Einfluss der Mehrachsigkeit der Belastung auf die Kriechporenbildung und die zeitliche Schädigungsen

FKM 2000
Issue number 251
Project no. 213

Abstract:
This project investigated the influence of multiaxiality on the formation of creep pores in the steels 14MoV6-3 1 OCrMo9-1 0 and X10CrMoVNb9-1. For this purpose, internal pressure tests were carried out on smooth and notched hollow cylinders. In order to be able to map component-relevant degrees of multi-axiality, some of the specimens were subjected to additional axial forces. The use of applied HT strain gages made it possible to determine and evaluate the local strain during loading. After reaching different strain values, the samples were removed, examined metallographically and characterized using different damage parameters. It was found that if the load condition is not known, no correlation can be derived between the surface image of the damage and its depth progression over the wall thickness. In parallel to the experimental investigations, inelastic finite element (FE) analyses were carried out using the ABAOUS program system. The creep law according to Graham and Walles was used via a user-defined subroutine CREEP to calculate the flow and creep behavior. The parameters of the creep law were identified by adapting them to uniaxial creep tests. For the steel 14MoV6-3, which has a pronounced tendency to creep damage due to micropores, a clear dependence of the pore number density on the largest principal strain and on the multiaxiality quotient was found. A relationship developed for this connection, in combination with the FE analysis, allows the approximate calculation of the temporal and local damage development in component-like geometries. The steel 1 OCrMo9-1 0 (air quenched and tempered) only showed pore formation for high multiaxiality values, but this only had an insignificant effect on the component behavior. In the case of the steel X10CrMoVNb9-1, a clear batch influence on creep ductility and pore formation was recognizable. Component tests on pipe bends made of 14MoV6-3 and 1 OCrMo9-1 0 subjected to operational stresses confirmed the correlations found on the samples between creep pore formation and maximum principal strain and multiaxiality quotient. FE analyses were used to calculate the temporal development of damage at various positions over the wall thickness of a smooth hollow cylinder under internal pressure and confirmed by experimental investigations. Furthermore, FE analyses were carried out for a pipe bend made of 14MoV6-3 under the load types internal pressure and internal pressure with superimposed bending moment. The calculated damage development corresponds to experience, according to which the location of the onset of damage shifts from the extrados to the intrados due to a bending moment. Scope of report:
222 p., 119 pictures, 16 plates, 60 lit. Start of work:
01.07.1996 End of work:
30.06.1999 Funding body:
AVIF (funding no. A105) Research bodies:
State Materials Testing Institute (MPA) University of Stuttgart Head:
Prof. Dr.-lng. habil. E. Roos TU Chemnitz Chair of Materials in Mechanical Engineering Head:
Prof. Dr.-lng. l.W. Meyer Processors and authors:
Dr.-lng. habil. P. lenk, Dipl.-lng. D. Proft : Dr. rer. nato A. Kußmaul, Dipl.-lng. R. Fischer Chairman of the working group:
Dipl.-lng. B. Hahn, Technip Germany GmbH Chairman of the Advisory Board:
Dipl.-lng. J. Rabe, Sachsen ring AG