Interfacial Fracture Properties Research Articles

Mixed mode fracture properties of interface for composite MPC and cement concrete specimen with asymmetric semicircular bending beam

This paper investigates the interface fracture behavior of composite magnesium phosphate cement (MPC) and concrete asymmetric semicircular bending beam (ASCB) specimens under various loading conditions including pure mode I, mixed mode I&II, and pure mode II. Initially, finite element simulations are employed to compute and analyze the basic geometric characteristics of the ASCB specimens.. Subsequently, experimental tests are performed to determine the flexural strengths for different pre-crack lengths, and the critical stress intensity factors of ASCB specimens are obtained through testing. Then, parameters for the interface cohesive model are derived. Finally, the interface cohesive model for the composite MPC and concrete ASCB specimen is validated through numerical simulation. The present work show that a pure mode I opening crack represents the weakest form of the structure, and the flexural strength decreases with an increase in precrack length. The crack resistance at the repair interface is approximately 60% lower than the bearing capacity of pure mode II fractures. Intensity factor envelope analysis reveals that mixed mode I&II fractures should be avoided in composite structures experiencing complex stress states. The cohesive model effectively captures the interfacial bonding performance. When combined with the extended finite element method (XFEM), the cohesive model facilitates accurate simulation of the specimen’s interface fracture, demonstrating consistency with experimental results.

Multiscale experimental characterisation of mode-I interfacial fracture behaviour of vitrimer composites

Vitrimer composites with bond- exchange reactions offer significant advantages in terms of repair and recyclability. The mechanical properties of such composites can be designed by modifying the epoxy/anhydride ratio, thus allowing their interface properties to be customised. In this study, the mode-I interfacial fracture properties of vitrimer carbon fibre composites with different epoxy/anhydride ratios are investigated experimentally and numerically. The results show that composites with an epoxy/anhydride group ratio of 1:0.5 exhibit the highest fracture toughness, with a maximum value of 1.6 mJ/mm2. Meanwhile, the analysis of the composites’ microscopic fracture morphology indicates their good bonding performance with carbon fibres. Subsequently, a multiscale numerical approach is developed to simulate the mode-I fracture response of composite laminates and establish a trilinear cohesive model to simulate the macroscopic interfacial fracture behaviour. In this approach, a matrix elastic–plastic constitutive model and the J-integral method are applied to obtain the stress distribution in the fibre-bridging phase via a double cantilever beam fracture test. The macroscopic fracture behaviour obtained via simulation is consistent with the experimental results. Therefore, the proposed multiscale numerical simulation method, which correlates the matrix properties with macroscopic fracture parameters, allows the interlaminar properties of composites with novel matrices to be evaluated effectively.

Interfacial fracture performance of engineered cementitious composites and fire-damaged concrete

This study investigated the interfacial fracture properties of engineered cementitious composites (ECC) and fire-damaged concrete using bi-material wedge splitting specimens. The full load versus crack mouth opening displacement (CMOD) curves of the bi-material specimens were obtained using wedge splitting tests, and the fracture toughness and fracture energy were calculated. The effects of the maximum temperature experienced by the concrete (20–700 °C) and the interfacial roughness (0–5 mm) on the interfacial damage mode, fracture toughness, and fracture energy were studied. The results indicated that when the maximum temperature experienced by the concrete was lower than 400 ℃ or the interface was smooth, the damage mode of the specimens was primarily adhesive failure. However, when the maximum temperature experienced by the concrete was equal to or greater than 400 °C and the interface was rough, cohesive failure often occurred in the specimens. Owing to the change in the damage mode, the bi-material specimens had the highest values of the fracture toughness and fracture energy at 400 °C. When the maximum temperature experienced by the concrete exceeded 400 °C, both the fracture toughness and fracture energy decreased with the increasing temperature. In this study, the fracture toughness and fracture energy of the bi-material specimens first increased and subsequently decreased with the increaseing roughness, and the maximum fracture toughness and fracture energy values were obtained when the interface roughness was 3 mm. The study results would provide a reference for the surface treatment when ECC was used in the strenthening of fire damaged concrete.

Prediction of interfacial tensile bond strength in 3D printed concrete based on a closed-form fracture model

Interfacial bond strengths in 3D printed concrete may affect the deformation compatibilities among the extruded filaments and the anisotropy of concrete. However, the previous predictions were size dependent inevitably based on the assumption of interfacial continuity and homogeneity. This work aims to propose a fracture model capable of predicting the realistic tensile bond strength (ft) and fracture toughness (KIC) of interfaces between filaments and layers in 3D printed concrete. To reflect the discontinuity and heterogeneity of interfaces, a discrete number (β) and a microstructure characteristic parameter (G) were proposed. A simple linear relationship of the maximum fracture load (Fmax) related to ft or KIC was established, and thus, the realistic interfacial ft and KIC can be determined after obtaining Fmax from the tests on the specimens with any sizes. Subsequently, three-point bending tests were performed to study the interfacial fracture properties of printed concrete with various contents of manufactured sand. The results show that the addition of manufactured sand improved the interfacial ft and KIC between filaments but had little effect on the interfacial fracture parameters between layers. The anisotropic behavior of the 3D printed concrete was clarified by evaluating the predicted ft and KIC along different directions. This research brings novel insights into the interfacial behaviors in 3D printed concrete.

Fracture properties of a concrete-epoxy mortar interface with precoating treatment applied through image correlation technology

Random defects on concrete surfaces are a key factor affecting the bonding property of concrete–epoxy mortar interfaces. In this study, an epoxy–acetone solution was employed to pretreat such defects on concrete surfaces, and resin concentrations of 20, 40, 60, and 80 wt% diluted by acetone were used. The fracture mechanical properties and propagations of the fracture process zone (FPZ) of 14 concrete–epoxy mortar composite specimens were analysed using digital image correlation technology and the four-point bending test. The results revealed that there was a great influence of resin concentration on the fracture properties of the concrete-epoxy mortar interface. Precoating solution with an appropriate resin concentration (20 ∼ 40 wt%) could effectively delay crack formation at the interface and markedly improve the bearing capacity, stiffness, ductility, FPZ length, and energy release rate of the specimens. The precoating solution with a resin concentration of 40 wt% exhibited the optimal repair effect on the concrete surfaces. However, the improvement from the pretreatment with high resin concentrations (60 ∼ 80 wt%) on the fracture properties was less than satisfactory. The toughening mechanism of this precoating solution was analysed through scanning electron microscopy, which revealed that the concrete surface could be effectively repaired and improved by the precoating treatment with an appropriate resin concentration, which in turn enhanced the interfacial connection performance between epoxy mortar and concrete.

Multi-material additive manufacturing: effect of process parameters on flexural behavior of soft-hard sandwich beams

Purpose Understanding the effect of process parameters on interfaces and interfacial bonding between two materials during multi-material additive manufacturing (MMAM) is crucial to the fabrication of high-quality and strong multi-material structures. The purpose of this paper is to conduct an experimental and statistical study to investigate the effect of process parameters of soft and hard materials on the flexural behavior of multi-material structures fabricated via material extrusion-based MMAM. Design/methodology/approach Sandwich beam samples composed of a soft core and hard shells are fabricated via MMAM under different printing conditions. A design of experiments is conducted to investigate the effect of the print speed and nozzle temperature on the flexural behavior of soft-hard sandwich beams. Analysis of variance and logistic regression analysis are used to analyze the significance of each process parameter. The interfacial morphology of the samples after the flexural tests is characterized. Thermal distributions during the MMAM process are captured to understand the effect of process parameters on the flexural behavior based on inter-bonding formation mechanisms. Findings Experimental results show that the soft-hard sandwich beams exhibited two different failure modes, including shell failure and interfacial failure. A transition of failure modes from interfacial failure to shell failure is observed as the nozzle temperatures increase. The samples that fail because of interfacial cracking exhibit a pure adhesive failure because of weak interfacial fracture properties. The samples that fail because of shell cracking exhibit a mixed adhesive and cohesive failure. The flexural strength and modulus are affected by the nozzle temperature for the hard material and the print speeds for both hard and soft materials significantly. Originality/value This paper first investigates the effect of process parameters for soft and hard materials on the flexural behavior of additively manufactured multi-material structures. Especially, the ranges of the selected process parameters are distinct, and the effect of all possible combinations of the process parameters on the flexural behavior is characterized through a full factorial design of experiments. The experimental results and conclusions of this paper provide guidance for future research on improving the interfacial bonding and understanding the failure mechanism of multi-material structures fabricated by MMAM.

Study on the fracture performance for rock-concrete interface in the high geothermal tunnel environment

This study investigated the effects of the hot-dry geothermal tunnel environments on the interface fracture properties of rock-concrete composite materials. The interface fracture energies and fracture toughnesses in mode I and II of the rock-concrete specimens were experimentally investigated by the wedge splitting test. The interface fracture energies were calculated based on the P-CMOD curves, and the crack propagation length was obtained via the digital image correlation (DIC) technology. The initial fracture toughnesses and unstable fracture toughnesses of the rock-concrete interface were calculated by the finite element method. Before the finite element models of the rock-concrete composite specimens were established, a genetic algorithm was adopted to determine the cohesive force distribution at the rock-concrete interface. The correlation between the fracture behavior and the mode ratio was also investigated in this paper. The results show that the hooked-end steel fibers can markedly enhance the interface fracture energy which reached up to 161 N/m at 28 days. The opening mode fracture is the main destruction mechanism during the crack propagation. The hot-dry geothermal tunnel environment can always reduce the interface fracture toughness, and this reduction is pronounced in a higher temperature curing environment. The sliding mode fracture is more prone to occur in a higher temperature curing environment. Furthermore, the introduction of hooked-end steel fibers can significantly improve fracture toughnesses, and this promotion is even more remarkable at a later curing age. The group with the addition of hooked-end steel fibers at the ages of 3 days and 28 days were 0.059 MPa·m1/2 and 0.085 MPa·m1/2, and 0.138 MPa·m1/2 and 0.186 MPa·m1/2 for the initial and unstable fracture toughnesses, respectively.

Numerical analysis of the crack paths produced by fibre–matrix interface failure in cross-ply LFRP laminates

The so-called matrix failure, also named inter-fibre failure, is one of the main failure mechanisms in long fibre reinforced polymers (LFRPs). This mechanism is characterized by the debonding of some fibres when transverse loads are diving the failure process. In the present study, the prediction of cracks initiation and growth within fibre–matrix interfaces of the 90° layer in [0,90n]s laminates is aimed. To this end, the behaviour of the fibre–matrix interface is characterized using a Linear Elastic Brittle Interface Model (LEBIM) that has been implemented in the commercial FEA code Abaqus ® and applying a solution algorithm built in Python called the Sequentially Linear Analysis (SLA). The results point out the capability of the debonding process to represent the generation of transverse cracks, showing how the onset and growth of interface cracks within a laminate are influenced by different factors such as the local distribution of fibres, the value of the fibre–matrix interfacial fracture properties and the thickness of the 90° layer.

Accurate computational modelling for impacts of microcapsule size and interfacial fracture properties on the fracture of self-healing concrete

The fracture of microcapsules in the encapsulation-based self-healing concrete is the most important aspect to release the healing agents and hence heal the cracks. This paper studied computationally the impacts of the microcapsule size and the interfacial fracture proprieties between the microcapsule and the concrete on the fracture mechanism of the self-healing concrete (SHC). The proposed modelling combined the extended finite element method (XFEM) and cohesive surface technique to model the fracture of uniaxial tensile test SHC specimens. When compared to the zero thickness cohesive element approach on the same specimens, the proposed model shows high accuracy in determining load carrying capability and fracture pattern. The interfacial fracture properties and core-shell thickness of the microcapsule determine whether it fractures or debonds. The microcapsule with the thinnest shell is more likely to be fractured.

Accurate computational modelling for impacts of microcapsule size and interfacial fracture properties on the fracture of self-healing concrete

Accurate computational modelling for impacts of microcapsule size and interfacial fracture properties on the fracture of self-healing concrete

Modeling anisotropic fracture in a metal-fiber reinforced composite system

Hybrid structures consisting of metal and composites can be applied to specific requirements of different applications. The computational modeling of composites is quite complex compared to homogeneous and isotropic materials like metals because of the heterogeneity introduced due to the presence of different phases such as matrix, fiber and matrix-fiber interface, and anisotropy due to the fiber alignment. The crack propagation in a composite material depends on a combination of various damage modes, namely, fiber pull-out, matrix cracking, delamination. The strength and stiffness of the composite depend on the mechanical and fracture properties of the individual phases, and the fiber inclination. The metal-composite interface is modeled using the cohesive zone approach. A nonlocal diffused approach is proposed to model the anisotropic failure in composites reinforced with unidirectional and woven fibers and the interaction of the crack with the interface. Parametric studies are conducted to understand the role of fiber orientation and interface fracture properties of the system. The proposed model is illustrated through numerical examples to understand various failure mechanisms in a metal-composite system.

Investigations on fracture properties and analytical solutions of fracture parameters at rock-concrete interface

To investigate fracture properties and find analytical solutions of fracture parameters at rock-concrete interface, three-point bending tests were performed on the composite rock-concrete specimens with different degrees of interface roughness. Numerical simulations were conducted to analyse the crack propagation and the fracture process zone evolution at rock-concrete interface. For convenient applications in practice, a series of analytical solutions were derived or curve-fitted to calculate the fracture parameters of rock-concrete interface. The results indicate that the roughness degree has significant effects on the fracture properties of rock-concrete interface. With the increase of the roughness degree, the fracture energy, the critical crack length and the double-K fracture parameters exhibit obvious increasing tendencies. Meanwhile, the ratio of the unstable fracture toughness of rock-concrete interface to concrete is much less than that of the initial fracture toughness, indicating the much weaker cohesive effect of rock-concrete interface compared with concrete. In addition, with the increase of the roughness degree, the length of the fully formed FPZ and the corresponding ratio of the crack propagation length to the ligament length decrease. The characteristic length of rock-concrete interface is proved to decrease with the increase of the roughness degree, indicating larger brittle behaviour with the increase of the roughness degree. Finally, a series of analytical expressions were curve-fitted or derived to calculate the fracture parameters of rock-concrete interface under three-point bending loading, including the mode-I stress intensity factor, the critical crack length and the characteristic length of rock-concrete interface.

Interaction of anisotropic crack phase field with interface cohesive zone model for fiber reinforced composites

A new phase field model considering the interfacial damage for different configurations of a fiber reinforced composite is proposed and formulated. Crack and non local interface are considered to be diffused. A coupled traction separation law based on a potential function is adopted to represent the behavior of the interface. Anisotropy is introduced into the elastic equilibrium by considering the distinct contributions of fiber and matrix in different modes. The present model captures the predominant failure phenomena in a composite such as matrix failure, delamination by considering the role of fiber orientation, interface fracture properties and configuration of lamina. The proposed formulation is extended to a fiber reinforced composite lamina consisting of two fiber families oriented in different directions. Parametric studies are conducted to understand the effect of anisotropy parameter, length scales, fracture properties of fiber, matrix and interface on crack propagation and mechanical response of the whole system. Numerical examples are performed to validate the proposed model, understand the anisotropic crack growth for unidirectional and woven fiber reinforced composites, study the interaction of anisotropic crack with composite-composite interface and metal-composite interface.

Interface Strength, Damage and Fracture between Ceramic Films and Metallic Substrates.

Interface strength, damage and fracture properties between ceramic films and metallic substrates affect the service reliability of related parts. The films’ thickness, grain size and residual stress affect the interface properties and fracture behavior, thus related studies attract great attention. In this paper, the interface damage evolution and fracture behavior between ceramic films and metallic substrates were simulated by developing a three dimensional finite element model of alumina films on Ni substrates with cohesive elements in the interfaces. The interface fracture energy as a key parameter in the simulation was firstly determined based on its thermodynamic definition. The simulation results show the Mises stress distribution and damage evolution of the film/substrate structures during uniaxial tensile loading. Specially, when grain size of the films is in nanoscale, the interface strength increases obviously, agreeing with the previous experimental results. The effects of residual stress on interface properties was further simulated. The interface strength was found to decrease with increasing radial residual force and the axial residual pressure increases the interface strength. When the thickness of the films increases, the interface strength keeps a constant but the speed of interface damage becomes faster, that is, the thicker films show catastrophic fracture. The underlying mechanism of damage speed was analyzed. Understanding these size effects and the effects of residual stress is helpful to guide the design of related parts.

Influence of extremely cold environmental conditions on interfacial fracture phenomenon of aerospace grade unidirectional composites

An investigation of interfacial fracture modelling of carbon fibre reinforced plastic (CFRP) laminates at the atmosphere similar to the cruise condition of an aircraft has been carried out in this article. The Mode I & Mode II fracture tests are carried out using specimen of aerospace grade composite (AS4/914) at−550C. Compliance based methods for estimation of crack growth have been adopted for monitoring during the fracture tests. A new set of thermally influenced interfacial fracture properties are evaluated for AS4/914 laminates. A modified traction – separation law has been derived for Mode-I loadings considering the influence of fibre bridging under influence of extremely cold environmental conditions. This law has been evaluated from the superposition of traditional bilinear law and derived bridging law. A significant reduction in interlaminar fracture toughness has been observed due to the fragile nature of the matrix under cold environment. Experimentally obtained interfacial fracture properties are implemented into the numerical formulation. Extended Isogeometric Analysis augmented with Cohesive Zone Modelling (XIGA-CZM) for unidirectional CFRP laminate has been enhanced and enriched with thermally influenced fracture toughness properties for further investigation. Results obtained from the present XIGA-CZM formulation shows a good agreement with experimentally obtained results. Scanning Electron Microscope (SEM) observation of fractured surfaces are carried out to investigate the nature of crack propagation in CFRP laminate at−550C.

Experimental and Numerical Study on Fracture Characteristics of Interface between In Situ Engineered Cementitious Composites and Steel Deck

In this study, engineered cementitious composite (ECC) is used as the pavement of orthotropic steel deck bridge and an epoxy adhesive is used to achieve wet‐bonding between the steel deck and cast‐in‐place ECC. To investigate the fracture properties of bimaterial interface, the double cantilever beam (DCB) and 4‐point end notched flexure (4ENF) specimens were used to obtain the fracture toughness, and virtual crack closure technology (VCCT) was used to calculate the energy release rates. A mixed fracture criterion was also established based on the blister test in this study. In addition, for the phenomena of water accumulation in the interface cracks, the hydrodynamic pressure under load was evaluated with a two‐way fluid‐solid coupling model and the propagation mechanism of cracks at the water‐bearing interface was explored. The results showed that the energy release rates at the crack front showed obvious nonuniform distribution characteristics. The blister test indicated that a mixed fracture was in good agreement with the linear fracture criterion. The fracture effect produced by the hydrodynamic pressure of the interfacial water‐bearing crack was far less than the fracture toughness of the interface, which indicated that the hydrodynamic pressure could hardly destroy the interface at one time but might cause the erosion fatigue damage of the interface.

Experimental and XIGA-CZM based Mode-II and mixed-mode interlaminar fracture model for unidirectional aerospace-grade composites

This article presents a fracture model for evaluation of Mode-II and Mixed-Mode (Mode-I + II) interlaminar fracture properties of unidirectional laminated composites. Mode-II and Mixed-Mode (Mode-I + II) interlaminar fracture tests have been carried out on End-Notched Flexure and Mixed-Mode bending specimens, respectively. The non pre-craked specimens are tested under pure Mode-II and Mixed-Mode loading conditions for the estimation of energy required to initiate crack growth from the natural crack tip. Pre-cracked specimens have been tested under pure Mode-II loading conditions to investigate the nature of delamination propagation from the sharp crack tip. A new set of interfacial fracture properties has been evaluated for AS4/914 laminates. An expression has been developed to correlate the experimentally obtained energy release rate (ERR) and equivalent crack growth (Δa) using a compliance based beam method. The curve-fitted expression between ERR and Δa is further introduced to the cohesive zone model for numerical modelling. Fractured surfaces at the final fracture load point in non pre-cracked specimens during Mode-II fracture tests are examined using scanning electron microscopy technique. Numerical simulations of crack initiation and propagation for all fracture tests have been performed using a combined formulation of fracture mechanics and damage mechanics. The introduction of experimentally obtained interlaminar interfacial properties into a combined formulation of extended isogeometric analysis and cohesive zone model shows a good agreement with experimentally obtained results.

Computational Determination of Interface Fracture Properties for Concrete by Inverse Analysis

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Cancellous bone and PMMA cement interfacial fracture properties evaluation using heaviside digital image correlation/wedge splitting test method

Balloon Kyphoplasty is a minimally invasive surgery, which has acquired great importance recently for treating compressive bone fractures by balloon inflation and PMMA cement injection (Achatz et a...

Determination of interface fracture properties by micro- and macro-scale experiments in nacre-like alumina

The mechanical properties of brick-and-mortar composites depend on their interface fracture properties, which have not been evaluated to date, preventing a rational optimization of the microstructure and of the resulting mechanical properties. Micro-(cantilever) and macro-scale (Single Edge Notched Bending) tests on nacre-like alumina both result in crack initiation at the interface between the platelets. We assess crack initiation and predict the failure force by means of 2D and 3D finite element simulations employing the same fracture modeling approach at both scales, namely the coupled criterion. The interface fracture properties are determined by means of inverse identification based on both micro- and macro-scale experiments. The interface exhibits typical values of 438 MPa tensile strength and 1.96 J/m2 fracture toughness. The forces at crack initiation predicted employing these parameters are in good agreement with the forces measured experimentally for both micro- and macro-scale tests. The quantitative determination of the interface fracture properties should help the design and optimization of this class of brick-and-mortar materials.