Three-dimensional Interface Element Research Articles

Delamination failure of composite top-hat stiffeners using finite element analysis

The paper presents the finite element analysis of top-hat stiffeners (transversely loaded keel support structure) under a static load where splitting–delamination is the primary mode of failure. A set of experiments is conducted on the composite top-hat stiffeners with three different lay-up arrangements. The experimental study, together with the finite element modelling to capture the delamination failure, is presented. Fracture initiation is predicted using an interlaminar-strength-based criterion. A fracture-mechanics-based formulation is used to predict delamination propagation by connecting the composite layers with two-dimensional and three-dimensional interface elements using the commercially available MSC Marc Mentat 2008 r1 finite element software package. Reasonable agreement between the experiments and finite element analysis was achieved. The reserve strength identified by the experimental testing is successfully modelled. The factors affecting the fibre–matrix interface strength are studied. The failure location and mode for fracture initiation and propagation are determined.

Numerical Analysis of a Slope Stabilized with Anchors

The three-dimensional shear strength reduction method is used to evaluate the stability of an idealized slope stabilized with anchors, where the soil-anchor interaction is simulated by zero-thickness three-dimensional interface elements, and the effects of the direction angle, position, spacing on the slope stability are numerical studied. The results show that the reinforcing mechanisms of anchors in slopes are to increase the shearing resistance on the slip surface，and the failure mechanism, predicted by SSR, agrees well with the critical slip circle given by Bishop’s simplified method. The better stabilizing effects can be obtained when the anchors are installed with a small angle between the anchor and the horizontal direction, and slightly closer to the slope toe.

A new 3D interface element for three dimensional finite element analysis of FRP strengthened RC beams

The analysis of interfacial stresses in structural component has been the subject of several investigations but it still requires more effort and studies. In this study a general three-dimensional interface element has been formulated for stress and displacement analyses in the interfacial area between two adjacent plate bending element and brick element. Interface element has 16 nodes with 5 degrees of freedom (DOF) in each node adjacent to plate bending element and 3 DOF in each node adjacent to brick element. The interface element has ability to transfer three translations from each side of interface element and two rotations in the side adjacent to the plate element. Stiffness matrix of this element was formulated and implemented in three-dimensional finite element code. Application of this element to the reinforced concrete (RC) beam strengthened with fiber reinforced polymer (FRP) including variation of deflection, slip between plate and concrete, normal and shear stresses distributions in FRP plates have been verified using experimental and numerical work of strengthened RC beams carried out by some researchers. The results show that this interface element is effective and can be used for structural component with these types of interface elements.

Three-Dimensional Nonlinear Finite-Element Analysis of Prestressed Concrete Beams Strengthened in Shear with FRP Composites

Nonlinear finite-element (FE) analysis was carried out to investigate the structural response of prestressed concrete (PC) beams strengthened with fiber reinforced polymer (FRP) composites in shear. Development of the FE model for concrete structures dominated by shear, in particular for FRP-strengthened concrete structures, requires careful consideration in choosing the appropriate elements and constitutive laws to simulate the proper failure mode. The paper presents a new three-dimensional technique to model FRP-strengthened prestressed concrete beams. Most previous work has dealt with two-dimensional analysis of FRP-strengthened reinforced concrete beams. The novel attributes of the proposed model lie in the description of the three-dimensional constitutive material models for each component. The model accounts for the softening behavior of concrete under a triaxial state of stress. A new three-dimensional interface element necessary to capture the debonding failure was proposed. In particular, the effect of the out of plane stress behavior of the FRP-concrete interface, which is currently unavailable through experimental measurements, was carefully evaluated. The use of mechanical anchors to improve the bond behavior was properly simulated. In addition, the prestressing operation and precracking effects were also simulated in the model through a phased analysis technique, which makes it possible to predict the response with respect to the time-dependent behavior of elements and materials. The FE model developed in this study was calibrated through comparison with test results. This paper reports not only on the fundamental investigation of the strengthening effect of FRP composites for PC beams but also on the identification of the damage mechanisms and the progression of failure. The model was shown to provide a good level of correlation with experimental data, and could therefore be used to conduct extensive parameter studies.

Development of a Special Interface Element Between Brick and Plate Bending Elements

In this study a special three-dimensional interface element has been formulated for stress and displacement analyses in bonded joint between two adjacent plate bending and brick elements. Interface element has 16 nodes with 5 degrees of freedom in each node adjacent to plate bending element and 3 D.O.F in each node adjacent to brick elements. The interface element has ability to transfer three translations from each side of interface element and two more rotations in the side adjacent to the plate element. Stiffness matrix of this element was formulated and implemented in three dimensional finite element code. Using experimental and numerical work of strengthened RC concrete beams carried out by researchers, application of this element including variation of deflection, slip between plates and bricks, normal and shear stresses distributions in FRP plates have been verified. The results show, that this interface element is effective and can be used for structural components with this type of interface element.

A fatigue degradation law for cohesive interface elements – Development and application to composite materials

A cohesive zone interface element degradation law is presented for analyzing delamination crack propagation under cyclic loading. Development of the law is based on a detailed study of the numerical cohesive zone and the extraction of strain energy release rate from this zone, enabling a direct link with experimental Paris Law data. The law is implemented using three-dimensional interface elements within the explicit finite element code LS-Dyna. Validation is presented by way of application to composite material fatigue fracture toughness tests; Double Cantilever Beam for Mode I, End Notch Flexure for mode II and Mixed Mode Bending for the mixed mode case. In all cases good agreement with experimental data available in the open literature and/or theoretical solutions was obtained.

Development of three-dimensional interface elements for coupling of non-matching hexahedral meshes

Gluing of a non-matching interface between dissimilar meshes is one of challenging tasks in computational mechanics. The interface element method (IEM) has been developed using an appropriate interpolation scheme between partitioned finite element meshes. The continuity of displacements across the interface is satisfied exactly, and the completeness of interface element shape functions provides a reasonable transfer of strain fields between dissimilar finite element meshes. Research related to the IEM has been mainly accomplished in two-dimensions, because the construction of interface elements in three dimensions is not as simple as the case of two-dimensions. In this paper, a new scheme is presented to construct the interface elements for connecting dissimilar hexahedral finite element meshes with an arbitrarily curved non-matching interface. Element edges crossing any other edges in an interface region are modified into continuous intersection polygons to eliminate overlays and gaps between dissimilar meshes, and these polygons are divided into triangles to create prism-shaped interface elements. Numerical experiments on a linear elasticity problem with non-matching meshes illustrate the effectiveness of the method.

Prediction of Fretting Fatigue Behavior of Metals Using a Fracture Mechanics Approach with Special Consideration to the Contact Problem

A fracture mechanics model has been developed to estimate the fretting fatigue strength and the service life of structural components. Integrated in this model is a contact problem solver that is automated to deal with the geometric and material nonlinearities of the problem. A three-dimensional interface element was developed to model the constitutive laws of the interface. The results demonstrated the capability of the model to predict the conditions under which small fretting-induced fatigue cracks are arrested. The model was validated by predicting the S-N curves produced experimentally for Inconel 600 at high temperature. The prediction of the fretting fatigue limit was found to be in excellent agreement with the experimental results.

Damage analysis in composite laminates by using an interface element

A numerical analysis is performed to study an impact damage accumulation problem in composite laminates. A special three-dimensional interface element is developed based on the cohesive model. The element enables the mesh independent configurations of a crack to be calculated and can treat contact problems of the delaminated area. The energy stored in the element per unit area is defined as a function of continuous relative displacements of the delaminated surface. The energy stored before the perfect separation of the interface is equal to the interlaminar fracture toughness. The softening cohesive relations between the tractions and the relative displacements are given by differentiating the energy function with respect to the relative displacements. The maximum value of traction may coincide with interfacial bonding strength. The element is incorporated in a commercially available finite element code. Crack propagation problems under pure Mode I and Mode II loading conditions for three-dimensional models are calculated to show the validity of the present element. The convergence of solution with mesh refinement is examined. The analytical solutions converge smoothly and agree well with the theoretical ones. The present method may be a good tool to simulate the damage accumulation problem of CFRP laminates.