The current paper presents a comprehensive overview of weld quality control and assurance of welded structures where the major failure prevention is due to fatigue loading. It gives the drawbacks and limitation of quality control systems, international weld quality standards, and guidelines used in today's weld production. Furthermore, in recent development in quality control and assurance of welded structures, a new online method is presented. The main target is to enable a complete, online evaluation of large quantities of welds in an accurate and repeatable fashion. Information gathered will not only be used for determining the weld quality level with respect to the fatigue strength but also to be evaluated for use in improved process control, in welding power sources, and robot control systems. It is verified that the new online method, a new laser scanning technology, and algorithms can successfully be used as modern tools for automated unbiased geometrical weld quality assurance and implemented in weld production environment.
The influence of surface roughness on the fatigue strength in high strength steels and different cutting processes are studied. Fatigue testing is conducted on S700 and S960 material for different plate thicknesses cut in dog bone specimens using oxygen, plasma, laser and waterjet cutting. The surface roughness is measured for all specimens and residual stress measurements are carried out. Estimations of the fatigue strength are made based on the measured surface roughness and the ISO 9013:2002 standard for thermal cutting quality tolerances. The testing shows a 15-70 % increase in the fatigue strength compared to the estimation, proving a weak connection between the surface quality levels in ISO 9013:2002 and the fatigue test results. Different codes and design recommendations (IIW, EC3 and EN 13001) for fatigue strength of cut surfaces are compared with the fatigue test results which clearly shows an increased fatigue strength with enhanced quality and steel grades. However, the codes and design recommendations do not allow for any fatigue strength improvement with improved quality and increased yield strength.
Keywords: High strength steels / fatigue assessment / thermal cutting / quality / surface roughness / welded structures / cut edges Schlü sselwö rter: Hochfeste Stä hle / Bewertung des Ermü dungsverhaltens / thermisches Schneiden / Gü te / Oberflä chenrauheit / geschweißte Verbindungen / Schneidkanten Corresponding author: T. Stenberg, KTH Royal Institute of Technology, Department of Aeronautical and Vehicle Engineering,
A selection of reliable measurement systems that are able to measure the toe radius along the weld bead in a T-joint has been studied. The results show that the currently used methods and gauges do not provide the required accuracy when measuring the toe radius. The gauges are handled differently by different operators -even when using a vision system -which makes the current evaluation methods subjective and unreliable.Therefore, an algorithm has been developed that assesses weld bead surface data and automatically identifies and calculates the toe radius and the toe angle along the weld. The results obtained by the algorithm are consistent with reference measurements and it is possible for the algorithm to be used in improving the process and quality control during welding.
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