Crushing and Fracture of Lightweight Structures

Publication: ResearchPh.D. thesis – Annual report year: 2003

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The overall objective of the present study has been to develop rational analytical and numerical calculation models to quantify the consequences of collision accidents. The work has primarily been focused on high speed craft (HSC) built in lightweight materials such as aluminium and sandwich. Crushing experiments conducted on full-scale aluminum plate intersections reveal that the crushing behaviour is highly affected by material fracture during the deformation. Several fracture criteria from the literature have been reviewed and three fracture models have been compared with material experiments covering a wide range of stress states. It is found that a fracture criterion by Rice and Tracey (1968) agrees well with the experiments with a high triaxiality and that a fracture criterion by Cockcroft and Latham (1968) agrees well with the experiments with a low or negative triaxiality. Based on these two fracture models a new fracture criterion, denoted RTCL fracture criterion, is proposed and the fracture criterion is implemented in the FE-program LS-DYNA as a user subroutine. The crushing behaviours of the full-scale aluminum plate intersections have been simulated with LS-DYNA and the implemented fracture criterion and the simulations agree well with the experiments. New closed form solutions for the dissipated energy during axial compression of aluminum plate intersections have been developed and the effect of fracture is included analytically based of the fracture criterion by Cockcroft and Latham (1968). Good agreement between the analytical models and the experiments is found. The crushing behaviour of two high speed ferries has been analysed with the numerical and analytical methods and the results are compared with the existing regulations for high speed craft (HSC). Several failure criteria for first-ply failure of unidirectional composites (UD), from the literature, are compared with experiments conducted on composite specimens. It is found that a failure criterion by Chang and Chang (1987) agrees well with the experiments on UD. A progressive failure procedure by Chang and Chang (1987) has been implemented in a small laminate computer program and as a user subroutine in LS-DYNA. Simulations of the progressive damage behaviour of laminated composites during deformation show that the response is reasonable well predicted by the progressive failure procedure. Crushing tests have been conducted on six full-scale sandwich intersections and the crushing responses have been simulated with LS-DYNA and the implemented progressive failure procedure. The rsults show that the ultimate force agrees well with the experiments while the crushing force after this is significantly under predicted.
Original languageEnglish
Publication dateJul 2003
StatePublished
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