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Additive Manufacturing of Shape Memory Alloys, Ohio Third Froniter, Christoph Haberland, Jason Walker

Processing of Nickel-Titanium shape memory alloys (NiTi) is by no means easy because all processing steps can strongly affect the properties of the material. Hence, near-net-shaping technologies are very attractive for processing NiTi due to reduction of the processing route. Additive Manufacturing (AM) provides especially promising alternatives to conventional processing because it offers unparalleled freedom of design. We use Selective Laser Melting (SLM) for processing high quality NiTi parts. We have shown that a careful control of process parameters is of great importance. Furthermore, we have characterized structural and functional properties like shape recovery, referring to the shape memory effect in Ti-rich SLM NiTi, or pseudoelasticy in Ni-rich SLM NiTi. It is shown that both types of shape memory effects can be adjusted in SLM NiTi by the choice of the raw material and processing strategy. By comparing the properties of SLM NiTi to those of conventionally processed NiTi, we have clearly shown that SLM is an attractive manufacturing method for production of high quality NiTi parts.

It is shown that it is crucial to adjust the process parameter set-up in a way that dense material can processed but the impurity pickup is kept to a minimum and the transformation temperatures are affected as little as possible. Additionally, it is shown that high quality SLM NiTi can be produced which meets the requirements for impurity contents of medical applications. Finally, this work shows that SLM NiTi exhibits distinct functional properties like shape memory and pseudoelasticity which compares favorably with the properties of conventionally processed NiTi. Thereby, this work clearly proves that AM in general, and SLM in particular, provide a promising technique to produce complex NiTi parts which may not be producible with any other method.

Shape Memory Actuation for Medical Device, Ohio Third Frontier, Masood Taher Andani

So far, in most of the developed shape memory alloy (SMA) based medical devices, SMA material is subjected to simple uniaxial tension or pure torsion loading/unloading conditions. In these simple cases, the SMA element would provide a unique stress-strain hysteresis-like pro le which is associated with the force/torque requirement of the device at a constant temperature. But there are also potential applications, in which the required force/torque pro les are more complex than simple hysteresis loops resulted from simple tension or torsion loading/unloading. In such cases, using combined tension-torsion loading paths might be a solution to achieve a more versatile response. Another driving force is that today's development in the manufacturing and processing techniques of SMAs is leading to the freedom in fabrication of complex SMA parts and structures with loading modes other than simple tension or torsion.

Intra-ventricular assistive device for end stage congestive heart failure patients, Ohio Third Frontier, Milad Hosseinipour

In an attempt to produce a less invasive alternative to current ventricular assistive devices, we have designed a novel intra-ventricular VAD for end stage congestive heart failure patients. VADs are approved by FDA as Bridge to Transplantation Therapy (BTT), Bridge to Recovery Therapy (BRT) and permanent or Destination Therapy (DT) for patients at NYHA Class IV as an alternative to heart transplant. While all current devices require open-heart surgery, the flexible structure and thin active membrane, made of Ionic Polymer Metal Composites (IPMC) and Shape Memory Alloys (SMA), enables transcatheter implantation and thus eliminates the need for a thoracotomy. Moreover, exerting almost no shear stress on blood cells and having no stagnant points reduces the risk of hemolysis and thrombosis. In order to define the average working conditions and physiological needs, hemodynamics of an eligible patient is first examined. Different motion mechanisms are then evaluated to find the one that has the maximum volume displacement and also mimics the natural motion of the heart. As the preliminary evaluation of the device, 1D results of an FEM solution of the governing differential equation of the electrochemical behavior of IPMCs are found to check the compliancy of IPMCs with those needs defined by hemodynamic and motion analyses. Although modeling and simulation results provided in this paper are for left ventricle, the same progressive design and test processes are also applicable for the right ventricle.

Toward a variable stiffness ankle foot orthosis, NSF, Ehsan Tarkesh, Liberty Deberg, Minal Bhadane, Morteza Gorzin

Drop foot can primarily be caused by stroke, cerebral palsy, multiple sclerosis, or neurological trauma. The two major complications of drop foot are slapping of the foot after heel strike (foot slap) and dragging of the toe during swing (toe drag). The current treatment options like Ankle Foot Orthosis (AFO) and Functional Electrical Stimulation, while offering some biomechanical benefits, do not adapt to different walking conditions and fail to eliminate significant gait complications. This study proposes a novel Active Ankle Foot Orthosis design that combines an AFO and combinations of shape memory alloy (SMA) wires. The key feature of SMA is its ability to undergo seemingly large plastic strains and subsequently recover these strains when a load is removed or the material is heated. Because of this distinct thermomechanical behavior, SMA can potentially resolve some of the gait complications associated with use of an AFO.

Identification, Simulation and Control of an Ankle Foot Orthosis, NSF, Mohammadhassan Sofla

This project resulted in a dynamic model for human ankle. System identification theory is used to obtain ankle models for able-bodies as well as drop-foot patients. It is shown that ankle dynamics can be estimated by a combination of linear and nonlinear functions. altHemmerstein model is chosen to identify the models since torque-angle behavior of the ankle in walking is nonlinear and hysteresis. The identified models with over 95% fitness are further validated with experimental data collected in motion analysis lab from able-bodies as well as drop-foot patients. Such dynamic models are of high importance in designing and studying the next generation ankle foot ortheses or prostheses. Furthermore, this modeling can be used in developing controller for an active powered assistive device.

A variable stiffness transverse mode shape memory alloy actuator as a minimally invasive organ positioner, Ohio Third Frontier, Walter Anderson

Actuators are needed in the medical field where space is limited. This work is on an organ positioner used to position the esophagus away from the left atrium to avoid the development of an esophageal fistula during atrial fibrillation ablation procedures. altSMA actuators classically have been wire, or one dimensional, due to the ease of predicting the response. However, with computational impetus, robust finite element algorithms can be implemented. Within this work, a subroutine was implemented into the finite element framework to predict the midspan load capacity of a near equiatomic NiTi specimen in both the super elastic and shape memory regimes. The purpose of the simulations and experimental results was to develop a design envelope for the organ-positioning device. Monotonic tensile tests were performed to develop the material properties as inputs to the subroutine and good agreement between the simulated predictions and the experimental transverse loading results are shown. alt The transverse loading experiments were conducted at several different temperatures leading to the ability to design a variable stiffness actuator. This is essential because the actuator must not be too stiff to injure the organ it is positioning. Extended further, geometric perturbations were applied in the virtual model and the entire design envelope was developed.

Finite element study of a shape memory alloy bone implant, Ohio Third Frontier, Majid Tabesh, Zohreh Karbaschi and Ahmadreza Eshghinejad

Osteoporosis is a common bone disease especially in elderly people. Bone degradation as the result of osteoporosis causes loosing of screws implanted in the bone during or after surgery. A new device, which is designed to mitigate this adverse effect, has been studied.alt The functionality of an expandable-retractable pedicle screw is evaluated. This specially designed pedicle screw that has the ability to expand and retract by taking the benefits of Nitinol elements is described in detail. This function is verified by experiment and compared to the results of the numerical simulation model in Abaqus, which is used to analyze shape memory alloy materials thermo-mechanical behavior. This simulation tool is the combination of the numerical implementation of shape memory alloy constitutive thermo-mechanical modeling into the Abaqus UMAT Fortran subroutine and the Abaqus finite element solver.

The effect of the designed pedicle screw in mitigating the loosing effect has also been studies. Pullout test is a common way of evaluating a bone implant.alt The pullout force of a normal screw out of a normal bone was simulated with finite element in Abaqus and compared with the results of the expandable ones in osteoporotic bone. These results showed the enhanced purchase of the designed pedicle screw in the pullout test.

Design, analysis and evaluate of a collapsible/expandable intervertebral cage, Ohio Third Frontier, Cory Chapman, Walter Anderson

One of three most common causes for disability in people aged 45 to 65 is pain or discomfort in the lower back. Intervertebral fusion procedures are growing in commonality for the correction of spinal injuries such as those that can lead to pain in the lower back as well as weakness or numbness in the lower extremities. Procedures such as these share a high risk of injury that coaltincides with the rewards of decompression of nerves and relief from debilitating pain. To reduce the risk of injury, an intervertebral cage designed for this procedure must be strong, stable, and easily implanted. Further improvements to the spinal fusion construct can be made by making it less invasive and thus minimize associated recovery times.

A preliminary design was developed utilizing shape memory alloys to allow for the cage to expand and collapse to provide a smaller surgical footprint.alt Experimental analysis and development of a torsional model for shape memory alloys was completed to aid in optimization of the cage design. Upon successful completion of experimentation a proper wire diameter was selected and the developed torsional model’s efficacy was evaluated and confirmed for utilization in the design and evaluation of future cage constructs as well as other devices utilizing the SMA in torsion.

Development and control of a magnetorheological mount, US DOT, The Nguyen and Shou Wang

The NVH in modern vehicles is mainly due to the involvement of multiple power sources working in different modes and the switching among them. This feature can lead to shock and vibration over a wide range of frequencies.alt It has been proven that passive vibration isolators, e.g. elastomeric and hydraulic, are not sufficient to deal with this problem. Active mounts are effective but they are expensive and can lead to stability problems. Research has shown that semi-active vibration isolators are as effective as active mounts while being significantly less expensive.

In this study, a novel shock and vibration isolator in the form of a magnetorheological (MR) mount is introduced. MR fluids are smart fluids, which respond to magnetic fields. Using these fluids it is possible to transform a passive hydraulic vibration isolator to a semi-active device. The semi-active MR mount presented in this project is unique because it utilizes the MR fluid in two configurations flow (or valve) and squeeze modes to mitigate shock and vibration. over a wide range of frequency.

Modeling, simulation, and control of hydraulic hybrid vehicles, US EPA and Southwest Research Institute, Christopher Schroeder, Xianwu Zeng, and Amin Mohaghegh Motlagh

Hydraulics (often called fluid power) offers the best solution for hybridizing heavier vehicles such as SUV’s, trucks and buses to improve fuel economy. Using conventional gasoline engines under a parallel hybrid, US EPA/NVFEL testing and modeling programs project a 34% fuel economy improvement for a large 4WD SUV.alt For a 2WD midsize automobile the same technology provides a 50% improvement in fuel economy. The power collected from the regenerative braking phase is stored in a high-pressure accumulator and then released to the driveshaft during the acceleration phase. This technology is effective for heavy-class vehicles with frequent stop-and-go schedules. However, noise and vibrations are the one of the main challenges to this technology.

It turns out that the pump/motor accounts for the most significant source of noise, vibration and harshness. The dynamics of the pump/motor and particularly the modeling of dynamic forces caused by a bent-axis pump/motor unit was a focus of this project.alt A mathematical model of bent axis pump/motor has been developed which is capable of predicting the forces in bearings attached to the pump/motor case. The forces are calculated in time and frequency domain.

The information obtained from this study can be used to study the vibration response of the chassis as well as design the smart mounts with variable stiffness and the damping to develop anti-vibration systems for this technology.

Development of a shape memory alloy actuator for mirror positioning, Ohio Board of Regents, Eric Williams, Gordon Shaw, and Chad Mikrut

Automobile designers are continuously trying to improve the safety and comfort of new car models. In many cases this translates to the need for less expensive and compact actuators. There are many features that are commonly found in cars that utilize electromechanical type actuators.alt Power mirrors are one such application that has been becoming more and more standard on cars today. A cost effective mirror actuator was designed and built that utilizes shape memory alloy (SMA) wires to position the external side mirrors. A robust control algorithm is developed for the mirror to provide stable and accurate positioning. This variable structure controller provides accurate positioning without adding unnecessary complexity to the computational requirements for the mirror. Experimental results are compiled to show the tracking response of the SMA mirror actuator.

Modeling and control of ferromagnetic shape memory alloy actuators, UT Foundation, Honghao Tan

In this project, a comprehensive approach is used to model the behavior of FSMA actuators. To this end, an enhanced phenomenological model for FSMA actuators is developed and integrated with dynamics of the actuator as well as the dynamics of an electromagnet to study the hysteresis behavior of the system.alt In order to improve the accuracy of the model, a field-induced strain model is combined with the strain decomposition and Kelvin-Voigt model to account for the inherent damping effect of the material.

Simulations have been performed and the results are compared with the experimental measurement to verify the model. The closed loop simulations results indicate that the inherent nonlinearities of the material are the main challenges for position control with FSMA actuators. A Variable Structure Controller (VSC) is proposed to overcome these issue. The algorithm improves both the transient response and tracking performance of the FSMA actuators. A SMA wire based experimental setup is constructed to verify the effectiveness of the control algorithm for the FSMA based actuators.

Mitigating concussion: an innovative football helmet, Jacobson Center for Clinical & Translational Research, Ehsan Izadi

Helmets are the primary safety devices for various sports, including football. A well-designed helmet is generally believed to be effective protection against head injuries and concussions.alt However, there are a multitude of cases where the helmet has failed in protecting the player, resulting in head injuries. These injuries include massive trauma to the brain resulting in coma, paralysis or even death. Therefore, there is the need for a more effective football helmet.

The helmet material that acts as an energy absorber is the most important parameter in helmet design. The main objective of this study is to investigate the impact response and energy absorption capability of different shock absorbing materials, in order to find an alternative safer and more effective design. The resulting design is expected to be more effective in the reducing impact force and decreased related head injuries.alt To this end, various types of head injuries and their main causes have been reviewed. Theoretical and experimental techniques are used to compare the efficiency of different energy absorbing materials including the foam paddings (used in current helmets). Additionally, alternative designs are proposed. A new padding structure has been developed and tested in a football helmet. The impact performance of an off the shelf helmet is compared to the proposed design. Drop tests based on the NOCSAE standard were performed. Results of these tests show the effectiveness of the designed padding in reducing the possibility for head injuries.