# MAT8

Bulk Data Entry Defines the material properties for linear temperature-independent orthotropic material for two-dimensional elements.

Attention: Valid for Implicit and Explicit Analysis

## Format

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
MAT8 MID E1 E2 NU12 G12 G1,Z G2,Z RHO
A1 A2 TREF Xt Xc Yt Yc S
GE F12 STRN
RAYL ALPHA BETA

## Example

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
MAT8 171 30.+6 1.+6 0.3 2.+6 3.+6 1.5+6 0.056
28.-6 1.5-6 155.0

## Definitions

Field Contents SI Unit Example
MID Unique material identification.
Integer
Specifies an identification number for this material.
<String>
Specifies a user-defined string label for this material entry. 2

No default (Integer > 0 or <String>)

E1 Modulus of elasticity in longitudinal direction (also defined as fibre direction or 1-direction) 7

No default (Real ≠ 0.0)

E2 Modulus of elasticity in lateral direction (also defined as matrix direction or 2-direction) 7

No default (Real ≠' 0.0)

NU12 Poisson's ratio ( $\frac{{\epsilon }_{2}}{{\epsilon }_{1}}$ for uniaxial loading in 1-direction). Note that ${\nu }_{21}=\frac{{\epsilon }_{1}}{{\epsilon }_{2}}$ for uniaxial loading in 2-direction is related to $\upsilon$ 12, E1, E2 by the relation $\upsilon$ 12 E2 = $\upsilon$ 21 E1.

No default (Real)

G12 Inplane shear modulus.

No default (Real > 0.0)

G1,Z Transverse shear modulus for shear in 1-Z plane.

Default = blank (Real > 0.0 or blank)

G2,Z Transverse shear modulus for shear in 2-Z plane.

Default = blank (Real > 0.0 or blank)

RHO Mass density.

No default (Real)

A1 Thermal expansion coefficient in 1-direction.

No default (Real)

A2 Thermal expansion coefficient in 2-direction.

No default (Real)

TREF Reference temperature for the calculation of thermal loads. 3.

Default = blank (Real or blank)

Xt, Xc, Yt, Yc Allowable stresses or strains in the longitudinal and lateral directions. Used for composite ply failure calculations.

No default (Real > 0.0)

S Allowable for in-plane shear stresses or strains for composite ply failure calculations.

No default (Real > 0.0)

GE Structural Element Damping Coefficient.

TREF and GE are ignored, if a MAT8 entry is referenced by a PCOMP entry.

No default (Real)

F12 Tsai-Wu interaction term for composite failure.

Default = 0.0 (Real)

STRN Indicates whether Xt, Xc, Yt, Yc, and S are stress or strain allowables.

Default = blank (Real = 1.0 for strain allowables, blank for stress allowables)

RAYL Continuation line flag for material-dependent Rayleigh damping.
ALPHA Material-dependent Rayleigh Damping coefficient for the mass matrix.

Default = blank (Real ≥ 0.0)

BETA Material-dependent Rayleigh Damping coefficient for the stiffness matrix.

Default = blank (Real ≥ 0.0)

1. The material identification number/string must be unique for all MAT1, MAT2, MAT8 and MAT9 entries.
2. String based labels allow for easier visual identification of materials, including when being referenced by other cards. (example, the MID field of properties). For more details, refer to String Label Based Input File in the Bulk Data Input File.
3. If G1,Z and G2,Z values are specified as zero or are not supplied, a penalty term is used to enforce very high transverse shear stiffness.
4. An approximate value for G1,Z and G2,Z is the inplane shear modulus G12. If test data is not available to accurately determine G1,Z and G2,Z for the material and transverse shear calculations, the value of G12 may be supplied for G1,Z and G2,Z.
5. Long field format can be used.
6. The option of interpreting Xt, Xc, Yt, Yc, and S as strains is only available for composite definitions (PCOMP or PCOMPG) using the Maximum Strain (STRN) failure criterion. In this case, the STRN flag indicates whether Xt, Xc, Yt, Yc, and S are stress or strain allowables. For the STRN failure criterion, if the STRN field on MAT8 is set to "blank", the strain allowables are calculated from the corresponding stress allowables.

For all other failure criteria Xt, Xc, Yt, Yc, and S are always interpreted as stresses, regardless of the value of the STRN flag.

7. The value of E1 should be greater than that of E2 for the material to be stable. If E1 < E2, the material matrix becomes indefinite leading to an unstable material.
8. For material-dependent Rayleigh damping, the equivalent viscous damping, $C$ , is defined as:(1)
$C=\text{ALPHA}*M+\text{BETA}*K$
Where,
ALPHA and BETA
Defined on the RAYL continuation line on the material entry
$M$
Mass matrix
$K$
Stiffness matrix
Supported solutions for material-dependent Rayleigh damping on MAT8:
• Direct Frequency Response
• Modal Frequency Response
• Direct Transient Response
• Modal Transient Response
• Nonlinear Transient Analysis
• Explicit Dynamic Analysis
9. This card is represented as a material in HyperMesh.