ANSYS失效准则

Failure Criteria

Failure criteria are commonly used for orthotropic materials. They can

be input using either the

FC

commands or the

TB

commands. The

FC

command

input is used in POST1. The

TB

command input is used directly in the

composite elements and is described below.

The failure criteria table is started by using the

TB

command (with

Lab

= FAIL). The data table is input in two parts:

the failure criterion keys

?

the failure stress/strain data.

?

Data

not

input

are

assumed

to

be

zero.

See

the

ANSYS,

Inc.

Theory

Reference

for an explanation of the predefined failure criteria. The six failure

criterion keys are defined with the

TBDATA

command following a special

form of the

TBTEMP

command [

TBTEMP

,,CRIT] to indicate that the failure

criterion keys are defined next. The constants (C1-C6) entered on the

TBDATA

command are:

Table 2.2 Orthotropic Material Failure Criteria Data

Constant

1

Meaning

0 - Do not include this predefined criterion.

1 - Include this predefined criterion.

-1 - Include user-defined criterion with subroutine USRFC1.

Maximum Strain Failure Criterion - Output as FC1 (uses strain constants 1-9)

2

Maximum Stress Failure Criterion - Output as FC2 (uses stress constants 10-18)

Options are the same as for constant 1, except subroutine is

USRFC2.

3

Tsai-Wu Failure Criterion - Output as FC3 (uses constants 10-21)

0 - Do not include this predefined criterion

1 - Include the Tsai-Wu strength index

2 - Include the inverse of the Tsai-Wu strength ratio

-1 - Include user- defined criterion with subroutine USRFC3

4-6

User-defined Failure Criteria - Output as FC4 TO FC6

0 - Do not include this criterion.

-1 - Include user-defined criteria with subroutines USRFC4, USRFC5, USRFC6,

respectively.

The

failure

data,

which

may

be

temperature-dependent,

must

be

defined

with

the

TBDATA

command following a temperature definition on the

TBTEMP

command. Strains must have absolute values less than 1.0. Up to six

temperatures (

NTEMP

= 6 maximum on the

TB

command) may be defined with

the

TBTEMP

commands.

The

constants

(C1-C21)

entered

on

the

TBDATA

command

(6 per command), after each

TBTEMP

command, are:

TBDATA

Constants for the

TBTEMP

Command

Constant

-

(Symbol)

-

Meaning

f

1

- (

?

xt

) - Failure strain in material x-direction in tension (must be

positive).

f

2

-

(

?

xc

)

-

Failure

strain

in

material

x-direction

in

compression

(default

= -

) (may not be positive).

f

3

- (

?

yt

) - Failure strain in material y-direction in tension (must be

positive).

f

4

-

(

?

xc

)

-

Failure

strain

in

material

y-direction

in

compression

(default

= -) (may not be positive).

f

5

- (

?

zt

) - Failure strain in material z-direction in tension (must be

positive).

f

6

-

(

?

xc

)

-

Failure

strain

in

material

z-direction

in

compression

(default

= -) (may not be positive).

f

7

-

(

?

xy

)

-

Failure

strain

in

material

x-y

plane

(shear)

(must

be

positive).

f

8

-

(

?

yz

)

-

Failure

strain

in

material

y-z

plane

(shear)

(must

be

positive).

f

9

-

(

?

zx

)

-

Failure

strain

in

material

x-z

plane

(shear)

(must

be

positive).