Challenge

A COPV with a history of Failure.

Solution

Developed a model to determine the underlying mechanisms.

Result

The underlying mechanism was determined to explain the rupture and explosion of the rocket.

Rocket Engine COPV

The material model considered is a rate-independent version of the nonlinear kinematic hardening model proposed by Chaboche. The constitutive equations are based on linear isotropic elasticity, a von Mises yield function and the associated flow rule.

Note:

Although this material model was originally believed to be important it became clear later that this was only a secondary effect.

With sufficient number of re-uses, the aluminum pressure vessel could possibly develop a Ratcheting problem.

Typical COPV Liner

Explanation of Failure Mechanism

• Understanding the actual installed boundary conditions

• As stress increases on the relatively soft aluminum tank, the strength is exceeded and the hot compressed Nitrogen gas is released into the rocket fuel creating an explosion.

• If fixed on one end the expansion can drive the aluminum liner out the other end.

• As the hot (soft) aluminum pushes out the stronger carbon will force this to fold and crease the tank, creating sharp corners with stress concentration.