Cohesive Zone Finite Element Model Research Articles

Effects of randomly distributed interface cohesive strength on the delamination of the REBCO tapes

This paper investigates the effect of randomly distributed interface cohesive strength on the initiation and propagation of delamination of the REBCO tapes. A three-dimensional cohesive zone finite element model (FEM) is established with consideration of randomly distributed interface cohesive strength satisfied three-parameter Weibull distribution, which is used to analyze the influence of the randomness of interface cohesive strength on the delamination performance of tapes under transverse tensile. The simulation results show that the boundary for delamination beginning predicted by the model, considering the randomly distributed interface cohesive strength, has a random character and is closer to the actual situation. Furthermore, parameters that are important to the random Weibull distribution are also investigated. It is shown that the scale parameter and the minimum interface cohesive strength have negligible influence on the delamination strength. Meanwhile, it has a significant impact on the peak value of the stress at delamination initiation in the REBCO layer and its position. For a particular Weibull distribution, its median can be used as constant interface cohesive strength to simulate the macroscopic delamination behavior of the tapes, accurately and efficiently.

Investigation on insertion mechanism of ultrasound guided insertion process based on numerical simulation

AbstractThe insertion of finer Z‐pins is the key factor for increasing the reinforcement effects of Z‐pinned composite laminates. This paper presents a three‐dimensional cohesive zone finite element (FE) model for revealing the insertion mechanism of the ultrasound guided insertion process of fine Z‐pins. The prepreg fracture is modeled based on the cohesive elements, where fracture toughness is obtained from the double insertion method. The contact between the needle and prepreg is simulated by LuGre dynamic friction model. According to model simulation and relevant experiments, compared with nonvibratory insertion, smaller insertion force, earlier surface fracture and slighter ply crimp can be observed in the ultrasound guided insertion process. In addition, the prepreg forms an initial crack firstly after needle insertion, followed by a final crack due to needle extraction and prepreg springback. The effects of needle diameter on the insertion force and crack length are discussed. It can be concluded that larger needle diameter can lead to greater insertion force and initial crack length, but has little effect on the final crack length.

Analysis of mechanical failure at the interface between graphite particles and polyvinylidene fluoride binder in lithium-ion batteries

The capacity fade corresponding to the mechanical failure of active materials is one of hurdles to overcome in the widespread of echo-friendly vehicles. However, the mechanisms of the mechanical failure at the electrode are not fully understood. In this study, the initiation and propagation of debonding at the interface between an active particle and a binder are investigated using a coupled electrochemical-mechanical and cohesive-zone finite-element model. The effects of particle sizes and lithiation kinetics on the progressive growth of interfacial debonding are studied, and critical states of charges are determined. The normal and shear tractions at the interface are systematically analyzed to understand their role in debonding behavior. The simulation results show that the interfacial debonding is less likely to happen as the particle size and C-rate increase, which is opposite to the inner-particle fracture behavior. The numerical study indicates that there is a trade-off between the inter-particle failure and inner-particle fracture. This study suggests that the binder effect needs to be included in the theoretical model for better understanding of the mechanical failure at the electrode. The debonding failure maps provided from the study can assist in engineering design of active materials and safe operation of batteries.

Recycled Stone/ABS particulate composite: Micromechanical finite element fracture analysis

New stone composite samples, fabricated using nano- to micro-sized recycled granite particles with irregular shapes and random distribution within a ABS matrix, demonstrate a highly nonlinear and complex fracture behavior. To model this behavior, a mixed mode cohesive zone finite element model is identified using the single-leg bending (SLB), in order to represent the granite particles-ABS interfacial debonding. An inverse methodology is then proposed to determine the parameters of the cohesive zone (CZM). A direct method based on J-integral approach is employed to determine the effective parameters of the traction-separation law. A two dimensional micromechanical extended finite element model (XFEM) of the composite is generated using X-ray micro-computed tomography (XMT) to mimic the actual shape of the particles. Finally, the identified cohesive model parameters have been employed to simulate the crack growth within the granite particulates/ABS composite. The comparison of the numerical and experimental results of the SLB test demonstrated the effectiveness of the proposed simulation framework.

Uncertainty analysis of hydraulic fracture height containment in a layered formation

The prediction of hydraulic fracture height growth is of extreme interest in various engineering practices. To fully understand the dependence of the fracturing height in complex underground geological structures, it is crucial to develop theoretical and numerical hydraulic fracturing models to identify the key variables and their interactions to hydraulic fracture height containment. In this work, we adopt a three-dimensional hydro-mechanical coupling cohesive zone finite element model supported by logging data from a practical engineering project. A novel response surface method with Box–Behnken design is introduced to evaluate the statistical significance of tested variables and to forecast the optimal variable combinations for hydraulic fracture height. The key controlling variables are sorted according to their statistical significance from the analysis of variance, and only the minimum lateral stress ratios in mudstone layer and conglomerate layer are highly statistically significant. The minimum lateral in situ stress contrast is the predominant influence of fracture height containment regarding to their significant negative correlation, while the Young’s modulus contrast is probably not an important parameter in terms of direct control of fracture height. Upon optimization, 41 optimized variable combinations were achieved and could be served as references in regulating this engineering practice or even similar events.

Predicting environmental degradation of adhesive joints using a cohesive zone finite element model based on accelerated fracture tests

A framework was developed to predict the fracture toughness of degraded adhesive joints by incorporating a cohesive zone finite element (FE) model with fracture data of accelerated aging tests. The developed framework addresses two major issues in the fracture toughness prediction of degraded joints by significant reduction of exposure time using open-faced technique and by the ability to incorporate the spatial variation of degradation with the aid of a 3D FE model. A cohesive zone model with triangular traction-separation law was adapted to model the adhesive layer. The degraded cohesive parameters were determined using the relationship between the fracture toughness, from open-faced DCB (ODCB) specimens, and an exposure index (EI), the time integration of the water concentration. Degraded fracture toughness predictions were done by calculating the EI values and thereby the degraded cohesive parameters across the width of the closed joints. The framework was validated by comparing the FE predictions against the fracture experiment results of degraded closed DCB (CDCB) joints. Good agreement was observed between the FE predictions and the experimental fracture toughness values, when both ODCB and CDBC were aged in the same temperature and humidity conditions. It was also shown that at a given temperature, predictions can be made with reasonable accuracy by extending the knowledge of degradation behavior from one humidity level to another.

Finite-Element Simulation of a Hydraulic Fracture Interacting With a Natural Fracture

Summary In this paper, the problem of a hydraulic fracture (HF) interacting with a pre-existing natural fracture (NF) has been investigated with a cohesive zone finite-element model. The model fully couples fluid flow, fracture propagation, and elastic deformation, taking into account the friction between the contacting fracture surfaces and the interaction between the HF and the NF. The effect of the field conditions—such as in-situ stresses, rock and fracture mechanical and geometrical (initial conductivity of the NF) properties, intersection angle, and the treatment parameters (fracturing fluid viscosity and injection rate)—on the HF propagation behavior has been analyzed. The finite-element-modeling results provide detailed quantitative information on the development of various types of HF/NF interaction, interfacial stress distribution, fracture-geometry evolution, and injection-pressure history, and allow us to gain an in-depth understanding of the relative roles of various parameters. The value of a parameter calculated as the product of fracturing-fluid viscosity and injection rate can be used as an indicator to gauge if crossing or diverting behavior is more likely. In addition, using a finite-element approach allows the analysis to be extended to include the effects of fluid leakoff and poroelastic effect, and allows the study of HF height growth through a system of nonhomogeneous layers and their bedding planes.

Comparison of cohesive zone elements and smoothed particle hydrodynamics for failure prediction of single lap adhesive joints

ABSTRACTThis research investigates the use of a meshless smoothed particle hydrodynamics (SPH) method for the prediction of failure in an adhesively bonded single lap joint. A number of issues concerning the SPH based finite element modelling of single lap joints are discussed. The predicted stresses of the SPH finite element model are compared with the results of a cohesive zone based finite element model. Crack initiation and crack propagation in the adhesive layer are also studied. The results show that the peel stresses predicted by the SPH finite element model are higher and the shear stresses are lower than those predicted by the cohesive zone finite element model. The crack initiation and propagation response of the two models is similar, however, the SPH finite element model predicted a lower failure load than the cohesive zone finite element model. It is concluded that the current implementation of SPH method is a promising method for modelling cohesive failure in bonded joins but requires further development to allow for interfacial crack growth and better stress prediction under tensile loading to compete with existing methods.

Determination of interfacial adhesion energies of thermal barrier coatings by compression test combined with a cohesive zone finite element model

Determination of interfacial adhesion energies of thermal barrier coatings is important for understanding failure mechanisms and predicting their lifetime. Combined compression test with a cohesive zone finite element model, it is shown that the interfacial adhesion energy is in the range of 100–130J/m2. Based on the nonlinear delamination theory, the critical interfacial adhesion energy of delamination is 120J/m2 and the corresponding loading phase angle is −56°. With the increase of the half-length of the crack, the crack propagation tends to be steady with a steady-state interface energy release rate of 150J/m2, and delamination experiences almost pure mode II. These results obtained from finite element simulations and theoretical analyses are in good agreement with the available values determined by other testing methods reported in the literatures, which confirms the validity of this method.

Numerical study on interaction of surface cracking and interfacial delamination in thermal barrier coatings under tension

The interaction of surface cracking and interfacial delamination in thermal barrier coatings under tension is investigated by using a cohesive zone finite element model. It is found that the surface crack density has a significant effect on the initiation and propagation of interfacial delamination. The interfacial delamination length decreases with increase of the surface crack density. The influence of ceramic coating thickness and interfacial adhesion parameters on surface cracking and interfacial delamination is discussed. It is shown that the saturated crack densities decrease with increase of the ceramic coating thickness and interfacial delamination length, and the critical surface crack density without interfacial delamination decreases as the interfacial adhesion energy increases. The results imply that the larger the surface crack density and interfacial adhesion energy are, the less the probability of interfacial delamination.

Microscopic model for fracture of crystalline Si nanopillars during lithiation

Silicon (Si) nanostructures are attractive candidates for electrodes for Li-ion batteries because they provide both large specific charging capacity and less constraint on the volume changes that occur during Li charging. Recent experiments show that crystalline Si anodes expand highly anisotropically through the motion of a sharp phase boundary between the crystalline Si core and the lithiated amorphous Si shell. Here, we present a microscopic model to describe the size-dependent fracture of crystalline Si nanopillars (NPs) during lithiation. We derive a traction–separation law based on the plastic growth of voids, which, in turn, is used in a cohesive zone-finite element model. The model allows for both the initiation of cracking and crack growth. The initial size and spacing of the nanovoids, assumed to be responsible for the fracture, together with the computed facture toughness, are chosen to conform to recent experiments which showed the critical diameter of Si NPs to be 300–400 nm. The anisotropy of the expansion is taken into account and that leads naturally to the observed anisotropy of fracture. The computed work of fracture shows good agreement with recent experimental results and it may be possible to use it to describe the failure for other loading and geometries.

Cohesive zone modeling of ductile tearing process in brazed joints

Ductile tearing process in low carbon steel brazed joints with copper filler metal is studied using the Cohesive Zone Model. The Cohesive Zone Model is characterized by two parameters related to the cohesive strength and cohesive energy. A new method is developed to estimate the Cohesive Zone Model parameters through direct experimental measurements and numerical modeling. The cohesive energy of the brazed joints is obtained from the fracture test results performed on the single-edge notched bend specimens. Based on the obtained cohesive energy parameter, the fracture test is simulated using a cohesive zone finite element model. A unique value for the joint cohesive strength is determined by best fitting the finite element results to the experimental load-crack mouth opening displacement curves. The merit of the characterized Cohesive Zone Model is explored by finite element modeling of the tensile test performed on the single-edge notched tension specimens. The load-crack mouth opening displacement curve obtained from the finite element modeling conforms to the corresponding tensile test results. Furthermore, the effect of the crack tip stress constraint on the plastic zone shape and size is successfully captured by the model. The good agreement between the finite element simulation results and the experimental data demonstrates the applicability of the Cohesive Zone Model for fracture analysis of the brazed joints.

Finite element modelling of viscosity-dominated hydraulic fractures

Hydraulic fracturing is a highly effective technology used to stimulate fluid production from reservoirs. The fully 3-D numerical simulation of the hydraulic fracturing process is of great importance to developing more efficient application of this technology, and also presents a significant technical challenge because of the strong nonlinear coupling between the viscous flow of fluid and fracture propagation. By taking advantage of a cohesive zone method to simulate the fracture process, a finite element model based on existing pore pressure cohesive finite elements has been established to simulate the propagation of a viscosity-dominated hydraulic fracture in an infinite, impermeable elastic medium. Selected results of the finite element modelling and comparisons with analytical solutions are presented for viscosity-dominated plane strain and penny-shaped hydraulic fractures, respectively. Some important issues such as mesh transition and far-field boundary approximation in the cohesive finite element model have been investigated. Excellent agreement between the finite element results and analytical solutions for the limiting case where the fracture process is dominated by fluid viscosity demonstrates the capability of the cohesive zone finite element model in simulating the hydraulic fracture growth.

Modeling Fracture and Delamination of Spray-Applied Fire-Resisting Materials under Static and Impact Loads

A specially developed two-dimensional cohesive zone finite element (CZFE) scheme is applied to simulate the fracture and delamination phenomena that occur in spray-applied fire-resisting material (SFRM) on steel structures. A cohesive zone material model for the SFRM is introduced and utilized to model both the internal cohesion in SFRM and the interfacial adhesion at the steel-SFRM interface. The CZFE model is validated by comparing predictions from the model with results from an adhesion test conducted at ambient temperature. The validated model is successfully applied to simulate the spontaneous initiation and propagation of cracks in the SFRM under static and impact loads. Results from the numerical studies indicate that the proposed model is capable of predicting the initiation and propagation of cracks within the insulation material and at the interface. The results show that the development of transverse cracks in the insulation layer help prevent further delamination of the SFRM. Also, it was found that for larger thicknesses of insulation, delamination occurs at less direct tension or flexural stresses. Results from impact simulations show that there is an optimum insulation thickness for resisting the delamination induced by impact loads.

A partition of unity‐based multiscale approach for modelling fracture in piezoelectric ceramics

AbstractThe development of models for a priori assessment of the reliability of micro electromechanical systems is of crucial importance for the further development of such devices. In this contribution a partition of unity‐based cohesive zone finite element model is employed to mimic crack nucleation and propagation in a piezoelectric continuum. A multiscale framework to appropriately represent the influence of the microstructure on the response of a miniaturized component is proposed. It is illustrated that using the proposed multiscale method a representative volume element exists. Numerical simulations are performed to demonstrate the constitutive homogenization framework. Copyright © 2009 John Wiley & Sons, Ltd.

Cohesive zone finite element-based modeling of hydraulic fractures

ABSTRACT Hydraulic fracturing is a powerful technology used to stimulate uid production from reservoirs. The fully 3-D numerical simulation of the hydraulic fracturing process is of great importance to the effcient application of this technology, but is also a great challenge because of the strong nonlinear coupling between the viscous ow of uid and fracture propagation. By taking advantage of a cohesive zone method to simulate the fracture process, a finite element model based on the existing pore pressure cohesive finite elements has been established to investigate the propagation of a penny-shaped hydraulic fracture in an infinite elastic medium. The effect of cohesive material parameters and uid viscosity on the hydraulic fracture behaviour has been investigated. Excellent agreement between the finite element results and analytical solutions for the limiting case where the fracture process is dominated by rock fracture toughness demonstrates the ability of the cohesive zone finite element model in simulating the hydraulic fracture growth for this case.

Modelling inter- and transgranular fracture in piezoelectric polycrystals

A cohesive zone finite element model for quasi-static fracture of piezoelectric polycrystals is proposed. Interface elements are used to model both inter- and transgranular fracture. Electromechanical constitutive relations are derived by enhancing commonly used mechanical traction-opening laws with relations for a parallel plate capacitor. Numerical simulations demonstrate that the proposed model correctly mimics several experimentally observed phenomena. Most importantly the switch from mainly intergranular to mainly transgranular fracture with increasing grain size is modelled correctly. The model also correctly mimics the influence of an electric field on the ultimate load.