Debonding Propagation Research Articles

Revised notched coating adhesion test to account for plasticity and 3D behaviour

Specialized polyamide-imide coating on a CuSn10Pb10 substrate, a material combination utilized often in modern bearing applications, is fabricated using the solvent casting method. The coating adhesion is studied using the well-known notched coating adhesion (NCA) test. Conventionally, the critical strain required to cause the debond propagation is determined by visual observation and indirectly linked to measured strain data to calculate fracture toughness. Here, digital image correlation (DIC) is used to systemically study the coating deformations during testing that enables quantitative determination of the instantaneous debond length. With the introduced method, the critical strain to induce the debond of the coating and the propagation of the debond can be determined for non-elastically behaving specimens reliably. The coating’s debond onset is studied with virtual crack closure technique (VCCT) here. The method can take 3D effects into account in detail and provides a sophisticated method to determine the critical energy release rate. Additionally, cohesive zone modelling (CZM) is used to simulate debond progression. Nonlinear stress–strain responses are observed taking place both with the coating and the substrate materials. The results emphasize that the coating plasticity has a remarkable role in the test behaviour which needs to be taken into account in the revised analysis.

Direct visualization of interfacial debonding in FRP structure using an AIE molecule

Interfacial debonding is one of dominant damage types in fiber-reinforced polymers (FRPs). Therefore, monitoring the initiation and propagation of interfacial debonding in FRP is crucial for evaluating the health state of composites. The present work developed a direct visualization method using 1,1,2,2-tetrakis(4-nitrophenyl)ethene (TPE-4N) with aggregation-induced emission property, to detect the interfacial debonding in FRPs. To do so, TPE-4N was deposited on basalt fiber using dip-coating method, and the coated fiber was embedded into polydimethylsiloxane to fabricate corresponding composites. The results showed that TPE-4N molecule could correlate the invisible strain information in composites with the fluorescence signal under mechanical stimulus, and this could be quantitatively expressed by the grayscale value of materials. Interestingly, the debonding strain of composites (5.25%) obtained by the present method was much lower than the one (6.93%) obtained by the traditional strain measurement, suggesting that the fluorescence technique developed in this study was an effective way for in-situ and direct visualization of damage process in FRP structure.

XFEM and CZM modeling to predict the repair damage by composite patch of aircraft structures: Debonding parameters

In this work, a model based on the combination of two approaches XFEM and CZM, has been used to predict the damage of repairs by composite patch (patch/adhesive/plate assembly). This degradation is analyzed in terms of adhesive damage considering both initiation and propagation of interfacial debonding. The interfacial cohesive zone of the patch/adhesive/plate system is defined by its cohesive properties and its resistance to debonding estimated from the displacement-load curves.This study highlights, as a function of the adhesive properties of the plate/patch interface, the competition between two degradation mechanisms: adhesive damage (through a mechanism of initiation and propagation of patch debonding from the plate) and plate damage (through a phenomenon of crack initiation and propagation emanating from notch). It also highlights, depending on the nature of the interface, four physical parameters: the bending deflection of the repaired plate, the displacement path of the patch-reinforced plate, the debonding resistance and the interfacial shear stresses, characteristic of the adhesive joint damage and their interactions with the interface. This is the originality of this study. Results show that XFEM simulations based on the CZM model allow adequate prediction of the damage of the patch/adhesive/plate assemblies.

Progressive damage visualization and tensile failure analysis of three-dimensional braided composites by acoustic emission and micro-CT

Tensile failure and damage visualization based on progressive damage mechanics of three-dimensional braided composites were investigated. The complementary nondestructive testing technology combining acoustic emission with X-ray micro-computed tomography was used to analyze signal parameters, mechanical performance and internal damage morphology. The damage evolution results indicate that progressive damage will result in the reduction of Felicity ratio, stiffness stability and ultimate carrying capacity of specimen. The tightening cracks and load oscillation are the omens of instability failure and catastrophic failure of the specimen respectively. The specimen mainly experiences the initiation and propagation of cracking and debonding but there are multiple damage mechanisms in the failed specimen, which is consistent with the fact that deformation is not obvious until the huge deformation occurring in the final failure. In addition, longitudinal cracks first develop along the path of the least resistance between yarns under low tensile stress, and transverse cracks initiate and propagate along a relatively straight path under high tensile stress. In brief, progressive increasing tensile load can eventually cause instantaneous catastrophic failure to the specimen.

Interface bond between FRP systems and substrate: Analytical modeling

In the field of external strengthening and repairing of existing reinforced concrete structures, steel reinforced polymers (SRP) systems have emerged as a competitive alternative to the use of the more common carbon and glass fiber reinforced polymer (FRP) composites. Experimental investigations have frequently shown the potentials of these innovative composite systems in improving the performance of deficient structural members. At the same time, additional studies are needed to expand the existing knowledge and either to provide design recommendations or to develop specific guidelines. The paper fills some of the foregoing knowledge gaps by presenting an analytical investigation on the bond behaviour between SRP and concrete in which closed-form solutions are derived to predict the entire debonding propagation process. In particular, accurate and simplified local shear stress-slip (τ-s) laws are employed in the proposed modelling from which different expressions for the interfacial shear stress distribution, the axial stress profile and the concrete-SRP relative displacement (slip) are developed and commented in the paper; analytical estimates of the SRP effective bonded length are provided as well as relationships for calculating the maximum axial stress (or peak force) at SRP laminate debonding.The analytical procedure was, firstly, applied to simulate some single-lap shear tests performed in a previous experimental program with the purpose to investigate the influence on the debonding propagation process of the following main parameters: a) concrete strength, b) concrete surface finish and c) steel tape density. Then, the comparisons between the numerical simulations and the experimental results available for some bond tests have allowed for verifying the accuracy of the proposed modelling.

Study of EMI-Based Damage Type Identification in a Cracked Metallic Specimen Repaired by a Composite Patch

Using adhesively bonded composite patch repairs has been increased in various industries to improve the structural integrity of cracked metallic structures in recent decades. Monitoring of crack propagation and composite patch debonding, as two dominant failure mechanisms in this repair technique, plays a significant role in the integrity assessment of the component. This research conducts an experimental investigation on the simultaneous monitoring of these two failure mechanisms in a cracked metallic specimen repaired by a composite patch. For this purpose, the electromechanical impedance method was used to evaluate the feasibility of recognizing the type of damage at any phase of total damage propagation process. Two piezoelectric sensors were implemented, one mounted on the metal and the other on the composite patch. Investigation of impedance spectrums and damage index trends showed that debonding and crack propagation produce different effects on the measurements made by sensors. These differences were used as a basis of identifying the type of damage. As a result, some features were introduced to classify the type of damage in each step of damage propagation.

Numerical study on the toughening effect of the fiber bridging on delaminated composite stiffened panel

In this paper, the debonding behavior of a fiber reinforced composite panel, under flexural loading conditions, is numerically studied. Two material systems, respectively insensitive and sensitive to the fiber bridging phenomenon, are considered. The toughening effect of the fiber bridging phenomenon, on the debonding propagation, is analyzed. An innovative numerical procedure, able to consider GIc variations with the crack length, is proposed. The results of numerical models are compared to evaluate the fiber bridging sensitivity effects on the maximum attained load and on the delaminated area.

Debonding Mechanisms at the Particle-Binder Interface in the Li-Ion Battery Electrode

Interfacial debonding is one of the reasons for capacity fade and impedance increase in Li-ion batteries. In this study, the debonding behavior of the active particle from the binder was investigated during the progress of lithiation/delithiation. Using the cohesive zone model, the progressive interfacial debonding was simulated by two-way coupling of the lithium diffusion and mechanical damage. The role of the interfacial traction forces and relative displacements were analyzed in the damage development and debonding propagation. The effect of the interfacial fracture was investigated on the evolution of state of charges and stresses within the particle and binder. The simulations revealed that debonding starts from the edge of the interface; and once it happens, rapidly propagates toward the inner region of the interface. The interface debonding enhanced the extent of the average state of charges due to the additional ionic flux through the newly created surfaces. The developed model can be extended to study the performance change due to the mechanical failure in Li-ion batteries by implementation in the cell-scale model. In addition, understanding the fundamental mechanisms of interfacial debonding will help engineers design more robust electrodes with better mechanical integrity.

Effect of surface preparation of substrate on bond tensile strength of thin bonded cement-based overlays

The paper focuses on the debonding between a cement-based overlay and a concrete substrate under a mechanical loading. Two categories of substrate surface preparation were considered: Sawing the Substrate and Sand Blasting of the casting surface of the substrate. Untreated substrate surface used in its original state was taken as the Reference Surface. The overlay material investigated was a cement-based mortar. Direct tensile tests perpendicular to the overlay-substrate interface were carried out at the age of 28 days and the results (tensile strength, residual post peak behavior) are presented and discussed. Attention was paid to the Sand Blasted surface which is a more realistic model of practical field conditions. The debonding propagation under monotonie and fatigue loading was monitored for sand blasted surfaces using the Digital Image Correlation technique. Results indicate that both surface preparation technique has its own efficiency level and gives different roughness. Among the techniques used, greater bond strength improvement was observed with the sawn substrate surface than with the sandblasted one. Moreover, under cyclic loading, major debonding along the interface occurs from the first cycle to the 20000th cycle and is negligible thereafter.

Reliability analysis of metal‐composite adhesive joints under debonding modes I, II, and I/II using the results of experimental and FEM analyses

AbstractIn the present study, the experimental and finite element (FE) analyses are first carried out to investigate the deboning behavior of metal‐composite adhesive joints under modes of I and mode II loading. To conduct an FE on the debonding propagation, cohesive zone method (CZM), as well as maximum nominal stress and energy criteria, is applied. In the reliability analysis, to achieve the probability of debonding growth (PODG), limit state functions are formulated based on the energy release rate. To that end, the first‐order reliability method (FORM), the second‐order reliability method (SORM), and the Monte Carlo simulation (MCS) are used to calculate the PODG. The effect of initial debonding length on the PODG in all mentioned modes is investigated. Results obtained from reliability analysis reveal that the random variables including the initial debonding length, width, and thickness are the most sensitive variables to ascertain the PODG.

Mechanical Behavior of Fiber-to-concrete Interface in Textile Reinforced Concrete: Theoretical Model

This paper presents a theoretical solution of a reinforcement-to-concrete interface model under pull-push loading. Expressions for the interfacial shear stress distribution and load-displacement history are derived for different loading stages. The full debonding propagation process is discussed in detail and the analytical solutions are verified by comparing with existing theoretical models. Results of the analytical solution are presented to illustrate how the bond length and local bond-slip law affect the interfacial bond behavior. While the case study in this paper is on textile reinforced concrete, the analytical solution is equally valid to similar mechanical cases such as rebar reinforced concretes.

Experimental and numerical study of process-induced defects and their effect on fatigue debonding in composite joints

Laboratory coupon joints for fatigue debonding tests usually have narrow width and a through-width initial disbond. However, realistic structural joints are much wider and may contain process-induced defects and accidental damage; both are much smaller than the joint width. Small and discrete damage may behave differently from the idealised through-width disbond crack. This has brought a question on whether the laboratory coupon joint can accurately represent the fatigue behaviour of wider structural joints. This paper presents an experimental and numerical study of fatigue behaviour of a wide bonded lap joint with a process-induced defect of semi-circular shape. Fatigue debonding propagation was monitored by ultrasound inspection. Fatigue life was predicted using a normalised strain energy release rate parameter calculated by finite element method, and the adhesive material fatigue crack growth rate data measured under single and mixed mode conditions. Simulation of process-induced defect and validation by experiments have brought a better understanding of fatigue debonding behaviour in wide joints containing realistic damage. Suggestions are given for fatigue fracture tests of bonded joints.

Calculation of stress intensity factors of matrix crack tip in particle reinforced composites using the singular Voronoi cell finite element method

In this paper, a new singular Voronoi cell finite element method (S-VCFEM) is proposed to study the initiation and propagation of interfacial debonding and matrix cracking in particulate reinforced composite. Composites with large-scale inclusions and cracks can be easily simulated with this model. A new assumed stress hybrid variational functional is derived from the element energy function to accommodate the interface traction reciprocity on bonded interface and the interface traction-free on debonded interface and matrix crack surface. S-VCFEM is achieved through enhancements in stress functions in the assumed stress hybrid formulation. In addition to polynomial terms and interaction terms, singular stress terms of Williams expansion are added for stress functions, which are adaptively enriched to accurately capture the crack-tip stress concentrations. After obtaining the stress field, calculation of stress intensity factors is performed, using the least square method based on stress value obtained numerically in the S-VCFEM. The efficiency of the method is verified against numerical results obtained by ABAQUS with XFEM module for the same problem considering a matrix-crack and a debonded interface.

High-order crack propagation in compressed sandwich panels

The response and the debonding mechanisms in axially compressed sandwich panels with an interfacial delamination are investigated using a nonlinear model. The mathematical model combines the extended high-order sandwich panel theory with a cohesive interface modeling. It includes the first-order shear deformation kinematic assumptions for the face sheets and high-order small deformations kinematic assumptions that account for out-of-plane compressibility for the core. The interfaces bond the face sheets and the core by means of traction–displacement gap laws. These interfacial laws can describe a diversity of physical conditions. In particular, interfacial debonding nucleation and propagation are described using cohesive laws that introduce the interfacial nonlinearity into the model. Geometrical nonlinearity of the face sheets is introduced in order to capture the instability associated with the buckling of the delaminated face sheet. The cohesive interfaces and others parameters are calibrated to match experimental results taken from the literature for a sandwich specimen subjected to an end-shortening compression. The instabilities due to the in-plane compression, together with the existence of delaminated regions and their tendency to grow, prompt buckling of the delaminated face sheet as well as nucleation and propagation of the interfacial debonding. The theoretical quantification of this complex mechanism compares well with the experimental results in terms of the physical response, the nucleation and propagation of the interfacial crack, and the evolution of local/global geometrical instabilities. In addition, the analysis explores debonding mechanisms that are beyond the capabilities of the experimental technique. Finally, the sensitivity of the response and the associated geometrical and interfacial instabilities to the boundary conditions are investigated.

Interaction of interfacial debonding and under-film corrosion propagation at the edge of the blistering area of epoxy coating

Interaction of interfacial debonding and under-film corrosion propagation at the edge of the blistering area of epoxy coating

Using blister test to predict the failure pressure in bonded composite repaired pipes

The design and qualification of composite repairs for pipelines usually requires hydrostatic tests for the determination of the failure pressure. In this work, the use of a shaft blister test to assess the failure pressure of composite repairs is proposed. Blister tests were conducted to investigate the interfacial debonding of a composite plate bonded to steel substrate. The blister test specimen represents a composite repair applied to a pipeline with a defect. The onset debonding load is used to predict the failure pressure. A 3D digital image correlation (DIC) has been used to follow up the debonding propagation and evaluate the blister shape. 3D finite element model with a cohesive zone model has been used to simulate loaded shaft blister test. A good correlation between blister tests results and finite element simulation results was obtained. The validated finite element model was used to predict failure pressure in bonded composite repaired pipes with different values of defect diameter and repair thickness. The results show that the blister test could replace hydrostatic tests for the analysis of the composite repairs performance.

Consistent application of periodic boundary conditions in implicit and explicit finite element simulations of damage in composites

This paper presents an implementation-dedicated analysis of Periodic Boundary Conditions (PBCs) for Finite Element (FE) models incorporating highly non-linear effects due to plasticity and damage. This research addresses fiber-reinforced composite materials modeled at micros-scale level using a Representative Volume Element (RVE), where its overall mechanical response is obtained via homogenization techniques. For the sake of clearness, a unidirectional ply with randomly distributed fibers RVE model is assumed. PBCs are implemented for implicit and explicit FE solvers, where conformal and non-conformal meshes can be used. The influence of applying PBCs in the reliability of the mechanical response under tension and shear loading is assessed. Furthermore, the Poisson effect and the consistency of damage and fiber debonding propagation through the periodic boundaries are reported as well as their impact on the homogenized results. Likewise, numerical aspects like computational performance and accuracy are evaluated comparing implicit- versus explicit-based solutions.

دراسة عملية وتحليل العناصر المحددة لتاثير التسخين على قوة الانسلاخ لسلك النيتينول مغمور داخل بولي اثيلين خطي منخفض الكثافة

هذا البحث يقدم دراسة نشوء الانسلاخ لسلك نيتينول مفرد سبيكة ذاكرة الشكل داخل بولي اثيلين خطي منخفض الكثافة مصفوفة مركبة دراسة باستخدام فحص السحب. الهدف من هذا البحث دراسة فحص السحب لتحقق من قوة التداخل لمركب بوليميري في حالتين, مع تنشيط سلك النيتينول وبدون تنشيط . في هذا البحث سيكة ذاكرة الشكل سلك نيتينول قطر 2 مليمتر شكل مستقيم كامل التصليب قد استخدم. الدراسة شملت العملي وتحليل العناصر المحددة واخيرا المقارنة بينهم. يعد فحص السحب فحصاً اساسياً بسبب نتائجه لها علاقة بسلوك المواد المركبة الذكية. فحص السحب قد نفذه بواسطة آلة اختبار الشد العالمي نوع (لاري) , ذو سعة حمل 50 كيلو نيوتن, سرعة الفحص 1 ملم/دقيقة قد استخدمت. نفذت نمذجة العناصرالمحدد بوساطة انسيز الاصدار 15. نتائج فحص السحب اثبتت عند تنشيط سلك النيتينول المغمورداخل مصفوفة المضيف بولي اثيلين خطي منخفض الكثافة, قوة الانسلاخ حوالي 74 نيوتن, لكن في حالة بدون تنشيط حوالي 106 نيوتن. اجهاد قص الانسلاخ في التنشيط حوالي 0.73 ميكا باسكال, لكن بدون تنشيط حوالي 0.99 ميكا باسكال. خلال التنشيط النسبة لاجهاد قص الانسلاخ تقل بي 30.47% و 30.13%, على التوالي. نسبة الخطأ بين النتائج العملية والانسزز 8% في حالة التنشيط و 5.7% في حالة بدون تنشيط.

Sandwich panels under interfacial debonding mechanisms

The paper presents a nonlinear approach to investigate the behavior of composite sandwich structures with transversely compressible core, under static and dynamic loading conditions. The proposed model, formulated in the 2D framework, incorporates moving mesh cohesive modeling, crack initiation and nucleation at core/skin interfaces. Interface elements are used to predict debonding mechanisms, whereas shear deformable beams and two-dimensional plane stress elements identify skin and core behavior, respectively. In this framework, interfacial crack onset, layer kinematic and debonding propagation effects are correctly simulated. The moving mesh technique, combined with a multilayer formulation, ensures a reduction of the computational costs, required to predict crack onset and progressive evolution of debonding phenomena. Cohesive models for sandwich core/skin interfaces are calibrated by means of comparisons with numerical and experimental data with respect mode I and mode II configurations. Moreover, a parametric study to address the influence of the loading rate and sandwich characteristics on both static and dynamic frameworks is proposed.

Low energy impact on the interface of bamboo-steel composites

ABSTRACTThe bamboo-steel composite structure is a newly developed structure, combining Phyllostachys Pubescens (also called Moso bamboo) plywood and cold-formed thin-walled steel with structural adhesive. The aim of this study is to investigate the debonding propagation mechanism in detail at the bamboo-steel adhesive bonding interface (bamboo-steel interface) under low-energy impact using a progressive failure model. A three-dimensional cohesive zone model with reloading traction-separation law was adapted to simulate and characterize the progressive adhesive debonding at the bamboo-steel interface. Results show that the model can predict the failure behavior of the bamboo-steel interface under low-energy impact. The stress distribution and debonding propagation of the bamboo-steel interface were analyzed. The results reveal that the debonding is mostly due to the shear stress and the tensile peeling stress at the impact loading stage and the unloading stage, respectively. Furthermore, analyses of the impact failure show that the shear stress at the impact loading stage is generated by the tangential sliding between the steel sheet and bamboo plywood due to different flexural stiffness, while the tensile peeling stress at the unloading stage is due to the normal separation owing to different rebounding of the two different materials.