New experimental determination of fatigue strength of tubular truss joints in steel grades up to S690

Alain Nussbaumer, Farshid Zamiri Akhlaghi
CRC press, 2015
Conference paper

In this paper research work on welded butt weld connections between hot-rolled seamless tubes and steel castings are presented. Comparison is made between different weld preparations for the butt welds including different steel grades, repair methods, the influence of residual stresses and a study on large scale trusses. The steel grades investigated include S550QH as well as S690QH to complement previous test results on lower steel grades. These investigations are intended to lead towards the development of a concept for improving the fatigue life for bridges using such end-to-end connections.

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Alain Nussbaumer, Farshid Zamiri Akhlaghi
CRC press, 2015
Conference paper

Abstract

Official source

https://infoscience.epfl.ch/record/215460?ln=en

About this result

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Welding simulation of tubular K-joints in steel S690QH

Jean-Marie Drezet, Alain Nussbaumer, Farshid Zamiri Akhlaghi

Residual stress state in planar tubular K-joints, in the chord within the gap region between the two braces, is studied using numerical weld modelling. The motivation comes from past full-scale fatigue tests on tubular trusses made of various steel grades with sizes typical of bridge trusses, which shows that the cracking occurs at the hot spots located in this region. Residual stress field characterization is needed in order to assess its role in fatigue cracking, especially for the case of cracks occurring on the compression brace side. Comparison between residual stress field in a Y-joint and a K-joint is made to assess the significance of restraining effect in the gap region. Phase transformations during welding and cooling down are determined and their impact on the final residual stress state is evaluated. Computed residual stresses are compared to the neutron diffraction measurements. Transient thermal field and cooling times substantially affect phase transformations. Therefore, their accurate reproduction in the analysis is important.

CRC press2015

Alternative stress definition and residual stress effects in fatigue design of welded tubular structures

Claire Acevedo, Luís Costa Borges, Alain Nussbaumer, Farshid Zamiri Akhlaghi

Steel tubular truss are lightweight, aesthetical and used in many different applications. These structures are sensitive to fatigue and specific verification methods have been developed for them, in particular by CIDECT [2001]. Due to assembly and welding, these structures contain large internal self-balanced stresses. Since tensile residual stresses tend to open cracks, they have a detrimental influence on the fatigue crack propagating under cyclic traffic loadings. Different studies on the behaviour of tubular structures have been focussing on the behaviour of tubular K-joints, one very much use type of joint, with tubes having low diameter to thickness ratios, for use in particular in bridge applications. In these cases, the CIDECT rule for reduction of fatigue strength with thickness becomes very penalizing and one has to see if alternatives are possible (changing the stress definition and/or the thickness effect formula). Also, many joints have members loaded under compression, such as upper chord joints in a truss. In these cases, tensile residual stress effect on fatigue life can be set apart from external loads effect. With welding imperfections acting like microcracks, residual stress can make the difference between a fatigue microcrack beginning to grow or not. Indeed, residual stress can raise the crack driving force above the threshold value. Moreover, it also influences the rate of crack propagation and therefore the residual stress distribution is essential to estimate accurately the crack development under fatigue loads. In this paper, work on the effects of size and residual stresses on fatigue life of tubular joints carried out at EPFL is summarised.

Shaker Verlag2013

Fatigue (material)

In materials science, fatigue is the initiation and propagation of cracks in a material due to cyclic loading. Once a fatigue crack has initiated, it grows a small amount with each loading cycle, t

Residual stress

In materials science and solid mechanics, residual stresses are stresses that remain in a solid material after the original cause of the stresses has been removed. Residual stress may be desirable o

Welding

Welding is a fabrication process that joins materials, usually metals or thermoplastics, by using high heat to melt the parts together and allowing them to cool, causing fusion. Welding is distinct f