FLD Damage

The maximum strains that a sheet material can sustain prior to the onset of necking are referred to as the forming limit strains. A forming limit diagram (FLD) is a plot of the forming limit strains in the space of principal (in-plane) logarithmic strains. The FLD damage initiation criterion is intended to predict the onset of necking instability in sheet metal forming.

See Also
In Other Guides
Damage Initiation for Ductile Metals

In the discussion that follows "major" and "minor" limit strains refer to the maximum and minimum values of the in-plane principal limit strains, respectively. The major limit strain is usually represented on the vertical axis and the minor strain on the horizontal axis. The line connecting the states at which deformation becomes unstable is referred to as the forming limit curve (FLC). The FLC gives a sense of the formability of a sheet of material. Strains computed numerically can be compared to a FLC to determine the feasibility of the forming process under analysis.

The FLD damage initiation criterion requires the specification of the FLC in tabular form by giving the major principal strain at damage initiation as a tabular function of the minor principal strain and, optionally, temperature, ε m a j o r F L D ( ε min o r , θ ) . The damage initiation criterion for the FLD is given by the condition ω F L D = 1 , where the variable ω F L D is a function of the current deformation state and is defined as the ratio of the current major principal strain, ε m a j o r , to the major limit strain on the FLC evaluated at the current values of the minor principal strain, ε min o r ; and temperature, θ :

ω F L D ⁢ = ε m a j o r ε m a j o r F L D ( ε min o r ,   θ ) .
Input Data Description
Major Principal Strain The maximum value of the in-plane principal limit strain, ε m a j o r .
Minor Principal Strain The minimum value of the in-plane principal limit strain, ε min o r .
Use temperature-dependent data Specifies material parameters that depend on temperature. A Temperature field appears in the data table. For more information, see Specifying Material Data as a Function of Temperature and Independent Field Variables.
Number of field variables Specify material parameters that depend on field variables. Field columns appear in the data table for each field variable you add. For more information, see Specifying Material Data as a Function of Temperature and Independent Field Variables.
Use damage evolution Damage evolution defines how the material degrades after one or more damage initiation criteria are met. Select the check box, and specify settings in the Damage Evolution group box; these settings are described in Damage Evolution.