Cohesive Zone Elements Research Articles

Membrane mode enhanced cohesive zone element

PurposeIn certain cases, traction–separation laws do not reflect the behaviour sufficiently so that thin volumetric elements, Internal Thickness Extrapolation formulations, bulk material projections or various other approaches are applied. All of them have disadvantages in the formulation or practical application.Design/methodology/approachDamage within thin layers is often modelled using at cohesive zone elements (CZE). The constitutive behaviour of cohesive zone elements is usually described by traction–seperation laws (TSLs) that consider the (traction separation) relation in normal opening and tangential shearing direction. Here, the deformation (separation) as well as the reaction (traction) are vectorial quantities.FindingsIn this contribution, a CZE is presented that includes damage from membrane modes.Originality/valueMembrane mode-related damaging effects that can be seen in physical tests that could not be simulated with standard CZEs are well captured by membrane mode–enhanced cohesive zone elements.

Analysis of crack-arrest design features for adhesively bonded composite joints: An experimental and numerical study

In this paper a systematic experimental and numerical study on mechanical design features to arrest fatigue crack growth in adhesive joints is performed. A material model for fatigue crack growth analysis based on a cohesive zone element formulation is presented together with a methodology to compare design features and to identify and quantify fundamental crack-arrest mechanisms. Results show that the influence of crack-arrest design features on fatigue crack growth can be successfully modelled using the developed material models and a mesoscopic representation of design features. A combination of reduced crack front loading via local reinforcement and Mode I reduction from through-thickness reinforcement are necessary to efficiently arrest crack growth. A simple local reduction of peel stresses does not lead to a sustainable crack-arrest and should therefore be avoided. Additionally, the two-dimensional growth of a crack in an adhesive joint can be exploited by increasing the effective crack front length. Finally, it is shown that a compression preload applied to the mechanical design features introduces through-thickness stresses to the adhesive that significantly reduce local fatigue crack growth rates.

Technical Note: An inversion algorithm to estimate maximum and minimum horizontal stress based on field test data for sleeve fracturing

An algorithm is developed to estimate maximum and minimum horizontal stress using experimental data from sleeve fracturing experiments. The algorithm is developed by analyzing the crack initiation, propagation and interaction behavior between primary and secondary cracks based on the Finite Element Method with Cohesive Zone elements. Five key quantities can be obtained from data curves and comprise the basis of the algorithm in a manner consistent with an approximate model based on stress analysis around the borehole. The algorithm has been validated by 100 synthetic data cases covering various parameter combinations. Moreover, quantifying the degree of uncertainty in the stress prediction indicates strongest dependence on detecting when the borehole deformation from the first fracture(s) is impacted by growth of secondary fracture(s). Validity based on simulated data motivates new methods for high resolution strain sensing during sleeve fracturing especially for the purpose of accurately detecting secondary fracture initiation.

Numerical analysis of injection-induced fault reactivation using hydro-mechanical coupled finite element model with cohesive zone elements

Numerical analysis of injection-induced fault reactivation using hydro-mechanical coupled finite element model with cohesive zone elements

Computational evaluation of long-term ravelling susceptibility of Permeable Friction Courses (PFC)

Ravelling is a main distress in Permeable Friction Courses (PFC). This damage process is enhanced by the presence of moisture and ageing, which further reduces the overall durability of the mixtures. This study uses Finite Element (FE) methods to assess long-term ravelling susceptibility of PFC. Different two-dimensional (2D) PFC microstructures were randomly generated through a Microstructure Generator (MG) and Discrete Element (DE) gravimetric methods. These microstructures were located on top of a conventional pavement and subjected to a moving wheel load under different traffic operation conditions. PFC ravelling was assumed to occur at the asphalt mortar located at the stone-on-stone contacts. The linear viscoelastic and fracture properties of the PFC asphalt mortar were experimentally obtained after subjecting the material to long-term ageing conditions and multiple water moisture cycles, which represent several in-service years. Zero thickness Cohesive Zone Elements (CZE) were included within the mortar-mortar contacts of the PFC to better quantify the potential initiation of ravelling. The results show that the ravelling susceptibility of a PFC is drastically affected by the loading conditions (e.g., load magnitude, vehicle breaking over the pavement, vehicle speed) and the environmental and mechanical degradation of the asphalt mortar when subjected to in-service conditions.

Study on toughening mechanisms of pyrolytic carbon interface layer in Cf/ZrB2-SiC composites using in-situ tensile experimental and numerical methods

The toughening mechanism in continuous fiber toughened ZrB2-SiC ceramic matrix (Cf/ZrB2-SiC) composites was studied upon introduction of pyrolytic carbon coating at the fiber/matrix interface. The real-time deformation behavior, surface crack initiation and evolution of Cf/ZrB2-SiC composites under tensile load were studied using in-situ scanning electron microscopy (SEM) to determine the typical damage modes and toughening mechanisms. A refined microscopic representative volume element (RVE) inserting the cohesive zone elements was established to study the PyC interface layer damage by using finite element method. It was found that PyC interface layer damage induced by thermal residual stress (TRS) was one of critical factors affecting the mechanical performance of the Cf/ZrB2-SiC composites. The critical thickness of the interface layer was also further determined by analyzing the effect of interface layer thickness on the distribution of TRS, which can guide the design of PyC interface layer for manufacturing the Cf/ZrB2-SiC composites.

2D and 3D simulations of dynamic delamination in curved unidirectional CFRP laminates subjected to moment/axial combined loading

Dynamic failure of 30-ply curved unidirectional CFRP laminate under quasi-static moment/axial combined loading used in the experiments of Tasdemir (2018) is investigated numerically. 2D and 3D explicit finite element analyses are carried out using cohesive zone elements and contact interactions to simulate progressive delamination. In both analyses, dynamic delamination initiates at the maximum radial stress location. The resultant crack propagation in both 2D and 3D simulations is observed to be intersonic in the arm regions, with lower crack tip speeds observed for the 3D case. In 3D simulations, a non-uniform crack front is observed, with the crack nucleating at the middle of the width, propagating to the edges and both arms at sub-Rayleigh speed before continuing to propagate in the arms at intersonic speeds. Intermittent local contact regions are observed in 2D simulations behind the crack tip, which are also observed in the 3D simulations at the free edge with a continuous contact line reaching the middle of the crack front, emphasizing the three-dimensional nature of the delamination growth. Load-displacement curves of both 2D and 3D simulations show good correlations with experimental results.

Modeling of interface failure in a thermal barrier coating system on Ni-based superalloys

In the present work, microstructural analysis and finite element modelling are employed to study interface cracking behaviour in a thermal barrier coating (TBC) on a single-crystal Ni-based superalloy. The cohesive zone elements are implemented in the model to simulate interfacial debonding between the top-coat (TC), thermally grown oxide (TGO) and bond-coat (BC). To evaluate the effect of the interface geometry on the residual stress state and cracking behaviour, two units of the TGO profile are analysed: a regular sinusoidal undulation with constant thickness and an irregular (unevenly thick) TGO layer with symmetrical penetrations into the TC and BC layers. It has been found that the morphology of the TGO layer influences not only the magnitude and distribution of residual stresses but also governs the mechanisms of interfacial failure. For the regular TGO shape, the debonding cracks form at the peak of TGO/BC interface and at the valley of TC/TGO interface. Whereas only the TC/TGO interfacial debonding is observed in case of the irregular TGO profile. The debondings induce the stress redistribution in TBC layers that depends on which interface and to what extent is damaged. The TBC system with the regular TGO layer appears to be a more prone to interface failure than that one with the irregular TGO shape. However, much higher compressive stresses in the TGO layer are observed in the latter case. Possible scenarios of the TBC failure in terms of further cracks propagation are discussed.

Finite Element model of concrete repaired by High Molecular Weight Methacrylate (HMWM)

Epoxy is widely used to fill concrete cracks that are less than a millimeter in width to protect the steel rebars from corrosion. However, the mechanical behavior of epoxy-repaired concrete remains vastly unknown. In order to understand whether or not epoxy can be used to recover the mechanical properties of damaged concrete, we provide a quantitative assessment of concrete repaired by injection of High Molecular Weight Metacrylate (HMWM). Uniaxial compression tests and three-point bending tests were conducted on cut-and-repaired specimens. The experiments were simulated with the Finite Element Method (FEM), in which concrete was assigned a constitutive model that combines continuum damage mechanics and plasticity and in which the concrete/HMWM interface was modeled with bilinear softening cohesive zone elements (CZEs). The numerical model was calibrated and validated against the experimental results. Steel-reinforced concrete (RC) beams were subjected to three-point bending to produce cracks. The beams were then repaired and reloaded. We used Digital Image Correlation (DIC) to identify the zones of high maximum principal strain after the first loading cycle. These zones were modeled with repaired concrete elements and HMWM CZEs to simulate the second load cycle. The load-displacement curves, damage distributions and strain fields obtained numerically are in agreement with those obtained experimentally, which validates the proposed model. Our simulation results suggest that HMWM can penetrate cracks of width 0.01 mm and above by gravity. We also found that HMWM reparation increases concrete stiffness and strength if cracks in concrete members are over 0.1 mm in width, in which case, the load capacity of repaired RC beams is 30–40% higher than that of as-built RC beams.

Size effect in flexural behaviour of unidirectional GFRP composites

In this paper, the size effect in unidirectional (UD) laminated glass-fibre reinforced plastic (GFRP) composites subjected to quasi-static bending loading was investigated: the sensitivity of a specimen’s mechanical behaviour and failure mechanism to its geometry was studied. Composite beams with different numbers of 0° unidirectional plies were tested and their post-deformation structures were analysed microscopically. In the subsequent simulations, the intraply damage was modelled using continuum damage mechanics, implemented as a user-defined VUMAT subroutine in ABAQUS/Explicit, while cohesive zone elements were employed to characterize the delamination between different plies. It was observed that the flexural failure triggered the multiple delaminations; their location was studied. The influence of the size effect on the bending response of the UD composite beams was analysed in depth. The findings of the current study can be used to design modern structures made of composite materials.

Applying Membrane Mode Enhanced Cohesive Zone Elements on Tailored Forming Components

Forming of hybrid bulk metal components might include severe membrane mode deformation of the joining zone. This effect is not reflected by common Traction Separation Laws used within Cohesive Zone Elements that are usually applied for the simulation of joining zones. Thus, they cannot capture possible damage of the joining zone under these conditions. Membrane Mode Enhanced Cohesive Zone Elements fix this deficiency. This novel approach can be implemented in finite elements. It can be used within commercial codes where an implementation as a material model is beneficial as this simplifies model preparation with the existing GUIs. In this contribution, the implementation of Membrane Mode Enhanced Cohesive Zone Elements as a material model is presented within MSC Marc along with simulations showing the capabilities of this approach.

Veneer-based timber circular hollow section beams: Behaviour, modelling and design

Various forms of timber hollow structural profiles have either been proposed in the literature or are already commercially available. Tests performed on Circular Hollow Section (CHS) beams showed failure modes not usually encountered in timber structures. For relatively thin-walled profiles, a sudden failure in the compression zone, with the opening of the cross-section, was observed. To confidently use and market CHS timber products, design rules considering all possible failure modes must be developed. This paper presents a Finite Element (FE) model of CHS timber beams which captures all experimentally observed failure modes. Cohesive zone elements were used to model the quasi-brittle failure modes of the timber material. The model was validated against ten experimental tests performed on CHS of three different cross-sectional slenderness and manufactured from juvenile hardwood Gympie messmate (Eucalyptus cloeziana) rotary peeled veneers. The model was found to accurately capture the measured structural behaviour and resulted in an average experimental-to-predicted bending capacity ratio of 1.02. The model was also used to explain the mechanisms leading to the sudden compressive failure mode. A parametric study was finally performed on 72 CHS beams of different cross-sectional slenderness. Results showed a strong correlation between the cross-sectional slenderness ratio and section capacity. Design rules are proposed and discussed.

Micron-scale experimental-numerical characterization of metal-polymer interface delamination in stretchable electronics interconnects

Understanding the mechanical behavior and failure mechanisms of stretchable electronics is key in developing reliable and long-lasting devices. In this work a micron-scale stretchable system consisting of an aluminum serpentine patterned interconnect adhered to a polyimide substrate is studied. In-situ experiments are performed where the stretchable sample is elongated, while the surface topography is measured using a confocal microscope. From the resulting height profiles the microscopic three-dimensional deformations are extracted using an adaptive isogeometric digital height correlation algorithm. The displacement information is compared to realistic numerical simulations, in which the interface behavior is described by cohesive zone elements. It is concluded that despite fitting the traction separation law parameters, the model fails to correctly capture the distinct out-of-plane buckling (with magnitude of a few micron) of the interconnect. The model is updated with residual stresses resulting from processing and crystal plasticity induced behavior (decreased yield strength) in the aluminum layer, but both measures are not resulting in the experimentally observed deformations. Finally, mixed-mode cohesive zones are implemented, in which the properties are different in the shear and normal direction. After fitting the corresponding parameters to the experimental data, the model shows realistic in-plane and out-of-plane deformations. Also a predictive simulation for a different geometry results in the correct experimentally measured behavior. It is concluded that the aluminum-polyimide interface mode-angle dependency explains the observed microscopic failure mode of local delamination and buckle formation.

Experimental and numerical investigation of transverse shear behavior of glass-fibre composites with embedded vascular channel

Interply and interplay damage behavior of glass fiber composites with microvascular channels were investigated in this study. Short beam flexural tests and finite element analysis were performed according to ASTM D2344 for two stacking configurations, [90/0]3s and [0/90]3s. Specimens with and without channel (control specimens) were analyzed to investigate the channel effect in detail. In the finite element simulations, the intraply matrix damage was modeled using a continuum damage mechanics based LarC04 damage initiation criterion, implemented via a user-defined VUMAT subroutine in ABAQUS/Explicit. Interlaminar damage was modeled using cohesive zone elements that were introduced between the plies. Experimentally and numerically obtained load-displacement curves and failure patterns were in good agreement. The influence of the presence of vascular channel on the flexural response of the composite short beams was in-depth analyzed. An increase in the shear strength of channeled specimens was observed for [90/0]3s compared to the control samples.

Nonlinear augmented finite element method for arbitrary cracking in large deformation plates and shells

AbstractThis article presents a nonlinear augmented finite element method (N‐AFEM) for the analysis of arbitrary crack initiation and propagation in large deformation plates and shells. The FE formulations for plate/shell elements and a shell‐like cohesive zone element, both with explicit consideration of geometric nonlinearity, have been derived in detail. The geometrically nonlinear shell‐like cohesive element has the essential feature of 3D but with crack displacements directly extracted from midplane shell element nodes, which enables an accurate description of crack propagation in shells and plates under large deformation. Furthermore, a novel augmentation process that can explicitly account for the discontinuous displacement fields of cracked elements without the need of extra nodes or nodal DoFs has been develop based on a nonlinear Newton‐Raphson method. The numerical performance of the N‐AFEM in modeling a number of benchmark shell/plate fracture problems demonstrates that the method is efficient, accurate, and robust.

Sequential multiscale model to study crack tip behavior in bi-crystalline graphene

The aim of this research article is to develop a sequential multiscale model to study the inter-granular fracture behavior in bi-crystalline graphene. A multiscale model encompasses the microscale behavior at a macroscale level. A sequential multiscale model was developed by defining the traction separation law (TSL), using atomistic simulations, which was later on used to quantify damage in cohesive zone elements in continuum based finite element based simulations. Sequential multiscale models constitute developing bi-crystalline graphene configuration in the environment of molecular dynamics and capture the intergranular crack propagation in graphene. In the molecular dynamics based simulations, symmetrical and asymmetrical tilt grain boundaries were generated in conjunction with edge crack. The TSL derived from these simulations helps in improving the accuracy of continuum level models for predicting intergranular fracture. Spatial stress distribution in the vicinity of the crack tip as well as stress values were captured and compared for atomistic levels with a continuum level for the validation of sequential multiscale models.

Numerical analysis of different fracturing mechanisms between supercritical CO2 and water-based fracturing fluids

Hydraulic fracturing using water-based fluid consumes a large amount of freshwater resources and pollutes a reservoir by substantially decreasing its matrix permeability. To address the problems caused by water-based fracturing fluids, the possibility of using SC-CO2 as a fracturing fluid was studied for its special properties (such as low viscosity, high density, and miscibility with hydrocarbons). Previous experimental studies have indicated that SC-CO2 is superior to water-based fracturing fluid in inducing complex fractures at the laboratory scale, while the mechanism of complex fractures induced by SC-CO2 remains unclear. This study develops a new numerical model to simulate the different performances of SC-CO2 fracturing and water-based fluid fracturing to determine the mechanisms of complex fractures. The numerical model couples an unsteady flow model based on the pore-scale network method and a solid model using the finite element method with cohesive zone elements. The unsteady flow model reproduces a two-phase flow considering viscous and capillary forces at the pore scale. Our simulation results show that both viscous and capillary forces contribute to the different fracturing performances between SC-CO2 and water-based fluid. The capillary force should be considered in the flow model when simulating fracturing in low matrix permeability rock.

Impact Damage Characteristics of Carbon Fibre Metal Laminates: Experiments and Simulation

In this work, the impact response of carbon fibre metal laminates (FMLs) was experimentally and numerically studied with an improved design of the fibre composite lay-up for optimal mechanical properties and damage resistance. Two different stacking sequences (Carall 3–3/2–0.5 and Carall 5–3/2–0.5) were designed and characterised. Damage at relatively low energy impact energies (≤30 J) was investigated using Ultrasonic C-scanning and X–ray Computed Tomography (X-RCT). A 3D finite element model was developed to simulate the impact induced damage in both metal and composite layers using Abaqus/Explicit. Cohesive zone elements were introduced to capture delamination occurring between carbon fibre/epoxy plies and debonding at the interfaces between aluminium and the composite layers. Carall 5–3/2–0.5 was found to absorb more energy elastically, which indicates better resistance to damage. A good agreement is obtained between the numerically predicted results and experimental measurements in terms of force and absorbed energy during impact where the damage modes such as delamination was well simulated when compared to non-destructive techniques (NDT).

A cohesive-element-based model to evaluate interfacial behavior of casing–cement sheath for high-pressure, high-temperature wellbore integrity considering casing eccentricity

In this article, the finite element model considering the casing eccentricity of high-pressure, high-temperature wellbore integrity is established, where the cohesive zone element is introduced to evaluate the mechanical behavior of the casing–cement sheath interface. In this analysis, the bilinear traction–separation law is used to estimate the interfacial failure, and a damage factor is simultaneously defined to describe the damage evolution of the cohesive element. In addition, to achieve the interfacial separation, the pressure fluctuation inside the casing is applied. Using the finite element approach, we investigate the effect of mechanical parameters including Young’s modulus, Poisson’s ratio, thermal conductivity of the cement sheath, and pressure fluctuation inside the casing on the interfacial failure of the casing–cement sheath. The simulation results show that the damage factor increases with the increase in the mechanical parameters including Young’s modulus and Poisson’s ratio of the cement sheath and the casing pressure fluctuation. We also observe that the maximum damage factor under higher thermal conductivity is higher than that under lower thermal conductivity for the casing concentricity, while it is lower than that under lower thermal conductivity for the casing eccentricity. This indicates that the casing eccentricity has an important impact on the damage factor. What’s more, the casing eccentricity can change the location where the maximum damage factor occurs.

A model for fast delamination analysis of laminated composite structures

Delamination is one of the major failure mechanisms for composites and traditionally the simulation requires high expertise in fracture mechanics and dedicated knowledge of the Finite Element Analysis (FEA) tool. Yet, the simulation cycle times are high. Geometrically nonlinear analysis approach, which is based on the Reissner-Mindlin-Von K´arm´an type shell facet model, has been implemented into the Elmer FE solver. Altair ESAComp software runs the Elmer Solver in the background. A post-processing capability, which enables the prediction of the delamination onset from the FEA output, has been implemented into the AltairESAComp software. A Virtual Crack Closure Technique (VCCT) specifically developed for shell elements defining the Strain Energy Release Rate (SERR) related to the different delamination modes at the crack front is used. The onset of delamination is predicted using the relevant delamination criteria that utilize the SERR data and material allowables in the form of fracture toughness. The modeling methodology is presented for laminates including initial through-the-width delamination. Examples include delamination in the solid laminate and debonding of the skin laminate in the sandwich structure. Rather coarse FE mesh has proved to yield good results when compared to typical approaches that utilize the standard VCCT or Cohesive Zone Elements.