AbaqusExplicit接触问题

1、1. Abaqus/Explicit中的接触形式双土 Interactions,出现接触形式定义。分为通用接触(General contact 面 面接触(Surface-to-Surface contact 和自接触(Self-contact)。1. 通用接触 General contact通用接触用丁为多组件，并具有复杂拓扑关系的模型建模。General contact algorithm? The contact domain spans multiple bodies (both rigid and deformable)? Default domain is defined auto

2、matically via an all-inclusive element-based surface? The method is geared toward models with multiple components and complex topology。? Greater ease in defining contact model2. Surface-to-Surface contactContact pair algorithm? Requires user-specified pairing of individual surfaces? Often results in

3、 more efficient analyses since contact surfaces are limited in scope3. 自接触(Self-contact)自接触应用丁当部件发生变形时，可能导致自己的某两个或多个面发生接触 的情况。如弹簧的压缩变形，橡胶条的压缩。?容易使用？ “自动接触” ？节省生成模型的时间？通用接触算法一般比双面接 触算法快机械约束形式? 运动依从 Kinematic contact method（只有接触对形式可用，General contact不可用）默认的运动接触公式达到的计算精度与接触条件相一致。在多数情况下，它 工作得很好。但是在某些情况下，

4、如抖动接触，使用罚函数接触会更容易得到收敛的解。不能为刚体-刚体接触建模。?罚函数（通用接触和接触对均可使用）Penalty contact method罚函数接触算法中接触约束的严格性低丁运动学算法。罚函数算法可以处理更一般类型的接触；比如，刚体之间的接触。因为罚函数算法在模型中引入附加刚度，该附加刚度将影响稳定时间增量。Abaqus/Explicit自动计算由与接触力相关的侵彻距离引入的“弹簧”冈Q度或“罚”刚度。但是必须考虑相关的影响：应该尽量减少对稳定时间增量的影响。在所有的分析中，允许的侵彻不可以太大。?对丁接触对算法：通过在*CONTACT CONTROLS选项指定SCALE PE

5、NALTY参数，用户可 以缩放默认的罚刚度。?对丁通用接触算法：可以使用 *CONTACT CONTROLS ASSIGNMENT, TYPE=SCALE PENAL TY 选项缩放罚刚度。综上，多数情况下，运动依从算法和罚函数算法将得到几乎一致的结果。然 而，在某些情况下，一种方法可能比另一种方法更可取。如果需要知道kinematic algorithms和penalty algorithms之间的区别，那就 需要啃理论教材了(当然看abaqus帮助文件也可以).简略的说：1) penalty algorithms,(罚函数法)在被abaqus检测到接触距离以内的节点之间定义罚刚度，进而来迭

6、代出接 触力。在每一个时间步先检查各从节点是否穿透主面。如没有穿透则进入下一个时 问步；如果穿透，则在该从节点与被穿透主面问定义罚刚度， 引入一个较大的界 面接触力，其大小与穿透深度、主面的刚度成正比。2) kinematic algorithms先在一定时间内检查所有未与主面(master surface)接触的从节点(slavenode),看是否在此时间内穿透了主面。如果存在穿透则缩小时间步，使那些穿 透主面的从节点都不贯穿主面，而使其正好到达主面。在计算下一时间步之前， 对所有已经与主面接触的从节点都施加约束条件，以保持从节点与主面接触而不 贯穿。此外还应检查那些和主面接触的从节点所届单

7、元是否受到拉应力作用。如受到拉应力，则施加释放条件，使从节点脱离主面。就abaqus接触计算的初级使用来说，如果接触对中有刚体，一般用 penalty algorithms；如果接触对是弹性体，有限选 Kinematic algorithms.无刚体的接触， 建议直接用Kinematic algorithms试算。总结：1) 接触面存在刚体，用penalty算法2) 接触面之I可的相对运动方向平行丁接触面，用 penalty算法3) 弹性碰撞分析不可用 hard-kinematic算法。碰撞之中塑性变形控制的接 触分析4) penalty算法一般会减小稳定时间增量5) 接触计算与以下情况耦合时

8、推荐 penalty算法：constraint equation, multi-point constraint, tie constraint, embedded element constraint, or kinematic constraint6) breakable bond model 模拟，必须用 hard kinematic contact 。碰撞应该用罚函数法吧，要是用运动学算法时需要划分较细的网格以避免能 量的丢失。kinematic contact要求更严格，不允许出现穿透，而 penalty contact允许。默 认的Penalty stiffness为弹性刚度的10

9、%,所以如果是解决塑性变形问题的话， 二者算出来的结果相差不大。penalty对切向的相对位移的接触比较有效。3.初始运动学依从关系Abaqus/Explicit不允许接触表面的初始过盈。?接触表面的节点将被调整，删除分析之前的初始过盈：?只移动接触表面的节点。?对丁分析过程第一个分析步定义的接触对，由丁调整表面引起的位移不产 生初始应变或应力。?在随后的分析步中：?对丁接触对算法，调整将产生应变。?对丁通用接触算法，忽略初始过盈。Contact Formulations接触程式，包括1. Contact discretization 接触离散化Where is the constraint

10、applied ?接触约束应用在哪？? Node-to-surface? Surface-to-surface2. Constraint enforcement 执行接触How is the constraint enforced ?接触约束怎么执行？? Default (Explicit )? Direct (Lagrange multipliers) Standard? Penalty methodStandard? Augmented Lagrange (Lagrange multipliers combined with penalty method) Standard3. Conta

11、ct tracking (relative sliding)跟踪接触How does the constraint evolve ?接触约束怎么发展？? Finite sliding? Small slidingContact DiscretizationNode-to-surface technique:节点和面接触? Default method for contact pairs接触对的默认接触定义方法。? Not available for general contact 不适用于 General contact? Nodes on one surface (the slave sur

12、face) contact the segments on the other surface(the master surface).从面上的节点接触主面的面。? Contact is enforced at discrete points (slave nodes)在从面节点处执行接触。从面需要划分较细的单元来提高精度和消除应力振动即消除应力噪声。Use of a“ matched mesh ” across the contact interface will eliminatesthlustion noise。Surface-to-surface technique 面面接触? Onl

13、y method for general contact Alternative method for contact pairs? The method considers the shape of both the master and slave surfaces.? Contact is enforced in an average sense over the slave surface.当面面接触用丁接触对时，contact pairs和general contact区别不大，主要的区别在丁使用方便性和性能表现 erformanceoSurface-to-SurfaceSlave

14、SurfaceNode-to-SurfaceSlave surfaceMaster surfaceMaster surfaceThe contact pressure contours are much smoother and the peak contact stress is in very close agreement with the analytical solution using the surface-to-surface approach,Analytical CPRESSmax = 3.01e+05Node-to-surfaceSurface-to-surface

15、9; slave surfaceSome penetratron may be observed at individual nodes; however, large, undetected penetrations of master nodes into the slave surface do not occur可以看出Node-to-Surface参与接触节点个数较少。而S-to-S较多对丁面面接触，个别点小的穿透可能会出现，但是不会发生漏检测到的主面穿透Finite-Sliding Contact FormulationsFeaturesSurface-To-SurfaceNode

16、-To-SurfaceContact stresses 接触应力More accurate if surface representation is adequateLess accurate with mismatched meshesShell and membranethickness壳村膜S厚度ConsideredConsidered only for small slrdingInternal smoothing'1 of the master surface 主面的内部平滑Not requiredRequired for finite sliding.Smoothing i

17、s also performed for the anchor point calculation in small sliding.Extension zone for master surface 主固延伸Not requiredRequired for finite sliding.Finite-Sliding Contact FormulationsFeaturesSurface-To-SurfaceNode-To-SurfaceMemory requirement and solver cost内存消耗和求解效率Generally requires creased memory an

18、d solution time (particularly if the master surface is more refined than the slave).Default constraintenforcement默认执行约Penalty method束 g卜Direct methodRobustness稳定性Minimizes snagging and adds stabihty at the edges and comers.Contact EnforcementHard contact:In Abaqus/Standard, the default contact behav

19、ior is “ hard ” contactThe behavior is described by a contact property known as the pressure-penetration curve (alternative behavior can be specified; discussed later).Physically"hard” pressure vs, penetration behaviorh = 0p, contact pressureNo pressureAny pressure> possible when in contactN

20、o penetration;Xno constraint requiredConstraint enforced；positive contact pressureh, penetrationThe desired behavior (no penetration) is achieved using an enforcement method.理想的没有穿透的接触行为可以用三种强化方法来获得。Three numerical methods are available in Abaqus/Standard to achieve or approximate “ hard ” contact c

21、onditions:Direct enforcement method:Strict enforcement of pressure-penetration relationship using the Lagrange multiplier method.严格压力-穿透关系，用拉格朗日乘法算法。Pros and cons of direct enforcement 优缺点Advantages: Accuracy constraint is satisfied exactly.Disadvantages:Adds to equation solver cost.求解代价高Additional

22、variable per contact constraint, which enlarges the system of equations to be solved.Restricts elimination order for sparse solver, which can degrade performance.Potential convergence difficulties.潜在的收敛问题。Abrupt change from zero contact stiffness (while contact is inactive) to infinite contact stiff

23、ness (while contact is active).从 0 刚度到无穷刚度变化的剧烈。Difficulties with overconstraints.Overlap between contact constraints and MPC ' s, etc.Penalty method:Approximate enforcement using penalty stiffness.用罚刚度近彳以。The penalty method is a stiff approximation of hard contactNo pressurea p, contact pressur

24、ep, contact pressureAny pressure卜 possible when in contactNo pressurek、penalty stiffnessh, penetrationStrictly-enforced hard contactI h, penetrationPenalty method approximation of hard contact罚刚度可以是：Linear (default):线性? Easier convergence.容易收敛? Better suited for problemsinvolving firm contact.较适用丁硬面

25、接触。? Difficult to choose stiffness appropriate for all regimes.难以选择刚度值适用丁所有情况。Nonlinear:非线性? The lower initial stiffness makes it better suited for problems involving chattering.初始的小刚度值适合丁解决包括颔振的接触。? The higher final stiffness helps reduce penetrations.高的最终冈|度降彳氐穿透? Convergence overall can be more d

26、ifficult.收敛较困难。Default penalty stiffness：默认的刚度值? Abaqus折中选择刚度：刚度小，过度穿透。冈Q度大， 收敛速度；Lagrange multiplier DOF are needed to avoid ill-conditioning.? The default penalty stiffness is based on a representative stiffness of the underlying elements.A scale factor is applied to this representative stiffness

27、to set the default penalty stiffness; its magnitude is higher in Abaqus/Standard than in Abaqus/Explicit.默认刚度不合适，可以设置比例系数调节。? Order-of-magnitude changes are recommended隹荐? If the scale factor > 100, Abaqus will automatically invoke a variant of the method that uses Lagrange multipliers to avoid i

28、ll-conditioning issues. 如果日匕例系 数大丁 100,自动采用Lagrange multipliers来避免病态。罚刚度值：? Stiff or blocky problems：硬的或短而结实的接触。默认刚度值产生结果：比的上direct method的精确度。Requires less memoryand CPU time。? Bending-dominated problems弯曲占主导地位的接触：默认刚度值会被缩减但是不显著影响精确度。Scale back two orders of magnitude without any significant loss o

29、f accuracy.Scaling back the penalty stiffness for bending-dominated problems sometimes dramatically increases the convergence rate缩减刚度值还或许会提高收敛率。 Example: Hertz contact15% differencePenetration Stress 1 f .47% difference4482E-62492EVHertz contact resultsDirect Lagrange:Penalty (default):Penalty (Sf

30、= 0.01)：可以看出对丁 Hertz接触，默认的罚刚度值和 Direct Lagrange结果最接近。Advantages:Significantly improved convergence ratesBetter equation solver performance. No Lagrange multiplier DOF unless contact stiffness is very high.Good treatment of overlapping constraints.Disadvantages:Small amount of penetration. Typically

31、insignificantMay need to adjust the penalty stiffness in some casesUsed by default for each of the following: General contact、Contact pairs with the finite-sliding, surface-to-surface formulation。 Automatic contact pair detection capability in Abaqus/CAE。Augmented Lagrange method:Approximate enforce

32、ment using penalty method with augmentation iterations; not discussed further here.Used by default for: 3D self contact with node-to-surface discretizationDirect enforcement (Lagrange muKiplier method)Penalty methodAdvantagesDisadvantagesAdvantagesDisadvantages Exact constraint enforcement (no penet

33、ration) Lagrange multipHe& add to equation solver cost, Sensitive to chatteringconvergence problems, Oifficuil la treat overconstraints improved convergence due to numerical softening No Lagrange multiplier degrees of freedom Avoids overoonstfaini issuefi Some penetration exists (smalE) Need to

34、adjust penalty stiffness in some casesp, contact pressureDirect enforcementNo pressure入Some numerical "softening” with penalty or augmented Lagrange enforcementI ht penetrationContact tracking (relative sliding)Finite slidingKinematically, finite sliding of deformable bodies against each other allows the most general relative motion between the bodies:? Arbitrarily large sliding is allowed.? Arbitrarily large rotations and deformations of the surfaces are allowed.?任意大的滑动和转动都允许。接触对和通用接触中均可以使用。Small slidingSmall sliding assumes that the relative motion per slave node