Large Scale Magnetostrictive Valve Actuator  James A. Richard*, Elizabeth Holleman* and David Eddleman*  Abstract  Marshall Space Flight Center’s Valves, Actuators and Ducts Design and Development Branch developed  a large scale magnetostrictive valve actuator. The potential advantages of this tech nology are faster,  more efficient valve actuators that consume less power and provide precise position control and deliver  higher flow rates than conventional solenoid valves. Magnetostrictive materials change dimensions when  a magnetic field is applied; this property is referred to as magnetostriction. Magnetostriction is caused by  the alignment of the magnetic domains in the material’s crystalline structure and the applied magnetic field lines. Typically, the material changes shape by elongating in the axial direction and constricting in  the radial direction, resulting in no net change in volume. All hardware and testing is complete. This paper  will discuss: the potential applications of the technology; overview of the as built actuator design; discuss problems that were uncovered during the development testing; review test data and evaluate weaknesses  of the design; and discuss areas for improvement for future work. This actuator holds promises of a low  power, high load, proportionally controlled actuator for valves requiring 440 to 1500 newtons load.  Introduction  Magnetostrictive materials change dimensions when a magnetic field is applied; this property is referred  to as magnetostriction. Magnetostriction is caused by the alignment of the magnetic domains in the  material’s crystalline structure and the applied magnetic field lines. Typically, the material changes shape by elongating in the axial direction and constricting in the radial direction, resulting in no net change in  volume. The response is proportional to the applied field strength and occurs in microseconds. Most metals exhibit  this property. Nickel, for example, increases in length (strain) by approximately 40 parts per million in a  sufficiently strong magnetic field. Materials which produ ce strains greater than 600 PPM are known as  "giant" magnetostrictive or “smart” materials. Terfenol-D, produced by Etrema Products, Inc., produces  strains from 800 to 1200 PPM in fields as low as 2000 Oersteds (Oe) and is, currently, the only commercially available magnetostrictive material. Even though this is considered to be “Giant” scale  magnetostriction, the net motion is only 0.025 mm per 25 mm of material  The load carrying ability of the material is limited by the maximum stress the material can withstand;  therefore, the load density is far greater than conventional actuators power systems. Current solenoids  are limited to about 2.3 MPa, pneumatic systems to about 10 MPa and hydraulic system to 20 MPa. The yield strength of magnetostrictive materials is over 69 MPa, giving it a load density that is 3 times the best  available. The material is only limited by the small stroke.  Discussion  Approach:   The approach was to build a mechanical advantage system that will utilize a magnetostrictive  actuator to operate a large valve (25-mm size) at high flow demand. ER33 hoped to demonstrate the  valve will be as fast as a solenoid valve, precise as a hydraulic valve and lighter than either for its size.  Accomplishments:   All hardware and testing is comp lete. The valve performance was acceptable, but  strokes were not as predicted.  * NASA Marshall Space Flight Center, Huntsville, AL  Proceedings of the 39th Aerospace Mechanisms Symposium, NASA Marshall Space Flight Center, May 7-9, 2008  45