Today's Aerospace Research Articles

Quantifying the Reliability Performance of a Guided Wave-Based SHM System Using Piezoelectric Wafer Actuator Sensors

The adoption of structural health monitoring systems can bring important benefits to the aerospace industry. However, the current implementation of SHM technologies in today's aerospace industry remains limited. One of the primary obstacles hindering the adoption of SHM technologies is the challenge associated with assessing the reliability of SHM systems. In aerospace applications, SHM hardware is exposed to harsh environments, including high or low temperatures, vibrations, moisture, and radiation. Consequently, the long-term performance of SHM systems is adversely affected. This study delves into various issues related to the evaluation of SHM system reliability and performance quantification, placing special emphasis on guided wave-based SHM using Piezoelectric Wafer Actuator Sensors. We present experimental and numerical modeling examples designed to illustrate the detrimental effects of aging at the unitary sensor and sensor network levels. Conclusions are drawn regarding the current challenges in quantifying system reliability, emphasizing relevant performance metrics such as the probability of detection, localization, and false call rates.

THE INFLUENCE OF MANUFACTURING TECHNOLOGY ON THE MECHANICAL PROPERTIES OF THE LAYERED COMPOSITE

The share of composites in today's aerospace industry is steadily increasing. Layered composites are the most popular in aviation. There are a number of methods of their manufacture, each with specific characteristics. One of the most popular simple methods are the technique using a hydraulic press to apply pressure, the vacuum bag method and the infusion method. They are all widely used and useful in individual and mass production, and allow the same types of composites to be made, but due to the differences, the resulting composites, despite having the same structure, may have different properties. In order to verify this observation, an experimental study of the same carbon fabric-reinforced polymer layered composites made by the methods mentioned above was carried out. The mechanical properties of the composites were studied, with a particular focus on their resistance to low-energy impact loading. The results of the study indicate that the composites produced by the infusion method have the best mechanical properties, and with the selected manufacturing technology parameters, the method using a hydraulic press produced the composite with the lowest surface mass.

Regionalization of microstructure and mechanical properties of Ti6Al4V transition area fabricated by WAAM-LMD hybrid additive manufacturing

Wire arc additive manufacturing (WAAM) and laser melting deposition (LMD) are two typical additive manufacturing technologies that fabricate large components and small complex structures. However, the composite manufacturing process of these two technologies is rarely reported. WAAM-LMD hybrid additive manufacturing is a feasible method to satisfy the dual requirements of production efficiency and structural accuracy in today's aerospace field. In this study, a 10-mm-thick wall structure was manufactured by this process. The microstructure in different areas was characterized using optical microscopy, scanning electron microscopy and electron backscattered diffraction to elucidate the formation mechanism of the interfacial microstructure. Meanwhile, the tensile properties were tested in different directions and regions of the component. The results indicate that the combined effect of WAAM and LMD areas lacks obvious defects. The average grain size of the bonding region is closer to the bottom of the LMD region and smaller than that of the WAAM region. Clear grain preference orientations and variant orientations were observed from the bottom to the top of the transition zone, which is affected by different thermal histories between the arc and the laser. In addition, equiaxed crystals and columnar crystals coexist in the remelting zone under the combined action of two factors: the epitaxial growth with columnar crystals and the high cooling rate of the molten pool. The properties of tensile specimens in different directions have few differences. However, the elongation obviously changes in the binding zone. Furthermore, the cleavage fracture gradually transforms into ductile fracture from the bottom to the top in the transition area.

From Jennies to JATO

The First World War was seminal to the development of military aeronautics and aircraft/aerospace manufacturing in California. While flight innovators Glenn L. Martin and Glenn H. Curtiss made key prewar contributions to military aviation within the state, it was America's entry into the war that was the primary catalyst to the establishment of military air facilities as well as a constellation of small, federally contracted airplane factories within California. Using Sacramento's aviation training school at Mather Field and the airplane factory at North Sacramento's Liberty Iron Works as case studies, this article details the ways that World War I was an early catalyst to the statewide embrace of the seemingly limitless potential of aviation, what many then referred to as “air-mindedness.” An intimate look at both Liberty Iron Works and Mather Field reveals how World War I made Sacramento a martial city, strongly committed to a century of pursuing, and playing host to, military aeronautics and aircraft/aerospace production, as manifested by today's Mather Airport (until 1993, Mather Air Force Base) and aerospace giant Aerojet-General, an early innovator of jet-assisted take-off (JATO) and the indirect progeny of Liberty Iron Works. Several factors related to the advent of World War I—most notably, the promise of economic growth, the allure and mystery of flight, and the local prestige that comes with contributing to national defense—inculcated Sacramentans (and Californians) with an adoration for the military, a sense of regional independence, a reverence for the economic promise of the aircraft and aerospace industry, and an aviation-centered mentality that would endure into the twenty-first century.

Quantifying the roles of human error and his/her state-of-health: use of the double-exponential-probability-distribution-function

The probabilistic predictive modelling (PPM) approach in human-in-the-loop (HITL) related aerospace problems enables one to predict, quantify, assure and even specify the probability of the outcome of an aerospace mission or a situation when the performance of a never-perfect human, never-100%-reliable instrumentation (equipment), never absolutely predictable response of the object of control (aero or spacecraft), uncertain and often harsh environment, as well as the interaction (interfaces) of these uncertainties, contribute jointly to the likelihood of such an outcome. The objective of this paper is to generate thinking on how to advance the state-of-the-art in today's aerospace human psychology and particularly, on how to quantify, by both modelling and experimentation, the HITL related effort when the HF and equipment/instrumentation performance contribute jointly to the outcome (success and safety) of an aerospace mission or an extraordinary situation.

Quantifying the roles of human error and his/her state-of-health: use of the double-exponential-probability-distribution-function

The probabilistic predictive modelling (PPM) approach in human-in-the-loop (HITL) related aerospace problems enables one to predict, quantify, assure and even specify the probability of the outcome of an aerospace mission or a situation when the performance of a never-perfect human, never-100%-reliable instrumentation (equipment), never absolutely predictable response of the object of control (aero or spacecraft), uncertain and often harsh environment, as well as the interaction (interfaces) of these uncertainties, contribute jointly to the likelihood of such an outcome. The objective of this paper is to generate thinking on how to advance the state-of-the-art in today's aerospace human psychology and particularly, on how to quantify, by both modelling and experimentation, the HITL related effort when the HF and equipment/instrumentation performance contribute jointly to the outcome (success and safety) of an aerospace mission or an extraordinary situation.

Supply Networks as Complex Systems: A Network-Science-Based Characterization

Outsourcing, internationalization, and complexity characterize today's aerospace supply chains, making aircraft manufacturers structurally dependent on each other. Despite several complexity-related supply chain issues reported in the literature, aerospace supply chain structure has not been studied due to a lack of empirical data and suitable analytical toolsets for studying system structure. In this paper, we assemble a large-scale empirical data set on the supply network of Airbus and apply the new science of networks to analyze how the industry is structured. Our results show that the system under study is a network, formed by communities connected by hub firms. Hub firms also tend to connect to each other, providing cohesiveness, yet making the network vulnerable to disruptions in them. We also show how network science can be used to identify firms that are operationally critical and that are key to disseminating information.

Luisella Giulicchi in Aerospace Today [Amperes: Current Affairs from Around the World

If anyone knows about Women in Aerospace Today, it is Luisella Giulicchi, a spacecraft engineering manager and 18-year veteran at the European Space Agency (ESA) in The Netherlands with more than two decades working in space programs and technologies. At the recent IEEE Nuclear and Space Radiation Effect Conference, Giulicchi told the story of how women remain a minority in management and engineering in today's aerospace domain and drew from her personal experiences and made suggestions about what engineers can do.

Systems engineering: Program empowerment for 21st century aerospace projects

The unprecedented technical complexity and integration required in today's aerospace operations is staggering compared with ten years ago. Aerospace systems today are complex “systems of systems” that require the integration of established, legacy equipment and new and diverse technologies. Integration often results in less system behavior predictability, increasingly complex development, and implementation challenges.

Cryocooler reliability issues for space applications

Analyzing cryocooler reliability has been problematic from the beginning. Classic reliability analyses rely on statistical sampling and comparing failure modes to other similar systems where statistical results are available. These approaches do not apply to cryocoolers, particularly cryocoolers for aerospace applications. The industry has not built enough total cryocoolers, let alone a single type of cooler, to provide any meaningful statistical sample. This forces us to rely on comparing failure modes of similar systems to that of the cryocooler, which leads to the next problem; today's aerospace cryocooler is designed to have no failure modes. What can it be compared to? Any classic reliability study performed on a cryocooler makes several critical assumptions that completely dominate the results. Change the assumptions and you get a different answer; the results are dictated by the assumptions not the hardware. There are no easy answers to these problems. This paper attempts to show why classic reliability studies do not apply to cryocoolers and that as an industry we must work together to show that all cryocoolers have high levels of reliability.

Wearable computers open a new era in support resource management

Our aerospace customers are demanding that we drastically reduce the operating and support costs of our products. In today's aerospace maintenance environment, the vast majority of maintenance technicians are using paper technical publications, with fixed troubleshooting trees, and manual or semi-automated post maintenance documentation. Interactive Electronic Technical Manuals (IETMs) are at this time being deployed with portable maintenance aids, often an electronic notebook-sized data presentation system, some with expert system based troubleshooting aids. Many of the IETM based systems still require post maintenance documentation and, the maintenance control function is at best, updated when each maintenance task is completed and the vehicle departs. Advances in wearable computer technologies allow us to integrate the maintenance technician with a highly automated, tightly managed support system that will significantly reduce support costs and turn-around times while improving the quality of maintenance. A "Portable Maintenance Terminal" is a wearable computer configured to meet a maintenance technician's information and communication needs. The Portable Maintenance Terminal (PMT) will place the maintenance technician in the loop with the support system. Wearable computers are intended for use in locations where easy access to a desktop computer or laptop is not practical, or where operators are required to have their hands on the job rather than being busy with a computer. The wearable PMT can provide a hands-free, heads-up, networked computing environment.

Thermal Characterization of Honeycomb Core Sandwich Structures

Honeycomb core sandwich structures are an integral pan of many of today's aerospace structures. The need to know the thermal properties of these structures in order to perform thermal stress analyses provides the motivation for this research. The estimation approach used here to determine the thermal properties involves the minimization of a least squares function containing both measured and calculated values. A combined one dimensional conductive/radiative heat transfer model was used for the analysis of the structure. Experimental designs for the collection of temperature response data were optimized by maximizing the temperature derivatives with respect to the unknown thermal properties and by a scaled confidence interval approach. The experimental parameters optimized were the heating time and the total experiment time. Experiments were conducted at temperatures ranging from 295 K to 495 K. The thermal properties estimated at these temperatures included the face sheet capacity, the conduction area of the core, and the emissivity in the interior of the core. These parameters exhibited a great deal of correlation, or interaction. A penalty function method was developed to perform the parameter estimation in a constrained fashion, and it was found that the parameters could be simultaneously estimated despite the presence of correlation.

Nonlinear finite element analysis of composite beams and arches using a large rotation theory

Today's aerospace industry has advanced to the point of using optimum design techniques in virtually all applications. In structural elements, orthotropic fiber composite materials have emerged as lighter, stronger and a more easily manufactured solution to the material application aspect of design. Composites have the distinct advantage of being designed and built to many different desired specifications by varying materials, amount of matrix/fiber and orientation. As with many high performance applications, the analysis techniques of fiber composites are more complicated than for the simpler counterparts. This research has been directed to capturing large cross-sectional rotation incorporating a geometrically nonlinear finite element composite arch model. The model was derived and simplified from a (two-dimensional) 2-D shell theory that has been demonstrated to be accurate for large displacements and only moderate rotations. The current effort uses a similar potential energy based finite element model with through-the-thickness shear. Large rotation kinematics are derived in a vector format which includes a tangent function in the in-plane displacement relationship. Previously published research (Creaghan and Palazotto, 1994; Palazotto and Dennis, 1992) used a small angle approximation to simplify stiffness expressions, limiting those theories to moderate cross-sectional rotation angles. This tangent function is modeled by a series representation of the angle and thereby preserving the existing degrees of freedom. The approach decomposes the Green strain components into convenient forms for inclusion in the potential energy function which is then extended to a nonlinear finite element solution method. The potential energy is simplified by substituting the new rotation function for the previous rotation angle. Riks and displacement control are used to show solutions to several nonlinear arch problems. Other published analytical and experimental results are compared with the current research. This work is a simple extension of a previously published large displacement/moderate rotation theory (Creaghan and Palazotto, 1994), but the results show significant improvement when large cross sectional bending angles are present.

Evolution and application of CFD techniques for scramjet engine analysis

Capabilities developed over the past several years in the area of computational fluid dynamics (CFD) have provided today's aerospace engineer with an extremely powerful tool for analysis of complex flowfields of interest. A recent resurgence in the interest in hypersonics has resulted in an increased effort in the development of supersonic combustion ramjet (scramjet) engines as an efficient means of propulsion for aircraft and missiles flying above Mach 5. Use of CFD techniques to design and analyze scramjet engine concepts is proving an invaluable asset, with applicability ranging from the use of simple inviscid codes for parametric studies of various inlet geometries to the use of unsteady Navier-Stokes codes with chemistry models to investigate the details of complex phenomena in a scramjet combustor. This article discusses the evolution of computational fluid dynamics with reference to milestones in scramjet research in the United States, followed by an overview of some applications of available computational capabilities to the design and analysis of scramjet engines being developed at the Johns Hopkins University Applied Physics Laboratory and at the NASA Langley Research Center. Finally, future directions in the application of CFD to the development of scramjet engines are discussed.