Analysis Of Debonding Research Articles

Effectiveness of some technical standards for debonding analysis in FRP-concrete systems

Debonding failure is a key issue in strengthening and retrofitting of existing concrete structures via fiber-reinforced polymers (FRP). In this paper, strength models proposed by different technical guidelines for predicting the debonding load and the effective bond length in FRP-concrete systems are consistently summarized and compared. By referring to the recent specialized literature, a wide database of experimental data - collected from debonding tests associated to FRP based on carbon, glass and basalt fibers - is defined and analyzed. As a result, soundness and effectiveness of some available technical indications are critically assessed, by highlighting the influence of both FRP stiffness (mainly related to the fiber type) and FRP application system. Moreover, a least-square-fitting calibration of theoretical predictions with respect to the experimental evidence is proposed and applied, resulting in the definition of a novel set of values for the empirical correction coefficients occurring in the analyzed strength models. Accordingly, proposed results pave the way towards the effective refinement of actual technical standards for debonding analysis in FRP-concrete systems.

Finite element analysis of intermediate crack debonding in fibre reinforced polymer strengthened reinforced concrete beams

The performance of the fibre reinforced polymer (FRP) to reinforced concrete (RC) interface is vital to ensure desired design capacity. Without proper understanding of the interfacial behaviour it is impossible to develop an effective, efficient, and rational bonding technique. This paper presents the results of a comprehensive numerical investigation aimed to assess and better understand the debonding behaviour caused by different types of intermediate flexural crack distributions in FRP–RC strengthened beams. The model is based on damage mechanics modelling of concrete, a bilinear bond–slip relationship with softening to represent the interface, and a discrete crack approach to simulate crack propagation. The model also highlights how crack propagation and debonding is affected by the rate of change of moment. It is shown that the variation of crack spacing and rate of change of moment can significantly affect debonding crack propagation and strain development in the internal and external reinforcement, which directly influences debonding load.

Analysis of skin-stringer debonding in composite panels through a two-way global-local method

Analysis of skin-stringer debonding in composite panels through a two-way global-local method

Analysis of skin-stringer debonding in composite panels through a two-way global-local method

According to various experimental results, stiffened panels under compressive loading are prone to debonding between the skin and the flange of the stringer. In this paper, a novel two-way global-local coupling approach is presented that is able to model progressive separation of the skin and stringer in stiffened CFRP panels under compression. The main goal of this methodology is to examine skin-stringer debonding at two levels of accuracy, taking advantage of the fast calculations at the global level and assessing in detail the damage propagation at the local level. First, critical areas are defined in a global model with a standard mesh, and local models with a considerably finer mesh are created by means of a submodeling technique. Secondly, a local model analysis is conducted, in which cohesive elements are applied to simulate debonding. Particularly important is the appropriate information exchange in both directions between the different steps of the coupling analysis. Averaged degraded properties are defined at the local model level and transferred back to the global level. The applied compressive load is increased and induces a progression in skin-stringer separation. The global-local coupling loops are repeated until panel failure occurs. The approach is applied to a case of a representative one-stringer stiffened panel and to a stiffened panel for which test results are available. A good correspondence with reference results and test results demonstrates the effectiveness of the global-local approach presented.

Analysis of debonding in bio-inspired interfaces obtained by additive manufacturing

The present work is focused on the analysis of fracture in adhesive bonded Double Cantilever Beam (DCB) specimens with 3D printed nylon substrates. The substrates were obtained using selective laser sintering of polyamide powder and embed sub-surface channels with circular and square cross-section. The proposed strategy allows to mimic the crack trapping effect already observed in a multitude of biological materials, that is originated by the spatial modulation of the driving force available for crack growth. Mechanical tests have shown that the channels induce load fluctuations in the global load-displacement response. A significant increase in the total dissipated energy was observed with respect to bulk samples, i.e. no channels. The observed fluctuations in the global response were associated to the sequential storage and sudden release of elastic energy. Indeed, the spatial modulation of the stiffness around the interfacial region ultimately affects the crack driving force.

Modeling and analysis of debonding in a smart beam in sensing mode, using variational formulation

Using basic electro-elastic formulation and variational formulation, a higher order finite element model has been developed for the analysis of debonding in a smart cantilever beam. Full length piezo patch embedded at the top and bottom of the aluminium core has been assumed to be de-bonded. The debonding has been incorporated at the interfaces between piezo patches and the core, at the mid span of the beam for one third length of the beam. The effect of debonding in sensing mode has been analysed by presenting the induced potential, axial displacement, axial/transverse electric field and stresses for fully bonded and de-bonded smart cantilever beam. The variation in electric potential, electric field, axial displacement/strain/stress and shear strain/stress observed in case of debonding demonstrates that the mechanics of debonding is complex coupled electro-mechanical behaviour. In the de-bonded beam, the induced potential at the free piezo surface and at the interfaces shows a sinusoidal variation from root to the tip as compared to the linear variation in bonded beam. This is attributed to the non-linear bending moment variation from root to the tip in case of de-bonded beam. The maximum stress in debonding increases nearly 1.5 times to that of bonded beam sensing at various locations.

A half-analytical elastic solution for 2D analysis of cracked pavements

This paper presents a half-analytical elastic solution convenient for parametric studies of 2D cracked pavements. The pavement structure is reduced to three elastic and homogeneous equivalent layers resting on a soil. In a similar way than the Pasternak's modelling for concrete pavements, the soil is modelled by one layer, named shear layer, connected to Winkler's springs in order to ensure the transfer of shear stresses between the pavement structure and the springs. The whole four-layer system is modelled using a specific model developed for the analysis of delamination in composite materials. It reduces the problem by one dimension and gives access to regular interface stresses between layers at the edge of vertical cracks allowing the initial debonding analysis. In 2D plane strain conditions, a system of twelve-second order differential equations is written analytically. This system is solved numerically by the finite difference method (Newmark) computed in the free Scilab software.The calculus tool allows analysis of the impact of material characteristics changing, loads and locations of cracks in pavements on the distribution of mechanical fields. The approach with fracture mechanic concepts is well suited for practical use and for some subsequent numerical developments in 3D.

Crack growth and debonding analysis of an aluminum pipe repaired by composite patch under fatigue loading

In this study, the behavior of a cracked aluminum pipe, repaired by glass/epoxy composite patch, is investigated under fatigue tension loading through the experimental test and numerical modeling. While most previous investigations on crack growth problems assume that the composite patch is tied to the cracked panel, in this study debonding of the adhesive layer between the pipe and the composite patch is modeled besides crack growth in the aluminum pipe. The crack growth is modeled through XFEM framework while cohesive elements are implemented to consider debonding in the adhesive layer. It is shown that such a numerical model can present more realistic behavior of the structure in comparison to similar experimental tests. Three different shapes of composite patches are then considered to investigate the debonding procedure during fatigue loading of the cracked pipe. A parametric study is also presented for such a cracked repaired pipe to observe the effect of fiber orientation on fatigue crack growth. Finally the debonding is studied in a repaired pipe with an inclined crack. These parametric studies would lead to reaching optimized designs of patch repaired pipes under fatigue loading.

Acoustic emission monitoring and finite element analysis of debonding in fiber-reinforced polymer rebar reinforced concrete

The acoustic emission technique is widely used for mechanical diagnostics and damage characterization in reinforced concrete structures. This article experimentally investigated the feasibility of debonding characterization in fiber-reinforced polymer rebar reinforced concrete using acoustic emission technique. To this end, carbon-fiber-reinforced polymer rebar reinforced concrete specimens were prepared and they were subjected to pullout tests to study the interfacial debonding between concrete and reinforcement. Test results showed that the debonding failure between concrete and reinforcement was characterized by the total peeling off of the helical wrapping layer of the carbon-fiber-reinforced polymer reinforcement. The response of acoustic emission activity was analyzed by descriptive parameters, such as cumulative acoustic emission hits, amplitude, and peak frequency. The evolution of debonding failure is thus characterized by these acoustic emission parameters. The results demonstrated a clear correlation between the damage evolution of carbon-fiber-reinforced polymer rebar pullout and the acoustic emission parameters. In addition, finite element analysis was adopted to study the stress field during the pullout of the reinforcement. The simulation results agreed well with the experimental investigations.

Progressive failure analysis of scarf-repaired composite laminate based on damage constitutive model

A three-dimensional finite element model for scarf-repaired composite laminate was established on continuum damage model to predict the load capacity under tensile loading. The mixed-mode cohesive zone model was adopted to the debonding behavior analysis of adhesive. Damage condition and failure of laminates and adhesive were subsequently addressed. A three-dimensional bilinear constitutive model was developed for composite materials based on damage mechanics and applied to damage evolution and loading capacity analyses by quantifying damage level through damage state variables. The numerical analyses were implemented with ABAQUS finite element analysis by coding the constitutive model into material subroutine VUMAT. Good agreement between the numerical and experimental results shows the accuracy and adaptability of the model.

Role of interfacial damage modeling in finite element analysis of intermediate crack debonding failure of FRP-plated reinforced concrete beams: A numerical investigation

This study presents a numerical investigation into the effects of interfacial damage on the bond behaviors of the interfaces between two adjacent cracks in a fiber-reinforced polymer-plated reinforced concrete beam. The interfaces investigated herein refer to both fiber-reinforced polymer-to-concrete interface and steel-to-concrete bonded interface which were well represented in this study by a simplifying fiber-reinforced polymer-to-concrete bonded joint or steel bar-to-concrete bonded jointed joint loaded at their two ends, aiming to simulating the interaction between two adjacent flexural cracks in the fiber-reinforced polymer-plated reinforced concrete beams. Parametric studies were carried out using nonlinear finite element model built in ABAQUS to investigate the effects of a number of significant factors such as bond length, ratio of loads applied at the two ends (i.e. load ratio), and types of bond–slip models, with the main objective being to clarify the effect of interfacial damage (i.e. bondline damage) during slip reversals on the bond behaviors of the interfaces. The numerical results show that in finite element analysis of intermediate crack debonding of fiber-reinforced polymer-plated reinforced concrete beams where multiple cracks may exist, an appropriate consideration of the interfacial damage during slip reversals is necessary in order to achieve accurate predictions on the behavior of fiber-reinforced polymer-to-concrete bonded interfaces, while for the steel bar-to-concrete interface, the consideration of the interfacial damage has insignificant effect on the numerical results if the yield strength and bar diameter are in their practical range.

Size effect in the debonding failure of FRP strengthened beams

The paper studies the potential size effect in the debonding failure of beams strengthened with fiber reinforced polymer composite materials. For that purpose, a framework for the debonding analysis of such large-scale strengthened beams is developed. The model combines high order modeling with fracture analysis and crack growth simulation through equilibrium paths. The analysis overcomes the inherent problem of length scales variation and its computational implications through a one-dimensional high order extended finite element approach. The results reveal a size effect with intermediate crack debonding stability characteristics that change from small scale beams to large scale ones.

Analysis of interfacial debonding in shape memory alloy wire-reinforced composites

One of the common types of failure in shape memory alloy (SMA) wire-reinforced composites is interfacial debonding between the fiber and the matrix. In this paper, a three dimensional finite element model for an SMA wire-reinforced composite is developed based on cohesive zone modeling to predict interfacial debonding between the SMA wire and the surrounding matrix. The interfacial debonding is also experimentally investigated by conducting a number of pull-out tests on steel as well as Nitinol wires embedded in an epoxy matrix. To evaluate the presented method, the developed finite element analysis is employed to simulate a single wire pull-out test for ordinary (e.g. steel) wires. In order to simulate SMA wire pull-out, a 3D SMA constitutive model is implemented into the commercial finite element software ABAQUS using a user material subroutine (UMAT). An acceptable agreement is shown to exist between the theoretical results and the experimental data, indicating the efficiency of the proposed approach to model interfacial debonding in SMA wire-reinforced composites.

Studies of fiber-matrix debonding

In this paper, the debonding of a single fiber-matrix system of carbon fiber reinforced composite (CFRP) AS4/Epson 828 material is studied using Cohesive Zone Model (CZM). The effect of parameters namely, maximum tangential contact stress, tangential slip distance and artificial damping coefficient on the debonding length at the interface of the fiber-matrix is analyzed. Contact elements used in the CZM are coupled based on a bilinear stress-strain curve. Load is applied on the matrix, tangential to the interface. Hence, debonding is observed primarily in Mode II.Wide range of values are considered to study the inter-dependency of the parameters and its effect on debonding length. Out of the three parameters mentioned, artificial damping coefficient and tangential slip distance significantly affect debonding length. A thorough investigation is recommended for case wise interface debonding analysis, to estimate the optimal parametric values while using CZM.

Intermediate crack-induced debonding analysis for RC beams strengthened with FRP plates

This paper presents the analysis of intermediate crack-induced (IC) debonding failure loads for reinforced concrete (RC) beams strengthened with adhesively-bonded fiber-reinforced polymer (FRP) plates or sheets. The analysis consists of the energy release and simple ACI methods. In the energy release method, a fracture criterion is employed to predict the debonding loads. The interfacial fracture energy that indicates the resistance to debonding is related to the bond-slip relationships obtained from the shear test of FRP-toconcrete bonded joints. The section analysis that considers the effect of concrete‟s tension stiffening is employed to develop the moment-curvature relationships of the FRP-strengthened sections. In the ACI method, the onset of debonding is assumed when the FRP strain reaches the debonding strain limit. The tension stiffening effect is neglected in developing a moment-curvature relationship. For a comparison purpose, both methods are used to numerically investigate the effects of relevant parameters on the IC debonding failure loads. The results show that the debonding failure load generally increases as the concrete compressive strength, FRP reinforcement ratio, FRP elastic modulus and steel reinforcement ratio increase.

A micromechanical debonding analysis of fiber-reinforced composites due to curing residual stress

The representative volume element method is used to investigate the interface debonding of fiber-reinforced composites due to curing residual stress. First, the interface debonding behavior is characterized by means of the cohesive zone model, and the effects of curing residual stresses on the fiber/resin interface debonding are also studied using the cure hardening instantaneously linear elastic model. Second, debonding envelops of the representative volume element are obtained for tension loading, shear loading and mixed loading, respectively, which indicate that the curing residual stresses will have an important influence on the maximum principal stress and have no effects on the debonding initiation location and the propagating path. Finally, the relationships between the fiber versus resin aspect ratio γ and the maximum principal stress at the fiber/resin interface of the representative volume element in fiber-reinforced composites are investigated as well.

Theoretical analysis of interfacial debonding and fiber pull-out in fiber-reinforced polymer-matrix composites

A theoretical model is proposed to predict the interfacial debonding length and fiber pull-out length in fiber-reinforced polymer-matrix composites. The stress and displacement fields of fiber and matrix are derived considering the dual phase region model, and the relation between the pull-out length and debonding length of fiber is obtained. The interface debonding criterion is given based on the energy release rate relation in an interface debonding process. The formulas are applied in glass fiber-reinforced epoxy composites to demonstrate the newly theoretical model. The theoretical predictions of present model agree well with the experimental results. Several parameters studies are performed to analyze the debonding length and the pull-out length of fiber in glass fiber-reinforced epoxy composites.

Use of cohesive zone models to design automotive bonded joints

Cohesive-zone models have been widely used for the analysis of interface debonding. In this paper, three of these models are used to study a set of debonding problems. A comparative analysis of the three models is carried out; results are presented and discussed for numerical simulations referring to both single-mode and mixed-mode situations. The results show that the differences between the load-deflection curves obtained for the three models considered, become more evident by increasing the stiffness of the specimen. Considering that the most common joint configuration in automotive industry is the lap-shear joint, the main conclusion of this work is that the joint stiffness will not affect the computational response obtained with the three different models studied here.

Experimental Analysis of Debonding of Skin/Stringer Interfaces under Cyclic Loading and Ageing

An experimental investigation aiming to characterize the fatigue failure mechanisms and effect of ageing of skin/stringer interfaces is presented. A simplified specimen known as a “stringer foot specimen” is used. The effects of local design, of the angle of plies located at the interface and of moisture ageing are studied. Among other results, it is shown that a quasi-infinite fatigue life can be obtained under 33% of the static damage initiation load for all designs. In the framework of multi-level analysis, this study is a preliminary investigation to study cyclic buckling of composite stiffened structures.

Progressive debonding analysis of composite blade root joint of wind turbines under fatigue loading

In this paper, progressive debonding of the blade root joint of a 660kW wind turbine under cyclic loading is studied. Progressive fatigue debonding of this adhesive joint is analyzed using cohesive zone interface modeling. The blade is subjected to various loadings such as aerodynamic forces, centrifugal force, weight, and force due to the change in wind direction. A user defined material subroutine is used in the ANSYS finite element code to predict both the crack (debonding) initiation and propagation in the adhesive joint under variable amplitude fatigue loading. The required material properties such as the critical strain energy release rate and the Paris law constants are characterized experimentally through the well-known tests for different fracture modes: double cantilever beam (DCB) for mode-I (opening mode), end notch flexure (ENF) for mode-II (shearing mode) and mixed mode bending (MMB) for mixed mode conditions. These tests are performed for composite to aluminum interfaces, which are representative of the actual material used in the manufacturing of the wind turbines blades. The experiments are performed under both static and fatigue loading. The predicted initiation and progressive damage results from numerical analyses are verified by experimental results for simple joints. It is illustrate that the maximum length of the deboned area after a typical overloading is about 8% of the total height of the root joint and during the fatigue loadings it would increase to about 40% of the total height after 1month normal operation. The developed numerical analysis tool can then be used to predict the debonding initiation and propagation in the root joint of the wind turbine blades.