Let's get acquainted with this study:
For pipe intersection FEA analysis on ABAQUS, both hex and shell elements have their advantages and disadvantages, but generally, hex elements are preferred. Here's a breakdown to help you decide in a nutshell:
• Solid elements are useful/suitable for geometrically non-linear analysis (increasingly large displacements, rotations, and shearing)
• Initial stress stiffness and pressure load stiffness due to surface loads are included, allowing for the use of these elements.
• When finite strains are considered, the formulation employs true stress/ force per unit area and the integrated rate of deformation as strain measure.
Boundary Conditions of the analysis (remain the same for both element types)
Material: AISI 4130
Force: 1000N
Clamps on both open ends to lock DOFs.
In this case study, we first analyzed: C3D8R elements,
Hex elements (hexahedral elements):
C – Continuum
3D – Three Dimensional
8 – 8 nodes
R- Reduced Integration
Figure 1: Global element type selection in Mechanical scenario creation app on 3DExperience Platform
Figure 2: Representation of the hex mesh at the junction of intersection of the pipes
Figure 3: representation of the mesh on the face of the pipe
Figure 4: sweep mesh specs
Results with C3D8R (linear hex elements)
Figure 5: Von mises stress with C3D8R elements
Figure 6: Displacement with C3D8R elements
Advantages:
- More accurate representation of complex 3D geometry, especially around the intersection.
- Less prone to shear locking, a numerical issue that can affect results in some analyses.
- Generally, lead to more converged solutions (reaching a stable answer) with fewer elements.
Disadvantages:
- Can be more difficult to mesh complex geometries, especially if there are sharp corners or transitions.
- May require more computational resources due to the higher number of nodes per element.
Results with S4R (linear shell elements) :
S - Shell
4 - 8 Nodes
R - Reduced Integration
Figure 8: Global element type selection in Mechanical scenario creation app on 3DExperience Platform
Figure 9: representation of the shell mesh on the face of the pipe
Figure 10: Representation of the hex mesh at the junction of the intersection of the pipes
Figure 11: Von Mises stress with S4R elements
Figure 12: Displacement with S4R elements
S8R (non-linear shell elements):
S - Shell
8 - 8 Nodes
R - Reduced Integration
Figure 13: Global element type selection in Mechanical scenario creation app on 3DExperience Platform
Figure 14: representation of the shell mesh on the face of the pipe
Figure 15: Representation of the hex mesh at the junction of the intersection of the pipes
Figure 16: Von Mises stress with S8R elements
Figure 18: Displacement with S8R elements
Advantages:
Easier to mesh complex geometries compared to hex elements.
Can be more efficient for some types of analyses, especially with simpler geometries.
Disadvantages:
Less accurate than hex elements for complex 3D geometries, particularly around the intersection.
More prone to shear locking, which can require special techniques to mitigate.
May require more elements to achieve the same level of accuracy as hex elements (in this case wedge elements were added to compensate for the topology change at the junction of the intersection)
Observations:
C3D8R
It can be noted that the Von Mises Stress for C3D8R (hexahedral elements) ranges between
And the maximum displacement: 5.25mm
S4R
It can be noted that the maximum Von Mises Stress for S4R ( linear shell elements) were
and the maximum displacement: 4.97mm
S8R
It can be noted that the maximum Von Mises Stress for S8R (non-linear shell elements) were
and the maximum displacement: 8.24mm
Conclusion:
- The complexity of the pipe intersection: For simpler intersections, shell elements might be sufficient. However, for complex geometries with curved transitions or branches, hex elements are highly recommended for better accuracy.
- The type of analysis: If you're performing a linear static analysis, shell elements might be acceptable. However, for non-linear analysis involving large deformations or contact, hex elements are generally preferred.
- Your experience with meshing: If you're new to FEA meshing, shell elements might be easier to start with. However, with some practice, hex elements can be created efficiently.
