Browsing by Author "Marquis, Gary B."

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The effect of interacting small defects on the fatigue limit of a medium carbon steel
(2016) Åman, Mari; Okazaki, Saburo; Matsunaga, Hisao; Marquis, Gary B.; Remes, Heikki
A4 Artikkeli konferenssijulkaisussa
Structural steels contain various material irregularities and natural defects. These cause local stress concentrations, from which fatigue cracks tend to initiate. Two defects in close proximity to each other may affect local stress distributions and thus, begin to interact. In this paper, the effect of interacting small cracks on the fatigue limit is systematically investigated in a medium carbon steel. The growth of interacting cracks, as well as the characteristics of non-propagating cracks and microstructural aspects were closely examined via the plastic replica method. It was found that although the fatigue limit is essentially controlled by the mechanics of interacting cracks, based on their configuration, the local microstructure comprised of ferrite and pearlite has a statistical scatter effect on the behaviour of interacting cracks and non-propagating thresholds. With respect to the fatigue limit, when two defects were in close proximity, they behaved as would a larger single defect. However, with greater spacing between defects, rather than mechanical factors, it is the local microstructure which determines the location and characteristics of non propagating cracks. Copyright (C) 2016 The Authors. Published by Elsevier B.V.
A guideline for fatigue strength improvement of high strength steel welded structures using high frequency mechanical impact treatment
(2013) Marquis, Gary B.; Barsoum, Zuheir
A4 Artikkeli konferenssijulkaisussa
In the past decade, high frequency mechanical impact (HFMI) has significantly developed as a reliable, effective and user-friendly method for post-weld fatigue strength improvement technique for welded structures. This paper presents a proposed fatigue design and assessment guideline for HFMI improved welded joints. Stress analysis methods based on nominal stress, structural hot spot stress and effective notch stress are discussed. The document especially considers the observed extra benefit that has been experimentally observed for HFMI treated high strength steels. The proposal is considered to apply to steel structures from plate thickness 5 to 50 mm and for yield strengths ranging from 235 MPa to 960 MPa. Several fatigue assessment examples are also provided. Lessons learned concerning appropriate HFMI procedures and quality assurance measures are presented. Due to differences in the HFMI tools and the wide variety of potential applications, certain details of a proper treatment procedures and quantitative quality control measures are presented generally. It is proposed that specific details should be documented in a HFMI Procedure Specification for each structure being treated. It is hoped that this guideline proposal will provide a stimulus to researchers working in the field. (C) 2013 The Authors. Published by Elsevier Ltd.