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G. Junak, M. Cieśla and J. Tomczak

Abstract

This paper addresses numerical analyses of the bending process for tubes made of the X70 steel used in gas distribution pipe-lines. The calculations performed under the research involved simulation of processes of tube bending with local induction heating. The purpose of these calculations was to establish process parameters making it possible to develop pipe bends of geometric features conforming with requirements of the applicable standards. While performing the calculations, an analysis was conducted to determine the probability of occurrence of folding and fractures according to the Cockcroft-Latham criterion.

Open access

M. Cieśla, G. Junak and A. Marek

The paper addresses results of fatigue testing of light metal alloys used in the automotive as well as aerospace and aviation industries, among others. The material subject to testing comprised hot-worked rods made of the AZ31 alloy, the Ti-6Al-4V two-phase titanium alloy and the 2017A (T451) aluminium alloy. Both low- and high-cycle fatigue tests were conducted at room temperature on the cycle asymmetry ratio of R=-1. The low-cycle fatigue tests were performed using the MTS-810 machine on two levels of total strain, i.e.Δεc= 1.0% and 1.2%. The high-cycle fatigue tests, on the other hand, were performed using a machine from VEB Werkstoffprufmaschinen-Leipzig under conditions of rotary bending. Based on the results thus obtained, one could develop fatigue life characteristics of the materials examined (expressed as the number of cycles until failure of sample Nf) as well as characteristics of cyclic material strain σa=f(N) under the conditions of low-cycle fatigue testing. The Ti-6Al-4V titanium alloy was found to be characterised by the highest value of fatigue life Nf, both in lowand high-cycle tests. The lowest fatigue life, on the other hand, was established for the aluminium alloys examined. Under the high-cycle fatigue tests, the life of the 2017A aluminium and the AZ31 magnesium alloy studied was determined by the value of stress amplitude σa. With the stress exceeding 150 MPa, it was the aluminium alloy which displayed higher fatigue life, whereas the magnesium alloy proved better on lower stress.

Open access

M. Cieśla and G. Junak

Abstract

The research material used in the study was the martensitic creep-resistant steel P92 used for the manufacture of pipes being part of power generation units subject to heavy load. The research problem focused on two issues. The first one was to analyze how the plastic deformation cumulated in the material in low-cycle fatigue conditions affects the characteristics of the material in creep conditions in a temperature of 600ºC. The other one was concerned with analysis of a reverse situation, i.e. how the initial plastic deformation of the material in creep conditions changes the mechanical characteristics of the steel under low-cycle fatigue conditions in a temperature of 600ºC.

Open access

M. Cieśla, G. Junak, J. Tomczak, R. Findziński and T. Kawała

Abstract

The paper contains the results of theoretical and experimental research on the tube bending process used in the manufacturing of X10CrMoVNb9-1 steel tubes with dimensions 530 × 90 mm. An innovative technology in which the tube bending is coupled with local induction heating and the results of finite-element numerical modelling of tube bending using Simufact Forming 11.0 software are presented. A change of the geometry in the cross-section of the bend area was subjected to analysis, including the ovalization of the cross-section and the wall thickness in the regions subject to tension and compression. The geometrical features of the bend determined on the basis of numerical calculations were compared with the measurement results obtained in industrial conditions. Basic mechanical properties of the tube in the as-delivered condition and of the fabricated tube bend were determined using tensile, hardness, impact, low-cycle fatigue and creep tests. It was proved that the tube bend made of the X10CrMoVNb9-1 steel, obtained by the proposed technology, meets the requirements of the applicable standards.

Open access

M. Cieśla, F. Binczyk, G. Junak, M. Mańka and P. Gradoń

Abstract

Paper presents the assessment of impact of heat treatment on durability in low-cycle fatigue conditions (under constant load) in castings made using post-production scrap of MAR-247 and IN-713C superalloys. Castings were obtained using modification and filtration methods. Additionally, casting made of MAR-247 were subjected to heat treatment consisting of solution treatment and subsequent aging. During low-cycle fatigue test the cyclic creep process were observed. It was demonstrated that the fine-grained samples have significantly higher durability in test conditions and , at the same time, lower values of plastic deformation to rupture Δϵpl. It has been also proven that durability of fine-grained MAR-247 samples can be further raised by about 60% using aforementioned heat treatment.

Open access

M. Cieśla, R. Findziński, G. Junak and T. Kawała

The purpose of the paper was to analyse the effect of diverse heat treatment parameters (normalising and tempering) on mechanical characteristics of the material used to develop ϕ508x20 tube bends made of the 10CrMo9-10 steel by application of induction heating. The research conducted included tests of basic mechanical properties as well as low cycle fatigue and creep at the temperature of 500°C. With reference to the results thus obtained, it has been established that there is a relationship between mechanical properties of bends and individual features of their microstructure conditional to the heat treatment parameters. Among other conclusions drawn in the research, it has been found that the main structural factor conditioning the mechanical properties of bends was the grain size. Heat treatment parameters characterised by lower temperature and shorter tempering time triggered changes in the material microstructure, such as increased grain comminution. The effects of the said changes included improvement of strength characteristics (Rm, Rp0,2) as well as increased material durability under conditions of fatigue and creep. Main criterion-specific mechanical properties and geometric features of the bends developed conformed with the relevant requirements of reference standards (PN-EN 10216-2, PN-EN 12952).