Failure of thinwalled structures under impact loading
Licentiate thesis, 2013
Thinwalled structures are widely used for different applications, e.g. maritime structures,
vehicles, off-shore structures, aircraft fuselage, ship panels etc., and due to their application
they might be exposed to high strain rate loads as blast loads. Obviously, thinwalled
structures must be capable of withstanding these loads to a certain degree. In order
to investigate how failure takes place and to design structures resistant to blast loads,
advanced numerical modelling techniques are required. This work is intended to develop
a framework capable of analysing ductile fracture in terms of prediction of crack initiation
and propagation applicable to thinwalled steel structures exposed to high strain rates.
Of particular interest is the application to large scale structures for which an effcient
numerical procedure is required to obtain the accurate response of the structure.
In the first paper, dynamic crack propagation in elastoplastic thinwalled structures is
explored. In this development, a hypoelastic-inelastic modelling framework is employed
where the Johnson and Cook phenomenological model is incorporated. Thereby the
uence of the temperature and the plastic strain rate dependencies are accounted for,
which is of signiffcant importance for analyses of the thinwalled structure exposed to blast
loading. The shell kinematics are represented utilising a 7-parameter shell formulation
including extensible directors and a second order inhomogeneous thickness deformation.
In order to describe the through-the-thickness displacement discontinuity, the shifted
version of XFEM is employed when localisation is predicted. Furthermore, the resisting
force of the process zone is represented by a damage-viscoplastic cohesive zone model.
In order to verify the model, different examples are carried out and compared against
In the second paper, the objective is to enhance details of the crack path without the
incorporation of standard remeshing procedures. Due to dealing with large thinwalled
structures, it is of particular importance to represent the crack tip and kink inside the
cracked element. To this end, in addition to the macroscopic continuous and discontinuous
displacement fields, a discontinuous
uctuation field with a Dirichlet boundary condition
is employed at the element subscale level. This subscale enrichments provides an enhanced
representation of the discontinuous kinematics within the crack tip element. One advantage
of the current method is that a local model reduction is carried out, using dynamic
condensation, so that the spatial discretisation of the domain remains intact. In order to
verify the new methodology, different examples are carried out and compared against the
standard XFEM enrichment.
thinwalled shell structures
phantom node method