A preliminary theoretical effort has provided a robust three dimensional energy based model of magnetostrictive wave propagation in a general cubic magnetostrictive material. Under high intensity impact we predict that the wave front will split between a higher velocity elastic precursor wave and a lower velocity, strongly dissipative, magnetostrictive shockwave. The wave front solution strongly depends on longitudinal pre-stress level and initial magnetization state. We may expect that a significant portion of the magnetostrictive wave deformation will be reversible under the application of well chosen field paths. In combination these technical characteristics therefore present an opportunity to develop magnetostriction based shock hyper-toughness in safety critical civil and military structures utilizing relatively shock tough magnetostrictive materials such as Terfenol-D particle based composites or homogenous Galfenol rods.
The present work examines how the characteristics of the large thermal-compressive response of a 20 vol. % NiTi fiber 6082-T0 composite change with variations in the value of maximum tensile strain imposed during a preceding room temperature tensile process. We observe that the self thermal compression process is shifted to higher temperatures with increasing maximum room temperature tensile strain, and that the maximal thermal compression versus temperature slope becomes larger as the maximum tensile strain is increased from 4 to 6% and then becomes smaller as the maximum tensile strain is further increased to 7%.
Magnetostrictive Terfenol-D particle actuated epoxy polymer matrix composites were prepared with polyamine and anhydride cured epoxy polymer matrices. The different matrix epoxies exhibited large differences in glass transition and creep behavior. The differences in matrix thermal-mechanical properties resulted in important differences in temperature dependant damage behavior and magneto-elastic strain output in the Terfenol-D particle actuated epoxy polymer matrix composites.
The present paper presents cyclic strain amplitude and longitudinal strain measurements of longitudinally compressed Terfenol-D particle samples subjected to magneto-strain cycling. A comparison is made of the responses of material strain cycle tested at temperatures near the matrix glass transition start temperature, and material strain cycle tested at a temperature near the matrix glass transition finish temperature. The cyclic strain amplitude of the material was significantly larger when tested at a temperature near the matrix glass transition finish temperature. A useful range of longitudinal applied stress exists where the composite suffers little apparent degradation. Beyond this range the composite exhibits steadily decreasing cyclic strain amplitude with increases in longitudinal compressive stress magnitude.
The paper presents an incremental hysteretic magneto-elastic constitutive description of pseudo-cubic ferro-magnetostrictive alloys, which may be used to predict the magneto-elastic response of these materials under quite general applied magnetic field and stress processes. These processes may include fully saturated major loop, unsaturated minor loop or more general types of magnetic field processes. Local stress and domain wall pinning non-uniformities assumed in the development of the model result in smooth and continuous hysteretic magnetization and magnetostriction curves which follow the magnetization and magnetization anhysteretics with a non-constant offset. Comparisons between model results and a set of high quality measurements show that the model is agrees well with experimental curves when the magnetization response is dominated by inhibited domain wall motion.
The present paper develops a one dimensional magneto-elastic model of a magnetostrictive fiber actuated polymer matrix composite material which accounts for a strong visco-elastic response in the polymer matrix. The visco-elastic behavior of the composite polymer matrix is modeled with a three parallel Maxwell element visco-elastic model, the magneto-elastic behavior of the composite fibers is modeled with an anhysteric directional potential based domain occupation theory. Example calculations are performed to identify and explain the dynamical behavior of the composite. We observed that the increasing and decreasing limbs of the magnetization and magnetostriction loops are offset at middle levels of applied field. This offset is a consequence of the interaction of the time varying fiber stress caused by matrix viscosity with a multi-domain state in the fiber. The small increase in fiber longitudinal compressive stress due to matrix viscosity under increasing field inhibits the occupation of domains with magnetization orientations near the fiber longitudinal direction. As a consequence, the summed longitudinal magnetization and magnetostriction is reduced as compared to the decreasing field limb. This results in an apparent hysteresis loop in the magnetization and magnetostriction curves even though the model does not include magneto-elastic hysteresis in the fibers.
The present work develops a quantitative theory of the self thermal-plastic response of NiTi shape memory alloy actuated metal matrix composite materials. Model calculations are compared with existing experimental data obtained from a testing procedure consisting of an initial room temperature, 5% tensile elongation process, and a subsequent room temperature to 120 degree(s)C unconstrained (external stress free) heating process. During the unconstrained heating process the composite fiber actuators attempt to recover pseudo-plastic strain imparted during the room temperature tensile prestrain process. As the temperature increases, the fiber stress-temperature state enters increasing phase transformation intensity, resulting in strong increases in fiber longitudinal tensile stress, matrix longitudinal compressive stress and composite compressive longitudinal external strain. Sufficient temperature brings the matrix stress state to the point of plastic yield. The composite then exhibits a very unusual, self thermal-plastic compression response, recovering approximately 2.2% strain.
The present experimental effort characterizes the development of damage in two different forms of experimental magnetostrictive composite material. This effort is intended to identify the various forms of damage mechanisms operating in the two very different materials, and to identify how the development of fine scale damage influences the overall magnetostrictive behavior and performance. Optical examination of as-magneto-strain cycled Terfenol-D particle actuated epoxy matrix composite material strongly suggests the following primary damage processes, particle fracture under cyclic internal stress, severe degradation of the particle to epoxy matrix interfacial bond, and ultimate sample failure by matrix crack coalescence leading to complete granulation.
We report cyclic strain measurements form an experimental Terfenol-D actuated polymer matrix composite. Basic material constitutive response are identified as functions of frequency. Anhysteric theory is used to quantitatively model the behavior of the composite. Insight provided by the analysis is used to suggest material design changes leading to improved composite performance.
Vibration control in structures often requires the addition of viscoelastic constrained layer damping treatments. In critical applications, however, the low strength of the viscoelastic material and the threat of delamination prevent the use of these treatments. In this paper we present a means of how to overcome these difficulties by using high strength shape NiTi fibers to increase the damping of aluminum structures. Specifically, we show that the introduction of high strength, shape memory alloy fibers into an aluminum beam can result in a significant increase in the passive damping response of the beam. The objective of our research is to develop passive and active structural materials that can be sued in applications that demand high loss factors, strength, and high reliability. The development of the NiTi fiber reinforced aluminum matrix composite beam is a first important step towards achieving this objective.
The present work reports macroscopic thermal mechanical and in-situ neutron diffraction measurements from a 22.9 volume percent, 50.7 at percent Ni-Ti fiber actuated 6082-T6 aluminum matrix composite and 6082-T6 homogeneous aluminum control material subjected to an initial room temperature 4 percent tensile elongation and unloading process followed by a subsequent room temperature to 120 degrees C unconstrained heating process. During the unconstrained room temperature to 120 degrees C heating process, the composite exhibited a pronounced, nonlinear thermal contraction, while the homogeneous control exhibited the expected linear thermal expansion. The composite thermal compression was clearly the result of a powerful shape memory response in the NiTi fiber actuators.
A new theory is presented of the nonlinear magneto-elastic behavior of magnetically dilute magnetostrictive particulate composites. The theory assumes a uniform external magnetic field is operating on a large number of well distributed, crystallographically and shape parallel ellipsoidal magnetostrictive particles encased in an elastic, nonmagnetic composite matrix. The aspect ratio of the particulates may vary between 1 to infinity and the volume fraction of the particulates may vary between zero and one. Example calculations show that the model is able to provide qualitatively correct magnetostriction curves for both homogeneous Terfenol-D rod and experimental Terfenol-D particulate actuated epoxy matrix composites.
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