Przemysław Golewski

Spot Welding–Adhesive Joints: Modelling and Testing

Modelling and testing of hybrid joints obtained by combination of two simple techniques, i.e., by application of spot welding and adhesive, is reported. The joints were subjected to uniaxial tension. The experiments were performed for: 1) a pure joining of the parts by spot welding and 2) spot welding–adhesive joining of the structural elements. A new experimental method was elaborated with application of two digital image correlation (DIC) systems. The method allowed for online monitoring of the deformation process of the joined elements with complex shapes. Modelling of the hybrid joints response to mechanical loading was performed by ABAQUS code. Damage process in the adhesive layer was taken into account. The obtained results lead to the conclusion that the strengthening of joints by the application of adhesive significantly improves static strength and energy absorption. The visible degradation process of the adhesive layer which started prior to the maximum value of force carrying the hybrid joint was obtained.

Loadings in Thermal Barrier Coatings of Jet Engine Turbine Blades

This book discusses complex loadings of turbine blades and protective layer Thermal Barrier Coating (TBC), under real working airplane jet conditions. They obey both multi-axial mechanical loading and sudden temperature variation during starting and landing of the airplanes. In particular, two types of blades are analyzed: stationary and rotating, which are widely applied in turbine engines produced by airplane factories

The Analysis of Heat Transfer and Thermal Stresses in Thermal Barrier Coatings under Exploitation

Effectiveness of internal combustion turbines in aero-engines is limited by comparatively low temperature of exhaust gas at the entry to turbine of the engine. A thermal efficiency and other capacities of turbine strongly depend on the ratio of the highest to the lowest temperature of a working medium. Continuous endeavour to increase the thermal resistance of engine elements requires, apart from laboratory investigations, also numerical studies in 3D of different aero-engine parts. In the present work, the effectiveness of the protection of turbine blades by thermal barrier coating and internal cooling under thermal shock cooling was analysed numerically using the ABAQUS code. The phenomenon of heating the blade from temperature of combustion gases was studied. This investigation was preceded by the CFD analysis in the ANSYS Fluent program which allows for calculation of the temperature of combustion gases. The analysis was conducted for different levels of the shock temperature, different thickness of applied TBC, produced from different kinds of materials.

Protective Thermal Barrier Coatings

The goal of using TBCs is, e.g. to reduce thermal conductivity between exhaust gases and the blade material, anti-corrosion protection and increased wear resistance.

Cracks path growth in turbine blades with TBC under thermo – mechanical cyclic loadings

Blades of combustion turbines are extremely loaded turbojet elements, which transmit operative energy onto a rotor. Experiences of many years indicate, that cracks initiation and propagation in the blades during the operation time can cause destruction not only of the engine, but sometimes an airplane. In high temperature one of the most often occuring interactions in the turbine engine are time variable force fields, caused by non-stationary flowing of an exhaust gas and aerodynamical interaction of the engine elements. The extremal thermo-mechanical loadings initiate gradual degradation process of the blades as a result of fatigue and material creep. More often Thermal Barrier Coatings (TBCs) are applied on the turbine blade surface to provide protection not only against the high temperature but also against aggressive environment. The paper presents the advantages of applying of the TBC layers for increase of the cracks resistance to gradual degradation of the turbine blades. The level of save values of thermo-mechanical loading was estimated. Analysis of critical values of loading leading to crack initiation, further growth and the final blade fragmentation was performed. The most efforted places of the turbine blades were selected and crack paths due to thermo-mechanical cyclic loading were determined.

Effect of Tolerance in the Fitting of Rivets in the Holes of Double Lap Joints Subjected to Uniaxial Tension

The study focused mainly on one of the parameters of mount technology - tolerance for fitting the rivet in the hole in riveted and hybrid (riveted adhesive) joints. The research included numerical simulations of double lap joints with four rivets arranged in two rows and subjected to uniaxial tension. Simulations were carried out in Abaqus both for the purely mechanical and the hybrid joints. The connections without clearance (neat-fit) and with clearance of 0.2 mm, as well as with interference of-0.2 mm. The presence of clearance in one of the holes in the hybrid joint causes a decrease in the capacity of the hybrid connection by about 15% in configuration 1 (Fig. 2). This decrease can be even higher (21%) in the worse clearance placement, i.e. in configuration 2 (Fig. 2). The study shows that the occurrence of clearance in the holes can lead to dangerous consequences, so it is recommended to use holes calibration or develop a special type of rivet.

Experimental and Numerical Investigations of TBC Behaviour after Aging, Subjected to Tension and Bending

Thermal Barrier Coatings (TBCs) have been extensively used in aircraft engines to improve durability and performance. They protect critical engine parts such as blades and combustion chambers, which are exposed to high temperatures and corrosive environment.Testing of coated metallic alloys, subjected to ageing process, allows determination of the TBCs properties. In this paper we performed 2 tests: uniaxial tension and bending. The aging of samples was carried out in 1000°C for times: 48h, 89h, 185h and 353h. Thermally Grown Oxide (TGO) layer thickness (SEM observations) and the strain level corresponding to damage of the TBCs were determined experimentally.The experimental results were used to build numerical model in Abaqus program. Brittle cracking damage model was applied to describe of the TBC layer degradation. Surface based cohesive behavior was used to model delamination of the interface between a bond coat (BC) and a top coat (TC).The proposed numerical model describes with high accuracy experimental results.

Numerical and Experimental Analysis of Foreign Objects Impact into the Surface with TBC Coating

While the plane is maneuvering before start or landing, some solid particles (e.g. sand, dust, soil) can be sucked into an engine with the air. Their vast majority is stopped on the compressor blades, but the smaller ones are able to get into a hot part of the engine and cause erosion. Erosion is widely recognized as the second mechanism, after corrosion that reduces the TBC coating thickness. In many cases, erosion can completely remove it. Furthermore, TBC coatings are more susceptible to erosion due to their porous structure than full dense ceramic materials. In order to investigate the phenomenon of particles impact with diameter of 4mm, the pneumatic driven laboratory work station was built. The work station has an adjustable pressure, so that the foreign object may possess different kinetic energies. The pressure can be read on a digital pressure gauge and the shot release is done electrically. In addition, the work station has a universal cross table that provides precise positioning of the sample so as to be able to perform a dozen or so impacts in predetermined distance intervals. However, the most important component is the velocity measurement system which is used to determine the impact energy. The paper presents the results of 11 impacts made with different energies. The effect of complete destruction of the ceramic layer as well as indents without visible damage was achieved. Numerical simulations allowed to define the zones of stress influence of the individual indents. The brittle cracking model in Abaqus allowed the virtual representation of damage due to impact load.

The Deformation Process of Thin-Walled Box Beams Joined by Rivets under Three-Point Bending

This paper is focused on description of the mechanical response of the aluminum box-beams subjected to 3 point bending (3-PB). The main aim of this paper is to determine the effect of spacing between rivets on the equivalent stiffness and strength of the analised profile. The considered beams are composed of two sections: one of them is an aluminum omega profile and another is a composite flat sheet. Experimental tests were carried out for various spacing between rivets. Moreover, the corresponding numerical analyses by Finite Element Analysis (FEA) with application of the Abaqus software were done for estimate of the mechanical response of the box beams. The results show relationship between spacing of the rivets and values of carrying forces.

The Influence of Hybrid Material Parameters in Socked-pin Connection on the Value of Opening Force

Different types of techniques are used in joining of aircraft structures. The classical solutions are mechanical or bonding joining. A prospective alternative to the currently used connections (e.g. mechanical, adhesive and hybrid ones) is a socket - pin connection type. Generally, they are purely mechanical joints. Depending on the shape, they have different commercial names such as: Interlock, Snaplock, Snapfit Gridlock. The idea of these connections relies on the fact, that between the socket and the pin we need a suitable interference fit or specially formed clip to carry the load. The advantages of this type of connection of different structural parts is very fast assembly after pressing joined parts together. The use of socket - pin connection eliminates the presence of the human error and reduces production costs as an individual connection is made by CNC machine tools.The paper presents an analysis of the influence of a several technological problems concerning the socket and the pin manufacturing, on the value of force required for the joint connection and disconnection. A number of numerical simulations was made in ABAQUS program to examine the effect of such parameters as: the presence of interference fit, the use of spherical latches, the use of different rigidity in the shaft by making cuts with variable width and length, the use of different angles of inclination of the working part of the slot.