# PCNTX20

Bulk Data Entry Defines properties TYPE20 of a CONTACT interface for geometric nonlinear analysis.

## Format

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
PCNTX20 PID ISYM IEDGE GRNDID       EdgeAngle
IGAP   IBAG IDEL
FPENMAX
STFAC FRIC GAP TSTART TEND
IBC     INACTI VISS VISF
IFRIC IFILTR FFAC IFORM
FRICDAT C1 C2 C3 C4 C5 C6

## Example

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
PCONT 34
PCNTX20 34

## Definitions

Field Contents SI Unit Example
PID Property identification number of the associated PCONT.

No default (Integer > 0)

ISYM Symmetric contact flag.
SYM
Symmetric contact.
UNSYM
Main-secondary contact.

If SSID defines a grid set, the contact is always a main-secondary contact.

Default as defined by CONTPRM (Character)

IEDGE Flag for edge generation from secondary and main surfaces.
NO
No edge generation.
ALL
All segment edges are included.
BORD
External border of secondary and main surface is used.
FEAT
External border, as well as, features defined by FANG are used.

Default as defined by (Character)

GRNDID Optional nodes group identifier.

(Integer)

EdgeAngle Edges angle (used only if IEDGE = FEAT)

Default = 91 (Real)

If angle between two edges is smaller than EdgeAngle, the edge is considered.

IGAP Gap definition flag.
CONST
Gap is constant and equal to GAP. 6
VAR
Gap is variable (in space, not in time) according to the characteristics of the impacting surfaces and nodes. 7

Default as defined by (Character)

IBAG Airbag vent holes closure flag in case of contact.
0 (Default)
No closure.
1
Closure.

(Integer)

IDEL Flag for node and segment deletion.
0
No deletion.
1
When all the elements (shells and solids) associated to one segment are deleted, the segment is removed from the main side of the interface. Additionally, non-connected nodes are removed from the secondary side of the interface.
2
When a shell or a solid element is deleted, the corresponding segment is removed from the main side of the interface. Additionally, non-connected nodes are removed from the secondary side of the interface.

Default as defined by (Integer)

FPENMAX Maximum initial penetration factor (0 < FPENMAX < 1) 8

Default = 1.0 (Real)

STFAC Interface stiffness scale factor.

Default as defined by (Real ≥ 0)

FRIC Coulomb friction.

Default as defined by (Real ≥ 0)

GAP Gap for impact activation. 4 6

Default as defined by (Real ≥ 0)

TSTART Start time.

Default = 0.0 (Real ≥ 0)

TEND Time for temporary deactivation.

Default = 1030 (Real ≥ 0)

IBC Flag for deactivation of boundary conditions at impact applied to the secondary grid set.

Default as defined by (Character = X, Y, Z, XY, XZ, YZ, or XYZ)

INACTI Handling of initial penetrations flag. 9
0
No action.
1
Deactivation of stiffness on nodes.
2
Deactivation of stiffness on elements.
3
Change secondary node coordinates to avoid small initial penetrations.
5
Gap is variable with time but initial gap is slightly de-penetrated as:
${\text{gap}}_{0}=\text{gap}-{\text{P}}_{0}-0.05*\left(\text{gap}-{\text{P}}_{0}\right)$

Default as defined by (Integer = 0, 1, 2, 3, or 5)

Valid in explicit analysis: 0, 1, 2, 3 and 5.

Invalid entries are ignored.

VISS Critical damping coefficient on interface stiffness.

Default as defined by (Real ≥ 0)

VISF Critical damping coefficient on interface friction.

Default as defined by (Real ≥ 0)

IFRIC Friction formulation flag. 10
COUL
Static Coulomb friction law.
GEN
Generalized viscous friction law.
DARM
REN
Renard friction law.

Default as defined by CONTPRM (Character)

IFILTR Friction filtering flag. 11
NO
No filter is used.
SIMP
Simple numerical filter.
PER
Standard -3dB filter with filtering period.
CUTF
Standard -3dB filter with cutting frequency.

Default as defined by (Character)

FFAC Friction filtering factor.

Default as defined by (Real = 0.0 ≤ FFAC < 1.0)

IFORM Friction penalty formulation type. 12
VISC
Viscous (total) formulation.
STIFF
Stiffness (incremental) formulation.

Default as defined by (Character)

FRICDAT Indicates that additional information for will follow. Only available when = GEN, DARM or REN.
C1, C2, C3, C4, C5, C6 Coefficients to define variable friction coefficient in = GEN, DARM, or REN.

Default as defined by (Real ≥ 0)

1. The property identification number must be that of an existing PCONT Bulk Data Entry. Only one PCNTX20 property extension can be associated with a particular PCONT.
2. PCNTX20 is only applied in geometric nonlinear explicit dynamic analysis subcase which is defined by ANALYSIS = EXPDYN. It is ignored for all other subcases.
3. If FRIC is not explicitly defined on the PCONTX/PCNTX# entries, the MU1 value on the CONTACT or PCONT entry is used for FRIC in the /INTER entries for Geometric Nonlinear Analysis. Otherwise, FRIC on PCONTX/PCNTX# overwrites the MU1 value on CONTACT/PCONT.
4. In implicit analysis, different contact formulations are used for contact where secondary and main set do not overlap and where they overlap (self-contact).

In the case of self-contact, the gap cannot be zero and a constant gap is used. For small initial gaps, the convergence will be more stable and faster if GAP is larger than the initial gap.

In implicit analysis, sometimes a stiffness with scaling factor reduction (for example, STFAC = 0.01) or reduction in impacted thickness (if rigid one) might reduce unbalanced forces and improve convergence, particularly in shell structures under bending where the effective stiffness is much lower than membrane stiffness; but it should be noted that too low of a value could also lead to divergence.

5. If ISTF ≠ 1, the interface stiffness K is computed from the main segment stiffness Km and/or the secondary segment stiffness Ks.

The main stiffness is computed from Km = STFAC * B * S * S/V for solids, Km = 0.5 * STFAC * E * t for shells.

The secondary stiffness is an equivalent nodal stiffness computed as Ks = STFAC * B * V-3 for solids, Ks = 0.5 * STFAC * E * t for shells.

In these equations, B is the Bulk Modulus, S is the segment area, and V is the volume of a solid. There is no limitation to the value of stiffness factor (but a value larger than 1.0 can reduce the initial time step).

The interface stiffness is K = max (STMIN, min (STMAX, K1)) with:
• ISTF = 0, K1 = Km
• ISTF = 2, K1 = 0.5 * (Km + Ks)
• ISTF = 3, K1 = max (Km, Ks)
• ISTF = 4, K1 = min (Km, Ks)
• ISTF = 5, K1 = Km * Ks / (Km + Ks)
6. The default for the constant gap (IGAP = CONST) is the minimum of:
• t, average thickness of the main shell elements
• l/10, l - average side length of the main solid elements
• lmin/2, lmin - smallest side length of all main segments (shell or solid)
7. The variable gap (IGAP = VAR) is computed as: gs + gm
with:
• gm - main element gap with

gm = t/2, t: thickness of the main element for shell elements.

gm = 0 for solid elements.

• gs - secondary node gap:

gs = 0 if the secondary node is not connected to any element or is only connected to solid or spring elements.

gs = t/2, t - largest thickness of the shell elements connected to the secondary node.

gs = 1/2√S for truss and beam elements, with S being the cross section of the element.

If the secondary node is connected to multiple shells and/or beams or trusses, the largest computed secondary gap is used.

8. Maximum penetration value is set as a fraction of the actual gap (including variable gap):

Penmax = FPENMAX * gap

If the initial penetration of a secondary node is greater than the calculated maximum value (Penmax), the node will be deactivated from the interface (node stiffness deactivation).

9. INACTI = 3, is only recommended for small initial penetrations and should be used with caution because:
• the coordinate change is irreversible
• it may create other initial penetrations if several surface layers are defined in the interfaces
• it may create initial energy if the node belongs to a spring element
INACTI = 5 works as follows:
10. IFRIC defines the friction model.

IFRIC = COUL - Coulomb friction with FT ≤ FRIC * FN.

For IFRIC > 0, the friction coefficient is set by a function ( $\mu =\mu \left(p,V\right)$ )

Where, $p$ is the pressure of the normal force on the main segment and $V$ is the tangential velocity of the secondary node.

The following formulations are available:
• IFRIC = 1 - Generalized viscous friction law(1)
$\mu =\text{FRIC}+\text{C}1*\text{p}+\text{C}2*\text{V}+\text{C}3*\text{p}*\text{v}+\text{C}4*{\text{p}}^{2}+\text{C}5*{\text{v}}^{2}$
• IFRIC = 2 - Darmstad law(2)
$\mu ={\text{C}}_{1}*\text{e}\left({\text{C}}_{2}\text{V}\right)*{\text{p}}^{2}+{\text{C}}_{3}*\text{e}\left({\text{C}}_{4}\text{V}\right)*\text{p}+{\text{C}}_{5}*\text{e}\left({\text{C}}_{6}\text{V}\right)$
• IFRIC = 3 - Renard law
 $\mu ={C}_{1}+\left({C}_{3}-{C}_{1}\right)\cdot \frac{V}{{C}_{5}}\cdot \left(2-\frac{V}{{C}_{5}}\right)$ 0 ≤ V ≤ C5 $\mu ={C}_{3}-\left(\left({C}_{3}-{C}_{4}\right)\cdot {\left(\frac{V-{C}_{5}}{{C}_{6}-{C}_{5}}\right)}^{2}\cdot \left(3-2\cdot \frac{V-{C}_{5}}{{C}_{6}-{C}_{5}}\right)\right)$ C5 ≤ V ≤ C6 $\mu ={C}_{2}-\frac{1}{\frac{1}{{C}_{2}-{C}_{4}}+{\left(V-{C}_{6}\right)}^{2}}$ C6 ≤ V
Where,(3)
$\begin{array}{l}{C}_{1}=C1={\mu }_{s},{C}_{2}=C2={\mu }_{d}\hfill \\ {C}_{3}=C3={\mu }_{\text{max}},{C}_{4}=C4={\mu }_{\text{min}}\hfill \\ {C}_{5}=C5={V}_{\mathit{cr}1},{C}_{6}=C6={V}_{\mathit{cr}2}\hfill \end{array}$
• The first critical velocity Vcr1 must not be 0 (C5 ≠ 0). It also must be lower than the second critical velocity Vcr2 (C5 < C6).
• The static friction coefficient C1 and the dynamic friction coefficient C2, must be lower than the maximum friction C3 (C1 < C3 and C2 < C3).
• The minimum friction coefficient C4, must be lower than the static friction coefficient C1 and the dynamic friction coefficient C2 (C4C1 and C4C2).
11. IFILTR defines the method for computing the friction filtering coefficient. If IFILTRNO, the tangential friction forces are smoothed using a filter:

FT = α * F'T + (1 conref="../../bank/solvers_symbols_equations_r_b.dita#reference_xh2_vkk_pw/o2_sym_alpha" id="pcntx20_bulk_r_ph_z5p_lkn_l1b"/>) * F'T-1

Where,
FT
Tangential force
F'T
Tangential force at time t
F'T-1
Tangential force at time t-1
α
Filtering coefficient

IFILTR = SIMP conref="../../bank/solvers_symbols_equations_r_b.dita#reference_xh2_vkk_pw/o2_sym_alpha" id="pcntx20_bulk_r_ph_jwp_jkn_l1b"/> = FFAC

IFILTR = PER conref="../../bank/solvers_symbols_equations_r_b.dita#reference_xh2_vkk_pw/o2_sym_alpha" id="pcntx20_bulk_r_ph_ubz_jkn_l1b"/> = 2π dt/FFAC, where dt/T = FFAC, T is the filtering period

IFILTR = CUTF conref="../../bank/solvers_symbols_equations_r_b.dita#reference_xh2_vkk_pw/o2_sym_alpha" id="pcntx20_bulk_r_ph_jyd_kkn_l1b"/> = 2π * FFAC * dt, where FFAC is the cutting frequency

12. IFORM selects two types of contact friction penalty formulation.

The viscous (total) formulation (IFORM = VISC) computes an adhesive force as:

Fadh = VISF * √(2KM) * VT

FT = min ( $\mu$ FN, Fadh)

The stiffness (incremental) formulation (IFORM = STIFF) computes an adhesive force as:

Fadh = FTold + ΔFT

ΔFT = K * VT * dt

FTnew = min ( $\mu$ FN, Fadh)

13. This card is represented as an extension to a PCONT property in HyperMesh.