Interfacial Fracture Energy Research Articles

Bonding Behavior of Wet-Bonded GFRP-Concrete Interface

AbstractAn experimental study was conducted to investigate the interfacial behavior between glass-fiber-reinforced polymer (GFRP) plate and cast-in-place (CIP) concrete placed against this plate—a method known as wet-bonding. The experimental program consisted of 33 single-shear specimens with various initial placement times of concrete, durations of concrete curing, and interface preparations. Control specimens using a conventional dry-bonded technique were also tested. A model was proposed that was able to predict the interfacial ultimate pullout load and local shear stress-slip relationship of a wet-bonded interface with reasonable accuracy. It is shown that (1) wet-bonded interfaces exhibit lower capacity and interfacial fracture energy than dry-bonded interfaces although the load to cause initiation of debonding is not significantly different; (2) the time of initial placement of the CIP concrete onto the wet, set, or cured resin significantly influences the ultimate pullout load and interfacial frac...

GS0405-207 炭素-フェノール樹脂間界面接着強度に関する分子シミュレーション

The interfacial strength between carbon and phenolic resin is studied by using molecular dynamics simulations in order that carbon reinforced carbon matrix composites (C/C composites) has better strength development rates. Simulations are performed by two carbon fiber models, one of which has only carbon atoms and the other has carbon atoms and some fluorinated carbon groups. Carbon fiber models are regarded as two-layer graphite and phenolic resin model is treated as simple cross linked structures. All force field parameters are based on Dreiding force field. Tensile stress and interfacial fracture energy are calculated for the estimation of adhesive strength. Results of the model including fluorinated carbon groups get lower interfacial strength than that of having only carbon atoms.

Prediction of Load Capacity Variation in FRP Bonded Concrete Specimens Using Brownian Motion

In wet lay-up process, dry fiber sheets are saturated with a polymer and applied to the concrete surface by hand. This causes relatively large variation in properties of the cured FRP composite material. It is hard to know the exact mechanical properties of the FRP constructed by wet lay-up process. In addition, the stiffness of FRP changes during debonding process due to different amount of concrete attached to the debonded FRP at different locations. It is also inevitable to have considerable variations in the strength of concrete. Therefore, the behaviour of FRP bonded concrete members varies among specimens even when the same materials are used. The variation of localized FRP stiffness and concrete strength can be combined in a single parameter as variation of the localized interfacial fracture energy. In an effort to effectively model the effects of the variation of interfacial fracture energy on the load versus deflection responses of FRP bonded concrete specimens subjected to Mode I and Mode II loading, a random white noise using a one-dimensional standard Brownian motion is added to the governing equations, yielding stochastic differential equations. By solving these stochastic equations, the bounds of load carrying capacity variation with 95% probability are found for different experimental tests.

Interfacial Fracture Toughness of Multilayer Composite Structures

The interfaces in multilayer composite structures are susceptible to delamination due to the combination of active tensile and shear loads under operating conditions. A four-layer center crack composite beam in four-point bending is simulated to determine the interfacial fracture energy of the multilayer structure. The crack is propagating along the interface between the second and third layers. Based on the Euler–Bernoulli theory, the strain energy of the four-layer composite beam is derived. Strain energies before and after the propagation of the interfacial crack are calculated, which results in determining strain energy release rates. Analytical results for those rates are validated with the numerical data obtained by the finite element method. The effect of layer thickness of the composite beam on the interfacial fracture toughness is investigated through a parametric study.

Finite element analysis of composite T-joints used in wind turbine blades

This paper presents a finite element (FE) analysis of the fracture behaviour of composite T-joints with various fibre reinforcement architectures subjected to pull-out loading. The FE model accounts for the effect of interface strength and interlaminar fracture energy on the ultimate load to failure; a linear softening fracture based law is adopted to describe crack growth in the form of delamination. The numerical simulation shows that the failure load increases with increasing interlaminar strength, which controls delamination initiation. The FE also demonstrates that the failure load increases with increasing interface fracture energy and the delamination propagation depends largely upon the fracture energy, which is enhanced by introducing interlaminar veils or through-thickness tuft yarns (stitching). Predictions were validated using experimental data for E-glass fibre/epoxy T-joints subjected to a tensile pull-out loading. The load–displacement response from the FE analysis is in a good agreement with measurements, illustrating the effectiveness of through thickness tufting that results to progressive, a more ‘ductile’, rather than abrupt catastrophic failure.

Discrete element modelling of unidirectional fibre-reinforced polymers under transverse tension

The mechanical behaviour of unidirectional fibre-reinforced polymer composites subjected to transverse tension was studied using a two dimensional discrete element method. The Representative Volume Element (RVE) of the composite was idealised as a polymer matrix reinforced with randomly distributed parallel fibres. The matrix and fibres were constructed using disc particles bonded together using parallel bonds, while the fibre/matrix interfaces were represented by a displacement-softening model. The prevailing damage mechanisms observed from the model were interfacial debonding and matrix plastic deformation. Numerical simulations have shown that the magnitude of stress is significantly higher at the interfaces, especially in the areas with high fibre densities. Interface fracture energy, stiffness and strength all played important roles in the overall mechanical performance of the composite. It was also observed that tension cracks normally began with interfacial debonding. The merge of the interfacial and matrix micro-cracks resulted in the final catastrophic fracture.

Failure behavior of resorcinol–formaldehyde latex coated aramid short‐fiber‐reinforced rubber sealing under transverse tension

ABSTRACTComposites composed of rubber, sepiolite fiber, and resorcinol–formaldehyde latex‐coated aramid short fibers were prepared. Mechanical and morphological characterizations were carried out. To investigate the effect of interfacial debonding on the failure behavior of short‐fiber‐reinforced rubber composites, a micromechanical representative volume element model for the composites was developed. The cohesive zone model was used to analyze the interfacial failure. We found that computational results were in good agreement with the experimental results when the interfacial fracture energy was 1 J/m2 and the interfacial strength was 10 MPa. A parametrical study on the interface and interphase of the composite was conducted. The results indicate that a good interfacial strength and a choice of interphase modulus between 40 and 50 MPa enhanced the ductile behavior and strength of the composite. The ductile properties of the composite also increased with increasing interfacial fracture energy. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41672.

Deterioration of FRP-Concrete Interface under the Environment of Dry-Wet Cycling at High Temperature Based on Reliability Theory

Five conventional tests (Shapiro-Wilk test, Kolmogorov-Smirnov test, Cramer-von Mises test, Anderson-Darling test and Chi-Square test) were carried out in this paper to learn the probability distribution of fracture energy of FRP-concrete interface under the environment of dry-wet cycling at high temperature. The relationship between interfacial fracture energy and the number of cycles was established through nonlinear regression analysis. Then the reliability index and the probability of deterioration of FRP-concrete interface that uses experimental data as design values were analyzed according to the reliability theory. It is shown that the optimum distribution of interfacial fracture energy is lognormal distribution, and the relationship between logarithmic mean value of interfacial fracture energy and number of cycles is subject to the exponential function. As the cycle number increases, reliability index decreases rapidly while the probability of deterioration the other way around in the beginning, yet both are stabilized at a certain level eventually. The probability of deterioration has reached a high value in a few cycles in experiments.

Prediction of the bond–slip law in externally laminated concrete substrates by an analytical based nonlinear approach

To attain a suitable strengthening system for concrete structures, adequate stress distribution between externally bonded fibre reinforced polymer (FRP) materials and the substrate is required. With the growing application of the FRP in strengthening of the structures and in order to be able to sufficiently model the strengthened structure behaviour, the need for a generic bond relationship is increasing. Hence, this article introduces a simplified analytical method to define the bond–slip law of the FRP–concrete interfaces. The advantage of this procedure is that the model is developed only based on boundary conditions and therefore can be applied to any type of the adhesively bonded joints. Subsequently, the bond characteristics obtained from the proposed model is compared with the experimental results and the previous models. A modified single lap shear test set-up is adopted during the experiments. In addition, a new relationship is proposed for determination of the fracture energy corresponding to antisymmetric in-plane shear mode. Analytical analysis indicates that the interfacial fracture energy increases for the samples with thicker bondline or lower FRP-to-concrete width ratio.

Tensile Fracture of Welded Polymer Interfaces: Miscibility, Entanglements, and Crazing

Large-scale molecular simulations are performed to investigate tensile failure of polymer interfaces as a function of welding time $t$. Changes in the tensile stress, mode of failure and interfacial fracture energy $G_I$ are correlated to changes in the interfacial entanglements as determined from Primitive Path Analysis. Bulk polymers fail through craze formation, followed by craze breakdown through chain scission. At small $t$ welded interfaces are not strong enough to support craze formation and fail at small strains through chain pullout at the interface. Once chains have formed an average of about one entanglement across the interface, a stable craze is formed throughout the sample. The failure stress of the craze rises with welding time and the mode of craze breakdown changes from chain pullout to chain scission as the interface approaches bulk strength. The interfacial fracture energy $G_I$ is calculated by coupling the simulation results to a continuum fracture mechanics model. As in experiment, $G_I$ increases as $t^{1/2}$ before saturating at the average bulk fracture energy $G_b$. As in previous simulations of shear strength, saturation coincides with the recovery of the bulk entanglement density. Before saturation, $G_I$ is proportional to the areal density of interfacial entanglements. Immiscibiltiy limits interdiffusion and thus suppresses entanglements at the interface. Even small degrees of immisciblity reduce interfacial entanglements enough that failure occurs by chain pullout and $G_I \ll G_b$.

Interface delamination study of diamond-coated carbide tools considering coating fractures

Interface delimitation is one of the major failure modes of diamond-coated carbide tools in machining. On the other hand, diamond coatings are prone of cracking easily due to its brittleness, which may affect interface delaminations. To study any influence between the two failure modes, micro-scratch testing on diamond-coated carbide tools was conducted and finite element (FE) modeling was developed to simulate the scratching process. In scratch testing, normal and tangential forces as well as acoustic emission signals were recorded to detect coating delaminations and crack initiations. Scratched samples were also observed by optical microscopy to determine the corresponding critical load of delaminations and cracking initiations. In the FE scratch simulation, a cohesive-zone interface and the extended finite element method (XFEM) were applied to investigate delamination and coating fracture behaviors, respectively. The cohesive elements were based on a bilinear tractionseparation model and XFEM was implemented to model cracking behavior in a diamond coating with a damage criterion of the maximum principal stress.The major findings are summarized as follows. The coating fracture energy has a negligible effect on the critical load for interface delaminations, and similarly, the interface fracture energy has no effect on the critical load for coating cracking, indicating that the two failure modes are mostly uncoupled for the testing range in this study. From the experiments and simulations, it is estimated that the coating fracture energy of the samples tested in this research is in the range of 120 to 140J/m2, and the diamond-carbide interface fracture energy is from 77 to 192J/m2. Moreover, increasing the coating Young's modulus will increase the critical load for coating delaminations, but decrease the critical load of coating cracking.

Effects of hydrophobic agent content in macro-porous substrates on the fracture behavior of the gas diffusion layer for proton exchange membrane fuel cells

Although the adhesion between the macro-porous substrate (MPS) and micro-porous layer (MPL) of a gas diffusion layer (GDL) is a critical factor that affects the reliability and durability of proton exchange membrane fuel cells, systematic studies quantifying the interfacial fracture energy of GDL have not yet been reported. Therefore, in this study, the interfacial fracture energy of GDLs with different contents of hydrophobic agents in the MPS is quantitatively measured. GDL samples with 0, 5, 10, and 20 wt% of hydrophobic agent content are tested using double cantilever beam fracture mechanics tests. It is observed that the interfacial fracture energy of the GDLs increases as the content of hydrophobic agent increases, due to more favorable interactions between the hydrophobic agents of the MPL and MPS. Optical microscope, scanning electron microscope, and energy-dispersive X-ray spectroscope analyses are performed on the bare and delaminated surfaces in order to investigate the mechanism of the interfacial fracture energy increase of the GDLs.

Lifetime prediction for manganese cobalt spinel oxide coatings on metallic interconnects

To prevent chromium poisoning of cathodes in solid oxide fuel cells, metallic interconnects are coated with protective oxides. One commonly used coating is manganese cobalt spinel oxide (MCO). Although MCO acts as a barrier to oxidation of interconnects, formation of native oxide scales on interconnects still occurs. As a result of native scale growth during fuel cell operations, the strength of the MCO interface will degrade. In addition, the spallation is generally driven by the temperature coefficient of expansion mismatch between the native scales and the MCO. Thus MCO spallation is likely to be dependent on the thicknesses of the different layers and is most likely to occur when cooling the fuel cell from high operating temperatures. In this study, the effects of the native scale thickness on MCO spallation are explored. To obtain interfacial fracture energy as a function of native scale thickness, room temperature, four-point bend experiments are performed on coated interconnects with various native scale thicknesses. By comparing the evolving interfacial fracture energy from experiments with the interfacial fracture energy obtained from an analytical model, coating lifetime is predicted.

Fracture toughness of the sidewall fluorinated carbon nanotube-epoxy interface

The effects of carbon nanotube (CNT) sidewall fluorination on the interface toughness of the CNT epoxy interface have been comprehensively investigated. Nanoscale quantitative single-CNT pull-out experiments have been conducted on individual fluorinated CNTs embedded in an epoxy matrix, in situ, within a scanning electron microscope (SEM) using an InSEM® nanoindenter assisted micro-device. Equations that were derived using a continuum fracture mechanics model have been applied to compute the interfacial fracture energy values for the system. The interfacial fracture energy values have also been independently computed by modeling the fluorinated graphene-epoxy interface using molecular dynamics simulations and adhesion mechanisms have been proposed.

Spinel coatings on metallic interconnects: Effect of reduction heat treatment on performance

Typical manganese cobalt spinel oxide (MCO) coating processes involve both a reduction and an oxidation heat treatment to produce dense and well adherent coatings on metallic interconnects for solid oxide fuel cells (SOFCs). In a high volume production, to achieve the required cycle-time and capacity throughput, it is necessary to perform the reduction heat treatment in a continuous manner rather than batch firing. However, the continuous reduction heat treatment in furnaces requires large capital investments and also incurs high operating costs. Therefore, it is the reduction heat treatment that contributes to a significant portion of overall coating costs. For reduced cost and increased throughput, it would be preferable to eliminate the reduction heat treatment and oxidize the green coatings directly. However, it is anticipated that coatings without the reduction heat treatment would have poor adherence and density which would result in reduced functionality. In the present paper, the performances of MCO coatings processed with and without the reduction heat treatments are evaluated in terms of interfacial fracture energy from mechanical bend tests and area specific resistance (ASR) from electrical tests. Quantifying these mechanical and electrical properties allows for assessment of the benefits of the reduction firing.

English

Delamination is one of the most commonly observed failure modes in laminated composites. The existence of delamination in a structure can significantly reduce the stiffness and strength of the structure. The simulations of delamination are performed by two different methods: Virtual Crack closure Technique (VCCT) and Cohesive Zone Method (CZM).VCCT is a fracture mechanics approach which is widely used to compute energy release rates. CZM is a progressive event governed by progressive stiffness reduction of the interface between two separating faces which uses bilinear material behavior for interface delamination and fracture energies based debonding to analyze delamination of unidirectional Double Cantilever Beam (DCB) specimen. The proposed methods are validated with the benchmark results. The load-displacement response predicted by CZM agreed well with the benchmark results. The other approach, VCCT, also successfully simulated the load-displacement response curve but this method overestimated the critical load. Parametric study is carried out for a range of height of the beam and load-displacement response is studied.

RETRACTED: Mixed mode peeling of spinnable carbon nanotube webs

This paper presents the study on interaction behaviour of spinnable carbon nanotubes by the peel test technique. Spinnable nanotube webs are used as macro scale experimental specimens to determine the mixed mode interaction behaviour between them. Numerical simulations are conducted to determine and compare the interfacial fracture energy of the interfaces in different orientations peeled at the same peel angle. The numerical model simulates the Van der Waals energy between nanotube webs through implementation of a cohesive law. The peeling process is simulated by considering a failure criterion based on continuum damage mechanics. It is shown that the interfacial energy varied with the orientation angle and the peel angle. Interfacial energy for parallel nanotube configuration is much higher than the crossed nanotube configuration. Increase in peel angle reduces the phase angle magnitudes so that the loading condition transforms from mode – II to mode – I resulting into reduction of the forces required to detach spinnable nanotubes. Hence, this study explores the spinnable nanotube interaction mechanics through which slippage may easily occur among them. Thus, the reason behind nanotube yarn failure before reaching large macroscopic stresses is better understood even though individual spinnable nanotube found to be very strong.

Evaluation of the peel strength in Cu/epoxy thin film using a novel interfacial cutting method

Purpose– The purpose of this paper is to evaluate the relationship between the Cu trace and epoxy resin and to check the validity of surface and interfacial cutting analysis system (SAICAS) by comparing its results to those of the 90° peel test.Design/methodology/approach– In this study, the effects of surface morphology on the adhesion strength were studied for a Cu/epoxy resin system using a SAICAS. In order to evaluate the peel strength of the sample, the curing degree and surface morphology of the epoxy resin were varied in the Cu/epoxy resin system.Findings– The results indicated that the peel strength is strongly affected by the curing degree and the surface morphology of the epoxy layer. As the pre-cure time increased, the interactions between the epoxy resin and permanganate during the adhesion promotion process decreased, which decreased the surface roughness (Ra) of the resin. Therefore, the surface roughness of the epoxy resin decreased with increasing pre-cure time. The curing degree was calculated with the FTIR absorption peak (910 cm−1) of the epoxy groups. The high curing degree for the epoxy resin results in a coral-like morphology that provides a better anchoring effect for the Cu trace and a higher interfacial strength.Research limitations/implications– It is necessary to study the further adhesion strength, i.e. the friction energy, the plastic deformation energy, and the interfacial fracture energy, in micro- and nanoscale areas using SAICAS owing to insufficient data regarding the effects of size and electroplating materials.Originality/value– From findings, it is found that measuring the peel strength using SAICAS is particularly useful because it makes the assessment of the peel strength in the Cu/epoxy resin system of electronic packages possible.

On the interfacial fracture of porcelain/zirconia and graded zirconia dental structures

Porcelain fused to zirconia (PFZ) restorations are widely used in prosthetic dentistry. However, their susceptibility to fracture remains a practical problem. The failure of PFZ prostheses often involves crack initiation and growth in the porcelain, which may be followed by fracture along the porcelain/zirconia (P/Z) interface. In this work, we characterized the process of fracture in two PFZ systems, as well as a newly developed graded glass-zirconia structure with emphases placed on resistance to interfacial cracking. Thin porcelain layers were fused onto Y-TZP plates with or without the presence of a glass binder. The specimens were loaded in a four-point-bending fixture with the thin porcelain veneer in tension, simulating the lower portion of the connectors and marginal areas of a fixed dental prosthesis (FDP) during occlusal loading. The evolution of damage was observed by a video camera. The fracture was characterized by unstable growth of cracks perpendicular to the P/Z interface (channel cracks) in the porcelain layer, which was followed by stable cracking along the P/Z interface. The interfacial fracture energy GC was determined by a finite-element analysis taking into account stress-shielding effects due to the presence of adjacent channel cracks. The resulting GC was considerably less than commonly reported values for similar systems. Fracture in the graded Y-TZP samples occurred via a single channel crack at a much greater stress than for PFZ. No delamination between the residual glass layer and graded zirconia occurred in any of the tests. Combined with its enhanced resistance to edge chipping and good esthetic quality, graded Y-TZP emerges as a viable material concept for dental restorations.

Interfacial fracture of the fibre-metal laminates based on fibre reinforced thermoplastics

Abstract As the adhesion quality plays an important role in determining the mechanical performance and environmental stability of most types of fibre-metal laminates (FMLs), investigating the interfacial fracture properties becomes one of the key factors for the improvement. Adhesion of a self-reinforced polypropylene (SRPP) and glass fibre reinforced polypropylene (GFPP) based FML is evaluated experimentally. Single Cantilever Beam (SCB) tests were performed to access interfacial fracture energy (Gc) of the bi-material laminates and their associated interlayer materials. Simulations mimicking the experiments were also performed. The energy needed to fracture was obtained experimentally and also via stress intensity factor from the simulations. The test results show that good adhesion between the aluminium and fibre reinforced thermoplastics can be achieved using a sulphuric acid anodising surface pre-treatment. Further examination has shown that the edges of the test samples highlighted the presence of significant fibre bridging in the SRPP and plastics deformation in the GFPP.