ANSYS中接触单元参数设置要点

一、ANSYS接触单元几个关键选项的含义

The element KEYOPTS allow you to control several aspects of contact behavior.

·         Degrees of freedom (KEYOPT(1))

·         Contact algorithm (defaults to augmented Lagrangian) (KEYOPT(2))

·         Stress state when superelements are present (KEYOPT(3)) for 2-D surface-to-surface contact. (See note below for other meanings of KEYOPT(3).)

·         Location of contact detection point (KEYOPT(4))

·         CNOF Automated adjustment (KEYOPT(5))

·         Contact stiffness variation range (KEYOPT(6))

·         Time step control (KEYOPT(7))

·         Asymmetric contact selection (KEYOPT(8))

·         Effect of initial penetration or gap (KEYOPT(9))

·         Contact stiffness update (KEYOPT(10))

·         Shell thickness effect (KEYOPT(11)) (not applicable to CONTA176)

·         Behavior of contact surface (rough, bonded, etc.) (KEYOPT(12))

 1、KEYOPT(1)

Selects DOF

 2、KEYOPT(2)

Selecting a Contact Algorithm 

·         Penalty method (KEYOPT(2) = 1)

·         Augmented Lagrangian (default) (KEYOPT(2) = 0)

·         Lagrange multiplier on contact normal and penalty on tangent (KEYOPT(2) = 3)

·         Pure Lagrange multiplier on contact normal and tangent (KEYOPT(2) = 4)

·         Internal multipoint constraint (MPC) (KEYOPT(2) = 2)

  Compared to the penalty method, the augmented Lagrangian method usually leads to better conditioning and is less sensitive to the magnitude of the contact stiffness.

   相对罚函数法，扩大拉格朗日法不易引起病态条件，对接触刚度数值敏感性更小。

  Chattering Control Parameters（跳跃控制参数）

  The Lagrange multiplier methods (KEYOPT(2) = 3, 4) do not require contact stiffness, FKN and FKT. Instead they require chattering control parameters, FTOLN and TNOP, by which ANSYS assumes that the contact status remains unchanged. FTOLN is the maximum allowable penetration and TNOP is the maximum allowable tensile contact pressure.

   The behavior can be described as follows:

·         If the contact status from the previous iteration is open and the current calculated penetration is smaller than FTOLN, then contact remains open. Otherwise the contact status switches to closed and another iteration is processed.

·         If the contact status from the previous iteration is closed and the current calculated contact pressure is positive but smaller than TNOP, then contact remains closed. If the tensile contact pressure is larger than TNOP, then the contact status changes from closed to open and ANSYS continues to the next iteration.

   The objective of FTOLN and TNOP is to provide stability to models which exhibit contact chattering due to changing contact status. If the values you use for these tolerances are too small, the solution will require more iterations. However, if the values are too large, the accuracy of the solution will be affected since a certain amount of penetration or tensile contact force is allowed.

  参数FTOLN和TNOP 主要为结构提供稳定性，该类结构一般会因接触状态的改变而呈现出接触跳跃。

4、KEYOPT(4)

  Location of contact detection point

 The nodal detection algorithms require the smoothing of the contact surface (KEYOPT(4) = 1) or the smoothing of the target surface (KEYOPT(4) = 2), which is quite time consuming. You should use this option only to deal with corner, point-surface, or edge-surface contact (see Figure 3.13: "Contact Detection Point Location at Nodal Point"). KEYOPT(4) = 1 specifies that the contact normal be perpendicular to the contact surface. KEYOPT(4) = 2 specifies that the contact normal be perpendicular to the target surface. Use this option (KEYOPT(4) = 2) when the target surface is smoother than the contact surface.

 节点检测算法要求接触面光滑(KEYOPT(4) = 1)或目标面光滑(KEYOPT(4) = 2)，上述要求均造成计算耗时较大。一般用户仅在处理角点、点-面、边-面接触问题时才用到该选项。KEYOPT(4) = 1表明，接触单元方向垂直于接触面表面。KEYOPT(4) = 2表明，接触单元方向垂直于目标面表面。当目标面较接触面光滑时，使用KEYOPT(4) = 2。 

5、KEYOPT(5)

CNOF/ICONT Automated adjustment:

0 --  No automated adjustment

1 --  Close gap with auto CNOF

2 --  Reduce penetration with auto CNOF

3 --  Close gap/reduce penetration with auto CNOF

4 --  Auto ICONT

•  Use real constant CNOF to specify a contact surface offset.

CNOF specifies the positive or negative offset value applied to the contact surface.

Specify a positive value to offset the entire contact surface towards the target surface. Use a negative value to offset the contact surface away from the target surface.ANSYS can automatically provide the CNOF value to either just close the gap or reduce initial penetration  Set KEYOPT(5) =1/2/3.

• ICONT defines an initial closure factor (or adjustment band).

SetKEYOPT(5) =4.Use the real constant ICONT to specify a small initial contact closure. This is the depth of an "adjustment band" around the target surface.

Any contact detection points that fall within this adjustment band are internally shifted to be on the target surface .Only a very small correction is suggested; otherwise, severe discontinuity may occur (see Figure (b)).

  The difference between CNOF and ICONT is that the former shifts the entire contact surface with the distance value CNOF, the latter moves all initially open contact points which are inside of adjustment band ICONT onto the target surface.

 6、KEYOPT(6)

   Contact stiffness variation range

   The default method of updating normal contact stiffness is suitable for most applications. However, the variational range of the contact stiffness may not be wide enough to handle certain contact situations. In the case of a very small penetration tolerance (FTOLN), a larger normal contact stiffness is often needed. Furthermore, to stabilize the initial contact condition and to prevent rigid body motion, a smaller normal contact stiffness is required.

  默认的法向接触刚度更新方式对于大多数应用来说是合适的。然而，接触刚度的变化范围并不是足够大到处理某些特定问题。在穿透容差非常小的情况下，需要较大的法向接触刚度；而且，为了稳定初始接触状态，并阻止刚体运动，需要较小的法向刚度。

   The allowed contact stiffness variation is intended to enhance stiffness updating when KEYOPT(10) > 0 by calculating an optimal allowable range in stiffness for use in the updating shceme. To increase the stiffness variational range, set KEYOPT(6) = 1 to make a nominal refinement to the allowable stiffness range, or KEYOPT(6) = 2 to make an aggressive refinement to the allowable stiffness range.

  当KEYOPT(10) > 0时，通过刚度更新程序，软件可计算最优容许刚度范围，用来提高刚度更新速度。为了增加刚度变化范围，取KEYOPT(6) = 1可对容许刚度范围进行名义上的细化，取KEYOPT(6) = 2 可对容许刚度范围进行更积极改进。

7、KEYOPT(7)

  Time step control is an automatic time stepping feature that predicts when the status of a contact element will change and cuts the current time step back.

  Use KEYOPT(7) to take one of four actions to control time stepping, where KEYOPT(7) = 0 provides no control (the default), and KEYOPT(7) = 3 provides the most control.

8、KEYOPT(8)

  Asymmetric contact is defined as having all contact elements on one surface and all target elements on the other surface. This is sometimes called "one-pass contact." This is usually the most efficient way to model surface-to-surface contact. However, under some circumstances asymmetric contact does not perform satisfactorily. In such cases, you can designate each surface to be both a target and a contact surface. You can then generate two sets of contact pairs between the contacting surfaces (or just one contact pair; for example, a self-contact case). This is known as symmetric contact (or "two-pass contact"). Obviously, symmetric contact is less efficient than asymmetric contact. However, many analyses will require its use (typically to reduce penetration). Specific situations that require symmetric contact include models where

  If the meshes on both surfaces are identical and sufficiently refined, the symmetric contact algorithm may not significantly improve performance and may, in fact, be more "expensive" in CPU time. In such circumstances, pick one surface to be the target and the other the contact surface.

For a symmetric contact definition, ANSYS may find one side of a contact surface as closed and the other side of the surface as closed. In this case, it can be difficult to interpret the results. The total contact pressure acting on both sides is the average of the contact pressures on each side of the surface.

9、KEYOPT(9)

Effect of initial penetration or gap:

   接触刚度的更新方式

  接触法向和切向刚度有5种更新方式，如下：

·         KEYOPT(10) = 0, the contact stiffness will be updated at each load step if FKN or FKT is redefined by the user. Stiffness and other settings (ICONT, FTOLN, SLTO, PINB, PMAX, and PMIN) are averaged across contact elements in a contact pair. The default contact stiffness is determined by underlying element depth and material properties.

      FKN or FKT 在每个荷载步内更新，刚度值和其他数值均为平均值。

·         KEYOPT(10) = 1 (covers KEYOPT(10) = 0), the normal contact stiffness will be updated at every substep based on the mean stress of the underlying elements from the previous substep and the allowable penetration, FTOLN, except in the first substep of the first load step. The default normal contact stiffness for the first substep of the first load step is the same as described for KEYOPT(10) = 0. If bisections occur in the beginning of the analysis, the normal contact stiffness will be reduced by a factor of 0.2 for each bisection. The tangential contact stiffness will be updated at each iteration based on the current contact pressure, MU, and allowable slip (SLTO).

     FKN 在每个子步内更新， FKT 在每次迭代内更新，刚度值和其他数值均为平均值。

·         KEYOPT(10) = 2 (covers KEYOPT(10) = 1), the normal contact stiffness will be updated at each iteration based on the current mean stress of the underlying elements and the allowable penetration, FTOLN, except in the very first iteration. The default normal contact stiffness for the first iteration is the same as described for KEYOPT(10) = 0. If bisections occur in the beginning of the analysis, the normal contact stiffness will be reduced by a factor of 0.2 for each bisection. The tangential contact stiffness will be updated at each iteration based on the current contact pressure, MU, and allowable slip (SLTO).

      FKN 在每次迭代内更新， FKT 在每次迭代内更新，刚度值和其他数值均为平均值。

·         KEYOPT(10) = 3, same as KEYOPT(10) = 0, except stiffness and settings are not averaged across the contact elements in a contact pair. If bisections occur in the beginning of the analysis, the normal contact stiffness will be reduced by a factor of 0.2 for each bisection.

     同KEYOPT(10) = 0，只是刚度值和其他数值不为平均值。

·         KEYOPT(10) = 4, same as KEYOPT(10) = 1, except stiffness and settings are not averaged across the contact elements in a contact pair.

     同KEYOPT(10) = 1，只是刚度值和其他数值不为平均值。

·         KEYOPT(10) = 5, same as KEYOPT(10) = 2, except stiffness and settings are not averaged across the contact elements in a contact pair.

     同KEYOPT(10) =2，只是刚度值和其他数值不为平均值。

    In most cases we recommend that you use KEYOPT(10) = 2 to allow the program to update contact stiffnesses automatically.

    一般情况下，建议使用KEYOPT(10) = 2 ，允许程序自动更新接触刚度。

 

12、Using KEYOPT(12)

   Use KEYOPT(12) to model different contact surface behaviors.

• KEYOPT(12) = 0 models standard unilateral （单侧的）contact; that is, normal pressure equals zero if separation occurs.

• KEYOPT(12) = 1 models perfectly rough frictional contact where there is no sliding. This case corresponds to an infinite friction coefficient and ignores the material property MU.

• KEYOPT(12) = 2 models no separation contact, in which the target and contact surfaces are tied (although sliding is permitted) for the remainder of the analysis once contact is established.模拟不分离接触状态，一旦接触已经产生，在后续分析中目标单元和接触单元会粘结在一起，但在切向允许滑移

• KEYOPT(12) = 3 models "bonded" contact, in which the target and contact surfaces are bonded in all directions (once contact is established) for the remainder of the analysis.模拟粘结状态，一旦接触产生，在后续分析中接触单元表面将在各个方向均粘结于目标单元。

• KEYOPT(12) = 4 models no separation contact, in which contact detection points that are either initially inside the pinball region or that once involve contact always attach to the target surface along the normal direction to the contact surface (sliding is permitted).模拟粘结状态，在该状态中，接触测点或者在初始阶段就位于乒乓区域，或者在分析中间曾经产生过接触，均沿接触单元的法向粘结于目标单元表面，在切向可以滑移。

• KEYOPT(12) = 5 models bonded contact, in which contact detection points that are either initially inside the pinball region or that once involve contact always attach to the target surface along the normal and tangent directions to the contact surface (fully bonded).模拟粘结状态，在该状态中，接触测点或者在初始阶段就位于乒乓区域，或者在分析中间曾经产生过接触，均沿接触单元的法向和切向完全粘结于目标单元表面。

• KEYOPT(12) = 6 models bonded contact, in which the contact detection points that are initially in a closed state will remain attached to the target surface and the contact detection points that are initially in an open state will remain open throughout the analysis.模拟粘结状态，在该状态中，初始位于接触近区的接触测点在后续分析中依然粘结于目标单元表面；初始远离接触近区的接触测点在后续分析中依然脱离目标单元表面。

   For the no-separation option (KEYOPT(12) = 4) and the bonded-always option (KEYOPT(12) = 5), a relatively small PINB value (pinball region) may be used to prevent any false contact. For these KEYOPT(12) settings, the default for PINB is 0.25 (25% of the contact depth) for small deformation analysis (NLGEOM,OFF) and 0.5 (50% of the contact depth) for large deformation analysis (NLGEOM,ON). (The default PINB value may differ from what is described here if CNOF is input. See Using PINB for more information.)

   For the bonded-initial option (KEYOPT(12) = 6), a relatively large ICONT value (initial contact closure) may be used to capture the contact. For this KEYOPT(12) setting, the default for ICONT is 0.05 (5% of the contact depth) when KEYOPT(5) = 0 or 4.

二、接触单元实常数

• R1 and R2 define the target element geometry.

• FKN defines a normal contact stiffness factor.

• FTOLN is a factor based on the thickness of the element which is used to calculate allowable penetration.

• ICONT defines an initial closure factor (or adjustment band).

• PINB defines a "pinball" region.

• PMIN and PMAX define an allowable penetration range for initial penetration.

• TAUMAX specifies the maximum contact friction.

• CNOF specifies the positive or negative offset value applied to the contact surface.

• FKOP specifies the stiffness factor applied when contact opens or the damping coefficient for standard contact.

• FKT specifies the tangent contact stiffness factor.

• COHE specifies the cohesion sliding resistance.

• TCC specifies the thermal contact conductance coefficient.

• FHTG specifies the fraction of frictional dissipated energy converted into heat.

• SBCT specifies the Stefan-Boltzmann constant.

• RDVF specifies the radiation view factor.

• FWGT specifies the weight factor for the distribution of heat between the contact and target surfaces for thermal contact or for electric contact.

• ECC specifies the electric contact conductance or capacitance per unit area.

• FHEG specifies the fraction of electric dissipated energy converted into heat.

• FACT specifies the ratio of static to dynamic coefficients of friction.

• DC specifies the decay coefficient for static/dynamic friction.

• SLTO controls maximum sliding distance when MU is nonzero and the tangent contact stiffness (FKT) is updated at each iteration (KEYOPT(10) = 2).

• TNOP specifies the maximum allowable tensile contact pressure.

• TOLS adds a small tolerance that extends the edge of the target surface.

• MCC specifies the magnetic contact permeance (3-D only).

1）PMIN and PMAX

  define an allowable penetration range for initial penetration.

   Use real constants PMIN and PMAX to specify an initial allowable penetration range. When either PMAX or PMIN is specified, ANSYS brings the target surface into a state of initial contact at the beginning of the analysis 。If the initial penetration is larger than PMAX, ANSYS adjusts the target surface to reduce penetration. If the initial penetration is smaller than PMIN (and within the pinball region), ANSYS adjusts the target surface to ensure initial contact. Initial adjustment for contact status is performed only in translational modes.

ANSYS工程结构数值分析p442

接触单元不得穿透目标面，但目标单元可以穿适接触面。对于刚体—柔体接触，目标面总是刚体表面，而接触面总是柔体表面。对于柔体—柔体接触，选择不同的接触面或目标面可能会引起不同的穿透旦，从而影响求解结果，可根据“凸密柔高小为接触面”的原则确定，即：

凸面定义为接触面，平面或凹面为目标面；
较密网络的面定义为接触面，较粗网格的面为目标面；
较柔(软)的面定义为接触面，较刚(硬)的面定义为目标面
高阶单元定义为接触面，低阶单元为目标面；
较小的面定义为接触面，较大的面为目标面。
 

2）接触性能说明 摘自 ANSYS非线性分析指南 接触分析

   更多内容参考：http://www.docin.com/p-229651760.html