Ansys Simulation World 2021: Validating Composite Materials
How we used Ansys ACP and Mechanical to model anisotropic carbon fiber structures, predicting composite failures before manufacturing physical parts.
Carbon fiber is a designer’s dream and an engineer’s challenge. Unlike isotropic materials like steel or aluminum, which exhibit uniform strength in all directions, carbon fiber is highly anisotropic. Its strength depends entirely on how the individual fiber sheets are layered, oriented, and bonded.
Designing a high-performance bicycle frame without simulation is a guessing game. This post details our presentation at Ansys Simulation World 2021, focusing on how we used advanced solvers to model composite behaviors and prevent failures before laminating a single layer of carbon.
Table of contents
- The Anisotropic Material Challenge
- Optimizing Layups with Ansys Composite PrepPost
- Predicting Interlaminar Failure Modes
- Summary: Quantifying Composite Behavior
The Anisotropic Material Challenge
When engineering a custom carbon frame, you cannot rely on simple wall-thickness math. Carbon fiber tubes are constructed from multiple layers (plies) of uni-directional and woven fabrics.
If you align all the fibers along the length of the tube, it will be incredibly stiff in bending but will crush easily under clamping or torsional loads. To achieve high torsional stiffness and crash resistance, you must orient plies at alternating angles (e.g., 0°, 45°, 90°). Calculating the structural interaction of these layers manually is practically impossible.
KEY TAKEAWAY: Without high-fidelity composite modeling, engineers are forced to add excessive plies to guarantee safety, which defeats the weight-saving purpose of using carbon fiber in the first place.
Optimizing Layups with Ansys Composite PrepPost
At Simulation World 2021, we explained our layup simulation workflow. We use Ansys Composite PrepPost (ACP) to design the composite structure layer by layer:
- Defining the Ply Book: We input the exact fiber orientation, thickness, and material parameters for every carbon ply.
- Mapping CAD Coordinates: ACP maps the ply geometries onto the complex 3D shape of our frame CAD models, adjusting the fiber angles to match surface contours.
- Simulating Layup Draping: The software models how the carbon fabric stretches and deforms when pressed into the physical mold, identifying areas where fibers might bundle or wrinkle.
Figure 1: High-fidelity finite element analysis mapping mechanical loads across a complex frame.
Predicting Interlaminar Failure Modes
The most dangerous composite failure modes are hidden. A frame may look perfect on the outside while suffering from delamination — the separation of adjacent carbon plies under load.
Using Ansys Mechanical, we simulated interlaminar shear stresses. The software highlighted stress concentrations at the junctions of the bottom bracket and chainstays. This insight allowed us to adjust the overlap length of the plies, shifting reinforcement to where it was needed most and eliminating unnecessary weight in low-stress zones.
Summary: Quantifying Composite Behavior
Advanced simulation turns carbon layup from an artisanal trial-and-error craft into a highly predictable, repeatable science.
Key takeaways:
- Anisotropic optimization requires FEA: Predicting the behavior of complex composite plies requires dedicated solvers.
- ACP prevents draping errors: Modeling fabric deformation before manufacturing avoids physical mold defects.
- Isolate interlaminar stress: Focus ply-transition reinforcement on high-shear zones to maintain safety without adding weight.
Q&A
Q: What material parameters are needed for ACP to work? A: You must input the orthotropic properties of the carbon/resin matrix, including Young’s modulus, shear modulus, Poisson’s ratio, and tensile/compressive limits in all material directions.
Q: Do these simulations match real-world break tests? A: Yes. Our physical static overload tests regularly match Ansys failure location and load predictions within a 5% margin.