Load
10 N
Design target for the suspended center load.
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Lightweight structures case study
3D Lattice Structure Design
Design, simulation, and testing of a lightweight load-bearing structure
Design Load 10 N
Span 150 mm
Failure 18.2 N
Member Dia. 2 mm
Overview
A lightweight printed frame designed to carry load efficiently across a constrained span.
This project involved designing, 3D printing, and testing a lightweight lattice structure capable of supporting a 10 N load over a 150 mm square opening while minimizing material usage.
The engineering challenge was not simply making the part strong. The design needed to balance strength, stiffness, mass, manufacturability, and buckling resistance while remaining printable as a single-piece PLA structure.
CAD modeling, ANSYS simulation, iterative redesign, and physical load testing were used together to move from an overbuilt pyramidal frame to a more efficient bridge-like final geometry.
Design Requirements
The structure had to be light, printable, and strong enough to pass a defined load case.
The requirements forced the design away from arbitrary material addition and toward efficient load paths.
Span
150 mm
Structure bridged a square opening between supports.
Build
Single piece
Geometry had to print as one continuous lattice.
Members
12+
Minimum member count with identical cross sections.
Section
Circular
Common member profile for uniform stiffness behavior.
Objective
Minimum mass
Reduce material while maintaining load-bearing capacity.
Engineering Principles
The final geometry was shaped around stability, not just stress.
Lightweight lattices often fail through buckling or manufacturing defects before reaching an ideal material stress limit. The design process treated member layout, member length, and print quality as primary engineering variables.
Tension and compression load paths
Tension members primarily carry axial stress, while compression members can fail through instability before material yield.
Buckling governs slender compression members
Euler buckling was treated as the dominant risk, so member length and end conditions mattered as much as stress magnitude.
Shorter members improve stability
Reducing unsupported length raised buckling resistance and helped the final design carry load with thinner members.
Circular cross sections simplify behavior
Round members provided consistent bending stiffness independent of loading direction and were practical to model and print.
Triangulation controls deformation
Triangular substructures converted the frame into stable load paths instead of relying on flexible rectangular spans.
Print direction affects real strength
FDM anisotropy, layer bonding, supports, and local defects were considered because printed PLA does not behave like an ideal solid.
Initial Design
The first concept was strong, but inefficient.
The initial design used a stacked pyramidal structure with 72 members and an estimated mass of about 30 g. It easily carried the design load, but that performance came from excess material rather than an optimized load path.
ANSYS results showed a stress safety factor of about 10.77 and an eigenvalue buckling multiplier of about 24. In practical terms, the design was far beyond the required 10 N load case and included many zero-force members that did little structural work.
Members 72
Mass ~30 g
Buckling Mult. ~24
Design Iteration
Removing inactive members reduced mass and improved material utilization.
The second design removed unnecessary members, especially around the base corners, reducing the frame to 48 members and about 21 g.
Stress distribution improved and the stress safety factor dropped to about 1.35, which was much closer to the material-use objective. However, the model still contained zero-force members and left room for additional optimization.
Members 48
Mass ~21 g
Stress FOS ~1.35
Final Design
The final frame uses bridge-like load paths and shorter compression members.
The final design reconfigured the frame to spread stress more evenly while reducing the risk of compression-member buckling. The pyramidal apex was replaced by intersecting bends, and the full perimeter support was replaced with a bridge-like structure that touched two sides of the span.
A central opening was maintained for the loading setup. Members were set to a 2 mm circular diameter, which was the smallest practical size for reliable printing on the Bambu Labs P1P while still surviving support removal.
Member diameter 2 mm
Failure mode Buckling
Simulation
ANSYS simulation showed that buckling, not yield, controlled the final design.
The final model used PLA material properties, mesh refinement, a distributed load at the top, and simple supports at the base faces to represent the table-contact condition.
A
Model Setup
ANSYS Mechanical was used with PLA material properties including an elastic modulus of 3 GPa and Poisson's ratio of 0.35. A refined mesh was applied to the slender members.
Mesh 0.05 in element sizing
The mesh needed enough resolution to capture deformation and buckling behavior without producing a noisy model.
B
Boundary Conditions
The load was distributed over the upper loading face rather than applied as an ideal point force. The base used simple supports on the contact faces because the structure could slide slightly on the table surfaces.
Load case 10.01 N applied at the top
This better represented the physical test fixture, where force was transferred through the hanging weight setup.
C
Result
The final design was predicted to safely carry the 10 N design load. The governing simulation result was eigenvalue buckling rather than von Mises stress.
10 N buckling FOS 2.1468 simulated
That margin supported moving forward to physical printing and incremental load testing.
Testing
The printed structure survived the design load and failed above the target.
The test setup placed the lattice across a 150 mm gap between two tables. Load was applied through hanging weights attached near the center of the structure, then increased incrementally until failure.
The structure survived 10.01 N and 15.41 N without failure, then failed at about 18.20 N. The first-failure load was estimated near 17.5 N based on the experimental data.
10.01 N No failure
1.748 estimated experimental safety factor
15.41 N No failure
1.136 estimated experimental safety factor
18.20 N Failure
0.962 estimated experimental safety factor
Simulation vs Experiment
The model overpredicted physical performance by roughly 20 to 23 percent.
Simulation correctly identified buckling as the controlling failure mode, but the experimental structure failed earlier than the idealized ANSYS model predicted.
The difference was consistent with real additive-manufacturing behavior: the printed part had lower effective infill density, layer anisotropy, small defects from FDM printing, and possible support-removal damage. Those imperfections reduced the strength of slender members and created local stress concentrations.
Load Stress FOS Buckling FOS Difference
10.01 N 3.0199 2.1468 22.8%
15.41 N 1.9617 1.3945 22.76%
18.20 N 1.6610 1.1807 22.73%
Manufacturing Considerations
Printability set a practical lower bound on structural efficiency.
The final shape required removable supports because the load point sat above the base plane. Support removal became a real design constraint because the same slender members that reduced weight were also vulnerable to handling damage.
Testing and slicer review made 2 mm the practical minimum member diameter. Smaller members improved mass efficiency in theory, but print quality dropped and the risk of cracking during support removal increased.
The final design therefore balanced structural efficiency with the realities of FDM PLA fabrication: anisotropic layer behavior, support scars, infill assumptions, and the need to remove material without damaging the load path.
Results
The final design met the 10 N requirement and provided experimental margin.
The final printed structure successfully supported the required 10 N load over the 150 mm span and remained intact through 15.41 N.
Failure occurred at about 18.20 N, validating the core design approach while also showing the importance of accounting for real manufacturing effects in simulation.
Key Takeaways
Buckling dominates lightweight structures.
For slender printed members, stability can govern before material yield becomes the limiting condition.
Efficient load paths matter more than member count.
Removing inactive members made the design lighter and more meaningful structurally.
Simulation needs manufacturing reality.
Idealized solid PLA does not fully capture infill, layer bonding, support damage, and print defects.
3D printing constraints shape the design.
The minimum practical member diameter was set by printability and support removal, not just analysis.
Iteration is essential for optimization.
The project moved from a safe but inefficient frame to a lighter bridge-like geometry through repeated CAD, simulation, printing, and testing cycles.
Image Gallery
Extracted report visuals from CAD, simulation, buckling, manufacturing, and testing.
Click any image to open the extracted report asset at full size.