The mechanical and fatigue characteristics of superelastic NiTi thin plates in the large strain area were obtained by tensile and pulsating 4-point bending tests to establish the design guidelines for the ferromagnetic shape memory alloy (FSMA) composite actuator and its fatigue life. The stress-strain curves of NiTi thin plates were found to be strain rate dependent. The finite element analysis (FEA) result using the stress-strain curve measured by tensile test is in good agreement with the experimental results of the 4-point bending tests. The relationship between the maximum bending strain and the number of cycles to failure in pulsating 4-point bending fatigue tests was obtained as well as an analysis of the fatigue fracture surfaces of NiTi thin plates.
Bio-inspired actuation, such as flapping of flying insect, has been an attracted research subject because of their superior
maneuverability at low Mach number flight. Flapping mechanism of biological flying insects and birds have been
identified as the promising ones for future micro- or nano- air vehicles (MAV or NAV) for stealth surveillance
applications. The kinematics of flapping wings is very complicated, including flapping and rotating. One promising
thorax actuator design to mimic motions of flapping wings is based on ferromagnetic shape memory alloy (FSMA)
composite which is made of superelastic SMA and soft iron. FSMA composite has been proved as a promising actuator
material for fast responsive and robust actuators based on hybrid mechanism. We designed a prototype thorax actuator
based on the FSMA composite and hybrid mechanism concept. Our preliminary tests show that the NiTi/polymer
composite wing swings back and forth with 60 degree at 22Hz which is close to its resonance frequency. Toward the
end of each flapping cycle, the wing also rotates due to the inertia force as passive rotation. The flapping angle is so
large that a high stress is induced on the NiTi wing frame near the fixture therefore a stress-induced martensite
transformation (SIM) occurs with large elastic strain. Because of this superelastic property of NiTi, the wing frame will
spring back.
An improved version of the membrane actuator has been designed and constructed based on our previous diaphragm actuator. It consists of ferromagnetic shape memory alloy composite (FSMA) diaphragm and an electromagnet system. The actuation mechanism of the membrane actuator is the hybrid mechanism that we proposed previously. The high momentum airflow will be produced by the oscillation of the circular FSMA composite diaphragm driven by electromagnets close to its resonance frequency. This membrane actuator is designed for the active flow control technology on airplane wings. The active flow control (AFC) technology has been studied and shown that it can help aircraft improve aerodynamic performance and jet noise reduction. AFC can be achieved by a synthetic jet actuator injecting high momentum air into the airflow at the appropriate locations on aircraft wings. Due to large force and martensitic transformation on the FSMA composite diaphragm, the membrane actuator can produce 190 m/s synthetic jets at 220 Hz. A series connection of several membrane actuators is proposed to construct a synthetic jet actuator package for distributing synthetic jet flow along the wing span.
The DARPA Sponsored Compliant Surface Robotics (CSR) program pursues development of a high mobility, lightweight, modular, morph-able robot for military forces in the field and for other industrial uses. The USTLAB and University of Washington Center for Intelligent Materials and Systems (CIMS) effort builds on USTLAB proof of concept feasibility studies and demonstration of a 4, 6, or 8 wheeled modular vehicle with articulated leg-wheel assemblies. A collaborative effort between USTLAB and UW-CIMS explored the application of Shape Memory Alloy Nickel Titanium Alloy springs to a leg extension actuator capable of actuating with 4.5 Newton force over a 50 mm stroke. At the completion of Phase II, we have completed mechanical and electronics engineering design and achieved conventional actuation which currently enable active articulation, enabling autonomous reconfiguration for a wide variety of terrains, including upside down operations (in case of flip over), have developed a leg extension actuator demonstration model, and we have positioned our team to pursue a small vehicle with leg extension actuators in follow on work. The CSR vehicle's modular spider-like configuration facilitates adaptation to many uses and compliance over rugged terrain. The developmental process, actuator and vehicle characteristics will be discussed.
A new membrane actuator based on our previous diaphragm actuator was designed and constructed to improve the dynamic performance. The finite element analysis was used to estimate the frequency response of the composite membrane which will be driven close to its resonance to obtain a large stroke. The membrane is made of ferromagnetic shape memory alloy (FSMA) composite including a ferromagnetic soft iron pad and a superelastic grade of NiTi shape memory alloy (SMA). The actuation mechanism for the FSMA composite membrane of the actuator is the hybrid mechanism that we proposed previously. This membrane actuator is designed for a new synthetic jet actuator package that will be used for active flow control technology on airplane wings. Based on the FEM results, the new membrane actuator system was assembled and its static and dynamic performance was experimentally evaluated including the dynamic magnetic response of the hybrid magnet.
A new diaphragm actuator based on the ferromagnetic shape memory alloy (FSMA) composite is designed where the FSMA composite is composed of ferromagnetic soft iron and superelastic grade of NiTi shape memory alloy (SMA). The actuation mechanism for the FSMA composite plate of the actuator is the hybrid mechanism that we proposed previously. This diaphragm actuator is the first design toward designing a new synthetic jet actuator that will be used for active flow control technology on airplane wings. The design of the FSMA composite diaphragm actuator was established first by using both mechanical and ferromagnetic finite element analyses with an aim of optimization of the actuator components. Based on the FEM results, the first generation diaphragm actuator system was assembled and its static and dynamic performance was experimentally evaluated.
A micromechanics approach is proposed to calculate the stress-strain relationship of a polycrystalline Fe-Pd ferromagnetic shape memory alloy. It is modeled as consisting of spherical grains, which are grouped according to their orientations with respect to the loading axis. Therefore, the internal stress and elastic energy are accumulated as straining proceeds due to the strain differences between differently oriented grains. In the present study, the energy dissipation of the interface movement is also considered. Furthermore, a stress-magnetic field-temperature phase transformation diagram is constructed. The magnetic field induced transformation is found to be insignificant based on thermodynamics model. The cases of Fe-Pd and NiMnGa systems are examined for 3D phase transformation diagram.
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