This function allows the user to define the FLD curve and other parameters
for FLD evaluation. The program displays the FLD CURVE AND OPTION window, as
shown in Figure
8.6.2.
Figure 8.6.2 FLD Curve and Option
1.
DEFINE CURVE BY
l FLC (From index
file)
If the user has defined FLC curve during pre-processing, the program
will automatically include FLC curve in output idx file. Postprocessor will
obtain FLC curve data from idx file by default. The type of FLC curve in idx
file is engineering strain. If the FLC curve used by the user is in true strain
format, when inputting in pre-processor, the strain transforms to engineering
strain format, and then input to pre-processor, or adopts the subsequent File
method to define.
Refer to APPENDIX A for detailed information about INDEX (idx) file
format.
l n,r,t
If FLC curve is not defined in pre-processor, then the FLC (From index
file) option mentioned above is not activated. The program obtains n, r, t
parameters from idx file by default, and then gets the FLC curve approximately according
to Keeler’s formula. If the user does not assign idx file or have *.idx file (for
example, the user opens result file calculated by earlier DYNAFORM version), the
program adopts a group of default n, r, t parameters to calculate FLC curve. At
this time, the user should adjust n, r, t manually to obtain the proper FLD
curve.
Keeler’s formulas used in Post are:
;
;
.
The shape of FLC is determined by the formulas below:
;
.
l File
Define FLD curve by importing curve file (*.fld). Figure 8.6.3 shows an example of .fld curve file format. The user
may refer to the format to create fld file. $FORM LIMIT DIAGRAM is the necessary
keyword, other keywords are optional. Safety Margin defines the distance between
safety margins in critical condition. Type defines the curve type, 0 for true
strain, 1 for engineering strain, 2 for engineering strain in terms of percentage.
There is no FLD curve type in the old FLD format,and the curve type is determined
by FLD parameter in etapost.config which is configuration file of
post-processor program. So when using the old FLD curve, the user should add
type messages in FLD file or adjust the FLD parameters in the configuration
file to match with FLD curve.
Figure 8.6.3 FLD curve file format
2.
CURVE TYPE
This function allows the user to select the engineering or true strain
for FLD evaluation.
3.
PARAMETERS
l FLD0
FLD0 is the lowest point on the forming limit curve. The user can move
the forming limit curve along the Y-axis by changing the FLD0 value.
l SAFETY MARGIN
The user can define the size of the region which has crack tendency.
SAFETY MARGIN shows the range below the forming limit curve. The default is set
to the value which is 0.1 less than the fracture limit curve.
l ALLOWABLE
THINNING
The allowable thinning of material in bi-oriented stretch mode is
usually set to 30%.
l ESSENTIAL
THINNING
The function determines the minimum deformation percent required by the
material to reach sufficient deformation. The default is 2%.
l ALLOWABLE
THICKENING
The function determines the shrink percent for the material not to
wrinkle. The default is 1%.
4.
CURVE FILTER
This function is used to divide FLD into 8 regions. Each region is
shown in a unique color. An example of FLD is shown in Figure 8.6.4.
Figure 8.6.4 An Example of FLD Analysis
All the regions except CRACK and SAFE can be turned off via options in CURVE
FILTER.
5.
SHOW FLD WINDOW (toggle)
This function allows the user to close or show FLD window.