## User Function USF_Damage

**User Function Fortran File:** `USF_Damage.f90`

**Function 1 Name:** `EnhancementFactor`

**Function 2 Name:** `SourceDamage`

### General Description

USF_Damage.pdf

The first function changes the rheology of the damage ice by impacting the enhancement factor.

The second function is used to compute the source term of the advection-reaction solver.

### SIF contents

The required keywords in the SIF file for this User Function are:

Constants
Dev Tensile Strength Modifier = Real 0.05 ! standard deviation for the stress threshold distribution
End
Body Force 1
DGD Source = Variable Damage
Real Procedure "ElmerIceUSF" "SourceDamage"
End
Material 1
Glen Enhancement Factor = Variable Damage
Real Procedure "ElmerIceUSF" "EnhancementFactor"
Damage Enhancement Factor = Real 2.00 ! damage enhancement factor
Damage Parameter sigmath = Real 0.05 ! stress threshold for damage increase
End

Additionnally, for output visualisation, the damage criterion Chi is saved as a variable named **Chi**, which need to be exported in a solver, such as :

Solver 3
Equation = Sij
Procedure = "ElmerIceSolvers" "ComputeDevStress"
[...]
Exported Variable 1 = Stress[Sxx:1 Syy:1 Szz:1 Sxy:1 Syz:1 Sxz:1]
Exported Variable 1 DOFs = 6
Exported Variable 2 = -dofs 1 "Chi"
[...]
End

### Examples

A 3D example can be found in `[ELMER_TRUNK]/elmerice/Tests/Damage`

.

### Reference

Krug, J., J. Weiss, O. Gagliardini and G. Durand, 2014. Combining damage and fracture mechanics to model calving, The Cryosphere, 8, 2101-2117, doi:10.5194/tc-8-2101-2014.