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 stiffness variation range (KEYOPT(6))
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)
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。
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.
KEYOPT(7) = 0: No control. The time step size is unaffected by
the prediction. This setting is appropriate for most analyses when
automatic time stepping is activated and a small time step size is
allowed.
KEYOPT(7) = 1: Time step size is bisected if too much
penetration occurs during an iteration, or if the contact status
changes dramatically.
KEYOPT(7) = 2: Predict a reasonable increment for the next
substep.
KEYOPT(7) = 3: Predict a minimal time increment for the next
substep.
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
The distinction between the contact and target surfaces is not
clear.
Both surfaces have very coarse meshes. The symmetric contact
algorithm enforces the contact constraint conditions at more
surface locations than the asymmetric contact algorithm.
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.
Effect of initial penetration or
gap:
0 --
Include both initial geometrical
penetration or gap and offset
1 --
Exclude both initial geometrical
penetration or gap and offset
2 --
Include both initial geometrical
penetration or gap and offset, but with ramped effects
3 --
Include offset only (exclude
initial geometrical penetration or gap)
4 --
Include offset only (exclude
initial geometrical penetration or gap), but with ramped
effects
KEYOPT(9) provides the following
capabilities:
To include initial penetration
from both geometry and contact surface offset, set KEYOPT(9) = 0.
This is the default.
To ignore initial penetration from
both effects, set KEYOPT(9) = 1. When KEYOPT(12) = 4 or 5, this
setting for KEYOPT(9) will also ignore the initial force in
open-gap springs, thus creating an initially "perfect" contacting
surface having no initial forces acting across the contact
interface.
To include the defined contact
surface offset (CNOF) but ignore the initial penetration due to
geometry, set KEYOPT(9) = 3. When KEYOPT(12) = 4 or 5, this setting
for KEYOPT(9) will also ignore the initial force in open-gap
springs, thus creating an initially "perfect" contacting surface
having no initial forces acting across the contact
interface.
For problems
such as an interference fit, over-penetration is expected. These
problems often have convergence difficulties if the initial
penetration is step-applied in the first load step. You may
overcome convergence difficulties by ramping the initial
penetration over the first load step, see Figure 3.20: "Ramping Initial
Interference". The
following KEYOPT(9) settings provide ramped
capabilities:
To ramp the total initial
penetration (CNOF + the offset due to geometry), set KEYOPT(9) =
2.
To ramp the defined contact
surface penetration, but ignore the penetration due to geometry,
set KEYOPT(9) = 4.
For both of the above KEYOPT(9)
settings, you should also set KBC,0 and not specify any external loads in the
first load step. Also, be sure that the pinball region is big
enough to capture the initial interference.
10、 KEYOPT(10)
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).
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