Microstructure evolution of Mg-Zn-Zr magnesium alloy against soft steel core projectile

The study aimed to shed light on the post deformation and damage behavior of an extruded Mg-Zn-Zr alloy under a ballistic impact.The results revealed that the initial microstructure consisted of both{0001}basal and{1010}prismatic fiber texture.After impact,adiabatic shear bands,pronounce different twinning in big grains,,<c>,and<c+a>types of dislocations,and grain refinement through twinning induce recrystallization accommodated the strain,and absorbed∼65.7%of the energy during impact carried by a soft steel projectile.Interestingly,the deformation behavior at the top broad sides of the crater was entirely different.The weak basal texture was changed to a strong prismatic texture,which was further proved by typical sigmoidal compressive stress-strain curves.A revised model for the development of the ultra-fine grains adjacent to the crater has been proposed.The microhardness and yield strength was∼33%and∼40%higher and chiefly ascribed to strain hardening in ultra-fine grained near the surface of the perforation path.The exit of the perforation path was severely damaged and forms onion-shaped concentric rings which were comprised of melted zones,dimples,and cracks.Based on the all interesting findings,this study can be a clue for the development of the lightweight Mg alloy for military and aerospace applications.

Formation of internal cracks in steel billets during soft reduction

To investigate the formation of internal cracks in steel billets during soft reduction, fully coupled thermo-mechanical finite element models were developed using the commercial software ABAQUS, also casting and soft reduction tests were carried out in a laboratory strand casting machine. With the finite element models, the temperature distribution, the stress and strain states in the billet were calculated. The relation between internal cracks and equivalent plastic strain, as well as maximal principal stress was analyzed. The results indicate that tensile stresses can develop in the mushy zone during soft reduction and the equivalent strain nearby the zero ductility temperature （ZDT） increases with decreasing solid fraction. Internal cracks can be initiated when the accumulated strain exceeds the critical strain or the applied tensile stress exceeds the critical fracture stress during solidification.

Improvement of center segregation in high-carbon steel billets using soft reduction

Center segregation is the main reason for cup fracture of high-carbon wire rod during drawing. Therefore, to continuously produce cast billets with very low center segregation is an important objective. The soft reduction technology is considered to be an effective method to minimize center segregation. To elucidate the effect of soft reduction on the internal quality of high-carbon steel billets, soft reduction was applied with different solid fractions in the core area of billets in a laboratory casting machine. A coupled temperature/displacement finite element model was developed to calculate the solid fraction using the commercial software ABAQUS. Center segregation, center porosity, homogeneity of elements, and equiaxed crystal zone were obviously improved by applying soft reduction, especially when the solid fraction was less than 1.0. The optimal results were obtained when the solid fraction was approximately 0.9.

Numerical Comparative Study on the Effective Replacement Thickness of Traditional Stone Coarse Aggregate or Steel-Slag Aggregate Mixtures in Improved Soft Fine Soils

This study uses Steel Slag Coarse Aggregate (SSCA) as a mixture replacement, preamble material to improve soft soils, which is economic, and has good effect environment. Recently, the development and utilization of by-product, waste and recycle materials must be studied and investigated as a source of improved material for soft soils as, an economic and good effect environmental. The study analyzes effects of both replaced mixtures, (SSCA) or (TSCA) on improved soil bearing capacity and expected settlement after verifying the model. Numerical modeling of the one of real store loaded strip using, PLAXIS, 2D, strain deformation behavior to achieve field visible and measured deformations of untreated soft soil. Numerical studies were devolved to investigate geomechanics parameters improved to compare between using (SSCA) or (TSCA) as, replacement mixture. Results demonstrate that using (SSCA) improved compressibility and strength of shallow soft soil layer significantly than using (TCSA) mixture, while (SSCA) improved strip footing ultimate bearing capacity, (UBC), by 84.4% compared with increase of 20.5% when using (TCSA) mixture at the same thickness. In addition, the study highlights the effective (SSCA) replacement thickness ranges between (0.65 ~ 0.80) footing width.

Macrosegregation Quality Criteria and Mechanical Soft Reduction for Central Quality Problems in Continuous Casting of Steel

In order to study the central quality of continuously cast tool steel slabs, the simple model has been developed to simulate the macrosegregation quality criteria. The model calculates different quality criteria such as average macro-segregation level criterion “ASL”, its fluctuation level “FSL” and its segregation quality number “SQN”. These criteria are calculated based on the previous measurements of carbon and sulfur concentrations distributions in final region of spray zones and centerline area of lower and upper slab sides. The effect of mechanical soft reduction Technique “MSR” on the slab centerline quality is examined and analyzed. The model results show that MSR affects the quality of centerline areas significantly by different ways based on the casting speed. The experimental and theoretical results clarify that the qualities of different slab sides are different for all collected samples. The model results show also that the accuracy of the macro-segregation quality criteria increases quantitatively with increasing the number of analyzed segregated elements. Therefore, the macrosegregation quality criteria and their distributions can be considered as the most simple and vital tool to evaluate the various slab qualities. Finally, the mechanism of centerline segregation formation with mechanical soft reduction is discussed in this study.

Dynamic Soft Reduction for Continuously Cast Rail Bloom

Center porosity and centerline segregation in continuously cast bloom can be minimized by the well-known method of dynamic soft reduction. Metallurgical results of soft reduction previously employed in continuous bloom casting for heavy rail steel in Panzhihua Iron and Steel Group were not fully achieved because of the improper soft reduction process. Therefore, experiments for optimizing the process parameters of soft reduction for bloom were carried out. The results show that the proportion of the center porosity, which is less than 1.0, increases from 28.41% to 99.81%, while the proportion of the centerline segregation class increases from 40.91% to 100%, and the proportion of the central cavity increases from 92.05% to 100%, whereas the center carbon segregation index decreases from 1.17 to 1.05. The internal quality and the mechanical performance of the rails produced from continuously cast blooms meet the requirement of high-speed tracks of 350 km/h.

拉森钢板桩在软土地层深基坑支护中的应用

拉森钢板桩作为一种低碳环保、可回收的建筑材料,在各类建筑中发挥着重要的作用。以蕲春县某河道整治项目为例,选取了基坑支护工程中2个典型剖面,介绍了拉森钢板桩在软土地层中的应用,并将天汉软件设计计算结果、MIDAS GTS NX数值模型分析结果与基坑监测结果进行对比分析,三者得到的支护结构位移、受力数值较为一致,表明天汉深基坑设计软件的客观合理性及可靠性非常高,施工前可以用MIDAS GTS NX数字模拟来预测及引导施工。

SMART/ASTC dynamic soft reduction technology and its application on the bloom continuous caster at Pangang

The SMART/ASTC dynamic soft reduction technology of VAI and its application on the 6-strand bloom continuous caster at Pangang, China are presented. The operation results show that soft reduction technology is effective to improve the inner quality of continuously cast blooms. At Pangang, both the central porosity and the central segregation ratings are no more than 1.0, the central shrinkage cavity rating is no more than 0.5, and the central segregation index of carbon is no more than 1.05. Rails made from the blooms have excellent quality and are used for high-speed tracks.

Formation of internal cracks during soft reduction in rectangular bloom continuous casting

To investigate the formation of internal cracks in GCrl 5 bearing steels during the soft reduction process in rectangular bloom con- tinuous casting, fully coupled thermomechanieal finite element models were developed using the commercial software MSC.MARC, and microstructures and fractographs were also observed. With the finite element models, the contours of temperature, equivalent plastic strain, and equivalent vun Mises stress were simulated. It is observed that the fracture surfaces of internal cracks are covered by cleavage or quasi-cleavage facets. The region of internal cracks in the intergranular brittle fracture mode is in the mushy zone between the zero ductility temperature （ZDT） and the zero strength temperature （ZST）. The simulated equivalent plastic strain in the crack region is 2.34%-2.45%, which is larger than the critical strain （0.4%-1.5%）, and the equivalent von Mises stress is 1.84-5.05 MPa, which is within the range of criti- cal stress （3.9-7.2 MPa）, thus resulting in the occurrence of internal cracks. Reducing the soft reduction amount from 3 to 2 mm can lower the stress under the critical value.

Technical improvements of Baosteel EAF bloom caster production line

This paper presents the improvements on equipment and process technologies of Baosteel EAF Bloom Caster Production Line.By using the new VOD equipment,super low carbon super 13Cr was successfully made;By applying and developing the Soft Reduction technology,very good results were achieved on high quality steel grades such as tire cord steel,bear steel,hi-alloy steel;the ladle Anti-Slag Detector is normally applied,based on the detail analysis during the performance test period,the Detector gives out slag entrapment alarms 7-9 s average before slag flows into tundish.By optimizing production control points of each key process,great achievements are realized on high quality steel grades such as tire cord steel,bear steel,hi-alloy steel and hi-S/Al steel,etc.Some achievements and technical indices are presented,too.

格栅式钢板桩与桩筏基础集成的基坑支护技术

针对软土地质基坑工程,提出格栅式钢板桩与桩筏基础集成的基坑支护技术,通过设置纵向双排钢板桩与横向钢板桩或钢板组成格栅式钢板桩,以提高支护结构强度与刚度,并与桩筏基础协同工作,以解决结构下部软土层承载力较差的问题,并提高支护结构稳定性。以某管廊工程为依托,通过计算分析与技术对比,论证集成支护技术的安全性与可行性。

一种纯弯曲耗能阻尼器的力学性能分析及优化设计

提出了一种新型纯弯曲耗能阻尼器。通过理论计算给出了耗能钢板与限位移钢板的高度关系,对耗能钢板进行三角形开孔设计,通过理论计算给出单次加载下各尺寸耗能钢板不会产生剪切屈服的最大开孔率,通过数值模拟得到了耗能系数最大时的开孔高度与开孔底边长度。利用有限元软件对影响钢板耗能的几何参数进行力学分析。结果表明:耗能钢板的厚度与限位移钢板的高度对阻尼器的耗能系数影响较大,耗能钢板的宽度和数量对其影响较小。最后通过正交试验给出一个耗能性能强的阻尼器尺寸。

软磁不锈钢环样和棒样磁性能测量结果差异及其机理分析

随着自动控制领域对软磁不锈钢磁性能和综合性能的要求越来越高,软磁不锈钢的磁性能检测变得越来越重要。首先介绍了软磁材料的起始磁化曲线和正常磁化曲线,然后对软磁不锈钢磁性能检测中标准规定的环样法和棒样法(磁导计法)的磁性能测试结果进行比较和分析,对存在差异的原因进行了探讨,并对以后在测量中可能采取的措施进行了介绍。实验证明,环样法和棒样法间磁性能的差异是普遍存在的一种现象。受测试方法的限制,只有采取合理的措施,才能得到供需双方都能认可的测量结果。

循环荷载作用下钢桩-软黏土接触面剪切特性研究

目前,中国海上风电工程的建设已进入快速发展阶段。海上风电机常采用大直径钢管桩作为基础,然而现在的桩基承载力设计预测方法往往基于小直径柔性桩,不适用于大直径刚性桩。因此需要研究海上桩基桩-土界面的相互作用,来对海上大直径刚性桩基的设计预测方法进行优化。使用循环荷载作用下钢桩-软黏土大型接触面剪切试验数据,建立法向循环荷载作用下钢与黏性土接触面剪切试验的离散元模型,对各个细观参数进行标定,分别研究动荷载频率和幅值对剪切特性的影响,并进行了细观机理分析。数值模拟结果表明动荷载频率和幅值越大,钢与黏性土接触面强度越小,其中动荷载幅值的影响较为明显。通过细观机理分析可以发现:动荷载频率和幅值越大,接触面处黏性土的颗粒位移越小;静荷载下黏性土的颗粒间作用力大于动荷载下的颗粒间作用力;动荷载会导致颗粒间的扰动,从而使接触面强度减小。研究结果可以为海上风电桩基承载力的准确预测提供理论基础。

HUW组合钢板桩在软土地基深基坑工程中的 适应性分析

目的:本研究旨在分析HUW组合钢板桩在软土地基深基坑工程中的结构适应性,以期为相似地区深基坑工程提供理论支持。方法:基于某软土地区科技产业园深基坑工程,运用ABAQUS有限元软件,通过增量法模拟实际开挖过程,计算正常开挖下的结构变形和土体位移,从而分析HUW组合钢板桩在实际工程中的结构可行性。结果:随着基坑的逐层开挖,基坑边缘的沉降值逐步增大,尤其在软土地基条件下,地表沉降现象更为明显。针对6.3米深基坑的开挖,HUW组合钢板桩的最大水平位移为22.78毫米,符合基坑施工规范的要求。结论:HUW组合钢板桩在实际工程中具备可行性,可为类似工程提供理论参考。但土体受侧向约束的影响,在边界区域会形成局部隆起,因此需对边坡边缘进行加固处理。

新型装配式软钢阻尼器梁柱节点的抗震性能及其时程分析研究

本文研究的是一种软钢阻尼器梁柱节点,并根据有无软钢阻尼器模拟的框架结构,在不同的地震波进行时程分析,为该节点的设计和建筑施工提供参考。利用ABAQUS有限元软件的数值模拟,对有无软钢阻尼器两种节点建模分析,从两种节点的滞回曲线、骨架曲线、耗能能力、刚度退化等抗震性能进行定量分析。结果表明有阻尼器的节点各力学性能均强于无阻尼器的节点,并且在有控情况下可以显著消耗建筑结构的地震能量,减小地震反应。因此本节点在有控情况下有利于装配结构在高烈度地区的推广使用,可以有效提高装配式结构的抗震性能,为装配式建筑施工在实际应用中提供参考。

改善70钢连铸小方坯芯部质量的工艺实践

为了改善70钢连铸方坯的芯部质量,通过调整拉速、过热度、二冷比水量和压下工艺进行工业试验研究。结果表明:当压下工艺为2/2/4/7/7时,通过低过热度、高拉速或降低二冷比水量均可以改善铸坯中心碳偏析;但是在2.60 m/min高拉速或0.46 L/kg低二冷比水量浇注时,降低了铸坯的冷却速度,导致1#拉矫机处的固相率较低,坯壳厚度不足,压下时产生中间裂纹。当从2#拉矫机开始实施压下,压下工艺为0/2/5/7/6时,不仅中间裂纹有明显的改善,而且中心碳偏析也得到有效的控制,测得中心碳偏析度仅为1.02,铸坯芯部质量较好。

弹簧钢60Si2Mn轻压下工艺调试及质量改进

分析了弹簧钢60Si2Mn(/%:0.58~0.62 C,1.65~1.85 Si,0.80~0.90 Mn,≤0.020 P,≤0.015 S)的210 mm×210 mm连铸方坯中心区域碳偏析和残余缩孔的原因,认为高碳钢在凝固过程中选分结晶和两相区铸坯长度较长,钢水无法补缩导致。利用现有连铸机7组拉矫机的轻压下功能,在不改变连铸工艺参数,保证弹簧钢60Si2Mn铸坯表面质量的前提下,通过模拟计算对铸坯凝固终点进行了理论研究。在此基础上,对不同拉矫机及不同压下量方案进行了优化试验,并分析了连铸方坯的低倍质量,找出了最优的轻压下工艺方案。结果表明:现有工艺装备条件下,采用5#拉矫机3 mm压下量、6#拉矫机5 mm压下量和7#拉矫机2 mm压下量的压下工艺,铸坯内部没有压下裂纹,能够控制残余缩孔在0.5级以下,中心碳偏析指数在1.04~1.10之间的比例达95%左右,实现了改善铸坯残余缩孔和中心碳偏析的目的,同时弹簧钢60Si2Mn采用轻压下工艺时单组拉矫机压下量不超过6 mm。

张靖皋长江大桥南航道桥南塔防撞方案研究

张靖皋长江大桥南航道桥为主跨2300 m的双塔双吊跨钢箱梁悬索桥,桥下船舶通航密度大、船舶平均吨位大、船舶碰撞概率高、南塔所受船撞力计算值大。经综合分析,传统被动防撞方案均不能很好满足南塔防撞要求,故提出采用锁口钢管桩围堰外挂软体护舷的新型防撞方案。该防撞方案通过在承台外围设锁口钢管桩围堰形成裙墙,在围堰外侧外挂软体护舷,并在围堰与承台之间空隙处填充耗能材料实现防撞及消能,裙墙同时兼作临时施工围水设施以及起到永久冲刷防护和船撞消能作用。为验证新型防撞装置的防撞效果并选择合适的耗能材料,进行船桥碰撞有限元分析。最终采用填充沙粒的新型防撞装置方案,该方案可削减36.68%南塔承台撞击力,防撞效果好。新型防撞方案施工简单,后期仅需对钢管桩作防腐处理,撞后便于修复,工程造价低。

深厚软岩地质钢管桩可打性分析及沉桩试验

在深厚软岩施工的钢管桩,其桩尖入岩深度存在不确定性。依托实际工程,通过可打性分析、现场足尺沉桩试验和承载力测试开展深厚软岩地质钢管桩的沉桩施工试验研究。结果表明:在深厚软岩施工的钢管桩,桩尖宜采取敞口形式,尽量减小打桩过程中的土塞效应,保证钢管桩的入岩深度;泥岩中打桩时的土塞效应系数可较静载时的取值适当小,泥质灰岩中的土塞效应系数可参考静载时的取值,直径1 000 mm敞口钢管桩土塞系数可取0.45,直径1 200 mm时可取0.33;当锤击能量有限时,入深厚软岩的钢管桩终锤贯入度可相比常规地质的贯入度适当减小,可将1 mm/击作为终锤标准。