The Best Guide to Shell VS Membrane Element Abaqus

In the realm of finite element analysis (FEA), selecting the appropriate element type is crucial for accurate and efficient modeling of complex structures. Among the various element types available, shell and membrane elements are commonly used for analyzing thin-walled structures such as aircraft fuselages, automobile bodies, and civil engineering components like bridges and buildings (Shell VS Membrane). While both shell and membrane elements serve to model thin structures, they have distinct characteristics and applications that make them suitable for different types of analyses.

In this blog post, you will learn the differences between Shell, Membrane and Plate elements.

1. Shell VS Membrane

In the realm of Finite Element Analysis (FEA), membrane and shell elements serve distinct but occasionally overlapping purposes, each tailored to specific structural requirements and behaviors. Let’s see the overview of Shell VS Membrane.

Membrane elements are designed to model planar structures where bending stiffness is negligible, focusing exclusively on in-plane forces. These elements are ideal for simulating surfaces subjected primarily to axial loads or planar stresses, such as tension structures like fabric membranes, sails, and certain thin slabs.

The primary characteristic of membrane elements is their ability to transfer loads directly to supporting structures without any resistance to bending, making them efficient for analyzing structures where out-of-plane deformations are insignificant.

Conversely, shell elements combine the properties of both membrane and plate elements, capable of resisting both in-plane and out-of-plane forces. This dual capability makes shell elements suitable for curved or bent structures that experience a combination of axial and flexural loads.

Examples include aircraft fuselages, pressure vessels, and complex architectural forms. Shell elements can be further categorized into thin and thick shells. Thin shells are used when transverse shear deformations are negligible, while thick shells account for significant shear deformations, capturing both shear and bending behaviors. This makes shell elements versatile and essential for accurately modeling complex geometries and structural behaviors where both in-plane and bending stiffness are critical.

Now let’s define each one in detail and also tell you about a third party involved, Plate elements.

2. What are Membrane elements? | Membrane Element Abaqus

Characteristics of Membrane element Abaqus:

• Behavior: Membrane elements model planar structures with little to no bending stiffness, focusing solely on in-plane forces.
• Stiffness: Only in-plane stiffness is considered; these elements do not resist out-of-plane forces.
• Load Transfer: Applied loads on membrane objects transfer directly to supporting structural objects, whereas meshed shell objects resist a portion of the load through flexural deformation.

Applications:

• Staircase Slabs
• Precast Slabs
• Ramp Slabs
• Deck Slabs
• Profile Slabs

Usage Rationale:

Membrane elements are ideal for structures that primarily experience axial loads or planar stresses. They are particularly useful in modeling surfaces where flexural deformations are negligible, such as tension structures (e.g., fabric structures and membranes). In these scenarios, membrane elements effectively transfer loads directly to the supporting structures, ensuring accurate stress distribution.

3. What are Shell elements?

Characteristics:

• Behavior: Shell elements combine the properties of membrane and plate elements, capable of simulating both in-plane and out-of-plane stiffness.
• Types:
  • Thin Shells: Used for structures where transverse shear deformation is negligible.
  • Thick Shells: Used when shear deformations are significant.
• Stiffness Calculation: Both in-plane and out-of-plane stiffness, along with shear deformation, are calculated by the program during analysis for thick shells, capturing both shear and bending deformations.

Applications:

• Aircraft Fuselages
• Ship Hulls
• Car Bodies
• Building Roofs
• Pressure Vessels
• Pipes

Usage Rationale:

Shell elements are suitable for curved or bent structures that experience a combination of in-plane and out-of-plane loads. They are essential in accurately modeling complex geometries and behaviors in structures like aircraft skins and pressure vessels.

3.1. Thin Shell vs. Thick Shell Elements

Thin Shell Elements:

• Behavior: Calculate both in-plane and out-of-plane stiffness without considering significant shear deformations.
• Applications: Common in RC beam and slab structures, irregular slabs, PT slabs, flat slabs, and shear walls.

Thick Shell Elements:

• Behavior: Account for in-plane and out-of-plane stiffness along with significant shear deformations.
• Applications: Used in scenarios where shear deformation is significant, such as raft slabs, foundation pads, and column capitals in flat slab designs.

4. What are Plate elements?

Characteristics:

• Behavior: Plate elements can resist out-of-plane loads by developing flexural stiffness and can also sustain in-plane forces.
• Types:
  • Thin Plates: Used when transverse shear deformation is negligible.
  • Thick Plates: Used when transverse shear deformation is significant and must be accounted for.

Applications:

• Flooring Systems in Buildings
• Bridge Decks

Usage Rationale:

Plate elements are used in flat, thin structures subjected to out-of-plane loading, such as floors and bridge decks. They effectively model bending and shear behaviors, making them essential in the design of structures where these forces are predominant.

5. Which element should we use?

Selection Criteria:

• Geometry: Curved structures generally require shell elements, while flat structures may use plate or membrane elements.
• Material Properties: Different materials may necessitate different elements based on their stiffness characteristics.
• Loading Conditions: The type of load (axial, bending, shear) significantly influences the choice of element.
• Accuracy: The desired level of accuracy and the importance of capturing specific deformations guide element selection.

Or you can consider this:

• Use membrane elements for very thin structures where bending is negligible (e.g., fabric).
• Use plate elements for flat plates where bending is the primary concern (e.g., shelves).
• Use shell elements for more complex structures with curvature or significant in-plane stresses (e.g., pressure vessels, car hoods).

6. Conclusion

Membrane, plate, and shell elements are crucial in FEA, each serving unique purposes based on the structural requirements. Membrane elements are used for purely in-plane forces, plate elements for out-of-plane bending with negligible thickness, and shell elements for combined in-plane and bending behaviors in curved structures (Shell VS Membrane). Understanding these elements’ characteristics and applications ensures accurate and efficient FEA simulations, leading to safer and more innovative structural designs. As FEA technology advances, the capabilities and applications of these elements will continue to expand, further enhancing engineering and design possibilities.

Here is the summarization of Shell VS Membrane VS Plate elements in one glance.

Keywords: Shell VS Membrane, Plate elements, Membrane element Abaqus

Did you know you can find more specific info about Membrane element Abaqus in the Abaqus documentation. Or click on the link below to see some practical examples of Shell, Plate, and Membrane elements:

membrane, plate, shell

Also, you can find useful info about elements in Abaqus in this article: Introduction to Abaqus element types