Lode应力参数与应力参量之间的内在联系及屈服准则的推广

从塑性力学应力Ｌｏｄｅ参数着手，深入研究了应力Ｌｏｄｅ参数与各应力参量之间的内在联系，并对塑性理论中屈服准则进行了合理推广。对塑性理论及其应用具有重要意义。     

主剪应力的应力莫尔圆解法

本文提出了主剪应力的应力莫尔圆解法，给出了主剪应力方向的判定方法，对于塑性力学及其在工程上应用具有价值和意义。     

关于对理想刚塑性材料本构方程的见解

本文对Ｌｅｖｙ－Ｍｉｓｅｓ增量理论的若干论述进行了综合分析，指出了其中的不足，提出理想刚塑性材料的应力—应变关系为应力偏张量各分量之比决定应变增量各分量之比，应变增量的大小由瞬时位移条件决定的新论述。最后用Ｌｏｄｅ实验说明了新论述的正确性。     

辊锻三维变形过程的数值模拟研究

利用商品化软件Deform3D建立了辊锻变形过程的刚粘塑性有限元系统模型 ,对圆 -椭圆 -圆型槽系中的辊锻变形过程进行了三维数值模拟 ,研究了辊锻三维变形过程中材料的流动速度场、应力应变场的特征及其动态演化过程 ,讨论了不同变形参数对应力应变的影响。     

LY12超塑性成形有限元分析

基于LY12铝合金超塑性材料属性建立了弹-粘塑性本构模型。利用该本构模型并结合最大等效应变速率控制压力变化算法对LY12铝合金板超塑性圆杯成形进行数值模拟，得到圆杯变形过程中的应力应变分布、板料厚度变化及所需成形时间。根据模拟获得的优化压力时间曲线对圆杯进行超塑性气压胀形加载实验，制件厚度分布与模拟结果非常接近。     

金属板料塑性应变比的影响因素分析

进行了室温下的单向拉伸试验;采用数字图像相关测量方法 (DIC方法),测量了AA5754和Q235B的塑性应变比随着试样塑性变形的变化规律。分析了应变水平和材料厚度对两种材料塑性应变比、平均塑性应变比和凸耳参数的影响。结果表明两种金属板料的塑性应变比均不是恒定的,随着塑性变形量的变化而变化。在材料刚进入塑性变形状态时,塑性应变比急速上升至最大值,在随后阶段则呈现下降;对于不同厚度的试样,其塑性应变比随应变水平的变化趋势基本一致;材料的凸耳参数受应变水平的影响比较小。     

冲裁间隙变化对冲裁件断面质量影响的力学分析

分析了冲裁过程中断面光亮带、断裂带、圆角和毛刺形成阶段,运用塑性增量理论、应力莫尔圆方法和粘着磨损法则,来分析影响光亮带和断裂带、圆角和毛刺形成的力学因素,得出确定模具合理间隙值是获得高质量冲裁件的关键因素。     

Cr-Mo-V钢焊接接头塑性损伤的非线性超声评价

采用非线性超声纵波技术对汽轮机转子钢30Cr2Ni4MoV焊接接头不同程度塑性损伤试样进行了超声非线性信号的检测.结果表明,超声非线性参数随着焊接接头试样塑性应变或损伤的加剧而显著上升;对于同一加载情况下的试样,与母材和热影响区相比,焊缝中心的非线性参数变化最大.同时,利用透射电子显微镜对不同塑性应变焊缝中心微观结构进行观察,发现位错密度的增加是导致非线性参数随着塑性应变增大的主要原因.     

A508-3核电大锻件用钢连续冷却贝氏体的相变塑性

用Gleeble-3500热模拟试验机研究了A508-3钢在单轴压应力下的连续贝氏体相变诱发的相变塑性.借助于从膨胀曲线分离相变塑性应变的数据处理方法,获得了压应力对贝氏体相变塑性的影响规律.结果表明:基于Greenwood-Johnson模型的贝氏体相变塑性参数K随着外加压应力的增大而增大,并且相变塑性应变占总应变的比重显著增加.相变塑性应变随贝氏体相变进行逐渐增大,增速先快后慢.     

C-Mn结构钢拉伸变形过程中空穴形核的研究——结构钢韧性断裂机理研究之一

本文比较了各种可能揭示钢中空穴的方法,采用一系列具有增量塑性应变的光滑拉伸试棒调查C-Mn结构钢空穴的形核。并根据本研究提出的分析程序,确定了空穴的临界形核应变以及在形核应变时的相对空穴体积。     

Evaluation of Plastic Deformation During Metal Forming by Using Lode Parameter

In the present research, the relationship between the strain increment and Lode parameter was obtained by using Lode parameter and Levy-Mises equation. The quantitative relation between different strain increments was presented and the relationship between plastic deformation types and Lode parameter was demonstrated. The relations between plastic deformation types and stress states were revealed and they were applied into typical metal forming process. The strain types in the workpiece were analyzed based on the numerical visualization of the values of Lode parameter. This research reveals the important role of the Lode parameter in the analysis of metal flow behavior during metal forming process.     

应力三轴度和罗德参数对铝合金材料韧性断裂的影响

大量研究表明应力三轴度对韧性断裂有重要影响。然而,最新研究表明,与应力偏张量第三不变量相关的罗德参数也是影响韧性断裂的重要因素。采用7075铝合金制成的缺口圆棒和凹槽平板试样分析了应力三轴度和罗德参数对韧性断裂的影响及相应的微观机理。通过准静态拉伸试验和数值模拟得到应力三轴度、罗德参数及失效轨迹,同时利用扫描电镜分析了试样不同应力状态下的空穴演化规律。结果表明,应力三轴度和罗德参数对破坏应变有重要影响,并且罗德参数的影响随应力三轴度的增加而降低。断口分析表明,孔洞的尺寸随着应力三轴度的增大而减小,不同罗德参数的空穴形态明显不同。二级孔洞的成核速率和生长程度也受罗德参数的影响。     

TA15钛合金热挤压过程中金属变形行为及组织分析

运用MSC.Marc有限元软件对TA15钛合金热挤压变形过程进行有限元模拟,得到热挤压成形过程中应力场和应变场分布情况。对有限元模拟所得到的应力、应变数据进行后处理,利用应力偏量不变量J2进行变形分区,采用罗德系数对塑性区内材料的应变类型进行划分。结合有限元模拟结果以及变形分区和变形类型的划分,对热挤压实验后的试样进行组织取样,在不同温度条件下对试样进行微观组织观察,分析微观组织的演化规律,这对于分析金属挤压成形问题及其在实际中的应用具有重要意义。     

Yield criterions of metal plasticity in different stress states

Five types of tensile tests were conducted to study the yield behavior of 2A12-T4 aluminum alloy. Parallel finite element models were built for each test and solved with ABAQUS with different yield criterions. The result shows that any of the four criterions: von Mises yield criterion, Tresca criterion, Twin-Shear criterion and yon Mises criterion with hydrostatic pressure correction, overestimates the yield strengths of the specimens. Rather than hydrostatic pressure, Lode stress parameter is the key factor that affects the differences between experimental and simulation results. Based on this concept, a new yield model with Lode dependence modified from yon Mises criterion is postulated. Although one more parameter needs to be confirmed, the simulation results of this yield model are better than those of other criterions.     

铝合金圆环压缩过程中的分流行为

利用有限元方法对不同圆环压缩过程中的分流行为进行模拟研究,揭示铝合金圆环压缩过程中分流行为的产生机理,并利用罗德系数、J_2应力偏量不变量等特征量对成形机理进行分析.结果表明:外侧施压时,随着高径比增大,难变形区明显扩大,向内侧流动的金属量逐渐减少,分流面位置明显左移;内侧施压时,随着摩擦因子增大,塑性区内应变类型由均一压缩类变为3种共存,此时向内侧流动的金属量增大,其流动分界面相对右移.     

屈服准则统一表达式的推广及切块法的改进

本文通过定义广义罗代应力参数 ,推导出新的屈服准则统一公式 ,它是经典的基于主应力的屈服准则统一表达式的推广。作者根据这一基于正应力的屈服准则统一表达式 ,改进了金属塑性成形理论中的切块法 ,有利于获得更合理的分析结果。     

Experimental and numerical investigation on pure aluminum by ECAP

The equal channel angular pressing(ECAP) experiments were carried out with industrial pure aluminum and an in-house mould. The comparison of material grain size before and after ECAP was performed by applying the technique of electron back scattered diffraction(EBSD). The results show that the grains in the material after ECAP are refined and the yield stress and ultimate strength are increased. In order to investigate the deformation mechanism during ECAP and the reason for driving grain size refinement, three-dimensional numerical simulations of the ECAP process were carried out. Based on the Lode parameter analysis, the deformation of the material sample is found very complicated, not just pure shear during extrusion through the angular channel. The simulation confirms that a strong strain gradient in the sample material is imposed by the ECAP.     

Failure characteristics of a dual-phase steel sheet

Failure in ductile sheet metal structures is usually caused by one, or a combination of, ductile tensile fractures, ductile shear fractures or localised instability. In this paper the failure characteristics of the high strength steel Docol 600DP are explored. The study includes both experimental and numerical sections. In the experimental sections, the fracture surface of the sheet subjected to Nakajima tests is studied under the microscope with the aim of finding which failure mechanism causes the fracture. In the numerical sections, finite element (FE) simulations have been conducted using solid elements. From these simulations, local stresses and strains have been extracted and analysed with the aim of identifying the fracture dependency of the stress triaxiality and Lode parameter.