Cohesive Element Technique Research Articles

Delamination buckling of a laminated composite shell panel using cohesive zone modelling

Abstract Laminated composite shell panels take part in several engineering structures. Due to their complex nature, failure modes in composites are highly dependent on the geometry, direction of loading and orientation of the fibers. However, the design of composite parts is still a delicate task because of these fiber failure modes, which includes matrix failure modes or other so-called interlaminar interface failure such as delamination, that corresponds to the separation of adjacent layers of the laminate as a consequence of the weakening of interface layer between them. In this work, impact-induced delamination represented as a circular single delamination is investigated, as it can reduce greatly the structural integrity without getting detected. Furthermore, attention is focused on its effect upon the post-buckling response and the compressive strength of a composite panel. The delamination buckling was modelled using the cohesive element technique under Abaqus software, in order to predict delamination growth and damage propagation while observing their effects on the critical buckling load.

Study on vertical multifracture propagations in deep shale reservoir with natural fracture network

AbstractBuilding a complex fracture network in a deep shale gas reservoir during multicluster hydraulic fracturing is challenging. On the one hand, hydraulic fractures tend to propagate along shale bedding planes, thus leading to a limited hydraulic fracture height; on the other hand, under the effect of high in situ stress and weak plane of fractures, multihydraulic fractures can hardly initiate and propagate uniformly. All of these will jeopardize the performance of hydraulic fracturing. This paper considers the influence of natural fracture network, shale beddings, fracturing‐fluid leakage, and high in situ stresses, and builds a numerical model to simulate multifracture propagations along vertical direction during hydraulic fracturing in deep shale reservoirs. The model is developed based on the theory of solid–fluid coupling and finite element method with pore pressure cohesive element technique are used to simulate multicluster fracture initiation and propagation. Moreover, the model is verified by published experiment data, and a good agreement between model and experiment results is observed. The influences of pump rate and fracturing‐fluid viscosity on fracture geometry are discussed, and the flow dynamics around each perforation cluster under different perforation parameters are also studied. Finally, suggestions to improve overall outcome of multicluster hydraulic fracturing are also provided.

Fracture behavior and self-sharpening mechanisms of polycrystalline cubic boron nitride in grinding based on cohesive element method

Unlike monocrystalline cubic boron nitride (CBN), polycrystalline CBN (PCBN) shows not only higher fracture resistance induced by tool-workpiece interaction but also better self-sharpening capability; therefore, efforts have been devoted to the study of PCBN applications in manufacturing engineering. Most of the studies, however, remain qualitative due to difficulties in experimental observations and theoretical modeling and provide limited in-depth understanding of the self-sharpening behavior/mechanism. To fill this research gap, the present study investigates the self-sharpening process of PCBN abrasives in grinding and analyzes the macro-scale fracture behavior and highly localized micro-scale crack propagation in detail. The widely employed finite element (FE) method, together with the classic Voronoi diagram and cohesive element technique, is used considering the pronounced success of FE applications in polycrystalline material modeling. Grinding trials with careful observation of the PCBN abrasive morphologies are performed to validate the proposed method. The self-sharpening details, including fracture morphology, grinding force, strain energy, and damage dissipation energy, are studied. The effects of maximum grain cut depths (MGCDs) and grinding speeds on the PCBN fracture behavior are discussed, and their optimum ranges for preferable PCBN self-sharpening performance are suggested.

Characterization of sandwich composite T-joints under different ageing conditions

High-tech demands of the aviation industry require a detailed knowledge of the mechanical and structural response of composite structures. This contribution presents experimental investigations on composite honeycomb sandwich T-joint connections. To understand the effect of loading and ageing on the adhesively bonded joints, quasistatic tension experiments have been performed with the original T-joints and with two sets of artificially aged specimen. The accelerated ageing was enforced by thermal cycling with temperatures in the range of -35°C to 70°C.The failure behavior of the original and the aged specimens are compared to provide primary data for analyzing the behavior of honeycomb sandwich T-joints in limit conditions. A fractographic analysis is performed to determine the failure modes. Additionally the provided data are verified with three-dimensional finite element analyses using a cohesive element technique. The achieved results provide not only new data for designers but can also be used for future computational models of sandwich structures.

The phase-field approach as a tool for experimental validations in fracture mechanics

In a phase-field approach to fracture crack propagation is modeled by means of an additional continuous field. In this paper, two problems of linear elastic fracture mechanics are studied experimentally and numerically in order to evaluate the practicability of the phase-field approach and to validate the measured parameters. At first, a three-point bending experiment of silicon dies is simulated assuming static plate bending. Then, wave propagation and spallation in a Hopkinson bar test are analyzed in a dynamic regime. The simulations show that phase-field fracture reproduces the experimental results with high accuracy. The results are comparable to other fracture simulations, e.g., the cohesive element technique. In total, the phase-field approach to fracture is capable of tracking crack evolution in a very convenient and quantitatively correct way.

Analysis of the stress states and interface damage in a particle reinforced composite based on a micromodel using cohesive elements

In this work, uniaxial tensile loading was simulated to explain the effect of the interface and varying particle shapes in particle reinforced composite models based on experiments. The cohesive element technique was applied alongside an ABAQUS user-subroutine UVRAM. The effect of the interface thickness and strength were also considered. The simulation results for various stress states (such as stress triaxiality, soft coefficient and Lode parameter) and the interface degradation Scalar Stiffness Degradation Variable (SDEG) were analyzed in detail. The particle shape and interface geometry strongly influenced the distribution of stress states, eventually influencing the integrity of the particle reinforced composites. Particles with a large aspect ratio that were also perpendicular to tensile loading direction were easy to crack, while those with a smaller aspect ratio were prone to interface debonding from particle poles.

Multi-Scale Fe Modeling Inconel718 Machining Process and Crack Initiation of Brittle Particle

nconel718 is particle reinforced metal matrix composites widely applied in important fields. To evaluate the impact of particles on the machined subsurface in Inconel718 during high-speed machining operation, a multi-scale orthogonal cutting finite element (FE) model is established. A cohesive element technique is adopted to predict particle crack initiation process. The multi-scale FE model is validated with experimental data in terms of cutting forces and chip morphology. The simulation reveals that particle has a great influence on surface roughness and the feed force when particles are located in the sub-surface within the depths of 30μm, and the cutting process has less effect on the particle crack initiation when the particles in the depths of more than 40μm or deeper. The interaction effects generated from particle sizes in the same depth are investigated on the cutting process and particle crack initiation.

Parametric Study on Cohesive Element for Composite Fuselage Model

In this paper, a numerical simulation on a new fabrication miniature composite fuselage structure- a woven composite laminated with an adhesively bonded butt joint under the axial compression loading is presented. A FEA via Abaqus/Explicit was utilized to capture the complete compressive responses to predict the crushing behaviour and its mechanical strength from the initial compression loading till its final failure mode. A woven C-glass fiber/epoxy 200 g/m2 composite laminated [908] with the orthotropic elastic material properties is modeled as a continuum composite layup in the proposed numerical model. The adhesively bonded joint progression was modeled using the cohesive element technique. The proposed model was used to observe the crushing load and collapse modes under the axial compression impact. The finite element results showed a good agreement with the experimental results under the actual quasi-static tests. The validation code was extended to further undergo parametric studies in order to visualise the effect of angle orientations and special laminate cases as to attain the optimum design criteria for the proposed composite structure.

A generalized cohesive element technique for arbitrary crack motion

A computational method for arbitrary crack motion through a finite element mesh, termed as the generalized cohesive element technique, is presented. In this method, an element with an internal discontinuity is replaced by two superimposed elements with a combination of original and imaginary nodes. Conventional cohesive zone modeling, limited to crack propagation along the edges of the elements, is extended to incorporate the intra-element mixed-mode crack propagation. Proposed numerical technique has been shown to be quite accurate, robust and mesh insensitive provided the cohesive zone ahead of the crack tip is resolved adequately. A series of numerical examples is presented to demonstrate the validity and applicability of the proposed method.