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Material parameters for design in duplex stainless steel: experimental results and finite element analysis
2001 (English)Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

The thesis is conceived in effort to provide necessary data for a EU project within 5th framework research proposal called ECOPRESS (Economical and safe design of pressure vessels applying new modern steels). The main objective of the research project is to investigate improvements of the utilisation of new high performance steels implementing “modern design by analysis and structural integrity calculation methods and validate this methods with extensive experimental tests for the practical use”. The main objective of this thesis is to gain knowledge and collect characteristics of the material for the application of duplex steel (EN 1.4462) in economical pressure vessel design. Uniaxial tensile tests were carried out to establish material parameters of both the duplex (EN 1.4462) and the weld material. The well known anisotropic behaviour for the duplex stainless steel was verified. In order to study the fracture behaviour, of duplex stainless steel, a suitable membrane test set-up was developed. After verifying that the test set-up was feasible, 12 membrane tests were performed. The tests were divided into three different specimens, plain, butt-welded and specimen with welded nozzle. The strain, which could be measured with gauges, was limited to 6 %. In order to estimate the strains at failure in the specimen a finite element analysis was performed. The global behaviour (pressure-bulge relation) from the experimental results was compared with the isotropic FE-model in order to verify the model. ABAQUS, a finite element code is used in this thesis. The FE results show very good agreement with the performed membrane tests in terms of global behaviour (ascending and descending part of the pressure-bulge curve). As long as the strain gauges are in operation the membrane test results are in a rather good agreement with the FE results. The total in-plane strain at failure is approximately 40%, and the equivalent plastic strain is 50% at failure. These results are obtained from FEA. A stiffer behaviour (pressure-bulge curve) is obtained for specimens with butt welds and welded nozzle compared to the plain specimen behaviour. In order to estimate the utilization of the duplex material in the design codes, a typical pressure vessel were designed according to the Swedish Pressure vessel code. A non-linear analysis is performed to estimate the ultimate limit load. The study of this pressure vessel showed that the design code is rather conservative regarding the utilization of the duplex stainless steel. Ultimate limit load according to FEA using elastic plastic isotropic hardening material (yield stress 590 MPa and strength 830 MPa) is 17.2 MPa. If the elastic plastic material parameters (yield stress 590MPa) are used than the ultimate load is 12.7 MPa. Hand calculation model according to the Swedish code with the manufacturer recommendation of the yield stress fy=460 MPa gives ultimate load pressure 5.2 MPa.

Place, publisher, year, edition, pages
Keyword [en]
Technology, pressure vessels, duplex stainless steel, FEA, structures, material characteristics, biaxial tension
Keyword [sv]
URN: urn:nbn:se:ltu:diva-45724ISRN: LTU-EX--01/353--SELocal ID: 36593ee7-a616-4da3-a4b1-a77bf29f93c1OAI: diva2:1019021
Subject / course
Student thesis, at least 30 credits
Educational program
Civil Engineering, master's level
Validerat; 20101217 (root)Available from: 2016-10-04 Created: 2016-10-04Bibliographically approved

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