Carbon fiber safety cage

Composite Structure Design for the Transition flying car

Role: system lead

Mechanical Engineer, Installation and Test Engineer

Led the design and optimization of the carbon fiber passenger safety cage of the Terrafugia Transition "roadable aircraft" prototype

Created Outer Mold Line as well as detailed part level CAD for vehicle and interior structural components including A and B beams, passenger seat "bath tub" and monocoque fuselage.
Established detailed success criteria for passenger safety structures based on Federal automotive crash safety standards as well as flight loading requirements.
Learned and used Catia V5 advanced surfacing and composite design/static analysis tools to design the individual structures of the safety cage as well as develop a prototype composite laminate design for use in the prototype vehicle.

Successes:

Developed technique to design efficient outer mold line based on draping of uni-directional carbon fiber, which allowed for significant weight and material cost savings.
Created detailed Ply Books for each component that illustrate the ply-by-ply make-up of each part, and worked with composite fabrication team to develop best practices and create high-quality parts for the prototype vehicle.
Prototype design of safety cage validated by third party non-linear dynamic analysis of entire vehicle structure.
Aircraft structure was built as designed and has had no issues or failures throughout drive and flight testing.

A-Pillar Draping Analysis

Visualization of shear deformation of the carbon fiber strands in the uni-directional laminate on the A-Pillar. Used this analysis to help drive the geometry of the beams and outer mold line.

Outer Mold Line CAD

OML CAD was iterated in conjunction with early structural analysis to accommodate changes based on the draping evaluation described in the previous image.

FEA: Forward Beam

The forward beam is the interface between the aluminum crush rails and the rest of the safety cage. In a crash, this beam is responsible for supporting the deceleration of the entire vehicle through the safety cage and guiding it into the crush rails.

FEA: Forward Beam

As the keystone of the crash safety structure, the forward beam was the first focus of the analysis. There are a number of evaluation methods used for composite analysis. The Tsai-Wu failure criteria was chosen as the primary, which returns a likelihood of laminate failure based on 8 specific failure modes of composite structures, including both fiber and matrix (epoxy) failures.

FEA: Forward Beam

The aluminum crush rail interface is represented by the dark blue rectangle in the middle of the beam.

Forward Beam and Crush Rail

View of the forward beam as installed in the vehicle. The aluminum crush rail can be seen in the left of the image and suspension components for the driver-side front wheel in the right of the image. Aluminum-to-carbon fiber bonding is used extensively throughout the vehicle.

Forward Beam Laminate Design

The forward beam was optimized by iterating the detailed laminate makeup ply by ply. This image shows a visualization of a carbon fiber cloth patch being applied to the beam.

FEA: Forward Beam

The analysis tools create detailed material properties for each element independently allowing for very detailed optimization of the laminate.

FEA: Center Console

The deceleration of most of the vehicle's mass is transferred to the forward beam through the center console structure. The large swath of red around the kink in the center console illustrate areas where the model is predicting laminate failure.

FEA: Center Console

A magnified view of strain helps identify the areas of the structure requiring reinforcement.

FEA: Center Console

Laminate iterations were done in small increments as any local change in stiffness can have dramatic effects down stream of the change. Moving slowly allows for better optimization in the end. This image shows an improvement in the stiffness of the kink in the center console.

FEA: A-Pillar, B-Pillar and Engine Beam

All of the mass not decelerated through the center console is handled by the engine beam - spanning the width of the vehicle - and channeled through the A and B pillars to the forward beam.

FEA: A-Pillar, B-Pillar and Engine Beam

Being smaller in height than the center console and of a geometry largely dictated by the outer mold line, these beams required thicker laminates to accomplish their jobs.

Transition Prototype

On the tarmac in Plattsburgh, NY for flight testing of the fully assembled vehicle.