Obtaining softening factors was added

StructureHelperLogics/NdmCalculations/Cracking/ICrackStrainLogic.cs

@@ -0,0 +1,17 @@
+using StructureHelperCommon.Models.Forces;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace StructureHelperLogics.NdmCalculations.Cracking
+{
+    internal interface ICrackStrainLogic
+    {
+        StrainTuple BeforeCrackingTuple { get; set; }
+        StrainTuple AfterCrackingTuple { get; set; }
+        double SofteningFactor { get; set; }
+        StrainTuple GetCrackedStrainTuple();
+    }
+}