# PCNTX7

Bulk Data Entry Defines properties TYPE7 of a CONTACT interface for geometric nonlinear analysis.

## Format

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
PCNTX7 PID
ISTF ITHE IGAP   IBAG IDEL ICURV IADM
GAPFAC GAPMAX FPENMAX
STMIN STMAX MESHSIZE DTMIN IREMGAP
STFAC FRIC GAP TSTART TEND
IBC     INACTI VISS VISF BMULT
IFRIC IFILTR FFAC IFORM SENSID
CURVDAT G1 G2
FRICDAT C1 C2 C3 C4 C5 C6
THEDAT RTHE     TINT ITHEF

## Example

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
PCONT 34
PCNTX7 34

## Definitions

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

No default (Integer > 0)

ISTF Stiffness definition flag. 5
0
The stiffness is computed according to the main side characteristics.
1
STIF1 is used as interface stiffness.
2, 3, 4 and 5
The interface stiffness is computed from both main and secondary characteristics.

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

ITHE Heat contact flag.
0 (Default)
No heat transfer.
1
Heat transfer activated.

(Integer)

IGAP Gap definition flag.
CONST
Gap is constant and equal to GAP. 6
VAR3
Gap is variable (in space, not in time) according to the characteristics of the impacting surfaces and nodes. 7

Default as defined by CONTPRM (Character = CONST, VAR, VAR2, or VAR3)

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

(Integer)

IDEL Node and segment deletion flag.
0
No deletion.
1
When all the elements (shells, 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 CONTPRM (Integer)

ICURV Gap envelope with curvature. 8
0
No curvature.
1
Spherical curvature.
2
Cylindrical curvature.
3
Automatic bicubic surface.

(Integer)

0 (Default)
Not activated.
1
Interface update according mesh size.
2
Interface update according mesh size, penetration and angle.

(Integer)

GAPFAC Gap scale factor (used only when IGAP = VAR2 and VAR3).

Default as defined by CONTPRM (Real ≥ 0)

GAPMAX Maximum gap (used only when IGAP = VAR2 and VAR3).
0
There is no maximum value for the gap.

Default as defined by CONTPRM (Real ≥ 0)

FPENMAX Maximum fraction of initial penetration. 12

(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)

MESHSIZE Percentage of mesh size (used only when IGAP = VAR3).

Default = 0.4 (Real, 0.0 < MESHSIZE ≤ 1.0)

DTMIN Limiting nodal time step. 18
IREMGAP Flag to deactivate secondary nodes if element size < gap value, in case of self-impact contact. 19
1 (Default)
No secondary node deactivation.
2
Deactivate secondary nodes.

(Integer)

STFAC Interface stiffness scale factor.

Default as defined by CONTPRM (Real ≥ 0)

FRIC Coulomb friction.

Default as defined by CONTPRM (Real ≥ 0)

GAP Gap for impact activation. 4 6

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. 12
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 and initial gap is adjusted as:
${\text{gap}}_{0}=\text{gap}-{\text{P}}_{0}$
6
Gap is variable with time but initial gap is slightly de-penetrated as:
${\text{gap}}_{0}=\text{gap}-{\text{P}}_{0}-0.05*\left(\text{gap}-{\text{P}}_{0}\right)$

Invalid entries are ignored.

Default as defined by CONTPRM (Integer)

VISS Critical damping coefficient on interface stiffness.

Default as defined by CONTPRM (Real ≥ 0)

VISF Critical damping coefficient on interface friction.

Default as defined by CONTPRM (Real ≥ 0)

BMULT Sorting factor. Can be used to speed up the sorting algorithm. Is machine-dependent.

Default as defined by CONTPRM (Real ≥ 0)

IFRIC Friction formulation flag. 13
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. 14
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 (Real = 0.0 ≤ FFAC < 1.0)

IFORM Friction penalty formulation type. 15
VISC
Viscous (total) formulation.
STIFF
Stiffness (incremental) formulation.

Default as defined by CONTPRM (Character)

SENSID Sensor identifier to activate/deactivate the interface. 20

No default (Integer)

If a sensor identifier is defined, the activation/deactivation of the interface is based on SENSID instead of TSTART or TSTOP.

CURVDAT Indicates that additional information about ICURV will follow. Only available when ICURV = 1 or 2.
G1 First grid identifier (used only when ICURV = 1 or 2).

(Integer)

G2 Second grid identifier (used only when ICURV = 2, ignored when ICURV = 1).

(Integer)

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)

(Integer)

PADM Criteria on the percentage of penetration (used only when IADM = 2).

Default = 1.0 (Real)

(Real)

THEDAT Indicates that additional information about ITHE will follow. Only available when ITHE = 1.
RTHE Heat conduction coefficient (used only when ITHE = 1). 17

(Real)

TINT Interface temperature (used only when ITHE = 1).

(Real)

ITHEF Heat contact formulation flag (used only when ITHE = 1, Integer).
0
Exchange between constant temperature in the interface and shells (secondary side).
1
Heat exchange between pieces in contact.

No default (Real)

DRAD Maximum distance for radiation computation (used only when ITHE = 1).

A very high value of DRAD is not recommended as it may reduce the performance of the solver.

No default (Real)

FHEATS Frictional heating factor of the secondary (used only when ITHE = 1). 23

No default (Real)

FHEATM Frictional heating factor of the main (used only when ITHE = 1). 23

No default (Real)

1. The property identification number must be that of an existing PCONT Bulk Data Entry. Only one PCNTX7 property extension can be associated with a particular PCONT.
2. PCNTX7 is only applied in geometric nonlinear analysis subcases which are 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 then 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. If IGAP = VAR, the variable gap is computed as gs + gm

If IGAP = VAR2, the variable gap is computed as max(GAP, min(GAPFAC * (gs+gm), GAPMAX)

If IGAP = VAR3, the variable gap is computed as max(GAP, min(GAPFAC * (gs+gm), MESHSIZE * (gsl+gml), GAPMAX)

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.

• gml - length of the smaller edge of element.
• gsl - length of the smaller edge of elements connected to the secondary nodes.

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

The variable gap is always at least equal to GAP.

8. If ICURV = 1, a spherical curvature is defined for the gap with node_ID1 (center of the sphere).

If ICURV = 2, a cylindrical curvature is defined for the gap with node_ID1 and node_ID2 (on the axis of the cylinder).

If ICURV = 3, the main surface shape is obtained with a bicubic interpolation, respecting continuity of the coordinates and the normal from one segment to the other.

In case of a large change in curvature, this formulation might become unstable (will be improved in future version).
If the contact occurs in a zone (main side) whose radius of curvature is lower than the element size (secondary side), the element on the secondary side will be divided (if not yet at maximum level).

If the contact occurs in a zone (main side) whose radius of curvature is lower than NRadm times the element size (secondary side), the element on the secondary side will be divided (if not yet at maximum level).

If the contact occurs in a zone (main side) where the angles between the normals are greater than Angladm and the percentage of penetration is greater than Padm, the element on the secondary side will be divided (if not yet at maximum level).
12. 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 is recommended for airbag simulation deployment.

INACTI = 6 is recommended instead of INACTI = 5, in order to avoid high frequency effects into the interfaces.

If FPENMAX is not equal to zero, nodes stiffness is deactivated if penetration > FPENMAX*GAP, regardless of the value of INACTI.

13. IFRIC defines the friction model.

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

For IFRIC > 0 the friction coefficient is set by a function ( $\mu$ = $\mu$ (p, V)), 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
 $\mu ={C}_{1}+\left({C}_{3}-{C}_{1}\right)·\frac{V}{{C}_{5}}·\left(2-\frac{V}{{C}_{5}}\right)$ 0 ≤ V ≤ C5 $\mu ={C}_{3}-\left(\left({C}_{3}-{C}_{4}\right)·{\left(\frac{V-{C}_{5}}{{C}_{6}-{C}_{5}}\right)}^{2}·\left(3-2·\frac{V-{C}_{5}}{{C}_{6}-{C}_{5}}\right)\right)$ C5 ≤ V ≤ C6 $\mu ={C}_{2}-\frac{1}{\frac{1}{{C}_{2}-{C}_{4}}+{\left(V-{C}_{6}\right)}^{2}}$ C6 ≤ V

Where,

(3)
$\begin{array}{l}{C}_{1}=C1={\mu }_{s},{C}_{2}=C2={\mu }_{d}\hfill \\ {C}_{3}=C3={\mu }_{\text{max}},{C}_{4}=C4={\mu }_{\text{min}}\hfill \\ {C}_{5}=C5={V}_{cr1},{C}_{6}=C6={V}_{cr2}\hfill \end{array}$
• 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 (C1C3) and C2C3).
• The minimum friction coefficient C4, must be lower than the static friction coefficient C1 and the dynamic friction coefficient C2 (C4C1 and C4C2).
14. IFILTR defines the method for computing the friction filtering coefficient. If IFILTNO, the tangential friction forces are smoothed using a filter:(4)
${\text{F}}_{\text{T}}=\alpha ·{\text{F}\prime }_{\text{T}}+\left(1-\alpha \right)·{\text{F}\prime }_{\text{T}-1}$
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="pcntx7_bulk_r_ph_dmj_vtb_k1b"/> = FFAC
• IFILTR = PER conref="../../bank/solvers_symbols_equations_r_b.dita#reference_xh2_vkk_pw/o2_sym_alpha" id="pcntx7_bulk_r_ph_dwt_vtb_k1b"/> = 2πdt/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="pcntx7_bulk_r_ph_stz_vtb_k1b"/> = 2π * FFAC * dt, where FFAC is the cutting frequency
15. IFORM selects two types of contact friction penalty formulation.
The viscous (total) formulation (IFORM = VISC) computes an adhesive force as:(5)
$\begin{array}{l}{\text{F}}_{\text{adh}}=\text{VISF}*\left(\surd 2\text{KM}\right)*{\text{V}}_{\text{T}}\\ {\text{F}}_{\text{T}}=\text{min}\left({\mu \text{F}}_{\text{N}},{\text{F}}_{\text{adh}}\right)\\ \end{array}$
The stiffness (incremental) formulation (IFORM = STIFF) computes an adhesive force as:(6)
$\begin{array}{l}{\text{F}}_{\text{adh}}={\text{F}}_{\text{Told}}+\Delta {\text{F}}_{\text{T}}\hfill \\ \Delta {\text{F}}_{\text{T}}=\text{K}*{\text{V}}_{\text{T}}*\text{dt}\hfill \\ {\text{F}}_{\text{Tnew}}=\text{min}\left({\mu \text{F}}_{\text{N}},{\text{F}}_{\text{adh}}\right)\hfill \end{array}$
16. Exchange between shell and constant temperature contact TINT.
17. RTHE is the inverse of thermal resistance (units: [W/(m2*K)]).
18. Secondary segment contact is deactivated when the segment kinematic time step calculated for this contact is lower than DTMIN.
19. With IREMGAP = 2, this allows the element size < gap values:

In case of self-impact contact, when curvilinear distance (from a node of the main segment to a secondary node) is < gap*sqrt(2) (in initial configuration), then this secondary node will not be taken into account by this main segment, and it will not be deleted from the contact for the other main segments.

20. When SENSID is defined for activation/deactivation of the interface, TSTART and TSTOP are not taken into account.
21. If FRAD is not equal to zero, and d, the distance from the secondary node to the main segment, is in the range: Gap < d < DRAD, then radiation is calculated. The radiant heat transfer conductance is calculated as:(7)
${h}_{\mathit{rad}}={F}_{\mathit{rad}}\left({T}_{m}^{2}+{T}_{s}^{2}\right)\left({T}_{m}+{T}_{s}\right)$
(8)
${F}_{\mathit{rad}}=\frac{\sigma }{\frac{1}{{\varepsilon }_{1}}+\frac{1}{{\varepsilon }_{2}}-1}$
Where,
$\sigma$
Stefan Boltzman constant
${\epsilon }_{1}$
Emissivity of the secondary surface
${\epsilon }_{2}$
Emissivity of the main surface
22. If FRAD is not equals to zero, then the default value of DRAD is calculated as the maximum of:
• upper value of the gap (at time 0) among all nodes
• smallest side length of secondary element
23. Frictional energy is converted into heat when heat transfer is activated (ITHE > 0) on the interface. Options FHEATS and FHEATM are used to control this option.

When FHEATS and FHEATM = 0, the conversion of the frictional sliding energy to heat is not activated. Non-zero values of FHEATS and FHEATM define the fraction of this energy which is converted into heat and transferred to the secondary and main, respectively.

The frictional heat QFric is defined as:

If IFORM = 2 (a stiffness formulation):
• Secondary: (9)
${Q}_{\mathit{Fric}}={\mathit{Fheat}}_{s}\cdot \frac{\left({F}_{\mathit{adh}}-{F}_{T}\right)}{K}\cdot {F}_{T}$
• Main: (10)
${Q}_{\mathit{Fric}}={\mathit{Fheat}}_{m}\cdot \frac{\left({F}_{\mathit{adh}}-{F}_{T}\right)}{K}\cdot {F}_{T}$

(ITHEF=1)

If IFORM = 1 (a penalty formulation):
• Secondary: (11)
${Q}_{\mathit{Fric}}={\mathit{Fheat}}_{s}\cdot C\cdot {V}_{T}^{2}\cdot dt$
• Main: (12)
${Q}_{\mathit{Fric}}={\mathit{Fheat}}_{m}\cdot C\cdot {V}_{T}^{2}\cdot dt$
(ITHEF=1)
24. This card is represented as an extension to a PCONT property in HyperMesh.