ANSYS中单元COMBIN39能否用于模拟物体间的接触？

  一、结论

  COMBIN39可用于模拟物体间切向的粘结滑移，只能近似模拟法向仅能压不能拉的特性。该单元的特性为仅能受拉不能受压（更适用于弹簧和拉索）。当的确需要模拟法向接触性能时，建议使用LINK180（ offers compression-and-tension, tension-only, and compression-only options），但LINK180的长度不能为零。有时接触共面或线，无长度，使用LINK180模拟法向非常不方便。可用COMBIN39近似模拟法向，手工输入第三象限受压区的力-变形曲线，第一象限只需一个点即可，而且其斜率要非常小，表明承受的拉力很小。

  二、ANSYS 16.0版本HELP介绍

  1、COMBIN39：nonlinear spring

   COMBIN39 is a unidirectional(单向) element with nonlinear generalized force-deflection（广义力-变形） capability that can be used in any analysis. The element has longitudinal or torsional （纵向或扭转）capability in 1-D, 2-D, or 3-D applications. The longitudinal option is a uniaxial tension-compression element with up to three degrees of freedom at each node: translations in the nodal x, y, and z directions. No bending or torsion is considered. The torsional option is a purely rotational element with three degrees of freedom at each node: rotations about the nodal x, y, and z axes. No bending or axial loads are considered.

The element has large displacement capability for which there can be two or three degrees of freedom at each node.

   2、 COMBIN39 Input Data

    The element is defined by two (preferably coincident) node points and a generalized force-deflection curve. The points on this curve (D1, F1, etc.) represent force (or moment) versus relative translation (or rotation) for structural analyses, and heat (or flow) rate versus temperature (or pressure) difference for a thermal analyses. The loads should be defined on a full 360° basis for an axisymmetric analysis.

The force-deflection curve should be input such that deflections are increasing from the third (compression) to the first (tension) quadrants（力-变形数据应从第三象限的受压区递增到第一象限的受拉区）. Adjacent deflections should not be nearer than 1E-7 times total input deflection range（相邻变形之差不能太小）. The last input deflection must be positive. Segments tending towards vertical should be avoided（线段尽量避免垂直）. If the force-deflection curve is exceeded, the last defined slope is maintained, and the status remains equal to the last segment number. If the compressive region of the force-deflection curve is explicitly defined (and not reflected), then at least one point should also be at the origin (0,0) and one point in the first (tension) quadrant（若是第三象限的受压区的力-变形曲线是手工输入的话，则原点和第一象限必须至少各有一个点）. If KEYOPT(2) = 1 (no compressive resistance), the force-deflection curve should not extend into the third quadrant. Note that this tension-only behavior can cause convergence difficulties similar to those that can be experienced by contact elements. See the Contact Technology Guide, as well as various contact element descriptions, for guidelines on overcoming convergence difficulties. Note that the number of points defining the loading curve (20 points) can be effectively doubled by using the reflective option.

Slopes of segments may be either positive or negative, except that the slopes at the origin must be positive （原点处的斜率必须为正，其他处的线段斜率可正可负）and, if KEYOPT(1) = 1, slopes at the ends may not be negative. Also, if KEYOPT(1) = 1, force-deflection points may not be defined in the second or fourth quadrants and the slope of any segment may not be greater than the slope of the segment at the origin in that quadrant.

Alternately, the element may have more than one type of degree of freedom (KEYOPT(4) > 0). The two nodes defining the element should not be coincident, since the load direction is colinear with the line joining the nodes. The longitudinal option (KEYOPT(4) = 1 or 3) creates a uniaxial tension-compression element with two or three translational degrees of freedom at each node. No bending or torsion is considered. 

KEYOPT(2)

Element behavior under compressive load:

 3、COMBIN39不支持单元生死

       Special Features

Large displacement

Linear perturbation

Nonlinearity

Stress stiffening

注明：9.1. Elements Supporting Birth and Death：If an element supports birth and death, it is indicated in the “Special Features” section of the documentation for that element.

  三、应用

  1、ANSYS help算例  

   2、参考  博士论文 2002 杨勇型钢混凝土粘结滑移基本理论及应用研究_杨勇.caj  p132 1.4.2粘结滑移本构关系的应用