Papers by Author: Tomasz Sadowski

Abstract: A description of processes of formation and propagation of cracks in material requires the knowledge of all fracture mechanics parameters, i.e.: K_Ic, K_IIc and K_IIIc. In this study a new testing method and estimation of the fracture toughness in Mode III (antiplane shear) of concretes containing: 0, 20 and 30% volume content of the class F fly ash (FA) was proposed. Fracture toughness tests were performed on axial torsion machine MTS 809 Axial/Torsional Test System. The studies examined effect of FA additive on the parameter K_IIIc. In order to determine the fracture toughness K_IIIc a special device was made. Experimental investigation under third mode fracture was carried out both in young and mature concrete composites (after: 3, 7, 28, 90, 180 and 365 days). 20% addition of FA as well as a 30% addition of FA causes a reduction in fracture toughness of young concrete. After 28 days of couring a significant increase of the K_IIIc was noticed in composites with a 20% additive of FA while concrete mixtures with a higher additive of FA still had lower analyzed fracture mechanics parameter.

Abstract: This paper presents the results of Mode I fracture toughness tests of concrete with fly ash (FA) loaded in Mode I. Concrete composites with the addition of 0%, 20% and 30% siliceous FA were analysed. Fracture toughness tests were performed on a MTS 810 testing machine. The studies examined the effect of FA additive on the quasi-static fracture toughness K_Ic^S. The analysis of the results revealed that a 20% FA additive causes an increase of K_Ic^S value, while a 30% FA additive causes a decrease on fracture toughness. Additionally, the results demonstrate the possibilities of practical application of ARAMIS system for analysing the development of defects in the micro-structure of concretes containing FA additives. This system can be useful for macroscopic estimation of crack propagation.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: Indentation in brittle solids involves many complex phenomena related to cleavage and contact, as well as intrinsic stress singularities, which are almost impossible to capture with traditional continuum approach and FEA at mesoscale. In case of a two-phase ceramic composite [1–3] the number of unknown material and interfacial constants, that have to be calibrated experimentally, increases rapidly [4, 5]. In this paper, nanoindentation in zirconia-toughened alumina (ZTA) is modelled using discrete (peridynamical) approach

Abstract: In the jet engine the temperature of exhaust gases should be as high as possible, from the point of view of its efficiency. The value of this temperature is limited by toughness of the turbine blades material. Superalloy Inconel 625, which is commonly used in aerospace industry, indicates 13% less yield point in 800^OC than in 25^OC. The temperature of exhaust gases can reach 1500^OC. The blade material has to be protected due to this fact. The one possibility of turbine blade protection is using of thermal barriers coatings (TBC). The coating has a very low thermal conductivity and therefore it protects against the thermal shock failure of the substrate material. The TBC can be manufactured as: 1) monocrystalline, 2) layered structures (e.g. [1-3]) or 3) as a functionally graded material (e.g. [4-7]). The differences between the properties of blade material and TBC can lead to significant increase of the high shear stresses in the substrate-TBC interface.In this paper numerical analyses of cooled turbine blade with various kinds of functionally graded thermal coatings were performed. The main aim was to find the optimal material properties distribution of the functionally graded TBC to avoid damage initiation and growth between TBC and substrate. In the calculations the effect of temperature on material properties both mechanical and thermal was taken into consideration.

Abstract: Cellular materials represent a new class of materials; main parameters that characterize the cellular structure are relative density, shape of the cell (open or closed), wall thickness and cell diameter. The purpose of this paper is to investigate the microstructure of foams materials and also to determine the flexural properties of this rigid PUR foams using Digital Image Correlation (DIC). The rigid PUR foams cells morphology and pore distribution for three densities (100, 145 and 300 kg/m³) were studied before testing through scanning electron microscopy. Determination of flexural properties was carried out on rectangular beam samples using ARAMIS 2D system. This method provides a substantial increase in accuracy for measuring strain and is based on the calculation of surface deformation using a set of digital images from undeformed stage to different deformed stages. The specimens were subjected to static three points bending tests with loading rate of 2 mm/min, at room temperature and loading was applied in rise direction of the foam. Experimental results show that main mechanical properties such as flexural modulus and flexural strength values increases with increasing of density.

Abstract: 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.

Abstract: A numerical procedure of assessment of Thermal Stress Intensity Factors (TSIFs) of an edge crack in a strip made of Functionally Graded Material (FGM) subjected to thermal cooling process was elaborated. In order to perform it own subroutines in ABAQUS code were created. The analyzed ZrO₂+Ti₆AlV material in the form of the FGM is applied as cylinder liners (Thermal Barrier Coatings TBC) of aircrafts engines and is subjected to extremely quick temperature changes during the engine work. Therefore estimation of the TSIF to determine fracture process in the ZrO₂+Ti₆AlV material is important for designing of the structural element thermal protection and further safety of aircrafts passengers.