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ABSTRACT
Rubber-like materials such as sealant with recent developments in formulation are widely used in various structural components, especially in aerospace industry with many applications such as the sealing of bolted joints on aircraft. The objective of this paper is to assess the load transfer distribution in bolted-sealed joints through an approach coupling both experimental and numerical tests. Quasi-static and relaxation tests under uniaxial and pure shear loading were carried out to determine the parameters of phenomenological hyperelastic laws and of the generalized Maxwell model for the sealant PR 1782 C2. The fastener is an alloy steel bolt with a protruding head when the substrates are made from aluminum 2024-T3. Experimental and numerical quasi-static tests were then performed on double-lap bonded and bolted-sealed joints under in-plane loading. The numerical tests are done using 2D and 3D Finite Element (FE) models; they involve the visco-hyperelastic behavior previously assessed for the sealant. Accounting for visco-hyperelasticity makes it possible to better estimate the load transfer between bolt and sealant layer. Typically, the bolt load transfer rate is derived from numerical output for different sealant thicknesses. In the considered geometrical joint configuration, the sealant load contribution is between 7% and 13% according to the sealant thickness. Methodology and results provide a solid basis for the fatigue strength prediction of bolted-sealed joints.
Nomenclature
| Cij | = | polynomial hyperelasticmaterial coefficients (MPa) |
| Dk | = | compressibility coefficients (1/MPa) |
| Ei | = | elastic modulus (MPa) of Maxwell arm i |
| E∞ | = | elastic modulus (MPa) of elastic arm |
| gi | = | shear relaxation modulus ratio of Maxwell arm i |
| Ii | = | invariants of Green-LaGrange strain tensor |
| = | reduced invariants of Green-LaGrange strain tensor | |
| Ii,SS | = | invariants of Green-LaGrange strain tensor for simple shear transformation |
| Ii,PS | = | invariants of Green-LaGrange strain tensor for pure shear transformation |
| Ii,UAT | = | invariants of Green-LaGrange strain tensor for uniaxial tensile transformation J = volumetric strain |
| l | = | substrate part outside the overlap (mm) |
| q | = | edge pitch of joint overlap (mm) |
| t | = | thickness of sealant layer (mm) |
| W | = | strain energy density (J/m3 in SI) |
| w | = | joint width (mm) |
| κk | = | compressibility modulus (MPa) |
| λi | = | stretch in axis i |
| σi | = | stress in axis i (MPa) |
| τi | = | relaxation time (s) of Maxwell arm i |
| τ | = | bolt load transfer rate |
| ϕ | = | bolt diameter (mm) |
| Subscripts | = | |
| eng-PS | = | engineering stress under pure shear loading |
| eng-UAT | = | engineering stress under uniaxial loading |
| Abbreviations | = | |
| FE | = | Finite Element |
| HBB | = | Hybrid Bolted/Bonded |
| PS | = | Pure shear |
| UAT | = | Uniaxial tensile |
Acknowledgments
The authors would like to acknowledge the sponsors of MIAM project, as well as the researchers and technicians at ISAE-SUPAERO Department of Mechanics, Structures and Materials (DMSM) and INP-ENIT Production engineering laboratory (LGP) for their supports and advices. The authors gratefully acknowledge Occitanie Region and Université Fédérale de Toulouse Midi-Pyrénées ISAE-SUPAERO.
Disclosure statement
No potential conflict of interest was reported by the author(s).