Robert Rabb

Evaluation of Shear Thickening Fluid Kevlar for Large Fragment Containment Applications

Application of a shear thickening fluid (STF) treatment to neat Kevlar has been reported to improve fabric ballistic performance, for impacts of 0.22 caliber fragment simulating projectiles at velocities near 800 feet per second. In recent research, the authors have evaluated the ballistic performance of STF Kevlar in a series of impact experiments performed using larger projectiles and thicker targets, at impact velocities near 1,000 feet per second, including two different fabric boundary conditions. The experimental results indicate that under these test conditions, the impact protection afforded by STF Kevlar is at best equivalent to that provided by neat Kevlar at the same areal density. In addition, the ballistic performance of STF Kevlar was found to be strongly dependent on fabric target boundary conditions, with the best performance obtained in a friction sensitive target configuration that is not representative of current body armor, orbital debris shielding, or turbine blade containment systems.

Numerical simulation of oblique impact on orbital debris shielding

Summary Hybrid particle-finite element methods have been proposed as a modeling methodology well suited to the problem of hypervelocity impact simulation. To evaluate the use of such numerical methods for orbital debris shielding design, a series of simulations have been conducted using a three dimensional hybrid particle-finite element code now under development. Two sets of oblique impact simulations, one for a single bumper Whipple shield and one for a dual bumper or stuffed Whipple shield, have been compared to published ballistic limit equations, the latter derived from experiment. The results indicate that hybrid particlefinite element methods can provide an accurate and computationally tractable approach to the simulation of orbital debris shield performance.

Course development in interdisciplinary controls and mechatronics

As the future of engineering education emphasizes more interdisciplinary work, one logical starting point for this evolution is for faculty from different academic departments to work together. Engineering educators cannot ignore the real worldpsilas shifting focus to interdisciplinary engineering, and they should adapt as well. Similar to the total engineering process as a team effort, the engineering education process also benefits from excellent communications among a diversity of team members. This paper highlights a classical dynamical modeling and controls course with students from two different disciplines: electrical engineering and mechanical engineering. Faculties from both departments teach every semester. Sections are assigned to individual instructors but all activities are planned jointly. Course administration is the role of a course director and this role alternates between the two departments each semester. Responsibilities throughout the semester are shared between the instructors. This organizational structure is important, allowing the interdisciplinary faculty team to synchronize their efforts, each contributing their individual strengths and resources to promote student learning and faculty development. The approach is being applied to the development of a new course, Mechatronics. This paper provides details that illustrate the structure and benefits of this interdisciplinary administrative model.

Simulation of Large Fragment Impacts on Shear-Thickening Fluid Kevlar Fabric Barriers

Hybrid-particle-element methods developed for woven fabric impact modeling offer a new computational approach to fabric barrier design. Simulations performed using this technique have shown good agreement with small fragment impact experiments, and they capture the complex multilayer fabric dynamics observed in high-speed videos of impact testing. In recent research, the numerical method has been applied and evaluated in large fragment impact simulations, and it has been extended in order to model the inertial, thermodynamic, and energy dissipation properties of shear-thickening fluid Kevlar®. Simulations of large fragment impacts at velocities near 1000 ft=s show good agreement with neat Kevlar test data for perforated targets, but they diverge at near-ballistic limit conditions. Consistent with the experiment, the simulations indicate that, for the particular fabric and fluid combination investigated, shear-thickening fluid treatment does not improve the ballistic performance of neat fabric barriers when measured on an areal density basis. The simulations also suggest that shear-thickening effects may not play a major role in determining the ballistic performance of the augmented fabric.

Control Theory in Practice: Magnetic Levitation

A device that levitates a steel ball beneath an electromagnet is used for educational purposes at the United States Military Academy, West Point, New York. Students in the course “Mechatronics” engage in a set of laboratory exercises with the device to reinforce classroom learning. Mechatronics is a senior-level course that introduces the interdisciplinary design of smart systems. Students in the electrical engineering and mechanical engineering programs take the course together, and the material is taught by a team of instructors from both academic departments. The Magnetic Levitation experiments are the primary means of teaching the classical analog control portion of the course. Other aspects of the course involve interfacing microcontrollers with sensors and actuators, and digital control. The magnetic levitation device fits easily on a two-person workbench and requires a power supply and oscilloscope. An infra-red emitter / detector pair is used to sense ball position for a feedback compensator. Students first learn classical control theory in a co-requisite course, “Dynamic Modeling and Control.” Modeling principles are introduced in the context of the magnetic levitation system as an unstable plant to be controlled. The system can be simulated by models ranging from simply linear to more complex to teach the trade-off between model fidelity and model development effort. The students derive the nonlinear governing equations and then linearize the equations and develop the transfer function of the plant. Students design a compensator and simulate the resulting stabilized system with Matlab and Simulink software. Students build their compensator on a solderless project board to levitate the steel ball. A proven lead-type compensator using two resistors and a capacitor is readily provided to students that struggle with their own compensator design so that all teams may enjoy the fruit of a successful experiment. As a laboratory aid, the magnetic levitation system allows for basic and advanced approaches to both theoretical study and practical investigation of a nonlinear, unstable system control. The comparison of measured results to predicted behavior leads to insight about how the physical system is modeled by mathematics. Students write a case study describing the system in detail including characterization of the sensors and actuators. Instructors report that the hands-on nature motivates students to excel. Surveyed students cite the hands-on activities as relevant applications that help develop deeper understanding and greater appreciation for the concepts learned in the classroom. The students are motivated to learn by the fascination of defying gravity.

Simulation of Large Fragment Impacts on Neat and STF Kevlar Fabric Barriers

Hybrid-particle element methods developed for woven fabric impact modeling oer a new computational approach to fabric barrier design. Impact simulations performed using this technique show good agreement with experiment and capture the complex multilayer fabric dynamics observed in high speed videos of impact testing. In recent research the numerical method has been extended, in order to model the inertial, thermodynamic, and energy dissipation properties of shear-thickening uid (STF) Kevlar. Simulations of large fragment impacts, at velocities near 1,000 feet per second, demonstrate the ability of the extended formulation to quantify the relative ballistic performance of neat and STF Kevlar fabric barriers. The simulations indicate that impact energy dissipation in STF Kevlar can be accurately described by a rate-independent dissipation model, suggesting that shear thickening eects may not play a major role in determining the ballistic performance of the augmented fabric.

Numerical Simulation Of Impact Effects On Multilayer Fabrics

High strength fabrics provide lightweight impact protection and are employed in a wide range of applications. Examples include body armor for law enforcement and military personnel and orbital debris shielding for the International Space Station. Numerical simulation of impact effects on fabric protection systems is difficult, due to the complex woven structure of the fabric layers and the typical application of fabrics in a multilayer configuration. Recent research has applied a new particle‐element method to the simulation of impact effects on multilayer fabrics, applicable over a wide range of impact velocities, for use in body armor and orbital debris shielding design applications.

Dynamic Modeling and Control: Interdisciplinary Faculty Teamwork and Techniques

As the future of engineering education emphasizes more interdisciplinary work and more work performed in teams, one logical starting point for this evolution is for faculty from different academic departments to work together. Engineering educators cannot ignore the real world’s shifting focus to interdisciplinary engineering, and they should adapt as well. Similar to the total engineering process as a team effort, the engineering education process also benefits from excellent communications among a diversity of team members. This paper highlights a classical dynamical modeling and controls course with students from two different disciplines: electrical engineering and mechanical engineering. Faculty from both departments teach every semester. Sections are assigned to individual instructors but all activities are planned jointly. Course administration is the role of a course director and this role alternates between the two departments each semester. Responsibilities throughout the semester are shared between the instructors. This organizational structure is important, allowing the interdisciplinary faculty team to synchronize their efforts, each contributing their individual strengths and resources to promote student learning and faculty development. The instructors engage in meaningful dialogue concerning their assignments, lesson preparations, laboratory exercises, and their results. The information flow between instructors from different departments encourages faculty learning by pushing the instructors beyond their own discipline. This paper provides details that illustrate the structure and benefits of the course. Advantages to empowering an interdisciplinary faculty are also described. The approach described allows the students to benefit from the work of an interdisciplinary faculty team enriching the students’ understanding through real world projects and examples that have aspects of multiple disciplines.© 2008 ASME