# PCNTX24

Bulk Data Entry Defines properties TYPE24 of a CONTACT interface for geometric nonlinear analysis.

## Format

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
PCNTX24 PID
ISTF
GAPMAXs GAPMAXm
STMIN STMAX IGAP0 IPEN0 IPENMAX IPENMIN
STFAC FRIC   TSTART TEND
IBC     INACTI VISS
IFRIC IFILTR FFAC   SENSID
FRICDAT C1 C2 C3 C4 C5 C6

## Example

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
PCONT 34
PCNTX24 34

## Definitions

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

No default (Integer > 0)

ISTF Stiffness definition flag. 5
0
The stiffness is computed according to the main side characteristics.
2, 3, 4 and 5
The interface stiffness is computed from both main and secondary characteristics.

Default as defined by CONTPRM (Integer = 0, ..., 5)

GAPMAXs Secondary maximum gaps.

(Real)

GAPMAXm Main maximum gaps.

(Real)

STMIN Minimum stiffness (Only with ISTF > 1).

Default as defined by CONTPRM (Real ≥ 0)

STMAX Maximum stiffness (Only with ISTF > 1).

Default as defined by CONTPRM (Real ≥ 0)

IGAP0 Gap modification flag for secondary shell nodes on the free edges.
0
No change
1
Set gap to zero for the secondary shell nodes

(Integer)

IPEN0 Initial penetration detection flag.
0
Default method. Excludes the initial auto-impacts in the same part (shell and solid elements only). IPEN0 = 1 takes into account the initial auto-impacts in the same part, but in some complex situations, wrong initial penetrations might be given.
1
Method 1 (including auto-impact in each part).

(Integer)

IPENMAX Maximum initial penetration: Penetration higher than this value will not be taken into account.

(Real)

IPENMIN Minimum initial penetration: Penetration higher than this value will be taken into account.

(Real)

STFAC Interface stiffness scale factor.

Default as defined by CONTPRM (Real ≥ 0)

FRIC Coulomb friction.

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

INACTI Handling of initial penetrations flag.
0
Only tiny initial penetrations (1.0e-08) will be taken into account. Ignores the initial penetrations, but the contacts are not deleted, new contact will be well detected once the penetrations are disappeared.
1
All initial penetrations will be ignored.
-1
All initial penetrations will be taken into account.
5
Similar to the one of interface TYPE7, but once the initial penetration is gone, the new contact will be detected using not-adjusted gap (P0 is reset to zero)GAP is variable with time and initial gap is adjusted as follows:
Where, P0 is the initial penetration.
${\text{gap}}_{0}=\text{gap}-{\text{P}}_{0}$

Default as defined by CONTPRM (Integer = 0, 1, -1, or 5)

VISS Critical damping coefficient on interface stiffness.

Default as defined by CONTPRM (Real ≥ 0)

IFRIC Friction formulation flag. 8
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. 9
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 CONTPRM (Character)

FFAC Friction filtering factor.

Default as defined by CONTPRM

SENSID Sensor identifier to activate/deactivate the interface. 12

No default (Integer)

If a sensor identifier is defined, the activation/deactivation of interface is based on the sensor and not on TSTART or TSTOP.

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

Default as defined by CONTPRM (Real ≥ 0)

1. The property identification number must be that of an existing PCONT Bulk Data Entry. Only one PCNTX24 property extension can be associated with a particular PCONT.
2. PCNTX24 is only supported for geometric nonlinear explicit dynamic analysis subcase 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 gap is computed automatically (similar with IGAP = VAR on PCNTX7) for each impact 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.

gm and gs are limited separately by GAPMAXm and GAPMAXs before the gap computation.

7. The coefficients C1 conref="../../bank/solvers_symbols_equations_r_b.dita#reference_xh2_vkk_pw/sym_c_6" id="pcntx24_bulk_r_ph_rtr_tsg_x1b"/> are used to define a variable friction coefficient $\mu$ .
8. IFRIC defines the friction model.

IFRIC = COUL - Coulomb friction with FTFRIC * 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 = GEN - 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 = DARM - 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 = REN - 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 or equal to the maximum friction C3 (C1C3 and C2C3).
• The minimum friction coefficient C4, must be lower than or equal to the static friction coefficient C1 and the dynamic friction coefficient C2 (C4C1 and C4C2).
9. 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"/>) * 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"/> = FFAC

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

10. 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 + $\text{Δ}$ FT

$\text{Δ}$ FT = K * VT * dt

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

11. When SENSID is defined for activation/deactivation of the interface, TSTART and TSTOP are not taken into account.
12. When the contact type is the symmetric surface to surface, the output normal contact forces in TH file are correctly calculated if the two surfaces are well separated.
13. For implicit test: Interface TYPE24 is now only available with SMP. The default of ISTF will be set to 4. The default INACTI will be set to -1.
14. This card is represented as an extension to a PCONT property in HyperMesh.