Study on the deformation theory of a parabolic part based on solid granules medium forming

Solid granules medium forming (SGMF), a new flexible die forming technology, uses solid granules instead of a rigid male or female die (or elastomer, liquid) for sheet metal drawing. The good fluidity and compressive capacity of a solid granules medium can improve the forming limit of complex shell parts. The sheet metal drawing process of SGMF is a compound process of drawing and bulging, which is very different from the conventional drawing process. A parabolic part is used as the research object for a study of the forming process. Two concepts, drawing weight and bulging weight, are originally proposed in the sheet metal drawing of SGMF (replacing the rigid male die), and the corresponding expressions are obtained. The computational formulas of geometrical conditions and strain in the sheet metal drawing of SGMF are established, and the radius of the strain dividing circle is obtained by calculation. The established theoretical model is applied to the research object, an aircraft part, to analyze the forming process. The results show that the proposed theory can be applied to analyze the strain in different deformation regions of SGMF. This original theory provides a new theoretical analysis for studying the sheet metal drawing of SGMF.     

Investigation on the factors influencing the thickness distribution of superplastic-formed components

In the superplastic sheet forming process, the uniformity of the sheet's final thickness distribution is vital for ensuring the good mechanical quality of the formed components. The influences of the component shape and the contact friction on the final thickness distribution were investigated in this work by using finite element method on a series of axisymmetric models. It was concluded that shape optimization and friction elimination are required to get uniform thickness distribution, and eventually to improve the mechanical quality of the formed components. The constitutive equation of the Ti-6Al-4V superplastic material was also determined on the basis of experimental data.     

汽车桥壳滑动式液压胀形工艺分析

基于ABAQUS软件平台对桥壳滑动式液压胀形工艺进行数值模拟研究,确定胀形压力与管坯轴向压缩量的关系,避免管坯在胀形过程中出现胀裂或者失稳、褶皱等缺陷,得到壁厚合理、成形效果良好的试件。研究结果表明：预成形中采用较低的初始内压,待模具完全合模后增加内压至管坯完全贴膜,可以提高壁厚分布的均匀性。采用该种加载路径可以获得理想的胀形结果,对实际生产具有重要的指导意义。     

预应力混凝土板桩-冠梁协同支护作用机理

以湖岸支护工程为例,基于有限元模拟研究了支护结构内力及变形、地表沉降、基坑隆起以及土压力分布情况,探讨了桩顶锚固形式和板桩嵌固深度,得到板桩-冠梁协同支护体系工作机理。 研究表明:板桩-冠梁协同支护体系的桩土协同作用机制与有锚板桩相似,桩体变形呈现中部鼓出状,主动土压力呈R 形分布;桩顶冠梁锚固以及桩底嵌固作用是影响板桩支护性能的重要因素,板桩最佳嵌固深度比为0.69~0.79。 研究成果可为相关板桩支护的设计和工程应用提供参考借鉴。     

An analytical model for predicting sheet springback after V-bending

INTRODUCTION As an important manufacturing method, bending has been widely used in modern industries to produce stamping parts such as frames, channels, braces, brackets and other structural parts. The understanding and development of bending mechanics are aimed at achieving two kinds of information which are very important for industrial production. One is to predict springback for dies design and compensation in order to obtain high dimension accuracy of bending parts. The other is to …     

薄片漏斗试样的应变等效换算与Zr-4合金疲劳寿命估算

完成了Zr-4合金薄片漏斗小试样的横向等幅应变疲劳试验;提出了薄片漏斗试样细腰部与薄片等直试样疲劳损伤等效的局部损伤等效假设;基于弹塑性有限元分析,建立了Zr-4合金薄片漏斗小试样横向测试应变向轴向应变转换的应变等效转换模型,该模型考虑了几何效应和泊松效应;结合实验结果,提出了用于Zr-4合金应变疲劳寿命估算的Manson-Coffin(M-C)模型。研究表明:薄片漏斗小试样及其应变等效转换模型可以有效应用于薄片金属材料的低周疲劳试验和寿命估算;国标推荐的应变换算公式应用于薄片漏斗小试样的Zr-4合金疲劳寿命估算会带来很大安全余量。     

带凸缘圆筒件壁厚与板料厚度的数值模拟分析

在传统理论计算的基础上,借助abaqus软件进行数值模拟分析,主要讨论在不同板料厚度下成形带凸缘圆筒件的应力分布和变化情况,以及壁厚的变化情况,找出其应力和壁厚随板料厚度变化的规律。验证理论计算的科学性和合理性,同时也反应数值模拟的参数比理论计算更精细化,为该类零件的成形工艺提供借鉴和参考。     

On the role of the constitutive model and basal texture on the mechanical behaviour of magnesium alloy AZ31B sheet

The recently developed elastic-viscoplastic self-consistent model with various self-consistent schemes was applied to study the effect of basal texture on the mechanical behavior of magnesium alloy AZ31B sheet. The influence of the basal texture was investigated using various initial textures generated by artificially tilting the measured texture of the reference AZ31B sheet around in a transverse direction. The material parameters for the various models were fitted to experimental uniaxial tension and compression along the rolling direction and were then used to study the effects of the basal texture on the yield stress, R value, ultimate stress and uniform strain under uniaxial tension. The effect of the basal texture on sheet metal forming was further assessed by calculating the limit strain under in-plane plane strain tension. An assessment of the predictive capability of polycrystal plasticity models was made based on comparisons of predictions and experimental observations. Among the available self-consistent approaches, the Affine self-consistent scheme resulted in the best overall performance.     

Visualization of structured packing with laser induced fluorescence technique: Two-dimensional measurement of liquid concentration distribution

A method of using laser induced fluorescence(LIF)technique was applied to two-dimensional measurement of the liquid concentration distribution in the 250Y structured packing sheet. The experimental structured packing sheet was made of perspex so that the laser could pass through it. The visualization of the distribution of the liquid concentration in the structured packing sheet was realized. The calibration of the thickness and liquid concentration was carried out firstly and the regression formula I=kcd was acquired, in which concentration c and the liquid film thickness d were both considered. Then the liquid feed of uniform tracer(rhodamine)concentration entered the perspex structured packing from the top under different spraying densities. The corresponding thickness of liquid film on the packing was calculated. Finally, tracer(rhodamine)with a high concentration was injected only at one fixed point of the structured packing under different spraying densities of the liquid. With the known liquid film thickness, the concentration distribution of the tracer can be calculated inside the structured packing sheet.     

带凸缘圆筒件成形数值模拟

拉深成形中凸、凹模圆角半径一直都是成形的关键,严重影响成形的质量。以板料成形理论和abaqus软件为基础,探讨带凸缘圆筒件拉深成形过程中凸、凹模圆角半径的影响。结果表明：拉深成形过程中,板料最大应力主要集中在凸、凹模圆角半径处;在一定范围内拉深时采用较大的圆角半径,整形以后侧壁的厚度也较大;但凸、凹模圆角半径处的壁厚变化则刚好相反,随着首次拉深圆角半径的增大,壁厚逐渐变薄,甚至出现破裂和折叠;运用有限元数值模拟能很好地预测其成形缺陷,并可对计算参数进行优化。     

炉底辊和氧气管道鼓包剖析

对Cr25Ni20Si2炉底辊和20#钢氧气管道两例鼓包缺陷实例进行了剖析。结果表明:炉底辊鼓包是由于严重的疏松缺陷及沿晶腐蚀裂纹引起的,氧气管道在试压过程中产生鼓包则与内部存在较严重的粗大条状夹渣有关。     

Finite element modeling of superplastic co-doped yttria-stabilized tetragonal-zirconia polycrystals

Yttria-stabilized tetragonal-zirconia polycrystals (Y-TZP) have been shown to have superplastic properties at high temperatures, opening a way for the manufacture of complex pieces for industrial applications by a variety of techniques. However, before that is possible, it is important to analyze the deformation and fracture mechanisms at a macroscopic level based on continuum theory. In this paper, an elastic-plastic material model with a theoretical large deformation is constructed to simulate the true stress-true strain relationships of superplastic ceramics. The simplified constitutive law used for the numerical simulations is based on piecewise linear connections at the turning points of different deformation stages on the experimental stress-strain curves. The finite element model (FEM) is applied to selected tensile tests on 3-mol%-Y-TZP (3Y-TZP) co-doped with germanium oxide and other oxides (titanium, magnesium, and calcium) to verify its applicability. The results show that the stress-strain characteristics and the final deformed shapes in the finite element analysis (FEA) agree well with the tensile test experiments. It can be seen that the FEM presented can simulate the mechanical behavior of superplastic co-doped 3Y-TZP ceramics and that it offers a selective numerical simulation method for advanced development of superplastic ceramics.     

Strain Monitoring and Stress Analysis of a Post-Prestressed Tunnel Liner

The strain monitoring and stress analysis of a new type of post-prestressed tunnel liner were carried out. The instrumentation block of the tunnel liner, with the dimensions of 12.06 m in length, 6 500 mm in diameter, and 650 mm in thickness, was post-prestressed with the unbonded tendons, each of which consists of 8 pieces of double-looped strands and the axial spacing of the tendons is 500 mm. Concrete strain meters, rebar meters, load cell and zero-stress meters were installed for the strain monitoring. The tensioning loads were applied incrementally in three cycles (50%, 77% and 100%) at the concrete age of 28 d and the tensioning work lasted for 187.1 h. Strain readings were taken before and after each cycle during tensioning period and at the specified time interval after tensioning period. It is found that concrete creep developed over tensioning period is 30% of total strain and 41.5% of elastic strain respectively. Prestress force in the unbonded tendon and concrete stress in the liner were evaluated according to the observed strain variations. Both of them are time-dependent, and about 5.3%, 8.3% and 9.0% of the prestress losses are observed at the age of 1 d, 30 d and 60 d respectively after stressing. The distribution of prestress in the liner is relatively uniform and meets the design requirement.     

车身用6061-T6铝合金薄板电阻点焊工艺参数研究

采用MULTISPOT MI-100电阻焊机,对车身用6061-T6铝合金薄板实施电阻点焊,研究并得到电阻点焊最佳工艺参数。然后,运用正交试验方案和极差分析方法对电阻焊工艺参数进行试验和进一步优化设计。在对2mm厚度的6061-T6铝合金薄板进行搭接电阻点焊后,分析焊接外观并完成拉伸测试,测试结果表明:当焊接电流60KA、焊接压力0.63MPa、板材厚度2.00mm时,试样所获得的点焊接头无明显缺陷,成型较好,具有良好的焊接质量和外观,其抗拉剪力值最大为5.583KN。     

板料成形模拟及其在汽车覆盖件冲压过程中的应用

基于板料成形模拟的必要性和汽车覆盖件成形的复杂性 ,提出有限元分析是模拟复杂三维板料成形问题的有力工具 .介绍了动态显式有限元法的原理和特点 ,讨论了国际现有的各种商用软件 ,论述了汽车覆盖件模拟的国内外应用现状 .以某新型汽车前门外板为例 ,运用显示有限元分析软件Dynaform对前门外板冲压过程进行了计算机模拟分析 ,预测冲压过程中可能出现的各种工艺缺陷 ,例如坯料的破裂 ,并以模拟结果为依据提出改进方法 .     

12%Cr转子钢高温应变疲劳及微观组织研究

在对12%Cr转子钢在室温、566℃和600℃时进行应力-应变试验时,当滞后环曲线基本稳定后,分别选择不同循环周次卸载下未断的试样,然后重新安装一个试样在同一应力-应变曲线下进行再次试验,直到有试样失效为止.采用应变控制,应变幅分别为0.7%和1.4%,应变速率为0.004/s.用透射电镜对不同循环周次的试样进行观察,在600℃以及室温下都可观察到循环硬化现象,透射电镜研究表明,在室温和高温条件下都有位错胞出现,随着温度的增加动态回复的影响变得非常明显,高温下位错的密度明显降低,其中的位错胞经过600℃1 h回火仍然清晰可见.     

经高效熔体处理的易拉罐用铝材的高温流变应力行为

采用动态热模拟试验技术探讨了经高效熔体综合处理和均匀化退火后的易拉罐用铝材在高温压缩变形过程中，变形温度和应变速率对其稳态流变应力行为的影响规律。结果表明，该材料在高温变形时的稳态流变应力与应变速率、变形温度均满足Arrhenius方程，其中更满足双曲正弦函数关系；该材料的热变形是受热激活控制的塑性变形过程。     

石墨波齿复合垫片的性能和应用分析

介绍了由金属和石墨构成的波齿复合垫片的结构、性能、应用和试验研究方法,指出了需要进一步研究和解决的问题。对波齿复合垫片采用正交试验方法,设计了三因素三水平试验方案,并对垫片及其骨架的性能分别采用有限元模拟计算和试验进行分析。研究显示该垫片具有良好的压缩回弹性能和密封性能,适用于压力波动较大的场合。     

碳纤维布约束高强混凝土的研究

基于 8个碳纤维布约束高强混凝土棱柱体试件的试验 ,研究了碳纤维布对提高高强混凝土抗压强度和改善其变形性能的作用 .试验发现 ,包裹碳纤维布可以提高试件的抗压强度 ,并有效地改善混凝土的变形性能 ,其效果随碳纤维用量的增加而更加显著 .在试验基础上 ,根据理论分析和对试验结果的整理 ,归纳出碳纤维布约束高强混凝土的应力 应变全曲线方程 .最后 ,利用提出的全曲线方程编制计算机程序 ,分析了包裹碳纤维布对提高高强混凝土压弯构件的强度和延性的作用     

76例片状增生性瘢痕切除并刃厚皮片移植或瘢痕上皮回植术对比研究

目的:探讨片状增生性瘢痕外科手术治疗的方法及疗效。方法:对76例片状增生性瘢痕采用随机分组进行增生性瘢痕切除并刃厚皮片移植术;增生性瘢痕切除、瘢痕上皮回植术两种手术方法比较性研究。结果:两种方法在疗效上无显著差异(P>0.05),但手术野数目和住院时间存在显著差异(P<0.05)。结论:片状增生性瘢痕可以采用瘢痕切除、刃厚皮片移植或瘢痕上皮回植术治疗,瘢痕上皮回植术优于刃厚皮片移植术。