利用纳米压入的反演分析法确定金属材料的塑性性能

建立了一种确定金属材料塑性性能的方法,即利用有限元数值模拟对纳米压入过程进行反演分析,确定金属材料的屈服极限和应变强化指数.首先在不考虑材料加工硬化的情况下,对纳米压入过程进行反演修正模拟,当模拟曲线同正向分析曲线相吻合时,确定金属材料的代表性应力;其次在考虑不同应变强化指数的情况下,采用相同的方法确定金属材料的代表性应变;最后结合量纲分析确定金属材料的应变强化指数,继而确定金属材料的屈服极限.经过实验验证,该方法具有较高的精度.     

射孔枪毛刺和胀枪及其应力强度三维仿真

为了获得射孔枪动态应力分布规律,准确分析胀枪程度和毛刺外翻高度,应用LS-DYNA软件,以7″×12. 65mm TP140套管和5″×11. 00 mm 32CrMo4射孔枪组合为例,建立了射孔弹-射孔枪(含盲孔)-套管三维有限元模型,采用网格不固定、不依附于质点、可相对坐标系作任意运动的ALE法,结合算子分离算法,实现爆轰过程、药型罩固流转化、射流高速侵彻射孔枪的大变形和流固耦合仿真。结果表明,射孔枪产生4. 3 mm外凸毛刺,套管外壁产生1. 8 mm外凸毛刺,枪套间累计毛刺高度为5. 2 mm,如果间隙接近或小于5. 2 mm,易发生卡枪。射孔枪平均孔径为Φ18. 7 mm,套管平均孔径为Φ7. 7 mm,说明穿透射孔枪盲孔过程消耗了大量能量,盲孔壁厚设计应引起重视。在射孔枪各孔相连的宽为125 mm的宽带内,其最小应力也达到了774 MPa,均超过材料屈服强度,在高爆轰压力作用下,将产生向外鼓胀,即会发生所谓的"胀枪"。     

射孔枪射孔过程数值模拟及参数控制

采用有限元方法模拟了射孔枪射孔过程,研究了各个参数对射孔过程中毛刺生成及开孔边缘形状的影响。研究表明,射流速度、管壁盲孔半径以及盲孔深度的增加,均有利于降低毛刺生成的高度,并使射流开孔的边缘趋于圆滑,对提高射孔枪的性能有利。材料延展性的变化对毛刺生成和开孔边缘形状也有非常明显的影响。在内部膛压达到100MPa之前,在管壁上仅开一个孔和开完孔之后的射孔枪膛压—最大应力曲线非常接近;但当内部膛压达到100MPa之后,仅开一个射孔的管壁承载能力较所有开孔之后的管壁,其承载能力有一定程度的增加。     

车用铝合金AA5182温热成形研究

基于M-K模型分别结合Hill48、Barlat89和YLD2000屈服准则,预测了AA5182铝合金在温热条件下的成形极限。在不同温度下进行AA5182铝合金的温热成形极限实验,获得了材料在不同温度下的成形极限实验数据。比较分析实验结果与预测结果,表明Barlat89屈服准则比其他两个屈服准则更适用于预测AA5182铝合金在温热条件下的成形极限。同时,分析了温度和应变速率敏感指数的变化对成形极限预测结果的影响。结果表明,材料成形极限会随着温度的升高或者应变速率敏感指数的增大而增加。应变速率敏感指数的变化对预测得到材料成形极限的形状也会产生影响。     

镀锡钢薄壁罐胀形壁厚变化分析

为了提高薄壁罐气压胀形的成形质量,减少壁厚严重减薄而产生皱折、破裂等成形缺陷,使用钣金成形专用软件模拟薄壁罐气压胀形过程。分析了成形3个阶段金属流动情况、壁厚变化、应力和应变分布规律以及罐坯成形极限,中间阶段对胀形结果影响明显,壁厚减薄、应力和应变的最大值发生在胀形的最大变形区。试验验证与模拟分析吻合。     

钛合金焊接应力应变的数值模拟

采用数值模拟方法研究在移动热源情况下钛合金焊接应力应变发展过程。研究结果表明:钛合金焊接应力应变发展模式与铝合金和不锈钢等材料不同。无论是在点状加热还是移动热源情况下,在残余状态,钛合金焊缝均处于卸载状态,并未达到拉伸屈服。熔池内的金属是在两侧有压缩塑性应变的框架下熔化的;冷却过程中,焊缝也是在已有的压缩塑性应变的框架下的拉伸,虽然焊缝承受扣伸塑性应变,但不足以完全抵消已产生的压缩塑性应变,残余状态仍为负的不协调应变。     

工艺参数对简单断面型钢辊弯成型过程的影响

采用B3样条有限条法研究成型工艺参数（如弯曲角增量、带材厚度、材料屈服极限、翼缘长度、腹板宽度和机架间距等）对槽钢辊弯成型过程带材边部纵向薄膜应变峰值的影响。带材边部纵向薄膜应变峰值随着弯曲角增量、带材厚度、材料屈服极限、翼缘长度和腹板宽度增加而增加，随着机架间距的增大而减小。研究结果与辊弯成型过程中观察到的现象完全一致。     

一种建立板料成形极限应力图的新方法

基于塑性理论建立了比例加载条件下双向拉伸应力应变关系,结合Swift分散性失稳准则,提出了一种建立板料成形极限应力图的方法。分别应用Hill 48和Hosford屈服准则以及单向拉伸性能参数,建立了铝合金板(r<1)和薄钢板(r>1)两种材料的成形极限应力图(FLSD),分析表明,不同的屈服准则的选取对于成形极限应力曲线有不同的影响,对于不同类型的材料屈服准则的影响程度也不同。与由通常的成形极限图(FLD)转换所得到的成形极限应力图(FLSD)进行了对比分析,结果表明,所提出的方法计算过程更为简便,并能较为准确地建立成形极限应力图,可以作为复杂加载路径下的成形极限破裂判据。     

屈服强度对前罩外板拉延成形及回弹影响的数值模拟

基于Auto Form软件模拟了前罩外板的拉延成形过程,研究了屈服强度对前罩外板成形过程及减薄率分布、塑性变形量及主、次应变的影响,系统地分析了其对前罩外板回弹性能的影响。结果表明,随着屈服强度的增加,前罩外板的拉延成形性逐渐降低,最大减薄率、塑性变形量及主、次应变分布逐渐增大;回弹不仅与屈服强度变化导致的不同变形量有关,还与其应变状态有关。     

汽车骨架矩形管弯曲成形极限值的研究

<正>达到极限最大弯曲角度的讨论目的为研究金属薄壁矩形管件绕弯成形时质量缺陷的截面畸变形式,对管件的宽度扩展率、中面高度缩减率、壁厚减薄率三者进行定义都参考文献。研究材料为JAC590Y,是汽车车身结构中常用的一种高强钢材料,屈服强度为395MPa,抗拉强度为615MPa,     

Flow stress evaluation of zinc copper and carbon steel tubes by hydraulic bulge tests considering their anisotropy

The object of this paper is to evaluate the stress–strain characteristics of annealed C26800 zinc copper tubes and AISI 1215 carbon steel tubes considering their anisotropic effects by hydraulic bulge tests and tensile tests. In this analytical model, Hill's orthogonal anisotropic theory was adopted for deriving the effective stresses and effective strains under a biaxial stress state. The tube thickness at the pole, bulge height and the internal forming pressure were measured simultaneously during the bulge tests. The effective stress–effective strain relations could be determined by those measured values and this analytical model. The flow stress curves of C26800 copper and AISI 1215 carbon steel tubes obtained by this approach were compared with those obtained by the tensile test with consideration of material's anisotropy. The finite element method was also adopted to conduct the simulations of hydraulic bulge forming with the flow stress curves obtained by the bulge tests and tensile tests. The analytical forming pressures versus bulge heights were compared with the experimental results to validate the flow stress modeling proposed in this paper.     

Deformation behavior of TC 1 titanium alloy sheet under double-sided pressure

In order to investigate the influence of normal stress through thickness on the formability of sheet metal, the viscous pressure bulge（VPB） tests of an annealed TC1 titanium alloy sheet were carried out under two different conditions： double-sided pressure bulging and conventional single-sided pressure bulging. The automated strain analysis, measurement environment （ASAME） and scanning electron microscope（SEM） were used to study the strain distributions and the fracture morphology of bulged specimens. It is found that thickness strain is increased for double-sided pressure bulging specimens, and the limiting dome height（LDH） of double-sided pressure bulging specimens is increased by 31.8% compared with conventional single-sided pressure bulging specimens. The dimples in fracture surface for double-sided pressure bulging specimens are larger and deeper than those for conventional single-sided pressure bulging specimens. The results indicate that normal stress through thickness is helpful in improving the formability of titanium alloy sheet metal.     

On Practical Forming Limits in Superplastic Forming of Aluminum Sheet

In this paper, the superplastic forming (SPF) potential of two fine-grained 5083 aluminum alloys were studied under various stress states with the use of both high temperature tensile testing and pneumatic bulge testing. Experiments with the pneumatic bulge test were performed at temperatures ranging from 475 to 525 °C under three different strain paths ranging from equi-biaxial to approaching plane strain. The effects of temperature on total elongation, m-value, final thickness distribution, dome height, and cavitation were investigated for the case of uniaxial and equi-biaxial stretching. Increased temperature in bulge forming was found to improve the thickness distribution in the formed parts, but did not have a significant effect on dome height. The shape of the forming limit diagram (FLD) was found to be significantly different than that of FLDs commonly used in room temperature stamping. Results indicate that determination of forming limits in SPF cannot be represented with a simple FLD and additional metrics such as external thinning and internal cavitation need to be considered to determine a material’s SPF potential. This article was presented at Materials Science & Technology 2006, Innovations in Metal Forming symposium held in Cincinnati, OH, October 15-19, 2006.     

Determination of the flow stress of magnesium AZ31-O sheet at elevated temperatures using the hydraulic bulge test

Elevated temperature hydraulic bulge tests for Mg AZ31-O alloy sheets were conducted using a submerged tool, designed to minimize the temperature variation in the sheet. Experiments were conducted between room temperature and 225 °C, at various approximate true strain rates. Bulge profiles at different bulge heights were measured using a CMM and the best radius values were calculated through least-square fit using several measured points. Residual plots were made to demonstrate the amount of deviation from a sphere with increasing bulge height. Measured and calculated bulge radius and thickness values were compared with the available analytical models. Amount of error that occurs in flow stress calculation by deploying the well-known membrane theory was investigated.     

Analysis of tube bulge forming in an open die considering anisotropic effects of the tubular material

In this paper, a mathematical model considering the anisotropic effects of the tubular material was proposed to examine the plastic deformation behavior of a thin-walled tube during bulge forming processes in an open die. In the formulation of this mathematical model, the forming tube is considered as an ellipsoidal surface. Non-uniform thinning in the free-bulged region and sticking friction between the tube and die are also considered. In this analytical model, Hill's orthogonal anisotropic theory was adopted for deriving the effective stress and effective strain under a bi-axial stress state. The effects of the anisotropic values on the forming pressure and maximum bulge height were discussed. Experiments of bulge forming using annealed A6011 aluminum tubes were conducted. The analytical results of forming pressure were compared with the finite element simulations and the experimental data. The validity of this newly proposed model was verified.     

油田废旧射孔枪修复再制造技术

射孔完井是目前国内外使用最广泛的一种完井方法,目前射孔枪管通常为一次性使用,一旦经过射孔作业,多数做报废或降级处理,造成很大的浪费,因此对射孔枪进行再修复制造十分必要。通过对射孔枪管体的结构分析,开发设计了射孔枪体和补贴片的新结构,采用焊条电弧焊打底,φ(Ar)80%+φ(CO2)20%气体保护焊填充和盖面,模拟实际井下条件检测射孔枪管耐压性。结果表明,优化的废旧射孔枪管体结构和补贴片的设计使接头焊接质量达到设计要求指标。     

钛的熔模铸造的选择强化技术

介绍了金属材料在高速高压状态下的一些物理特性，如在强冲击载荷下的本构关系、控制方程，加载和卸载的波动特征，动态屈服效应及动态破坏特征等以及轻气炮试验装置和测量技术的应用。文章对金属材料的动态形变方式也进行了讨论。     

Combined experimental and numerical analysis of bulge test at high strain rates using split Hopkinson pressure bar apparatus

High strain rate bulge test technique which is introduced in this paper adopts a rubber-pad as pressure carrying medium to bulge a sheet metal at high velocity using split Hopkinson pressure bar (SHPB) system. The experimental set-up is based on conventional hydraulic bulge test which is modified to mount on SHPB. The thickness thinning of the sheet metal during the test will be considered as a measure of true strain of the bulged sheet. The theoretical approach is developed in this study to attain pressure–strain curves of sheet metals during high strain rate bulge forming process. This approach is followed by a finite element simulation of the process in ABAQUS/Explicit software. To verify the developed method, analytical and finite element methods are compared with experiments.     

高强度钢激光拼焊板成形性能的模拟试验研究

传统的杯突试验不适合具有不同厚度组合的激光拼焊板的性能参数测量。通过对传统的杯突试验模具进行改进,准确测出高强度钢激光拼焊板和母材的IE值,检验了它们适应拉胀成形的极限能力,分析胀形区域厚度、应变等分布情况,观察裂纹的起始位置和形状,从而评定激光焊接的质量。     

Simulation of High-Temperature AA5083 Bulge Forming with a Hardening/Softening Material Model

High-temperature bulge forming of AA5083 aluminum sheet was simulated with the commercial finite element (FE) code ABAQUS™. A material model that is strain rate sensitive and accounts for strain hardening and softening was used. Results were compared with data from AA5083 bulge forming experiments at 450 °C where the gas pressure was a prescribed constant value. The results show that the material model is capable of predicting the deformation and thinning behavior at different constant pressure levels. In ancillary simulations, time-varying pressure profiles were computed (rather than prescribed) with an internal ABAQUS™ routine that attempts to maintain the strain rate at the bulge dome pole within a specified range. The time-varying profiles, for which no experimental AA5083 bulge forming data exist, can be programmed into existing bulge testing instrumentation to validate the associated predictions of bulge dome height and thinning. The present effort represents a necessary step toward predicting gas pressure profiles by coupling the pressure profile with a desired sheet deformation rate.