The effect of clamping stress on the fatigue strength of bonded high-strength steel interfaces
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RESEARCH PAPER
The effect of clamping stress on the fatigue strength of bonded high-strength steel interfaces Susanna Hurme & Gary B. Marquis
Received: 15 October 2012 / Accepted: 29 January 2013 / Published online: 13 February 2013 # International Institute of Welding 2013
Abstract It is well known that the fatigue strength of a welded joint does not increase proportionally with steel strength. For this reason, alternative joining techniques for high-strength steels are of great interest. Some studies have shown that hybrid joints, which combine mechanical fasteners and adhesives, have improved fatigue resistance as compared to welded joints in high-strength steel structures. For reliable design, an in-depth understanding of the clamped and bonded interface under cyclic loading is needed. In this study, the napkin ring specimen geometry has been chosen for a series of constant-amplitude fatigue tests. The test setup provides a bonded interface with well-defined normal and shear stress boundary conditions. Test conditions included four different static normal pre-stresses for the gritblasted surface finish and one pre-stress level for the fine ground. Fatigue strengths of all the pre-stress/surface type conditions were obtained by a statistical method. For gritblasted surfaces, the bonded specimens with high static normal pre-stresses behaved identically to the non-bonded specimens with the same pre-stress, i.e. the fatigue strength was not improved by the addition of adhesive even though the static strength had previously been shown to improve significantly for the same conditions. Keywords (IIW Thesaurus): Hybrid joint . Bonded joint . Fatigue tests . Fretting fatigue . Interface fracture Nomenclature N Fatigue cycles Nf Fatigue cycles to failure Doc. IIW-2347, recommended for publication by Commission XVI “Polymer Joining and Adhesive Technology”. S. Hurme (*) : G. B. Marquis Department of Applied Mechanics, Aalto University, P.O. Box 14300, 00076 Aalto, Finland e-mail: [email protected]
q δa δath Ca Cf CIIp CIIres
Clamping stress, normal static stress between interfaces Relative displacement amplitude between the interfaces of the napkin ring specimen Threshold relative displacement amplitude at N=2× 105 cycles below which the fatigue test was always a run-out Shear stress amplitude (mode II) transferred across the interfaces during cyclic loading computed at the centreline of the contact surfaces Fatigue strength–shear stress amplitude corresponding to no failure at N=2×106 Measured interface mode II shear strength during quasi-static loading Interface mode II shear strength during quasi-static loading measured after two million fatigue cycles
1 Introduction High-strength steels (HSS) are increasingly used to provide light weight and improved strength in structures. However, the endurance of a HSS structure depends strongly on the welded joints, whose fatigue strength does not increase proportionally with the steel strength. Hybrid joints, where the good properties of adhesives and mechanical fastener
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