Additive Manufacturing (AM) is growing in importance as a fabrication process for the space industry, enabling weight and cost savings through optimized designs for components. The use of AM gives aerospace engineers an alternative to more traditional manufacturing processes, but also retains the challenge of producing parts without defects. These problems can be approached using nondestructive methods such as X-ray Computed Tomography (CT) and Finite Element Modelling (FEM) to inspect geometries and quantify the impact of defects on the mechanical properties of a part, taking into account factors such as internal stress from metal cooling during fabrication.

Structural analysis of solid rocket motors is challenging for several reasons, but the most important of these is the complex behavior of the propellant. The mechanical response of a solid propellant is time and temperature dependent. The complexity of the mathematical analysis of the propellant depends on the loading conditions, but for some loading situations, the linear viscoelasticity assumption is reasonable. In particular, linear viscoelasticity is perhaps the most appropriate material behavior description for use in the simulations of stresses related to storage conditions. Typically, simulations use a viscoelastic model in the form of a Prony series and a Williams–Landel–Ferry (WLF) equation. The parameters in these models are derived from stress relaxation experiments, making the stress relaxation experiment a key viscoelastic test, analogous to the tensile test for linear elastic materials.

Microelectromechanical systems (MEMS) three-axis acceleration threshold sensors have been developed to measure acceleration threshold levels using voltage switching when the threshold is reached. 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.

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.

RINGFEDER POWER TRANSMISSION (Westwood, NJ) has announced the launch of its new RfN 5571 series flange coupling for heavy industry. RINGFEDER® flange couplings provide a superior solution to standard press fits. Equipped with the Ringfeder Shrink Disc this new series eliminates the needs for additional components such as keyways or shims. Eliminating the need for heating and cooling of the part reduces installation complexity. RINGFEDER® flange couplings are slip fit with frictional engagement achieved by torqueing the shrink disc screws. Available with hexagon head screws or hexagon socket head cap screws. Some of the advantages provided by this system are: a stronger connection than keyway systems, no wear parts, higher torque carrying capacity, backlash-free shaft hub connection, and a high level of true running accuracy.

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MRO providers are discovering ways to innovate their procedures while remaining viable and profitable through the current downturn in government spending. Read more at http://articles.sae.org/13268.

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.

Ongoing efforts to increase fuel efficiency, tactical mobility, and payload capacity in aerospace design have driven engineers to find numerous ways to reduce mass through the extensive use of lightweight materials such as composites, aluminum, and plastics. Use of these lightweight materials can create other issues, however, such as finding safe and reliable ways to fasten assemblies that provide complete assurance of joint integrity under the severe conditions of shock, vibration and thermal cycling common in aerospace applications.

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.

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.