linear material prperties

2.4 Linear Material Properties

The material properties used by the element type are listed under "Material Properties" in the input table for each element type. A brief description of all

material properties not described with the elements is given in Table 2.4-1 at the end of this section. These properties (which may be functions of

temperature) are called linear properties because typical non-thermal solutions with these properties require only a single iteration. Properties such as stress-

strain data (described in Section 2.5.1) are called nonlinear properties because an analysis with these properties requires an iterative solution. Linear materials

that are required for an element, but which are not defined, use the default values as described below (except that EX and KXX must be input with a non-zero

value). Any additional materials are ignored. See Section 2.1 of the ASYS Theory Reference for material property details.

For orthotropic materials, the X,Y, and Z part of the label (e.g. EX, EY, and EZ, or KXX, KYY, and KZZ) refers to the direction (in the element coordinate

system) that that particular property acts in. The Y and Z directions of the properties default to the X direction (e.g., EY and EZ default to EX) to reduce the

amount of input required. In addition, PRYZ and PRXZ default to PRXY; NUYZ and NUXZ default to NUXY; GXY defaults to EX/(2(1+PRXY)) and GYZ

and GXZ default to GXY for isotropic materials (for orthotropic materials, actual values of GXY should be input; if not input, GXY defaults to

EX*EY/(EX+EY+2*PRXY*EX).

Important: If properties KXX, KYY, and/or KZZ vary with temperature, this denotes a nonlinear analysis problem.

Poisson's ratio may be input in either major (PRXY, PRYZ, PRXZ) or minor (NUXY, NUYZ, NUXZ) form, but not both for a particular material. The major

form is converted to the minor form during the solve operation [SOLVE]. For isotropic materials, the major and minor forms are equivalent. Solution output is

in terms of the minor form, regardless of how the data was input. If no Poisson's ratio properties are input, the minor form is used by default and 0.3 is used

for NUXY. If the major form is to be used, PRXY must be input. If a zero value is desired, input the label (NUXY or PRXY) with a zero (or blank) value.

Poisson's ratio should not be equal to 0.5 for an isotropic material.

Material dependent damping (DAMP) is an additional method of including structural damping for dynamic analyses and is useful when different parts of the

model have different damping values. If DAMP is included, the DAMP value is added to the BETAD value as appropriate (see Section 15.3 of the ASYS

Theory Reference). Special purpose elements, such as COMBIN7, LINK11, CONTAC12, MATRIX27, FLUID29, and VISCO88, generally do not require

damping. However, if material property DAMP is specified for these elements, the value will be used to create the damping matrix at solution time.

For axisymmetric analyses, the X, Y, and Z labels refer to the radial (R), axial (Z), and hoop ( ) directions, respectively. Orthotropic properties given in the

R,Z, system should be input as follows: EX=ER, EY=EZ, and EZ=E . An additional transformation is required for Poisson's ratios. If the given R,Z,

properties are column-normalized (see Section 2.1 of the ASYS Theory Reference), NUXY=NURZ, NUYZ = NUZ = (ET/EZ) *NU Z, and NUXZ=NUR .

If the given R,Z, properties are row-normalized, NUXY=(EZ/ER)*NURZ, NUYZ=(E /EZ)*NUZ =NU Z, and NUXZ=(E /ER)*NUR .

EMIS defaults to 1.0 if not defined; however, if defined with a 0.0 (or blank) value, EMIS is taken to be 0.0.

When you use the MP command to enter values for the thermal coefficient of expansion ( ), the program interprets those values as mean values, taken with

2.4 Linear Material Properties (UP19980821 ) http://www.ansys.stuba.sk/html/elem_55/chapter2/ES2-4.htm#S2.4

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respect to some common datum or definition temperature. For instance, suppose you measured thermal strains in a test laboratory, starting at 23° C, and took

readings at 200°, 400°, 600°, 800°, and 1000°. When you plot this strain-temperature data, the slopes of the secants to the strain-temperature curve would be

the mean values of the coefficient of thermal expansion, defined with respect to the common temperature of 23° (To). (The discussion which follows also uses

another term, the instantaneous value of the coefficient of thermal expansion. The slopes of the tangents to this curve represent the instantaneous values.)

The program calculates structural thermal strain as follows:

where:

T = element evaluation temperature

TREF = temperature at which zero thermal strains exist (TREF or MP,REFT commands)

(T) = mean coefficient of thermal expansion, with respect to a definition temperature (in this case, same as TREF)

If the material property data is in terms of instantaneous values of , then you need to convert those instantaneous values into mean values as follows:

where:


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Tn = temperature at which a mean value is being evaluated

To = definition temperature at which the mean values are defined (in this case, same as TREF)

If the values are based upon a definition temperature other than TREF, then you need to convert those values to TREF. This can be done using the

MPAMOD command. Also see Section 2.1.3 of the ASYS Theory Reference.

Specific heat effects may be input with either the C (specific heat) property or the ENTH (enthalpy) property. Enthalpy has units of heat/volume and is the

integral of C x DENS over temperature. If both C and ENTH are specified, ENTH will be used. ENTH should be used only in a transient thermal analysis. For

phase change problems, the user must input ENTH as a function of temperature using the MP family of commands [MP, MPTEMP, MPTGE�, and

MPDATA].

Properties may be input in tabular form (value vs. temperature) or as a fourth order polynomial (value = f(temperature)). If input as a polynomial, however,

evaluation is done by PREP7 at discrete temperature points and converted to tabular form. The tabular properties are then available to the elements. Property

evaluation is done at the element matrix formulation level of the solution phase. Evaluation is done by linear interpolation of the tabular data at (or near) the

element center temperature (or, for the thermal elements, at the integration point temperatures). Film coefficients are evaluated as described with the SF

command. See Section 13.4 of the ASYS Theory Reference for additional details. Property evaluation at element temperatures beyond the supplied tabular

range assumes a constant property at the extreme range value. An exception occurs for the ENTH property, which continues along the last supplied slope.

Table 2.4-1 Material Property Labels

Label Units Description

EX

Force/Area

Elastic modulus, element x direction

EY Elastic modulus, element y direction

EZ Elastic modulus, element z direction

ALPX

Strain/Temp

Coefficient of thermal expansion, element x direction

ALPY Coefficient of thermal expansion, element y direction

ALPZ Coefficient of thermal expansion, element z direction

REFT Temp Reference temperature (as a property) [TREF]

PRXY

None

Major Poisson's ratio, x-y plane

PRYZ Major Poisson's ratio, y-z plane

PRX Z Major Poisson's ratio, x-z plane

NUXY Minor Poisson's ratio, x-y plane

NUYZ Minor Poisson's ratio, y-z plane


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NUXZ Minor Poisson's ratio, x-z plane

GXY

Force/Area

Shear modulus, x-y plane

GYZ Shear modulus, y-z plane

GXZ Shear modulus, x-z plane

DAMP Time K matrix multiplier for damping [BETAD].

MU None Coefficient of friction (or, for FLUID29 and FLUID30 elements, boundary admittance)

DENS Mass/Vol Mass density

C Heat/Mass*Temp Specific heat

ENTH Heat/Vol Enthalpy (e DENS*C d(Temp))

KXX Heat*Length / (Time*Area*Temp) Thermal conductivity, element x direction

KYY Thermal conductivity, element y direction

KZZ Thermal conductivity, element z direction

HF Heat / (Time*Area*Temp) Convection (or film) coefficient

EMIS None Emissivity

QRATE Heat/Time Heat generation rate (MASS71 element only).

VISC Force*Time / Length2 Viscosity

SONC Length/Time Sonic velocity (FLUID29 and FLUID30 elements only)

RSVX Resistance*Area / Length Electrical resistivity, element x direction

RSVY Electrical resistivity, element y direction

RSVZ Electrical resistivity, element z direction

PERX Charge2 / (Force*Length) Electric permittivity, element x direction

PERY Electric permittivity, element y direction

PERZ Electric permittivity, element z direction

MURX

None

Magnetic relative permeability, element x direction

MURY Magnetic relative permeability, element y direction

MURZ Magnetic relative permeability, element z direction

MGXX Charge / (Length*Time) Magnetic coercive force, element x direction

MGYY Magnetic coercive force, element y direction


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MGZZ Magnetic coercive force, element z direction


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linear material prperties

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