Interface Debonding Length Research Articles

Inverse parameter identification framework for cohesive zone models based on multi-island genetic algorithm

Composite interfaces are commonly simulated by cohesive zone models with the key challenge being the calibration of interfacial parameters. A novel inverse identification framework is presented in this paper to determine the interface parameters of cohesive zone models. This approach employs the multi-island genetic algorithm to obtain the key parameters of cohesive zone model which can reproduce the experimental observations. Utilizing two independent metrics, namely the load-displacement response and the debonding length history, an objective function is formulated to give the framework inherent robustness. The interface debonding length is used to uniquely determine the debonding properties of the specimen. To demonstrate the feasibility of the proposed framework, the strength-based cohesive zone model is taken as an example. The inverse algorithm is adopted to identify the interface parameters of both the double cantilever beam (DCB) experiments and the fixed-ratio mixed-mode (FRMM) tests. The robustness, accuracy and sensitivity of the framework are validated through the double cantilever beam test. The findings indicate that the numerical results align closely with the experimental data, confirming that the interface parameters identified by the proposed framework can reproduce the experimental results.

Multiscale homogenization numerical study on the mechanism of interface debonding detection for steel–concrete composite structures with multichannel surface wave measurements

In order to understand the interface debonding detection mechanism for steel–concrete composite structures (SCCSs) efficiently using multichannel analysis of surface waves (MASW) when the heterogeneity and randomness of the mesoscale structure of concrete are considered, mesoscale homogenization numerical analysis on surface wave propagation in SCCSs is carried out. Firstly, for exploring the theoretical dispersion characteristics of surface waves in SCCSs, dispersion curves of both Lamb wave and Rayleigh wave of three different layering scenarios, including single-layer, two-layer, and three-layer composite models where concrete is treated as homogeneous material, are investigated. Meanwhile, the effect of the steel plate thickness on the dispersion curves is studied. Secondly, to evaluate the effect of mesoscale structure variation of concrete in SCCSs on surface waves, a random aggregate method (RAM) is employed to establish the mesoscale model of concrete composed of randomly distributed aggregates with different shapes. Thirdly, for enhancing numerical simulation efficiency on surface wave propagation, an equivalent homogenization approach and Voigt parallel model are developed to establish the mesoscale homogenization models of SCCSs. Dispersion curves from forwarding analysis on surface wave measurement of the mesoscale models are compared with the corresponding theoretical dispersion curves to reveal surface wave attribution and optimum layering scenarios of SCCSs for MASW method. The influence of mesoscale concrete variation on surface wave fields in SCCSs using equivalent homogenization models is investigated comprehensively and compared with that of the corresponding mesoscale models. Finally, the feasibility of the proposed MASW method for interface debonding length estimation is validated, and wavelength selection criteria of excitation signals considering interface dimension, as well as steel plate thickness, are discussed. The results from the mesoscale homogenization numerical study can provide helpful guidance on the practical application of MASW-based debonding detection for SCCSs where concrete is heterogeneous.

Modeling of micro-annulus propagation along cementing interface in stimulated horizontal wellbore

ABSTRACT Once there are micro-annulus at cementing interfaces in the process of reservoir stimulation, it is easy to form fluid channeling in the later development. Fluid channeling reduces the efficiency of reservoir development and even the service life of oil and gas wells. Based on the characteristics of ‘multi-stage’ in stimulated reservoir volume, a mathematical model was set up to calculate the interface debonding length driven by hydraulic pressure. The propagation process of micro-annulus in stimulated reservoir volume was also analyzed. The results show that the propagation speed of the micro-annulus gradually slows down with the progress of fracturing. Meanwhile, the debonding azimuth of the micro-annulus and the cement elastic modulus have dominant effects on the propagation length. It is recommended that the setting position of the packer be outranged from the debonding area of the cementing interface in the design of the stimulated reservoir volume scheme to avoid fluid channeling between the stages. This study can predict the unsealing length of cement sheath during hydraulic fracturing as a reference for the optimization of fracturing parameters.

Effect of pre-fatigue loading on tensile damage and fracture of fiber-reinforced ceramic-matrix composites

In this paper, the effect of pre-fatigue loading on tensile damage and fracture of fiber-reinforced ceramic-matrix composites (CMCs) is investigated using a micromechanical approach. Under cyclic fatigue loading, the fiber/matrix interface shear stress degrades with applied cycles due to the damage mechanism of the interface wear. The micro stress field of the damaged composite including matrix cracking, fiber/matrix interface debonding, and fiber failure is obtained for the fiber and the matrix axial stress and the fiber/matrix interface shear stress in the interface wear region, interface debonding region, and the interface bonding region, respectively. The fracture mechanics approach, stochastic matrix cracking model, and global load sharing (GLS) criterion are used to determine the interface debonding length, matrix cracking density, and fiber failure probability at higher applied stress level considering the damage mechanism of the interface wear. The effects of fiber volume, matrix cracking, fiber/matrix interface shear stress, fiber strength, pre-fatigue peak stress, and number of cycles on pre-fatigue tensile damage and fracture of SiC/SiC composites are analyzed. The experimental tensile damage and fracture of SiC/SiC composites with and without pre-fatigue loading are predicted for different interface properties.

Temperature-dependent proportional limit stress of SiC/SiC fiber-reinforced ceramic-matrix composites

AbstractIn this paper, the temperature-dependent proportional limit stress (PLS) of SiC/SiC fiber-reinforced ceramic-matrix composites (CMCs) is investigated using the micromechanical approach. The PLS of SiC/SiC is predicted using an energy balance approach considering the effect of environment temperature. The relation between the environment temperature, PLS, and composite damage state is established. The effects of the fiber volume, interface properties, and matrix properties on the temperature-dependent PLS and composite damage state of SiC/SiC composite are analyzed. The experimental PLS and interface debonding length of 2D SiC/SiC composites with the PyC and BN interphase at elevated temperatures are predicted. The temperature-dependent PLS of SiC/SiC composite increases with the fiber volume, interface shear stress and interface debonding energy, and the matrix fracture energy and decreases with the interface frictional coefficient at the same temperature.

A time-dependent tensile constitutive model for long-fiber-reinforced unidirectional ceramic-matrix minicomposites considering interface and fiber oxidation

In this paper, a time-dependent tensile constitutive model of long-fiber-reinforced unidirectional ceramic-matrix minicomposites is developed considering the interface and fiber oxidation. The relationship between the time-dependent tensile behavior and internal damage is established. The damage mechanisms of time-dependent matrix cracking, fiber/matrix interface debonding, fiber failure, and the oxidation of the interface and fiber are considered in the analysis of the time-dependent tensile stress–strain curve. The fracture mechanic approach, matrix statistical cracking model, and fiber statistical failure model are used to determine the time-dependent interface debonding length, matrix crack spacing, and the fiber failure probability considering the time-dependent interface and fiber oxidation. The effects of the fiber volume, fiber radius, matrix Weibull modulus, matrix cracking characteristic strength, matrix cracking saturation spacing, interface shear stress, interface debonding energy, fiber strength, fiber Weibull modulus, and oxidation time on the time-dependent tensile stress–strain curves, matrix cracking density, interface debonding, and fiber failure are discussed. The experimental time-dependent tensile stress–strain curves, matrix cracking, interface debonding, and fiber failure of four different unidirectional SiC/SiC minicomposites for different oxidation time are predicted. The composite tensile strength and failure strain increase with the fiber volume, fiber strength, and fiber Weibull modulus, and decrease with the oxidation time; the fiber/matrix interface debonding length increases with the fiber radius and oxidation time and decreases with the interfacial shear stress and interface debonding energy; the fiber/matrix interface oxidation ratio increases with the interfacial shear stress, interface debonding energy, and oxidation time and decreases with the saturation matrix crack spacing.

Damage evolution and lifetime of fiber-reinforced ceramic-matrix composites under stress-rupture with stochastic loading at intermediate temperatures

In this paper, the stress-rupture of fiber-reinforced ceramic-matrix composites (CMCs) with stochastic loading at intermediate temperature is investigated. There are four different stochastic loading sequences under stress-rupture are considered with different loading time and time spacing. The micro stress filed of the damaged CMCs, the damage models of the matrix cracking, fiber/matrix interface debonding, and fiber failure consider the stochastic loading and time-dependent interface and fiber oxidation. The damage evolution of the stress-rupture strain, fiber/matrix interface debonding length and interface oxidation length, and the broken fibers fraction versus the time curves of SiC/SiC composite subjected to four different stochastic loading sequences are analyzed. The effects of the fiber volume, matrix crack spacing, fiber/matrix interface debonding energy, fiber/matrix interface shear stress, and environmental temperature on the damage evolution and lifetime of SiC/SiC composite are discussed. The experimental damage evolution and lifetime of SiC/SiC composite under stress-rupture with stochastic loading are predicted. Under stress-rupture with stochastic loading, the stress-rupture lifetime decreases with the stress level, and the frequency of the stochastic loading; the stress-rupture lifetime increases with the fiber volume, and decreases with environmental temperature; and the time for the interface complete debonding increases with the fiber volume, matrix crack spacing, interface debonding energy and interface frictional shear stress in the slip and oxidation region, and decreases with the temperature.

Modeling matrix multicracking development of fiber‐reinforced ceramic‐matrix composites considering fiber debonding

AbstractIn this paper, the effect of fiber debonding on matrix multicracking development of different fiber‐reinforced CMCs is investigated using the micromechanical approach. The Budiansky–Hutchinson–Evans shear‐lag model is adopted to analyze the fiber and matrix stress distributions of the damaged composite. The fracture mechanics approach is used to determine the fiber/matrix interface debonding length. Combining the critical matrix strain energy criterion and fracture mechanics fiber/matrix interface debonding criterion, the stress‐dependent matrix multicracking development is analyzed for different fiber volume fraction, fiber/matrix interface properties and matrix cracking characteristic stress. The experimental matrix multicracking development of unidirectional C/Si3N4, SiC/Si3N4, SiC/CAS, SiC/CAS‐II, SiC/SiC, SiC/Borosilicate and mini‐SiC/SiC composites are predicted.

Interfacial adhesion assessment in flax/epoxy and in flax/vinylester composites by single yarn fragmentation test: Correlation with micro-CT analysis

Despite the academic interest in using plant fibres as reinforcement in polymer composites to replace glass fibres, the industrial exploitation of resulting composites in semi- or structural applications is still limited. This is mainly due to the poor adhesion at the plant fibre/polymer matrix interface dictated by their surface chemistry and strong hydrophilic behaviour. In the present work, an assessment of the interfacial adhesion at the yarn scale has been carried out. Fragmentation tests have been performed on flax/epoxy and flax/vinylester single yarn composites. High-resolution microtomography has allowed a 3-D reconstruction of the breaking area of the flax yarn. The flax/epoxy system has shown the lowest values of critical fragment length and interfacial debonding length, and the highest values of IFSS. For both epoxy and vinylester samples, it was found that the breakage of flax has been mainly concentrated in the peripheral zone of the yarn.

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.

Influence of fiber failure on fatigue hysteresis loops of ceramic matrix composites

An analytical methodology has been developed to investigate the influence of fiber failure on fatigue hysteresis loops of ceramic matrix composites in this article. During fatigue loading, matrix cracking, interface debonding and fiber failure occur upon first loading to the fatigue maximum stress. Matrix cracking space and interface debonding length are obtained by matrix statistical cracking model and fracture mechanics interface debonding criterion. Based on the assumption of global load-sharing criterion for the load distribution between the unbroken and broken fibers, an approach to determine fiber failure probability during fatigue loading for the degradation of interface shear stress and fiber strength is developed in this analysis. Upon unloading and subsequent reloading, stress—strain hysteresis loops develop as fiber sliding relative to matrix in the interface debonded region. The unloading interface counter slip length and reloading new slip length are obtained by the fracture mechanics interface debonding criterion. The effects of characteristic fiber strength, fiber Weibull modulus, and fatigue maximum stress on fiber failure during fatigue loading, and then on the shape, location, and area of the fatigue hysteresis loops are investigated. The fatigue hysteresis loops of three different ceramic composites corresponding to different cycles are predicted and agree well with the experimental data.

An Approach to Estimate Interface Shear Stress of Ceramic Matrix Composites from Hysteresis Loops

An approach to estimate interface shear stress of ceramic matrix composites during fatigue loading has been developed in this paper. By adopting a shear-lag model which includes the matrix shear deformation in the bonded region and friction in the debonded region, the matrix crack space and interface debonding length are obtained by matrix statistical cracking model and fracture mechanics interface debonding criterion. Based on the damage mechanisms of fiber sliding relative to matrix in the interface debonded region upon unloading and subsequent reloading, the unloading counter slip length and reloading new slip length are determined by the fracture mechanics method. The hysteresis loops of four different cases have been derived. The hysteresis loss energy for the strain energy lost per volume during corresponding cycle is formulated in terms of interface shear stress. By comparing the experimental hysteresis loss energy with computational values, the interface shear stress corresponding to different cycles can then be derived. The theoretical results have been compared with experimental data of three different ceramic composites.

A Numerical Simulation of Time-Dependent Interface Failure Under Shear and Compressive Loads in Single-Fiber Composites

We performed a numerical simulation of a time-dependent interfacial failure accompanied by a fiber failure, and examined their evolution under shear and compressive loads in single-fiber composites. The compressive load on the interface consists of Poisson’s contraction for matrix resin subjected to longitudinal tensile load. As time progresses, compressive stress at the interface in the fiber radial direction relaxes under the constant longitudinal tensile strain condition for the specimen, directly causing the relaxation of the interface frictional stress. This relaxation facilitates the failure of the interface. In this analysis, a specific criterion for interface failure is applied; apparent interfacial shear strength is enhanced by compressive stress, which is referred as quasi-parabolic criterion in the present study. The results of the stress recovery profile around the fiber failure and the interfacial debonding length as a function of time simulated by the finite element analysis employing the criterion are very similar to experimental results obtained using micro-Raman spectroscopy.

2925 一方向複合材料のクリープ寿命予測(S27-2 複合材料の動向とその加工技術(2),S27 複合材料の動向とその加工技術)

Delayed fractures in carbon-fiber-reinforced polymer matrix composites can be observed even at room temperature due to an accumulation of micromechanical damages, such as time-dependent interfacial debondings or fiber breakage. In this study, the creep-rupture time in unidirectional composites consisting of carbon fiber reinforcement and vinylester resin is predicted under consideration of the progress of interfacial debonding which decreases rupture strain of the composites due to increase of the stress recovery length in time. The decrease of the rupture strain in unidirectional composites is formulated based on the global load sharing, which assumes that lost load distribution involved a fiber break is uniformly redistributed to all the intact residual fiber in the range of the stress recovery length. Time-dependency of the stress recovery length including the interfacial debonding length is analytically and experimentally investigated using carbon/vinylester single-fiber composite as a function of time and specimen strain. The creep rupture prediction is completed by means of putting the increase of stress recovery length into it. The validity of this creep rupture prediction is discussed by investigation of the residual strength after quasi-creep test, which must be derived by the formulated creep rupture prediction.

Time-Dependent Interfacial Debonding Propagation in Single Fiber Composite

Interfacial debonding propagation is one of the most important problems for long-term creep in unidirectional composites because the strength of the unidirectional composites decreases with increase of the interfacial debonding length. In this study, time-dependent interfacial failure was investigated by using the Micro Raman Spectroscopy. The specimen was single fiber composite consisting of one carbon fiber embedded in the vinylester resin. It was subjected to a constant strain to assume the long-term creep in the unidirectional composites. To discuss the timedependent interfacial debonding propagation behavior, a time-dependency of a criterion for interfacial debonding propagation in the SFC must be determined. In this paper, the time-dependent boundary condition of the interfacial debonding was obtained from experimental results, and the interfacial debonding propagation was formulated. Here, the compression stress applied to the interface in the fiber radius direction was formulated as a function of time on the consideration of Poisson contraction and thermal residual stress. The interfacial debonding propagation and variation of the fiber axial strain distribution as a function of time were formulated by using the following three parameters : a relaxation of the frictional stress, an interfacial shear viscoelastic behavior and the time-dependent boundary condition at the interfacial debonding tip. These formulations showed a good agreement with the corresponding experimental results.

20107 フラグメンテーション試験による繊維強度の評価 : 試験速度を考慮した評価方法の提案(界面の強度,OS10 先進材料の力学と強度)

Single fiber fragmentation test is one of the methods to evaluate strength of a fiber embedded in matrix resin. This method has two advantages; the Weibull parameter can be obtained from a few tests and an actual strength of the embedded fiber in practice can be obtained. This test evaluates relationship between the fiber strength and the fiber length. However, the fiber length is defined by the length of the gage length divided by the number of fragment points, and the fiber length is overestimated. Therefore, in the conventional evaluation, the fiber strength is not independent to interfacial strength and test speed. To assume the exact fiber length, an interfacial debonding length and a stress recovery length must be considered. In this study, the new corrected evaluation to generalize the fiber strength is suggested. To discuss the validity of the method, several fragmentation tests are performed under the condition of the various interfacial strength and the various test speed.

Effect of Water Absorption on Interaction between Matrix Cracking and Fiber Bridging for Stress Corrosion Cracking of PMC

The effect of water on fiber bridging of polymer matrix composites (PMCs) has been studied for stress-corrosion cracking (SCC). The fiber bridging during crack propagation in the PMC was observed directly using a transparent polymer matrix. Specimens were immersed and weighed just before conducting the crack propagation test. The contribution of mechanical degradation caused by the water to the bridging was measured as a function of weight gain due to water absorption. The critical energy release rate of the matrix decreased with increase of the water absorption. The energy release rate of a bridged crack varied with the water absorption. To investigate the variation in the bridging mechanism under the water environment, we calculated the bridging stress the σt and the bridging contribution to crack propagation resistance ΔG based on a single-fiber bridging mechanism with the interfacial debonding length and the interfacial debonding energy. The debonding length was measured directly, and the debonding energy was obtained in a fragmentation test. The calculation showed that the increase in the interfacial debonding length influenced the fiber bridging mechanism.

Prediction of creep rupture in unidirectional composite: Creep rupture model with interfacial debonding and its propagation

This paper describes a creep rupture model that takes into account the interfacial debonding and its propagation around broken fibers in unidirectional fiber-reinforced polymers. The interfacial debonding is accompanied by fiber breaks under a longitudinal tensile load, and the interfacial debonding length depends on both the fiber stress at the moment of the fiber breaks and the properties of the interfacial adhesion. In this paper, the interfacial debonding length, its propagation as a function of time, the probability of fiber breaks and an interfacial shear stress are investigated by fragmentation tests with a single glass fiber embedded in each vinylester resin specimen. Subsequently, it was found that a relationship between the fiber strength and the fiber effective length, the length of the debonding length and stress recovery length subtracted from one fiber length, was log linear, and that the larger the fiber stress, the longer was the interfacial debonding length. Next, creep tests were performed to investigate the creep constants of the vinylester resin, and interfacial debonding propagation tests were also performed to identify the interfacial debonding-propagation behavior as a function of time using single fiber composites subjected to constant strains. We modified the creep rupture model by taking into account the interfacial debonding length, which has a time-dependent characteristic, into a conventional Curtin–McLean creep rupture model. It was found that the predicted creep rupture time of the modified model was shorter than that of the conventional model and that there was no threshold creep stress in the modified model unlike in the conventional model because the interfacial debonding propagation makes the prediction creep rupture time lower as time progresses.

212 単繊維モデル複合材料における界面き裂の時間依存特性 : はく離部の界面摩擦応力の緩和を考慮した界面はく離進展(OS 高分子/高分子基複合材料(1))

Interfacial debonding propagation is very important problem for long-term creep in unidirectional composites because material's properties of the unidirectional composite decrease with increase of the interfacial debonding length. In this study, time-dependent interfacial failure was investigated by using the Raman Micro Spectroscopy. The specimen was single fiber conposite consisting one carbon fiber embedded in the vinylester resin and it was subjected to constant strain condition to assume the long-term creep in the unidirectional composites. The interlace between the carbon fiber and the vinylester resin is relatively weak; therefore interfacial frictional stresiss is one of the most important factors, which dominated the interfacial debonding propagation. In this paper, the compression stress applied to the interface in the direction of fiber rudius direction is calculated as a function of time on the consideration of Poisson compression and thermal residual stress. The interfacial frictional stress is assumed to be dominated by the Coulomb's friction and compared with the Experimental results. The interfacial debonding propagation is discussed by using the relaxation of the frictional stress. Long-term behavior of the interfacial debonding propagation is predicted in the single fiba composites.

941 一方向 FRP のクリープ寿命予測 : 繊維破断部近傍の界面はく離を考慮したクリープ破断モデル

This paper describes the creep rupture model considering the interfacial debonding and its propagation from the end of broken fibers in unidirectional polymer matrix composites reinforced by glass fibers. Interfacial debonding is accompanied with fiber breaks under the tensile load, which develops longer. In the present study, the interfacial initial debonding length, the fiber strength and the interfacial shear stress are investigated by the fragmentation test. The interfacial debonding propagation is also investigated by the creep test or the constant strain test with the use of a single fiber within a polymer matrix specimen. The interfacial debonding length is taken into the modified Curtin-McLean's creep rupture model. This modified creep model does not have the threshold stress, because the failure stress in this model decreases according to the interfacial debonding propagation as time progresses. The predicted life of a creep rupture is shorter than that of the conventional model and there is no threshold stress in the long-term creep.