Development of assessment methods for residual stresses at site joints of large-scale steel structures

Field of Research: Welding Residual Stress; Fatigue Strength

Duration: 01.01.2013 – 30.06.2015

Abstract

Fatigue-assessment of welded steel structures in structural engineering, shipbuilding, crane construction and railway vehicle construction is still subject to difficulties. One reason is given by the uncertainties of the influence of residual stresses and strains caused by the welding process. These negatively affect the fatigue properties and may lead to high costs for additional straightening work.

Residual welding stresses and strains may be influenced by clamping and the weld sequence as well as hot or cold straightening. These procedures require knowledge of the stresses and strains to be expected and of influencing factors.

The estimation of stresses and strains can generally be achieved by a numerical simulation of the heat input from the welding process with a subsequent structural analysis considering temperature dependent material parameters. Because of the nonlinearity the numerical analysis is expensive and not widely-used in practice so far. The application to large-scale structures is still limited by extensive modeling, long calculation times and availability of the needed powerful hardware.

The aim of the project is the investigation, calculation and assessment of welding residual stresses and their influence on the fatigue strength at site joints of large-scale steel structures. A simplified approach for the calculation of residual stresses and strains is to be developed, in order to estimate the consequences of the welding process prior to the assembly. Further the development of the residual stresses under working loads and the influence on fatigue strength shall be investigated. Also the influence on residual stresses of production tolerances such as gap with and offset is to be considered in the analysis.

In collaboration with the Institute of Joining and Welding Technology at the Technical University of Braunschweig experimental end numerical investigations are performed.

The experimental investigations are carried out on structures based on frame corners found in ship structures. The residual stress at the site joint is measured and analyzed in the initial condition. Afterwards fatigue tests are done to determine the fatigue strength of the structures.

Beside the experimental investigations numerical simulations are done. Using transient three-dimensional analysis the welding residual stresses and strains are calculated for the investigated structure and validated by measurements. Then the influence of production tolerances is analyzed to determine their influence on the stress distribution at critical points of the structure.

Publications:
  • Friedrich N.; Fricke W.; Klassen J.; Hensel J.; Nitschke-Pagel T.: Development of methods for evaluation of residual stresses in assembly joints of large steel structures. Proc. of 2nd European Steel Technology and Application Days (METEC & ESTAD2015), Düsseldorf 2015.
  • Friedrich N.; Fricke W.; Klassen J.; Hensel J.; Nitschke-Pagel T.: Numerische und experimentelle Untersuchung von Schweißeigenspannungen an Montagestößen und deren Einfluss auf die Schwingfestigkeit. Proc. of 33th ANSYS Conference & CADFEM Users Meeting, Bremen 2015.

Persons:

Prof. Dr.-Ing. Wolfgang Fricke

Dipl.-Ing. Nils Friedrich