Implemented surface constraint member function to choose whether a no…

…dal integration rule should be installed on the surface. The fixed normal displacement now sets a non-nodal integration rule.

FEBioMech/FEFixedNormalDisplacement.h

@@ -52,6 +52,9 @@ class FEFixedNormalDisplacement : public FESurfaceConstraint
 
     // allocate equations
     int InitEquations(int neq) override;
+
+	// we don't use nodal integration for this constraint
+	bool UseNodalIntegration() { return false; };
 
 protected:
     void Update(const std::vector<double>& Ui, const std::vector<double>& ui) override;

FEBioXML/FEBioConstraintsSection.cpp

@@ -288,7 +288,7 @@ void FEBioConstraintsSection25::Parse(XMLTag &tag)
 					const char* szsurf = tag.AttributeValue("surface");
 					FEFacetSet* pface = mesh.FindFacetSet(szsurf);
 					if (pface == 0) throw XMLReader::InvalidAttributeValue(tag, "surface", szsurf);
-					if (GetBuilder()->BuildSurface(*psurf, *pface, true) == false) throw XMLReader::InvalidAttributeValue(tag, "surface", szsurf);
+					if (GetBuilder()->BuildSurface(*psurf, *pface, psc->UseNodalIntegration()) == false) throw XMLReader::InvalidAttributeValue(tag, "surface", szsurf);
 				}
 
                 // get the nodeset for other constraints

FECore/FESurfaceConstraint.h

@@ -41,4 +41,9 @@ class FECORE_API FESurfaceConstraint : public FENLConstraint
 
 	// return the surface
 	virtual FESurface* GetSurface() { return 0; }
+
+	// we need an integration rule for all surfaces. 
+	// By default, this was always assumed to be a nodal integration rule
+	// but this is not always desired, so derived classes can override this
+	virtual bool UseNodalIntegration() { return true; };
 };