FDM technology is among the most widely used additive manufacturing technologies. The most popular materials are ABS and PLA, but lately nylon has been used more often. The aim of the paper is to ...determine the impact of infill pattern and continuous fiberglass reinforcement on the tensile properties of additively manufactured composite material. The samples were made of Onyx as matrix material on a Markforged Onyx Pro printer, with and without varying fiberglass volume fraction. In addition, five different infill patterns (solid, triangular, rectangular, hexagonal and gyroid) were investigated. The experimental results revealed that infill patterns have different effects on the tensile strength and elastic behavior of the material, but the consumption of material and time should also be considered. The use of continuous fiberglass reinforcement significantly improves the tensile characteristics of the material. Proper arrangement of fibers in multiple layers can give better tensile properties of the material.
Loads at vital steel structures occur during their production and assembly (residual stresses), during the execution of functional tasks in exploitation (stationary and dynamic loads) and during the ...disturbed process of exploitation (non-stationary dynamic loads). Considering the fact that stress concentrators, corrosion and unpredictable effects that occur during exploitation must be taken into account as well, it is clear that loading of vital structures during the design phase can not be represented with a model in which the parameters change uniformly. Therefore only experimental non-destructive tests performed at large steel structures during exploitation enable the assessment of their current condition, need for particular repairs and assessment of integrity. In that way the data necessary for determination of causes of degradation of material and welded joints at structures, for the evaluation of mutual influence of equipment parts, as well as for determination of functionality and reliability of operation of drive systems. This primarily refers to vital steel structures of bucket-wheel excavators, dredgers and cranes, as well as to vital steel structures at hydroelectric equipment, thermal power plant equipment, bridges etc. This paper presents the analysis of causes for the occurrence of damages at the support structure of the boom of the bucket-wheel excavator, which is operating at the open pit coal mine near Kostolac (Serbia), that was executed on the basis of non-destructive tests. The paper also contains the procedure for the repair of damaged structure through the application of adequate welding, performed at existing and newly produced components, and the assessment of structural integrity after the repair based on non-compliances detected during the design process, as well as during the making of the support structure of the bucket-wheel excavator boom due to inadequate radiuses defined during the processes of design and production and due to the existence of flaws on the surface and within welded joints.
Knowing the material properties is of a crucial importance when planning to manufacture some structure. That is true for the steel structures, as well. Thus, for the proper planning of a certain ...steel part or a structure production, one must be aware of the properties of the material, to be able to make a qualified decision, which material should be used. Considering that the manufacturing of steel products is constantly growing in various branches of industry and engineering, the problem of predicting the material properties, needed to satisfy the requirements for the certain part efficient and reliable functioning, becomes an imperative in the design process. A method of predicting four material properties of the two stainless steels, by use of the artificial neural network (ANN) is presented in this article. Those properties were predicted based on the particular steels’ known chemical compositions and the corresponding material properties available in the Cambridge Educational System EDU PACK 2010 software, using neural network module of MathWorks Matlab. The method was verified by comparing the values of the material properties predicted by this method to known values of properties for the two stainless steels, X5CrNi18-10 (AISI 304), X5CrNiMo17-12-2 (AISI 316). The difference between the two sets of values was below 5% and, in some cases, even negligible.
In this paper are presented results of tests and analyses of complex dynamic loads carried out on the bucket-wheel excavator SchRs 650/5 × 24 Krupp, as well as assessment of service life of vital ...welded structures of a bucket-wheel excavator boom subjected to cyclic loading with a variable amplitude through the use of experimental tests carried out in order to determine operational strength and growth of a fatigue crack for one structural part. Bucket-wheel excavator was built by “Thyssen Krupp” company, Germany. Outer loads, or in other words digging forces for the overburden and coal have been calculated on the basis of measured values of actual current intensity of the bucket-wheel drive and recorded output values of changeable loads. Correlations between the power of the bucket-wheel drive system and adequate hourly production, depending on the overall digging resistance which affects the stress condition of the bucket-wheel, were also determined. Results of the theoretical and experimental analysis of natural and forced oscillations of the support structure for various exploitation conditions are presented in first part of the paper. Deformations εi determined by tensometric measurements on the rotating shaft of the bucket-wheel were converted into tangential stresses through the introduction of the modulus of elasticity and Poisson's ratio, which, along with the polar moment of inertia of the cross-section, define the moment of rotation on the bucket-wheel shaft. Through the use of the load - strength comparison method (maximization of the ratio of load and strength indicators) the application factor of the gear with the largest number of turns KA has been determined.
In the second part of the paper methodological approach for the assessment of service life of vital welded structures of a bucket-wheel excavator boom was presented. Assessment was done in order to determine operational strength and growth of a fatigue crack, through the use of experimental tests. Realized researches and results presented in this paper offer great possibilities for the analyses of behaviour of vital welded structures of the bucket-wheel boom. By the application of the measurement device with 8 channels for registration and processing of electric signals HBM Spider 8 and measurement tapes HBM 6/350 × XY31 deformations were measured at vital welded structures of the boom in the area of the bucket-wheel. The objective of the test is to determine if there is a possibility of occurrence of plastic deformations or initial cracks due to fatigue at vital welded structures and to obtain data which define crack growth.
•Specific digging resistances per knife at highest loads are 20% higher than the average value for overall measurements.•Hourly production N(Qe) show that the bucket-wheel excavator during operation cannot reach the designed capacity of Qt=4212 m3/h.•Determined application factor KA=1.6 is smaller than the one prescribed in standards for the gearbox of the excavator drive (KA=1.75-2.0).•In exploitation there is a possibility of the occurence of resonance due to their matching, and therefore of the occurence of damaging of critical cross-sections.•Fracture mechanics parameters have shown that the service life of the welded structure if a new edge crack occuris 4.55 years.
Due to difficult pandemic situation with COVID-19 decease, as well as due to current geopolitical circumstances in the world, we are facing the shortage of steel and therefore the impossibility of ...delivering the contracted products within the agreed deadlines. It is thus necessary to find suitable steel for replacement. The procedure for selecting one such steel for substituting the deficit steel 25CrMo4, for the purposes of producing a responsible welded assembly, is described in this paper. After the careful analysis, the steel 42CrMo4 was taken into consideration as a possible substitute material. Prior to applying the new selected steel, it was necessary to perform the following tests: analyze its chemical composition, determine its most important mechanical properties and evaluate its weldability. Then, the optimal welding and heat treatment technologies were determined, so that the quality of the responsible welded structure would meet all the requirements, as the structure made of originally used steel. For the new steel, all the mentioned and some additional tests were conducted and the appropriate welding technology was prescribed. To verify the selected technology, appropriate tests were conducted on the model welded samples, the results of which are presented in this paper. Based on the analysis of the obtained results, it was concluded that the 25CrMo4 steel can be replaced by the 42CrMo4 steel, however, with the mandatory application of appropriate supplementary measures.
During the process of regeneration of machine parts, certain phenomena occur that have a significant impact on the loss of their working ability. Hereditary properties are expressed by the ...interdependence of geometric and physical-mechanical-metallurgical parameters of gear teeth created during the technological operations of regeneration of worn teeth by hard-facing. The influence of the type of additional material (electrodes and their combinations) on the tribological characteristics of welded gear teeth was considered, whereby the so-called hard additional materials were applied. Those are the additional materials that give the required surface hardness of the teeth without subsequent thermal or thermochemical treatment. This research did not involve the regeneration of specific worn gears removed from machine systems, but the new gears were made, which were then damaged and then regenerated by hard-facing using the shielded metal arc welding (SMAW) procedure. Thus, all the tested gears were made of the same material, belonged to one batch and were machined on the same machines with the same machining regimes. The tests were performed on samples made of 20MnCr5 steel for cementation, on a tribometer by the “block on disc” method, which was designed to simulate the operating conditions of coupled teeth of concrete gears in the exploitation conditions. Based on the conducted tribological tests, the average coefficients of friction and topography of the surfaces were determined by measuring the wear trace and it was defined which additional materials give the best tribological characteristics of the surfaces of gears regenerated by hard-facing.
The aim of this paper is to show wear properties of different types of filler metals aimed for hard facing and exploitation in dry condition. Testing of wear resistance is done in laboratory on ...prepared samples/models in order to simulate real exploitation conditions. Samples were made by hard facing of carbon steel using 4 different filler metals. Hard facing was done by using MMA welding method in three layers with enough height so samples could be made. After samples were made, the hardness and microstructure of all zones of hard facing were determined. Testing of wear resistance is done using block on disc contact on samples made from pure weld metal. As a parameter for estimates of the wear resistance of models it was used volume of worn material in mm3. Metallographic investigations and hardness measurements were used as additional parameter for drawing the conclusions.
This paper presents an analysis and the test results of certain physical properties of the rock materials excavated from quarries in Serbia. The four rock aggregates, considered in this analysis, are ...used for building the driveway constructions' layers on roads, streets, airports and base layers on railways. To that purpose, both the general and specific technical properties (petrographic, physical, mechanical and technological) of those rocks must be known to users. The four rocks, whose physical properties are analyzed, are the most important types of the building stones: limestone, dolomite marble, calcite-dolomite marble and andesite. Their physical properties tested included volumetric mass, specific mass (density), porosity and water absorption. The service life, reparation jobs and maintenance procedures of the construction machinery parts, which come into direct contact with building materials like rocks and stones, strongly depend on those stones' properties. The four tested rock materials belong into a group of the massive rocks with various porosities and tendency to absorb water.
The procedure for experimental determination of the longitudinal and lateral residual stresses in the multi-layer hard-faced plates, made of the hot work tool steel used for forging dies ...manufacturing, is presented in this paper. The objective of this research was to establish the influence of the multi-layer hard-facing on residual stresses in the thin and thick plates, which could later, in exploitation, cause the appearance of cracks and fracture. The influence of tempering on decreasing the residual stresses was monitored, as well. The plates were hard-faced in three layers, while the stresses were measured by the magnetic method. The obtained results have shown, among others, that the residual stresses are higher in the thick plates, as well as that the proper regime of the heat treatment can significantly reduce the level of residual stresses.
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