的调整接触厚度来补偿。因此在任何分析的时间点，如果检测到突然的穿透，程序不会施加任何很大的力也不会移动任何节点。但接触力会阻止进一步的穿透。
English Version:
Provided herein are some very brief notes on LS-DYNA contact. Not all thecontact types or contact options are discussed.
[For a comprehensive review of contact in LS-DYNA, see the four-part series on contact modeling in the archived FEA information Newsletters available at…www.feapublications.com The four parts of the series are in the August, September, October, and December 2001 newsletters.]
Automatic vs. Non-automatic:
Automatic contacts are recommended for most explicit simulations. Non-automatic contacts (in which contact orientation is important) are sometimes used for metal forming simulations where the geometries are very straightforward and contact surface orientation can be reliably established before the simulation is conducted. Non-automatic contacts are generally recommended for implicit simulations.
TYPES:
Type 13 contact (contact_automatic_single_surface) is a single surface contact (no master surface is defined) that always considers shell thickness and has no orientation. Thus it‘s necessary that shell surfaces be modeled with at least a small gap between them. To avoid initial penetrations, the gap should be no less than the average thickness of the two shells potentially in contact. No gap is necessary between solid elements. The contact searching algorithm for type 13 contact is more complex than for type 3 (contact_surface_to_surface) or a3 (contact_automatic_surface_to_surface), i.e., type 13 can handle situations such as shell edge to surface, and to some extent, beam to shell surface. As with any single surface contact type, resultant forces are not directly retrievable in the RCFORC file; one must define a contact_force_transducer_penalty in order to retrieve the contact forces. The article ―contact.13vs26″ provides additional information on contact_automatic_single_surface and contrasts it to contact_automatic_general.
Type 3 contact (contact_surface_to_surface) contact is a surface-to-surface (two-way) contact where shell thickness consideration can either be turned on or off either in *contact or *control_contact (*contact has priority). The orientation of the contact segments is important with this contact type as the shell only looks in one direction for potential contact.
In a two-way contact such surface_to_surface, nodes on the slave side are first checked for penetration thru the master surface and then master nodes are checked for penetration thru the slave surface. The exception is this approach is when segment-based contact is invoked by setting SOFT=2.
Contact type a3 has no orientation (a shell looks for potential contact from either side of the shell midplane) and always considers shell thickness, so in this regard, it‘s quite similar to a type 13 contact.
Table 6.1 in the 950 Keyword User‘s Manual lists the maximum penetration d that defines when a penetrating node is released from contact consideration. This distance d is different for a type 3 contact than for a type 13 contact.
Some notes on contact parameters: SOFT
SOFT is the first parameter on Optional Card A of *contact….The default value of SOFT is 0. SOFT=1 is more or less the same as SOFT=0. EXCEPT in the way the contact stiffness is determined. SOFT=2 is a radical departure from SOFT=0, both in the way contact stiffness is determined but also in the manner that the search for penetration is conducted. SOFT=2 invokes what is called ―segment-based contact‖. For notes regarding contact with SOFT= 1 and 2, see the articles ―contact.soft1″ and ―contact.soft2″, respectively.
IGNORE
At any point during the simulation, if a node is suddenly found to be below the surface (say, it was moving very fast and wasn‘t detected before penetration), the old style (IGNORE=0) algorithm just moves the node to the master surface without applying any forces (we term this ―shooting node logic‖). If the shooting node logic is turned off (SNLOG=1), then you get large forces suddenly appearing, and negative contact energy. If IGNORE is set to 1 then the shooting node logic flag SNLOG has no affect. Rather the amount of sudden penetration is noted and compensated for by adjusting the contact thickness locally. So at any time during the simulation, if a sudden penetration is detected, the program doesn‘t apply any large forces nor are any nodes moved. Contact forces, however, will resist FURTHER penetration. jpd 12/2002 revised 4/2003
revised 9/2003 auto vs. non-auto
12.Contact Soft 1 接触Soft=1
通过在*Contact卡的选项卡A中设置Soft=1所调用接触方程与缺省的罚函数接触方程的区别不如Soft=2接触算法大。除了在确定接触刚度方面不一样外，Soft=1和Soft=0是差不多的。Soft=1方法基于考虑稳定性的时间步来计算接触刚度。换句话说，你可以把soft=1的接触看作是一组简单弹簧质量系统，其中每一个都有与实际仿真分析中用到的时间步相匹配的Courant 时间步。对软材料与刚硬材料的接触或两个接触面的网格密度不一致情况，Soft=1通常比Soft=0更有效。
当Soft=1时，采用通过soft=0 & soft=1计算得到的最大的刚度值。因此如果soft=0刚度更大，减小SOFSCL将没有效果。
K = max(SLSFAC*SFS*k0, SOFSCL*k1) 其中：
k 是罚刚度
SLSFAC是用户在*Control_contact中输入的选项 SFS 是用户在*Contact卡3中输入的选项 SOFSCL 是用户在*Contact选项卡A中输入的值 k0 是从材料体积模量和单元尺寸计算得到的刚度 k1 是从节点质量和计算时间步计算得到的刚度
注意：对于双面接触，像*contact_automatic_surface_to_surface，在上面的方程中用SFM替换SFS(在*contact卡3中输入)
English Version:
The contact formulation invoked by setting Soft=1 on optional card A of *contact is not so radical a departure from the default penalty contact formulation (Soft=0) as the Soft=2 contact formulation. Soft=1 is more or less the same as Soft=0 EXCEPT in the way the contact stiffness is determined. Soft=1 calculates contact stiffness based on stability considerations taking into account the timestep. In other words, you can liken Soft=1 contact to a group of simple spring-mass systems, each with a Courant timestep matched to the actual timestep used in the simulation. Soft=1 will generally be more effective than Soft=0 for soft materials contacting stiff materials or where the mesh densities of the two contacting surfaces are dissimilar.
When SOFT=1, we use the max of the stiffness as calculated by soft=0 and soft=1. Therefore reducing SOFSCL has no effect if the soft=0 stiffness is larger.
k = max(SLSFAC*SFS*k0, SOFSCL*k1)
where k is the penalty stiffness SLSFAC is user input on *CONTROL_CONTACT SFS is user input on *CONTACT card 3 SOFSCL is user input on *CONTACT optional card A k0 is the stiffness calculated from material bulk modulus and element dimensions k1 is the stiffness calculated from nodal masses and the solution time step.
Note: For two way contact like *CONTACT_AUTOMATIC_SURFACE_TO_SURFACE, replace SFS with SFM
(user input on *CONTACT card 3) in the above equation.
13.LS-DYNA中夹层板(sandwich)的模拟
在LS-DYNA中夹层板(sandwich plate)通常有三种方式来模拟
1. 采用几层体单元来模拟，当板比较薄，沿厚度方向单元尺寸比较小，时间步很难提高，
2. 中间的夹层材料用体单元模拟，外面的包层材料用shell单元模拟，在体单元和壳单元之间用Contact_tied (_offset)卡建立粘接关系，
3. 用一层壳单元来模拟。对材料*Mat_composite_damage和*mat_enhanced_composite_damage打开层板理论选项(*control_shell卡LAMSHT项设置为1)
对最后一种方式，需要定义*intergration_shell卡片。例如下面这个层合板：
*INTEGRATION_SHELL 1,8,0
-.9722, .02778, 1 -.9167, .02778, 1 -.6667, .22222, 2 -.2222, .22222, 2 .2222, .22222, 2 .6667, .22222, 2 .9167, .02778, 3 .9722, .02778, 3 *PART material 1 1 11