Mechanical Components

Damping Measurement for Wafer-Level Packaged MEMS Acceleration Sensors

Microelectromechanical system (MEMS) three-axis acceleration threshold sensors have been developed to measure acceleration threshold levels using voltage switching when the threshold is reached. Determining damping coefficients is important for categorizing how each threshold sensor or switch operates. Switches with different damping coefficients result in different mechanical impedances and response times. Analytical and numerical methods to model damping coefficient values based on empirical data are needed to characterize three-axis acceleration sensors; traditional methods use the displacement of an underdamped system to calculate the damping ratio.

Posted in: Briefs, Defense, MEMs, Sensors, Measuring Instruments, Sensors and actuators, Switches

Rotating Detonation-Wave Engines

All Navy aircraft and missiles use gasturbine engines for propulsion. Many ships are also dependent on gasturbine engines to generate both propulsive power and electricity. These engines are fundamentally similar to engines used to power commercial airplanes. Future ships moving to an “all electric” paradigm for the propulsion system will still require these gas-turbine engines to generate electricity for the propulsion system and also for other critical onboard systems. Because of the amount of power required by modern warfighting ships, and the prospect that this power requirement will only increase, there is a strong interest in improving the specific fuel consumption of these engines.

Posted in: Briefs, Mechanical Components, Electric power, Fuel economy, Gas turbines, Marine vehicles and equipment, Military aircraft, Missiles

Thermal Analysis and Microhardness Mapping in Hybrid Laser Welds in a Structural Steel

The concept of combining a laser welding system with a conventional arc welding system (GTAW) was first proposed in order to improve the stability of the laser welding system and to allow greater flexibility in part fit-up. Prior research stated that using a YAG laser at a power of 3 kW, one was able to hybrid laser weld a 4-mm-thick aluminum alloy at a speed of 4 n/min. For a mild steel plate, butt welding at 1 m/min with 5 kW of 6-mm-thick plate was realized. Just as significantly as the weld speed was the ability to hybrid laser weld with gaps up to 1.5 mm in a plate 6 mm thick. The glass metal arc welding (GMAW) laser hybrid process can increase the gap bridging ability, i.e., it appreciably broadens the range of tolerances with regard to edge preparation quality. The arc’s energy input in the hybrid welding process also permits control of the cooling conditions. Via the keyhole, the laser beam brings about easier ignition of the arc, stabilization of the arc welding process, and penetration of the energy deep into the material. The improvement of the energy input leads to a greater welding depth and speed being achieved with the hybrid process compared with individual processes on their own.

Posted in: Briefs, Mechanical Components, Lasers, Welding, Steel, Thermal testing

Encapsulated Ball Bearings for Rotary Micro Machines

Microelectromechanical systems (MEMS)-fabricated silicon rotary elements for micro-motors, micro-generators, and micro-turbomachinery have received growing attention with applications in power conversion and actuation. Within these technologies, the bearing mechanism is the primary determinant of device performance and reliability. Active bearings, such as magnetic or electrostatic, have the advantage of being controlled during the operation, but at the cost of the accompanying circuitry. Passive bearings span a large range of velocities that include center-pin bushings with low revolution rates possible, and hydrostatic or hydrodynamic bearings with high revolution rates possible.

Posted in: Briefs, Mechanical Components, Microelectricmechanical device, Bearings

Reverse Pressure Capable Finger Seal

Each finger seal consists of a number of multiple thin metal laminates, each with a multitude of flexible projections that are referred to as “fingers.” To form a functional seal, multiple laminates are formed into a stack, with each laminate oriented so that the slots between its fingers cover the slots of the neighboring laminates. For protection and support of the laminates, forward and aft cover plates are placed on each side of the finger seal stack. A high pressure exists on one side of the seal, providing a driving force to push the air from one side of the seal to the other.

Posted in: Briefs, Mechanical Components, Coatings Colorants and Finishes, Seals and gaskets

Reactive Structure and Smart Armor for Future Ground Vehicles

AReactive Structure Technology (RST) is a new class of smart structure that can react to external excitations (such as blast or ballistic impacts) in a carefully designed way using the energy pre-stored internally or from the external excitations to counteract the hazardous loading or perform other desired tasks. A reactive structure deflects an incoming projectile in order to protect a vehicle body. When a projectile hits the face plate (armor), the embedded sensors feed the impact signal to a control unit, and actuators are triggered to move the faceplate. The movement of the faceplate deflects the projectile and significantly reduces the possibility of penetration in the back plate.

Posted in: Briefs, Mechanical Components, Sensors and actuators, Active safety systems, Protective structures, Military vehicles and equipment

Variable-Thrust, Multiple-Start Hybrid Motor Solutions

Interceptor boost propulsion has traditionally been dominated by solid rocket systems due to their responsiveness and high mass fraction capabilities. However, increased costs of handling these flammable motors, the need to evolve more and more insensitive munitions, the static thrust profile created at propellant casting, and the inherent performance limitations of solid propellants have motivated the interest in exploring alternate technologies.

Posted in: Briefs, Mechanical Components, Solid propellants, Product development, Hybrid engines

Wheel Force Transducer

Aconcept wheel force transducer has been developed that can measure the forces and moments between a tire and a road on a High Mobility Multi-purpose Wheeled Vehicle (HMMWV or Humvee) driven under off-road conditions. The proposed wheel force transducer is an important step in correcting the gap in current tire testing and modeling knowledge to ensure that future off-road vehicle models and simulation efforts are conducted with confidence. In order to obtain tire characteristics over off-road terrain, cost-effective field test equipment was required.

Posted in: Briefs, Mechanical Components, Tires and traction, Wheels, Test equipment and instrumentation, Off-highway vehicles and equipment

Nozzles for Focusing Aerosol Particles

Several nozzles have been designed to aerodynamically focus aerosol particles into a small-diameter jet, so that individual particles can be illuminated by a laser beam and their light scattering and/or laser-induced fluorescence (LIF) spectra can be measured. An additional nozzle can aerodynamically puff selected particles out of the airstream so that they can be sorted and collected.

Posted in: Briefs, Mechanical Components, Nozzles, Test procedures, Aerodynamics

Parallel Hybrid Vehicles Using Fuzzy Logic Control

A fuzzy logic controller for hybrid vehicles with parallel configuration was proposed. Using the state-of-charge (SOC) of the energy storage, the driver command, and the motor/generator speed, a set of rules was developed. The fuzzy logic controller can determine the split between the electric motor and the internal combustion engine to achieve better fuel economy and low emission performance without losing vehicle performance.

Posted in: Briefs, Mechanical Components, Fuzzy logic, Architecture, Hybrid electric vehicles, Vehicle performance