Jack Samuelsson

Development of Weld Quality Criteria Based on Fatigue Performance

Historically, production technology researchers and structural design researchers have had only limited dialogue and each group has focused on their own narrow field of interest. This has led to inconsistencies in the definition of so-called “weld class systems” which have been primarily developed based on concepts related to good workmanship but have little or no relation to the actual performance of the welded structure. Additionally, some of the quality measures in existing systems are qualitative and, thus, subjective. In recent years, Commission XIII of the International Institute of Welding (IIW) has been promoting research and developing the technical background needed to develop a weld quality guideline which quantitatively relates weld acceptance criteria to the expected structural performance (primarily fatigue strength). A new weld class system with this same objective has recently been developed as a Volvo Group Standard. This system is described in this paper. The new standard has three quality levels for fatigue; as-welded normal quality, as-welded high quality and post-weld treated quality. It contains acceptance limits which are consistent with the expected fatigue strength and which can more objectively handle revisions. This new system will help in the development of new structures with lower weight and increased reliability.

Fatigue design of lightweight welded vehicle structures: influence of material and production procedures

Structural details and components in many types of products are continuously subjected to variable amplitude loading during operation. Fatigue loading and fatigue damage is thus the most common failure mode for the mentioned equipment in operation. The influence of the material grade, weld quality and fabrication procedure have a major impact on the structural durability of welded vehicle structures. The comprehensive research work within the Nordic research and development community have contained development of finite element modelling of complex structures, including crack growth in two- and three-dimensional fatigue testing of welded small-scale specimen and full-scale components, investigations of weld defects and flaws (e.g. cold laps) and weld roots. An important part of these projects is related to simulation and measurements of formation and relaxation of residual stresses. Within these projects three new quality systems, for welded and cast components and for cut edges, have been developed based on a scientific ground and a fitness for purpose design philosophy. Volvos new weld class system, which is an open standard, is now a base for the revision of the international weld quality system ISO 5817. In this article the major findings in these research activities are briefly presented and discussed.