PGASK

Format

Example

Definitions

Comments

1. All gasket element property entries must have unique identification numbers.
2. PGASK refers to two material entries, MGASK and MAT1. MGASK defines the thickness-direction and transverse shear behaviors of the gasket material, and MAT1 defines the membrane behavior of the gasket material.

   The thickness-direction stiffness is defined with the unit of stress per unit displacement (the pressure-closure distance relationship for the thickness compression), the transverse shear stiffness is defined with either the unit of stress per unit displacement or the unit of force per unit area, and the membrane stiffness is defined with the unit of force per unit area (the stress-strain relationship).

3. The gasket material coordinate system can be defined as the element local coordinate system (CORDM = -1) or a prescribed system (CORDM = Integer ≥ 0). The material local 3-direction is taken as the gasket thickness direction, and the material local 1-direction and 2-direction are taken as the gasket membrane principle directions. If the angle between the thickness direction (the material local 3-direction) and the default one (the element local 3-direction) is larger than 20 degrees, a warning will be provided.
4. The initial thickness includes initial open gap and initial void of the gasket.
5. The total closure of a gasket element consists of the mechanical closure and the thermal closure:(1)
   $$C_{total}=C_{mech}+C_{thermal}$$
   The thermal closure, $C_{thermal}$ , is calculated as:(2)

   $$C_{thermal}=ALPHA*\left(T_{ref}-T\right)*\left(H0-GAP-VOID\right)$$
   The effective closure, $C$ , which is used to determine pressure with the loading/unloading of tables defined in the MGASK card, is calculated as:(3)

   $$C=C_{mech}-GAP$$

   If there is no initial open gap (GAP=0), $C$ and $C_{mech}$ are identical.

6. The sealing status of gasket is detected with the leakage pressure. If the gasket pressure is larger than the leakage pressure, it is detected to be sealed - the output status index value is 1; otherwise, it is leaking - the output status index value is 0.
7. STABMT is recommended to be 1 or a non-zero Real number if the gasket membrane or transverse shear stiffness is zero. STABMT=1 has the same effect as STABMT=-0.001, that is, this type of automatic stabilization stiffness is 0.1% of the initial compressive stiffness of the thickness behavior.
8. STABSP is recommended to be 1 or a non-zero Real number if some of the gasket nodes are not supported, for example, some extend outside of contact projection zone. STABSP=1 has the same effect as STABSP=-0.05, that is, this type of automatic stabilization stiffness is 5% of the initial compressive stiffness of the thickness behavior.
9. For gasket elements with thickness-direction behavior only (GASK1D=1):
   • The structural properties defined for transverse shear and membrane behaviors are ignored, including STABMT, STABSP and relevant moduli and coefficients defined in MIDG and MID1 fields.
   • A local coordinate system, with local 3^rd direction along the thickness direction overwrites the displacement coordinate system of each gasket grid (the CD field on GRID). For the enforcement of single-point constraints (for example, with SPC entry), the component ‘3’ always represents the thickness direction, regardless of the original CD field assigned on the GRID entry.
10. Gasket elements with thickness-direction behavior only (GASK1D=1), cannot have shared nodes with other type of elements, including full-behavior gasket elements (3D Gasket). Contact is required for the connection to the rest of the structure. Some rules and restrictions are:
    • Gasket elements with thickness-direction behavior only must act as the secondary side.
    • Only small-sliding Node-to-Surface (N2S) contact is supported.
    • Frictional coefficients are invalid; for type STICK or FREEZE the tangential stiffness will be ineffective.
11. The continuation entry is optional.
12. This card is represented as a property in HyperMesh.