Debonding Behavior Research Articles

Temperature and rate dependent debonding behaviors of precision glass molding interface

AbstractThe glass‐to‐mold adhesion in precision glass molding could severely degrade the quality of molded optics and shorten the lifespan of the precious molds. Since the consequences of adhesion take effect during the separation between glass and molds, it is important to investigate the debonding behaviors of a typical glass molding interface. To this end, here we perform a probe tack test procedure for borosilicate glass BK7, where debonding is conducted at molding temperature and specific velocity. We fully characterize the debonding behaviors using the peak adhesion stress σmax and the work of debonding Wdeb. Experiments show that when temperature is decreased from 690°C to 655°C at 10 μm/s, σmax continuously increases, while Wdeb first increases but then sharply decreases. When the debonding velocity is increased from 10 to 50 μm/s at 680°C, σmax also increases while Wdeb overall decreases. Therefore, the debonding behaviors are highly temperature and rate dependent. More importantly, depending on the debonding conditions, three debonding types are identified, that is, the cohesive bulk deformation, the cohesive‐interfacial transition and the interfacial fracture. The cohesive type can be converted into the interfacial fracture, by either decreasing temperature or increasing the debonding velocity. Based on the Wdeb criterion, the three debonding regimes can be clearly distinguished. Finally, analyses on the temperature and velocity experimental results are unified by incorporating the reduced crack velocity aTvc. The dependences of both viscoelasticity and Wdeb on aTvc qualitatively explain the transition condition for different debonding types. Concerning these findings, the work of debonding not only supplements the characterization of adhesion strength, but also throws insightful light on revealing the debonding mechanisms.

Strain Response Characteristics of RC Beams Strengthened with CFRP Sheet Using BOTDR

This paper presents the structural behaviors of reinforced concrete (RC) beams that have been strengthened with carbon-fiber-reinforced polymer (CFRP) sheets experimentally and numerically. Test specimens were subjected to four-point bending, and structural behavior was observed using a strain gauge and a Brillouin optical time domain reflectometer (BOTDR) sensor. Non-linear finite element analysis was conducted to examine the applicability and reliability of numerical models using the commercial finite element code, LS-DYNA. In the results, the de-bonded section between the beam substrate and CFRP sheet affected the initial crack in the structure, while the ultimate load, which is related to structural failure, was unaffected. The predicted results correlated well with the experimental observations in terms of the trend of the load-displacement curve, initial crack load, ultimate load and failure mode. Additionally, it is shown that the de-bonding behaviors in the interface were examined using the strain distributions for the CFRP sheets through the experiment and numerical simulations.

Finite element modeling and simulation of the fiber–matrix interface in fiber reinforced metal matrix composites

The properties of fiber–matrix interface in the fiber reinforced metal matrix composites (MMCs) have been investigated in the past with the use of push-out test. The finite element (FE) analysis which is used to model the push-out test helps the composite’s designer in optimizing the interfacial properties. A two dimensional planar FE model is presented for investigating the properties of interface. Cohesive layer concept is used to model the interface with a specified thickness. The initial response of the cohesive element is assumed to be linear elastic. The maximum nominal stress criterion is used to define the damage initiation and the damage evolution is defined in terms of fracture energy. The simulation results show that the cohesive layer behaves almost like the matrix for the linear elastic deformation prior to damage. It is concluded that the values of Young’s modulus and shear modulus for the cohesive layer can be taken equal to that of the matrix material for the finite element simulation of the debonding behavior of these MMCs. Furthermore, it is observed that the shear stress at which damage initiates can be determined by using the cohesive layer concept for the interface. Once a damage initiation criterion is met, material damage occurs in accordance with the defined damage evolution law. The complete failure of the interface takes place when the stress becomes zero. However, the interface behavior needs to be defined in a more sophisticated way so as to model the stepwise debonding and failure evolution once the complete debonding has occurred.

Quantitative investigations on multi-layer interface debonding behaviors for sisal fiber reinforced composites using acoustic emission and finite element method

Complete interfacial performances of sisal fiber (a typical plant fiber) reinforced composites (SFRCs) during the single fiber pull-out experiments were investigated experimentally with numerical simulation in the present study. The single SFRCs were found to present three-interface failure. The failure behaviors of the three interfaces were characterized by in-situ acoustic emission technique and identified as interfacial failure between technical fiber and matrix, that between elementary fibers and that between micro-fibrils of cell walls using microscope observation. Statistical analysis was employed to evaluate pull-out probability of technical fiber, elementary fibers and micro-fibrils. The embedded fiber length was concluded to dominate the failure modes of SFRCs. To further gain insight in the complete failure processes and mechanisms of the multi-layer SFRCs, a triple-interface finite element model was developed based on the cohesive zone law. Quantitative comparisons of applied stress between numerical predictions and experimental results surmised that the triple-interface model could accurately describe the multi-stage pull-out behaviors of the single SFRCs.

Finite element modelling of dynamic bonding behaviours between fibre reinforced polymer sheet and concrete

In this study, dynamic debonding behaviour between fibre-reinforced polymer (FRP) and concrete is numerically investigated by using finite element code LS-DYNA. A three-dimensional (3D) finite element (FE) model is built and a bond-slip model is incorporated into the simulation of interfacial bond between FRP and concrete. To validate the accuracy of the numerical model, experimental results from 42 dynamic single shear tests on FRP-concrete joints are employed. The debonding load and shear slip responses, FRP strain distributions, and interfacial bond-slip responses are compared between the numerical and experimental results. It is found that the numerical model is capable of predicting the debonding behaviours under various loading rates. In addition, an analytical dynamic bond strength model is proposed to predict the ultimate debonding strain and debonding load by incorporating the dynamic increase factor and strain rate. In addition, a semi-empirical model is proposed to predict the ultimate debonding strain and debonding load by incorporating the dynamic increase factor and strain rate. The semi-empirical model is validated against the numerical results and 119 experimental tests with a good correlation.

Influence of the carbon interface on the mechanical behavior of SiC/SiC composites

SiC/SiC composites reinforced with 3rd generation SiC fibers (Hi-Nicalon S and Tyranno SA3 fibers) are promising candidates for thermomechanical applications in high technology industries. Both composites exhibited a pseudo-ductile mechanical behavior but the HNS/PyC/SiC composite reaches higher failure strains than TSA3/PyC/SiC ones. The mechanical behavior of SiC/SiC composites is linked to the way PyC is bonded to the fiber surface. Analyses have shown that these interactions and the Fiber/Matrix debonding behavior depend strongly on the nature of the carbon on the SiC fiber surface, which is different according to the SiC fiber. In order to understand the mechanism governing the chemical adhesion at the PyC/SiC fiber interface, the formation, the chemistry and the structure of the surface carbon layer were studied. Understanding the origin of this carbon has allowed elucidating the local interaction mechanisms of the studied SiC/SiC composites.

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.

Critical energy release rate for interface delamination of asymmetrical specimen

The interface debonding is a major failure mode of composite structures. In this paper, the debonding behavior of the structurally asymmetric interfaces is studied, and the calculating method of the critical energy release rate of such debonding interfaces is proposed. The experimental results show that the critical energy release rate calculated in this paper is more in line with its intrinsic physical attribute of being a material constant, which proves the effectiveness of the proposed method.

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.

Micro-scale numerical study of fiber/matrix debonding in steel fiber composites

Fiber/matrix debonding behavior of steel fiber composites is analyzed using a parametric finite element modeling procedure and compared with conventional composites with carbon and glass fibers. Cohesive surfaces are applied to fiber–matrix interface to simulate the debonding behavior, while the interface strength properties of steel fiber are obtained with and without surface treatment. The effect of various parameters on the debonding behavior is investigated, including stress concentrations, fiber diameter, fiber shape, and fiber volume fraction, using the parametric model. The influence of stress concentrations is determined to be much lower than the debonding strength. Debonding damage is more evident in larger fibers compared to smaller ones. Earlier and sudden interface separation is observed with the polygonal steel fibers compared to the circular ones. Increase in the fiber volume ratio increases the debonding opening distance but does not affect the opening angle significantly. The results can be useful for assessing possibilities to use steel fibers to increase toughness of the composites in comparison with glass and carbon reinforcement.

Numerical simulation of the debonding behavior of fiber reinforced metal matrix composites

Finite element analysis (FEA) is performed for investigating the debonding behavior of fiber reinforced metal matrix composites (MMCs). An Axisymmetric cylindrical and three dimensional solid finite element (FE) models without interface are constructed which consist of a stainless spring steel wire as fiber reinforcement and an aluminium alloy as matrix. Numerical simulation is carried out with both the spherical and cylindrical indenters. The simulation results obtained in this work are compared with the experimental findings reported in the past. The initial part of load–displacement curve for cylindrical indenter is linear in nature as compared to the non linear behaviour with the spherical indenter. This shows that the non linearity is because of the shape of the indenter and not due to other reasons such as incorrect modeling. The coefficient of friction does not affect the response regarding the load–displacement curve. A large gap between the experimental and simulation curves for the elastic region is due to stiffness of the experimental setup. The simulation curve shows continuous increase in the value of load which is due to the absence of definition of failure criterion. The axisymmetric FE model presented in this study shows the capability to simulate the debonding behaviour of fiber reinforced MMCs. However, it can be improved further with the implementation of cohesive layer concept for modeling the fiber–matrix interface. In future work, the FEA of the axisymmetric model with interface using the cohesive zone modeling (CZM) for the interface will be carried out.

Kirigami-inspired multiscale patterning of metallic structures via predefined nanotrench templates

Reliable fabrication of multiscale metallic patterns with precise geometry and size at both the nanoscale and macroscale is of importance for various applications in electronic and optical devices. The existing fabrication processes, which usually involve film deposition in combination with electron-beam patterning, are either time-consuming or offer limited precision. Inspired by the kirigami, an ancient handicraft art of paper cutting, this work demonstrates an electron-beam patterning process for multiscale metallic structures with significantly enhanced efficiency and precision. Similar to the kirigami, in which the final pattern is defined by cutting its contour in a paper and then removing the unwanted parts, we define the target multiscale structures by first creating nanotrench contours in a metallic film via an electron-beam-based process and then selectively peeling the separated film outside the contours. Compared with the conventional approach, which requires the exposure of the whole pattern, much less exposure area is needed for nanotrench contours, thus enabling reduced exposure time and enhanced geometric precision due to the mitigated proximity effect. A theoretical model based on interface mechanics allows a clear understanding of the nanotrench-assisted selective debonding behaviour in the peeling process. By using this fabrication process, multiscale metallic structures with sub-10-nm up to submillimetre features can be reliably achieved, having potential applications for anti-counterfeiting and gap-plasmon-enhanced spectroscopy.

Parametric Study of Flexural Strengthening of Concrete Beams with Prestressed Hybrid Reinforced Polymer

The strengthening method of using hybrid fiber reinforced polymer is an effective way to increase the strengthening efficiency and lower the cost. This paper focuses on simulating the flexural behavior of reinforced concrete beam strengthened by prestressed C/GFRP (Carbon-Glass hybrid Fiber Reinforced Polymer) with different hybrid ratios and prestress levels. An elastoplastic damage constitution is used to simulate the mechanical behavior of concrete. A cohesive zone model under mixed mode is adopted to describe the debonding behavior of the FRP-concrete and concrete-steel interface. The results show good agreement with the experiment in the load-deflection curve, load-stress curve of steel, and HFRP. Furthermore, the failure mode of concrete and FRP debonding obtained from numerical simulation is the same as the test. Considering the improvement of the bending capacity, stiffness, and ductility of the strengthened beam in this paper, the best hybrid ratio of carbon to glass fiber is 1:1, and the suitable prestress level is between 30 and 50% of its ultimate strength.

Interfacial crack propagation between a rigid fiber and a hyperelastic elastomer: Experiments and modeling

The interfacial adhesion between a metal fiber and an elastomer plays a key role in maintaining the structural integrity of stretchable interconnect composites under large strains, but their interfacial adhesion mechanisms have remained elusive. To this end, the interfacial debonding behavior and physical mechanisms between a rigid metal fiber and hyperelastic elastomer matrix are investigated by means of fiber pullout tests and numerical modeling. An improved cylindrical specimen is adopted for a copper fiber pulling out from polydimethylsiloxane (PDMS). A numerical model is developed to simulate the interfacial cracking using the Yeoh hyperelastic model and cohesive damage model. We report a first-of-its-kind experimental observation on the pullout process of a rigid fiber from elastomers. The results demonstrate that there exist three stages in the fiber pullout process: elastic deformation, interfacial debonding and interfacial friction. The interfacial shear strength between the rigid fiber and the PDMS is proportional to the reciprocal of the mixing ratio of the PDMS, and the interfacial friction stress varies inversely with the 1.25 power of the mixing ratio. Enhancing the mixing ratio of the PDMS decreases the strength of both the PDMS and the interface between the PDMS and the metallic materials while increasing their ultimate stretch due to a decrease of chemical crosslinking degree within the PDMS and at the interface between the PDMS and the metallic materials. The results obtained from the numerical model agree well with the experimental data. This work can aid in the design of advanced stretchable interconnect composites.

Rate effects on fiber–matrix interfacial transverse debonding behavior

The rate effect of fiber–matrix interfacial debonding behavior of SC-15 epoxy with S-2 glass and aramid fiber reinforcements was studied via in-situ visualization of the transverse debonding event. In this study, the debonding force history, debonding initiation, debonding crack velocity, and crack geometry were characterized using a quasi-static load frame and a modified tension Kolsky bar at loading velocities of 0.25 mm/s and 2.5 m/s. Cruciform-shaped specimens were used for interfacial transverse debonding between SC-15 epoxy matrix and two types of fiber reinforcements. The load history and high-speed images of the debonding event were simultaneously recorded. A major increase was observed for the average peak debonding force and a minor increase was observed for the average crack velocity with increasing loading velocity. The crack geometry of the cruciform specimens under both loading velocities was also tracked. Scanning electron microscopy of the recovered specimens revealed the debonding direction along the fiber–matrix interface through angled patterns on the failure surface.

High-performance fiber reinforced concrete as a repairing material to normal concrete structures: Experiments, numerical simulations and a machine learning-based prediction model

High-performance fiber reinforced concrete (HPFRC) has been reported as a repairing material to normal concrete (NC) structures due to its predominant mechanical performance. Here, we investigate the debonding behavior between HPFRC and NC subjected to direct shear loading. HPFRC specimens are fabricated and experimentally calibrated to determine the compressive and bending (i.e., flexural) strengths. HPFRC-NC samples are fabricated using two bonding strategies, i.e., mechanical surface treatments with and without chemical agent. Direct shear loading is applied to test the HPFRC-NC debonding behavior. A finite element (FE) model is developed to predict the direct shear debonding response. The FE model is validated by the experimental observations and then used to characterize the debonding behavior with various geometric and material parameters, as well as bonding interface treatments. Subsequently, a robust machine learning model is developed to formulate the shear debonding strength of HPFRC-NC with those influencing parameters. Design examples are presented to illustrate the efficiency of the proposed machine learning model in describing the debonding response of HPFRC-NC. A sensitivity analysis is further conducted to investigate the contribution of the chosen predictors to the debonding behavior of HPFRC-NC. The reported HPFRC and machine learning-based prediction model provide powerful tools to address repairing issues in various existing normal concrete structures.

Deformation mechanism and fatigue life of an Al-12Si alloy at different temperatures and strain rates

The low-cycle fatigue (LCF) deformation mechanism and fatigue life of an Al-12Si alloy were investigated at different temperatures and strain rates. With increasing temperature, the fatigue life increases at first and then reduces, which is derived from the deformation mechanism. At the lower temperatures, the primary Si cracking induced by piling-up of dislocations dominates fatigue damage behaviors. Both of increasing temperature and reducing the strain-rate can restrain the phase cracking, thus increase fatigue life. However, with further increasing temperature, the micro-scale void caused by dislocation annihilation dominates the phase debonding behavior, leading to the decrease of fatigue life.

Numerical Simulation for Synergetic Deformation of Optical Fiber Sensor and Asphalt Mixture

Owing to the structural and material differences, data obtained by distributed optical fiber sensors (OFS) for asphalt pavement strain measurement lack of precision. For better understanding OFS measurement mechanism and investigating the measurement error correction, this study analyzed the synergetic deformation of OFS and asphalt mixture (AM) under load. Firstly, a three-dimensional AM single-edge notched beam (SEB) model with OFS was established and verified using the discrete element method. Secondly, the micro-crack propagation of SEB model during loading procedure was analyzed to explore the debonding behavior between OFS and AM. Thirdly, strain development of OFS and AM was investigated during fracture stage and post-fracture stage. Finally, a measurement error correction method was developed based upon the materials and test conditions in this study. Results demonstrate that debonding occurs on OFS surface when macro-crack extends across OFS position. The key to making the strain measurement accuracy is to ensure the effective bonding between OFS and AM. In addition, this study provides a framework used to develop the measurement error correction, and the research results give the theoretical foundation for data selection and error correction of asphalt pavement strain measurement and crack detection using distributed optical fiber sensors.

Numerical and Experimental Study on the Cracking Behavior of Marble with En-Echelon Flaws

En-echelon fractures have been commonly observed in nature. To understand the interaction of en-echelon flaws, numerical simulation with flat-jointed model and laboratory experiment has been conducted on specimens containing en-echelon flaws of various configurations. With reliable micro-parameters of the flat-joint contact through a comprehensive calibration, numerical results reveal a strong interaction in flaw configurations of extensional bridges but a mild interaction in flaw configurations of contractional bridges. The patterns of linking cracks are found to be dependent on the flaw configurations. Furthermore, two typical linking cracks, tensile and shear cracks, are identified in terms of contact force evolution, crack development, micro-components and damage zone width. Experimental results not only verify the above conclusions given by simulation, but also provide more distinctions between tensile and shear cracks in grain scale. Based on these findings, an empirical correlation is suggested between debonding behavior in PFC models and microcracking behavior in laboratory experiments. Finally, the tendency of crack initiation stress and peak stress in simulation and experiment is compared and explained with respect to the flaw-array angle. A good agreement between simulation and experiment indicates the capability of the flat-jointed model of PFC2D in handling complex crack coalescence problems in rocks.

Simulation and Analysis on Fiber Reinforced Rubber Matrix Sealing Composite Based on Cohesive Zone Model

A finite element model on the single fiber pull-out test of short fiber reinforced rubber matrix sealing composites (SFRC) were established. The effects of the interphase properties on the interfacial stress distribution and initial debonding strain are investigated based on the cohesive zone model (CZM). The influences of interphase thicknesses and elastic modulus on the interfacial debonding behavior of SFRC are obtained. The results show that the interfacial initial debonding strain increases with the increasement of interphase thickness, and it decreases with the increasement of interphase elastic modulus. An interphase thickness of 0.4 μm and an interphase elastic modulus of about 750 MPa are optimal to restrain the initiation of the interfacial debonding.