4.40 COMBIN40 Combination

Figure 4.40-1 COMBIN40 Combination Element

4.40.1 Input Data

If the element is used in an axisymmetric analysis, these values (except GAP) should be on a full 360° basis. A spring constant of 0.0 (for either K1 or K2, but not both) or a damping coefficient of 0.0 will remove these capabilities from the element. The mass, if any, may be applied at node I or node J or it may be equally distributed between the nodes.

The gap size is defined by the fourth element real constant. If positive, a gap of this size exists. If negative, an initial interference of this amount exists. If GAP=0.0, the gap capability is removed from the element. The FSLIDE value represents the absolute value of the spring force that must be exceeded before sliding occurs. If FSLIDE is 0.0, the sliding capability of the element is removed, that is, a rigid connection is assumed.

A "break-away" feature is available to allow the element stiffness (K1) to drop to zero once a limiting force |FSLIDE| has been reached. The limit is input as -|FSLIDE| and is applicable to both tensile breaking and compressive crushing. A "lock-up" feature may be selected with KEYOPT(1). This feature removes the gap opening capability once the gap has closed.

The force-deflection relationship for the combination element is as shown in Figure 4.40-2 (for no damping). If the initial gap is identically zero, the element responds as a spring-damper-slider element having both tension and compression capability. If the gap is not initially zero, the element responds as follows: when the spring force (F1+F2) is negative (compression), the gap remains closed and the element responds as a spring-damper parallel combination. As the spring force (F1) increases beyond the FSLIDE value, the element slides and the F1 component of the spring force remains constant. If FSLIDE is input with a negative sign, the stiffness drops to zero and the element moves with no resisting F1 spring force. If the spring force becomes positive (tension), the gap opens and no force is transmitted. In a thermal analysis, the temperature or pressure degree of freedom acts in a manner analogous to the displacement.

The element has only the degrees of freedom selected with KEYOPT(3). The KEYOPT(3)=7 and 8 options allow the element to be used in the thermal analysis (with thermal equivalent real constants).

A summary of the element input is given in Table 4.40-1. A general description of element input is given in Section 2.1.

Table 4.40-1 COMBIN40 Input Summary

Element Name	COMBIN40
Nodes	I, J
Degrees of Freedom	UX, UY, UZ, ROTX, ROTY, ROTZ, PRES, or TEMP (depending on KEYOPT(3) below)
Real Constants	K1, C, M, GAP, FSLIDE, K2 Note-If GAP is exactly zero, the interface cannot open. If GAP is negative, there is an initial interference. If FSLIDE is exactly zero, the sliding capability is removed. If FSLIDE is negative, the break-away feature is used.
Material Properties	None
Surface Loads	None
Body Loads	None
Special Features	Nonlinear (unless both GAP and FSLIDE equal zero), Adaptive descent
KEYOPT(1)	0 - Standard gap capability 1 - Gap remains closed after initial contact (lock-up)
KEYOPT(3)	0, 1 - UX (Displacement along nodal X axes) 2 - UY (Displacement along nodal Y axes) 3 - UZ (Displacement along nodal Z axes) 4 - ROTX (Rotation about nodal X axes) 5 - ROTY (Rotation about nodal Y axes) 6 - ROTZ (Rotation about nodal Z axes) 7 - PRES 8 - TEMP
KEYOPT(4)	0 - Produce element printout for all status conditions 1 - Suppress element printout if gap is open (STAT=3)
KEYOPT(6)	0 - Mass at node I 1 - Mass equally distributed between nodes I and J 2 - Mass at node J

4.40.2 Output Data

• nodal degree of freedom results included in the overall nodal solution
• additional element output as shown in Table 4.40-2

STAT describes the status of the element at the end of this substep for use in the next substep. If STAT=1, the gap is closed and no sliding occurs. If STAT=3, the gap is open. If STAT=3 at the end of a substep, an element stiffness of zero is being used. A value of STAT=+2 indicates that node J moves to the right of node I. STAT=-2 indicates a negative slide. A general description of solution output is given in Section 2.2. See the ANSYS Basic Analysis Procedures Guide for ways to view results.

Figure 4.40-2 COMBIN40 Behavior

The following notation is used in Table 4.40-2:

A colon (:) in the Name column indicates the item can be accessed by the Component Name method [ETABLE, ESOL] (see Section 2.2.2). The O and R columns indicate the availability of the items in the file Jobname.OUT (O) or in the results file (R), a Y indicates that the item is always available, a number refers to a table footnote which describes when the item is conditionally available, and a - indicates that the item is not available.

Table 4.40-2 COMBIN40 Element Output Definitions

Name	Definition	O	R
EL	Element number	Y	Y
NODES	Nodes - I, J	Y	Y
CENT: X, Y, Z	Center location XC, YC, ZC	-	Y
SLIDE	Amount of sliding	Y	Y
F1	Force in spring 1	Y	Y
STR1	Relative displacement of spring 1	Y	Y
STAT	Element status	1	1
OLDST	STAT value of the previous time step	1	1
UI	Displacement of node I	Y	Y
UJ	Displacement of node J	Y	Y
F2	Force in spring 2	Y	Y
STR2	Relative displacement of spring 2	Y	Y

1. If the value of STAT is:
1 - Gap closed (no sliding)
2 - Sliding right (node J moving to right of node I)
-2 - Sliding left (node J moving to left of node I)
3 - Gap open

Table 4.40-3 lists output available through the ETABLE command using the Sequence Number method. See Chapter 5 of the ANSYS Basic Analysis Procedures Guide and Section 2.2.2.2 of this manual for more information. The following notation is used in Table 4.40-3:

Name - output quantity as defined in the Table 4.40-2

Item - predetermined Item label for ETABLE command

E - sequence number for single-valued or constant element data

Name	Item	E
F1	SMISC	1
F2	SMISC	2
STAT	NMISC	1
OLDST	NMISC	2
STR1	NMISC	3
STR2	NMISC	4
UI	NMISC	5
UJ	NMISC	6
SLIDE	NMISC	7

4.40.3 Assumptions and Restrictions

The real constants for this element are not allowed to be changed from their initial values. Also, the element may not be deactivated with the EKILL command. The nonlinear options of the element operate only in the static and the nonlinear transient dynamic analyses. If used in other analysis types, the element maintains its initial status throughout the analysis. A gap condition capability is also included in the reduced linear transient dynamic analysis (see the GAP module of PREP7). A 0.0 value for GAP or FSLIDE removes the gap or sliding capability, respectively, from the element. The mass, if any, is one-dimensional. The element requires an iterative solution if GAP and/or FSLIDE are nonzero.

A stiffness (K1 or K2) must be defined if the gap capability is used. Unreasonably high stiffness values should be avoided. The rate of convergence may decrease as the stiffness increases. If FSLIDE is not equal to zero, the element is nonconservative as well as nonlinear. Nonconservative elements require that the load be applied very gradually, along the actual load history path, and in the proper sequence (if multiple loadings exist). Only the lumped mass matrix is available.

4.40.4 Product Restrictions

ANSYS/LinearPlus

• This element does not have damping or the slider capability. The C real constant (R2, the damping coefficient) is not allowed. R2 should be input as a blank. The real constants FSLIDE and K2 are not allowed.
• The PRES and TEMP degrees of freedom are not allowed. KEYOPT(3) cannot be set to 7 or 8.

KEYOPT(3)8