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This paper presents follow-on material and conclusions to a previously published paper that presented work to develop and validate life prediction models for SiC device packaging [ 1 ]. The first step in this work was to determine the most probable failure modes in the device packaging. After determining the expected dominant failure modes of a SiC semiconductor packaging, appropriate models were identified and applied to the packaging in order to track remaining useful life. Once failure modeling was completed, the life prediction models were validated. Validation consisted of accelerated life testing designed to stress specific parts of the device package so as to stimulate the desired failure mechanism. This paper will review the three testing methodologies designed to excite the three dominant failure mechanisms in the electronic packaging. These tests can be broken into two types of general tests: power cycling and high temperature reverse bias testing (HTRB).

High altitude, high speed flight will push vehicles into regions wherein the density of the surrounding medium is so low that vehicle aerodynamics cannot be described on the basis of the continuum equations of fluid motion. Typical flight trajectories and the characteristic flow regions they traverse are illustrated, and the prediction techniques based on molecular flow physics are outlined. Some analytical, experimental, and flight test results which clearly illustrate the importance of low density effects on the flight performance of vehicles -- particularly lift, drag, and moment -- are discussed. The data presented bring out some fundamental physical principles of molecular interactions in the definitions of aerodynamic behavior, and some of the underlying physical mechanisms are discussed. Molecule-to-molecule interaction is only one of the processes which determine flow field characteristics.

The use of aluminum is rapidly gaining acceptance for structural applications in the automotive industry. While laser beam welding offers many advantages for joining of aluminum alloys, it also possess certain inherent characteristics that differentiates laser beam welding of aluminum alloys from ferrous materials. These characteristics include aluminum's high reflectivity, large differences in vapor pressure between aluminum and many of its alloying constituents, and relatively low surface tension and viscosity in the molten state. This paper addresses process requirements for effective laser beam welding of aluminum alloys designed primarily for automotive applications and characterization of welded joints commonly used in the automotive industry.

This study evaluates the shear-thinning effects of a commercial Viscosity Index (VI) improver in a variety of mineral oil base stocks to produce a series of viscosity grades from 0W-20 to 20W-50. All of these fluids also include a DI package in addition to an olefin copolymer VI improver and base oil. The Penn State high shear capillary viscometer was used to collect the primary data at shear rates of up to 106 s-1 and at 10 to 177°C. Data are fitted to a double truncated power law model to determine the incipient non-Newtonian shear rate Υ̇1, the power law index n, and the incipient second Newtonian shear rate Υ̇2. These parameters are found to be smooth functions of temperature and polymer concentration in the different base stocks. Using the data obtained from OW-20, 10W-30, and 20W-50 SAE grade formulations, these parameters (Υ̇1, Υ̇2 and n) are correlated as functions of temperature, polymer concentration, and a viscosity temperature property of the base oil.

Statement of the Problem: Since the Airline Deregulation Act of 1978 the U.S. Airlines have experienced many changes involved with the competitive free market system. For one they have been forced to change their thinking which now lets the balance sheets and bottom line dictate their routes, schedules and pricing. Another is they are forced to operate at lower budgets looking at ways of attracting customers while reducing costs. Both these changes have resulted in the airlines operating close to bankruptcy. With this in mind we see many of the Airlines operating an older fleet of aircraft and not replacing them with newer aircraft. The same is true for the Department of Defense who's mainstay bomber and transport fleet is on average 20 plus years old. So what can the DOD and the airlines do together under the auspices of Dual Use so as to reduce costs and improve their operations?

The effect of minimum stress on the fatigue life has been assessed for an angle-plied nylon cord-reinforced elastomer composite which represents the bias aircraft tire carcass. The S-N curves were established under constant minimum stress rather than constant R-ratio. In this manner, all data points in each S-N curve could be associated with the same level of creep stress. Composite laminate specimens exhibited a normal failure sequence of fiber-matrix debonding developing into the delamination under cyclic tension. A trend of longer fatigue life of the composite was clearly observed at a given stress amplitude with a higher level of minimum stress. The use of a higher level of minimum stress also caused the increase of the fatigue endurance limit of the composite. The trend of longer fatigue life with a higher level of minimum stress stems from the fact that the stress and strain are not linearly related to each other.

This paper presents the results of a study in which the free rolling behavior of a F-16 tire was numerically modeled. The tire contact patch normal and shear stresses as well as the displacement distributions were obtained from a three dimensional finite element computer program used at the Wright-Patterson Air Force Base, Ohio. It is shown how the predicted deflections are in reasonable agreement with the rated load vs. deformation characteristics, while predicting the effective rolling radius using a theoretical solution. A significant development of this work is the formulation and execution of a finite difference algorithm to evaluate the contact patch slip velocity distribution by methodically manipulating the above computer program results. Slip velocities are then utilized in assessing the rate of slip energy generation at the contact patch, which directly contributes to tire wear. Finally, it is shown how even a low brake slip ratio can increase the contact patch slip energy.

The main objective of this research was to apply an optical technique called fringe projection to quantifying the aircraft tire deformation and strains. The proposed fringe projection technique, using a single light source and a grating, requires no image superposition. Thus, the measurement is not very sensitive to vibration. Three different types of tires in static and dynamic conditions, subjected to different amounts of tire deflections, were tested. A common practice in three dimensional optical measurement is that a fixed reference plane has to be established, from which a fixed reference point is selected. The main technical difficulty in this research is that a tire subjected to an applied load not only moves and rotates, but deforms as well. Therefore, the selected reference point changes its position in three dimensions all the time.

The question of how the static strength of angle-plied nylon cord-reinforced rubber composites simulating aircraft tire carcass is affected by damage accumulation or materials degradation was examined in this study. Upon cyclic loading at 1 Hz, residual tensile strength was gradually lowered with the progression of fatigue damage. The degradation of the residual strength became more drastic toward the end of the fatigue life because of worsening delamination. In contrast, the residual strength after cyclic loading of 10 Hz exhibited a rapid decrease at the beginning of the fatigue life, presumably due to thermal degradation, and then remained virtually constant throughout the life. Acoustic emission (AE) activities were monitored to assess the extent of damage and to explore a possibility of indirect monitoring of residual strength of composites.

A multi-axial dynamic test instrument was designed to perform wear testing of actual aircraft tires as well as tread/carcass composite specimens under laboratory loading conditions which simulate the elements of take-off, landing and taxiing operations. The wear tester consists of a self-spinning abrading head, mounted on the actuator of a servo-hydraulic test system, which faces either (1) the tread surface of a composite specimen clamped by a horizontal stretch frame or (2) the tread region of actual inflated tires. The test concept has been partially proven in the case of tread/carcass composite specimens by building a proto-type test apparatus and operating it successfully. In the current test set-up, the specimen is subjected to static tension to simulate a circumferential load in the tire footprint and the tread surface is in periodic contact with an abrading head under a specific level of pressure.

Although radial tires have been used in automobiles, they are still in the stage of testing for a possible future use in aircraft. An important consideration is the tire's average life when subjected to various loading conditions. Along with this consideration, tire deformation is one of the concerns. This paper presents a study of deformation comparison between F16 bias and radial aircraft tires subjected to loading conditions against flat plate and flywheel with different percentages of tire deflection and different yaw angles. Optical fringe projection technique is used to determine the three dimensional tire deformation. Like any other similar optical technique, the deformed surface is measured relative to the selected reference point. Therefore, in order to find the absolute geometry of the deformed tire surface, a close-range fiber optic displacement sensor was installed to accurately detect the point's height change in a direction parallel to the wheel axle.

This paper presents an optical technique called fringe projection to measure three dimensional tire deformation subjected to different loads, percentages of deflection and yaw angles. Unlike the well-known Moire method, the proposed technique uses a single light source and a grating, thus requiring no image superposition. As a result, the measurement is not as sensitive to vibration as the Moire method. The fringe projection also differs from the commonly used optical inspection technique in manufacturing industry via line scanning known as structured light, which cannot be applied to dynamic deformation measurements. The recently developed subpixel resolution was employed to accurately locate the optical fringe centers, which in turn improves the accuracy in 3-D geometry determination. A fiber-optic displacement sensor was also placed close to the tire sidewall in order to measure the deformational change of a selected reference point.

The intrinsic wear behavior of tire tread materials bonded to carcass plies was examined under static footprint load and static axial pretension. Relying on a specially designed test apparatus, the abrasion action was induced with constantly changing directions and cyclic change of sliding speed. A series of wear tests was performed for parametric studies. The morphology of resulting wear surfaces was examined to understand wear mechanisms. The wear process of tire tread materials consisted of a mechanical mode of abrasion when sliding speed was below a critical level. For this range of sliding speed, the extent of tread wear was found to be simply dependent on the cumulative number of abrading head revolution which reflects the total sliding distance. The relationship between the amount of wear and cumulative number of abrading head revolution deviated from linearity when the rotational frequency of abrading head reached a critical level.

This paper reports tests to determine the effect of R- l34a-oil mixtures on condensation in a 1.32 mm hydraulic diameter extruded aluminum tube used in automotive refrigerant condensers. The tests were performed at 8 kW/mz heat flux for 600, 1000, and 1800 kg/m2s mass velocity with 3.25,6, and 10% oil concentration (by mass). At low vapor qualities, oil increases the condensation coefficient (h), and at vapor qualities above 50%, oil reduces the h-value. The h-reduction is more severe at increased oil content. Oil increases the pressure gradient, and the pressure-gradient increase is more severe at higher oil concentration.

The advent of stainless steel automotive exhaust systems presents a significant opportunity for powder metallurgy (P/M) parts and the inherent economic advantages of this near net shape metalworking technology. A study was performed to determine the viability of ferritic P/M stainless steel parts for exhaust applications such as coupling flanges and hot exhaust gas oxygen sensor (HEGOS) bosses. In order to help achieve the automotive industry's stated goal of extending the functional life of exhaust components while remaining competitive, the authors developed a program to develop a database of the mechanical properties and performance characteristics of several grades of P/M stainless steel. Among the data generated and analyzed for these ferritic alloy systems are room temperature, tensile stress-strain curves, fatigue and endurance properties, hardness levels, and corrosion resistance.

This paper reports the results of a limited flight evaluation of Direct Lift Control (DLC) on a modified B-52 aircraft. The evaluation was made in conjunction with concluding flights of the Load Alleviation and Mode Stabilization (LAMS) Program and represents the first flight testing of a blended closed loop DLC system on an aircraft of this size and weight. By allowing the pitch and heave motions in the longitudinal axis to be decoupled, the system provided positive control of altitude displacements while holding pitch attitude constant. In both ILS approaches and aerial refueling tasks, controllability was significantly improved and pilot workload was reduced.

Atomic Absorption Spectroscopy is widely used in the petroleum industry for determination of the zinc concentration of new engine oils. Many of the methods in use rely on dilution of the sample with kerosene followed by aspiration into the AA. It has been shown that such methods are subject to matrix interferences from other additive components. One previously identified interferent is the VI improver included in the lubricant formulation. This study is directed at determining the cause of the VI improver generated interference. Included in the study is an examination of the effects of different chemical type and molecular weight polymers. Also included is a comparison of dispersant and non-dispersant VI improvers of similar molecular weight. Some potential methods of eliminating the interference are also examined.

Delivery of a lubricant as a vapor mixed with a carrier gas provides a method of controlling the delivery rate of the lubricant. Temperatures in the range of 370 to 800 C are high enough to produce a lubricating film from tricresyl phosphate [TCP] vapor delivered in nitrogen as a carrier gas. The solid film lubricant formed by this delivery system provides excellent lubrication for a four-ball wear tester run at 370 °C. Deposit rates are compared for TCP vapor delivered lubrication over a temperature range using stainless steel and quartz surfaces. The deposit rate is sensitive to TCP concentration in the carrier gas. The deposit rates of the TCP decomposition products versus time are reported. Having been demonstrated in laboratory tests, the Vapor Phase [VP] concept is being pursued for hot section lubrication of the advanced (low heat rejection) diesel engines.

Directed Energy Weapons (DEW) require switches that are capable of switching hundreds to thousands of amperes of current at thousands of volts potential. Present and near term available devices must be packaged in parallel and in series to achieve the power ratings required for DEW applications. High voltage silicon (Si) devices such as recent advances in MOS turn-off thyristors (MTOs) can be used along with the high speed, soft-recovery Trench Oxide P-i-N Schottky (TOPS) diodes to reach high power density and high efficiency. However, wide bandgap, high thermal conductivity silicon carbide (SiC) power switches and diodes in development offer orders of magnitude improvement in terms of power density and power efficiency, and are much more ideal for DEW applications. In addition, SiC power switches can be operated at much higher temperatures than silicon (present developments to at least 300°C) with an increased Radiation Hardness.

Advanced centrifugal compressor vapor cycle refrigeration systems are being tested extensively in the laboratory before they are introduced to new affordable fighter aircraft. It was determined that further testing was needed to establish the effects on a centrifugal compressor system due to high and rapidly varying G forces encountered during fighter aircraft maneuvers. Flight weight aircraft vapor cycle components were tested up to 4Gx, 4Gy and 9GZ on the Air Force Armstrong Laboratory Dynamic Environment Simulator Centrifuge Facility under the Integrated Closed Environmental Control System (ICECS) Program at Wright-Patterson AFB, Ohio. The tests demonstrated that a properly designed digital controlled integrated vapor cycle system will operate in the variable G field (9GZ) of a fighter aircraft. It showed that heat exchangers can be designed with minimum effect to gravity “G” fields. The future for vapor cycle systems in new affordable aircraft looks promising.