diff --git a/src/phase_damage_isobrittle.f90 b/src/phase_damage_isobrittle.f90
index 9d5b4f508..2d501b58f 100644
--- a/src/phase_damage_isobrittle.f90
+++ b/src/phase_damage_isobrittle.f90
@@ -96,7 +96,6 @@ end function isobrittle_init
 
 !--------------------------------------------------------------------------------------------------
 !> @brief calculates derived quantities from state
-! ToDo: Use Voigt directly
 !--------------------------------------------------------------------------------------------------
 module subroutine isobrittle_deltaState(C, Fe, ph,en)
 
@@ -110,16 +109,13 @@ module subroutine isobrittle_deltaState(C, Fe, ph,en)
     epsilon
   real(pReal) :: &
     r_W
-  real(pReal), dimension(6,6) :: &
-    C_sym
 
 
-  C_sym = math_sym3333to66(math_Voigt66to3333(C))
-  epsilon = 0.5_pReal*math_sym33to6(matmul(transpose(Fe),Fe)-math_I3)
+  epsilon = math_33toVoigt6_strain(matmul(transpose(Fe),Fe)-math_I3)
 
   associate(prm => param(ph), stt => state(ph), dlt => deltaState(ph))
 
-    r_W = 2.0_pReal*dot_product(epsilon,matmul(C_sym,epsilon))/prm%W_crit
+    r_W = (0.5_pReal*dot_product(epsilon,matmul(C,epsilon)))/prm%W_crit
     dlt%r_W(en) = merge(r_W - stt%r_W(en), 0.0_pReal, r_W > stt%r_W(en))
 
   end associate