Alan L. Browne

Shape memory alloy cables

Conventional structural cables (or wire ropes) are composed of steel wires helically wound into strands, which, in turn, are wound around a core. Cables made from shape memory alloy (SMA) wires are a new structural element with promising properties for a broad range of new applications. Among the many potential advantages of this form are increased bending flexibility for spooling/packaging, better fatigue performance, energy absorption and damping, reduced thermal lag, redundancy, and signicant design flexibility. Currently there are no known studies of SMA cables in the literature, so exploratory thermo-mechanical experiments were performed on two commercially available cable designs as part of an ongoing research program to systematically characterize their thermomechanical behavior and demonstrate their potential utility as adaptive or resilient tension elements.

Experimental validation of a magnetorheological energy absorber design analysis

A key challenge when designing linear stroke magnetorheological energy absorbers for high-speed impact is that high piston speeds in linear stroke magnetorheological energy absorbers induce high Reynolds number flows in the magnetic valve of the magnetorheological energy absorber, so that achieving high controllable dynamic range can be a design challenge. So far, the research on magnetorheological energy absorbers has typically assumed that the off-state force increases linearly with piston velocity. But at the higher piston velocities occurring in impact events, the off-state damping exhibits nonlinear velocity squared damping effects. This problem was recognized in our prior work, where it was shown that minor losses are important contributing factors to off-state damping. In this study, a nonlinear analytical magnetorheological energy absorber model is developed based on a Bingham-plastic nonlinear flow model combined with velocity squared dependent minor loss factors. This refined model is denoted as the Bingham-plastic nonlinear flow model with minor losses. From this Bingham-plastic nonlinear flow model with minor losses, an effective design strategy is presented for conventional magnetorheological energy absorbers. The Bingham-plastic nonlinear flow model with minor losses is validated via computational fluid dynamics simulation, so that magnetorheological energy absorber performance can be analytically verified before being manufactured. The magnetorheological energy absorber is fabricated and tested up to an effective piston velocity of 5 m/s by using the high-speed drop tower facility at the GM R&D Center. Comparison of our analysis with measured data is conducted, and the effective design of the magnetorheological energy absorber using the Bingham-plastic nonlinear flow model with minor losses is validated.

Nonlinear modeling of magnetorheological energy absorbers?under impact conditions

Magnetorheological energy absorbers (MREAs) provide adaptive vibration and shock mitigation capabilities to accommodate varying payloads, vibration spectra, and shock pulses, as well as other environmental factors. A key performance metric is the dynamic range, which is defined as the ratio of the force at maximum field to the force in the absence of field. The off-state force is typically assumed to increase linearly with speed, but at the higher shaft speeds occurring in impact events, the off-state damping exhibits nonlinear velocity squared damping effects. To improve understanding of MREA behavior under high-speed impact conditions, this study focuses on nonlinear MREA models that can more accurately predict MREA dynamic behavior for nominal impact speeds of up to 6 m s−1. Three models were examined in this study. First, a nonlinear Bingham-plastic (BP) model incorporating Darcy friction and fluid inertia (Unsteady-BP) was formulated where the force is proportional to the velocity. Second, a Bingham-plastic model incorporating minor loss factors and fluid inertia (Unsteady-BPM) to better account for high-speed behavior was formulated. Third, a hydromechanical (HM) analysis was developed to account for fluid compressibility and inertia as well as minor loss factors. These models were validated using drop test data obtained using the drop tower facility at GM R&D Center for nominal drop speeds of up to 6 m s−1.

Fluid Film Thickness Measurement with Moiré Fringes

A mathematical analysis of the application of moiré fringe contouring to fluid film thickness measurement is made. Two special cases are treated. The first considers the generation of contours with a collimated light source and distant observer. The second analyzes the fringe patterns viewed by an observer near the grid when there is a point source of light. Geometrical restrictions imposed on the experimental setup are detailed. Experimental results are included.

Behavioral Model and Experimental Validation for a Spool-Packaged Shape Memory Alloy Actuator

Shape memory alloy (SMA) based actuators have the potential to be lower mass, more compact, and more simplistic than conventional based actuators (electrical, hydraulic, etc); however, one of the key issues that plagues their broad use is packaging since long lengths of wire are often necessary to achieve reasonable actuation strokes. Spooling the wire around pulleys or mandrels is one approach to package the wire more compactly and is useful in customizing the footprint of the actuator to the available application space. There is currently a lack of predictive models for actuator designs with spooled packaging that account for the variation of stress and strain along the wires length and the losses due to friction. A spooling model is a critical step toward the application of this technique to overcome the packaging limitations on SMA actuators. This paper presents the derivation of an analytical predictive model for rotary spooled SMA actuators that accounts for general geometric parameters (mandrel diameter, wire length, wire diameter, and wrap angle), SMA material characteristics, loss parameters (friction), and the external loading profile. An experimental study validated the model with good correlation and provided insight into the effects of load and wrap angle. Based upon the model and experimental results, the main limitation to this approach, binding, is discussed. The analytical model and experimental study presented in this paper provide a foundation to design future actuators and insight into the behavioral impact of this packaging technique.

The Structure and Use of the GMR Combined Thermo-Mechanical Tire Power Loss Model

The operational structure and use of the General Motors Reseach Laboratories Combined Thermo-Mechanical Tire Power Loss Model are presented in this paper. The modular format of this tire power loss model is briefly reviewed. Descriptions of its three major analysis modules - thermal, dissipation, and deformation - are given. A flow chart is presented showing how these modules are interfaced to form an interactive, iterative model. Steps required to operate this model, procedures necessary to obtain and prepare the input data, and sample results obtained using the model are presented.

Shock load mitigation using magnetorheological energy absorber with bifold valves

Magnetorheological energy absorbers (MREAs) have been identified as a candidate for tunable impact energy absorber applications, meaning those in which a high shock load is applied during a short time period. In this study, we focused on the theoretical analysis, design and laboratory implementation of a compact high force MREA for shock and impact loads. This study included the design and fabrication of a flow-mode bifold MREA (magnetorheological energy absorber) that operates under piston velocities up to 6.71 m/s and the development of a hydro-mechanical analysis to predict MREA performance. Experiments were conducted both in the laboratories at UMCP (sinusoidal excitation) and at GM R&D (drop tower tests), and these data were used to validate the analysis. The hydro-mechanical model for the MREA was derived by considering lumped hydraulic parameters which are compliances of MR fluids inside the cylinder and flow resistance through the MR bifold valves. The force behavior predicted by the hydro-mechanical analysis was simulated for two classes of inputs: sinusoidal displacement inputs, and shock loads using a drop tower. At UMCP, sinusoidal inputs ranging up to 12 Hz with an amplitude of 12.7 mm were used to excite the MREA using three different MR fluids, each having an iron volume fraction of nominally 35%, 40% and 45%. Subsequently, drop tower tests were conducted at GM R&D by measuring MREA performance resulting from the impact of a 45.5 kg (100 lb) mass dropped onto the MREA shaft at speeds of 1, 2 and 3 m/s. Comparison of the simulations with experimental data demonstrated the utility of the hydro-mechanical model to accurately predict MREA behavior for the specified ranges of sinusoidal and shock classes of inputs.

Spool-packaging of shape memory alloy actuators: Performance model and experimental validation:

Shape memory alloy (SMA) actuators in the wire form are attractive because of their simplistic architecture and electrical operation, and their manufacturability at high yields and low cost. While SMA actuators are known for their superior work density among smart materials, packaging long lengths of SMA wire needed for moderate to large motions is an ongoing technical challenge. This article investigates spooling as a packaging approach to provide more compact actuator footprints. An analytical, quasi-static model is derived to provide a foundational tool for the analysis and synthesis of spool-packaged SMA wire actuators. The model predicts motion with respect to a generalized architecture, and specifiable geometric, material, and loading parameters. The model prediction accounts for the effects of local friction loss and bending strains, and for a “binding” limitation due to accumulated friction. An experimental validation study demonstrates the model’s ability to predict actuator motion well in terms of form and magnitude with respect to load and packaging geometry. This model provides a basis for a systematic application of spooled-packaging techniques to overcome packaging limitations of SMA, positioning SMA wire actuators as a viable alternative in many applications.

A Nonlinear Analytical Model for Magnetorheological Energy Absorbers Under Impact Conditions

Linear stroke magnetorheological energy absorbers (MREAs) can be used to adaptively control load-stroke profiles under impact loads. An appropriate and controllable dynamic range, defined as the ratio of the force at maximum field to the off-state force, as well as the off-state (minimum) damping force, must be specified in order to account for varying payload mass over a wide range of MREA operating velocities. A key challenge when designing MREAs for high speed impact conditions is that the high shaft speeds in linear stroke MREAs induce high Reynolds number flows in the magnetic valve of the MREA, so that high dynamic range canbe a design challenge. Previous studies demonstrated that the dynamic range, D, of an MREA under high speed drop impact test dramatically dropped to D≈1 as velocity rose to 6.6 m/s, where Reynolds number, Re>2000. Also, past research on MREAs typically assumed that the off-state force increases linearly with speed, but at the higher shaft speeds occurring in impact events, the off-state damping exhibits nonlinear velocity squared damping effects. This problem was recognized in our prior work where it was shown that minor losses are important contributing factors to off-state damping. In this study, a nonlinear analytical MREA model, based on the Bingham-plastic nonlinear flow model (BP model), is combined with semi-analytical minor loss factors to develop a BPM model. From this BPM model, an effective design strategy is presented for conventional MREAs and an MREA designed. The BPM model was validated via finite element analysis (FEA), so that MREA performance could be verified before manufacture. The MREA was fabricated and tested up to effective piston velocity of 5 m/s using the high speed drop tower facility at GM R&D Center. Comparison of our analysis with measured data shows that the BPM model can accurately predict off-state (passive) MREA performance under impact conditions, and the effective deign of the MREA using the BPM was validated.Copyright

Impact Performance of Magnetorheological Fluids

As part of an emerging effort in what is now termed the area of mechamatronics [1], an effort was begun to assess the suitability of MR (magnetorheological) material based devices for impact energy management applications. A fundamental property of MR materials is that their yield stress alters almost instantaneously (and proportionally) to changes in the strength of an applied magnetic field. Based on this property, MR based devices, if found suitable, would be desirable for impact energy management applications because of attendant response tailorability. However, it was identified that prior to adopting MR based devices for impact energy management applications several key issues needed to be addressed. The present study focused on one of the most significant of these, the verification of the tunability of the response of such devices at stroking velocities representative of vehicular crashes. Impact tests using a free-flight drop tower facility were conducted on an MR based energy absorber (shock absorber) for a range of impact velocities and magnetic field strengths. Results demonstrated that over the range of impact velocities tested — 1.0 to 10 m/s — the stroking force/energy absorption exhibited by the device remained dependent on and thus could be modified by changes in the strength of the applied magnetic field.Copyright