Size effect on strength of laminate-foam sandwich plates: Finite element analysis with interface fracture |
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| Authors: | Ferhun C Caner Zdeněk P Ba?ant |
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| Affiliation: | 1. Institute of Energy Technologies (INTE), School of Industrial Engineering (ETSEIB-UPC), Diagonal 647, E-08028 Barcelona, Spain;2. Civil Engineering and Materials Science, Northwestern University, 2145 Sheridan Road, CEE/A135, Evanston, IL 60208, USA;1. Materials Department, University of California, Santa Barbara, CA 93106 USA;2. Department of Mechanical Engineering, University of California, Santa Barbara, CA 93106 USA;1. Department of Aeronautics and Astronautics, University of Washington, Seattle, WA 98195, USA;2. Department of Civil and Environmental Engineering, Northwestern University, Evanston, IL 60208, USA;1. ISISE, Dep. Civil Eng., School Eng., University of Minho, Campus de Azurém, 4800-058 Guimarães, Portugal;2. CIVITEST – Pesquisa de Novos Materiais para a Engenharia Civil, 4760-042 Vila Nova de Famalicão, Famalicão, Portugal;1. Helmut-Fischer Korea, 462, Dogok-ro, Songpa-gu, Seoul 05574, Republic of Korea;2. Division of Materials Science and Engineering, Hanyang University, Seoul 133-791, Republic of Korea;3. Sensor System Research Center, Korea Institute of Science and Technology, 14-gil 5 Hwarang-ro, Seongbuk-gu, Seoul 136-791, Republic of Korea;4. School of Mechanical Engineering, Konkuk University, Seoul 143-701, Republic of Korea;1. Key Laboratory of Concrete and Prestressed Concrete Structural of the Ministry of Education, Southeast University, 210096 Nanjing, China;2. State Key Laboratory of Subtropical Building Science, South China University of Technology, 510641 Guangzhou, China |
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| Abstract: | Recent three-point bend tests of size effect on the strength of geometrically scaled sandwich beams of three types – with no notches, and with notches at the upper or lower skin–foam interface, which were previously evaluated using simplified sandwich beam theory and equivalent linear elastic fracture mechanics, are now reanalyzed more accurately by finite elements. Zero-thickness interface elements with a softening cohesive law are used to model fractures at the skin–foam interface, in the fiber composite skins, and in the foam. The fracture energy and fracture process zone length of a shear crack in foam near the interface are deduced by fitting an analytical expression for size effect to the test data. Numerical simulations reveal that small-size specimens with notches just under the top skin develop plastic zones in the foam core near the edges of the loading platen, and that small-size specimens with notches just above the bottom skin develop distributed quasibrittle fracture in the foam core under tension. Both phenomena, though, are found to reduce the maximum load by less than 6%. Further it is shown that, in notch-less beams, the interface shear fracture is coupled with compression crushing of the fiber–polymer composite skin. For small specimens this mechanism is important because, when it is blocked in simulations, the maximum load increases. The size effect law for notch-less beams is calibrated such that beams of all sizes fail solely by interface shear fracture. |
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