Cohesive Zone Model Research Articles

Investigation of microscale brittle fracture opening in diamond with olivine inclusion using XFEM and cohesive zone modeling

Inclusions trapped in diamonds are a fundamental source of information to probe the Earth’s interior, provided that the pressure conditions at which the diamond grew are correctly determined.This study explores the traditional assumptions in geothermobarometry for olivine-in-diamond host-inclusion systems by employing extended finite element methods (XFEM) and cohesive zone models (CZM) to quantify the contributions of brittle fractures to the relaxation of the residual stress of inclusions. Our analysis was performed assuming that the host-inclusion system does not contain fluids and that the unfractured minerals are elastically isotropic. Our models show that the damage initiation is solely dependent on the shape of the inclusion and on the fracture strength of the diamond host, while the fracture nucleation is influenced by both the size of the inclusion and the toughness of the diamond. Our findings indicate that, in dry systems, the amount of relaxation of residual stress of the inclusion due to the opening of brittle fractures is much lower than that due to the elastic interaction between the host and the inclusion. Moreover, the pressure release due to fractures is not substantially affected by the shape of the inclusion. We also show that the total relaxation of the residual pressure due to the combined effect of the elastic interaction and of the brittle deformation is lower than what is observed in natural samples, even when assuming fracture strength and toughness lower than those reported from experiments on single crystals of diamond. Such discrepancies suggest that in natural olivine-diamond systems additional mechanisms such as viscous or plastic deformation and/or the presence of preexisting defects and fluids in the host might play a relevant role in the relaxation of the residual stress. These findings underscore the need for advanced numerical tools that consider the complex interplay of the geometry of the host-inclusion system, the fracture properties, and the presence of fluids and defects in order to build more accurate models to constrain the geological history of diamonds.

Prediction of fracture toughness of a reactor pressure vessel steel in the ductile-to-brittle transition region based on a probabilistic cohesive zone model approach

The availability of irradiated material for the fracture-mechanical characterization of reactor pressure vessel steels in the context of surveillance programs is severely limited. Additional efforts are necessary to reduce the amount of material required for the determination of the reference temperature based on the Master Curve methodology. The objective of this study is the further development of a method for identifying the parameters of a cohesive zone model to simulate the fracture-mechanical behavior within the ductile-to-brittle transition region. A novel approach is proposed where statistically distributed numerical fracture toughness values are obtained by means of random spatial distributions of cohesive elements with either brittle or ductile fracture properties throughout the cohesive zone. Thereby, a numerical reference temperature is determined based on the ASTM E1921 standard and compared to the reference temperature obtained from tests on miniaturized CT specimens. It is shown that with the presented approach the reference temperature of a reactor pressure vessel steel can be predicted with high accuracy. Less material is required for the calibration of the model parameters than for an experimental determination of the reference temperature. Further development of the model is required to accurately predict the experimentally observed fracture toughness scatter within the transition region.

Simulating delamination in composite laminates with fracture process zone effects: A novel cohesive zone modeling approach

Simulating delamination in composite laminates with fracture process zone effects: A novel cohesive zone modeling approach

Application of equivalent distributed stress concept and modified cohesive zone model in elastic–plastic fracture mechanics analysis of surface cracks

Application of equivalent distributed stress concept and modified cohesive zone model in elastic–plastic fracture mechanics analysis of surface cracks

Enhancing Fracture Performance of Non‐Conductive Composite Adhesively Bonded Joints With Magnetically Aligned MWCNT/Fe₃O₄ Hybrid Nanofillers

ABSTRACTThe Mode‐I fracture behavior of non‐conductive composite adhesively bonded joints (ABJs) reinforced with multi‐walled carbon nanotube/iron oxide (MWCNT/Fe₃O₄) hybrid nanofillers aligned in different directions was studied using double cantilever beam (DCB) tests. Fe₃O₄ nanoparticles were chemically coated onto MWCNTs to explore the practical potential of these produced magnetically controllable nanofillers in high‐tech industries that require precise nanofiller alignment in specific directions. Nanofillers were aligned within the ABJ adhesive layer using a low magnetic field at 0°, 45°, and 90° relative to the crack growth path, verified by Raman spectroscopy. ABJs with 90° alignment exhibited the highest fracture energy, surpassing unreinforced and randomly dispersed specimens by 136% and 41%, respectively. In contrast, 0°‐alignment showed the lowest fracture energy, while 45° alignment demonstrated intermediate performance. Cohesive zone modeling simulated the ABJ damage behavior, and the effects of nanofiller alignment on macro and microscale fracture mechanisms were assessed using optical and scanning electron microscopy.

Investigation of casing failure mechanisms induced by hydraulic fracture dynamic penetration in heterogeneous shale gas reservoirs

The occurrence of casing failure in multi-lithology layered shale reservoirs is significantly influenced by the behavior of hydraulic fracture penetration. However, the mechanisms underlying casing failure during the dynamic penetration of hydraulic fractures in heterogeneous reservoirs remain largely unexplored. In order to study how the dynamic expansion law of hydraulic fractures in heterogeneous reservoirs affects casing stress, a Hydraulic Fracture-Heterogeneous Reservoir-Cement Sheath-Casing (HHCC) model has been developed based in the cohesive zone model framework. Furthermore, the reliability of the model is verified by comparing the simulation results with the experimental results. The focus of this study encompasses the analysis of casing stress distribution during both the initiation and dynamic penetration phases of hydraulic fracturing in heterogeneous reservoirs. Additionally, it investigates the effects of bedding surface bonding strength and temporary plugging technology on casing stress. Furthermore, mitigation strategies are proposed based on these findings, and the model is used to evaluate their effectiveness in reducing the risk of casing failure, particularly in the Weiyuan Block. The outcomes of this research yield critical insights aimed at preventing casing failure during hydraulic fracturing operations in heterogeneous shale gas reservoirs.

Effect of curvature angle and structural configurations on dynamic performance of honeycomb sandwich structures

The aim of this study is to investigate the effects of curve angle and structural parameters on ballistic performance of honeycomb sandwich structures. In the study, high-velocity impact simulations were performed in LS DYNA finite element program to investigate the effects of honeycomb structural parameters, curve angle, residual velocity, specific energy absorption (SEA) and damage mechanism. Progressive damage analysis based on the combination of cohesive zone model (CZM) and bilinear traction-separation law was performed. The ballistic limit value increased by 41.9% when the facesheet thickness increased by two times. When the cell wall thickness increased by five times, the ballistic limit value increased by 13.3%. When the core height was two times increased, the ballistic limit velocity value increased by 2.076 times. Although the ballistic limit velocity value of the CFRP Facesheet and Aluminum (Al) core sandwich structure is 7.14% lower than the all Al specimen, the SEA value is 9.47% higher. When the curve angle increases from 0˚ to 180˚, the ballistic limit value decreases by 22.8%. In general, this study provides useful information about the design of ballistic structures, parameters affecting their performance and their effects.

Experimental and numerical investigation on the tensile performances of bonded/bolted hybrid CFRP‐AL joints

AbstractReasonably designed hybrid joints can combine the advantages of both adhesively bonded and bolted joints, and have potential application value in improving the bearing capacity of the joint and ensuring structural safety. However, the failure behavior and damage mechanism of multi‐materials hybrid joints are not fully understood. In this paper, the mechanical performances of bonded, bolted, and hybrid CFRP‐aluminum alloy joints under tensile load were investigated using experiment and simulation methods. Based on the quasi‐static tensile test and fractography analysis, the mechanical behavior and damage mechanism of the three kinds of joints were studied, and the effects of hybrid effects were analyzed. The results demonstrated that there is no obvious co‐bearing effect between the adhesive layer and the bolt within the hybrid joint. Instead, a sequential load transfer behavior was observed. The hybrid joint showed more severe damage compared with the bolt joint, especially the CFRP delamination. Furthermore, a numerical model based on continuous damage mechanics (CDM) was established, the LaRC05 initial failure criterion and linear damage evolution were implemented to predict composite intra‐laminar failure, and the cohesive zone model (CZM) was used to simulate the inter‐laminar delamination and adhesive layer fracture. The model considers in situ effect, shear nonlinearity, and employs the selective parabola algorithm to improve computing efficiency. The comparison between experiment and simulation reveals that the model can accurately predict the mechanical performances of joints and capture the various failure modes.Highlights The performances of bonded, bolted, and hybrid CFRP‐aluminum alloy joints. The CDM model of CFRP includes LaRC05 criterion and stiffness degradation. Effect of damage constitutive models on the failure simulation of CFRP. Damage evolution and failure modes of three types of joints.

Adhesive damage of class V restorations under shrinkage stress and occlusal forces using cohesive zone modeling.

This study aims to investigate adhesive damage caused by the synergistic effects of polymerization shrinkage and occlusal forces via finite element analysis (FEA), based on damage mechanics with the cohesive zone model (CZM). The objective is to obtain the adhesive damage distribution and investigate how the material properties of resin composite impact adhesive damage. A 3D reconstruction model of an mandibular first molar was constructed through CBCT imaging, and a Class V cavity was prepared using computer-aided engineering (CAE) software. Common clinical resin composite and an universal adhesive were selected for restorative filling. A 3D FEA was performed, incorporating the pre-stress induced by polymerization shrinkage of the resin composite, followed by occlusal forces. The cohesive zone model (CZM) was employed to represent the adhesive damage. To emphasize the impact of synergistic loading on adhesive damage, three types of loads were separately applied to the model: polymerization shrinkage, occlusal forces, and combined loading. Subsequently, three clinical resin composites with varying polymerization shrinkage and elastic modulus were used as restorative materials. Sensitivity analysis was conducted on dozens of hypothetical materials to provide definitive results. Polymerization shrinkage was undergone by the cured resin composite, resulting in extensive adhesive damage. Occlusal forces induced microdamage in regions already damaged by shrinkage stress, especially in the gingival wall. Predictably, the regions with severe adhesive damage were prone to marginal microleakage. The properties of the resin composite can affect adhesive damage. The adhesive damage with bulk-fill resin composite was milder than that with flowable and conventional resin composite. The extent of adhesive damage correlated markedly positively with the polymerization shrinkage of the resin composite and mildly positively with its elastic modulus. Adhesive damage has been directly implicated in marginal microleakage. The cohesive zone model (CZM) can effectively elucidate the distribution of adhesive damage and provide a clear representation of the impact of varying material properties of resin composite on adhesive damage.

A novel anisotropic grain boundary cohesive zone model for fracture simulation of polycrystalline nickel-based superalloy

A novel anisotropic grain boundary cohesive zone model for fracture simulation of polycrystalline nickel-based superalloy

Regularized X‐FEM Modeling of Arbitrary 3D Interacting Crack Networks

ABSTRACTAn extension to the Regularized eXtended Finite Element Method (RX‐FEM) is proposed that allows arbitrary 3D cracks through a novel hierarchical enrichment algorithm. The technique avoids geometric consideration of how a crack cuts elements or intersects other cracks. Each crack is described separately in terms of its sign distance function and regularized step function, which are only recorded for nodes in the region where the gradient of the regularized step function is non‐zero. The algorithm creates a set of superimposed nodes, referred to as node twins, and elements, referred to as twinned elements, for each crack and determines the connectivity of the element twins using the involved crack indices. The displacement jump is calculated between each pair of element twins corresponding to the same crack, and a cohesive zone model (CZM) is formulated for each pair of twins to model crack opening. Following the theory for the novel method, several examples are presented that illustrate capabilities of the new method that the traditional RX‐FEM formulation lacked. A quasi‐2D example of offset crack propagation is considered and successfully compared with published results. Additionally, two 3D examples involving perpendicularly intersecting cracks are considered, illustrating the intersection of two crack fronts and correct partitioning of the domain into eight fragments due to three crossing cracks, respectively.

Numerical and experimental analysis of shear strength on SLM 3D-printed stainless-steel bonded joints enhanced by bio-inspired surface pattern

The performance of adhesive joints is significantly influenced by the surface texture of the adherends, making texture a crucial factor in their analysis and optimization. Existing literature on numerical modeling of bonded joints predominantly focuses on smooth surfaces, often neglecting the impact of surface patterns. As a result, there is limited understanding of how complex surface textures affect joint performance. Advanced surface textures, such as those inspired from biomimetic systems, have the potential to enhance joint strength. This study addresses this gap by developing two numerical models: one representing a smooth surface (without-texture) and another incorporating a biomimetic fish-scales (FS) texture. The models use Cohesive Zone Modeling with a local approach to simulate the effects of surface texture and adhesive behavior on block-shear joint performance. These models were validated through experimental block-shear tests on P1000 (polished with 1000-grit abrasive paper) and FS-textured stainless-steel joints. Experimental results demonstrated that the FS texture significantly improved joint strength by approximately 44% compared to the P1000 surface. This enhancement is attributed to better adhesive anchoring and extended contact area. Numerical results indicated that the model without-texture exhibited significant stress concentrations at the edges of the overlap, suggesting failure initiation in these regions. However, the FS texture caused repetitive stress peaks along the overlap, and the vertical walls of this texture effectively hindered crack propagation at the interface. Additionally, both models accurately predicted the maximum shear load and failure modes of the P1000 and FS bonded joints, demonstrating good agreement with experimental results, particularly for the hyper-elastic adhesive behavior.

Fatigue Life Prediction and Reliability Assessment of CFRP Adhesively Bonded Joints in Offshore Wind Turbine Blade Applications: A Physics‐Informed Data‐Driven Approach

ABSTRACTAdhesively bonded joints made of carbon fiber reinforced polymer (CFRP) are critical structures of offshore wind turbine blades, yet they are particularly susceptible to fatigue failure influenced by marine environmental factors. Current methodologies for predicting the fatigue life and assessing the reliability of these bonded joints face limitations due to insufficient data, modeling complexities, and inefficiencies. This study introduces a novel, physics‐informed, data‐driven approach to analyze the fatigue performance of CFRP adhesively bonded joints subjected to multi‐environmental stress, thereby improving fatigue life predictions and reliability assessments. Initially, an innovative method that integrates a physics‐informed data‐driven framework for predicting adhesive fatigue life and modeling reliability is proposed, utilizing the cyclic cohesive zone model (CCZM) alongside single‐hidden layer feedforward neural networks (SLFN). Multi‐environmental aging tests were conducted on CFRP‐bonded joints of varying dimensions, leading to the development of a physics‐informed fatigue analysis method based on CCZM. Furthermore, a reliability assessment and sensitivity analysis were performed to evaluate the impact of uncertainty factors. This research provides significant insights for the structural design and safety analysis of bonded structures in offshore wind turbine blades.

The effect of impactor shape on low velocity impact behavior of cylindrical sandwich structures with trapeozidal core

The aim of this study is to investigate the impact performance of a cylindrical sandwich structure with Trapeozidal core under different geometries of impactors using the finite element method. The effects of impactor shape, facesheets thickness and impact point on peak contact force, absorbed energy efficiency, maximum displacement and damage deformation are investigated. Progressive damage analysis based on the Hashin damage criterion was performed using MAT 54 material model in LS DYNA finite element program for low velocity simulations. The impact behavior was investigated by creating a Cohesive Zone Model (CZM) based on bilinear traction-separation law while providing the connection between the core structure and its surfaces. At the end of the study, it was determined that the contact force values at P2 were higher than P1. Peak force variation values for cylinder, cone and sphere tipped impactors at P1 and P2 points were 43.5%, 132.3% and 62.2%, respectively. Core support has a significant effect on the contact force. The peak force value and energy absorption efficiency value obtained with the Cone impactor are higher than the others. For all three impactors, it was determined that the largest and dominant damage type was matrix damage.

Experimental and numerical investigations on the mechanical properties of overmolded hybrid fiber reinforced thermoplastic composites

Abstract In this work, an anti-collision beam was manufactured through a thermoplastic composite overmolding (TCO) process. This process includes thermoforming of continuous glass fiber reinforced thermoplastic composite (CGFR-PP) and overmolding of short glass fiber reinforced thermoplastic composite (SGFR-PP). Double cantilever beam (DCB) and end-notched flexure (ENF) tests were performed to obtain the interfacial bonding fracture toughness between CGFR-PP and SGFR-PP, which was then used to establish a cohesive zone model (CZM). A continuum damage model (CDM) based on Tsai-Wu criterion was established to simulate the damage behavior of CGFR-PP. Tensile and bending tests on CGFR-PP and single lap shear (SLS) tests were conducted to verify the validity of the CDM and CZM. At last, the finite element model was used to predict the bending properties of the anti-collision beam, and the error of maximum load is approximately 5 %. Results reveal that the simulation results demonstrated a good agreement with the experimentally obtained force-displacement curves in terms of stiffness and maximum load.

Brittle failure analysis and modeling of high-burnup PWR fuel cladding alloys

Abstract The aim of this research is the development of methods for predicting mechanical behavior and identification of limiting conditions to prevent brittle failure of high-burnup (HBU) pressure water reactor (PWR) fuel cladding alloys. A finite element (FE) model of the ring compression test (RCT) was created to analyze the failure behavior of zirconium-based alloys with radial hydrides during the RCT. An elastic-plastic material model describes the zirconium alloy. The stress-strain curve needed for the elastic-plastic material model was derived by inverse finite element analyses. Cohesive zone modeling is used to reproduce sudden load drops during RCT loading. Based on the failure mechanism in non-irradiated ZIRLO® claddings, a micro-mechanical model was developed that distinguishes between brittle failure along hydrides and ductile failure of the zirconium matrix. Two different cohesive laws representing these types of failure are present in the same cohesive interface. The key differences between these constitutive laws are the cohesive strength, the stress at which damage initiates, and the cohesive energy, which is the damage energy dissipated by the cohesive zone. Statistically generated matrix-hydride distributions were mapped onto the cohesive elements and simulations with focus on the first load drop were performed. Computational results are in good agreement with the RCT results conducted on high-burnup M5® samples. It could be shown that crack initiation and propagation strongly depend on the specific configuration of hydrides and matrix material in the fracture area.

Cohesive zone approach to the cyclic response of cracked concrete beams reinforced with externally bonded FRP plate

To predict the cyclic response of concrete strengthened with FRP, this paper presents a new analytical solution, which uses the cohesive zone model (CZM). Based on the CZM, for intermediate crack-induced debonding, with intermediate flexural cracking of concrete beams repaired with FRP plate, the deteriorative effect of cyclic loading on the adhesive joints (interface) is investigated. To accomplish this aim, a cyclic damage process is coupled with a CZM to predict the cumulative damage evolution along the FRP-to-concrete interface as a function of the number of cycles. Comparing the results from the present model with those found in the literature shows that the constitutive model is able to accurately predict the overall cyclic loading response of concrete strengthened with FRP composites. The main advantage of the proposed model is that it gives the variation of the mid-span deflection, damage development, and interfacial stress distribution with increasing load cycles, and number of loading cycles. We conclude that cyclic degradation of the component materials significantly reduces the resistance and lifespan of the repaired structures.

Longitudinal Shear in Timber-Concrete Composites with Flexible Adhesive Connections-Experimental and Numerical Investigations.

Timber-concrete composites are established structural elements to combine the advantageous properties of both materials by connecting them. In this work, an innovative flexible adhesive connection in different configurations is investigated. Load-bearing capacity, stiffness, and the failure modes were first experimentally investigated by performing push-out tests. Subsequently, a numerical evaluation using ABAQUS 2017/Standard software was carried out in order to develop a three-dimensional numerical model. The Cohesive Zone Model (CZM) is employed to represent the adhesive characteristics at the contact areas between the Cross-Laminated Timber (CLT) and concrete elements. Three different connection configurations were evaluated, each consisting of five push-out specimens. The study investigates the impact of bonding surface area and the alignment of prefabricated glue strips with the load direction on the connection's longitudinal shear load-bearing capacity, stiffness, and slip modulus. In addition, the impact of cyclic loads and the impact of time on displacements were analyzed. The average load capacity of the full surface connection (type A) is 44.5% and 46.2% higher than the vertical adhesive strips (type B) and the horizontal adhesive strips (type C), respectively. However, the initial stiffness of the tested joints depends on the orientation of the prefabricated adhesive fasteners, being approximately 20% higher when the bonding elements are aligned parallel to the load direction compared to when they are oriented perpendicularly.

Determination of Strength Parameters of Composite Reinforcement Consisting of Steel Member, Adhesive, and Carbon Fiber Textile.

The main aim of the study was the determination of the strength parameters of composite bonded joints consisting of galvanised steel elements, an adhesive layer, and Carbon-Fiber-Reinforced Plastic (CFRP) fabric. For this purpose, shear laboratory tests were carried out on 60 lapped specimens composed of 2 mm thick hot-dip galvanised steel plates of S350 GD. The specimens were overlapped on one side with SikaWrap 230 C carbon fibre textile (CFT) using SikaDur 330 adhesive. The tests were carried out in three series that differed in overlap length (15 mm, 25 mm, and 35 mm). A discussion on the failure mechanism in the context of the bonding capacity of the composite joint was carried out. We observed three forms of joint damage, namely, at the steel-adhesive interface, fibre rupture, and mixed damage behaviour. Moreover, an advanced numerical model using the commercial finite element (FE) program ABAQUS/Standard and the coupled cohesive zone model was developed. The material behaviour of the textile was defined as elastic-lamina and the mixed-mode Hashin damage model was implemented with bi-linear behaviour. Special attention was focused on the formulation of reliable methodologies to determine the load-bearing capacity, failure mechanisms, stress distribution, and the strength characteristics of a composite adhesive joint. In order to develop a reliable model, validation and verification were carried out and self-correlation parameters, which brought the model closer to the laboratory test, were proposed by the authors. Based on the conducted analysis, the strength characteristics including the load-bearing capacity, failure mechanisms, and stress distribution were established. The three forms of joint damage were observed as steel-adhesive interface failure, fibre rupture, and mixed-damage behaviour. Complex interactions between the materials were observed. The most dangerous adhesive failure was detected at the steel and adhesive interface. It was also found that an increase in adhesive thickness caused a decrease in joint strength. In the numerical analysis, two mechanical models were employed, namely, a sophisticated model of adhesive and fabric components. It was found that the fabric model was very sensitive to the density of the finite element mesh. It was also noticed that the numerical model referring to the adhesive layer was nonsensitive to the mesh size; thus, it was regarded as appropriate. Nevertheless, in order to increase the reliability of the numerical model, the authors proposed their own correlation coefficients α and β, which allowed for the correct mapping of adhesive damage.

A concurrent multiscale model of stress-induced delamination behaviours of epoxy-impregnated rare-earth barium copper oxide superconducting pancake winding

Abstract Rare-earth barium copper oxide (REBCO) coated conductor (CC) tapes are promising for high-energy and high-electromagnetic field applications. In epoxy-impregnated REBCO superconducting coils, due to the weak c-axial strength of REBCO CC tapes, delamination induced by thermal-mismatch stress and Lorentz force significantly threatens stable operation. The commonly used numerical modelling methods mainly include homogenized model and refined model. The former can realize the efficient calculation of the overall physical field but lose the local details including interfacial delamination behaviour, while the latter can realize the refined calculation but cost massive calculation. In this study, combining with bilinear cohesive zone model (CZM), a two-dimensional axisymmetric concurrent multiscale model was developed to balance the efficiency-accuracy trade-off for numerically investigating the mechanical properties and interface failure behaviours of REBCO superconducting coils under cryogenics and high-electromagnetic field. In the presented model, the homogenized superconducting coil was firstly constructed based on composites homogenized approach to estimate the electromagnetic-thermal-mechanical properties at macro scale. Then, the ‘dangerous regions’ in the macro scale was recognized based on quadratic failure criterion and replaced with a refined model considering delamination failure defined by CZM. Finally, the two scales are linked through the coupling interface. The accuracy and efficiency of the concurrent multiscale model were validated by refined model for the cases of delamination behaviour during cooling and excitation.