用双剪屈服准则解刚塑性体轴对称平面应力问题

本文应用双剪屈服准则，用特征线法求解了刚塑性体轴对称平面应力问题，给出薄圆环在内孔壁受压扩孔的算例，结果表明，计算过程比应用Ｍｉｓｅｓ屈服准则简便，计算结果有较好的精度。     

用双剪应力屈服准则计算壳体的极限载荷

本文导出轴对称壳体的双剪应力屈服准则下的屈服条件，并求出某些特殊荷载下的圆锥壳和圆柱壳的极限载荷。     

金属玻璃切削加载的形变屈服准则与实验验证

以金属玻璃切削过程中的屈服形变为研究对象,引入源于岩土领域的M-C屈服准则来解决传统Treaca准则及Mises准则不能反映金属玻璃的应力敏感性问题。另外鉴于金属玻璃的温度敏感特性以及切削加工时较高的切削温升,将经过温度修正的改进型M-C屈服准则应用于金属玻璃的切削模型之中。切削力实验表明,基于传统屈服准则、不含温度项的M-C屈服准则以及经过温度修正的M-C屈服准则所建立的切削力模型中,后者的解析解与切削力实测值相比误差最小(平均误差8.92%),说明经过温度修正的M-C屈服准则可以较好地反映金属玻璃切削加载的切削力及材料形变过程,为后续金属玻璃切削机理的深入研究奠定了理论基础。     

广义合成偏应力椭球模型

本文从应力椭球的概念出发，建立了反映岩土类材料屈服与破坏的广义合成偏应力椭球屈服准则，该准则不仅反映了偏斜应力和静水应力对材料的屈服与破坏的贡献，而且反映了岩土类材料的屈服与破坏与静水应力呈非线性的关系以及静压屈服的特性。将该模型应用于混凝土，其结果与公开发表的文献和实验数据取得了很好的一致性。     

基于二阶组构张量的各向异性屈服准则

将四个屈服准则:Tresca准则、Mises准则、Mohr-Coulomb准则以及Drucker-Prager准则归类为剪切屈服准则。Tresca准则和Mohr-Coulomb准则是关于最不利截面的剪切屈服准则,而Mises准则和Drucker-Prager准则是关于各方向截面的剪应力和正应力的某种综合度量的八面体剪应力和八面体正应力的剪切屈服准则。从方向函数(ODF)的概念入手,将各方向截面的剪应力和正应力综合度量直接取为所有方向截面上的剪应力和正应力的平均。对各向同性材料,提出了平均剪切屈服度准则:当平均剪应力和平均正应力的组合达到某一极限值时,材料开始屈服。研究表明,平均剪切屈服准则与Drucker-Prager准则具有相同的形式,当不考虑平均正应力对屈服的影响时,它与Mises准则具有相同的形式。针对由各向异性损伤导致的材料各向异性强度问题,定义截面上的有效正应力和有效剪应力则分别为截面上的法向力和切向力与有效承载面积之比,基于截面上的有效应力提出了各向异性材料的平均剪切屈服准则。各向异性损伤引起的截面上有效应力放大系数为方向函数,可以采用二阶组构张量来近似表示,在任意坐标系中,各向异性屈服准则为应力分量的二次齐次式,导出了其中的系数与二阶组构张量之间的显式关系式。在二阶组构张量的主轴坐标系内,各向异性屈服准则与殷有泉的拓展Hill准则形式完全相同,当不考虑正应力对屈服的影响时,它与Hill准则具有相同的形式。     

解析Poly6-I屈服准则对3104-H19铝合金拉深制耳预测的研究

目的 研究解析Poly6-I屈服准则预测具有高各向异性的3104-H19铝合金本构关系的能力,并将其应用于有限元仿真分析中,以实现对3104-H19铝合金拉深制耳的精确预测。方法 分析解析Poly6-I屈服准则的表达形式,减少计算参数所需的试验个数,并与经典的Yld2004-18p屈服准则进行对比,验证它对高各向异性力学性能预测的能力,将其嵌入到有限元软件中进行杯型件拉深制耳模拟,验证模型的精确性和有效性。结果 对于高各向异性材料,解析Poly6-I屈服准则所使用的试验个数可以减少到11,它预测的3104-H19铝合金屈服轨迹的各向异性系数曲线和单向拉伸曲线与Yld2004-18p屈服准则预测的结果基本相同,杯型件拉深有限元模拟结果与试验结果基本一致。结论 与Yld2004-18p屈服准则相比,考虑高各向异性特性的解析Poly6-I屈服准则所使用的试验数据更少,且无须使用优化软件求取参数,更为方便。解析Poly6-I屈服准则能精确地预测3104-H19铝合金材料在杯型件拉深试验中的制耳个数及杯型件杯壁的成形高度。     

在复杂应力状态下厚壁圆筒的极限分析

应用双剪统一强度理论,考虑材料的拉压异性和同性,推导了在内压力和轴力联合作用下的厚壁圆筒的塑性极限载荷计算公式,并且绘制了其极限载荷线图。在这些计算公式中,当其系数取不同的值时,就能得到按Tresca屈服准则、线性逼近的Mises屈服准则和双剪应力屈服准则的计算结果。应用其极限载荷线图,根据其承受的载荷大小,就能判断厚壁圆筒是否达到了屈服极限状态。绘制了在不同屈服准则下的极限载荷线图,以便对其差异进行比较。     

弹粘塑性有限元分析中相对于几种屈服准则的H矩阵的统一格式

文献介绍了弹粘塑性有限无解的数值方法,给出了Mises屈服准则的H矩陈表达式。本文对工程中常用的四种屈服准则,即Mises,Tresca,Mohr-coulomb,Drucker-Prager准则,给出了H矩阵的统一格式,提供厂消除Tresca,Mohr-Coulomb准则奇异性的方法并给出了公式。     

各向异性板料屈服轨迹的研究

针对建立的十字形双向拉伸试验系统,利用有限元模拟优化得到的十字形试件,采用载荷控制方式对SPEN钢板和2024-O铝合金板进行了不同加载路径下的双向拉伸试验,得到了不同硬化阶段下的实验屈服轨迹,并与现有屈服准则Hill48、Hill79、Hill90、Hill93、Gotoh、Hosford、Barlat-Lian以及Mises的理论屈服轨迹进行了对比.结果表明:对于SPEN钢板,Hosford各向异性屈服准则得到的理论屈服轨迹与实验屈服轨迹符合得最好,其次是Mises屈服准则,Hill48屈服准则最差;对2024-O铝合金板,Barlat89、Hosford屈服轨迹与实验屈服轨迹符合得最好,Mises屈服准则最差.     

钴基高温合金GH188板材的屈服行为研究

目的 研究钴基高温合金GH188板材在不同应力状态下的屈服行为,并确定适用的屈服准则,为工程应用提供科学指导。方法 通过开展不同方向的单向拉伸试验得到基本力学性能参数,以轧制方向为参考方向,利用其真实应力-应变曲线标定Ludwik本构模型参数;根据国际标准设计十字形试件,利用ABAQUS软件对其等双拉加载进行有限元仿真,然后基于设计的试样对GH188高温合金板料进行不同载荷比例下的双向拉伸试验,并获取屈服点;结合以上数据,采用Mises、Hill48、Barlat89和Yld2000-2d 4种屈服准则对屈服轨迹、r值和应力值进行预测。结果 等双拉过程中,十字形试件中心区应力分布均匀且无切应力,表明试样的设计是合理有效的;4种屈服准则对试验屈服轨迹的平均预测误差相差不大,为(2±0.5)%,但整体而言,Hill48-σ的预测误差最大,Hill48-r和Barlat89屈服准则呈现相似的预测能力,误差约为20%,Yld2000-2d屈服准则预测精度最高,综合误差仅有2.41%,远远小于其他3种屈服准则的预测误差。结论 钴基高温合金GH188板材具有明显的各向异性,Yld2000-2d屈服准则可以精确地描述该材料在复杂应力状态下的屈服行为。     

屈服准则和硬化模型对5052铝板回弹仿真的影响

为选择适合于5052铝合金回弹仿真的材料模型,对LS-Dyna软件中4个材料模型MAT_36、MAT_122、MAT_125和MAT_226所采用的屈服准则和硬化模型进行了分析,采用这4个模型对5052铝板U形件的回弹进行了仿真,对回弹过程中圆角区的应力释放进行了讨论.同时,进行了U形件的回弹试验,并与仿真结果进行了比较.结果表明,4个材料模型中,基于Yoshida-Uemori随动硬化模型和Barlat’89屈服准则的材料模型MAT_226具有最好的回弹预测精度,由各向同性硬化模型和Hill’48屈服准则组合的材料模型MAT_122的回弹预测结果与试验结果的偏差最大.硬化模型对回弹预测精度的影响大于屈服准则的影响.     

Viscoelasticity and shear yielding onset in amorphous glassy polymers

In the present work, the effect of viscoelasticity on the yield behaviour of a polycarbonate, PC, was studied and the identification of a yield criterion which takes into account the effects of the mechanical history on the onset of plastic strain, was attempted. The attention was focused on the shear yielding plastic deformation process and different loading histories were performed under uniaxial compression: constant strain rate at different rates, stress relaxation at different applied strain levels, creep under different stress levels. Some tests were also carried out under shear loading, in which the hydrostatic stress component is equal to zero and its effect on the yield onset can be considered. For the definition of a yield criterion, different quantities, some already proposed in an analogous work on a styrene-acrylonitrile copolymer (SAN), were considered and determined at yield onset for each of the applied loading histories. The results obtained in this work show that the relative ratios of the viscoelastic strain over the overall strain and of viscoelastic energy over the deformation work are fairly constant irrespective of both loading history and stress state. The re-elaboration of the data previously obtained on SAN is consistent with these results. Discussing the experimental data, differences between the mechanical behaviour of the two glassy polymers were pointed out and a more difficult activation of the plastic deformation process of PC than SAN was generally observed.     

曲面积分求解椭圆模轴对称拔制

对模面曲线为椭圆的拔制圆棒问题设定了运动许可速度场，对该场以曲面积分确定了摩擦功率；以双剪应力屈服准则和变上限积分确定变形功率并得到拔制力的上界解析解。     

基于常规三轴试验的岩石双剪强度准则

基于岩土体的双剪强度理论和已有的一些岩石真三轴强度试验资料,提出了一个岩石双剪强度准则的推广型式,探讨了该强度准则相关参数的选取问题,验证了该强度准则的合理性,并指出双剪强度准则有一个)()(8mfgsqts=的函数表达型式。研究表明岩石的tc88/tt随平均主应力ms的变化而变化,当ms较小时tc88/tt比值较大,而当ms较大时tc88/tt比值较小。这种现象一方面论证了随着ms的增大,岩石有逐步向着均质化方向发展的趋势;另一方面也说明了在较低的ms应力水平下,Drucker-Prager强度准则对岩石类材料是不适合的。     

Effect of loading history and material’s structural state on the yield onset of a polymethylmethacrylate

Constant strain rate tests at different rates and stress-relaxation tests at different intensities of the applied strain were performed on a polymethylmethacrylate under uniaxial loading conditions. Shear yielding onset was properly determined for each of the applied loading histories. Following previous works, different quantities were evaluated at the onset of yielding to identify a parameter, which could be fit for the definition of a yield criterion that takes into account the effect of the mechanical history. The influence of the material structural state on the parameters’ values at the onset of yielding was examined too.     

宽板大曲率半径纯弯曲回弹量理论分析

针对各向异性板料的大曲率弯曲回弹问题,建立了服从Hill屈服准则和指数强化模型的平面应变纯弯曲的回弹理论模型。应用该模型计算了Numisheet’2002无约束柱面弯曲回弹的考题,与实验结果和其它理论模型计算值的对比表明,模型的回弹结果与实验值很接近,其精度优于其它算法。同时还表明,屈服准则的选取对预测板料回弹量有着较大影响,而强化模型的影响则不是很显著。     

Surface Yielding of Metals by X-ray Diffraction

Surface yielding of metallic material was measured with strain gage and X-ray diffraction methods.The results show that.when the residual stress in the transverse direction is involved,the surface yieldstrength should be evaluated with biaxial Mises criterion.For a medium carbon high strength steel,the yield strength of the bulk material is 581 MPa and the surface yield strengths for 0.05% and0.1%plastic strain are about 436 MPa and 463 MPa respectively.The 0.05% yield strength willapproximately increase to 788 MPa after shot peening.In the early stage of plastic deformation,strain hardening in the surface layer is quite different from that of the bulk sample.     

The effect of specimen thickness on the experimental and finite element characterization of CTOD in extra deep drawn steel sheets

Recent experimental results by us have indicated that the load-drop technique can serve as a valid fracture criterion for predicting elastic-plastic fracture in extra deep drawn (EDD) steel sheets or in predominantly plane stress conditions. The purpose of this investigation is to examine the validity of aJ-integral as a fracture parameter and theJ-CTOD relation for the determination of critical CTOD in predominantly plane stress fracture (CTOD-crack tip opening displacement). Fracture tests were performed and experimental results were generated on fracture behaviour of EDD (0·06%C) steel sheets with CT specimens and using ‘load-drop’ as a fracture criterion. Critical CTOD was determined by using theJ-CTOD relation in addition to several existing techniques. A full 3-D finite element model was formulated to verify the critical load, critical CTOD and plastic-zone size. The critical CTOD was shown to increase with increasing specimen thickness and appeared to be approaching a higher limiting value. The characteristic features of predominantly plane stress fracture or general yielding fracture mechanics are summarized in conclusion     

环形均布荷载作用下简支圆板的塑性极限分析

本文采用双剪统一屈服准则首次对受环形均布荷载作用下的简支圆板进行了塑性极限分析,得出了相应的统一解形式。已有的Tresca准则、Mises准则、双剪应力准则的解答是文中解答的特例或逼近,它可以适用于不同性状的拉压同性材料。用本文的解还可以推出多种荷载作用下简支圆板的塑性极限荷载。