abaqus系列之接触

接触笔记

1、Definingcontact pairs in ABAQUS/Standard

Afterthe selection of contact pair surfaces, three key factors must bedetermined when creating a contact formulation:
⑴the contact discretization;
⑵the tracking approach; and
⑶the assignment of “master” and “slave” roles to therespective surfaces.

1.1the contact discretization
ABAQUS/Standardoffers two contact discretization options: a traditional“node-to-surface” discretization and a true “surface-to-surface”discretization.

1.1.1Node-to-surface contact discretization
Traditionalnode-to-surface discretization has the following characteristics:
⑴The slave nodes are constrained not to penetrate into the mastersurface; however, the nodes of the master surface can, in principle,penetrate into the slave surface
⑵The contact direction is based on the normal of the master surface.

⑶ Theonly information needed for the slave surface is the location andsurface area associated with each node; The direction of the slavesurface normal and slave surface curvature are not relevant.Thus, theslave surface can be defined as a group of nodes—anode-based surface.

⑷ Node-to-surface discretization is available even if anode-based surface is not used in the
contact pair definition

Fig.1Node-to-surface contact discretization
1.1.2Surface-to-surface contact discretization
Tooptimizestress accuracy, surface-to-surface discretization considers theshape of both the slave and master surfaces in the region of contactconstraints.

Surface-to-surface discretization has the following keycharacteristics:
⑴ Contact conditions are enforced in anaverage sense over the slave surface, rather than at discrete points(such as at slave nodes, as in the case of node-to-surfacediscretization). Therefore, some penetration may be observed atindividual nodes; however, large, undetected penetrations of masternodes into the slave surface do not occur with this discretization. ⑵Surface-to-surface discretization is not applicable if a node-basedsurface is used in the

contact pair definition.

在某一个迭代步中,面对面的接触计算成本一般较点对面的接触的计算成本高,但多数情况下这个成本不会高很多,只有在下列情况下才会让计算成本急剧增大:
⑴模型的绝大部分区域被包含于接触中;
⑵当主动面比从属面网格划分还要精细时;
⑶Multiple layers of shells are involved in contact, such that themaster surface of one contact pair acts as the slave surface ofanother contact pair.

尽管如此,但点对面的接触需要花费更多的迭代步才能达到数值稳定,从某种意义上来说,在一个分析步中,无法判定到底是用点对面接触还是面对面接触计算成本低.

1.2 Contact tracking approaches
In ABAQUS/Standard there aretwo tracking approaches to account for the relative motion of the twosurfaces forming a contact pair in mechanical contactsimulations:
⑴ The finite-sliding tracking approach
⑵The small-sliding tracking approach
1.3 Fundamental choicesaffecting the contact formulation
Your choice of contactdiscretization and tracking approach have considerable impact on ananalysis. In addition to the qualities already discussed, certaincombinations of discretizations and tracking approaches have theirown characteristics and limitations associated with them. Thesecharacteristics are summarized in Table 1. You should also considerthe solution costs associated with the various contactformulations

Table 1 Comparison of contactformulation characteristics

1.4选择主动面和从属面的几个原则
⑴Analytical rigid surfaces and rigid-element-based surfaces mustalways be the master surface.

⑵A node-based surface can act only as a slave surface and always usesnode-to-surface contact.

⑶Slave surfaces must always be attached to deformable bodies ordeformable bodies defined as rigid.

⑷ Both surfaces in a contact pair cannot be rigid surfaces withthe exception of deformable surfaces defined asrigid 一般来说,当定义两个基于单元的面作为解除对作用面时,当存在一个较小的面和一个较

大的面时，一般将较小的面定义为从属面。当两个面大小接近时，选取较“硬”的面或单元

与点对面接触相比，面对面接触中主动面和从属面的选取，对计算结果的影响并不是很

大。但是，当错误的将网格粗糙的面定义为从属面时，此时也许会引起计算成本的急剧增加。

1.5定义接触对
为了定义一个接触对，必须指定一对接触面或者一个自接触的面，一个contactformulation。每一个接触对可以定义不同的作用面性质。

1.5.1Defining contact between two separate surfaces
Whena contact pair contains two surfaces, the master and slave surfacesarenot allowed toincludeany of the same nodes andyou must choose which surface will be the slave and which will be themaster.

ABAQUS/Standard定义接触默认采用的是有限滑移、点对面接触。如果定义的是小滑移，默认的也吃采用点对面接触。

1.5.2 用对称的主从接触对提高接触模拟精度
对于点对面接触，主动面上的节点很容易penetrate到从属面上去，此时，提高从属面
上单元的网格划分精度，有助于减少这样的刺入，提高运行速度。才外，让两个面都是基于
单元定义时，可以用symmetricmaster-slave method。To use thismethod, define two contact
pairs using the same two surfaces,but switch the roles of master and slave surface for the two
contactpairs. This method causes ABAQUS/Standard to treat each surface as amaster surface
and, thus, involves additional computationalexpense because contact searches must be conducted twice for the samecontact pair. The increased accuracy provided by this method must be
compared to the additional computational cost. surface_1,surface_2
surface_2, surface_1
1.5.2.1对称主从接触结果的解释
对于单一的主从接触，输出结果仅对从属面输出。而对称主从接触，每一个面都是从属

面，均输出计算结果。问题在于，两个从属面上的接触压力并不是相对的，也并不一定

相等，总的接触压力为两个面上的接触压力之和。

1.6给接触对赋予接触面定义
命令语句如下：
*CONTACTPAIR, INTERACTION=interaction_property_name *SURFACEINTERACTION, NAME=interaction_property_name 1.7选择接触面
除了小滑移、面对面接触之外，主动面必须为单一面。

三维梁单元、桁架单元，不能用来作为主动面，但却可以定义为从属面。二维梁单元、

桁架单元可以定义为主动面或从属面。

in ABAQUS/Standard. Edge-based surfaces on three-dimensional shellelements cannot be used in a contact analysis

1.8 结果输出

Youcan write the contact surface variables associated with theinteraction of contact pairs to the ABAQUS/Standard data (.dat),results (.fil), and output database (.odb) files. Allcontact pairresultsare given at the constraint points of the slave surface.The constraint points correspond to the slave nodes except in thecase of finite-sliding, surface-to-surface contact, in which caseeach slave facet contains multiple constraint points.

Youcan:
⑴request output associated with a given contact pair;
⑵request output associated with a given slave surface, includingcontributions from all of the contact pairs to which the slavesurface belongs; and
⑶limit the output by specifying a node set containing a subset of thenodes on the slave surface except in the case of finite-sliding,surface-to-surface contact.

下面为常用的接触输出语句：
*CONTACTPRINT, SLAVE=SURFNAME, MASTER=SURFNAME, NSET=NODESET以下为输出到.dat文件的结果形式：

对于结果的解释：
⑴This output request creates a table of output variables in theprinted data (.dat) file. Each
row of the table corresponds toa slave node in node set SNODES. The first column of the tableidentifies the slave node for that row. Because this is a mechanicalcontact simulation, the second column specifies the contact status atthe slave node. Since the contact property definition includes
⑵The OP status indicates that the slave node is not in contact withthe master surface. In
the sample output above, node 101 isopen and, consequently, the contact pressure variable
CPRESS iszero. The COPEN variable reports that this node is 0.66 length unitsaway from the
master surface.

⑶ TheST status indicates that the slave node is in contact with the mastersurface and is “sticking.” The frictional shear stress acting atthe node is below the critical shear stress , where p is the value ofcontact pressure shown under CPRESS. In the sample output above, node102 is sticking since the frictional shear stress CSHEAR1 is belowthe critical value of 2. (0.4 × 6.59).

The CSLIP1 variable is the total accumulated (integrated) slip at theslave node. The negative magnitude of CSLIP1 indicates that the nodehas moved in the negative first slip direction on BSURF. Accumulatedslip and slip directions are discussed in more detail below in“Output of tangential motion of the surfaces.”
⑷ The SLstatus indicates that the slave node is in contact with the mastersurface and it is sliding—the frictional shear stress is at thecritical shear stress ==. In the sample output above, node 103 issliding, and the frictional shear stress CSHEAR1 is equal to thefriction limit 1.73 (0.4 × 4.32).

⑸ In the absence of frictional properties when a slave node is incontact with the master

surface,its status reads CL for “closed.”

2、Modelingcontact interference fits in ABAQUS/Standard

2.1Resolving excessive initial overclosures

3、ABAQUS/Standard中接触模拟的常见错误

3.1解决初始接触的错误

3.1.1消除初始的过盈接触和张开
当两个不同Part的面接触时，由于单元网格不一致，很可能会在两个面之间留下小的gap或penetration。默认的，ABAQUS/Standard会将初始penetration当成interferencefits，并会相应地在接触一开始的时候处理掉，见“Modelingcontact interference fits in ABAQUS/Standard,” Section 29.2.4.

以保证接触刚开始时计算中没有计算中必须通过调整从属面位置来提高接触模拟精度，
penetration。当初始的clearance或overclosure与单元典型尺寸相比较小时，在小滑移接触模

拟中，你可以精确的指定clearance或overclosure，以消除初始的过盈接触和张开，见“Adjustingthe surfaces in a contact pair” in “Adjusting initial surfacepositions and specifying initial clearances in ABAQUS/Standardcontact pairs,” Section 29.2.5.

3.1.2消除刚体位移

的约束时，将会引起刚体位移，从何会引起数值奇异问题和大位移（“Numericalsingularity” warning messages and very largedisplacements）
动力分析中刚体位移不会引起数值奇异问题， 当一个体没有给予足够

29.2.12.

3.1.3解决过大的interferencefits
ABAQUS/Standardinterprets initial overclosures as interference fits, which it triesto resolve in the first increment of a step. If the initialoverclosures are an unintended result of mesh discretization, youshould use one of the methods discussed above to remove theoverclosures. In some cases the interference fit may be intended buttoo large for ABAQUS/Standard to resolve in a single increment. Inthis situation you should redefine the interference fit to allowresolution of the overclosures over multiple increments. See“Modeling contact interference fits in ABAQUS/Standard,” Section29.2.4, for more information.

3.2低精度表面（Poorlydefined surfaces）
粗糙的网格、不合适的单元和过度扭曲的表面形状，均可导致接触计算的中止。

3.2.1主控面定义重复节点
三维有限滑移接触分析中，应避免用相同坐标的节点定义不同的surface，这样的定义容易引起接缝或裂缝（seamor crack）。

开始时，虽然从CAE默认的视角来看，这个定义的面仍然是一个连续有笑的面，但当接触计算从属面上的点很可能滑落到这个seamor crack 中去，使得从属面上的某些节点被黏

附在主控面后面，从而引起计算的中止。类似的情况也会出现在finite-sliding,

surface-to-surfacecontact。

3.2.2避免沿表面边界的接触问题
有限滑移接触分析中，主控面必须定义得足够大，以至于可计算接触分析中所用可能存
在的位移。如果主控面定义不恰当，从属面上的从属点很可能在迭代计算过程中滑落到主控
面后面，引起振颤问题（chattering）
。 当计算过程中出现振颤问题时，msg文件中会有一个或几个从属点不停的循环出现闭合
和张开，此时，可在关键词*ContactPair 中实用参数Extension Zone来扩大主控面的尺寸，具体见“Extendingmaster surfaces and slide lines,” Section 29.2.8.

3.2.3面单元网格粗糙
如果面单元网格太粗糙，将会发生以下几个问题：
⑴主控面刺入从属面过多
在点对面接触中，当从属面单元网格过于粗糙，以至于主控面会很严重的刺入到从属面中去时，将会引起错误，此时应细化从属面单元网格。

虽然这种接触模式会有效抵制主控面刺入到从属面中，但当从属面网对于面对面接触，
格比主控面还要粗糙时，此时的计算成本将会变得非常大。

3.3接触模拟中的过多迭代

ABAQUS/Standard提供了一些方法，可以调整接触模拟迭代过程，以提高计算效率，

并不影响计算精度。

3.3.1Converting severe discontinuity iterations in weakly determinedcontact conditions

ABAQUS/Standard对规则平稳的迭代和严重不连续迭代加以区分。最普遍的严重不连

续现象有张开－闭合转变和静止－滑移的摩擦面行为转变。

在两种情形下，默认的算法会导致收敛问题或过多的小增量步。第一种情况是接触定义

不明确。例如，在冲压问题中，冲头与薄片在边界上发生接触，但冲头中心处定义并不明确。

典型的，该点处于接触状态时，接触压力会很小 当该点没有处于接触状态时，其张开距离

ABAQUS会经过多次迭代来判定其初始接触条件（因为每一次迭代会有不同的接触点其接 第二种情况是大接触问题，即一个模型中存在很多接触点（或接触对） 。在此种情况下，也会很小。这就会引起振颤问题。

就会放弃当前增量步，而尝试一个更小的增量步。对于有限滑移、面对面接触和几何线性小

滑移分析，并没有严格的hcrit距离规定。

默认情况下，hcrit等于通过单元表面几何体的半径。在下面几类情形中，有必要修改

hcrit距离值：

⑴主控面高度扭曲。如图，在迭代过程中，从属面节点b有可能落入到主控面，相当

于从属节点penetration主控面，overclosure即h，小于hcrit。此时迭代过程会尝试将节

点b移动到主控面上的投影c点处。为了避免此类迭代，可尝试指定一个较小的hcrit，强迫

ABAQUS/Standard 放弃当前操作，而尝试一个较小的增量步。

⑵ a node-based surface在接触面中存在时，ABAQUS/Standard将会无法计算得到一个合理的hcrit。当存在其它面接触队时，ABAQUS/Standard采用从属面上单元的averagedimension h
crit。如果没有其它接触对存在，ABAQUS/Standard将采用整体模型的acharacteristic 作为elementdimension。

⑶从属面形状变化剧烈
⑷软接触中允许较大的penetration。

命令语句如下：
hcrit*CONTACTPAIR, HCRIT=

4、Extendingmaster surfaces and slide lines

延伸主控面或滑移线，可以：
⑴在有限滑移问题中，可以避免从属面节点落入或滑道主控面背后；
⑵在小滑移问题中，当主控面与从属面没有相接时，可以保证从属面节点能在主控面
上找到一个投影点；
⑶能避免一些接触模型中数值计算问题；
⑷不能用来代替正确的接触；
⑸不能用来减少接触面下的单元数目（surfacebased on element）
⑹仅适用于点对面接触（node-to-surfacediscretization）

Fornode-to-surface contact you can specify the size of the extensionzone, e, as a fraction of the end segment or facet edge length (seeFigure 29.2.8–2). If e is set to zero, ABAQUS will not extend theends. The value given must lie between 0.0 and 0.2. Thedefault value is 0.1for node-to-surface contact; surface extensions are not available forsurface-to-surface contact。

命令语句如下：
*CONTACT PAIR, SMALL SLIDING, EXTENSION ZONE=e