1,721,138 research outputs found
Fracture energy in phase field models
Full text linkThe phase field approach to brittle fracture is based on smeared energetic representation of sharp fracture into surface. The passage between damaged and undamaged zones is influenced by an internal length scale parameter. In the present paper the approximation of fracture energy in phase field models is studied. Firstly, the diffusion equation of the phase field is numerically investigated. It is demonstrated through simple paradigmatic 2d and 3d cases that the fracture energy during crack initiation and propagation phenomena, such as crack branching and bifurcation, is strictly correlated with the internal length parameter. Moreover, it is shown that for finite value of the internal length parameter the dissipated energy does not depend only on the crack extension but on the geometrical configuration of fracture differently from the Griffith sharp approach. In particular, it is demonstrated that 3d cracks with same area may be characterized by different values of approximated fracture energy
Mesh refinement procedures for the phase field approach to brittle fracture
Full text linkTwo refinement procedures for phase field approach are proposed and their numerical performances are investigated in the solution of fracture problems. Starting from a coarse discretization of the domain, an energetic criterion is used to determine the active zones where damage initiates, evolves and mesh refinement is mandatory to accurately approximate crack topology. Moreover, the extension of the refined regions is strictly correlated with the size of the process zone defined by the optimal profile. Global and global/local refinement strategies are investigated. In particular, the global/local technique solves the displacement and phase field problems on a local mesh dynamically updated and adaptively refined during the computation. Once the solutions of the local problems are obtained, the phase field is interpolated back onto the original mesh, adequately refined where a damage threshold is exceeded. The performances of the refinement techniques are analyzed and compared in representative examples with stable and brutal crack propagation
Debonding Process of Masonry Element Strengthened with FRP
No full textAbstractThe influence of mortars joints in masonry substrate reinforced with FRP is investigated from the numerical point of view. The analysis has been conducted by means of a new interface model specifically developed to reproduce the debonding process oc- curring between an elastic thin body in adhesion with a cohesive support material. The model accounts for mode I and mode II of failure, considering the effect of the in-plane deformation of the interface, i.e. the possible elongation or confinement of the material constituting the interface. Numerical results are compared with experimental evidences showing good performances of the proposed model in investigating the transferring phenomena and in studying the influence of the presence of mortar joints in the masonry texture in the debonding process
Failure and complex crack patterns in hybrid laminates: A phase-field approach
No full textA powerful numerical instrument, which reproduces the complex failure mechanisms of hybrid laminates under in-plane loading conditions, is developed within the framework of phase-field modelling. The ruptures, strongly influenced by geometrical and mechanical properties of the plies and affected by the state of stress, are arranged as delamination of the adhesive interface and intricate crack patterns within the layers. Therefore, the mechanical response of a hybrid laminate is obtained by studying the simplified layup of two elastic-brittle solids connected by a cohesive interface. Explicit and well detailed simulations illustrate peculiar failure mechanisms, validated, when possible, against experimental results taken from the literature and compared to simplified analytical models. Different in-plane loading conditions are explored together with the possibility to include material anisotropy. The proposed model is a first attempt to provide an effective design tool for the understanding of the intriguing failure of hybrid laminates and the enhancement of their mechanical properties like ductility
An interphase model for the analysis of the masonry-FRP bond
No full textThe present paper deals with the problem of the detachment of fiber reinforced polymer (FRP) from a masonry support. In particular, a new interphase model simulating the mechanical bond between masonry and FRP is proposed. It is obtained as a system of two interfaces: one reproduces the response of the glue and of the skin-deep layer and it is characterized by a linear elastic behavior whereas the second describes the nonlinear response of the detachment layer. The effect of the possible confinement due to the stress components acting in the plane of the detachment layer is also considered. Two numerical applications are reported. The first illustrates a comparison between the experimental laboratory tests and numerical simulations, showing the good performances of the proposed model. The second application is specifically devoted to the investigation of the effects of the presence of mortar joints in the detachment mechanism
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