Failure analysis of an injection molded modular tail section on an autonomous underwater vehicle

Injection molded plastic (Ultem) pressure vessels are used as modular underwater vehicle body sections on the morpheus autonomous underwater vehicle at Florida Atlantic University. The bulk properties of the material were used in the design and analysis due to the lack of effective property data of the Ultem injection module which are actually dependent on the molding process. A series of test specimens were prepared and tested to determine the tensile strength, bending strength, shear strength and Young´s modulus achieved in the final modules. Implementation of the control surface actuators that penetrate the plastic pressure vessel requires an assessment of the desired failure mode of the system and an accurate structural model of the system components. A nonlinear finite element analysis of the actuator system including the plastic modules is developed as a quarter section in order to take advantage of the symmetry of the problem. Finally, failure modes are found using von Mises analysis