Debonding Behavior Research Articles

Debonding behavior of non-welded wrapped composite X-joints subjected to monotonic tensile load – numerical study and validation

The dominant failure mode in the non-welded wrapped composite joints made with GFRP composite material wrapped around steel circular hollow sections (CHS) is characterized as interface debonding. However, in the ultimate load joint experiments, debonding process was merely inferred from the surface strain distribution obtained by the digital image correlation (DIC). A thorough understanding and explicit illustration of debonding mechanism in wrapped composite X-joints is needed with help of finite element modeling (FEM), in order to provide prediction models for design of wrapped composite joints in engineering structures. In this paper, two FE models were developed to simulate the debonding behavior of small-scale and medium-scale wrapped composite 45° X-joints in monotonic tensile tests previously conducted by the authors. A new strategy of modeling complex composite geometry using 4-node tetrahedral elements (C3D4) without defining composite lay-up was proposed. The cohesive zone modeling (CZM) approach was utilized to simulate the debonding behavior of composite-steel interface with introduction of a new four-linear traction-separation law. The generated FE models were validated by good agreement between numerical and experimental results in terms of load-displacement response and surface strain distribution throughout the failure process at two joint scales. The validated models gained good insight into the joint debonding mechanism and determined the surface strain threshold for quantifying the debonding length. Development and validation of the FE models with unique set of parameters aligned well with the experiment results at two different scales is an important step for prediction and design of wrapped composite joints.

Impact of Bond-Slip Models on Debonding Behavior in Strengthened RC Slabs Using Recycled Waste Fishing Net Sheets.

This study investigated the performance of recycled waste fishing net sheets (WSs) as a sustainable strengthening material for reinforced concrete (RC) slabs. The primary challenge addressed is the debonding failure caused by the low bond strength at the WS-to-concrete interface. To analyze this, two full-scale RC slabs-one with and one without strengthening-were cast and tested under a four-point bending setup. Finite element (FE) models incorporating existing bond-slip laws were developed using the ABAQUS software to simulate the strengthened slab's behavior. A sensitivity analysis was performed to assess the impact of bond-slip parameters on the failure mechanism. Experimental results indicated that the WS-strengthened slab enhanced the RC slab capacities by 15% in yield load and 13% in initial stiffness. Furthermore, the maximum shear stress of 0.5τmax or interfacial fracture energy of 0.2Gf, compared to values proposed by Monti et al., enabled the simulation of the global response observed in the experiment.

Precise modulation of the debonding behaviours of ultra-thin wafers by laser-induced hot stamping effect and thermoelastic stress wave for advanced packaging of chips

Abstract Laser debonding technology has been widely used in advanced chip packaging, such as fan-out integration, 2.5D/3D ICs and MEMS devices. Typically, laser debonding of bonded pairs (R/R separation) is typically achieved by completely removing the material from the ablation region within the release material layer at high energy densities. However, this R/R separation method often results in a significant amount of release material and carbonized debris remaining on the surface of the device wafer, severely reducing product yields and cleaning efficiency for ultra-thin device wafers. Here, we propose an interfacial separation strategy based on laser-induced hot stamping effect and thermoelastic stress wave, which enables stress-free separation of wafer bonding pairs at the interface of the release layer and the adhesive layer (R/A separation). By comprehensively analyzing the micro-morphology and material composition of the release material, we elucidate the laser debonding behavior of bonded pairs under different separation modes. Additionally, we have calculated the ablation threshold of the release material in the case of wafer bonding and established the processing window for different separation methods. This work offers a fresh perspective on the development and application of laser debonding technology. The proposed R/A interface separation method is versatile, controllable and highly reliable, and does not leave release materials and carbonized debris on device wafers, demonstrating strong industrial adaptability, which greatly facilitates the application and development of advanced packaging for ultra-thin chips.

Numerical prediction on the fatigue debonding behaviour in a complex bi-material interface: A case study on wrapped composite joints

Debonding is one of the most critical failure modes for bonded joints under fatigue loads. Numerical prediction on the fatigue debonding behaviour of bonded interfaces with complex geometry still remains a problem. This paper proposes a numerical methodology based on fracture mechanics to predict crack growth in a complex bi-material interface and illustrates the prediction procedure by a case study on wrapped composite joints. Interface coupon tests provide the fatigue crack growth properties at the composite-to-steel interface used as inputs for finite element (FE) modelling. The FE model is calibrated against fatigue tests of small scale wrapped composite joints with different steel surface roughness subject to different load levels. A sensitivity analysis is conducted to investigate the influence of key modelling parameters. The calibrated model is validated against fatigue tests on upscaled joints. Good agreements are shown between the test and modelling results in terms of crack growth and stiffness degradation, demonstrating the potential of the proposed numerical methodology for predicting fatigue debonding behaviour of complex bi-material interfaces.

Numerical investigation of thermal influence on debonding behavior in composite structures through a friction and cohesive coupled model

AbstractThis study conducts an in-depth numerical analysis of debonding behavior in composite structures, with a particular focus on the critical role of thermal effects. Utilizing a frictional contact cohesive zone model, the research characterizes the debonding process while sequentially integrating thermal analysis to assess the impact of thermal loading. A thermomechanical coupled model is developed and implemented using the finite element software ABAQUS. The model's accuracy is validated through the Double Cantilever Beam (DCB) test, ensuring reliable results. The methodology involves a detailed finite element analysis, where thermal loads are applied to composite specimens, followed by mechanical loading to simulate debonding. The frictional contact cohesive zone model accurately captures the interface behavior under varying thermal conditions. Quantitative results indicate that thermal loading significantly affects the debonding process, with a noticeable increase in debonding initiation and propagation rates, highlighting the critical influence of thermal effects on structural integrity.

A comprehensive investigation on the performance of reconstruction of noncircular fiber-representative volume elements in unidirectional composites using diffusion generative models

This study employs diffusion generative models to reconstruct random representative volume elements (RVEs) of unidirectional composites with noncircular fibers. Microscope images of these composites were prepared and trained with denoising diffusion probabilistic model (DDPM), denoising diffusion implicit model (DDIM), progressive distillation diffusion model (PDDM), and deep convolutional generative adversarial network (DCGAN). Hyperparameter tuning was performed for both DDPM and PDDM, and the generated RVE images were evaluated using the two-point correlation function (TPCF), Fréchet Inception Distance (FID), and computational cost. Furthermore, finite element (FE) models were generated using these images, and FE simulations were conducted considering interfacial debonding behavior. The resulting stress and strain curves from these simulations were compared. The results show that DDPM demonstrated the best performance in final image quality, while PDDM maintained stable performance from the early stages of training. Additionally, both models exhibited excellent agreement with the original images, indicating high quality, diversity, and resemblance.

Investigation of the Adhesion and Debonding Behaviors between Warm-Mix Recycled Asphalt and Aggregates Based on Molecular Dynamics Simulation

Investigation of the Adhesion and Debonding Behaviors between Warm-Mix Recycled Asphalt and Aggregates Based on Molecular Dynamics Simulation

Fracture mechanisms of Al-steel resistance spot welds: The role of intermetallic compound phases

This study explores the mechanical and metallographic characteristics of Al-Steel dissimilar resistance spot welds (RSW), with a particular focus on the intermetallic compound (IMC) phases and their impact on fracture mechanisms. Detailed metallographic analyses and novel miniature lap shear tests with in-situ Digital Image Correlation techniques were conducted to observe the crack propagation behavior. The findings revealed that the IMC phases significantly influence the crack path and fracture mechanisms, leading to variations in fracture energy. Specifically, three distinct IMC phases were identified at the weld interface, each exhibiting unique structural and mechanical properties, with corresponding fracture energies of approximately 0.03 kJ/m2, 1.1 kJ/m2, and 7.5 kJ/m2. These variations highlight the critical role of the IMC phase in determining the fracture behavior of the weld. The study further supported the development and validation of a finite element (FE) model, incorporating a Cohesive Zone Model to simulate debonding behavior and the Hosford-Mean fracture criterion to predict ductile fracture in the Al fusion zone, thereby successfully linking local material characteristics to mechanical properties.

Strengthening and repair of RC beams using natural sisal Fabric-Reinforced Cementitious Matrix composite

The present work reports the results of an experimental program on the mechanical characterization of Reinforced Concrete (RC) beams externally strengthened/repaired by natural sisal Fabric-Reinforced Cementitious Matrix (FRCM) composite. For such, undamaged and pre-cracked RC beams were U-wrapped with a sisal FRCM composite and then tested under bending load. The results showed significant increases in shear strength, up to 25 % for beams with stirrups and 75 % for beams without them. The strengthened/repaired beams also presented stirrups yielding delay during the tests. When compared with other synthetic FRCM strengthening systems from the literature, the enhanced mechanical results of the present work were mechanically equivalent. The cracking pattern and debonding of the sisal FRCM wrap system were measured by the Digital Image Correlation (DIC) technique. The wrap application reduced the crack propagation and debonding behavior was not detected. Finally, the experimental results were confronted with an analytical approach guided by ACI 549.4R-20 and considered sufficiently accurate.

A new cohesive-based modelling of moisture-dependent mode II delamination of carbon/epoxy composites

The cohesive zone model (CZM) is widely employed for simulating delamination and debonding behaviour in engineering structures. However, the choice of CZM shape impacts the accuracy of simulation results. Therefore, the selection of a suitable Traction-Separation Law (TSL) with appropriate cohesive parameters is crucial. This study focuses on simulating the mode II delamination of unidirectional carbon/epoxy composites under varying moisture content levels (0%, 2.2%, 3.8%, and 5.3%) using the End Notched Flexure (ENF) test. Trapezoidal TSL (TTSL) with varying pseudo-plasticity parameter (Γ) was implemented and compared. A guideline was proposed in this study to aid in the selection of cohesive parameters, and a relationship between these parameters and moisture content was established. The results indicate that Γ = 0.99 yields a more accurate force-displacement response compared to Γ = 0. The estimated cohesive zone length falls within the range of 2.0–2.4 mm. During crack growth, the analysis reveals that, at the peak force, a region approximately 0.5–0.6 mm ahead of the crack tip undergoes total failure. Simultaneously, damage initiation occurs in the region 2.3–2.4 mm beyond the complete failure zone.

Effect of fluid scour on stress distribution of film-substrate system

Under strong fluid scour in special service environment, the film-substrate system is prone to weaken its mechanical properties due to the additional shear stress by fluid, resulting in film debonding. The present study establishes a mechanical model incorporating the fluid shear stress for a film-substrate system with partial debonding. The debonding length, scour strength and thermal mismatch are considered in the model, respectively. Fluid induces compressive stress on inflow side and tensile stress on outflow side. Potential debonding behavior of film by the additional shear stress is qualitatively analyzed. Results show that the compressive stress by fluid releases part of the tensile stress of thermal mismatch, may mitigate surface cracking of film. The surface scour effect is amplified by the partial debonding, and is further enhanced with the increase of debonding length. The unevenness of stress distribution at the interface is intensified by the debonding and fluid scouring. The fluid scour poses a potential threat to the film-substrate system.

Assessment of the properties of interface-modified bamboo aggregates for sustainable concrete construction

To alleviate the serious loss of gravel resources, reduce carbon emissions and improve the sustainability of concrete materials, this study presents an innovative approach to develop a novel eco-friendly bamboo aggregate concrete. The proposed method involves utilizing the abundant and renewable Phyllostachys edulis (Moso) bamboo to create a new type of bamboo aggregate, as a substitute for conventional gravel aggregates. This study modified the bamboo surface using a composite effect of epoxy mortar and polyurethane adhesive to realize the direct application of bamboo aggregates. Compared to unmodified and polyurethane-modified bamboo, epoxy mortar-modified bamboo showed significantly improved physical and mechanical properties. Anti-corrosion properties tests revealed that the modified bamboo, especially epoxy mortar-modified bamboo, was less affected by acidic and alkaline corrosion than the unmodified bamboo and the mass loss rate was almost zero. In the early stages of alkaline corrosion, the strength of the bamboo increased, and then began to decrease after 28 d. The removal of the outer green bamboo significantly improved the adhesion of the adhesive to the bamboo surface, as confirmed by pull-out tests. A sufficient bonding area between the epoxy mortar-modified bamboo and the cement matrix remained after compression damage, whereas obvious debonding behavior between the cement matrix and unmodified and polyurethane-modified bamboo was observed. In summary, epoxy mortar modification significantly improved the comprehensive performance of bamboo aggregates. This study is expected to help improve the utilization rate of bamboo, promote bamboo concrete, and develop sustainable materials.

The Influence of the Interface on the Micromechanical Behavior of Unidirectional Fiber-Reinforced Ceramic Matrix Composites: An Analysis Based on the Periodic Symmetric Boundary Conditions

The long-term periodicity and uncontrollable interface properties during the preparation process for silicon carbide fiber reinforced silicon carbide-based composites (SiCf/SiC CMC) make it difficult to thoroughly investigate their mechanical damage behavior under complex loading conditions. To delve deeper into the influence of the interface strength and toughness on the mechanical response of microscopic representative volume element (RVE) models under complex loading conditions, in this work, based on numerical simulation methods, a microscale representative volume element (RVE) with periodic symmetric boundary conditions for the material is constructed. The phase-field fracture theory and cohesive zone model are coupled to capture the brittle cracking of the matrix and the debonding behavior at the fiber/matrix interface. Simulation analysis is conducted for tensile, compressive, and shear loading as well as combined loading, and the validity of the model is verified based on the Chamis theory. Further investigation is conducted into the mechanical response behavior of the microscale RVE model under complex loading conditions in relation to the interface strength and interface toughness. The results indicate that under uniaxial loading, increasing the interface strength leads to a tighter bond between the fiber and matrix, suppressing crack initiation and propagation, and significantly increasing the material’s fracture strength. However, compared to the transverse compressive strength, increasing the interface strength does not continuously enhance the strength under other loading conditions. Meanwhile, under the condition of strong interface strength of 400 MPa, an increase in the interface toughness significantly increases the transverse compressive strength of the material. When it increases from 2 J/m2 to 20 J/m2, the transverse compressive strength increases by 28.49%. Under biaxial combined loading, increasing the interface strength significantly widens the failure envelope space under σ2-τ23 combined loading; with the transition from transverse compressive stress to tensile stress, the transverse shear strength shows a trend of first increasing and then decreasing, and when the ratio of transverse shear displacement to transverse tensile/compressive displacement is −1, it reaches the maximum. This study provides strong numerical support for the investigation of the interface properties and mechanical behavior of SiCf/SiC composites under complex loading conditions, offering important references for engineering design and material performance optimization.

Temperature-dependent debonding behavior of adhesively bonded CFRP-UHPC interface

The adhesively bonded structure, comprising carbon fiber-reinforced polymer (CFRP) and ultra-high-performance concrete (UHPC), enhances structural strength while reducing brittleness and strain softening behavior. However, the adhesively bonded structure is inevitably influenced by temperature variations throughout its service life. When the adhesive layer's temperature surpasses the glass transition temperature (Tg), significant damage occurs to the bond layer joint. To investigate the debonding behavior of the CFRP-UHPC interface at various temperatures, a series of three-point-bending tests were conducted at room temperature, 120 %Tg, 150 %Tg, and 160 %Tg. This study introduced a temperature degradation factor, employing a proposed maximum load capacity prediction formula to adjust both the test results and data from other researchers. By adjusting the cohesion parameters with the temperature degradation factor, a temperature-dependent mixed-mode cohesive zone model (CZM) was developed. The model's validity was confirmed through finite element (FE) analysis, considering two distinct experimental scenarios. The paper concludes that the proposed model effectively simulates interface debonding behavior across varying temperatures.

Characterization and Simulation of the Interface between a Continuous and Discontinuous Carbon Fiber Reinforced Thermoplastic by Using the Climbing Drum Peel Test Considering Humidity.

The objective of this paper is to investigate the debonding behavior of the interface between continuously and discontinuously fiber reinforced thermoplastics using the climbing drum peel test. The study emphasizes on the importance of considering different climatic boundary conditions on the properties of thermoplastics. Specimens with varying moisture contents, from 0m.% up to above 6m.% are prepared and tested. It is observed that an increase in moisture content from 0m.% to 2m.% results in an increase of the fracture surface energy from 1.07·103J/m2 to 2.40·103J/m2 required to separate the two materials, but a further increase in moisture to 6.35m.% conversely results in a subsequent decrease of the required energy to 1.91·103J/m2. The study presents an explanatory model of increasing plasticization of the polymer due to increased polymer chain mobility, which results in more deformation energy being required to propagate the crack, which is corroborated in SEM investigations of the fracture surface. A further increase in humidity leads to polymer degradation due to hydrolysis, which explains the subsequent reduction of the fracture energy. The experimental set up is modeled numerically for the first time with cohesive surfaces, which could successfully reproduce the effective force-displacement curve in the experiment by varying the interface parameters in the model over an influence length, allowing the conclusion of a process induced variation in the interface properties over a specific consolidation length.

Investigation of interfacial degradation mechanism and debonding behavior for degraded rubber asphalt-aggregate molecular system using a molecular dynamics method

This study aims to investigate the debonding damage behaviors in rubber asphalt-aggregate interfaces under different rubber degradation degrees from a molecular-scale perspective. The pull-off test was simulated using molecular dynamics (MD) to determine the damage patterns at the asphalt-aggregate interface. The digital image processing (DIP) technique was employed to quantify the percentages of cohesive debonding, and the radial distribution function (RDF) and mean square displacement (MSD) was performed to explain the adhesion and cohesion damage mechanisms. In addition, the pull-out test results were compared with the simulated values to verify the reliability of the asphalt-aggregate molecular model. The findings of this study reveal that the presence of rubber powder molecules enhances the cohesion among asphalt molecules and mitigates damage to the cohesion at the asphalt-aggregate molecular interface. As rubber degradation progresses, the damage mode undergoes a gradual transition from adhesive damage to cohesive damage at the asphalt-aggregate interface. At lower temperatures, there is an increase in the internal aggregation of asphalt molecules, and the debonding rate of asphalt molecules at the mineral-aggregate interface rises from 7.67% to 35.67% following complete rubber degradation. Conversely, at higher temperatures, the asphalt-aggregate molecular system is primarily governed by the bonding of “double bond” and “single bond” groups, with cohesive damage dominating the asphalt matrix. The pull-out test results showed similar trends with the simulated values, indicating that the asphalt-aggregate molecular model in this study was relatively reasonable. The present study provides some guidance on the damage behavior of degraded rubberized asphalt-aggregate interface.

Effect of temperature on interface debonding behavior of graphene/graphene-oxide on cement-based composites

Temperature effect easily affect the adhesion of graphene/graphene oxide (GO) on the cement-based composites originating from the weaker non-covalent bonding at the interface, leading to weakening of the cementitious composite properties. In this study, the interfacial debonding behavior of graphene/GO and cement-based composites was investigated for low to high temperatures (250∼550 K) using controlled molecular dynamics simulations. The maximum tensile force and work of adhesion both decrease with increasing temperature, and the value of GO is 5∼6 times that of graphene. Especially at the high temperature end, GO is still difficult to peel off (Fmax: 7.93×103 pN, Wmax:2129.60 Kcal/mol). Meanwhile, the insights into the distribution and concentration of functional groups have shown that high concentrations and edge functional groups can improve interface adhesion. Energy decomposition demonstrated that, compared to the Coulomb effect of charge and the prestress of surface wrinkles, the van der Waals effect plays a major role in interface adhesion. Entropy analysis further reveals the high temperature sensitivity of graphene and the low sensitivity of GO due to edge functional groups. We believe that the insight into the temperature effect of interface debonding behavior at nanoscale can provide theoretical support for the effective temperature working conditions of graphene/graphene-oxide on cement-based composites.

Investigation on interlayer debonding behavior of unidirectional composite laminates under cyclical hygrothermal aging duration effects

AbstractThe composite interlamination is the key part of load transfer and plays a decisive role in the overall mechanical performance of composite structures. The interlaminar property is predominantly influenced by the matrix resin which is easily affected by the hygrothermal environment. This paper delved into the effect of hygrothermal aging duration on the interlayer debonding behavior of unidirectional (UD) laminates. The pre‐cracked specimens were treated by hygrothermal aging with a period of 0, 15, 30, 60, 90, and 120 days. The double cantilever beam (DCB) tests were employed to evaluate the interlaminar property. The effect of hygrothermal aging on load–displacement responses, R‐curves, crack growth speed, and fracture surface topography was analyzed. The results revealed that the load‐bearing capacity of aged specimens presented a reduction of 18.6%–29.0% compared with unaged ones. The interlaminar fracture toughness of specimens subjected to 15 days of treatment decreased significantly compared with that of unaged specimens due to the increase of water absorption caused by hygrothermal aging. With the increase in hygrothermal aging time, the interlaminar fracture toughness peaked at 60 days because of the post‐curing effect, followed by a declining trend influenced by the dominant hygrothermal aging effect. The fiber bridging of aged samples was increasingly obvious, became the most prominent at 60 days, and then gradually reduced. The fiber bridging diminished the crack propagation speed, hindered interlaminar debonding, and contributed to the interlaminar toughening.Highlights The samples underwent hygrothermal aging for 0, 15, 30, 60, 90, and 120 days. Load ability of aged samples was at least 18.6% lower than that of unaged ones. R‐curves rose before the crack length of 79 mm and then tended to stabilize. Fracture toughness first decreased, then increased and reduced with aging time. Fiber bridging could hinder crack growth and improve the interlayer property.

Extension of service life: Novel approaches to repairing fatigue-damaged steel structures

This study addresses the challenge of repairing fatigue-damaged steel structures through innovative methods employing toughened epoxy adhesives and carbon fiber reinforced polymer (CFRP) laminates. Harsh environmental conditions and inadequate maintenance contribute to premature deterioration of civil engineering structures. Experimental investigations using compact tension (CT) specimens reveal significant improvements in structural integrity and residual life extension with double-sided CFRP application and appropriate adhesive selection. These findings underscore the importance of optimizing repair methods, offering valuable insights for enhancing structural durability. Further research is necessary to validate these methods for real-world application, particularly regarding debonding behavior and environmental influences.

Failure mechanism of bonding between natural fiber and cement matrix at high temperature

The debonding behavior of natural fibers with cement matrix at elevated temperatures has been investigated by introducing a new test method for measuring the interfacial shear strength between the fibers and the cement matrix in the field of cementitious composites research. In addition, the effects of shrinkage, surface roughness, and tensile strength changes of natural fibers on the interface at high temperatures were analyzed by characterizing the failure process of chemical bonding with the matrix due to changes in the surface functional groups of natural fibers. The results show that the bonding properties between natural fibers and the cement matrix gradually decrease with increasing temperature, which is due to the contraction of the natural fibers in the radial direction at high temperatures leading to debonding with the cement matrix on the one hand, and the degradation of chemical bonding enhancement due to the reduction of polar groups on the surface of the fibers on the other hand, which contributes to the reduction of the interfacial strength between the fibers and the matrix. In the post-high-temperature phase, the temperature dependence of the inherent material properties of the natural fibers leads to a decrease in the mechanical properties as an additional factor affecting the interfacial behavior. This work evaluates the durability of natural fibers in cement matrices under high temperature conditions from the viewpoint of their inherent physical properties and surface chemical properties, providing unique research ideas and insights for related studies. Meanwhile, a new experimental method is introduced in the field of fiber-reinforced cementitious composites interface research, which can be widely attempted to be used in the study of selective combinations of different fiber-matrix interfaces, fiber size selection, and fiber modification to optimize the overall performance of the composites, which is of great significance to the research in this field.