Wyniki wyszukiwania - Biblioteka Nauki

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Analysis of bonding layer quality in repair process of aircraft composite structure after impact damage

100%

Sałaciński M. , Orzechowski P. , Chalimoniuk M. , Leski A.

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2020

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tom R. 20, nr 3-4

134--141

EN

Aircraft composite structures made in autoclave prepreg technology are characterized by low porosity and high strength. Unfortunately, composite structures are susceptible to impact damage. Therefore in order to repair this type of structures, an advantageous method of structure restoration is the use of the two-step bonding method. This method relies on creating a composite patch cured in an autoclave and then bonding it into a previously prepared repair area in the repaired structure, created by removing the damaged layers. Thanks to this approach, the patch is produced in accordance with the production process of the repaired element and has similar properties including low porosity. A critical element of repair is the bonding layer between the patch and repaired structure. Difficulties in obtaining an appropriate consolidation pressure (compression) using a vacuum bag can cause local disbonding of the composite patch as well as porosity in the bonding layer. Porosity reduces the strength properties of the joint, and it also reduces its weather resistance, which may contribute to its gradual degradation. The article focuses on analysis of the influence of compression obtained by a vacuum bag on the porosity and thickness of the bonding layer. A professional line for the production of aircraft composites and a mobile system for composite repairs of aircraft structures were used to produce the samples. The computed tomography method was used to measure the porosity and thickness of the bonding layer.

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Modular Test Stand for Fatigue Testing of Aeronautical Structures - Verification of Assumptions

75%

Leski A. , Wronicz W. , Kowalczyk P. , Szmidt M. , Klewicki R. , Włodarczyk K. , Uliński G.

Fatigue of Aircraft Structures

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2020

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tom Iss. 12

78--91

EN

The Modular Test Stand was developed and manufactured to decrease the cost of fatigue testing and reduce the time of its completion as well as to enable testing specimens under more complex load conditions. The stand consists of three connected sections, similar to a wing box, all being loaded in the same way. Thanks to that, several specimens can be tested simultaneously. This configuration requires that stress and strain distribution should be reasonably uniform, as assumed in the design stage. The structure can be loaded with bending or torsion. A whole section, selected structural node or a specimen mounted in the structure as well as a repair or a sensor can be a test object. Two stands, one for bending and one for torsion were prepared. This paper presents the verification of the assumed strain and stress distributions on the skin panels. The measurements were performed with the use of Digital Image Correlation (DIC) as well as strain gauges. DIC measurements were performed on one skin panel of the central section. Five strain gauge rosettes were installed on both panels of the one section. In addition, one rosette was applied to one skin panel in each of two other sections. Measurements were performed on the stand for torsion as well as on the stand for bending. The results of DIC analysis and strain gauge measurement during torsion show uniform shearing strain distributions on the panels. During bending, on the tensioned side, the strains obtained indicate quite uniform strain distributions. On the compressed side, local buckling of the skin panels results in high strain gradients. Strain levels obtained with the use of a DIC analysis and strain gauge measurements were similar. Moreover, horizontal displacements of markers in the spar axis during bending was determined based on a series of photographic. The deflection line obtained in this way has a shape similar to arc, which is characteristic of the constant bending moment. The stand was tested with torsional and bending loads in order to verify the design assumptions. The results of strain distributions on the skin panels with the use of DIC and strain gauges as well as the deflection line of the spar axis indicate that the Modular Test Stand performs as assumed and can be used for tests.

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Impact of Carbon Nanotubes on the Mechanical and Electrical Properties of Silicone

75%

Sałaciński M. , Dydek K. , Leski A. , Kozera R. , Mucha M. , Karczmarz W.

Fatigue of Aircraft Structures

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2022

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tom Iss. 14

135--153

EN

This paper presents the results of a structure study of a dispersion composite on a silicone matrix with a filler in the form of multi-walled carbon nanotubes (MWCNTs). The study aims to determine the effect of the filler on the composite mechanical properties and electrical conductivity. Materials that are electrically conductive and exhibit high mechanical properties can find applications in high-strain sensors. During the study, the characteristic properties of the susceptible materials, silicone alone and silicone with different filler contents (4%, 6%, and 8% by weight), were determined after curing. Microscopic observations were performed to assess the influence of carbon fillers on the material structure and to determine the level of homogeneity of the material. Examination of mechanical properties facilitated the determination of the Shor A hardness (ShA), stiffness, and Poisson’s ratio of the cured composites, depending on the nanotubes’ content. In parallel with the study of mechanical properties, the effect of loading, and the associated deformation of the samples, on the conductivity of the composite was investigated. Based on the results obtained, a discussion was carried out on the type of conductivity characteristic of silicone with different filler content as well as depending on the level of deformation of the samples.