Debonding Behavior Research Articles

Adhesion strength of paraffin droplet impacted and solidified on metal substrate

Debonding of solidified splats is a crucial issue for thermal sprayed coatings, which greatly influences the performance and lifetime of industrial components. The purpose of this study is to provide an in-depth understanding of the effects of impact parameters as well as residual stress on the debonding behaviors, and the related adhesion strength and driving forces of single splats. In this study, debonding behaviors of molten paraffin droplets which were impacted and solidified on stainless steel substrates, were observed considering the effects of substrate pre-set temperature, drop height (impact velocity), and droplet temperature. It was found that the debonding is prone to take place at lower substrate pre-set temperatures, lower drop heights, and lower droplet temperatures. A scraping method was then employed to measure the adhesion strength of splats formed under various conditions. The results showed good accordance with debonding behaviors in the drop impact test. The scraping tests also indicated that the residual tensile stress in splats reduces the scraping forces and prevents the complete removal of splats during the scraping processes. Peeling stress and shear stress along the splat-substrate interface, which are driving forces for debonding, were calculated using coupled thermomechanical finite element analyses. The calculated driving forces were larger for lower drop heights and lower droplet temperatures under which the debonding was more easily to occur. The results of numerical simulations coupled with scraping tests provide reasonable explanations for observed debonding behaviors of single splats. This study provides a comprehensive understanding of the effects of several droplet impact variables and residual stress on the debonding behaviors, and the related adhesion strength as well as driving forces of single splats.

Enhanced Interfacial Properties of Carbon Nanomaterial–Coated Glass Fiber–Reinforced Epoxy Composite: A Molecular Dynamics Study

The weak interfacial adhesion has significantly affected the durability, long-term reliability, and performance of glass fiber–reinforced epoxy composites. The coating of graphene and carbon nanotubes on the glass fiber can have a positive effect on the strength, toughness, and thermal insulation performance of glass fiber-reinforced composites. However, the strengthening mechanism of carbon nanomaterial coating on the interfacial adhesion between glass fiber and epoxy has not been fully explored. In this work, the effect of graphene and single-walled carbon nanotubes (SWCNTs) on the interfacial properties of the glass fiber–reinforced epoxy has been investigated at atomistic scale. The graphene and SWCNTs are sandwiched between epoxy and silica to study the debonding behavior of the sandwiched structures. It is found that the interfacial energy is significantly improved with the incorporation of graphene and SWCNTs between epoxy and silica, causing an obvious improvement in adhesion stress for graphene coating and in debonding displacement for SWCNT coating. Compared with the epoxy/silica without coatings where the silica and epoxy detach from the contact surface, the sandwiched structures display different failure modes. The sandwiched structure with graphene coating fails at the epoxy matrix close to the interface, exhibiting a cohesive failure mode because of the relatively stronger interfacial interactions. The structures with SWCNTs fail at the interface between silica and SWCNTs, representing an adhesive failure mode due to the interlocking between SWCNTs and polymer chains. This work provides a theoretical guideline to optimize the interface adhesion of coated glass fiber–reinforced epoxy via structure design and surface modification of coating materials.

A nonlinear analytical model for predicting bond behavior of FRP-to-concrete/steel substrate joints subjected to temperature variations

The effective interfacial stress transfer mechanism plays an important role in the mechanical performance of externally bonded fiber reinforced polymer (FRP) strengthened structures. Therefore, a profound understanding of the effect of temperature variation on the bond behavior of FRP-to-concrete/steel joints is helpful to improve the engineering specification of FRP strengthening technology. This paper presented a new analytical approach aimed at predicting the bond and debonding behavior of FRP-to-concrete/steel bonded joints under thermal loading. The proposed analytical solutions were derived based on an exponential temperature-dependent bond-slip model, and these solutions had a rather good prediction accuracy compared with the experimental and finite element numerical results. Some discussions about the bond behavior under temperature variations were carried out with an example. Results of this study showed that with the increase of bond length, there existed an upper limit value for the failure temperature variation, as well as for the maximum FRP stress. Temperature-dependent bond-slip relation was shown to have a great effect on the distribution of FRP stress and interfacial bond stress, especially on the temperature variation–free end slip response.

Edge and Crack-Induced Debonding Analysis of FRP-Strengthened Concrete Beams Using Innovative Beam Finite Elements

In order to analyze the edge debonding and intermediate flexural crack–induced debonding of fiber-reinforced polymer (FRP)-strengthened concrete beams, several innovative beam finite elements were developed in this paper. The proposed elements were capable of modeling the concrete, adhesive layer, and FRP sheet in one macroscopic element. The explicit formulations of the proposed element stiffness matrices were given to simulate the adhesive layer in different loading stages. Comparisons against several numerical examples available in the literature were given to validate the proposed elements. The effects of the FRP tapering ends, load, and crack location on the interfacial shear stress within adhesive layers were effectively investigated using the proposed elements. It was found that the proposed elements could conveniently predict the edge and flexural crack–induced debonding behavior of FRP-strengthened beams with accuracy and computational efficiency.

Cement debonding behaviors of the various tibial components of the ATTUNE knee system and its predecessors: Is a cement-in-cement revision an alternative?

BackgroundAseptic loosening remains one of the most common causes of revision of the tibial component for total knee arthroplasty. A stable bond between implant and cement is essential for appropriate long-term results. The aim of our in vitro study was to investigate the maximum failure load of tibial ATTUNE prosthesis design alternatives compared with a previous design. In addition, cement-in-cement revision was considered as a potential strategy after tibial component debonding. MethodsThe experimental investigations of the maximum failure load of the implant–cement interface were performed under optimal conditions, without potential contamination. We compared the designs of the tibial components of the ATTUNE, ATTUNE S+ and P.F.C. Sigma. In addition, we investigated the cement-in-cement revision for the ATTUNE knee system replacing it with an ATTUNE S+. ResultsThe maximum failure load showed no significant difference between P.F.C. Sigma and ATTUNE groups (P = 0.087), but there was a significant difference between the P.F.C. Sigma and the ATTUNE S+ groups (P < 0.001). The analysis also showed a significant difference (P < 0.001) between the ATTUNE and the ATTUNE S+ groups for the maximum failure load. The ATTUNE S+ cement-in-cement revision group showed a significant higher failure load (P < 0.001) compared with the P.F.C. Sigma and ATTUNE groups. No significant differences (P = 1.000) were found between the ATTUNE S+ cement-in-cement and ATTUNE S+ group. ConclusionBased on these results, we found no design-specific evidence of increased debonding risk with the ATTUNE and ATTUNE S+ components compared with the P.F.C Sigma. Furthermore, the cement-in-cement revision seems to be an alternative for the revision surgery.

Fracture behavior of restored teeth and cavity shape optimization: Numerical and experimental investigation

ObjectivesSince restored teeth are subject to more damages than intact teeth, investigating their fracture behavior is important. However, so far, improvement of the debonding behavior of the restoration and fracture of restored teeth considering the geometry of the restoration and different restorative materials has remained understudied. The aim of this paper is to numerically and experimentally investigate the debonding behavior of the restoration in premolar teeth in order to reduce the stress of restoration thereby reducing the mechanical failure. Methodsthe fracture test for intact and Standard Class-II Mesial–Occlusal–Distal (MOD) restoration premolar teeth restored with several types of composite and conventional adhesive was performed in order to investigate their fracture behavior. The mechanical properties and fracture of composites as well as the adhesives used in experimental tests were obtained through separate standard mechanical tests. In addition, a number of composites and other adhesives were also chosen from other references, and by numerically simulating the fracture process of intact teeth and those restored with the materials of interest, the fracture behavior and yield load limit were investigated and predicted for them. Next, in order to reduce the stresses of bonding region and improve the damage behavior, using the stress-induced material transformation (SMT) optimization algorithm applied as code in finite element (FE) software, the shape of the restoration has been optimized based on different restorative materials. In order to confirm the numerical results, the fracture tests of teeth samples were performed with conventional and optimized restoration forms. Furthermore, using scanning electron microscopy (SEM) method, the fracture surface of the tested samples was examined. Resultssince the fracture behavior of teeth restored with different materials is different, the optimized MOD restoration would be also different for each of these restorative materials. By selecting TU-shape for the restoration in each of the samples, the debonding resistance and final fracture of teeth compared to the MOD restoration increased 51% in Pd and 11% in Pf for numerical results and 40% in Pd and 4% in Pf for experimental results. The obtained results suggest that choosing a proper shape for the restoration based on the properties of restorative materials leads to diminished normal and shear stresses and enhanced debonding resistance. Also, the yield load limit of the defective teeth would also improve considerably. SignificanceThe clinical importance of this study is to predict strength of restored teeth and cavity shape optimization under variable conditions. Also, this paper introduces effective parameters on strength reduction/enhancement to dentists.

A new progressive damage model for predicting the tensile behavior of the three-dimensional woven carbon/carbon composites using micromechanics method

A new progressive damage model for the three-dimensional (3 D) woven carbon/carbon (C/C) composites is developed at fiber-matrix level using the micromechanics method. A woven architecture based Representative Volume Element (RVE) model composed of yarns, matrix and yarn/matrix interface is constructed, in which the manufacturing void defects are accounted for. The fiber-matrix concentric cylinder model is employed as a repeating unit cell to represent the yarn, and the matrix micro strain field is computed analytically by the micromechanics method. The maximum stain criteria is utilized for fiber longitudinal breakage, and the Von-Mises criterion is applied for the damage initiation of matrix in both intra-yarns and inter-yarns. The damaged fiber and matrix are modeled by the stiffness degradation method combined with exponential damage evolution equations. The zero thickness cohesive elements governed by bilinear traction-separation constitutive are adopted for yarn/matrix interfacial debonding behavior. The micro progressive damage and failure behavior of the 3 D woven C/C composites subjected to tension is implemented through a developed user-defined material subroutine in commercial software ABAQUS. The predicted stress-strain response is in a good agreement with experimental results. In addition, the effect of manufacturing void defects is also examined by the developed model.

Debonding behaviors and micro-mechanism of the interface transition zone in sandstone-concrete interface in response to freeze-thaw conditions

Comprehensive understanding the micro-debonding behavior and micro-mechanism at the interface transition zone (ITZ) of rock-concrete interfaces is essential for protecting shotcrete in tunnels. The ITZ is a weak area of the rock-concrete interface and is vulnerable to freeze-thaw (F-T) deterioration. Such deterioration can cause tunnel support failure. We used nanoindentation technology, stereo microscopy, and scanning electron microscopy (SEM) and considered several F-T actions to obtain four primary findings: (1) The elastic modulus and hardness values of the ITZ decrease continuously as the number of F-T cycles increases, and the trends of these changes are highly consistent. However, the decline of hardness value exceeds that of the elastic modulus as F-T cycling continues. (2) The thickness of the ITZ has a positive correlation with the number of F-T cycles. For example, the ITZ thickness increases from 60 μm (0 F-T cycles) to 80 μm (20 F-T cycles). (3) The volume fraction of micropores at the interface has a positive linear correlation with the number of F-T cycles; however, the volume fractions of low-density (LD) calcium-silicate-hydrate (C-S-H) gel, high-density (HD) C-S-H gel, and calcium hydrate (CH) at the interface exhibit negative correlations with the number of F-T cycles. These relationships indicate that micropores exert a degradation effect in response to F-T conditions. (4) The ITZ has high porosity and low sensitivity to debonding near the sandstone side. ITZ debonding is induced by F-T cycles because frost expansion and thaw contraction are significantly different in sandstone and cement paste. This study provides a reference for understanding the behavior and mechanism of debonding in rock-concrete interfaces subjected to F-T conditions.

REVIEW OF INTERFACIAL DEBONDING BEHAVIOR OF ADHESIVE STRUCTURES WITH SOFT MATERIALS

Soft material has been widely used in soft robots, biomedicine, flexible electronics and other fields. In practical applications, soft material generally needs to be adhered to different types of substrate forming adhesive structures to accomplish specific functions. The interfacial performance of the adhesive system plays a key role in structural integrity and functional reliability. In this paper, the research efforts on the interfacial debonding behavior of adhesive structures with soft materials are systematically reviewed and summarized. The adhesive structures with soft materials can be classified into two types: (1) adhesive structures with “soft interface” in which stiff adherends are bonded by soft adhesives owning strong energy dissipative, typically viscoelastic, properties; (2) adhesive structures with “soft adherends” in which one or both of the adherends are significantly energy dissipative. In this paper, firstly, the specific mechanical characteristics and physical nature of the interfacial debonding behavior of the adhesive structures with soft materials are analyzed by comparing with those of the traditional “hard” adhesive structures. Secondly, the experimental characterization of the interfacial debonding behaviors of the adhesive structures with “soft interface” and “soft adherend” are summarized respectively. The effects of viscoelastic dissipative property of the adhesive interface and bulk adherends on the interfacial debonding mechanisms are analyzed respectively. Thirdly, the theoretical analysis methods for the interfacial debonding behavior of the adhesive structures with soft materials are reviewed and the relative theoretical models are summarized. Fourthly, the research progress of the numerical simulation, mainly based on the cohesive zone model (CZM) method, of the interfacial debonding behavior of the adhesive structures with soft materials is reviewed. Finally, based on the existing research progress, the challenges of the current research are put forward and the prospect of possible future research opportunities on the interfacial debonding behavior of adhesive structures with soft materials is discussed.

Investigation of interface debonding behaviour in a unidirectional SiC fibre reinforced Ti-17 composite by a single fibre push-out technique

The debonding behaviour at the fibre/matrix interface in a unidirectional continuous carbon-coated SiC fibre reinforced Ti-17 composite was investigated. Single fibre push-out testing on thin slice specimen by micro-indentation was employed to evaluate the interface debonding strength. In order to investigate interface debonding modes, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were utilised to observe the microstructure at the fibre/matrix interface region after the fibres were pushed out. It is found that the interface debonding strength is evaluated to be 108.2 MPa in the composite. The interface debonding occurs at the interface between the interface reaction zone (RZ) and the carbon coating on the fibre surface. The carbon coating/SiC fibre interface and the RZ/matrix interface remain intact after the fibre was pushed out.

A novel approach to assessing yarn/matrix (or yarn/yarn) in situ interfacial strength in 3D woven composites

A novel in situ experimental-numerical approach combining the meso-scale Digital Image Correlation (DIC) and a cohesive zone model (CZM) is proposed to assess the in situ interfacial strength of 3D woven composites. In order to obtain a specimen with interface damage as the dominant damage mode and simple internal structure, the specimen is particularly designed and cut into a dog-bone thin slice, which contains an in situ typical form of yarn/yarn or yarn/matrix interfacial structure. Benefiting from the simple internal structure of the specimen, the geometry of the numerical simulation model can be established quickly based on the micrographs of the specimen. A cohesive zone model is used to evaluate the debonding behavior of interface between yarn/yarn or yarn/matrix. With meso-scale DIC, tensile experiments are carried out on the particularly designed specimens. All specimens are broken at the yarn/yarn or yarn/matrix interface. Local strains obtained by meso-DIC show a consistent trend with that predicted by simulation, which proves the accuracy of the simulation model. The effects of interfacial parameters on the simulated strength are discussed. Through the combination of experiment and simulation results, the range of interfacial normal strength can be estimated.

Micromechanical finite element analysis of effect of multilayer interphase on crack propagation in SiC/SiC composites

The current study presents a micromechanical methodology to analyze the cracking behavior of a SiC/SiC composite with multilayer interphase using finite element method. To capture the constituent level damage initiation and propagation within the multilayer interphase, an axisymmetric unit-cell model was developed by discreetly modeling the fiber, the matrix, and the sublayers of interphase. Moreover, the cracking inside the interphase and debonding at the interfaces between different constituents were taken into account. The extended finite element method (XFEM) was applied to model the cracking inside the interphase and matrix. The cohesive surface approach was employed to describe the debonding behavior at all the interfaces. Adopting the proposed numerical approach, detailed local stress state and cracking behavior of SiC/SiC composites with multilayer interphase were analyzed. The results show that the multilayer interphase has a significant effect on the cracking behavior. Moreover, the growth length of secondary cracks had been demonstrated to be a useful parameter that is capable of connecting composites level behaviors and constituent level damages. From the various numerical methods used, the finite element simulation in conjunction with the XFEM and the cohesive surface approach is a precise and consistent way to analyze the crack propagation and prediction of failure for composites with multilayer interphase. The research provides a fundamental method for promoting the interphase design of SiC/SiC composites.

Multiscale modeling of unidirectional composites with interfacial debonding using molecular dynamics and micromechanics

In this study, a new multiscale micromechanical model based on the finite-volume direct averaging micromechanics (FVDAM) theory and molecular dynamics (MD) is constructed. It describes the interfacial debonding phenomena of unidirectional composites, whereby a solid fracture interface is incorporated with the FVDAM for the first time. To better elucidate the debonding behavior of the solid interface, a six-degrees-of-freedom (6-DoF) cohesive zone model (CZM) is proposed using MD simulation. The damage matrix Dc(k) in the kth subvolume of the interface is obtained using the 6-DoF CZM, and its explicit form is described herein to facilitate its implementation in commercial software packages. To verify the effectiveness of the model, both experimental data and numerical simulations were adopted for comparison. The experimental data of the unidirectional SiCf/Ti6Al4V composite were compared with the simulation results of FVDAM, and a good agreement was established. A finite element method-based unit cell model is constructed using ABAQUS for numerical validation, and homogenized responses and local fields are compared. The excellent correlations prove the effectiveness of the proposed model. Furthermore, the effects of thermal residual stress and fiber orientations are revealed, which may provide some useful information for the design and manufacture of composites.

Mixed-Mode Debonding Behavior between CFRP Plates and Concrete under Fatigue Loading

The cohesive zone model (CZM), which is capable of simulating the behavior of adhesively bonded joints subjected to static and fatigue loading, is widely accepted. In this study, fatigue peeling/shear of RC with externally bonded (EB) carbon fiber–reinforced polymer (CFRP) laminates under the mixed-mode implementation of the CZM is proposed. The procedure has been implemented in commercial software by programming the appropriate software-embedded subroutines. The main advantage of the proposed CZM is the use of coupled mixed-mode damage (shear-peeling), accounting for cumulative damage resulting from fatigue loading. Two-dimensional numerical simulations of the innovative double-lap-shear bonding test were performed by the proposed CZM. The excellent agreement between the simulated results and the experimental results are verified, and the good performance of the method as a predictive tool is demonstrated. Moreover, the peeling/shear propagation during loading can be effectively predicted.

Debonding Analysis of Adhesively Bonded Pipe Joints Subjected to Combined Thermal and Mechanical Loadings

In order to better understand the interfacial debonding behavior of pipe joints during the whole loading process, an analytical solution for the full-range behavior of adhesively bonded pipe joints under combined thermal and mechanical tensile loadings is presented in this paper. The solution was developed based on a simplified rigid-softening bond–slip model, and two cases with different softening region development were discussed. The analytical results were presented in a finite element model, and the effect of temperature on load–displacement curves and ultimate loads was shown based on the model. Through the nonlinear fracture mechanics, the analytical expressions of the interfacial shear stress and the load–displacement relationship can be obtained. The stress transfer mechanism, the interface crack propagation and the ductility behavior of the joints can be explained. This analytical result can help improve the potential application of fabricated structural components, precision instruments, oil and gas pipelines.

Molecular dynamics simulation of enhanced interfacial cohesive behavior of Ni-coated MWCNT/Mg composites

ABSTRACT Debonding processes of different Ni-coated MWCNT/Mg interface models were studied by molecular dynamics simulations, and the stress–displacement relationships of different interface models were obtained by fitting a modified exponential cohesive zone law for interface. In addition, the debonding behaviors of Ni-coated and uncoated MWCNT/Mg interface were compared. The results show that CNT wall numbers and inner diameters as well as interface orientations have significant effects on the Ni-coated and uncoated MWCNT/Mg interface cohesive-zone model parameters. Compared with the above two kinds of uncoated MWCNT/Mg interface models, the average values of the peak stress and the work of separation for the Ni-coated MWCNT/Mg interface models are both increased significantly, showing that the addition of a Ni-modified coating on the surface of MWCNTs can effectively enhance the adhesion capacity of the MWCNT/Mg interface.

The Mechanical Mechanism and Influencing Factors of Ice Adhesion Strength on Ice-Phobic Coating

Ice accretion can cause problems on polar ships, ocean platforms, and in other marine industries. It is important to understand the interface debonding behavior between ice and the surface of equipment. In this work, we created a mechanical model to analyze the interface debonding behavior between a square-based ice cuboid and an elastic coating base, using contact mechanics and fracture mechanics. Three-dimensional (3D) finite element (FE) simulation was used to simulate the interface debonding for normal and shear separation. A bilinear cohesive zone model (CZM) was used to simulate the interface between the ice cuboid and the elastic coating. We investigated the effect of the elastic modulus E of an elastic film on the critical detachment force Fc for normal and shear separation. The results showed that Fc increases with an increase of the elastic modulus of the elastic film. When E exceeds a certain level, Fc achieves a constant value and then remains stable. Finally, a series of epoxy/polydimethylsiloxane (PDMS) interpenetrating polymer-network (IPN) gel coatings with different elastic moduli were prepared. The ice tensile and shear adhesion strengths (σice and τice) of the coatings were measured. The results were roughly consistent with the results of the numerical simulation when E &lt; 1 MPa.

A Rate-dependent Continuum Damage Model for Dynamic Shear Debonding of CFRP-concrete Interface

Dynamic shear debonding behaviour in fibre reinforced polymer (FRP) strengthened concrete structures has been studied by some researchers through experiments and finite element (FE) simulations. However, there is still a lack of a continuum damage model to simulate dynamic debonding behaviour of CFRP-concrete interface using a method derived from nonlinear fracture mechanics (NLFM). To gain deeper insight into the dynamic fracture mechanics of carbon fibre reinforced polymer (CFRP)-concrete interface, a novel continuum damage model was proposed in this paper. Model analyses and regression test data were used to formulate the relationship between model coefficients and material parameters of tested specimens in literature. It was found that the dynamic enhancing effect on interfacial bond properties became more significant when a specimen has a larger CFRP load capacity or a lower concrete load capacity. The proposed damage model was verified through comparing numerical predictions of load-displacement curve and CFRP strain distribution along the bond length with published test results. Finally, based on a comparison with experimental study of specimens using basalt FRP and glass FRP, the proposed model was also found to be applicable to different types of FRP.

Modeling of FRCM strengthening systems externally applied on curved masonry substrates

Aim of the present paper is the proposal of a simple modeling approach for the numerical study of the bond behavior of Fiber Reinforced Cementitious Matrix (FRCM) reinforcements externally applied to curved substrates. The model consists of a schematization of the specimen strengthened by FRCM throughout spring elements representing both the substrate, matrix and reinforcement, and, moreover, the reinforcement-matrix interface layers. Regarding the latter, both tangential and normal behavior is opportunely modeled by separated springs in order to reproduce phenomena related to the mode I and mode II behavior. A further important feature of the proposed model is the coupling between normal and tangential springs in order to consider the effect of normal stresses arising at the reinforcement/matrix interface because of the geometric curvature of the substrate on the de-bonding behavior of the reinforcing system. Numerical analyses are presented in the paper with reference to experimental case studies deduced from literature. In particular, the authors propose a parameter setting procedure based on the experimental outcomes and some theoretical considerations.

Micro-mechanical model for ultra-high strength and ultra-high ductility cementitious composites (UHS-UHDCC)

This study finds that the slip-hardening parameter (β) increases with the increasing of PE (Polyethylene) fiber inclination for UHS-UHDCC (ultra-high strength and ultra-high ductility cementitious composites), the slip-hardening increasing coefficient (ω) is introduced to correct the β of ECC model. Therefore, the single PE fiber pullout micro-mechanical model is proposed, and this study defines the debonding behavior of PE fiber as the ‘physical debonding’. The pullout load–displacement curve of the single PE fiber and the single crack stress-opening curve verify the correctness of proposed micro-mechanical model for UHS-UHDCC. The first-crack stress (σfc, 5.78 MPa) and the fiber bridging complementary energy (Jb', 352.1 J/m2) satisfy the strength and the energy criteria, this ensures the realization of the tensile strain-hardening behavior. This study provides a theory basis for realizing the multi-cracking strain hardening behavior of UHS-UHDCC.