Effect of Prior Oxidation on Tensile Properties of Bare and Al3Ti Diffusion Aluminide Coated Near α Titanium Alloy Titan 29A

The effect of prior oxidation, for various durations up to 2,000 h in air at 650 °C, on the room temperature tensile properties of uncoated and Al₃Ti diffusion aluminide coated near α Ti alloy, Titan 29A, has been evaluated. The tensile properties of the uncoated alloy deteriorated with oxidation. Oxidation for just 100 h caused 11–13 % decrease in yield strength (YS) and ultimate tensile strength (UTS) of the alloy. The uncoated alloy exhibited brittle fracture within the elastic regime at significantly lower stress after oxidation for 2,000 h. On the other hand, the strength of the coated alloy remained unaffected even after 2,000 h of oxidation and the YS and UTS was similar to that of the un-oxidized alloy. The ductility of the coated alloy, however, decreased with the increase in oxidation duration. Such differences in the tensile behavior of the uncoated and coated alloy can be ascribed to the beneficial effect of the Al₃Ti diffusion aluminide coating in preventing surface embrittlement in the alloy during oxidation.     

Design and experimental implementation of an electromagnetic engine valve drive

In conventional internal combustion engines, engine valve displacements are fixed relative to crankshaft position. If these valves were actuated as a variable function of crankshaft angle, significant improvements in fuel economy could be achieved. To this end, a new type of electromagnetic valve drive system (EMVD) for internal combustion engines was more recently proposed. This EMVD incorporates a disk cam with a very desirable nonlinear profile which that functions as a nonlinear mechanical transformer. Modeling and simulation results showed significant advantages of this EMVD over previously designed electromagnetic engine valve drives. In this articles, we describe an experimental implementation of the proposed EMVD, which was developed to confirm these benefits. The EMVD apparatus was designed, constructed, and integrated into a computer-controlled experimental test stand. The experimental results confirm the benefits of using a nonlinear mechanical transformer in a motordriven engine-valve spring system, as seen in the small average power consumption and low valve seating velocity. In addition, a valve transition time sufficient for 6000-rpm engine operation was achieved. The results also suggest ways to improve the EMVD apparatus in the future.     

Cycle-Averaged Models of Cardiovascular Dynamics

Lumped-parameter time-varying electrical circuit analogs for the cardiovascular system are frequently used in medical research and teaching for simulating and analyzing hemodynamic data. Pulsatile models provide details of the intracycle dynamics of each heart beat. In some settings, however, such as when tracking a hospital patient's hemodynamic state over time, it is more useful to dynamically track the beat-to-beat or intercycle dynamics. Rather than introducing heuristic averaging during the model-building step, as is done in existing nonpulsatile models, we apply a short-term, cycle-averaging operation to the differential equations of the underlying pulsatile model to obtain cycle-averaged models. The cycle-averaging method preserves the dependence of the output variables on the model parameters. In this paper, we apply cycle averaging to a simple pulsatile cardiovascular model to derive a cycle-averaged model for cardiovascular dynamics. The resultant model captures the intercycle dynamics with relatively small approximation errors for a large range of perturbations in important system parameters