Finite element modeling of crack detection in aircraft structures using electrical current

Eddy Current Array Inspection of Zlin 142 Fuselage Riveted Joints

Full-scale aircraft structural fatigue testing exposes structural weaknesses by simulating the use of the aircraft in service and monitoring the development and expansion of fatigue cracks to guide the optimisation of aircraft structural design, the determination of service life and the development of maintenance and repair programmes. If crack damage is not detected in time, the uncontrolled expansion of the crack may lead to structural damage and prolong the test cycle. Therefore, it is crucial to achieve accurate detection of early cracks in fatigue testing of aircraft structures. Digital image technology is a new technology supported by a number of technical and theoretical achievements. In practical application, it relies on the support of computer functions, by converting image information into two-dimensional digital signals, thus realising various operations. In this paper, digital image processing techniques are used to deepen the backbone feature extraction network structure and improve the prediction scale of small targets, thus improving the performance of the model in terms of feature extraction and small defect detection. Experimental results show that the method can achieve accurate detection of small cracks, providing an effective technical approach for the automatic detection of cracks in aircraft structural fatigue tests. The technique of detecting cracks in aircraft structures using digital image processing also provides a new idea for research into improving aircraft endurance testing, which can be further developed with the aid of image technology.

The paper presents the application of ultrasonic guided waves for fatigue crack detection in metallic structures. The study involves a simple fatigue test performed to introduce a crack into an aluminium plate. Lamb waves generated by a low-profile, surface-bonded piezoceramic transducer are sensed using a tri-axis, multi-position scanning laser vibrometer. The results demonstrate the potential of laser vibrometry for simple, rapid and robust detection of fatigue cracks in metallic structures. The method could be used in quality inspection and in-service maintenance of metallic structures in aerospace, civil and mechanical engineering industries.

Coplanar capacitive technique is a relatively novel electro-magnetic Non-Destructive Testing (NDT) method that could be applied to the evaluation of materials by moving a set of electrodes on the surface of the specimen. In addition to the design-related parameters such as electrode shape, size, and the separation distance between the main electrodes, the material of the specimen affects the coplanar capacitive probe performance. In this paper, a 3D Finite Element Modeling (FEM) was employed to assess and identify the electric field behaviour as a function of material under test for non-conducting and conducting specimens with/without defect. Physical experiments were carried out by a pair of rectangular coplanar electrodes on an aluminium specimen with surface defects covered by a 5 mm thick plexiglass insulation layer to verify the simulation results and evaluate the performance of the probe. A good qualitative agreement was observed between the numerical simulations and experimental results.

. Production efficiency as well as the reduction of energy consumption and waste are the main drivers for the improvement of large-scale production in chemical industry. In addition, the demand for new processes – these days especially related to the chemical energy conversion as basis for the Energiewende – are additional triggers for innovation. Catalysis, well recognized by the public e.g. in form of the 3-way automobile catalyst, plays an important role for about 90% of all processes in chemical industry. The development of new and improved catalysts is a challenge for chemists – as is the search for new structural materials for mechanical engineers. Due to the often-necessary noble and thus expensive metals (e.g. palladium) in many catalysts, structural and chemical function have been developed separately in the two communities. Recent progress in catalytically active materials allows replacing expensive noble metals in selected catalytic processes by significant cheaper elements [1]. This offers the new perspective to combine structural and chemical functionality by innovative materials. Within this area, intermetallic compounds with their peculiar combination of crystal and electronic structure [2], represent an interesting class of materials to address this vision as will be shown in the contribution.

Cemented Paste Backfill (CPB) has become a useful practice in many modern operations around the world. This method is an innovative tailings disposal and underground mine backfilling scheme that returns much of this material to the underground stope field. Thus, it is of great interest for financial and security reasons to fully comprehend the mechanical performance of such underground CPB. Uniaxial compressive strength (UCS) is one of the most commonly used parameters for evaluating the mechanical performance of CPB. Electrical resistivity (ER) measurement, which is a method of nondestructive testing, can also be used to determine the mechanical properties of CPB. This study was undertaken to suggest a nondestructive testing method that would permit prediction of the UCS of a CPB within 90 days. Five CPB samples were prepared at different cement-to-tailing ratios (1/4, 1/6, and 1/8 by weight) and solid content (65 and 70 wt. %), and a curing period of 3–90 days was used for ER measurement. Seventy-five CPB samples were prepared with the same cement content as those used in the pastes for UCS tests cured for 3, 7, 28, 56, and 90 days. The results of the ER measurement show that the ER versus curing periods of 3–90 days first drop to a minimum value and then gradually increase with time. The greater ER values of CPB are reached when the greater cement-to-tailing ratio and solid content is used. A logarithmic relationship is established between the UCS and the ER of CPB at 90 days. It is possible that a nondestructive method could be developed to evaluate the strength of underground CPB based on the obtained logarithmic relationship with ER at 90 days.

In this paper we propose an original analytical modeling applied to electromagnetic (EM) systems, in the aim of performing an inversion scheme. The purpose consists in imaging cracks through eddy current sensors, the image being constituted by an estimation of the conductivity of the piece of metal under test, voxel by voxel. There are plenty of industrial applications in Non Destructive Evaluations for monitoring of cracks in structures: Aeronautics, Metallurgy, ships building and so on. For modeling, a relatively new developed technique, called ‘Distributed Points Source Method’ (DPSM) has been used. This original modeling was invented at Ecole Normale Superieure of Cachan in 2000, and since developed and patented in many kind of applications (Ultrasonics, Electrostatics…).

<div class="section abstract"> <div class="htmlview paragraph">Nondestructive tests are those tests which detect factors related to the serviceability or quality of a part or material without limiting its usefulness. Material defects such as surface cracks, laps, pits, internal inclusions, bursts, shrink, seam, hot tears, and composition analysis can be detected. Sometimes their dimensions and exact location can be determined. Such tests can usually be made rapidly. Processing results such as hardness, case depth, wall thickness, ductility, decarburization, cracks, apparent tensile strength, grain size, and lack of weld penetration or fusion may be detectable and measurable. Service results such as corrosion and fatigue cracking may be detected and measured by nondestructive test methods. In many cases, imperfections can be automatically detected so that parts or materials can be classified.</div> <div class="htmlview paragraph">The SAE Handbook describes the following nondestructive test methods:</div> <ol class="list nostyle"> <li class="list-item"> <div class="htmlview paragraph">SAE J359—Infrared</div></li> <li class="list-item"> <div class="htmlview paragraph">SAE J420—Magnetic Particle</div></li> <li class="list-item"> <div class="htmlview paragraph">SAE J425—Eddy Current</div></li> <li class="list-item"> <div class="htmlview paragraph">SAE J426—Liquid Penetrant</div></li> <li class="list-item"> <div class="htmlview paragraph">SAE J427—Penetrating Radiation</div></li> <li class="list-item"> <div class="htmlview paragraph">SAE J428—Ultrasonic</div></li> <li class="list-item"> <div class="htmlview paragraph">SAE J1242—Acoustic Emission</div></li> <li class="list-item"> <div class="htmlview paragraph">SAE J1267—Leakage Testing</div></li></ol> <div class="htmlview paragraph"><span class="xref">Table 1</span> summarizes the principal features of most of these tests. In addition to the tests described, other nondestructive tests exist which are less well established, but whose use is expanding. Among these are microwave tests, holography, and sonic tests. Microwaves are used to locate defects in nonmetallic substances and to determine some physical characteristics of those materials. Optical holography uses coherent light from a laser beam to detect strains and defects in materials by means of three-dimensional imaging and interferometry techniques. Acoustical holography uses ultrasonic waves to image discontinuities in the interior of solids. Recent refinements in sonic testing permit more objective determination of the physical properties of cast iron. Complete information concerning each nondestructive test can be obtained from books listed in the bibliographies of the aforementioned reports.</div> <div class="htmlview paragraph">Increasing consumer demand for product quality at reasonable cost has resulted in development of nondestructive tests which can be applied to materials and manufactured parts. Although a variety of complementary nondestructive methods is available, development time is generally required for application to specific materials or products. The effect of part contour, surface condition, heat treatment, composition variation, and other variables may limit the ability of certain tests to detect imperfections with desired accuracy.</div> <div class="htmlview paragraph">Nondestructive tests properly applied to basic material can add greater assurance of performance to design strengths, thereby affecting material and manufacturing economy. In addition, parts can be tested after each basic operation which is critical to service performance of the finished part. In-process nondestructive tests can also serve as basic components of feedback process control systems since all tests are based upon measurements which do not damage the material or part being inspected.</div></div>

The engineering risk of pressure equipment is closely related on the structure and material of equipment as well as the parameters such as pressure, temperature, medium environment, etc., which it withstands. In order to reduce and control the engineering risk of the pressure equipment, appropriate nondestructive testing method and testing chance must be adopted at the stages of design, manufacture and installation to control the product quality and assess its safety status at the operation stage of pressure equipment. In this paper the importance of nondestructive testing method and chance selection for pressure equipment is discussed based on engineering cases. This paper shows that nondestructive testing technique is an important means for product quality control of pressure equipment and is also important guarantee for its safe operation. Under the condition that appropriate nondestructive testing method and testing chance are selected, the engineering risk of pressure equipment can be minimized.

The search of a durable and low cost fiber reinforced cement concrete for construction works is an empirical challenge in developing countries. Economic scarcity have confined the use of carbon fibers in cementitious composites on a commercial level. Jute fiber has the potential to be used in reinforcement to surpass the inherent deficiencies in cementitious materials. In this research, jute fiber reinforced concrete is used to find out which test method is more reliable among destructive and non-destructive test methods. In recent years, one of the most challenging scientific method is intelligent defect detection. Non Destructive Testing (NDT) techniques are the most useful and the easiest methods due to their efficiency and low cost. The experimental process using Ultrasonic Pulse Velocity and Schmidt Rebound Hammer as Non-destructive Tests (NDT) are used in this paper to set up a correlation between the compressive strengths of compression tests and NDT values. These two tests have been used to find out the concrete quality by applying regression analysis models between compressive strength of jute fiber reinforced concrete and tests values. The relationship between compression strength of concrete collected from destructive test method and estimated results from NDT’s records using regression analysis are compared together to assess their reliability of prediction of concrete strength. The test results show that destructive test methods are the most reliable way to find out the original strength of test specimens. After destructive test methods, the rebound number method is more efficient in predicting the strength of concrete under certain conditions. Schmidt Hammer rebound tests is recommended to estimate the strength of concrete to reduce the number of cores taken from the structures in practical cases.

Non-destructive methods have many advantages over traditional test methods, especially since it does not damage the specimen, it can be used multiple times on the same specimen. These advantages also provide a great benefit in terms of following the property development in concrete as the same specimens are used which eliminates the variations related to the specimens. In this study, it is aimed to determine the damaged amount of concrete produced with different binders by electrical bulk resistivity, resonance frequency, and ultrasonic pulse velocity methods. Firstly, concretes containing different binders were produced, and along with the mechanical properties, ultrasonic wave velocity, resonance frequency, and electrical resistivity values of the produced concrete were determined at the 7, 28, and 90 days. Besides, the specimens were subjected to gradually increase compressive loads and non-destructive methods were used to estimate the extent of damage on specimens. It was attempted to establish a relationship between the damage on concrete specimens and the results obtained by non-destructive methods. Consequently, the compressive strength, electrical resistivity, ultrasonic pulse velocity and resonance frequency values of all specimens increased with the advancing age. It was concluded that the resonant frequency method is more successful than other methods in estimating the amount of damage in concrete.

The performance and reliability of Structural Health Monitoring (SHM) techniques remain largely unquantified. This is in contrast to the probability of detection (POD) and sensitivity of manual non destructive inspection methods which are well characterised. In this study factors influencing the rates of emission of Acoustic Emission (AE) signals from propagating fatigue cracks were investigated. Fatigue crack growth experiments were performed in 2014 T6 aluminium sheet to observe the effects of changes in crack length, loading spectrum and sample geometry on rates of emission and the probability of detecting and locating the fatigue crack. Significant variation was found in the rates of AE signal generation during crack progression from initiation to final failure. AE signals at any point in the failure process were found to result from different failure mechanisms operating at particular stages in the failure process.

Buildings constructed during early 70's & late 80's of the last century in India are found to be in distressed conditions due to inadequate specifications and poor construction practices. The continuous monitoring of concrete structures using suitable NDT (Non Destructive Testing) methods and use of possible restoration methods help in a considerable reduction of the rate of deterioration of concrete structures thereby increasing the life span of structures. NDT methods have greater advantage in evaluating the uniformity, homogeneity, approximate compressive strength, durability, the extent of corrosion of rebars in concrete etc. of damaged structures. The objective of the present study is to enhance the life of 50 year old existing hospital building (Partly RC and Brick masonry) in Kurnool, Andhra Pradesh. Condition assessments are carried out through a visual, field and laboratory evaluation of samples collected from the structure and results are presented in this paper. The paper also highlights the assessment of strength and durability of concrete to evaluate the extent of distress and damage in the building. Besides visual inspection, the Non Destructive Evaluation covering UPV & Rebound Hammer values and Half Cell Potential with respect to the status of corrosion of reinforcing bars and chemical tests on selected un-distressed RC columns, beams, and slabs are also presented and discussed. The repair and strengthening techniques using the latest materials and possible restoration works such as column jacketing, shotcreting, anticorrosive coatings, etc. have been suggested to enhance the life of the structure.

For the purpose of nondestructive testing (NDT), guided waves can be transmitted into a structure, and any defects or anomalies in the waves’ path modify the measured waves. Signal processing methods can be used to extract information about these features. In this work, an NDT method is demonstrated based on laboratory experiments for the case of a flat, rectangular, aluminum plate, which has a stiffener mounted underneath along the middle axis, such that the stiffener cannot be seen from the upper “outside” surface. Piezoelectric transducers are set up in a pitch-catch arrangement on this surface with the assumption that the location of the stiffener is unknown. When guided waves are induced in the plate by one of the transducers, the waves that are received by the other carry the information of the stiffener, as well as any defects in or boundaries of the structure. By transmitting from different points on a grid on the plate, the location and size of any geometry or material discontinuities can be identified. Hence, the developed algorithm reverse engineers the plate by mapping its edges and identifying the region of the stiffener.

PURPOSES: This study is to evaluate the dynamic modulus changes of permeable asphalt mixtures by using non-destructive impact testing method and to compare the dynamic moduli of permeable asphalt mixtures through repeated freezing and thawing conditions. METHODS: For the study, non-destructive impact testing method is used in order to obtain dynamic modulus of asphalt specimen and to confirm the change of dynamic modulus before and after freezing and thawing conditions. RESULTS : This study has shown that the dynamic moduli of asphalt concrete specimens consisting of 10%, 15% and 20% porosity are reduced by 11.851%, 1.9564%, 24.593% after freezing and thawing cycles. CONCLUSIONS : Non-destructive impact testing method is very useful and has repeatability. Specimen with 15% porosity has high durability than others.