Cohesive Zone Material Model Research Articles

An experimental and numerical study on the behaviors of adhesively-bonded steel double-hat section components under axial impact loading

A significant consideration in the deployment of adhesively-bonded joints in applications such as automotive body structures is their performance under impact loading. Due to the distinct behaviors of an epoxy-based structural adhesive under normal and shear loads combined with its propensity to undergo brittle fracture in cohesion and adhesion, special care needs to be taken in the constitutive modeling of such an adhesive as traditional Von Mises type yielding and elastoplastic material behavior do not seem to be applicable. In the current study, to start with, experimental load-displacement behaviors till failure of single lap shear and T-peel joints with steel substrates are predicted with the aid of a cohesive zone material model using LS-DYNA, an explicit nonlinear finite element analysis solver. With confidence established on cohesive zone modeling of the joints mentioned, the procedure is extended to robust prediction of the load-displacement responses and deformed shapes of steel double-hat section components subjected to axial impact loading. Three variants of steel hat section components have been considered from the viewpoint of joining of flanges with conventional discrete spot-welds, only continuous adhesive bonding, and a hybrid configuration with a combination of adhesive bonding and sparse spot-welds. The study reported here provides insights into mechanical behaviors of adhesively-bonded steel double-hat sections under impact loading, and demonstrates an efficient finite element modeling approach for adhesively-bonded steel hat sections using cohesive zone elements with fracture mechanics-based criteria for failure.

Development of a local bond shear stress-slip model of RC beams externally strengthened with FRP materials

This paper presents an analysis of the numerical investigation of RC beams, strengthened with CFRP and tested in flexure, using the ANSYS© numerical analysis code. In the first part of this paper, finite-element models of RC beams (control and CFRP-strengthened), subjected to four-point bending, are developed based on experimental tests as reported in the literature. Then, a 3D nonlinear finite-element analysis (NLFEAs) with perfect bonding, along with 12 cohesive zone material (CZM) models proposed by researchers in literature, are explored to simulate the behaviour of CFRP-strengthened RC beams. In the second part of this work, the compressive strength of the concrete and the elastic modulus of the epoxy resin are examined to study their effect on the same CFRP-strengthened RC beam. On the basis of those two studies, a bilinear CZM model is modified to predict the behaviour of RC beams strengthened with FRP materials, and interfacial shear debonding phenomena. The modified CZM model is verified against a database of experimental results that includes 23 RC beams, strengthened with FRP tested in flexure, with different concrete compressive strength, FRP modulus of elasticity and resin elastic modulus. The experimental and predicted ultimate loads are compared to verify the accuracy of the modified CZM model. The level of fitness between the modified CZM model and experimental results is elaborated with statistical metrics such as integral of the absolute error (IAE), root mean square error (RMSE) and coefficient of determination (R2). The results show good agreement between the experimental and predicted ultimate loads.

Repair Parameter Design of Outer Reinforcement Layers of Offshore Wind Turbine Blade Spar Cap Based on Structural and Aerodynamic Analysis

The influence of the outer reinforcement layers on the repair structure and aerodynamic performance was studied. Firstly, a continuous damage mechanics model was established, and the 3D Hashin criterion and cohesive zone material model were used to analyze the damage repair model. The failure load deviation was 5.5%. Secondly, on the basis of the γ−Reθ transition model and SST–ω turbulence model, the aerodynamic analysis model of DU300 airfoil was established. The numerical simulation results showed that the lift coefficient and pressure distribution at the angle of attack of 10° and 15° were deviated from the experimental values by 2%. Furthermore, 27 structural repair models, nine 2D aerodynamic repair models, and a 3D full-scale blade model were designed. It was found that, when the repair length accounted for 60% of the total model length, the failure load increased by 22%, but the aerodynamic power with the repair length of 10 m was decreased by 0.137%. When the repair area was large and the repair height was from 4 mm to 6 mm, the failure load was greatly increased by about 30%, and the aerodynamic pressure distribution and static pressure field fluctuated significantly. The results show that the structural and aerodynamic characteristics were closely related to the repair parameters.

Mode II- delamination modeling in multi-directional laminates using cohesive zone methodology under static and dynamic loading

Most of the ply-by-ply laminated composite structures are constrained by delamination type of failure under different loadings. There were attempts to develop modeling methods for delamination under static and dynamic loads in the past. Most of the earlier attempts are focused on the unidirectional laminates because of complexity involved in the multi-directional laminates. However, in the real life, many time multi-directional laminates are used. This paper is an effort to create such modeling methodology for multi-directional carbon composite laminates (with 0–0, 45–45 and 90–90 interfaces) under static and dynamic loads. For modeling the static load case, Ansys software is used with the in-built contact based cohesive zone material model. The mode II experiments were conducted on multi-directional carbon composite coupons as per ASTM standards and the load displacement behavior is verified using the finite element analysis (FEA) cohesive zone models (CZM). Mode II test coupons are modeled in 3D, and the delamination is captured in the analysis simulation. For dynamic loading, LS-Dyna is used with the in-built tiebreak contact-Dycoss-Option 9 capabilities which are almost similar to the cohesive zone elements. The results indicate that cohesive zone models can predict the delamination in the kind of materials under static and dynamic loading conditions. The modeling methods will be further improvised for both situations to make it more robust and ready for applications to aircraft engine components in consideration of delamination.

Numerical simulation of pre-cracked thin aluminum alloy skin repaired with a FRP patch: Pre-crack length studies

The fatigue life of a thin pre-cracked aluminium-alloy panel, repaired with Carbon Fiber Reinforced Plastics (CFRP) patch on one side, is investigated using a numerical model. CFRP plies of different lengths are used to form patch which in turn repair pre-cracked aluminium skin. Numerical studies are performed to determine variation in stress intensity factor (SIF) range and bulging out deflection of specimen subjected to minimum and maximum fatigue load. Patch width to pre-crack and length to pre-crack ratio are kept constant for different pre-crack studies. Numerical simulations are carried out for three different pre-crack length. Three different patch configurations are studied for each pre-crack length. Maximum stress considered is at 50 % yield strength of aluminium skin. The numerical model is simulated by using ANSYS 15.0, a Finite Element Analysis package. The interface behaviour between the skin and the patch is simulated by using cohesive zone material model (CZM). Stress intensity factor (SIF) is determined from J-integral results. Relation between SIF range and crack length can be used to determine fatigue crack propagation by invoking the Paris law. It is found that with increasing the patch length, ΔKI decreased significantly which may result into the increase of the fatigue life.

Non-linear analysis of one-way concrete slabs with carbon-fibre-reinforced polymer strips

Finite-element (FE) models of one-way spanning reinforced concrete slabs strengthened with carbon-fibre-reinforced polymer (CFRP) strips were constructed and analysed. The slabs, which had different-sized openings at different locations, were tested by the authors in a previous study. During the FE analysis, the effective failure modes were taken into account and the behaviour of the concrete–CFRP strip interface was modelled using a non-linear cohesive zone material model. The results of the FE analysis and experimental data were compared in terms of the ultimate load capacities of the slabs, load–displacement graphs, stress distributions and failure modes. The modelled results were found to be consistent with the experimental findings. The yield and ultimate shear force capacities, the yield and ultimate displacements and the yield stiffness of the slabs were calculated with average errors of 11.4%, 6.3%, 27.1%, 13.8% and 24.2%, respectively. After verification of the FE model, analyses of four additional slabs, not previously experimentally tested, were performed. An equation between the ultimate load capacity of a slab and opening size was developed based on the modelling results.

Flexural performance of RC T-beams strengthened with external double steel channel

Attaching steel channel to the side faces of reinforced concrete (RC) beam is a potential solution to the strengthening of existing structures. In order to eliminate debonding failure and bolt slipping, high-strength prestressed bolting and adhesive bonding were applied in this research to fix steel channel to RC T-beam. Experimental investigation was conducted on the flexural behavior of RC T-beam strengthened with double steel channel, and different methods of plate attachment were compared. It was indicated that the flexural performance of RC T-beam was significantly improved by steel channel. The capacity of strengthened specimen can be up to 5.1 times higher than that of RC T-beam. A three-dimensional (3D) numerical model with the application of cohesive zone material model was established in commercial software ABAQUS and validated by experimental results. A parametric study was further conducted to quantify the effects of different geometric parameters of steel channel (i.e. flange thickness, web thickness, flange width and total depth), and the depth of steel channel was found to have significant influence on its strengthening effect.

Cyclic Behavior and Modeling of Bolted Glulam Joint with Cracks Loaded Parallel to Grain

Under varying humidity and temperature conditions, with the constraint of metal fasteners to wood shrinkage, cracks along the bolt lines are generally observed in bolted glulam joints. A three-dimensional (3D) numerical model was established in software package ANSYS to investigate the cyclic behavior of bolted glulam joints with local cracks. A reversed cyclic loading was applied in the parallel-to-grain direction. The accuracy of numerical simulation was proved by comparison with full-scale experimental results. Typical failure modes were reproduced in the numerical analysis with the application of wood foundation zone material model and cohesive zone material model. The effect of crack number and length on the hysteretic behavior of bolted glulam joints was quantified by a parametric study. It was found that initial cracks impair the peak capacity and elastic stiffness of bolted glulam joints significantly. More decrease in capacity was observed in joints with more cracks, and longer cracks affect elastic stiffness more dramatically. Moreover, with the existence of initial cracks, the energy dissipated and equivalent viscous damping ratio of bolted joints are reduced by 24% and 13.3%, respectively.

Compressive behavior of glulam columns with initial cracks under eccentric loads

This paper investigates the mechanical performance of longitudinally cracked glulam columns under eccentric compression loads. Experimental investigation was conducted to explore the influence of initial cracks on the failure modes and load bearing capacity of glulam columns. Two different crack patterns named DC and IC, and two column lengths (i.e. 600 and 1100 mm) were considered in the experiments. It was indicated that these two crack patterns reduced the capacity of slender glulam columns and the difference of failure modes was observed between glulam columns with and without initial cracks. Further, a numerical model was developed and validated by the test results. With the application of cohesive zone material model, the propagation of initial cracks could be considered in the numerical modeling. A parametric study was carried out by the verified model and the influence of crack lengths and crack locations was further investigated. From the numerical analysis, it was found that through cracks reduced the capacity of glulam columns significantly. Also, crack location impacts the capacity of glulam columns and the extent of impact relates to the slenderness ratio of the columns, while cracks with different lengths have similar influence on the capacity of columns.

Novel Cohesive/Adhesive Ice Shedding Model for Spinner Cone

In turbofan engine, ice accretion on a spinner cone may lead to a decline in the engine aerodynamic performance and an increase of the vibration amplitude of the engine. The shedding ice debris from the spinner cone may damage fan blades and endanger flying safety. An understanding of the mechanisms responsible for the ice shedding process is necessary to optimize the design of spinner cone and de-icing system to avoid hazardous ice shedding. The combination of ice adhesive and cohesive failure leads to the complexity of the ice shedding from a rotating spinner cone. In this paper, a novel ice shedding model for a spinner cone with consideration of ice cohesive and adhesive failure is proposed. The cohesive zone material model is applied to simulate the initiation and propagation of ice/spinner cone interface crack. The extended finite element method is introduced to model crack growth inside the ice. The ice shedding process from a spinner cone is explained and analyzed by using the combination of cohesive zone material and extended finite element method. Some factors that affect the break-up and shedding of the ice are discussed, which include the mechanical properties of the ice and ice/spinner cone interface. A preliminary validation of this model is carried out through the comparison of numerical results and experimental data. This model can provide useful information for further study on the ice debris trajectory prediction and ice impact analysis.

Numerical Analysis of GFRP Interposed Lamella Effect on the Structural Behavior of Timber Beams

The use of numerical methods to simulate materials or civil structures behavior is an efficient tool to predict their performance in diverse specific applications and design situations. The authors propose a set of numerical parameters able to describe the effect of the two interposed GFRP lamellae on a structural member composed of three wood battens connected lengthwise with mechanical fasteners, further considered as the reference beam. The numerical simulation is carried out in several steps. Firstly, the numerical model is calibrated with the experimental test of the reference beam. Secondly, the two GFRP lamellae are introduced between the timber members and the stress state and deformations both in cross-section`s components and at their interface are examined. The material models used in simulations were chosen according to the type of efforts that occur in timber beams and their failure modes when subjected to bending. For the timber components an orthotropic material model was considered. For the GFRP components linear elastic until failure material model was introduced. The interfaces between timber/GFRP lamellae were modeled by using cohesive zone material model with separation-distance based debonding. The results show a good correlation with those experimentally obtained and the parameters provided by this numerical analysis may be reliably used for specific design situations.

РАСЧЕТНО-ЭКСПЕРИМЕНТАЛЬНОЕ ИССЛЕДОВАНИЕ ПРОЦЕССА РАЗРУШЕНИЯ СВЯЗЕЙ СЦЕПЛЕНИЯ ПРИ ВДАВЛИВАНИИ СТЕРЖНЯ ЖЕСТКОЙ АРМАТУРЫ В БЕТОН

Flexible fittings with corrugated surfaces are traditionally used to improve the bond and minimize its debonding with concrete. But rigid I-beam reinforcements, the type required for heavy load bearing, are not corrugated. The onset of the debonding process that occurs when rigid I-beam reinforcement was pressed into concrete was established through comprehensive calculations and experimentation. The aim of the paper was to define the parameters and types of fractures in the “steel-concrete” contact zone. The Cohesive Zone Material Model (CZM), provided by ANSYS Workbench software, was used with the bilinear behavior law on the contact layer and described the separation of “steel-concrete surfaces. A mathematical model of the contact boundary problem was solved by the finite element method. A comparison of calculations and experimentation confirmed that the bond for smooth rigid reinforcement for B35 class concrete is provided by adhesion; and it is best described by the CZM model. Distribution patterns of contact pressure in the contact zone and of shear stresses on the concrete faces and surfaces adjacent to the I-beam were revealed. The relative displacement of concrete when impacted by an external force was measured. Results of this investigation indicate that the mathematical model is consistent and reflects the experimental data.

Finite Element Modelling of Cure-dependent Mechanical Properties by Model-free Kinetic Analysis Using a Cohesive Zone Approach

A methodology for using model-free kinetic analysis for the determination of mechanical properties is presented. Furthermore, this approach is used in finite element simulations for the prediction of the failure behaviour of adhesively bonded joints using a cohesive zone material model. Therefore, kinetic analysis is combined with mechanical experiments such as the butt-bonded hollow cylinder as well as the tapered double cantilever beam for the description of adhesive failure in mode I in various states of the curing reaction. It is shown that model-free kinetic predictions together with degree of cure dependent material properties can be used in finite element simulations to predict the transient material behaviour during cure.

The role of yield stress on cracked thin panels of aluminum alloys repaired with a fRP patch

ABSTRACTThe aim of this study was to explore the effect of the yield stress of the cracked thin panels of aluminum alloys panel, repaired with one sided fiber reinforced polymer (FRP) patch, on the performance of the repair. Various different grades of aluminum alloys with thickness in the range of 1–1.3 mm were used as the skin material. The numerical simulation of the experimental results was done through ANSYS 15.0, using a cohesive zone material model (CZM model) at the interface of the skin and the patch. The effect of the far field applied stress was analyzed to simulate the initiation and the separation of the patch. In all the six cases, undertaken in this study, the patch separation occurred when the applied stress exceeded the yield stress of the skin by a small percentage. Even in the thinnest patch with its stiffness ratio of 0.28, the patch separated when the applied stress exceeded the yield strength of the skin material. In all the cases, the shear stress at the interface caused the slippage between the patch and the skin at the leading edge of the patch.

Numerical simulation of bone screw induced pretension: The cases of under-tapping and conical profile

Even though screw induced pretension impacts the holding strength of bone screws, its implementation into the numerical simulation of the pullout phenomenon remains a problem with no apparent solution. The present study aims at developing a new methodology to simulate screw induced pretension for the cases of: (a) cylindrical screws inserted with under-tapping and (b) conical screws. For this purpose pullout was studied experimentally using synthetic bone and then simulated numerically. Synthetic bone failure was simulated using a bilinear cohesive zone material model. Pretension generation was simulated by allowing the screw to expand inside a hole with smaller dimensions or different shape than the screw itself. The finite element models developed here were validated against experimental results and then utilized to investigate the impact of under-tapping and conical angle. The results indicated that pretension can indeed increase a screw's pullout force but only up to a certain degree. Under-tapping increased cylindrical screws’ pullout force up to 12%, 15% and 17% for synthetic bones of density equal to 0.08gcm−3, 0.16gcm−3 and 0.28gcm−3, respectively. Inserting a conical screw into a cylindrical hole increased pullout force up to 11%. In any case an optimum level of screw induced pretension exists.

Behavior and Failure Modes of Sandwich T-Joint Using Cohesive Zone Material Model and Contact Elements

One of the significant concerns of sandwich panels is their joints. T-joint is one the most common joint in sandwich structures. This paper deals with the numerical study of triangle T-joint under static loading. The results of numerical solution obtained by ANSYS modeling are verified with the results of experimental tests obtained in the literature. In general, the results obtained for anticipated failure load by numerical solution with the results of experimental test is in good agreement. Contact elements and cohesive zone material model are used to model the adhesive layer, hence debonding and fracture of adhesive is observed by the numerical modeling. Also, by using a written macro code in the ANSYS software, the ability of damage is explained for the core of sandwich panels; thus both the modes in fracture of T-joints (core shear failure in base panel and debonding of adhesive) are modeled. Core materials consist of Divinycell H100, H160, H250, and HCP70 are used for modeling sandwich panels, so that the function of joint is studied under different conditions of the sandwich core material. Nine different geometrical models are created by changing the base angle of the core triangle. The absorbed energy associated with different segments of the T-joint are used to investigate the effect of joint geometry and core material on the load transfer and failure mode of the T-joint.

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 parametric study of cylindrical pedicle screw design implications on the pullout performance using an experimentally validated finite-element model

The present study aims to the design of a finite-element model simulating accurately the pullout behaviour of cylindrical pedicle screws and predicting their pullout force. Three commercial pedicle screws, subjected to pure pullout from synthetic bone, were studied experimentally. The results were used for the design, calibration and validation of a finite-element model. Special attention was paid to the accurate simulation of the failure inside the host material under shear. For this purpose, a bilinear cohesive zone material model was adopted, controlling the mode-II debonding of neighbouring elements in the vicinity of the screw. Comparison between experimental and numerical results proved that the implementation of this approach can significantly enhance the accuracy of the numerical simulation of a screw's mechanical behaviour under pure pullout loads. The numerical model was used for the parametric study of various factors affecting the pullout performance of a cylindrical pedicle screw. It was concluded that the major parameter influencing the pullout force is the outer radius (increasing its value by 36% increases the pullout force by 34%). The influence of the purchase length of the screw is of similar quantitative nature. The respective dependence on the thread inclination, depth and pitch was significantly weaker.