Michał Sałaciński

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

Abstract 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.

Damage Detection and Size Quantification of FML with the Use of NDE

Abstract Composite materials have been developed in recent years. A new generation of structural composite materials for advanced aircraft is Fibre Metal Laminates (FML). They are hybrid composites consisting of alternating thin layers of metal sheets and fiber-reinforced composite material. FMLs have both low weight and good mechanical properties (high damage tolerance: fatigue and impact characteristics, corrosion and fire resistance). Quality control of materials and structures in aircraft is an important issue, also for Fibre Metal Laminates. For FML parts, a 100% non-destructive inspection for internal quality during the manufacturing process is required. In the case of FML composites, the most relevant defects that should be detected by non-destructive testing are porosity and delaminations. In this paper, a number of different non-destructive methods for the inspection of Fibre Metal Laminates were studied. The possibility of quality control of manufactured FML laminates - detection of defects as well as the procedures and processes are presented and discussed

Diagnostics of Composite Aircraft Structures Using Non-Destructive Tests with Thermographic, Ultrasound and Acoustic Methods

Diagnostics of Composite Aircraft Structures Using Non-Destructive Tests with Thermographic, Ultrasound and Acoustic Methods

Use of a composite repair patches to repair the upper air intake flap for the MiG-29 aircraft engine

Abstract The Composite Patch Bonded Repair (CPBR) is one of the most cost-efficient types of aircraft structure repair. In the CPBR, the damaged structure is reinforced by applying a composite patch. The boron-epoxy composite (BFRP) is a popular choice for these types of repair. The BFRP was utilized to repair the cracked resistance welding joints in the upper flap of the MiG-29’s RD-33 engine intake. In the present paper, the numerical results are shown, along with the comparative tests of the undamaged inlet flap, the damaged inlet flap and of the CPBR repaired inlet flap.

Influence of Metal Foil on Interface Stress State in CFRP Laminate

Various materials of high specific stiffness and strength are used in aircraft structures, therefore, methods of joining them are continually improved. Adhesive joining is the most popular method used in composite structures, however, mechanical joining is often necessary due to constructional reasons. Stress concentration around the hole (notch) and point load (fastener action) transfer into the structure are the main disadvantages of mechanical joints, especially, in composite structures. The bearing failure is the only global progressive mechanism of mechanically fastened laminates and therefore it is the acceptable one. Different attempts to improve bearing performance of laminates have been considered by many authors. One of the most interesting solutions is bonding the titanium foils (thin inserts) into the composite structure. The aim of the paper is analysis of a metal insert influence on the stress state around the hole. Specimens made of carbon fibre reinforced plastic and locally modified laminate (part of prepreg layer around the hole is replaced with a circular titanium foil) have been taken into account. The specimens were manufactured in a co-curing process using autoclave technology. Nonlinear analyses were carried out with Marc code. In a locally modified laminate, the main mechanism of load transfer is interlaminar shear stress. The area of load transfer is augmented by the area of metal-fibre adhesive joining. A significant part of the applied load is carried by titanium foils, then it is gradually transferred by means of shear stresses due to adhesion between titanium foils and laminate layers. Bearing performance depends on the insert material stiffness and its elasto-plastic behaviour. Bearing stiffness reduction is strongly influenced by parameters of the titanium-laminate adhesive interface.

Approach to Critical Crack Opening Displacement Modeling of Damage in Metal Sheets after Composite Patch Bonded Repair

Abstract The paper proposes a method of calculating the maximum displacement in the aircraft metal structure repaired by CPBR (bonded composite patch repair). The calculations were made based on specimens. The specimens were prepared according to the current requirements used in aviation. The 2024-T3 alloy metal sheet was a structure. To repair the structure used the boron-epoxy composite patch in prepreg technology was used. The metal structure was modeled as an isotropic elastic body. The metal structure coated with the composite patch was modeled as an orthotropic structure. Based on this, the stress was determined in the metal structure. The size opening displacement in the metal structure was determined based on the model of linear elastic fracture mechanics for the plane stress state. The calculation results were verified by measuring the displacement in laboratory conditions. The laboratory tests made it possible to demonstrate the accuracy of the proposed approach.

Composite Diagnostics with Use of Embedded PZT Transducers—A Smart Structure Example

Application of guided waves excited by a network of PZT transducers integrated with a given structure is one of the promising approaches to Structural Health Monitoring (SHM). The performance of a SHM system based on PZT network is rooted in two distinct areas of the technology development, that is: the hardware and the signal analysis. The first includes is the type of transducers used to built a network and the way of their integration with a monitored structure. For composites, beside the possibility of the transducers attachment to a surface of an element, also immersing of PZTs into their internal structure is available. In the article Barely Visible Impact Damage (BVID) detection capabilities of the embedded and surface attached PZT transducers are compared in broad frequency range of the excitation. The damage detection capabilities are compared in the range 100 – 350 kHz. In addition to purely qualitative detection of damages a new algorithm of their localization is proposed and compared between the embedded and surface attached transducers for the frequency optimal to detect BVIDs. This algorithm is a modified version of the RAPID imaging method, but suitable to be used also in the case of non-homogeneous sensor networks. Finally the performance of a system is verified with use of a composite panel having PZT transducers embedded into its internal structure. The network geometry was tailored to fulfill specific demands regarding the structural performance. doi: 10.12783/SHM2015/72

Conception of New Air Target SZERSZEŃ-2

Abstract The project to introduce modifications to the air target SZERSZEŃ has been undertaken by the Air Force Institute of Technology. SZERSZEŃ has been used by the Polish Army for 10 years, during which time a number of modifications were introduced. Given this fact, it was decided to develop a new version of this UAV based on the experience gained during its maintenance and operation. Another aspect of this project is to focus on improving the repeatability of production by optimizing the technology processes. To achieve this aim the new instrumentation for the production of composite parts in prepreg technology was designed. The paper reviews the production possibilities for this aircraft using a new technology and presents the advantages of the modified construction and the new technology.

Composite Aerospace Structure Monitoring with use of Integrated Sensors.

Abstract One major challenge confronting the aerospace industry today is to develop a reliable and universal Structural Health Monitoring (SHM) system allowing for direct aircraft inspections and maintenance costs reduction. SHM based on guided Lamb waves is an approach capable of addressing this issue and satisfying all the associated requirements. This paper presents an approach to monitoring damage growth in composite aerospace structures and early damage detection. The main component of the system is a piezoelectric transducers (PZT) network integrated with composites. This work describes sensors’ integration with the structure. In particular, some issues concerning the mathematical algorithms giving information about damage from the impact damage presence and its growth are discussed.

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

Abstract 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.