Abaqus User Element Research Articles

Nonlinear hyperviscoelastic modelling of intra-ply deformation behaviour in finite element forming simulation of continuously fibre-reinforced thermoplastics

A nonlinear hyperviscoelastic approach for modelling rate-dependent intra-ply deformation behaviour in FE forming simulation of continuously fibre-reinforced polymers is presented. This approach follows either a Voigt-Kelvin approach or a generalized Maxwell approach based on a multiplicative decomposition of the deformation gradient. The constitutive equations are implemented in a “Discrete Kirchhoff Triangle” shell formulation within an Abaqus user-element, including a physical decoupling of membrane and bending behaviour. The approach is parameterized for a thermoplastic UD-tape (PA6-CF) at different strain-rates and temperatures above the crystallization temperature and applied to iso-thermal forming simulation. Parametrization results reveal that only the generalized Maxwell approach represents the whole material characteristic. Moreover, a difference in forming behaviour is observed for the investigated temperatures and constitutive equations. The difference, however, is small, which reveals that iso-thermal forming simulation following a Voigt-Kelvin approach is suitable for prediction of forming behaviour within a suitable process window, where isothermal conditions are assumable.

A cohesive element with degradation controlled shape of the traction separation curve for simulating stress corrosion and irradiation cracking

A cohesive element with extended environmental degradation capability was developed and implemented into an Abaqus user element. The element uses a virgin and a fully degraded Traction Separation Law (TLS) as input. The use of the potential based PPR model enables flexibility in the softening shapes for both TSL. When the element is degraded, the TSL gradually goes from the shape of the virgin material to the fully degraded TSL shape. This transition was made with a new parameter χ that can govern a more ductile or brittle crack growth behaviour at degradation. The effect on the plastic zone due to changing the softening shape is shown, where the convex shaped softening TSL gives higher plastic dissipation and larger plastic zones than the concave and more brittle TSL. The new degradation method was evaluated against a Hydrogen Embrittlement (HE) experiment showing improved agreement with the experiment compared to the literature. The effect of different susceptibility zones at the crack tip was also investigated, showing that a uniform degradation throughout the susceptible zone is more influenced by the χ parameter than a triangular susceptible zone.

A finite element based real-space phase field model for domain evolution of ferromagnetic materials

This paper proposes a real-space phase field model solved by finite element method for giant magnetostrictive materials. The model is based on the thermodynamic theory of ferromagnetic materials and employs the time-dependent Ginzburg-Laudau (TDGL) equation to predict the domain evolution process. We have derived the corresponding finite element formulation which takes the mechanical displacement, the magnetic potential, and the magnetization vector as the field variables, according to variational principle. A multi-field coupling finite element has been developed through the ABAQUS user element subroutine module to simulate the coupling between mechanical and magnetic characteristics for microstructures with arbitrary geometries and boundary conditions. The simulation results of a general magnetic nanoring coincide well with the reports in literature, which confirms the validity of the phase field method developed. The magnetization processes have also been investigated for nanorings with different geometries. The results suggest that the vortex chirality and multi-stable magnetization states can be controlled by changing both the symmetry of loading situation and the geometrical configuration. The phase field model solved by finite element method is expected to be a useful tool for the design of high density magnetic random access memories.

Application of the first-order shear deformation theory to the analysis of laminated glasses and photovoltaic panels

Laminated plates and photovoltaic panels are composed of three layers, whereas the core layer, comprising the solar cells and their encapsulation, is more shear-compliant than the skin layers. First-order shear deformation theories (FSDT) like the Mindlin theory are usually applied to these laminated plates in combination with a homogenisation approach. If the differences in shear stiffnesses are too strong, the FSDT may fail to predict the deformation behaviour accurately. This paper evaluates the applicability range of FSDT to the laminated glass and photovoltaic panels. Furthermore, a user-defined element is integrated with the subroutine User Element in Abaqus. This element utilises a homogenisation approach to determine the effective material parameters. To verify the results of the finite element analysis, a closed-form series solution is applied. The attention is placed on the accurate representation of the boundary layer effects that are important for the strength analysis.

Numerical and experimental investigation on lap shear fracture of Al/CFRP laminates

Abstract This paper presents a new approach to numerically investigate the lap shear fracture of a hybrid laminate made of Carbon Fibre Reinforced Plastic (CFRP) and metal foil plies (e.g. aluminium), validated by corresponding experiments. The numerical Finite Element (FE) model of the hybrid laminate, subjected to lap shear fracture, is composed of five laminas with alternating metal/CFRP layers with cohesive elements lying within Al/CFRP interface. In the FE model, individual CFRP laminas are assumed as an orthotropic homogenized continuum under plane stress, and aluminium facesheets are modelled as an elastic–plastic continuum. The Al/CFRP interface is represented via quadratic cohesive elements, the constitutive law of which is an exponentially decaying law representing the degrading behaviour of the interface (implemented as user element in ABAQUS). The numerical model captures the experimentally obtained results with minimal error, and predicts the failure modes successfully. The influence of specimen geometry (e.g. overlap length, total length, and total width) on lap shear fracture response is analyzed in detail in this study, too, in order to confirm the specimen design for the test, as there is still no corresponding test standard for hybrid laminates.

Implementation of the Arlequin method into ABAQUS: Basic formulations and applications

This article is concerned with implementing the Arlequin method into the commercial finite element software ABAQUS and demonstrating its versatility in various typical applications. According to the basic idea of the Arlequin method, the particular formulations for the ABAQUS user element are presented. A unified method for calculating coupling matrices is proposed in an obvious and straightforward way. The user element subroutines for coupling two relatively independent models with different or same dimensions are developed. Four numerical examples are considered: One is to demonstrate the coupling of elements with the same element type but different grid density by the Arlequin method, and the other three examples involve different types of elements. The numerical results justify the correctness of the codes developed for the user defined elements as well as the feasibility of the Arlequin method which is successfully integrated into ABAQUS.

Influence of hydrogen coverage on the parameters of a cohesive zone model dedicated to fatigue crack propagation

Experimental studies indicate a deleterious influence of a hydrogenous environment on the fatigue crack propagation resistance of metallic materials. In order to provide a predictive tool to assess fatigue lifetime of structures subjected to hydrogen, an ABAQUS finite element model of a compact tension (CT) specimen has been developed. A cohesive zone model (CZM) with a specific traction-separation law is used in conjunction with an elastic-plastic bulk material to model fatigue crack growth. The traction-separation law has been developed to take into account the influence of cyclic loading on crack propagation. A special attention has been paid to develop the model in the framework of thermodynamics, i.e. to ensure that the dissipation remains positive at any time. In addition, the parameters of the traction-separation law depend on local hydrogen concentration. This traction-separation law was implemented using ABAQUS user element subroutine UEL which is used to predict the influence of hydrogen on fatigue crack growth rates. Given the similarity between heat and mass diffusion equations, the coupling between hydrogen diffusion and the mechanical behaviour of the material has been implemented using ABAQUS coupled temperature-displacement procedure.