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 formatand 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.