Solid State Phenomena Vol. 240

Abstract: This paper reports results of fatigue testing performed under fully reversible, load controlled uniaxial tension-compression. For this scheme of loading definition of relative damage indicator and cumulative damage indicator parameter was given and changes of such parameters during the life of the material were shown for two grades of steel. Simple damage criterion proposed by Johnson [6] was modified to define damage indicator parameter. Definitions of damage parameters based on proposed damage indicator and damage indicator parameter were also given. Damage curves showing changes of damage parameter as the function of the life fraction were shown to illustrate progress of damage during the life of the material.

Abstract: Development and application of composite materials in modern industry are very dynamic. Composite materials seem to be replacing steel and aluminium ones. Composites are a cheaper solution, with similar mechanical strengths. Generally, there are two types of joints in composite structures: mechanical and adhesively bonded ones. The aim of the study was to determine the feasibility of riveted joints in composites materials. Static tensile test method was used. In the test there was used one type of glass fabric (Interglas 92140) from which two types of composite samples were prepared. In each sample there was used the same type of fiber with the same fiber orientation – 3 layers. Samples had dimensions of 220x100 mm and thickness of approximately 1.5 mm. They were connected to each other with aluminium rivet nuts (from 1 to 3) and placed in a metal frame with a screw connection which was made of screws with nominal thread pitch M5. Screws were tightened with constant torque. It was to provide an axial force to the sample during the tensile test. The frame was placed between cross-bars of tensile machine INSTRON 8516. The samples were stretched at a speed of 0.05 mm/s at a distance up to 20 mm. During the tensile test displacement of the samples and pull force were registered. Depending on the fiber orientations and number of rivet nuts composite damage models were described. On the basis of the results the possibility of usage of aluminium rivet nuts connections in composite materials was determined.

Abstract: Effects of low-velocity-low-energy impacts on interlaminar damage extent in Glass/Epoxy laminate panels of [0°/90°]₁₀, [0°₁₀/90°₁₀], [0°₅/90°₅]₂, [0°₅/-45°₅/90°₅/+45°₅] layups were experimentally investigated. The tests were carried out at room temperature with the help of INSTRON CEAST9350 impact system. The initial impact energy was 18J, impactor mass equaled 4kg and the corresponding contact speed was 3 m/s. During the impacts panels were simply supported with a circular steel rings of inner diameters d=80mm. It was found that the amounts of dissipated energy substantially varied depending on the reinforcement sequence and that the lowest amount of energy was dissipated by the laminate panel of [0°/90°]₁₀ reinforcement stacking sequence while the highest one by the panel of [0°₁₀/90°₁₀] reinforcement stacking sequence. Such results suggested that clustering reinforcement layers of the same reinforcement orientation produced negative effects with the regard to the resistance of laminates against impact induced damage.

Abstract: Experimental research on mechanical properties of hardened polyethylene HDPE, is developed in the paper. The conditions of hydraulic impact simulation, caused by sudden opening or closing of the valve or by working pomp were adopted in the model. The created in such conditions shock wave moves at a high speed causing additional dangerous dynamic loadings, which lead to faster pipe wear process. The aim of this study is to determine Young's modulus of the pipe material in the cyclic load conditions. The assumed amplitude and frequency of the applied load relates to variation of the impact wave pressure also the speed of the disturbances propagation are taken from experimental measurement of the real water hammer. The measured Young's modulus is higher than that obtained from a static tensile test. The presented study arises from the need to verify the actual value of pipe material mechanical properties, i.e. longitudinal stiffness, for designing of hydraulic pipes under conditions of water hammer.

Abstract: The paper presents the results of investigation on seven glued laminated timber (GL24h class) bending beams. Bending strength and modulus of elasticity were determined. The beams were tested for four-point bending by loading them at a constant speed deflection. The strain gauge method and photoelastic coating technique were applied for strain distributions determination in selected cross-sections of the beams. Good agreement of the measurement results was obtained with both techniques. Application of the photoelastic coating technique enabled more detailed analysis of the beams failure mode, including timber defects influence on the strain distributions.

Abstract: Adhesive bonding is increasingly being applied as structural joining technique in highly reliable machines and appliances operating in the circumstances of variable thermomechanical loads.The manufactured specimens of the Epidian 57/Z-1 epoxy material had been subjected to cyclic thermal loading, with respect to a defined program, in a thermal shock chamber within a temperature range of ‑40°C to +60°C for 200 cycles. The accepted temperature range was typical for machinery maintenance, including the aircraft.The aim of the research was first of all determination of thermal load (fatigue), as well as the presence of notch effect on the resistance to fracture.A significant measure of the adhesive bonds quality is the repeatability of the strength examination results, both in the summary and long lasting tests. It is often more important criterion for the adhesive joint selection than higher strength of the joints using the particular adhesive.The obtained results of the conducted research have been elaborated statistically with respect to the appropriate scientific standards.

Abstract: Polymerization shrinkage of composite filling materials still becomes one of the most important features which decreases strength properties of reconstructed teeth crowns. From among various methods to reduce that disadvantageous phenomenon which are used in a dental practice sandwich filling processing of crown cavity seems to be the most effective one. The paper presents the results of the strength examination of the influence of the different ways of layered polymerization processing on the mechanical properties of modern hybrid micro composite material with regards to the following quantities: compressive strength, strain to fracture, modulus of elasticity and work to fracture.

Abstract: The paper presents the initial results of application of the high sensitivity grating interferometry (GI) method in order to measure the displacement and strain fields in copper and titanium coatings thermally sprayed onto alumina ceramic (Al₂O₃). The residual stresses had been relieved by iterative cutting method, which was applied twice. The displacement maps of u and v were measured after each cut and ε_xx and ε_yy maps were calculated. The results clearly show the presence of ε_xx strains relieved along the second cut. The comparison of both samples confirmed that residual strains in Ti/Al₂O₃ are more significant than in Cu/Al₂O₃ system. The result after relevant postprocessing had been supplemented with the sub-surface principal residual stresses measured in the selected point by the x-ray diffraction method and curvature measurements.

Abstract: This paper presents the results of experimental investigation of thin-walled GFRP laminate columns with square cross-section subjected to uniform compression. Column under consideration are made of eight ply laminate with different quasi-isotropic layer arrangement. The following three cases of layers arrangement are taken into consideration: CS1 [45/-45/45/-45]_S, CS2 [45/-45/0/0]_S and CS3 [45/-45/45/0]_S. The analysed columns have the length of 250 mm and following cross-section dimensions (width × height × thickness of the wall): 82 × 82 × 2.08 mm.The main aim of experimental investigation has been to compare the way of buckling load and postbuckling behaviour determinations. The layer arrangement influence on buckling load and postbuckling stiffness have been also checked. Two different methods (P-w² method and "inflection point" method) of determining buckling force P_cr and two different measurement technique (i.e. strain-gauges technique and stereographic transformations technique) have been employed.

Abstract: The work concerns the research of a propulsion system for an unmanned aerial vehicle MOSUPS in joined wing configuration. Modeling, analysis and experimental research of a statically unbalanced rotor of a ducted fan propulsion system has been conducted.The aim of the analysis was to determine the critical rotational speeds of the rotor due to the probable excitation of oscillations. Due to the complex geometry, Finite Element Method has been used for the calculations. In the study, the critical frequencies (and also rotational speeds) of the rotor as well as precessional instability, flexibly mounted in the bearings have been calculated. Campbell and SAFE diagrams have been presented.Furthermore, the paper presents the idea for a device for automatic dynamic balancing of the mentioned rotor. A mechanism for changing the position of the correction weights has been developed, allowing for a long term operation of rotating parts without the need to stop the unit and correcting the unbalance.The main motivation for work was to fully understand the working conditions of the propulsion system and dynamic properties of the rotor in order to carry out a proper assessment of their impact on the safe operation of the aircraft.