Algor Software Helps Researcher Investigate Composite Materials for Rocket Nose Cone

Sometimes, the best designs are quite simple, geometrically, and the most critical engineering takes place in selecting the material from which a product will be constructed. Elizabeth Mullins <tcsbrm@airmail.net> of Texas Computing and Simulation (TCS) in Arlington, Texas, knows this well.

Ms. Elizabeth Mullins (left) used Algor software to analyze a rocket nose cone (right) in order to determine the best material for construction.

Ms. Mullins analyzed a design for a rocket nose cone to determine the best material to use for construction of a new generation of 2.75-inch air-launched, free-flight artillery rockets (FFAR). The project was part of her requirement for a M.S. in Engineering Mechanics at the University of Texas at Arlington under a cooperative program with TCS. The manufacturing requirements for the Advanced Rocket System (ARS) program included the ability to mold a light-weight nose cone as a single piece while accurately maintaining a prescribed contour and minimizing production costs. The geometry of the model was simple and axisymmetric, but the choice of material was critical.

"My goal was to analyze the rocket nose cone to meet flight load requirements while reducing the weight and production costs using modern materials in new and novel ways," said Ms. Mullins.

About the ARS

The ARS is designed for the U.S. Navy and Marine Corps to be used for future amphibious and air strike warfare scenarios. The performance of ARS rockets is envisioned to have considerable improvement over the current 2.75-inch FFAR system, the HYDRA-70. The ARS has a burnout velocity of at least 1,000 meters per second from a ground launch - about 280 meters per second faster than the HYDRA-70's burnout velocity. The higher burnout velocity results in a flatter trajectory and a longer range. Flight time to a target is reduced, which increases the launch aircraft's survivability.

Investigating Materials

Ms. Mullins investigated a number of metal and polymer resins for the nose cone, but weight, production costs and other requirements reduced the choice to a composite material. These composites can be strengthened using fiber reinforcements such as fiberglass or carbon. In addition, other compounds can be added to the base resin to change heat conduction and electrical conductivity characteristics. Both of these characteristics are very important when designing a new rocket nose cone. In all, a matrix of over 30 different materials was considered in the analysis.

Analyzing the Nose Cone

To examine the rocket nose cone, linear stress analyses were used, including pressure, centrifugal acceleration, and inertial loadings. The pressure loading is a result of supersonic flight speed in excess of 1,340 meters per second, while the centrifugal loading is a result of the rocket being spin-stabilized in flight. The inertial loading is a result of the rapid acceleration during launch that can exceed 130 Gs.

The results of the finite element analyses were cross-checked against calculations using classical techniques from strength of materials and theory of elasticity. Since satisfactory agreement between methods was reached, Ms. Mullins could confidently select a material for the nose cone based on the analysis results.

These linear stress analysis results were used to determine the best material from which to create a rocket nose cone.
Maximum principal stress contour of the rocket nose cone tip	Minimum principal stress contour of the rocket nose cone tip	Von Mises stress contour of the rocket nose cone tip

Choosing the Best Material

Based on the stress analysis, any number of polymer materials would suffice for manufacturing purposes. However, the aerodynamic heating associated with high-speed flight would lead to melting, vaporization and ablation of conventional composite materials. As the high temperature requirement exists for only a few seconds, material selection was easily reduced to only those materials that had favorable stress, cost, electrical conductivity and heat resistance characteristics. It was recommended that a fiberglass-reinforced Ablative PEEK be chosen.

In addition to offering superior manufacturing characteristics at competitive pricing, Ablative PEEK can withstand temperatures of over 2000 degrees Fahrenheit while being electrically nonconductive. The ablation process forms a thin glass-like surface that chars and acts as a near-perfect insulation layer protecting the material beneath. The material needs only to maintain the protective layer for a few seconds during flight.

About Algor

"Algor software provides a cost-effective way to obtain good, solid FEA results," said Ms. Mullins. "This is particularly important to small companies, universities and consultants."

"I also appreciate that the software is continually being updated with additional capabilities and enhancements," concluded Ms. Mullins.

Algor at Work on Materials

Below are links to case histories about other Algor customers using their engineering expertise in the area of special materials.

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