Determination of Elastoplastic Mechanical Properties of the Weld and Heat Affected Zone Metals in Tailor-Welded Blanks by Nanoindentation Test

The elastoplastic mechanical properties of the weld and heat affected zone metals have comparatively major impact on the forming process of tailor-welded blanks. A few scholars investigated the elastoplastic mechanical properties of the weld and heat affected zone, but they only simply assumed that it was a uniform distribution elastoplastic material different from the base materials. Four types of tailor-welded blanks which consist of ST12 and 304 stainless steel plates are selected as the research objects, the elastoplastic mechanical properties of the tailor-welded blanks weld and heat affected zone metals are obtained based on the nanoindentation tests, and the Erichsen cupping tests are conducted by combining numerical simulation with physical experiment. The nanoindentation tests results demonstrate that the elastoplastic mechanical properties of the weld and heat affected zone metals are not only different from the base materials, but also varying between the weld metals and the heat affected zone metals. Comparing the Erichsen cupping test resulted from numerical with that from experimental method, it is found that the numerical value of Erichsen cupping test which consider the elastoplastic mechanical properties of the weld and heat affected zone metals have a good agreement with the experimental result, and the relative error is only 4.8%. The proposed research provides good solutions for the inhomogeneous elastoplastic mechanical properties of the tailor-welded blanks weld and heat affected zone metals, and improves the control performance of tailor-welded blanks forming accuracy.

NUMERICAL SIMULATION OF THE THERMO-MECHANICAL PROCESS FOR BEAM BLANK CONTINUOUS CASTING

The aim of this study was to simulate the solidification process of beam blank continuous casting, and then find the reasons for the typical defects of the beam blank. A two-dimensional transient coupled finite element model has been developed to compute the temperature and stress profile in beam blank continuous casting. The enthalpy method was used in the heat conduction equation. The thermo-mechanical property in the mushy zone was taken into consideration in this calculation. It is shown that at the mold exit the thickness of the shell had its maximum value at the flange tip and its minimum value at the fillet. The temperature had a great fluctuation on the surface of the beam blank in the secondary cooling zone. At the unbending point, the surface temperature of the web was in the brittleness temperature range under the present condition. To ensure the quality, it is necessary to weaken the intensity of secondary cooling. At the mold exit the equivalent stress and strain have higher values at the flange tip and at the web. From the spray 1 to the unbending point, the maximum values of stress and strain gradually moved to the internal section of the flange tip and the web. However, whenever, there were bigger stress and strain values near the flange tip and the web than in the other parts, it must be very easy to generate cracks at those positions. Now, online verification of this simulation has been developed, which has proved to be very useful and efficient to instruct the practical production of beam blank continuous casting.

前箱熔体温度对8011铝合金铸轧板坯组织性能的影响

为了稳定提高双零铝箔用铸轧坯料质量,使用电解铝液配料生产规格为7.0 mm×1300 mm的8011铝合金铸轧铝板卷,并利用光学显微镜(OM)、扫描电镜(SEM)、能谱仪(EDS)及电子万能拉伸试验机等手段,研究了不同前箱铝熔体温度(680,690,700,710℃)对8011铝合铸轧板坯微观组织和力学性能的影响.结果表明:随着前箱熔体温度的升高,铸轧板坯晶粒的尺寸呈略微增大再急剧变大的趋势,其抗拉强度和断后伸长率均呈先缓慢降低后急剧下降的趋势;当前箱熔体温度控制在680~700℃时,可获得综合力学性能较佳的铸轧板坯,其平均纵向抗拉强度和横向抗拉强度分别不低于141.87 MPa和138.84 MPa,平均纵向断后伸长率和横向断后伸长率分别不低于29.8%和26.4%.

Constitutive Model of Friction Stir Weld with Consideration of its Inhomogeneous Mechanical Properties

In practical engineering, finite element（FE） modeling for weld seam is commonly simplified by neglecting its inhomogeneous mechanical properties. This will cause a significant loss in accuracy of FE forming analysis, in particular, for friction stir welded（FSW） blanks due to the large width and good formability of its weld seam. The inhomogeneous mechanical properties across weld seam need to be well characterized for an accurate FE analysis. Based on a similar AA5182 FSW blank, the metallographic observation and micro-Vickers hardness analysis upon the weld cross-section are performed to identify the interfaces of different sub-zones, i.e., heat affected zone（HAZ）, thermal-mechanically affected zone（TMAZ） and weld nugget（WN）. Based on the rule of mixture and hardness distribution, a constitutive model is established for each sub-zone to characterize the inhomogeneous mechanical properties across the weld seam. Uniaxial tensile tests of the AA5182 FSW blank are performed with the aid of digital image correlation（DIC） techniques. Experimental local stress-strain curves are obtained for different weld sub-zones. The experimental results show good agreement with those derived from the constitutive models, which demonstrates the feasibility and accuracy of these models. The proposed research gives an accurate characterization of inhomogeneous mechanical properties across the weld seam produced by FSW, which provides solutions for improving the FE simulation accuracy of FSW sheet forming.

Investigation of the Process Parameters on the Blanking of AISI 304 Stainless Steel by Using Finite Element Method

Blanking is a major process and has a wide range of usage in manufacturing industry. The general concept of blanking seems a simple one but governing parameters are many and have a complex relationship which directly affect the quality of the produced parts （blanks） and also the energy efficiency of the process. The main problem is the lack of prediction capabilities of the effect of these parameters that lead to time, money and labor consuming trial and error procedures in experimental studies. Usage of FEM based programs to simulate blanking to obtain numerical results and observe the shearing mechanism is a cheap and a detailed way for industrial applications. In this study five different clearances （1%, 3%, 5%, 10% and 20%） and three different thicknesses （t = 2 mm, t = 3 mm and t = 4 mm） were used for simulation and experimental studies of the blanking process. Simulations were executed by using the FEM program, Deform 2-D. Investigations were made on the parameters related to crack progression like crack initiation and crack propagation angles, indentation angle, rollover angle and depth and also the related blanking energy values. The results of the present paper are in agreement with the results of experimental studies.

Research on horizontal electromagnetic continuous casting of copper tube blanks

The effect of commercial frequency electromagnetic field on the solidification structure and mechanical propertiesof copper hollow blanks prepared by horizontal continuous casting method was investigated. The results show thatwhen the electromagnetic field is imposed, columnar grains are evidently refined and fine equiaxed grains areobtained in the inner side of the cross-section. Moreover, with the increase of input current, the equiaxed grain regionwidens and the grains distribute more uniformly in the circumferential direction. Meanwhile, the mechanical properties areremarkably improved by the application of electromagnetic field. When the input current is 140 A, the tensile strengthincreases 15% and the elongation increases 10%. However, the electromagnetic field has no effect on the distribution ofmicroelements.

Research on microstructure and properties of boron/Q235 steel laser welded dissimilar joints under synchronous thermal field

The mechanical mismatch effect frequently occurs in the dissimilar materials welded joints, thus leading to plastic gradient at the interface between the weld and heat-affected zone(HAZ). In this work, the boron steel and Q235 steel were selected for laser tailor welding,which obtained boron/Q235 steel tailor-welded blanks(TWBs). The method of welding with synchronous thermal field(WSTF) was utilized to eliminate the mismatch effects in TWBs. The WSTF was employed to adjust cooling rates of welded joints, thereby intervening in the solidification behaviors and phase transition of the molten pool. Boron/Q235 steel was welded by laser under conventional and WSTF(300-600 ℃) conditions, respectively. The results show that the microstructure of weld and HAZ(boron) was adequately transitioned to ferrites and pearlites instead of abundant martensite by WSTF. Meanwhile, the discrepancy of microhardness and yield strength between various regions of welded joints was greatly reduced, and the overall plasticity of welded joints was enhanced by WSTF. It is indicated that WSTF can effectively contribute to reducing plastic gradient and achieving mechanical congruity in welded joints by restraining the generation of hardbrittle phase, which could significantly improve the formability of TWBs in subsequent hot stamping.

西洋参双排播种机设计与试验

针对西洋参人工播种劳动强度大及效率低、机械化播种技术及装备匮乏等问题,结合山东省弧面垄的种植农艺和西洋参窄密种植模式,设计西洋参双排播种机。通过西洋参的种子特征,设计种勺孔型尺寸;借助西洋参窄密种植模式,确定顶推式开穴种植方案;利用多连杆机构,控制种勺倾角及开穴器的运动,完成取种、开穴及落种工序的联动。该机主要由取种机构、开穴器、推种机构等组成,可一次完成取种、投种、播种作业,实现西洋参种子双排播种,提高西洋参的播种工作效率及质量。通过田间试验表明:西洋参播种机的播种合格率为92.76%、漏播率为4.58%、重播率为2.66%,符合西洋生播种要求及各技术指标要求。

曲线落料管冬季制作焊接工艺分析

转运站曲线落料管在物料转运时常常出现流通性不稳定、气密性差等,严重影响生产和操作人员的身心健康。为解决这些问题提出了新的曲线落料管制作工艺,即采用焊接代替法兰连接。以新疆某电厂对曲线落料管的冬季制作为例,介绍了落料管的焊接方法,其中特别阐述了冬季焊接工艺的特殊要求,以及焊前、焊后的处理方法。为保证焊接质量,对焊缝进行了探伤分析,对焊接试样进行了金相组织观察和力学性能测试。结果表明,焊接质量良好,拉伸性能接近母材的性能,弯曲性能合格。

基于改进YOLOv5s的铸坯表面缺陷检测系统

针对目前连铸坯表面缺陷检测方法存在检测准确率和效率低的问题,提出了一种基于改进YOLOv5s的连铸坯表面缺陷检测系统。首先,基于CycleGAN的域迁移能力和冷轧样本集实现铸坯复杂背景的简单化。其次,利用Ghost网络和GhostBottleneck重新构建YOLOv5s的特征提取骨架以达到轻量化网络结构提高检测速度的目的。最后,在YOLOv5s颈部模块中嵌入SE注意力机制以提升缺陷关键信息捕捉能力,从而提高检测准确率。实验结果表明,改进YOLOv5s在铸坯表面图像数据集上mAP指标达到93.6%,相较于原始的YOLOv5s,mAP指标提升了2.9%,计算量降低了2.5 FLOPs。能够满足铸坯表面缺陷检测系统的实时要求及准确率指标,并且降低了部署所需的计算资源。

Ti微合金化对235 MPa级碳素结构钢铸坯质量、性能的影响

针对常规中碳与低锰成分系设计的碳素结构钢连铸坯常出现角裂的质量缺陷,严重影响产品热装率,在原有设备工况的条件下,开展成分优化设计,利用微合金化元素Ti置换部分C元素,通过细晶强化和析出强化替代固溶强化,保证产品的机械性能。同时,利用Ti微合金化的高温液析TiN第二相粒子固定钢液中游离的N原子,提高铸坯高温塑性,改善铸坯角裂。经批量化生产应用评价,采用新成分设计的碳素结构钢Q235B角裂率得到了有效控制。

Al-5Ti-1B加入速度对8079合金铸轧铝板坯组织及力学性能的影响

目的优化晶粒细化剂Al-5Ti-1B的加入速度,以改善8079铝合金铸轧板坯质量。方法用电解铝液配料直接铸轧生产8079铝合金铸轧板坯,采用光学显微镜(OM)、扫描电子显微镜(SEM)和电子万能力学实验机等手段,研究了在晶粒细化剂Al-5Ti-1B加入速度(175、185、195、205 mm/min)不同时铝合金铸轧板坯显微组织和力学性能的变化规律,并对其影响机理进行了探讨。结果随着晶粒细化剂Al-5Ti-1B加入速度的增大,铸轧板坯晶粒尺寸先急剧减小后趋于平缓,其抗拉强度和断后伸长率先增大后减小。当加入速度为175 mm/min时,铸轧板坯晶粒尺寸约为110μm,其抗拉强度和断后伸长率分别为113.0 MPa和22%;当加入速度为185~195 mm/min时,铸轧板坯晶粒细小、分布均匀,尺寸为57~59μm,其抗拉强度不低于134.3MPa,断后伸长率不低于36.0%;当加入速度为205 mm/min时,铸轧板坯晶粒尺寸变化不大,尺寸约为56μm,但在基体组织中开始出现偏析聚集现象,力学性能急剧下降,抗拉强度仅为89.7 MPa,断后伸长率仅为16.7%。能谱检测结果表明,铸轧板坯夹杂缺陷主要由Ti、Al、O、Fe和Si等元素组成,夹杂缺陷的存在破坏了基体组织的连续性。结论当晶粒细化剂Al-5Ti-1B的加入速度为185~195 mm/min时,8079铝合金铸轧板坯具有更优的显微组织和力学性能。

双零铝箔坯料一次退火技术研究

通过对电解铝液铸轧法制备铝箔坯料的成分调配、精炼净化、晶粒细化、新型均匀化退火等技术,对双零铝箔坯料一次退火技术进行研究。对2.0 mm、1.75 mm、1.5 mm厚度退火坯料晶粒度和力学性能对比分析,确定“一次退火”最佳厚度为1.75 mm,同时抗拉强度达到160 MPa,延伸率达到4.3%,加工性能良好。

Damage mechanism and evaluation model of compressor impeller remanufacturing blanks:A review

The theoretical and technological achievements in the damage mechanism and evaluation model obtained through the national basic research program“Key Fundamental Scientific Problems on Mechanical Equipment Remanufacturing”are reviewed in this work.Large centrifugal compressor impeller blanks were used as the study object.The materials of the blanks were FV520B and KMN.The mechanism and evaluation model of ultra-high cycle fatigue,erosion wear,and corrosion damage were studied via theoretical calculation,finite element simulation,and experimentation.For ultra-high cycle fatigue damage,the characteristics of ultra-high cycle fatigue of the impeller material were clarified,and prediction models of ultra-high cycle fatigue strength were established.A residual life evaluation technique based on the“b-HV-N”(where b was the nonlinear parameter,HV was the Vickers hardness,and N was the fatigue life)double criterion method was proposed.For erosion wear,the flow field of gas-solid two-phase flow inside the impeller was simulated,and the erosion wear law was clarified.Two models for erosion rate and erosion depth calculation were established.For corrosion damage,the electrochemical and stress corrosion behaviors of the impeller material and welded joints in H2S/CO2 environment were investigated.KISCC(critical stress intensity factor)and da/dt(crack growth rate,where a is the total crack length and t is time)varied with H2S concentration and temperature,and their variation laws were revealed.Through this research,the key scientific problems of the damage behavior and mechanism of remanufacturing objects in the multi-strength field and cross-scale were solved.The findings provide theoretical and evaluation model support for the analysis and evaluation of large centrifugal compressor impellers before remanufacturing.

城市留白的管控机制研究

在目前人类对城市的认知及常态化的规划管理中,设置用地空间上的留白是应对社会发展过程中的不确定性和未知事件的重要手段。当前在国家空间治理体系改革的背景下,已有的空间资源有限,需要人们为未来可能发生的情况做出超前规划和预留一定留白空间。通过这种科学的超前规划布局空间,不仅可以为城市未来的发展提供弹性空间,还可以作为弹性缓冲来应对未来可能出现的突发事件。文章通过分析留白的理念溯源、现状背景,通过城市空间问题的梳理,以及目前面临的挑战阐述留白的必要性;从留白的特征、价值、落地阐述深化了对留白的认知;通过国内外留白的规划探索,梳理留白用地的管控机制;进而对城市的“留白”进行总结,分析目前的不足,为以后的研究奠定基础。

异型坯结晶器与铸坯热力耦合数值模拟

为研究异型坯连铸结晶器内铸坯凝固和变形过程,采用ABAQUS软件建立了异型坯连铸结晶器和铸坯的二维瞬态热力耦合有限元模型,编制ABAQUS用户自定义子程序GAPCON实现结晶器内壁和铸坯之间的传热模拟.计算模型中考虑了铸坯的凝固和热变形、气隙对传热的影响以及铸坯与结晶器之间的接触应力.分别对2种不同水缝设计结晶器进行了数值模拟,数值分析结果表明,小孔水缝设计的结晶器温度峰值较低、热面温度分布更均匀,因而比大孔水缝设计结晶器具有更长的使用寿命和更优的铸坯质量,这一结论与现场试验结果一致.

基于主成分分析与BP神经网络的激光拼焊板力学性能预测

为了预测并控制激光拼焊板的力学性能,本文通过对0.8～1.5mm的St12板及其镀锌板进行差厚、等厚拼焊,在此基础上建立了以焊接工艺参数为输入变量的基于主成分分析的BP神经网络拼焊板力学性能预测模型。通过实例验证表明,本文所建预测模型对拼焊板抗拉强度及伸长率的预测精度均达91%以上。充分表明该模型与试验结果吻合良好,验证了该预测模型的合理性及适用性。

基于变形区显微状态分析的精冲成形机理研究

通过实验和变形区流线变化、金相组织和显微硬度的变化,对精冲成形的过程、特点、精冲成形机理进行了研究。

基于双侧齿圈压边的厚板精密冲裁成形力学分析

针对普通冲裁方式获得的厚板冲裁件常存在尺寸精度低、断面质量差及翘曲严重等问题,采用双侧齿圈压边的方式对厚板精密冲裁成形进行模拟和力学分析,建立了厚板的精冲数学模型及有限元模型,研究了成形中应力应变问题及静水应力、材料流动的规律,并通过对6、8、10和12mm厚板进行有限元模拟,探讨了不同板厚对双侧齿圈压边精冲的影响,最后进行实验验证,分析结果表明双侧齿圈压边冲裁方式能够增加厚板剪切变形区的静水压力,充分发挥材料的塑性,提高厚板冲裁件断面质量。

8011铝箔坯料退火后AlFeSi相对气泡形成机理影响的研究

8011铝箔坯料退火后产生了贯通气泡和微鼓区,气泡内部出现了大量AlFeSi相富集。气泡是由于内部AlFeSi相的富集促进氢富集和氢析出,外部致密的氧化膜阻碍氢析出共同作用形成的。微鼓区的内部AlFeSi相较少,也形成了类似气泡的空腔。因此,AlFeSi相的富集不是气泡形成的必要条件。