Numerical simulation of residual stress field in green power metallurgy compacts by modified Drucker-Prager Cap model

Compaction process simulation and residual stress prediction of green PM compact were carried out with elasto-plastic 3D FEA based on the modified Drueker-Prager Cap model in Abaqus. The model parameters of the investigated powder Distaloy AE were determined as functions of relative density through typical mechanical property tests of powder. The model was implemented as a user subroutine USDFLD. Single sided compaction of a d20 ram^5 mm disk green compact of Distaloy AE was simulated, and the residual stress of the disk after ejection was predicted with FEA. The FEA results of the compaction process and the residual stress of the disk show good agreement with compaction experiments and X-ray diffraction measurements, which validates the model and its parameters. The results indicate that the compressive residual stresses exist mainly in a thin layer on the side surface, but the residual stresses are very small on the top and bottom surfaces.

基于Drucker-Prager/Cap模型的Ti-30Cu粉末轧制过程模拟

对钛和铜质量比为7∶3的Ti-30Cu混合粉末进行单轴压缩、巴西圆盘和模压试验,获得该粉末Drucker-Prager/Cap本构参数与相对密度的关系;利用Abaqus软件建立粉末轧制模型,研究喂料高度对板料相对密度的影响,并进行了试验验证;采用该模型研究了辊缝宽度、轧速对Ti-30Cu合金板料相对密度的影响。结果表明:在辊缝宽度为1 mm、轧速为10 mm·s^(-1)条件下,随着喂料高度由150 mm增加到300 mm,板料的相对密度增大,模拟结果与试验结果基本吻合,最大相对误差为2.15%,验证了轧制模型的有效性;随着喂料高度的增加、辊缝宽度或轧速的减小,板料的相对密度增大。

Finite Element Implementation of the Exponential Drucker-Prager Plasticity Model for Adhesive Joints

This paper deals with the numerical implementation of the exponential Drucker-Parger plasticitymodel in the commercial finite element software,ABAQUS,via user subroutine UMAT for adhesive joint simulations.The influence of hydrostatic pressure on adhesive strength was investigated by a modified Arcan fixture designed particularly to induce a different state of hydrostatic pressure within an adhesive layer.The developed user subroutine UMAT,which utilizes an associated plastic flow during a plastic deformation,can provide a good agreement between the simulations and the experimental data.Better numerical stability at highly positive hydrostatic pressure loads for a very high order of exponential function can also be achieved compared to when a non-associated flow is used.

3D numerical simulation of high pressure squeezing process with revised Drucker-Prager/Cap model

In order to investigate the sand mold strength after the aeration sand filling-high pressure squeeze moldingprocess,a tree-dimentional(3D)numerical simulation was introduced.The commercial finite element method(FEM)software ABAQUScombined with a revised Drucker-Prager/Cap model was used to simulate the squeeze compaction process.Additionally,the sand bulk density after the aeration sand filling process was tested by a specially designed experiment,which divided the whole sand bulk in the molding chamber into5x9regions and it was used as the input to simulate the squeeze process.During the simulation process,the uniform modeling simulation and the patition modeling simulation methods were used a d the3D numercal simulation results were compared with correlative benchmark testings.From the3D numerica simulation results,it can be concluded that the uniform sand bulk density distribution can obtain a high quality sandmold and the revised Drncker-Pager/Cap model is suitable for handling the situation with the complex paaern.The3D numerical simulation results can predict well the sand mold strength distribution and can be used as guidelines for the production practice.

基于修正Drucker-Prager Cap模型的金属粉末成形本构模型参数确定方法

针对修正Drucker-Prager Cap模型参数复杂且难准确获取的问题,提出一种采用相对简单实验操作结合联合仿真反演优化确定模型参数的方法,用于金属粉末成形的数值模拟。首先通过实验分析与理论推导,确定重点反演优化参数,即偏心距参数R;采用联合仿真反演优化方法,借助ABAQUS有限元及二次开发平台与MATLAB优化算法,对参数R进行反演计算,进而完成相关硬化参数的确定;以金属粉末Distaloy AE为例,讨论参数R不同函数表达形式的反演结果对粉末压制成形过程数值模拟的影响。研究结果表明,偏心距参数R2及其关联的硬化参数比R1在压制力、脱模力、相对密度和残余应力数值模拟方面具有更高的准确性。

基于Drucker-Prager/Cap模型的W–Cu20粉末轧制数值模拟

将Drucker-Prager/Cap塑性模型引入到高硬度W–Cu20粉末轧制有限元分析中,利用巴西圆盘试验、单轴压缩试验以及模压试验得到Drucker-Prager/Cap塑性模型参数,借助商业有限元软件ABAQUS以及Fortran自编的VUSDFLD子程序,建立粉末轧制的有限元模型,并与实际试验进行了比对。结果表明:模拟结果中的板料相对密度和板料厚度与实际实验结果吻合较好,最大误差为4.47%,说明Drucker-Prager/Cap塑性模型对粉末轧制工艺研究有参考意义。

钛合金粉末压制Drucker-Prager-Cap本构模型参数逆向识别

针对钛合金粉末压制成形,建立了Drucker-Prager-Cap本构模型参数的逆向识别流程。该流程结合模压实验,采用单纯算法,以数值模拟和模压实验的载荷-位移曲线差值最小化为目标函数。通过对传统实验和逆向识别两种方法进行比较验证,结果表明,经过逆向识别计算,目标函数值为0.0448。逆向识别有限元分析得到的最大压制力为36.18 kN,与模压实验值35.31 kN对比,误差为2.46%。且粉末的相对密度分布与实验结果基本一致,说明通过Drucker-Prager-Cap本构模型参数的逆向识别可以建立较为准确的本构模型。

冷模压制Ti-6Al-4V粉末的修正Drucker-Prager Cap本构模型

通过单轴压缩实验、径向压缩(巴西圆盘)实验和冷模模压实验建立了基于密度相关修正Drucker-Prager Cap (DPC)的Ti-6A1-4V粉末压制本构模型,利用ABAQUS有限元仿真软件的二次开发用户子程序USDFLD对该本构模型进行了模拟验证.综合考虑压制过程中实验装置变形对实验数据的影响,通过空压校正实验控制实验误差,建立了更加准确的修正DPC模型.结果表明:修正DPC本构模型可很好地应用于Ti-6Al-4V粉末压制过程的仿真模拟;当上模冲压力较小时(<50 MPa),模壁摩擦系数随上模冲压力的增加逐渐减小,当上模冲压力较大时(>50 MPa),模壁摩擦系数随上模冲压力的增加而基本趋于稳定.

基于Drucker-Prager Cap模型的装配式混凝土箱涵节段滞回性能研究

在利用有限元软件ADINA对预制钢筋混凝土箱涵结构进行滞回性能分析中,计算往往比较难收敛,而ADINA中提供的基于Drucker-Prager屈服条件、拉伸截断、帽盖硬化等准则的Drucker-Prager Cap模型,在对混凝土进行数值分析时收敛容易,且计算速度较快,并通过比较,发现采用基于该模型建立的数值模型计算得到的滞回曲线与试验得到的结果吻合程度较高,模拟结果较为准确。这一成果可以通过数值模拟的方式获得预制钢筋混凝土箱涵的滞回曲线与相关数据,可应用于预制箱涵节段抗震计算和设计。

A multiphysics-viscoplastic cap model for simulating blast response of cemented tailings backfill

Although a large number of previous researches have significantly contributed to the understanding of the quasi-static mechanical behavior of cemented tailings backfill,an evolutive porous medium used in underground mine cavities,very few efforts have been made to improve the knowledge on its response under sudden dynamic loading during the curing process.In fact,there is a great need for such information given that cemented backfill structures are often subjected to blast loadings due to mine exploitations.In this study,a coupled thermo-hydro-mechanical-chemical(THMC)-viscoplastic cap model is developed to describe the behavior of cementing mine backfill material under blast loading.A THMC model for cemented backfill is adopted to evaluate its behavior and evolution of its properties in curing processes with coupled thermal,hydraulic,mechanical and chemical factors.Then,the model is coupled to a Perzyna type of viscoplastic model with a modified smooth surface cap envelope and a variable bulk modulus,in order to reasonably capture the nonlinear and rate-dependent behaviors of the cemented tailings backfill under blast loading.All of the parameters required for the variable-modulus viscoplastic cap model were obtained by applying the THMC model to reproducing evolution of cemented paste backfill(CPB)properties in the curing process.Thus,the behavior of hydrating cemented backfill under high-rate impacts can be evaluated under any curing time of concern.The validation results of the proposed model indicate a good agreement between the experimental and the simulated results.The authors believe that the proposed model will contribute to a better understanding of the performance of hydrating cemented backfill under blasting,and also to practical risk management of backfill structures associated with such a dynamic condition.

Homology Modelling and Structural Comparisons of Capsid-Associated Proteins from Circoviruses Reveal Important Virus-Specific Surface Antigens

Circoviridae represent a growing family of small animal viruses. Some of these viruses have veterinary and medical importance, although, a vast amount of these newly discovered viruses have unknown effects on their hosts. The capsid-associated protein (Cap) of circoviruses is of interest because of its role in viral structure, immune evasion, host cell entry, and nuclear shuttling of viral components. The structure of the porcine circovirus 2 (PCV2) Cap has been solved and offered insight to these functions. Based on the crystallographic PCV2 Cap structure, models from circoviruses isolated from avian, fish, and mammalian hosts have been constructed and analyzed to better understand the roles of these proteins in the virus family. A high degree of conservation is observed in the models, however, the surface antigens differ among viruses. This is likely a reflection of the small genome harbored by circoviruses, and therefore the requirement of their few proteins to carry out specific vital functions, while maintaining enough variation to successfully infect their hosts. Here we describe the putative structures of a range of Cap proteins from circoviruses based on the crystallographic determination of porcine Cap, identifying key regions for function and inhibition of crystal formation.

塔里木盆地三大构造旋回油气成藏特征

塔里木盆地形成经历了南华纪—中泥盆世、晚泥盆世—三叠纪和侏罗纪—第四纪3大伸展-挤压构造旋回,其多旋回构造演化导致油气成藏和分布十分复杂。随着近年来盆地超深层已经成为油田的重点勘探领域,有必要对盆地的油气成藏规律进行深入探讨。本文基于最新的地震资料、钻井资料及油气地质资料,发现塔里木盆地油气规模成藏主力烃源岩为库车地区三叠系—侏罗系及塔西南地区石炭系—二叠系陆相烃源岩、台盆区寒武系海相烃源岩。盆内烃源岩及储盖组合的发育均受控于盆地3大伸展-挤压构造旋回,烃源岩的发育位置决定了塔里木盆地发育库车山前、北部坳陷、麦盖提斜坡及塔西南山前四大含油气系统。盆地在历经3大伸展-挤压旋回,其台盆区、库车前陆及塔西南前陆地区油气成藏组合差异大。台盆区发育石炭系膏泥岩与志留系—石炭系海相砂岩、奥陶系泥岩与灰岩、中寒武统膏盐岩与震旦系—寒武系白云岩储盖组合;库车地区发育新近系—第四系泥岩与砂岩、古近系膏盐层与白垩系砂岩、侏罗系泥岩与三叠系—侏罗系砂岩储盖组合;塔西南地区发育中新统泥岩-砂岩、古近系膏盐层与白垩系砂岩、石炭系—二叠系泥岩与碳酸盐岩储盖组合,分别组成了台盆区、库车及塔西南地区的上部、中部及下部组合。盆内烃源岩在加里东晚期、海西晚期—印支期、喜山期发生排烃,形成三期油气充注,结合塔里木盆地关键变革期的岩性、断裂、不整合及隆起的发育特征,构建了盆地三期成藏模式。

生物质挤压成型数值模拟及模孔参数优化

为研究生物质挤压成型过程中物料的变化规律,针对生物质材料在压实过程中逐渐变化的特性,以弹塑性理论为基础,通过一种修正的Drucker-Prager Cap材料本构模型,借助有限元分析软件ABAQUS及其二次开发子程序VUSDFLD模拟物料单向压制过程,并验证该模型的准确性。对环模单模孔的制粒过程进行模拟研究,设计正交试验获得模孔参数对成型密度以及比能耗的影响规律,进而对模孔参数进行优化分析。结果表明:修正的Drucker-Prager Cap本构模型能够准确的模拟生物质材料的挤压成型过程;增大锥孔深度以及锥孔锥度均可提高物料的成型密度和比能耗,以成型密度和比能耗为评价指标,最优参数组合为锥孔深度7mm,锥度60°。

黄土地基中能量桩群桩承载变形性状模型试验

基于室内缩尺试验研究了含能量桩群桩在4次冷热循环过程中的桩身热力学特性及桩基承载变形特性变化规律,分析冷热循环对桩土温度、承台沉降、桩顶荷载及桩身摩阻力的影响。试验结果表明:冷热循环过程中能量桩较浅位置处桩身及桩侧土温度始终高于较深处,热循环过程中能量桩的传热效率高于冷循环过程。冷热循环会使承台顶面的工作荷载及群桩中各基桩的桩顶荷载发生往复变化,相应地引起承台发生往复倾斜,热循环引起的承台倾斜稍大于冷循环。热循环引起的能量桩桩身上部摩阻力为负,下部为正,冷循环时则相反。

中西非裂谷系富油凹陷石油地质特征与勘探方向

基于地震、钻井、烃源岩测试分析等资料,对中西非裂谷系主要盆地富油凹陷石油地质特征进行研究,并探讨未来油气勘探方向。研究表明:中非裂谷系发育下白垩统湖相优质烃源岩,西非裂谷系发育上白垩统陆源海相优质烃源岩,两类烃源岩为中西非裂谷系油气富集提供了物质基础。中西非裂谷系发育包括基岩在内的多套储集层,并存在下白垩统、上白垩统和古近系3套区域盖层。晚中生代以来,受中非剪切带右旋走滑作用等地球动力学因素的影响,中西非裂谷系不同方向的盆地在裂谷作用期次、区域盖层发育层段、圈闭类型及成藏模式等方面存在差异。其中,北东—南西向盆地主要保存了早白垩世一期裂谷层序,区域盖层位于下白垩统裂陷期地层内,形成反转背斜、花状构造及基岩潜山等圈闭类型,发育“源储一体、源内成藏”及“源上储下、源下成藏”两种成藏模式;北西—南东向盆地具有多期裂谷叠置特征,发育上白垩统和古近系区域盖层,形成披覆背斜、断背斜、反向断块等圈闭类型,以“源下储上、源上成藏”为主要成藏模式。多期叠置裂谷盆地的源内成藏组合、强反转盆地的源内岩性油藏及页岩油是中西非裂谷系盆地未来勘探的重要领域。

采用基于特征的零件信息模型技术实现CAD／CAPP／CAM的集成

ＣＡＰＰ是工程设计的基本环节之一，是沟通ＣＡＤ与ＣＡＭ之间的桥梁．为了实现零件信息的交换和共享，通过统一的零件信息建模技术来实现ＣＡＤ／ＣＡＰＰ／ＣＡＭ的集成，它为ＣＡＤ／ＣＭＰ／ＣＡＭ的集成提供一条切实可行的途径．

机载MIMO雷达3-CAP杂波抑制方法

针对机载雷达面临的杂波抑制问题,在考虑阵元误差、通道误差和杂波起伏等误差因素对杂波特性影响的基础上,建立了机载MIMO雷达杂波数学模型,提出了一种基于MIMO雷达体制下的空时自适应新方法——M3-CAP方法。对接收信号进行时域滤波,选取被检测通道与其2个相邻通道为一组,进行自适应处理。该方法通过MIMO技术与3-CAP方法的有效结合,将波形分集的优势扩展到3-CAP方法中,显著提高了雷达系统自由度和杂波协方差矩阵估计精度。通过对不同雷达体制以及不同误差条件下杂波抑制性能的分析比较,结果表明:提出的M3-CAP方法的杂波抑制性能明显优于JDL-GMB、改进的JDL、3-CAP等方法。

大型梁式承台模型试验及跨中挠度简化计算方法研究

为了解大型梁式承台的力学性能,以某快速化改造工程的大型梁式承台为背景,按照缩尺比1∶10制作梁式承台模型进行力学性能试验,结合有限元计算,分析梁式承台结构受力、破坏模式、开裂情况等,并研究不同跨高比条件下梁式承台的受力特性。结果表明:在跨中荷载作用下,梁式承台受力大致可以分为线弹性阶段、裂缝发展阶段和屈服阶段3个阶段;线弹性阶段截面应力分布已不满足平截面假定,剪切效应对结构变形的影响不可忽略;模型最终破坏模式为弯曲破坏;裂缝主要表现为跨中弯曲裂缝和斜裂缝;跨高比越小,梁式承台剪切刚度越大。为考虑剪切效应对梁式承台变形的影响,拟合得出梁式承台跨中挠度的简化计算方法,将该方法计算值及规范计算值与试验值进行对比,可得在裂缝发展阶段,规范计算值与试验值偏差较大,所提方法计算值与试验值偏差较小,该方法可用于线弹性阶段及裂缝发展阶段梁式承台跨中挠度的初步估算。

海上风电打桩系统动力学建模与冲击动力特性分析

基于LS-DYNA建立3500 kJ海上风电打桩系统拒桩工况下的有限元模型,基于应力波原理分析打桩系统内部能量的传递和各部件的动力学响应。同时基于牛顿碰撞理论建立打桩系统的集中参数模型,该模型综合考虑各部件的质量和刚度,和有限元模型的分析结果较吻合。从而在该集中参数模型的基础上,分别分析替打刚度、替打和锤质量比、替打环刚度对打桩系统冲击力的影响规律,表明冲击力的主要影响参数为替打刚度。

砂土中斜桩-承台基础的水平承载特性研究

通过开展室内模型试验,研究了砂土中斜桩-承台系统的水平承载特性,重点分析了桩身倾角及桩身抗弯刚度两个因素对桩顶水平位移、桩身弯矩分布的影响。利用有限元方法开展了与模型试验相对应的三维有限元分析,两者所得结果的对比表明所采用的有限元分析方法能较好地反映斜桩在水平荷载下的受力和变形特性。为了更好地与工程实际相对应,基于上述数值分析方法开展了原型尺寸的数值参数分析,考虑了桩体的弹塑性力学特性,探究土体弹性模量、桩身刚度以及桩身长度对斜桩-承台系统水平承载能力的影响。计算结果表明,相较于改变桩身的抗弯刚度,土体弹性模量的变化对斜桩-承台系统水平承载能力的影响更为显著;当桩长小于25 m(25倍桩径)时,桩长的增加能较明显降低桩顶水平位移响应,当桩长超过该值时,斜桩水平承载能力的提升效率下降。此外,基于试验数据开展了多元回归分析,获得了斜桩-承台系统桩顶水平位移的半经验预测公式,该公式的预测值与试验实测值及数值参数分析计算值的吻合度均较高,具有良好的适用性,有望能为砂土中斜桩工程的设计和分析提供一定的参考依据。