Cohesive Interface Research Articles

Numerical study of delamination process of the CFRP composite

A quasi-static approach for an interface damage model, incorporating Rayleigh damping for viscoelastic carbon fiber reinforced polymer composites, is introduced. The interface traction-relative displacement behavior is modeled using a thin adhesive layer, similar to cohesive zone models. The problem is solved numerically with a semi-implicit time-stepping method. The cohesive interface model, integrated into the Finite Element Method, was applied to determine the critical force away from the crack tip. Results showed that the numerical delamination under mode I conditions aligned well with experimental data for the cohesive zone formulations studied. The numerical example demonstrates the effectiveness of the proposed model.

Buckling of thin films: Lateral growth and kinetic evolution of telephone cords

We conduct a thorough investigation of the lateral growth and kinetic evolution of telephone cord buckles within thin films, employing both experimental and numerical techniques. Our exploration begins with in-situ experiments conducted on annealed silicon nitride films, aimed at capturing empirical data on the formation and evolution of these distinctive patterns. These experiments yield valuable insights into the morphological changes of telephone cords, such as wave flipping and merging, which lead to the enlargement of buckles at double wavelengths and widths. Subsequently, we employ a combined approach of geometrically nonlinear plate modeling and surface-based cohesive interface framework within a finite element numerical model to analyze the interplay between buckling-induced delamination and growth triggered by mode mixity-dependent interfacial toughness. Through this integrated approach, we effectively capture the mutual evolution of buckling and delamination occurrences, thus highlighting their inherently dynamic nature. Our numerical simulations show that the width and wavelength of telephone cords are doubled, consistent with experimental findings.

Biological small molecule interface-modification fostering resilient interfacial chemistry for silicon-based anodes

Silicon-based materials, particularly at the microscale, are prone to rapid capacity fade due to substantial volume fluctuations during the charge-discharge cycles, significantly impeding their commercial viability. Constructing a stable solid electrolyte interface (SEI) is an effective means to improve the performances of silicon-based anodes. Here small biomolecules, tryptophan (Trp) and phytic acid (PA), are introduced as interface modifiers to optimize the interfacial chemistry of micron-silicon anodes. By engaging in the SEI formation process, these small biomolecules effectively regulate the chemical composition and mechanical properties of the formed SEI, fostering a more cohesive and durable interface. The simultaneous addition of PA and Trp has been observed to yield a synergistic effect, creating a tightly bonded and resilient SEI that confers markedly improved battery performances upon the co-modified micron silicon anodes. Density functional theory calculations reveal charge interactions between these small biomolecules and silicon particles, facilitating effective adsorption onto the silicon surface. Simultaneous adsorption of Trp and PA on silicon surface can significantly enhance adsorption strength, providing a compelling explanation for the observed synergistic effect of Trp and PA co-modification.

Hollow Cobalt Selenide-Carbon polyhedron sandwiched between reduced graphene oxide nanosheets: A superior anode material for lithium-ion batteries

In this work, a double carbon-confined sandwich-like CoSe/NCP/rGO composite was fabricated using an self-assembled method combined with a selenization treatment. In the composite, cobalt selenide (CoSe) nanoparticles were embedded in N‑doped hollow carbon polyhedrons (NCP) and sandwiched between reduced graphene oxide (rGO) nanosheets. The kinetics of electron/ion transport along with the structural stability of the composite were significantly enhanced by the layer-by-layer sandwiched hollow structure and the strong cohesive interface interaction between various components. The CoSe/NCP/rGO, when serving as LIB’s anode material, exhibited excellent performance. It demonstrated a high specific capacity with the value of 843 mAh/g at 1 A/g, superior high-rate capability with capacity remaining at 309 mAh/g at 10 A/g, long-term cycling stability with no noticeable capability fading over 1000 loops. More importantly, these results were achieved without additional conductive agents.

Recoverability degradation of adhesion between soft matters under uniaxial cyclic bonding–debonding: Modified cohesive interface model and numerical implementation

The main objective of this work is to propose a partial recoverable cohesive interface model, coupled with a bi-potential contact algorithm, to simulate the phenomenon of adhesion recoverability degradation under cyclic bonding–debonding between hyperelastic bodies. For this end, the proposed adhesion recoverability degradation model is constructed by defining the recovery of interface damage during the rebonding when two bodies come into contact, and a degradation factor related to the number of bonding–debonding cycles is introduced into the fully recoverable adhesion model to reduce energy dissipation after multiple cycles. Recoverability degradation includes adhesive stiffness and strength degradation, which is physically described as parallel, series and mixed arrays of adhesive bonds. Then, a finite element framework coupling the adhesion recoverability degradation model and the bi-potential contact algorithm is proposed, with Mooney–Rivlin hyperelastic material used to describe the soft matters. This framework is implemented in an in-house finite element code, with numerical examples demonstrating the model’s reliability. The proposed approach could be applied to investigate interfacial adhesion effects in fields such as flexible electronics and intelligent robotics.

An interface-based microscopic model for the failure analysis of masonry structures reinforced with timber retrofit solutions

This paper presents a refined Finite Element (FE) modeling strategy for analyzing the failure behavior of regular masonry structures reinforced with timber-based retrofit solutions. The proposed model schematizes the masonry as brick units, modeled using two-dimensional linear elastic plane stress elements, mutually joined through zero-thickness cohesive interface elements. These interface elements serve to reproduce the nonlinear behavior of masonry because of the occurrence of failure mechanisms of the mortar joints. Reinforced timber frame elements are modeled using truss elements that exhibit elastic brittle fracture behavior. The interaction between the masonry sub-structure and the reinforced timber frame system is accounted for using special constraint conditions that simulate the mechanical behavior of anchorage connections. The reliability of the proposed model in reproducing the failure behavior of masonry is assessed through comparisons with experimental and numerical data available in the literature. Additionally, the efficacy of the retrofit technique based on timber frame structures is investigated in detail through pushover analyses on a two-story masonry wall representative of real-life masonry buildings. The results indicate that the proposed retrofitting strategy is an effective and eco-friendly retrofit solution to enhance the in-plane bearing capacity of masonry structures subjected to horizontal forces.

Characterization and Modeling of Out-of-Plane Behavior of Fiber-Based Materials: Numerical Illustration of Wrinkle in Deep Drawing.

The characterization and modeling of the out-of-plane behavior of fiber-based materials is essential for understanding their mechanical properties and improving their performance in various applications, especially in the forming process. Despite this, research on paper and paperboard has mainly focused on its in-plane behavior rather than its out-of-plane behavior. However, for accurate material characterization and modeling, it is critical to consider the out-of-plane behavior. In particular, delamination occurs during forming processes such as creasing, folding, and deep drawing. In this study, three material models for paperboard are presented: a single all-material continuum model and two composite models using different cohesion methods. The two composite models decouple in-plane and out-of-plane behavior and consist of continuum models describing the behavior of individual layers and cohesive interface models connecting the layers. Material characterization experiments are performed to derive the model parameters and verify the models. The models are validated using three-point bending and bulge tests and show good agreement. A case study is also conducted on the application of the three models in the simulation of a deep drawing process with respect to wrinkle formation. By comparing the simulation results of wrinkle formation in the deep drawing process, the composite models, especially the cohesive interface composite model, show greater accuracy in replicating the experimental results, indicating that a single continuum model can also be used to represent wrinkles.

A phase-field framework for modeling multiple cohesive fracture behaviors in laminated composite materials

This work proposes a phase-field (PF) framework to characterize the multiple fracture behaviors and quasi-brittle failure mechanisms in fiber reinforced laminated composites. The multi-phase field model considering the distinct failure mechanisms of composites is first derived based on thermodynamic principles. A hybrid PF formulation is proposed through the reasonable definition of the energy functional for each field, and a PF regularized cohesive zone model (CZM) combined with Hashin failure criteria is achieved for the typical failure modes in composites. The proposed PF-CZM is endowed with a linear softening behavior and is proven to be independent of the internal length scale parameter. The multiple fracture modeling of composite laminates is achieved by coupling the PF model for intralaminar failure with the cohesive interface element for interlaminar one. The model’s validation is demonstrated by several representative numerical examples, and results show that both the intralaminar fiber/matrix fractures and the induced interlaminar delamination, as well as their complex interactions, are well captured by the proposed model.

Fracture and multiple-cracking modelling of strain-hardening cementitious composites

Strain-hardening cementitious composites (SHCC), composed of short fibres embedded within brittle matrix, exhibit distinctive pre-peak strain-hardening characteristics and remarkable tensile ductility. The fracture and failure process of SHCC, involving both hardening and softening stages as a result of matrix multiple micro-cracking and strain localization, is highly complex and poses a significant challenge for numerical modelling. In the present paper, a novel numerical framework, characterized by the bi-layer superposed cohesive zone strategy, is developed for the numerical modelling of fracture and multiple cracking of SHCC, at both the material scale and structural scale. The developed model is based on diffused cohesive interface model, but with adaptions to consider fibre bridging mechanism. The crack interface is simulated by two cohesive elements sharing the same nodes: one for the matrix-cohesion effect and the other for the fibre-bridging effect. Cohesive constitutive relations of matrix cohesion and fibre bridging are carefully assigned. The proposed model is first validated on the material scale through a uniaxial tension test. With the aid of a random material field, multiple-cracking phenomenon and stress fluctuation are successfully predicted by the model. The model is then applied to the structural fracture modelling, where four case studies, including both pure mode I and mixed mode fracture, are performed. The size effect and boundary effect on the fracture behaviour are well captured by the numerical modelling. The model proposed in the current work has the potential to be extended to the multiple cracking modelling of other materials.

Data-driven and physics-based methods to optimize structures against delamination

Composite materials and multi-material components often fail at their internal interfaces/adhesive joints, and hence special attention should be given to such catastrophic delamination events to guarantee the system’s functional requirements. So far, however, the majority of structural topology optimization problems have focused on optimal distribution of the bulk materials by considering interfaces as perfectly bonded. This motivates the introduction of optimization methods that explicitly take into account the role of the material interfaces to optimize structures against delamination. In this work, we propose a data-driven heuristic optimization approach for the identification of optimal cohesive interfaces with linearly graded fracture properties to increase the ability of the composite structure to withstand peeling. Moreover, for given cohesive interface properties, we investigate the applicability of the physics-based Solid Isotropic Material with Penalty (SIMP) topology optimization approach to optimize the internal structure of a substrate in problems where the stress field is affected by interface delamination.

Hygroscopic damage of fiber–matrix interface in unidirectional composites: A computational approach

The mechanical properties of fiber-reinforced composites are significantly affected by hygroscopic exposure. Recent experimental findings reveal that the diffusion of water molecules results in void formation at the fiber–matrix interface, contributing to ∼1% increase in porosity. This paper presents a computational micromechanics framework to analyze the damage behavior of unidirectional composites under hygroscopic aging and transverse loads. First, a mathematical relation for the porosity evolution with moisture content in the composite is obtained. Leveraging this correlation, the aged composite is modeled as a porous microstructure consisting of fiber, matrix, and voids at the fiber–matrix interface in finite element simulations. The fiber is considered elastic, and the matrix is modeled as an elastoplastic material using a pressure-dependent yield model to capture tension–compression asymmetry. A cohesive interface is considered between the fiber and matrix. Simulation results indicate that a void at the interface significantly influences plastic strain evolution and stress distribution, leading to early damage initiation and reduced strength. Previous works have indicated that matrix and inter-fiber voids do not have a significant impact on the strength of composites when their combined porosity is below 1%. On the contrary, this study demonstrates that a porosity of as low as 0.1% at the fiber–matrix interface can result in an 11% decrease in the transverse tensile strength of the composite. A parametric study is conducted to understand the fundamental effects of pore size, location, and relative position on the transverse tension, compression, and shear loading responses of a unidirectional composite. For a given moisture content, the predicted strength of the hygroscopic aged composite exhibits a lower and upper bound. The strengths observed in the experiments fall within the model-predicted range. Additionally, a computational method is proposed that incorporates the effects of porosity at the fiber–matrix interface into a modified cohesive strength. This method allows efficient computations and failure predictions for water or moisture-aged strength degradation of unidirectional composites.

Development of an UV-Resistant Multilayer Film with Enhanced Compatibility between Carboxymethyl Cellulose and Polylactic Acid via Incorporation of Tannin and Ferric Chloride.

Carboxymethyl cellulose (CMC) and polylactic acid (PLA) are recognized for their environmental friendliness. By merging them into a composite film, packaging solutions can be designed with good performance. Nonetheless, the inherent interface disparity between CMC and PLA poses a challenge, and there may be layer separation issues. This study introduces a straightforward approach to mitigate this challenge by incorporating tannin acid and ferric chloride in the fabrication of the CMC-PLA. The interlayer compatibility was improved by the in situ formation of a cohesive interface. The resulting CMC/TA-PLA/Fe multilayer film, devoid of any layer separation, exhibits exceptional mechanical strength, with a tensile strength exceeding 70 MPa, a high contact angle of 105°, and superior thermal stability. Furthermore, the CMC/TA-PLA/Fe film demonstrates remarkable efficacy in blocking ultraviolet light, effectively minimizing the discoloration of various wood surfaces exposed to UV aging.

Self-Amputating and Interfusing Machines.

Biological organisms exhibit phenomenal adaptation through morphology-shifting mechanisms including self-amputation, regeneration, and collective behavior. For example, reptiles, crustaceans, and insects amputate their own appendages in response to threats. Temporary fusion between individuals enables collective behaviors, such as in ants that temporarily fuse to build bridges. The concept of morphological editing often involves the addition and subtraction of mass and can be linked to modular robotics, wherein synthetic body morphology may be revised by rearranging parts. This work describes a reversible cohesive interface made of thermoplastic elastomer that allows for strong attachment and easy detachment of distributed soft robot modules without direct human handling. The reversible joint boasts a modulus similar to materials commonly used in soft robotics, and can thus be distributed throughout soft robot bodies without introducing mechanical incongruities. To demonstrate utility, the reversible joint is implemented in two embodiments: a soft quadruped robot that self-amputates a limb when stuck, and a cluster of three soft-crawling robots that fuse to cross a land gap. This work points toward future robots capable of radical shape-shifting via changes in mass through autotomy and interfusion, as well as highlights the crucial role that interfacial stiffness change plays in autotomizable biological and artificial systems.

The role of constitutive properties on the longitudinal compressive strength of composites

The longitudinal compressive strength of fibre-reinforced composites is often a limiting factor for structural design. This paper uses micromechanical finite-element analyses to examine how the constitutive properties of the matrix, fibres, and interface affect the composite’s strength. For a typical carbon/epoxy composite, the matrix shear strength has a larger effect than the modulus; a linear-elastic perfectly-plastic approximation of the matrix shear curve may overestimate the composite’s strength by over 15%. A pressure-dependent and dilatant matrix plasticity response may strengthen the composite by 30%, considering current uncertainties in friction and dilation angles of epoxy matrices. The finite shear modulus of carbon fibres may weaken the composite by more than 10%. Considering a cohesive interface using traction–separation laws significantly affects the predicted response of the composite, even for interfaces stronger than the matrix. Opportunities for improving the characterisation, modelling and performance of the constituents in terms of matrix plasticity, fibre shear modulus, and interface response are discussed.

A cohesive interface model with degrading friction coefficient

A cohesive interface model with degrading friction coefficient

Failure analysis of glass fiber and basalt fiber reinforced polymer composites under an extreme environment with high‐temperature, high‐pressure and H2S/CO2 exposure

AbstractFiber‐reinforced polymers composites (FRPs) are widely used in the industrial field, but their failure mechanism in extreme environments is usually unclear. In this work, the effect of high‐temperature, high‐pressure and H2S/CO2 extreme environment, similar to oil and gas field conditions, on raw fibers and unidirectional FRPs was investigated. The results showed that the glass fibers (GFs) suffered extensive degradation with the presence of metal sulfides in the precipitate, whereas basalt fibers (BFs) showed localized degradation. The flexural modulus of glass fiber reinforced polymer composite (GFRP) after degradation decreased by 28.8% compared to 25.6% for the basalt fiber reinforced polymer composite (BFRP). The interlaminar shear strength and flexural strength of the BFRP decreased by 20.3% and 24.7% respectively. In contrast, the GFRP had a reduction of 55.2% in flexural strength after degradation. Finite element method (FEM) analysis showed that the GFRP exhibited severe cohesive interface damage, while the primary failure mode of BFRP remained essentially unchanged with a combination of fiber damage and cohesive interface damage. This study confirms the superior degradation resistance of BF/BFRP over GF/GFRP in the simulated environment and highlights its promising application potential in oil and gas field service.Highlights Filament winding was used to fabricate the GFRP and BFRP. Revealed distinct surface morphology changes in GFs and BFs under simulated oil and gas field conditions. Superior degradation resistance of BFRP over GFRP was found in the extreme environment. Demonstrated superior chemical stability and mechanical properties of BFRP over GFRP. Used FEM to investigate the failure modes of FRPs before and after exposure.

Prediction of direct shear failure in blast-loaded reinforced concrete members

The occurrence of direct shear failure in structural members during the early phases of blast loading prior to the development of appreciable curvature can lead to sudden and catastrophic consequences for protected facilities exposed to near-field and/or close-in blasts. Thus, accurately predicting direct shear failure in structural members subjected to blast loads is crucial. Consequently, this paper presents a novel 3-D finite element (FE)-based cohesive interface modeling approach capable of capturing the shear slip near the supports and accurately predicting direct shear failure in blast-loaded reinforced concrete (RC) members. The validity of the proposed numerical model is established with experimental data. Three distinct blast load cases varying from distant to close-in are applied to verify the applicability and highlight the novelty of the proposed model. Results show that direct shear failure is inherently captured within the modeling framework of the proposed cohesive interface models, eliminating the need for externally adopted damage criteria seen in existing 3-D FE-based continuum models. Further, the effectiveness of the cohesive interface model in the accurate blast damage assessment of structural members is manifested by using pressure-impulse (P-I) diagrams.

Molecular Understanding of the Distinction between Adhesive Failure and Cohesive Failure in Adhesive Bonds with Epoxy Resin Adhesives.

In the development of adhesives, an understanding of the fracture behavior of the bonded joints is inevitable. Two typical failure modes are known: adhesive failure and cohesive failure. However, a molecular understanding of the cohesive failure process is not as advanced as that of the adhesive failure process. In this study, research was developed to establish a molecular understanding of cohesive failure using the example of a system in which epoxy resin is bonded to a hydroxyl-terminated self-assembled monolayer (SAM) surface. Adhesive failure was modeled as a process in which an epoxy molecule is pulled away from the SAM surface. Cohesive failure, on the other hand, was modeled as the process of an epoxy molecule separating from another epoxy molecule on the SAM surface or breaking of a covalent bond within the epoxy resin. The results of the simulations based on the models described above showed that the results of the calculations using the model of cohesive failure based on the breakdown of intermolecular interactions agreed well with the experimental results in the literature. Therefore, it was suggested that the cohesive failure of epoxy resin adhesives is most likely due to the breakdown of intermolecular interactions between adhesive molecules. We further analyzed the interactions at the adhesive failure and cohesive failure interfaces and found that the interactions at the cohesive failure interface are mainly accounted for by dispersion forces, whereas the interactions at the adhesive failure interface involve not only dispersion forces but also various chemical interactions, including hydrogen bonds. The selectivity between adhesive failure and cohesive failure was explained by the fact that varying the functional group density affected the chemical interactions but not the dispersion forces.

Methods and models for fracture mode partitioning: A review

In the problem of a crack lying in the interface between two dissimilar materials, the mathematical expressions for the stress and displacement fields, derived from linear elastic fracture mechanics, feature oscillatory singularities near the crack tip. This makes it impossible to define the mode mixity mathematically. To overcome this issue, several alternative methods for mode partitioning and analytical, semi-analytical, empirical, or combined models performing mode partitioning in linear elastic, mixed-mode fracture problems have been proposed over the last 35 years. This paper attempts the first review of the topic. It begins by recalling the fundamental scientific problem through reference on the fracture mechanics of bimaterial interfaces. Next, it collects over 36 models performing mode partitioning, proposes classifying them into five broad categories (models based on the global method, models based on the local method, models employing crack-tip force measures, models employing a cohesive interface, and special models), and describes and critically reviews them. A comprehensive discussion is then provided, and the paper closes with justification of concluding remarks and prospective directions for future research.

Computational multiscale modelling of material interfaces in electrical conductors

Material interfaces occur at various length scales and may exhibit significantly different properties than the surrounding bulk. Motivated by their importance for electrical engineering applications such as wire bonds and electrically conductive adhesives, the focus of the present work is on material interfaces in electrical conductors. In order to approximate the physical interphase (of finite thickness) as a (zero-thickness) cohesive zone-type interface in macroscale simulations, scale-bridging relations are established that relate the apparent electro-mechanical interface properties to the underlying microstructure. A finite element-based implementation is discussed with particular focus lying on the efficient calculation of the flux-type macroscale quantities and the associated generalised algorithmic consistent tangent stiffness tensors. Analytical solutions are derived for validation purposes and representative boundary value problems are studied.