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+---
+type: concept
+title: "Shell Locking Phenomenon"
+complexity: advanced
+domain: computational-mechanics
+aliases:
+  - shell locking
+  - locking phenomenon
+  - membrane locking
+  - shear locking
+created: 2026-05-28
+updated: 2026-05-28
+address: c-000045
+tags:
+  - concept
+  - finite-element-method
+  - shell-elements
+  - locking
+status: current
+related:
+  - "[[On-the-Finite-Element-Analysis-of-Shell-Structures]]"
+  - "[[Assumed Transverse Shear Strain Interpolation]]"
+  - "[[MITC4 Shell Element]]"
+  - "[[Displacement-Based Finite Element Formulation]]"
+  - "[[Shell Structure Asymptotic Behavior]]"
+  - "[[Uniform Optimal Convergence]]"
+sources:
+  - "[[On-the-Finite-Element-Analysis-of-Shell-Structures]]"
+---
+
+# Shell Locking Phenomenon
+
+## Definition
+
+Shell locking is a thickness-dependent finite element error in which a shell element becomes artificially stiff as the shell becomes thin. It appears as underpredicted displacements, stresses, strains, and strain energy, and as poor convergence in thin-shell bending or mixed-dominated problems.
+
+## How It Works
+
+The source connects locking to [[Shell Structure Asymptotic Behavior]]. Displacement-based shell elements may fail to approximate the pure bending displacement space of the [[Basic Shell Mathematical Model]]. The result is parasitic membrane or transverse shear strain in states that should be nearly strain-free in those modes.
+
+The paper distinguishes membrane locking from shear locking. Membrane locking appears in curved shells, while transverse shear locking can appear regardless of curvature when the interpolation cannot represent the thin-shell bending constraint.
+
+## Remedies
+
+Common remedies include reduced integration, incompatible or non-conforming modes, ANS, EAS, and MITC-style mixed interpolation. The source treats MITC as a particularly effective family because it interpolates selected tensorial strain components at tying points while trying to retain consistency and ellipticity.
+
+## Connections
+
+- [[Assumed Transverse Shear Strain Interpolation]] is the targeted shear-locking remedy used in the four-node shell thread.
+- [[MITC4 Shell Element]] is the practical low-order shell element thread that uses mixed interpolation to control locking.
+- [[Uniform Optimal Convergence]] is the desired behavior after locking has been controlled.
+- [[Shell Element Benchmark Testing]] describes how locking should be exposed using convergence curves and thickness variation.
+
+## Sources
+
+- [[On-the-Finite-Element-Analysis-of-Shell-Structures]]