Crack propagation in thin shells by explicit dynamics solid-shell models

A computational technique for the simulation of crack propagation due to cutting in thin structures is proposed. The implementation of elastoplastic solid-shell elements in an explicit framework is discussed. Finally, in the case of crack propagation, the issue of the selection of a propagation criterion is briefly discussed. Crack propagation is modelled making use of a so called “directional” cohesive approach

A thermodynamically consistent cohesive damage model for the simulation of mixed-mode delamination

This work is devoted to the formulation of a new cohesive model for mixed-mode delamination. The model is based on a thermodynamically consistent isotropic damage formulation, with consideration of an internal friction mechanism that governs the interaction between normal and shear opening modes

Crack propagation in shells due to impact against sharp objects

The present paper is concerned with the development of an effective finite element tool for the simulation of crack propagation in thin structures, induced by contact or impact against sharp objects. In particular the purpose is the refinement and further development of a recently proposed finite element approach for the simulation of the blade cutting of thin membranes [1]. Standard cohesive interface elements are not suited for the simulation of this type of cutting, dominated by the blade sharpness and by large failure opening of the cohesive interface. The new concept of “directional” cohesive element, to be placed at the interface between adjacent shell elements, where the cohesive forces can have different directions on the two sides of the crack whenever the cohesive region is crossed by the cutting blade, was introduced in [1] for elastic 4-node full-integration shell elements with dissipation localized inside the interface elements, in the framework of an explicit dynamics formulation. In the present paper the computational efficiency of the proposed approach is investigated by considering applications to different test problems, modifying the shell element kinematics. Some considerations about a reduced integration solid-shell element are here reported; the interaction between this kind of element and directional cohesive elements is under study

A fully explicit fluid-structure interaction approach based on the PFEM

The efficient numerical simulation of fluid-structure interaction (FSI) problems is of growing interest in many engineering fields. In the present work, a staggered approach for the solution of the FSI problem is proposed. The fluid domain is discretized with an explicit Particle Finite Element Method (PFEM) while the solid domain with a standard finite element method. The weakly compressible formulation of fluid flow, originally proposed in for the PFEM, is here used for the fluid domain. The PFEM has shown its capability in simulation of free surface flows in many applications. Thanks to the Lagrangian formulation, the free surface is directly defined by the current position of the particles, while the governing equations are imposed like in standard FEM. When the mesh becomes too distorted, a fast remeshing algorithm is used to redefine the connectivities. SIMULIA AbaqusExplicit has been used for the solution of the structural domain. The GC Domain Decomposition method is here used for the coupling: the problem is solved independently on each subdomain and then linked at the interface using a Lagrange multiplier technique. The proposed method allows for different time-steps in the two subdomains and for non-conforming meshes at the interfaces between the solid and fluid domains. Moreover, this approach guarantees an explicit coupling at the interfaces. 2D test-cases will be presented to validate the proposed coupling technique. The explicit scheme for both the fluid and solid subdomains, together with the explicit treatment of the coupling, makes this method appealing for applications in a variety of engineering problems with fast dynamics and/or a high degree of non-linearity

SOLID-SHELL FINITE ELEMENT MODELS FOR EXPLICIT SIMULATIONS OF CRACK PROPAGATION IN THIN STRUCTURES

Crack propagation in thin shell structures due to cutting is conveniently simulated using explicit finite element approaches, in view of the high nonlinearity of the problem. Solidshell elements are usually preferred for the discretization in the presence of complex material behavior and degradation phenomena such as delamination, since they allow for a correct representation of the thickness geometry. However, in solid-shell elements the small thickness leads to a very high maximum eigenfrequency, which imply very small stable time-steps. A new selective mass scaling technique is proposed to increase the time-step size without affecting accuracy. New ”directional” cohesive interface elements are used in conjunction with selective mass scaling to account for the interaction with a sharp blade in cutting processes of thin ductile shells

Selective mass scaling for multi-layer solid-shell discretization of thin-walled structures

The computational burden of an explicit dynamic analysis of thin-walled structures discretized with solid-shell elements can be very high, since the stability condition leads to extremely low time steps because of the small thickness. A selective mass scaling procedure ([1], [2],[3]) can be introduced to overcome this limitation. The technique proposed in [4] for single-layer 8-node solid-shell elements is here generalized to the case of multi-layer shells. The idea is to modify the mass matrix, scaling down the highest structural eigenfrequencies, so that the critical time step is determined only by the in-plane size of the elements, as with standard four-nodes shell meshes. Moreover, the resulting critical time step is shown to be independent of the number of layers used for the throughthe- thickness discretization. The accuracy of the proposed procedure and the computational gain are tested with the aid of numerical examples

8-Node solid-shell elements selective mass scaling for explicit dynamic analysis of layered thin-walled structures

To overcome the issue of spurious maximum eigenfrequencies leading to small steps in explicit time integration, a recently proposed selective mass scaling technique, specifically conceived for 8-node hexahedral solid-shell elements, is reconsidered for application to layered shells,where several solid-shell elements are used through the thickness of thin-walled structures. In this case, the resulting scaled mass matrix is not perfectly diagonal. However, the introduced coupling is shown to be limited to the nodes belonging to the same fiber through the thickness, so that the additional computational burden is almost negligible and by far compensated by the larger size of the critical time step. The proposed numerical tests show that the adopted mass scaling leads to a critical time step size which is determined by the element in-plane dimensions only, independent of the layers number, with negligible accuracy loss, both in small and large displacement problems