Detection of cracks in connections of riveted aircraft elements using EC Array technology

Autorzy zaprezentowali wynik badań fragmentów konstrukcji lotniczej z uszkodzeniami znajdującymi się poniżej pierwszej warstwy materiału. Do badań wykorzystano zestaw firmy OLYMPUS oparty na systemie OMNISCAN MX2 i głowicy EC ARRAY oraz porównawczo, zestaw MAUS V. Wyniki, w obu przypadkach przedstawiono za pomocą zobrazowania typu C. Interpretacja sygnałów pochodzących z wewnętrznych warstw konstrukcji przy zastosowaniu tradycyjnego zobrazowania typu A jest utrudniona, co wpływa zarówno na czas realizacji jak i wiarygodność otrzymanych wyników. Zastosowanie zobrazowania typu C ułatwia interpretację i raportowanie uszkodzeń. Ponadto głowica EC Array ze względu na dużą powierzchnię skanowania znacząco skraca czas realizacji badań. Istotnym elementem artykułu jest przedstawienie metodologii doboru parametrów do badań konstrukcji wielowarstwowych.The authors presented the results of tests of fragments of the aircraft structure with damage below the first layer of material. The OLYMPUS set based on the MX2 OMV and EC ARRAY head and comparative MAUS V kit were used for the research. The results, in both cases, are represented by C-type imaging. Interpretation of signals from the internal layers of the structure using traditional A-type imaging is difficult, which affects both for the duration of the implementation and the reliability of the results obtained. The use of C-type imaging makes it easier to interpret and report damage. In addition, the EC Array head, due to its large scanning area, significantly shortens the time of testing. An important element of the article is the presentation of the methodology for the selection of parameters for testing multilayer structures

In-Service Flaw Detection and Quantification in the Composite Structures of Aircraft

Taking into consideration the increased usage of composites for aircraft structures there is a necessity for gathering information about structural integrity of such components. During the manufacturing of composites as well as during in service and maintenance procedures there is a possibility for damage occurrence. There is a large number of failure modes which can happen in such structures. These failure modes affect structural integrity and durability. In this work modern approach for detection of composites damage detection such as: delaminations, disbonds, foreign object inclusion and core damage has been presented. This detection is possible with the use of advanced P-C aided Non Destructive Testing methods. In the article nondestructive testing results for the composite vertical tail skins on MiG-29 aircraft will be delivered as well as some results of F-16 horizontal stabilizer and W-3 helicopter main rotor blades. Moreover some results of the composite honeycomb and sandwich structures will be presented based on the materials used in the construction of gliders and small aircraft. Factors affecting structural integrity and durability of the composites will be highlighted as well as necessity of the inspection with the use of modern NDT techniques. At the end some effort with Structural Health Monitoring connected with possibility of condition monitoring of composites will be presented

Localization of Sound Sources during Full Scale Fatigue Test of the Vertical Stabilizer with the Acoustic Holography Technique

An acoustic holography and its practical applications in engineering began to develop at the end of the 20th century. Currently, this technique is being commonly used to locate sound sources. This paper presents the use of an acoustic camera to locate sound sources during the Full Scale Fatigue Test of the MiG-29 stabilizer. During fatigue tests, the tested structure issues a series of sounds in the form of glitches, creaks or beats. These sounds are typical for a structure subjected to dynamic loading, but they can also be a source of diagnostic information about places of fatigue failures. The paper presents the results of measurements made during the fatigue test. Thanks to the analysis of the measurement results, it was possible to identify areas that are the basic source of sounds

Diagnosis and Repair Technology of Damaged Elements of Casa Aircraft

Recently Polish Air Force has been equipped with new types of aircraft. New aircraft have many elements made of composites. Composites enable increasing performance but also pose new challenges. One of these challenges is the necessity of repairing after damage. This paper presents the results of the non-destructive inspection (MIA, conductivity, optical measurement ) of the C-295 plane after damage. Some parts made of composites and metal were damaged. In this paper, the authors propose a technology of repairing damaged parts

Using Sandblasting and Sol Gel Techniques for the Preparation of a Metal Surface and Their Effects on the Durability of Epoxy-Bonded Joints

The epoxy-bonded joints are widely employed in aerospace in the Composite Patch Bonded Repair (CPBR) method used for repair metallic and composite structures. The properties of epoxy usually meet the mechanical and environmental requirements, but the durability of bonded joints depends also on the surface preparation. The most common techniques used for the surface preparation are Forest Product Laboratory’s (FPL) technique and Phosphoric Acid Anodizing (PAA). Both methods ensure very good adhesion but they have some disadvantages. They require the application of toxic and aggressive acids, dangerous for the operator. Also, the use of acids for cleaning the surfaces can cause corrosion. The sandblasting treatment of metal surfaces ensures quite good adhesion. This technique requires neither specialist equipment nor the use of toxic substances. Recommended by the Royal Australian Air Force (RAAF) the technique is also used by the Air Force Institute of Technology. Sol Gel is a new product developed for the treatment of metal surfaces before bonding. It is not hazardous for the operator and it does not cause corrosion due to its specific chemical composition. The article describes the behavior of bonded joints between two metal surfaces prepared using sandblasting and Sol Gel. The investigations were carried out in various environment conditions according to the ASTM Standards

The Effect of Environmental Flight Conditions on Damage Propagation in Composite Sandwich Structure

The aim of the study was to determine the traceability of damage growth caused by inclusions of water in the composite sandwich structure. It was assumed that as a result of temperature changes during the flight and accompanying phase transformation, the zone containing water inclusions increases. The growth is caused by the destruction (mainly the tearing of walls) of the core. As part of the work, this assumption was verified experimentally. For the experiment to be successful it was necessary to simulate actual flight conditions. The simulation involved inducing phase transformations of water in the core cell as a function of time and temperature. Before and after the experiments the non-destructive tests using pulsed thermography were performed. The test results revealed an increase in the number of cells occupied by water. Adequate specimens were designed and manufactured. The study showed that cyclical changes in temperature affected the propagation of water in core sandwich structures. Further, it was found that the increase in the surface area of water-containing inclusions could be monitored using thermographic techniques

Monitoring of Crack Growth in a Structure Under a Composite Patch

In civil as well as in military aviation, boron, carbon and aramid fiber reinforced composites are employed for the repair of metal structures. After such composite bonded repairs, the monitoring of the repaired structure along with the composite patch and its bond is necessary. The paper describes the possibilities of utilizing NDT methods for periodical check-ups and examinations. Also, a novel approach to continuous monitoring of the repaired structure is presented

The Effect of Cure Cycle Time on the Properties of Epoxy-Bonded Joints

This paper presents the results of the study of the properties of epoxy-bonded joints. Depending on the parameters of cure cycles the epoxy adhesive film has got various mechanical properties. When it is possible to use cure parameters suggested in the data sheet of the adhesive film the best results are obtained. However, in aerospace applications the cure cycle depends on the thermal resistance of other aircraft elements including electrical equipment, cables, etc., and is different from the recommended in the data sheet. Composite Patch Bonded Repair (CPBR) is a special methodology, where the patch cure cycle and the bonding process must be carried out in one operation. The adhesive film cure cycle parameters depend on the prepreg cure cycle parameters. The purpose of this research is to define the influence of a prolonged cure cycle of the adhesive film on the bonded layer strength properties. The metal surface of the specimen has been prepared for bonding by sandblasting and the use of Corrosion Inhibiting Primer BR 127. The tests were performed with the use of Structural Adhesive Film AF 163-2 and two types of cure cycles: the cycle recommended by the data sheet - 121ºC/60 min and the prolonged one - 121ºC/105 min. After the cure cycle the thickness of the bonded layer was measured. Both specimens were comparatively tested during the following strength tests of the bonded layer: static breaking tests using the wedge and the shear strength investigations. The surface of the bonded layer was observed during the tests by an electronic microscope (100x, 200x), which made it possible to demonstrate the effect of the cure cycle on the porosity and observe the nature of the bonded layer damage – de-cohesive and de-adhesive

Predictive Models for Transient Loads of the Vertical Stabilizer of an Aircraft developed using Canonican Correlation Analision

Knowledge about loads occurring in the structure during aircraft operation is vital from the point of view of the damage tolerance approach to aircraft design. In the best-life scenario, such information could be available from a network of sensors, e.g. strain gauges, installed in the aircraft structure to measure local stresses. However, operational loads monitoring (OLM) systems are still not widely applied. Instead, what is available is a set of flight parameters, which by the laws of inertia and aerodynamics help determine the dominant part of loads acting on a given element. This paper discusses the canonical correlation analysis (CCA) as a method for selecting the flight parameters used to predict aircraft loads. CCA allows for the identification of both different modes of stress distribution as well as flight parameters which are best suited for their prediction. The paper presents the application of this method to identify loads acting on the vertical stabilizer of an aircraft