Full-scale strength test of airframe structure is performed due to safety requirement. With application of advanced materials such as carbon fibre reinforced polymers to primary structure, a new methodology of assessment the structure strength should be taken. There is observed an acoustic emission as the structure is loaded especially close to its strength limit. An efficiency of a strength test itself may be great improved by using structural health monitoring system with on-line information about the material local loading related to its limit. The experience is discussed in this study and processing of measured data is proposed.

Application of composite patch is a modern technology of fatigue crack repairing in aircraft industry. However, condition of bonded joint should be monitored in the service due to exposition of the structure to temperature and humidity as well as cyclic loading. For bonded joint inspection, an ultrasound method is used. Due to very thin layers of structure material, a technique of reflected waves in the metal sheet was developed. The experiment with technology test specimen was performed in the laboratory. The fatigue life of the repair was simulated. Acoustic emission was monitored and the actual size of disbonded area was analysed.

There are many experiments and measurements, where typical AE source location error 100-1000 mm is clearly unacceptable. In suggested paper problem of AE source location accuracy increasing will be discussed. Method based on fuzzy sets theory principles will be demonstrated using AE data recorded during fatigue test of small aircraft landing gear bracket.

Signals measured in ultrasonic nondestructive evaluation (NDE) of materials are masked by the characteristics of the measuring instruments, the propagation paths taken by the ultrasonic waves, and noise originating from various sources, including the electrical noise. Due to the band-limited characteristics of ultrasonic transducers, the received echoes are degraded by the transducer impulse response and show a relatively low time resolution. In order to remove the transducer impulse response in the presence of noise, deconvolution techniques are usually implemented. One of these deconvolution techniques is the Wiener filter. Implementation of an optimal Wiener filter requires estimation of the statistical distributions of both the desired signal and the noise present in this signal. In practical applications, this information is not readily available and needs to be somehow estimated. In this paper an iterative algorithm is proposed for estimating the power spectral density of the desired signal. This method uses the signal processed by the Wiener filter as an improved signal to update the power spectral density estimates. The results obtained from synthetic data indicate that the proposed method outperforms the conventional Wiener filter and could significantly improve the time resolution of the ultrasonic signals.

Simultaneous measurement of electromagnetic (EME) and acoustic (AE) emission signals resulting from mechanical loading of solids can be used to localize the arising cracks. In the 2D case, the localization methods are usually based on identifying intersection points of the circles drawn around the AE sensors (provided the time of the crack generation is known from the EME signal measurement) or hyperbolas, whose foci are situated in the AE sensors (when only AE signals are measured). When these methods are applied, the mechanical wave propagation velocity in the material under investigation must be known. However, if an excessive number of AE sensors is used, the different circle or hyperbola intersection points are not identical. In fact, these intersection points are only marking the boundaries of the region of probable crack generation. The information provided for the point in question in this way is not unambiguous. Therefore, to support the arising crack localization efforts, a new localization method has been designed, which is based on a conveniently selected error function being defined throughout the specimen bulk. The value of this function at any selected point of the specimen expresses, based on the signal measurement, the suitability of the particular point to be identified with the crack generation point. The point at which the error function value reaches a minimum is considered to be identical with the crack generation point. When applying this method, the mechanical wave propagation velocity in the solid need not be known. On the contrary, this method can be applied to the determination of the wave propagation velocity. Several error function types have been designed. The applicability of these methods has been verified experimentally, using a dedicated specimen which makes it possible to simulate the crack generation at an exactly specified point.

Stability of building structures is one of very important issues in the field of nondestructive defectoscopy. Taking into account the fact that most of concrete and reinforced concrete structures were created in the first half of last century, it is evident that a search for new and simple defectoscopic methods, allowing the researchers to determine the integrity of these building structures or their parts, is of primary importance. It is also essential to develop and/or refine the methods designed to estimate the lifetime of building structures. The current methods of nondestructive testing of building materials are suitable for the defectoscopy of homogeneous materials and simple-shaped bodies. Their application to inhomogeneous building materials is difficult in the case of small-sized cracks and defects uniformly distributed throughout the specimen. This is why non-destructive diagnostic methods (NDT) are acquiring growing importance, helping the researchers to evaluate properly the condition of a bridge and decide upon the most convenient method maintenance, repair or refurbishment of the bridge in question or its parts and schedule them accordingly. Reconstructions of motorway bridges are frequently accompanied with long-time restrictions of the number of motorway lanes, which result in considerable delays and consequent financial losses of the motorway users. If the application of NDT methods contribute to optimizing the bridge repair interventions and their scheduling in conformity with safety rules, then the costs of researching new NDT methods are fully justified. One of the methods, which is recognized worldwide as the most promising for the mentioned purposes, is the acoustic emission (AE) method. By contrast to most other NDT methods, AE is a comprehensible method, allowing both one-shot examination and long-term monitoring of the condition of the structure under consideration or its selected parts. The present paper deals with the use of the AE method from the viewpoint of its application to diagnosing the bridge structure reinforcement corrosion and its consequences.

The impedance spectroscopy method, one of the non-destructive testing methods, has been applied to characterize concrete specimens and track the changes in the frequency spectra before and after a sodium water-glass layer has been spread over its surface. Variations in the tan ��(f) and Im Z(f) or Re Z(f) plots have been observed and the specimen quality has been described using the predominant loss kind in the material in question. Our results appear to indicate a possible correlation between the n-factor obtained by this method and the specimen porosity. They can also indicate electric conductivity variances in the frequency spectra of the material under investigation.

The paper is focused to possibility of utilization of the non-linear phenomena arising in connection with the propagation of ultrasonic waves in solids to diagnostic ceiling slabs Hurdis. Breakdowns of ceiling structures made of Hurdis slabs have be problem in building industry of today. Since the early 90? several thousands of buildings with these ceilings were constructed. As a result of this failures may appear again in the following years. Therefore it is necessary to develop and check suitable methods enabling the testing of endangered ceiling structures and considering their static reliability. Non-lineary ultrasonic spectroscopy methods are based on the fact that a crack induced non-linearity makes an extremely sensitive material impairment indicator. Due to the presence of defects, the atom potential energy ceases to be exactly harmonic. Second and third harmonic frequencies signals arise. The intact material region generates almost zero non-linearity. Another important benefit results from the higher sensitivity in relation to the defect size and the system immunity to the measuring of smaller signal reflections, as the sample edges lack any non-linear properties and consequently, there are no narrow-band signals arising from these reflections. Non-linear ultrasound spectroscopy methods due to their supposed higher sensibility and more exact characterization of material quality and reliability appear as perspective for both aims.