360-deg profilometry: new techniques for display and acquisition

Two optical methods are proposed for shape measurement and defect detection of curved surfaces in the form of a complete 360- deg profile of the object. The first one is the standard structured light approach. Display of the resulting data is the emphasis of this section. The second approach uses modulated structured light with a scanning digital camera for faster and simpler data acquisition. Quantitative processing is done off-line while real-time moire produces enhanced display of the defects for qualitative analysis.published_or_final_versio

Parametric Study of a Turbofan Engine With an Auxiliary High-Pressure Bypass

A parametric study of a novel turbofan engine with an auxiliary high-pressure bypass (AHPB) is presented. The underlying motivation for the study was to introduce and explore a configuration of a turbofan engine which could facilitate clean secondary burning of fuel at a higher temperature than conventionally realized. The study was also motivated by the developments in engineering materials for high-temperature applications and the potential utility of these developments. The parametric study is presented in two phases. Phase I presents a schematic of the turbofan engine with AHPB and the mathematics of the performance parameters at various stations. The proposed engine is hypothesized to consist of three streams—core stream, low-pressure bypass (LPB) stream, and the AHPB or, simply, the high-pressure bypass (HPB) stream. Phase II delves into the performance simulation and the analysis of the results in an ideal set-up. The simulation and results are presented for performance analysis when (i) maximizing engine thrust while varying the LPB and AHPB ratios, and (ii) varying the AHPB ratio while maintaining the LPB ratio constant. The results demonstrate the variations in performance of the engine and a basis for examining its potential utility for practical applications

A Comparative Performance Analysis of the Novel TurboAux Engine with a Turbojet Engine, and a Low-Bypass Ratio Turbofan Engine with an Afterburner

Presented herein is a comparative performance analysis of a novel turbofan engine with an auxiliary combustion chamber, nicknamed the TurboAux engine, against a turbojet engine, and a low bypass ratio turbofan engine with an afterburner is presented. The TurboAux engine is an adaption of the low-bypass ratio turbofan engine, but with secondary combustion in an auxiliary bypass annular combustion chamber for thrust augmentation. The TurboAux engine is envisioned with the desire to facilitate clean secondary burning of fuel at temperatures higher than in the main combustion chamber with air exiting the low-pressure compressor. The comparative study starts by analyzing the turbojet engine and its performance with and without an afterburner segment attached. In parallel, the conventional turbofan and its mixing counterpart are analyzed, also with and without an afterburner segment. A simple optimization analysis of a conventional turbofan is performed to identify optimal ‘fan’ pressure ratios for a series of low-bypass ratios (0.1 to 1.5). The optimal fan pressure ratios and their corresponding bypass ratios are adapted to demonstrate the comparative performance of the varying configurations of the TurboAux engine. The formulation and results are an attempt to make a case for charter aircrafts and efficient close-air-support aircrafts. The results yielded increased performance in thrust augmentation, but at the cost of a spike in fuel consumption. This trade-off requires more in-depth investigation to further ascertain the TurboAux’s utility

Measurements of displacement around holes in composite plates subjected to quasi-static compression

Attempts to develop a whole-field, high sensitivity optical technque for measurement of load induced changes of thickness of composite plates are described. Graphite-epoxy plates of quasi-isotropic layup were used as test specimens. Changes of thickness of three plates, each with a central hole of different size, were measured as a function of applied compressive loads. The first test specimen showed localized zones where no holographic fringes were present, surrounded by zones of low fringe contrast. This was thought to be a result of localized motion or creep. Subsequent tests with an increased time interval between specimen loading and holographic exposure demonstrated no localized zones of absent fringes. No plausible explanation for radical differences in the quality of fringe patterns was found, although the use of specimens having a high quality mirrorized surface provided superior change of thickness patterns. Recommendations for further investigations and changes in test procedure are presented

Measure of displacement around holes in composite plates subjected to quasi-static compression

Contour maps of thickness changes were obtained for three quasi-isotropic graphite-epoxy plates with central holes, loaded in compression. Thickness changes were determined for six load increments from nearly zero to within a few percent of the failure load. The largest change of thickness occurred near the hole but not at the boundary of the hole. Below 90 percent of the failure load, the thickness changes were nearly proportional to load. Irregularities of thickness changes occurred in zones of compressive stresses and they were attributed to localized fiber buckling. A new optical technique was developed to measure thickness changes with high sensitivity. It utilizes a comparatively simple means of holographic interferometry on both sides of the specimen, followed by additive moire to obtain thickness changes as the sum of the out-of-plane displacements. Sensitivity was 12.5 x 10 to the -6 power in. per fringe order. The fringe patterns represent thickness changes uniquely, even when specimen warpage and consequent out-of-plane displacements are very large

Parametric Study of a Turbojet Engine With Auxiliary Bypass Combustion- The TurboAux Engine

A parametric study of a novel turbojet engine with an auxiliary combustion chamber, nicknamed the TurboAux engine is presented. The TurboAux engine is conceived as an extension of a turbojet engine with an auxiliary bypass annular combustion chamber around the core stream. The study presented in this article is motivated by the need to facilitate clean secondary burning of fuel at temperatures higher than conventionally realized from air exiting the low-pressure compressor. The parametric study is initiated by performing a simple optimization analysis to identify optimal ‘fan’ pressure ratios for a series of conventional low-bypass turbofan engines with varying bypass ratios (0.1 to 1.5). The fan pressure ratios for corresponding bypass ratios are chosen for studying varying configurations of the TurboAux engine. The article is presented in two phases – (i) Phase I presents the simulations carried out to arrive at an optimal configuration of a TurboAux engine and it formulation, (ii) Phase II presents simulations and results to compare the performance of a low-bypass turbofan engine to the TurboAux engine. The formulation and results are an attempt to make a case for charter aircrafts and efficient close-air-support aircrafts

Analysis of Inelasticity Effect Due to Damage on Stress Distributions in Composite Laminates

A damage mechanics model characterizing damage behavior of composite materials proposed earlier by the authors is employed to analyze the damage effects on stress field near the free edge in symmetrically laminated graphite/epoxy composites of finite dimensions under umaxial tension. A quasi-three-dimensional finite element analy sis is developed for the present investigation. The results from the damaged and undam aged stress distributions of [0/90°]s, [90/0°]s, and [±45°] s laminates are compared and examined. The processes of initiation and development of damage zone in these composite laminates are also discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/68869/2/10.1177_073168449301200805.pd

A Three-Dimensional Analysis of Symmetric Composite Laminates with Damage

Damage behavior of a symmetric composite laminate without an initial im perfection or macro-crack is analyzed based on a three-dimensional lamination theory under multi-axial loading. The global response of the laminate during the damaging pro cess is determined from the individual response of its constituent plies and their mutual relations. Some specific results are presented to illustrate the damage characteristics of several typical composite laminates when they are subjected to proportional loading. The application of the method to characterize damage initiation and growth in more complex structures is also discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/67341/2/10.1177_105678959300200304.pd

Determination of the characteristic directions of lossless linear optical elements

We show that the problem of finding the primary and secondary characteristic directions of a linear lossless optical element can be reformulated in terms of an eigenvalue problem related to the unimodular factor of the transfer matrix of the optical device. This formulation makes any actual computation of the characteristic directions amenable to pre-implemented numerical routines, thereby facilitating the decomposition of the transfer matrix into equivalent linear retarders and rotators according to the related Poincare equivalence theorem. The method is expected to be useful whenever the inverse problem of reconstruction of the internal state of a transparent medium from optical data obtained by tomographical methods is an issue.Comment: Replaced with extended version as published in JM