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Aviation technologies are developing due to the need for advancements at military field and the increase in commercial air transportation. The development of aviation technology also forces the development of Non- Destructive Testing (NDT) Standards. The accuracy of these inspections, their fast results and their applicability on many materials is one of the important issues to be studied. Eddy current testing, which has a significant advantage in terms of test speed and accuracy, is one of the main methods used in the non- destructive testing of aircraft parts. The test is used not only in metal and metal alloy materials, but also in composite materials with high conductivity such as carbon fiber to detect failures. Also, improvements at the eddy current test system and probes play a major role in the failure assessment of aircraft parts. In this article, comprehensive technical information about the eddy current testing method is given and the case studies are presented. [ABSTRACT FROM AUTHOR]

Mechanical properties of aircraft composite laminate after lightning strike are predicted and verified based on the combination of experiment and numerical simulation. Axial compression experiment of composite laminate containing lightning strike damage is carried out and failure modes of experimental samples under three kinds of electrical current waveforms are evaluated. The main failure modes include fiber fracture, matrix cracking and delamination. The final failure load decreases with the increase of actual integral action of lightning strike. Compression failure process of composite laminate is simulated using progressive damage analysis methods such as Hashin criterion, Maximum stress criterion and TSERPES criterion, respectively. Numerical simulation and experiment results are compared and coincided well. Percentage error of Hashin criterion is the minimum compared with those of TSERPES criterion and Maximum stress criterion. Stress concentration mainly appears in both angle sides on the fixed end and lightning damage regions of composite laminate. [ABSTRACT FROM AUTHOR]

Abstract: Corrosion and fatigue of aluminum alloys are major issues for the in-service life assessment of aircraft structures and for the management of aging air fleets. The aim of this work was to evaluate the effect of localized corrosion on fatigue crack growth (FCG) resistance of the AA2198-T851 Al-Li alloy (Solution Heat Treated, Cold Worked, and Artificially Aged), comparing it with the FCG resistance of AA2524-T3 (Solution Heat Treated and Cold Worked), considering the effect of seawater fog environment. Before fatigue tests, the corrosion behavior of 2198-T851 and 2524-T3 aluminum alloys was verified using open circuit potential and potentiodynamic polarization techniques. Fatigue in air and corrosion fatigue tests were performed applying a stress ratio (R) of 0.1, 15 Hz (air) and 0.1 Hz (seawater fog) frequencies, using a sinusoidal waveform in all cases. The results showed that the localized characteristics of the 2198-T851 and 2524-T3 aluminum alloys are essentially related to the existence of intermetallic compounds, which, due to their different nature, may be cathodic or anodic in relation to the aluminum matrix. The corrosive medium has affected the FCG rate of both aluminum alloys, in a quite similar way.Graphical Abstract: [ABSTRACT FROM AUTHOR]

An evolution from traditional hydraulic, pneumatic and mechanic components into general electrical system in the airplane featuring an extensive usage of electro-mechanical actuator has been in the spotlight for the last decade. The widespread availability of such actuators which are commonly driven by permanent magnet synchronous motors will, on the one hand, enhance an overall operating economy, yet on the other hand, it will post a newly generated challenge for the current on-board thermal control system since a large amount of waste heat will produce accompanied with the operation of these motors. An ineffective heat rejection path will cause an overheating inside the motors which will lead to a permanent damage easily. It is intolerable for an air-oriented complexity where the reliability, longevity and robustness are the top three priorities. Based on the operating characteristics of the on-board motors, a novel phase change material based motor packaging technology exploiting its huge latent heat is proposed in this paper. Thermal experiments were conducted to analyse the superiority of the proposed strategy quantitatively compared with the conventional fin-based packaging scheme in both constant and intermittent heat generation modes. Systematic design criteria, optimization, performance prediction, etc. were attained via dimensionless studies that aims to acquire a high applicability for more extensive occasions, which is remarked by the discovery of two critical dimensionless factors. [ABSTRACT FROM AUTHOR]

Electroless copper deposition on polyester fabric using glyoxylic acid (CHOCOOH) as a reductant has been investigated. Surface morphology, composition and crystal structure of copper coating on polyester fabric were characterised by scanning electron microscopy, energy-dispersive X-ray analysis and X-ray diffraction, respectively. The surface resistance of copper-plated polyester fabric was evaluated. When the concentration of glyoxylic acid was 12 g L−1, the deposition rate was 49.3 mg cm−2 h−1and the surface resistance was at a minimum of 24.8 mΩ sq−1, which has a potential application in electromagnetic interference shielding for aircraft. [ABSTRACT FROM AUTHOR]

The article represents the results of research on the application of technological wastes of aerosol gas dynamic suspension treatment of aircraft elements for the heavy metal ions sorption from industrial wastewaters. The recommendations on utilization of polluted sorbents by depositing in constructional materials are represented. [ABSTRACT FROM AUTHOR]

A computational models for the strength estimation of cracked aircraft lug are formulated. The crack growth propagation is investigated through the stress analysis and fatigue life calculation. The stress field around the crack tip and the stress intensity factor are evaluated by applying analytical approach. The fatigue life up to failure is simulated by employing two different crack growth laws. The estimations are compared with avaiable experimental data, and good correlation between different results are obtained. [ABSTRACT FROM AUTHOR]

Ceramic matrix composites made of carbon fibres and carbon matrix (C/C) are generally used for aircraft structures and brake discs due to their low density, and good thermal, mechanical, and tribological properties. Silicon carbide (SiC) can be introduced to the matrix to improve the performance of C/C composites, because it increases the hardness and thermal stability, and decreases the chemical reactivity, which leads to the improvement of tribological properties of C/C composites. Thus carbon-carbon silicon carbide (C/C-SiC) composites can be used at high temperature for the application of brake discs, friction clutches, etc. C/C-SiC composites are fabricated by three different methods: (i) chemical vapour infiltration (CVI), (ii) polymer infiltration and pyrolysis (PIP), and (iii) liquid silicon infiltration (LSI), among which LSI method is widely used for the fabrication of C/C-SiC composites due to higher mechanical and thermal properties. [ABSTRACT FROM AUTHOR]

Fiber-metal laminates (FMLs) composed of metal lamina and reinforcing fibers exhibit an improved crack growth resistance as compared to conventional aircraft materials. The crack resistance of a hybrid FML composite consisting of LY12M aluminum alloy lamina and prepreg layers of HS2 glass fibers and T700 carbon fibers has been experimentally investigated on tensile specimens at stress ratios R = - 1, 0.1, and 0.5. The crack growth rate data at positive stress ratios demonstrate a significant scatter and a large difference between specimen's back and front surfaces formed by 1-mm thick outer aluminum layers. This violation of the test standard requirements for metal materials in the performed FML tests presents a problem of determining a proper failure criterion for the engineering applications of FMLs. Based on the comparative analysis of FML crack resistance results obtained, some qualitative conclusions are drawn on solving this problem. [ABSTRACT FROM AUTHOR]

Adhesive bonding of structural aircraft materials depends upon a thorough understanding of factors that affect bond strength and durability. It is well known that surface preparation is critical to adhesive bond performance. However, little information is available regarding the effect of surface preparation procedures on adhesive bonding of high-temperature polyimide composites. Mechanical treatments such as hand sanding are commonly used for composite materials, and in general are known to improve the wettability of the surface as well as effect contaminant removal. Less is known about the influence of mechanical treatments on the surface chemistry. This article discusses the effects of mechanical surface preparation on the adhesive bond strength, durability, and failure mode of several high-temperature polyimide-based composites and adhesives. [ABSTRACT FROM PUBLISHER]

Many probability techniques have been proposed, but the inspection intervals for composite structures have not been comprehensively addressed. The present study focuses on the most frequent damage type, dent, and uses probabilistic approaches to analyze statistical characteristics of the damage based on maintenance data from a Chinese airline. Dent sizes are considered from three dimensions: the damage diameter, the damage depth, and the diameter/depth ratio. The life-cycle strength of a composite structure is obtained by Monte Carlo simulation, and the probability of failure is quantified corresponding to different inspection intervals. Maintenance cost is introduced, as another criterion, to optimize inspection intervals from both safety and economy. This method enables the dent damage to be assessed quantitatively, which can facilitate engineers from airlines or manufacturers to evaluate the damage tolerance of the composite structure and adjust their related inspection schedules flexibly. [ABSTRACT FROM AUTHOR]

The existing material classification is proposed to improve the inventory management. However, different materials have the different quality-related attributes, especially in the aircraft industry. In order to reduce the cost without sacrificing the quality, we propose a quality-oriented material classification system considering the material quality character, Quality cost, and Quality influence. Analytic Hierarchy Process helps to make feature selection and classification decision. We use the improved Kraljic Portfolio Matrix to establish the three-dimensional classification model. The aircraft materials can be divided into eight types, including general type, key type, risk type, and leveraged type. Aiming to improve the classification accuracy of various materials, the algorithm of Support Vector Machine is introduced. Finally, we compare the SVM and BP neural network in the application. The results prove that the SVM algorithm is more efficient and accurate and the quality-oriented material classification is valuable. [ABSTRACT FROM AUTHOR]

A case study for the cost optimization of aircraft structures based on the operating cost as an objective function is presented. The proposed optimization framework contains modules for estimation of the weight, manufacturing cost, nondestructive inspection cost, and structural performance; the latter is enhanced by a kinematic draping model that allows the fiber angles to be simulated more realistically. The case study includes five material systems: aircraft-grade aluminum, two types of resin-transfer molded noncrimp fabric reinforcements, and two types of M21/T800 prepreg. The results are compared in relation to each other, and it is shown that (depending on the estimated fuel burn share of the component) a different material system is favorable when optimizing for low-operating cost. [ABSTRACT FROM AUTHOR]

Many problems that are encountered in assessing the durability of a bonded structure used in industry are rather different from those that are addressed in academic studies of the subject. This article describes some of the experiences gained during a career using adhesive bonding in the maintenance of major aircraft fleets. [ABSTRACT FROM AUTHOR]

Abstract: The combined problem of skin damage detection and restoration quality assessment in lightweight stiffened aircraft panels via vibration testing is considered. Two methods that employ statistical estimation and hypothesis testing procedures and are capable of accounting for experimental uncertainty are introduced. The first is parametric and employs natural frequency and damping ratio interval estimates. The second is non-parametric and employs coherence function interval estimates. The methods’ effectiveness is assessed through laboratory experiments with a stiffened aircraft panel. The results of the study indicate the feasibility of the vibration-based methodology for tackling both the skin damage detection and restoration quality assessment problems. It is also shown that the first method is effective for the skin damage detection problem, while the second for both the skin damage detection and restoration quality assessment problems. [Copyright &y& Elsevier]

We consider a complex of problems of evaluating the residual lifetime of aircraft constructions after long-term operation. Some results of static and fatigue tests of a D16T-type aluminum alloy (in the as-delivered condition as well as after simulated and operating degradation) in air and a corrosive medium (3% NaCl solution) are presented. We have established characteristics that are the most sensitive to the degradation of constructional materials in the course of long-term operation. We also describe a new approach and correction factors for evaluating the fatigue durability of elements of aircraft constructions with regard for the degradation of materials. [ABSTRACT FROM AUTHOR]

Results of corrosion fatigue characterization of AA7075-T6 and AFI410 steel under different simulated marine environments and loading conditions are presented. In comparison with baseline tests conducted in laboratory air, corrosion fatigue experiments performed at l-Hz frequency in the presence of 1% NaCl environment indicated a substantial reduction in fatigue lifetime in the case of AA7075-T6, whereas AFI410 corrosion fatigue life was found to be statistically unaffected at l-Hz frequency in the presence of 1% and 3.5% NaCl. However, a reduction of frequency to 0.5 Hz significantly reduced the lifetime of AFI410 steel. On the other hand, Cd-plated AF1410 tested to study fatigue characteristics in a hydrogen-rich metal surface environment yielded minimal change in the lifetime. Atomic force microscope analysis was performed to discern features in fracture surface morphology leading to changes in lifetime of AFI410 and AA7075-T6 alloys. [ABSTRACT FROM AUTHOR]

The article evaluates the use of thermal non-destructive testing, pulsed thermography(PT) on certain aircraft applications. The experiment provided effective results to assess surface or near-surface defects on aerospace materials. The objective was to locate anchoring points of aircrafts through thermography. Still, the major lacunae was that the experiment depended on the depth and size, which restrict the application to near-surface defect imaging.

Abstract: The paper addresses the technologically important problem of replacement of chromate-based coatings for corrosion protection of aircraft. The Air Force requires development of environmentally compliant aircraft coating systems that perform adequately in terms of corrosion protection. Current Air Force corrosion inhibitor paint chemistry relies heavily on the use of Cr(VI) compounds in the form of strontium or barium chromate, which are incorporated into both the surface pretreatment and the primers. These corrosion inhibitor systems are very effective, but are known carcinogens and therefore must be eliminated. To address this problem, sol–gel-based surface treatments are being investigated as a potential replacement for the current chromate-based surface treatment. Experiments were performed to verify that sol–gel coatings can be used as barrier layers in complex coating systems. The results clearly demonstrated that epoxy-zirconate sol–gel coatings are a viable replacement for the currently used chromate-based surface treatments. [Copyright &y& Elsevier]

Fracture analysis of cracks along mechanically fastened joints is a central issue in the damage tolerance assessment of semimonoque aircraft structures. Nonlinear elastic-plastic finite element analysis, employing the crack-tip-opening-angle criterion, was used to evaluate residual strength of bolted lap-joint 2024-T3 aluminum panels with multiple site damage subjected to Mode-I loading. A total of 36 different crack configurations were analyzed and compared to the experimental results. The effect of different aspects of the finite element modeling procedure on the accuracy of the residual strength predictions was investigated. Modeling of the geometric details of the test panels, such as fasteners and antibuckling restraints, was found to have a considerable effect on the predicted residual strengths. The nonlinear analyses provided reasonable estimates of the residual strength. The numerical results were compared with residual strength predictions obtained from a semi-empirical link-up model. Both approaches were comparable in terms of accuracy when compared to the test data. [ABSTRACT FROM AUTHOR]

In this paper the movable-cellular-automata (MCA) method was applied to study the features of the fracture process and strength properties of ceramics specimen under different constraint conditions. Results of calculations showed that mechanism of fracture of ceramic materials is dependent on the surroundings or contact conditions. It is demonstrated that the MCA method has been successfully used for modeling fracture of the different types of materials and structures. [ABSTRACT FROM AUTHOR]

A strategy for fuzzy-probabilistic assessment of the impact of multiple-site fatigue damage (MSD) on the fatigue resistance of aging structures is developed. The residual strength of a structure may be significantly reduced by the existence of fatigue damage at multiple locations. Depending on the level of knowledge with which they are known, MSD-related parameters may be represented as either purely random variables or fuzzy random variables. The membership functions of the probabilistic characteristics of fuzzy random variables, namely, mean values and standard deviations are developed. Mechanistic and probabilistic models used to evaluate multi-site fatigue damage are also presented. A probabilistic solution strategy, employing a first-order reliability method, is combined with a response-surface-based fuzzy modeling approach to construct the possibility distributions of the probabilistic safety indicators (namely, reliability indices and failure probabilities) for components subjected to multiple-site fatigue damage. Instead of providing the traditional single-valued, purely probabilistic measure for reliability, the present formulation proves its merit in its ability to combine experimental data with expert knowledge to provide confidence bounds on the structural integrity of aging structures. Moreover, the predicted bounds are dependent on the level of knowledge regarding the fuzzy input parameters, with a greater knowledge producing more narrow bounds. An example problem is used to demonstrate the advantages of the proposed methodology. [ABSTRACT FROM AUTHOR]

The article presents information on the All-Union Institute of Aircraft Materials (VIAM). The institute was organized on June 28, 1932 with the aim of creating materials and developing methods for their production and making parts of aircraft structures. In the course of 70 years VIAM scientists created over 2000 grades of aircraft materials, which raised domestic aircraft and spacecraft to the highest world level. Since its first days VIAM combined the solution of specific problems it faced as the leading institute in the field of structural materials with the study of the general laws that determined the operating capacity of materials in structures.

Presents information on a study which investigated the strength of 2024-T3 aluminum panels with multiple site damage. Methodology of the study; Results and discussion on the study; Conclusions.

Evaluates the failure criteria development for dynamic high-cycle fatigue of ceramic matrix composites. Information on the resonant frequency effects; Fracture analysis of failed specimens; Conclusions.