add wiki

wiki/concepts/Reduced Integration and Hourglass Control.md

@@ -4,7 +4,7 @@ title: "Reduced Integration and Hourglass Control"
 complexity: advanced
 domain: computational-mechanics
 created: 2026-05-29
-updated: 2026-05-29
+updated: 2026-06-01
 address: c-000057
 aliases:
   - reduced integration
@@ -18,13 +18,17 @@ tags:
 status: current
 related:
   - "[[Abaqus Theory Manual]]"
+  - "[[Abaqus-Analysis-User-s-Guide-Volume-IV|Abaqus Analysis User's Guide Volume IV]]"
   - "[[Abaqus Element Library]]"
+  - "[[Abaqus Element Selection and Formulation]]"
+  - "[[Abaqus Continuum Element Families]]"
   - "[[Isoparametric Finite Elements]]"
   - "[[Solid Element Stiffness Integration]]"
   - "[[Shell Locking Phenomenon]]"
   - "[[Hybrid Incompressible Elements]]"
 sources:
   - "[[Abaqus Theory Manual]]"
+  - "[[Abaqus-Analysis-User-s-Guide-Volume-IV|Abaqus Analysis User's Guide Volume IV]]"
 ---
 
 # Reduced Integration and Hourglass Control
@@ -39,6 +43,8 @@ Reduced integration can reduce computational cost and, in some element families,
 
 The risk is rank deficiency: some displacement patterns can produce little or no strain energy at the reduced integration points. These patterns appear as hourglass or zero-energy modes. Abaqus controls them by adding artificial stiffness or related stabilization terms so the element remains usable without losing the intended benefits of reduced quadrature.
 
+[[Abaqus-Analysis-User-s-Guide-Volume-IV|Volume IV]] shows how this becomes a naming and selection issue. Many Abaqus element names use `R` to mark reduced integration, such as `C3D8R` and `S4R`, and the element family determines which hourglass-control assumptions are appropriate.
+
 ## Why It Matters
 
 Reduced integration is not just a cheaper quadrature rule. It changes the numerical behavior of the element and must be judged together with element topology, mesh distortion, material behavior, contact, and expected deformation mode.
@@ -47,10 +53,12 @@ Reduced integration is not just a cheaper quadrature rule. It changes the numeri
 
 - [[Isoparametric Finite Elements]] supplies the quadrature framework.
 - [[Abaqus Element Library]] places reduced integration among full, selective, and hybrid element choices.
+- [[Abaqus Element Selection and Formulation]] connects reduced integration to element suffixes and analysis-product availability.
+- [[Abaqus Continuum Element Families]] shows where reduced-integration solid and coupled-field variants appear.
 - [[Shell Locking Phenomenon]] is one reason under-integration or assumed-strain methods are introduced.
 - [[Hybrid Incompressible Elements]] is a more explicit mixed alternative for incompressible response.
 
 ## Sources
 
 - [[Abaqus Theory Manual]]
-
+- [[Abaqus-Analysis-User-s-Guide-Volume-IV|Abaqus Analysis User's Guide Volume IV]]