Title: Characterization and Modeling of the Magnetomechanical Behavior of Iron-Gallium Alloys

Department/Program Of Aerospace Engineering / Technology

Abstract: Magnetostrictive Iron-Gallium alloys (Galfenol) demonstrate moderate magnetostriction (~350 ppm) under very low magnetic fields (~100 Oe), have very low hysteresis, high tensile strength (~500 MPa), high Curie temperature (~675°C), are in general machinable, ductile and corrosion resistant. Therefore, they hold great promise in active vibration control, actuation, stress and torque sensing in helicopters, aircrafts and automobiles. To facilitate design of magnetostrictive actuators and sensors using this material, as well as to aid in making it commercially viable, it is necessary to perform a comprehensive characterization and modeling of its magnetomechanical behavior. This dissertation addresses some of these issues, focusing primarily on quasi-static characterization and modeling of the magnetomechanical behavior of single-crystal FeGa alloys with varying gallium content and along different crystallographic directions, and studying the effect of texture on the magnetomechanical behavior of polycrystals. Additionally, improved testing and modeling paradigms for magnetostrictive materials are developed to contribute to a better understanding and prediction of actuation and sensing behavior of FeGa alloys. In particular, the actuation behavior (λ-H and B-H curves) for 19, 24.7 and 29 at. % Ga <100> oriented single crystal FeGa samples are characterized and the strikingly different characteristics are simulated and explained using an energy based model. Actuation and sensing (B-σ and є-σ curves) behavior of <100> oriented 19 at. % Ga and <110> oriented 18 at. % Ga single crystal samples are characterized. It is demonstrated that the sensing behavior can be predicted by the model, using parameters obtained from the actuation behavior. The actuation and sensing behavior of 18.4 at. % Ga polycrystalline FeGa sample is predicted from the volume fraction of grains close to the [100], [110], [210], [310], [111], [211] and [311] orientations (obtained from cross-section texture analysis). The predictions are benchmarked against experimental actuator and sensor characteristics of the polycrystalline sample.

Project Intro: Smart materials display a large coupling of thermal, electrical or magnetic properties with mechanical properties enabling them to directly transduce energy from one form to another in an efficient manner. These properties have made them promising materials for actuation and sensing applications. Over the past two decades various smart materials, viz. shape memory alloys, piezo-electrics and magnetostrictive materials, which respectively transduce thermal, electrical and magnetic energy to mechanical energy, have been used as actuators and sensors in a wide range of fields: medicine, micro-positioning, atomic force microscopes, torque sensing and fuel injection systems in automobiles, sonar transducers for the Navy and control surfaces of helicopters and aircrafts.

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Keywords: Engineering, Aerospace Engineering, Materials Science, Applied Mechanics, Iron-Gallium, Magnetostrictive, energy-based model, magnetomechanical, characterization

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Title: A Ceramic Damage Model for Analyses of Multi-Layered Ceramic-Core Sandwich Panels Under Blast Wave Pressure Loading 

Abstract: Ceramics have been used as armor materials because of their high effectiveness in absorbing kinetic energy under extreme loading conditions such as ballistic impacts. This is possible because they have very high compressive strengths. Ceramics exhibit significant compressive strength even when pulverized by a ballistic projectile. In addition, ceramic armors are lightweight, compared to conventional steel armors that are much heavier and more cumbersome. However, the brittleness of ceramics under tension has limited their use to applications that require little deformation such as the torso of war fighters. 

                              A damage model for ceramic materials is developed and incorporated into the geometrically nonlinear solid shell element formulation for dynamic analyses of multi-layered ceramic armor panels under blast wave pressure loading. The damage model takes into account material behaviors observed from multi-axial dynamic tests on Aluminum Nitride (AlN) ceramic. The ceramic fails in a brittle or gradual fashion, depending upon the hydrostatic pressure and applied strain-rate. In the model, the gradual failure is represented by two states: the initial and final failure states. These states are described by two separate failure surfaces that are pressure-dependent and strain-rate-dependent. A scalar damage parameter is defined via using the two failure surfaces, based on the assumption that the local stress state determines material damage and its level. In addition, the damage model accounts for the effect of existing material damage on the new damage. The multi-layered armor panel of interest is comprised of an AlN-core sandwich with unidirectional composite skins and a woven composite back-plate. To accommodate the material damage effect of composite layers, a composite failure model in the open literature is adopted and modified into two separate failure models to address different failure mechanisms of the unidirectional and woven composites.

 Keywords: Engineering, Aerospace, Engineering, Mechanical, Applied Mechanics.

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Abstract : The technical challenges and the key research efforts in the field of nanomaterials for aerospace applications. Specifically, it focuses on carbon nanotube-reinforced polymers and materials produced by severe plastic deformation (SPD). Selected European projects and world conferences related to aerospace are included. The state of the art of polymer nanocomposite research is also reviewed. In the aerospace industry, there is a great need for new materials which exhibit improved mechanical properties. Materials possessing high strength at a reduced mass and size make lighter aircraft with lower fuel consumption. The development of new materials with tailored properties is a primary goal of today’s materials science and engineering. However, the possibility of obtaining improved mechanical properties by the conventional methods of cold working, solution hardening, precipitation hardening, etc., has been almost exhausted. We explicitly exclude any military R&D and applications, as this falls outside the mandate of Nanoforum. Our target audiences are twofold: non-experts of an academic level with a general interest in the potential of nanotechnology for aerospace applications, and experts involved in setting the strategic R&D agenda in this field. There are single wall and multi wall thicked carbon nanotubes(SWCNT and MWCNT). Mechanical features of CNT:Young's modulus: 1 TPa ',Tensile strength: 200GPa CNTs have been shown to provide desirable electrical properties for polymer matrix composites.The applications in aerospace industry are through thermal barrier and wear resistant coatings, sensors that can perform at high temperature and other physical and chemical sensors, sensors that can perform safety inspection cost effectively.
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