Fatigue strength of steel plate girder railway bridges with butt joints reinforced with one-sided rhomb-shaped cover plates

Due to the long period of service degradation, bridge structures require periodic technical inspections and assessment of the current load capacity. Since the 1970s, this assessment has been carried out according to the Fitness for Purpose criterion. From 2008, the PUK criterion has been replaced with the recommendations of the European Convention on Steel Structures (ECCS). As part of these recommendations, the authors decided to explain the previously obtained unrealistic values of the fatigue class Dsc of the bridge butt joints, covered with one-sided rhomb-shaped cover plates. The computational analysis performed with the FEM method gave excellent results which are briefly presented in the article.

Analysis of direct metal laser sintering ‒ DMLS and heat treatment influence on the Inconel 713C nickel alloy structure

The group of nickel based superalloys produced in the DMLS (Direct Metal Laser Sintering) process is limited to materials, which produced conventionally do not have properties to allow to use them for rotating components of aircraft engines. This work attempts to optimize the technological parameters of the DMLS process for the Inconel 713C nickel superalloy. A heat treatment was performed for selected samples to investigate the effect on the morphology of the Ni3Al phase. The microstructure analysis and hardness tests were carried out. The material after the DMLS process was characterized by the presence of much smaller dendrites than the cast material and exceeded its hardness. For the tested variants of heat treatment, the material was characterized by smaller sizes of the Ni3Al phase. In order to ensure the stability of the microstructure, an optimization of the dedicated heat treatment after the DMLS process is required, as the standard heat treatment for Inconel 713C cast nickel superalloy does not fully recrystallize the material.

Selected problems of design and pre-implementation studies of new types of manipulators

Conceptual development and testing of models and prototypes of manipulators, supporting the work of industrial robots, has become a specialty of the Department of Welding Engineering of the Warsaw University of Technology and ZAP Robotyka from Ostrow Wielkopolski. However, they are not typical devices, so their development requires a detailed analysis of many aspects, both functional and economic. Also the pre-implementation tests are not included in dedicated standards and must be based on previously developed experimental procedures. This article presents selected problems in the design and research of new types of manipulators, created as a result of joint research and development work.

Support with mechanical vibrations of welding processes ‒ review of own research

The article discusses the most important original achievements in the use of high-power mechanical vibrations with low and ultrasonic frequency in various welding processes such as MIG, MAG, TIG, RW, LW, diffusion welding and brazing in relation to various basic materials such as structural steel and aluminum alloys. Mechanical vibrations were introduced by means of ultrasonic vibrating systems and using the shot-blasting process, as well as acoustic influence. As part of the comparative research, the structure and hardness analysis of HV0.1 was presented. The obtained results indicate that both low-frequency and ultrasonic frequency vibrations significantly change the properties of the resulting structures affected by mechanical vibrations. The scale of these changes varies depending on the frequency and parameters specific to each of the welding processes used. The obtained results allow us to conclude that the skillful application of mechanical vibrations accompanying welding processes can contribute to the reduction of grain sizes, to change the depth or width of penetration and to lowering hardness in the sensitive heat affected zone area.

Repairability analysis of the energy gas turbine rotor blade second stage shroud by high-temperature brazing

The article considers the repair of the energy gas turbine rotor blade second stage shroud. The paper presents an analysis of the possibility of the repair consisting of the replacement of both labyrinth and honeycomb seals by the high-temperature brazing process. All the steps of the repair process were discussed and the results of microscopic metallographic evaluation using a light microscope and a scanning electron microscope were presented. Several advantages related to the use of this technology were indicated.

Determination of emission of iron oxides from the welding process on the basis of mathematical models

Oxygen in metals is most often present in the form of oxides, including: FeO, Fe2O3, Fe3O4. The complexity of the welding process means that oxygen compounds can enter both the liquid metal and the atmosphere, causing negative effects. A welder is exposed to harmful emission of oxides entering the human body through the respiratory system or pores in the skin. The essence of the problem is so serious that standards for air purity and determination of amount of oxides at workplaces have been introduced. The article presents the results of research on the influence of the welding current intensity on the emission of air pollutants (in particular the emission of iron oxides) of the inhalable and respirable fractions. The bench tests were carried out on the basis of the applicable standards for air quality at welding stations. Based on the test results, on the basis of the R program, mathematical models of the emission of iron oxides generated during the welding process were developed. It was observed that with the increase of the welding current, the average value of the emission of iron oxides – both the inhalable and respirable fractions – increases. For both fractions, it was also noted that the model values ​​are closer to the values measured in the model No. 1.

Influence of austenitic interlayer on the properties of stellite sur- facing welds after impact-hardening

Stellites (Co-Cr-W-C) are the specific group of coating materials used for surface modification of the engineering materials and for remanufacturing too. The aim of the paper was to research the influence of austenitic (308LSi) interlayer present on hardening level of stellite 1 and 6 after impact treatment. The samples have been cladded by TIG welding method with interlayer and without. Before impact hardening the samples have been visually and penetrant non-destructive tested. The samples after impact hardening have been tested by metallographic and Vickers hardness methods. The highest impact hardening effect have been revealed for coatings deposited with interlayer. The highest impact hardening effect was achieved for the padding welds produced with the interlayer, i.e. for stellite 1 (increased by 29.8%) and stellite 6 (increased by 42.7%). The hardening of the coating samples deposited without interlayer was lower and amounted to stellite 1 (increased by 13.7%) and stellite 6 (increased by 29.8%) respectively. The highest hardness values were obtained for impact-hardened cladded welds without the use of an interlayer (stellite 1; 790 HV0.1 and stellite 6; 732 HV0.1). The use of an interlayer reduces the hardness of the stellite coating while increasing the susceptibility to hardening and plastic deformation of the produced coating.

Butt welding of thin sheets of S960MC steel

The paper presents the application of MAG welding to TMCP steels (thermo-mechanically controlled processed) grade S960MC and 3 mm thick. In the analyzed joints, the research focused on their mechanical properties and changes in the heat-affected zone (HAZ) that occur in this type of steels. The hardness and tensile strength tests carried out showed a significant decrease in the properties of the joint compared to the declared values of the base material and the filler material used in the tests. In the case of hardness, it was a decrease of 34% in HAZ and by 15-21% in relation to the strength limit. Changes in HAZ properties of a joint correlate with changes in its structure.

Study of microstructure geometry and properties of laser beam welded joints made of S960QL structural steel and S304 corrosion-resistant steel

Contemporary grades of structural steels are produced using a very advanced thermo-mechanical treatment processes, so their properties strongly depend on the obtained structure. Corrosion-resistant austenitic steels have a high hot cracking tendency. Therefore, it is advantageous to use welding technologies, such as laser welding, that limit the size of the joint and its heat-affected zones and thus the deformations caused by the welding process. Laser welding is also characterized by small amount of heat transferred into the material during the process which limits the hot cracking tendency. During the tests, 8 samples made of S960QL steel and S304 steel, were prepared using a Trumpf TruDisk 3302 laser welding device. The produced samples were subjected to macro- and microscopy metallographic tests. Static tensile test and bend test were also performed as well as a hardness Vickers test under a load of 100N. Good quality joints were obtained, characterized by a small number of welding imperfections, small size of the weld and heat affected zone, as well as satisfactory mechanical properties.

Sliding of spherical ball on solid lubricating coating combined with wear process

In present paper we show results of ball-on-disk wear experiment of MoS2 film deposited on Ti6Al4V substrate. The ball materials is aluminum oxide. The tests are performed for different surrounding temperature conditions: 20 oC, 200 oC and 350 oC. It is shown that depth of the wear groove increases with increasing surrounding temperature. A finite element modeling approach is next developed to mimic the experimental observations of ball-on-disk wear process. It is based on the assumption of steady state condition developed during short time scale at contact region. The steady state results can next be applied to long time scale in which wear process is numerically simulated. Model results are compared with experimentally obtained wear groove and show satisfactory agreement.