数。结果表明,保压压力对于黑痕面积的影响远大于射出速度对其影响,但射出速度的提高不利于减少黑痕面积;在低的模温和高的料温下,黑痕面积出现最小值;而在高的模温和料温下,熔接线的区域则最小。工艺参数优化后,其生坯表面所形成的黑痕与熔接线面积较初始值分别减少了78.81%和83.85%。

推土机底盘支架螺纹联接改造方法

潜孔钻和推土机是矿山主要采矿设备,检修上述设备经常遇到行走部分无法恢复诸多问题,尤为突出的是支重轮座子的联接因长期在复杂环境中使用出现锈蚀、松旷等无法修复的难题,本方法着重论述如何有效恢复行走部分支重轮座子的联接问题,并进行了方案的可行性论证,提出了相应的修复方案。以便指导矿山生产。

齿辊的铸造工艺与生产控制

针对整体铸造的球团齿辊使用寿命低和易渗漏的问题,研制开发了一种三段式结构的生产工艺。通过选择合适的材质,设计合理的铸件结构、芯盒结构及浇注系统,以及热处理工艺,并借助铸造仿真凝固模拟,加强各工序质量控制,解决了齿辊打压漏水及使用寿命短的难题。实践证明,生产的齿辊耐磨性能好,使用寿命长。

含椭圆表面裂纹橡胶-钢球支座在扭转载荷下的断裂分析

通过非线性有限元方法对橡胶-钢球支座在扭转载荷作用下存在的椭圆表面裂纹情况进行了数值模拟,给出撕裂能与裂纹尺寸、载荷和橡胶层厚度的关系曲线.结果表明,对界面椭圆表面裂纹,同一裂纹深度,撕裂能随载荷的增加而增加,随橡胶层厚度的增加而减小.对橡胶层中间含椭圆表面裂纹,撕裂能随裂纹深度的增加而增加.最后,利用非线性回归工具得到撕裂能的经验计算式.