Progress in Aerospace Sciences最新文献

Hypersonic boundary layer (BL) transition generates a significant increase in viscous drag and heat flux, which leads to severe restrictions on the performance and thermal protection systems of hypersonic vehicles. Among various passive/active transition control strategies, acoustic metasurfaces demonstrate minimal effects on the mean flow but significantly suppress the Mack second mode. Therefore, it can be considered one of the most promising transition control technologies. Acoustic metasurfaces are planar metamaterial structures that comprise monolayer or multilayer stacks of subwavelength microstructures, which affect unstable modes via acoustic wave manipulations. This paper presents a review of the research progress made on acoustic metasurfaces for hypersonic BL stabilization over the past two decades. Acoustic characteristics and their corresponding stabilization effects on the first and second modes are compared and discussed. Recent improvements in the mathematical modeling of acoustic metasurfaces have been highlighted. An outline of the theoretical, numerical, and experimental investigations is then provided. Finally, a future research potential, especially for broadband design strategies and full direct numerical simulations, is prospected.

This paper presents an analysis of state-of-the-art of impact detection techniques for aerospace structural components as well as a study about the combination of two promising approaches for localizing an incidental impact event on a typical metallic aerospace structural component as test article. In the aeronautical scenario, some typical damaging events that may occur during service life are runway bird-strike, tool drop and debris impact. The last two cases produce generally high-frequency vibrations that are usually well predicted by ultrasonic techniques. The impacts from birds on the other hand produces vibrations in the lower or modal frequency range. The present work is focused on the possible combination of two methodologies: the first one, related to impacts inducing low-frequency vibrations, is based on the implementation of a Neural Network, while the second one, related to impacts inducing higher-frequency stress waves, is based on an acoustic source localization approach. Both numerical and experimental analyses were implemented on the same isotropic aluminum flat panel, and a possible combination of the experimental sensors arrangement will be discussed within the paper. The results have confirmed the positive performance of the neural network, opening to a more extended experimental campaign mainly oriented to the definition of the system precision, possible fault reconstruction and optimization in the data handling and reduction of computational effort. On the other hand, the main advantage of the acoustic emission formulation is that it does not require the knowledge of the wave velocity profile in the panel. Dependence of the guided wave velocity on the signal frequency for isotropic plates and, also on the wave propagation direction for anisotropic plates are the two major obstacles for acoustic source localization in a plate. Both these obstacles are avoided in this latter formulation.

In this article, a comprehensive overview of the global state-of-the-art in the development of aircraft passenger seat crashworthiness is presented. With the increasing use of aeroplanes as means of transport in everyday life, the probability of accidents and injuries has also increased. This trend makes the safety of human life a top priority for the airplane designers. Based on a large number of studies coming from different industrial branches, military organizations, and academic centers, this article presents a review of the crashworthiness of aircraft passenger seats from the aspect of research approaches, accident investigations, mechanism analysis of occupant injuries and aircraft damage, strategies of occupant protection, and crashworthy design (crash energy management design) and performance of aircraft structures during collision scenarios. Finally, the trends in scientific research regarding the improvement of aircraft seat structure design and material composition are summarized.

Structural Health Monitoring (SHM) systems provide a useful tool to diagnose any engineered structural system and eventual critical damage that may occur at any moment during the operational life. In the past two decades progress has been made in all the fields of SHM, from sensor technology to system integrated techniques. The common goal of any SHM system, whatever the specific application is, may be synthesized in three main points: identify structural deterioration stage, recognize its severity and evaluate the necessity to make a more detailed inspection or proceed to maintenance on condition, based on a potential hazard that may lead to a catastrophic failure. The implementation of such a system leads to making normal operations with the same safety levels but with more efficient maintenance procedures. In addition, it allows avoiding the oversizing of structural components extending the inspection and maintenance intervals. Both these results help to reduce the life-cycle cost of the specific engineered system as it is possible to perform maintenance when it is necessary, i.e. on-condition.

The current state of the art about the guided waves (GW) based structural health monitoring of aerospace composite structures is reviewed in this paper, looking at the implementation of the methodologies proposed and assessed by the authors and giving an outlook on what has been done by the scientific community.

The present manuscript aims to provide an overview of the phenomenon of the low-velocity impact behaviour of composite materials at room and in extreme temperature conditions, by comparing the results obtained on different fibre-matrix combinations and giving a comprehensive review of the impact behaviour and evolution of damage of marine and aerospace composites. The latter was chosen to reduce the environmental impact of plastic wastes. Experimental impact tests up to complete penetration and at different increasing impact energy levels, were carried out by a modular falling weight tower.

The ability of different Non Destructive Techniques NDT in detecting and evaluating barely-visible and invisible impact damage on composite laminates was tested. The aspect related to the damage is, in fact, crucial for these materials because of their inhomogeneity and anisotropy.

The conventional and largely used UltraSound technique, US, was adopted to investigate the delamination caused by low-velocity impact loads. The results were compared with Electronic Speckle Pattern Interferometry, ESPI, as well as with theoretical and semiempirical formulations for the delamination prediction.

The impact induced dynamic response and the failure behavior of aircraft structures continues to be a critical aeronautical engineering challenge in order to improve the passenger survivability after aircraft. It is the objective of this special issue to provide a review of the work at the University of Naples Federico II on failure modes of composite materials and structures and on techniques for impact detection and damage characterization. This review consists of six papers, starting with a review of the bird impact process and the validation of the smooth particle hydrodynamics (SPH) impact model for aircraft structures, followed by a paper on the design of a passenger seat with improved safety while minimizing cost and weight in compliance with prescribed certification rules. Two papers are dedicated to the description of the impact behavior of composite laminates and of the ultrasound propagation in composite laminates. An additional paper presents an overview of experimental techniques for impact detection and of a novel method combining deep learning and wave propagation-based methods to sense impacts that induce excitation spectra at low (modal) or medium-high frequency range through piezo-patches installed on the structure. The final paper provides an overview of the analytical and numerical modelling techniques for guided wave propagation studies and strategies for the implementation of Structural Health Monitoring systems.

The aim of this paper is to study the phenomenon of bird strike during each phase of the impact and to present a numerical model for its prediction in order to develop the best practices to make a structural component resistant to bird strike. To this end, the Smooth Particle Hydrodynamics (SPH) bird model is developed and validated based on experiments by Barber and Wilbeck and two papers by Guida et al. The experiments considered the impact of small birds on rigid flat panels. Guida et al. developed a 8 lb bird model to predict the impact on a deformable small leading-edge bay and on a full-scale leading edge. The hydrodynamic theory is applied to determine the shock pressure, the shock equation of state, the stagnation pressure and the steady-state equation for water with different porosities. Subsequently, the bird structure is analyzed for different bird geometries and target models. This analysis allowed to design critical components of an aircraft structure, such as the leading edge of the C27J aircraft tail cone in compliance with current aviation airworthiness requirements.

The growing use of composite materials for aerospace applications has resulted in the need for quantitative methods to analyze composite components. Ultrasonic guided waves constitute the physical approach for nondestructive evaluation (NDE) and structural health monitoring (SHM) of solid composite materials, such as carbon fiber reinforced polymer (CFRP) laminates. Ultrasound based NDE methods are commonly used in the aerospace field, but ultrasonic wave behavior can be complicated by the presence of material anisotropy, complex geometries (e.g., highly curved parts, stiffeners, and joints) and complex geometry defects. Common defects occurring in aerospace composites include delaminations, porosity, and microcracking. Computational models of ultrasonic wave propagation in CFRP composites can be extremely valuable in designing practical NDE and SHM hardware, software, and methodologies that accomplish the desired accuracy, reliability, efficiency, and coverage. Physics based simulation tools that model ultrasonic wave propagation can aid in the development of optimized inspection methods and in the interpretation of NDE data. This paper presents a review of numerical methodologies for ultrasound and guided wave simulation in fiber reinforced composite laminates summarizing the relevant works to date, different methods, and their respective applications.

The problem of precise characterization, analysis, and eventual identification of unknown materials arises in many fields and takes many forms, depending on the nature of the substances under study. In the first part of this paper we review common, modern mass spectrometry techniques applied to such studies. We also give an overview of improvements made to these technologies in recent years by Silicon Valley companies and other teams focused on precise biomedical research dependent upon sensitive techniques, yet applicable to a wide range of non-biological materials. In the second and third parts of the paper we review practical experiences applying these techniques to the simplest case of the characterization of solid materials (as opposed to liquids or gases) and comparing our results with previously undertaken isotopic analysis. In particular, we describe our correlations of that analysis with the patterns described by witnesses in a well-documented, still-unexplained incident, initially thought to be of aerospace origin, which gave rise to the deposition of unknown material, and by the investigators who handled it in the field and the laboratory. The lessons from this specific investigation are applicable to a wider range of issues in reverse engineering of complex, esoteric materials, and aerospace forensics.

Integrated System Health Management (ISHM) is a promising technology that fuses sensor data and historical state-of-health information of components and subsystems to provide actionable information and enable intelligent decision-making regarding the operation and maintenance of aerospace systems. ISHM fundamentally relies on assessments and predictions of system health, including the early detection of failures and estimation of Remaining Useful Life (RUL). Model-based, data-driven or hybrid reasoning techniques can be utilized to maximise the timeliness and reliability of diagnosis and prognosis information. The benefits of ISHM include enhancing the maintainability, reliability, safety and performance of systems. The next evolution of the ISHM concept, Intelligent Health and Mission Management (IHMM), delves deeper into the utilization of on-line system health predictions to modify mission profiles to ensure safety and reliability, as well as efficiency through predictive integrity. This concept is particularly important for Trusted Autonomous System (TAS) applications, where an accurate assessment of the current and future system state-of-health to make operational decisions (with or without human intervention) is integral to both flight safety and mission success. IHMM systems introduce the capability of predicting degradation in the functional performance of subsystems, with sufficient time to dynamically identify which appropriate restorative or reconfiguration actions to take in order to ensure that the system can perform at an acceptable level of operational capability before the onset of a failure event. This paper reviews some of the key advancements and contributions to knowledge in the field of ISHM for the aerospace industry, with a particular focus on various architectures and reasoning strategies involving the use of artificial intelligence. The paper also discusses the key challenges faced in the development and deployment of ISHM systems in the aerospace industry and highlights the safety-critical role that IHMM will play in future cyber-physical and autonomous system applications (both vehicle and ground support systems), such as Unmanned Aircraft Systems (UAS) Traffic Management (UTM), Urban Air Mobility (UAM) and Distributed Satellite Systems (DSS).