Interface Failure Process Research Articles

Biomimicry and topology optimization for adhesive toughness design in bonded heterogeneous films

Heterogeneous films have recently been extensively studied due to their superior material properties compared to homogeneous films. However, studies focusing on the design of heterogeneous films, especially with multi-material phases and structures, have been relatively scarce. This paper presents a bioinspired design methodology aimed at optimizing the mechanical properties of heterogeneous films through the strategic arrangement of stiff and soft material blocks. The heterogeneous film is represented as a composite beam and the interfacial failure process is simulated by a cohesive zone model. Then an optimization algorithm is employed to adjust the distribution of stiff materials within the soft film patch in the heterogeneous film. The results show that a nearly twofold increase in adhesive toughness for the optimized film compared to the original. Further discussions shed light on the energy distribution and variations in the fracture process zone size, providing insights into the observed enhancements. In terms of efficiency, the proposed optimization method distinctly outperforms the greedy method, demonstrating the potential for a more effective and efficient design of heterogeneous films with improved mechanical properties.

Mechanical properties and soil failure process of interface between grouser of tracked mining vehicle and deep-sea sediment

Tracked mining vehicles (TMVs) are key equipment in deep-sea mining systems and can easily slip when walking on soft sediments on the seabed. Thus, it is important to investigate the effect of track parameters and grounding-specific pressure on the shear interaction between mining vehicles and sediment. The sediment was simulated using a mixture of bentonite and water, and a shear test of the track with a single grouser and sediment was conducted. A numerical model of the track–sediment shear test was established, and the shear strength and failure mode of the sediment soil under the track action were examined. The results demonstrate that the peak shear strength of the track–sediment interface increases with an increase in the grounding-specific pressure, gradually increases with an increase in grouser height, and tends to stabilize at a given level of grouser height. Owing to the presence of the grouser, the deep-sea sediment transitions from the elastic state to the plastic state faster than the typical clay during the shear test. The variation law of peak shear strength at the track-sediment interface with the height of track grouser under different grounding-specific pressures was analyzed, and a modified shear stress-displacement relationship model was proposed. Wedge failure is the predominant method of failure for a single-grouser shear sediment soil at various heights. The primary factor affecting the horizontal disturbance range is the grouser height, and the range increases as the grouser height increases; the primary element affecting the vertical disturbance range is the grounding-specific pressure, and the range increases as the grounding-specific pressure increases. The relationship of the grouser height and cohesiveness with the interfacial shear strength was examined and a new shear stress–displacement relationship model that can accurately capture the shear mechanical behavior between the track and sediment under various grouser heights was proposed. In conclusion, the study findings could serve as a guide for the engineering design of a TMV walking system.

A modified phase-field model for cohesive interface failure in quasi-brittle solids

We formulate a modified phase-field model for cohesive interface failure in quasi-brittle solids. Our model has two novel features: (i) a traction–separation-damage law for damage process; (ii) an energetic degradation function controlled by critical gap ratio. This modification offers an attractive approach to simulate the cohesive interface failure process. We also provide a robust numerical solution strategy to treat the spatio-temporal evolution of cohesive interface failure. Our model is validated by two benchmark problems including the constant strain patch test and mode-I delamination test. The numerical simulations are compared with some published data. We proceed to apply this model to study the complex failure mechanism of a peeling test on bi-material plates and crack impinging on interfaces in different scenarios, where the effects of critical gap ratios and interface inclination angles are discussed.

Bond behavior of recycled aggregate concrete-filled steel tube after elevated temperatures

This paper experimentally investigated the interfacial bond behavior of recycled aggregate concrete-filled steel tubes (RACFST) after different temperatures (i.e., 20 °C, 200 °C, 400 °C, 600 °C). A total of 40 specimens (twenty circular columns and twenty square columns) were tested by means of push-out to study the effect of the following parameters: (a) experienced temperature (T), (b) mass replacement percentage of recycled coarse aggregate (γ) and (c) cross-section shape. The influences and mechanism of above parameters on bond behavior were discussed. The test results indicate that T and γ had different influences on bond behavior and interfacial damage resistance. The interfacial failure process of the square specimen was non-uniform compared with that of the circular specimen and its overall failure process was more brittle. The bond behavior and interfacial damage resistance of the circular specimen were generally stronger than those of the square specimen. Besides, applicability of several existing prediction formulas for bond strength was evaluated. Lastly, more accurate prediction formulas for bond strength and analytical models for bond stress-slip relationships were proposed.

Shear Characteristics between FRP-Concrete Bonding Interface

At present, fiber reinforced composite materials (FRP) are widely used in the reinforcement of concrete structures. The bonding interface between FRP plates and concrete is the key part of the strengthening of concrete structures with FRP plates. The bonding performance directly determines the success or failure of structural reinforcement. Based on the self-developed test device, the development of FRP and concrete in direct shear debonding test specimens, with the aid of advanced digital image correlation DIC technology, accurate measurement of specimen strain distribution on the surface of the FRP plate, and the FRP plate surface strain along the plate long distribution rule and the bond strength of the specimens was well researched, it reveals that the stripping of FRP and concrete interface failure process, and provides technical guidance for the treatment of FRP-concrete bond interface in practical projects.

Effect of Resin Coating and Sand Gluing on Interface Properties between Polypropylene Fibers and Concrete

This paper presents the results of resin coating and sand gluing on the acoustic emission (AE) characteristics in the interface failure process of concrete reinforced by polypropylene (PP) fibers. Interface property is an important performance of fibers reinforced concrete, and the pull-out test is the simplest and most effective mean to investigate interface behavior between concrete and fibers. In this study, the realistic bi-linear local bond-slip law and the AE results are employed in this work to derive expressions of interface stress distribution and present the detailed analysis. The results of AE test are used to explain interface stress propagation in the different loading stages. Interface failure energy is also described quantitatively for different interface mode in this work.

Modeling the Interfacial Debonding Behavior Between Steel Wire and Adhesive

Abstract A polyethylene pipe reinforced by winding steel wires (PSP) has been widely used in the petroleum, chemical, and water supply industries. The PSP has outstanding mechanical properties due to its unique composite structure. However, interfacial debonding between steel wire and adhesive sometimes occurs when the temperature and inner pressure increases to some extent in the application. In this study, the interfacial behavior between steel wire and adhesive was investigated and the interfacial failure process was analyzed. First, to acquire test data of interfacial failure, pull-out tests were conducted using specimens consisted of steel wire and adhesive. Specimens were prepared per the PSP manufacturing process, and a temperature change occurred in the specimens' preparation. Second, as the details of failure process could not be observed directly, finite element models were established to represent the mechanical behavior of the steel-polymer interface in-order to reproduce the debonding failure process. The thermal preload was taken into account in the model, and its influence on interfacial behavior was discussed. Contact surface with cohesive behavior was utilized to characterize the interfacial property. Finally, the interfacial failure process including stick–slip interaction and frictional sliding interaction was modeled in the simulation. The simulation result agreed well with the experimental data. Based on the finite element model, the cause and the distribution of thermal residual stress in pull-out specimen were illuminated. Further, it is discussed that how the stress distribution changes along the adhesive interface.

Modelling and Experimental Testing of Thick CFRP Composites Subjected to Low Velocity Impacts

The present paper investigates a modelling approach of experimentally tested thick panels made of Carbon Fibre Reinforced Polymers (CFRP). The coupons were made of 24 unidirectional (UD) laminae with a layup [45/0/-45/90]3s. The specimens were subjected to low velocity impact using a drop tower system. Several sensors, including a load cell and strain gauge, were utilized both for analysing the behaviour of the material against the impact and for performing a validation of the numerical models. Three energy levels were adopted: 8J, 10J and 12J.Numerical models were implemented into the finite element (FE) software LS-DYNA. A linear - elastic constitutive law with an instantaneous failure material was selected for mimicking the intralaminar behaviour of the carbon fibre composite. Enhanced Chang – Chang was adopted as the onset-of-failure criterion. This criterion is able to capture damage in different directions and permits the consideration (or not) of the shear behaviour in the failure equations. The capability of the model to capture the correct interface failure process was particularly emphasized and therefore cohesive elements with a bilinear traction – separation law were chosen for the reproduction of delamination. Finally, the experimental – numerical results were compared using first and foremost the overall delamination area and the curves force – time, force – displacement and absorbed energy – time as well as the strain measures obtained by the sensors.

Virtual testing method on graphite fiber/resin single-filament-composite test

ABSTRACTThe probability of successful tests in microdroplet tests is relatively low because of its high fiber failure rate caused by oversize embedded fiber length. Meanwhile, the scattering of the IFSS calculated by the maximum pull-out force is always high due to sensitive to the microscopic geometrical and experimental parameters. Hence, a set of suitable microscopic parameters are essencial but always determined by trial and error. In this paper, a virtual testing method on microdroplet test is introduced to simulate the test process and determine the appropriate test parameters, so as to increase the success rate and efficiency for actual test. Accurate response-displacement curve and IFSS are obtained and compared with those from actual test. Then we use this virtual experimental method to complete a sensitivity analysis of the experimental parameters. Finally, considering thermal residual stress and the interface debonding slip, the interface failure process and the stress transfer mechanism are discussed in detail and the damage propagation processes of the tough and brittle interfaces are described. Apart from guiding actual test, this virtual experiment method can be used for any single-filament-composite test and provide more detailed material information than actual experiments as well as a direct reference for optimum design.

Modeling of interfacial debonding propagation in sandwich panels

The paper presents a nonlinear model for the analysis of the process of debonding between a face sheet and the core in sandwich panels. The model incorporates the Extended High-Order Sandwich Panel Theory with a cohesive interface modeling of the crack nucleation and propagation at the interface between a face sheet and the core. The derivation of the model combines the first order shear deformation kinematic assumptions for the face sheets with the high order small deformations kinematic assumptions that include out of plane compressibility for the core. The cohesive interfaces combine the components of the sandwich panel together and introduce the nonlinearity and the interfacial failure process into the model by means of nonlinear traction-separation laws. The properties of the cohesive interface are calibrated and the proposed model is validated through comparison with experimental results taken from the literature. Two cases that include the Double Cantilever Beam (DCB) and the Cracked Sandwich Beam (CSB) specimens are considered. In the DCB test, the panel is subjected to a global mode I loading, while in the CSB test is subjected to a loading scheme that yields a global mode II. On the local scale, a mixed mode is observed in the two tests. For the CSB case, contact constraints between the debonded face sheet and the core are also included. The comparison of the analytical results with the experimental ones focuses on the initial linear response, the nucleation of the interfacial debonding crack, and the propagation of the crack. The comparison validates the model and explores the deobnding failure process in sandwich panels.

Study of type-II boundary behavior during SA508-3/EQ309L overlay weld interfacial failure process

Failure behavior of SA508-3/EQ309L overlay weld interface was analyzed. Residual stress measurement showed weld interface was in low stress state at transverse and longitude directions. SA508-3/EQ309L interface was a typical sandwich structure containing a white bright band ended with multi micro-voids type-II boundary. Element changes little around type-II boundary, but hardness varied a lot. The property difference and feature of multi voids made type-II boundary unstable, affecting weld property significantly. Induced shear and tensile tests were applied to study type-II boundary behavior. Under shear stress, type-II boundary suffered work hardening while under tensile stress, type-II boundary cracked first before EQ309L necking. Energy Dispersive Spectrometer (EDS) showed little element variation around type-II boundary. Electron Back-Scattered Diffraction (EBSD) indicated that most part of type-II boundary was ∑3 CSL grain boundary. Under tensile stress, dislocations crossed the boundary, leading to further stress concentration, so as to make the boundary crack under low positive stress.

Numerical study of excavation induced fractures using an extended rigid block spring method

This paper presents a numerical study of fracturing process induced by excavation around a gallery using an extended rigid block spring method (RBSM). The surrounding rock mass is characterized by an assembly of rigid blocks based on a degraded Voronoi diagram. The macroscopic mechanical behavior of rock is related to that of interfaces between blocks. The mechanical behavior of each interface is described by its elastic stiffness and failure criterion. The failure process of interface is controlled by both normal stress and shear stress. Both tensile and shear failures are considered. The macroscopic fracturing process is described by the coalescence of cracked interfaces. The rock structural anisotropy is taken into account through a spatial variation of elastic stiffness and failure strength of interfaces. A series of sensitivity studies are performed to investigate effects of gallery orientation, failure strength of interfaces and rock structural anisotropy on gallery deformation and fracturing. Numerical results are compared with in-situ observations in terms of fracture patterns.

Molecular dynamics simulation of asphalt-aggregate interface adhesion strength with moisture effect

This study developed an atomistic simulation framework based on the classical molecular dynamics (MD) method to study the moisture-induced damage at the asphalt-aggregate interface. The interface adhesion strength of the asphalt–quartz system was predicted using MD simulation for the first time. The interface stress-separation curve under tension that was obtained from MD simulation resembles the failure behaviour measured from the pull-off strength conducted at the macroscopic scale. The results show that the presence of moisture at the asphalt–quartz interface significantly reduces the interface adhesion strength. The interface failure process is affected by the chemical compositions of asphalt. The interface adhesion strength decreases as the moisture content increases or the temperature increases. It was found that the atomistic model size (number of atoms) and the loading rate in MD simulation have considerable effects on the predicted interface adhesion strength. The findings from MD simulation provide fundamental understanding of material failure at the atomistic scale that cannot be observed at the normal experimental testing environment for asphalt materials. The MD simulation results can be potentially calibrated and utilised as inputs for higher scale micromechanical models to predict bulk mechanical responses of asphalt mixtures.

Acoustic emission assessment of interface cracking in thermal barrier coatings

In this paper, acoustic emission (AE) and digital image correlation methods were applied to monitor interface cracking in thermal barrier coatings under compression. The interface failure process can be identified via its AE features, including buckling, delamination incubation and spallation. According to the Fourier transformation of AE signals, there are four different failure modes: surface vertical cracks, opening and sliding interface cracks, and substrate deformation. The characteristic frequency of AE signals from surface vertical cracks is 0.21 MHz, whilst that of the two types of interface cracks are 0.43 and 0.29 MHz, respectively. The energy released of the two types of interface cracks are 0.43 and 0.29 MHz, respectively. Based on the energy released from cracking and the AE signals, a relationship is established between the interface crack length and AE parameters, which is in good agreement with experimental results.

A study of transverse cracking in laminates by the Thick Level Set approach

In this paper, we present an analysis of the transverse cracking and interface failure process induced in layered materials (such as composite laminates) subjected to tensile loading, with a new level set based non-local modeling approach for damage growth (TLS: Thick Level Set). In particular, a 2D finite element model is built to study damage in a cross-ply laminate. The study aims at evaluating the capacity of the TLS method to predict evolution of damage at the ply level, including initiation, propagation, merging of cracks or delamination. We show how this numerical model is able to reproduce key features such as crack spacing saturation and other experimental observations.

Numerical simulation of damage and failure in brittle rocks using a modified rigid block spring method

This paper is devoted to the numerical simulation of damage and failure in brittle rocks using a modified rigid block spring method. The brittle rocks are represented by an assembly of rigid blocks based on a Voronoi diagram. The macroscopic mechanical behavior is related to that of interfaces between blocks. The mechanical behavior of each interface is described by a uniform distribution of normal and tangential springs, which together define the deformation and failure process of the interface. The elastic stiffness of springs can explicitly be related to the macroscopic elastic properties of material. The local failure process of interface is controlled by both normal stress and shear stress. Both tensile and shear failures are considered. Numerical simulations are presented and compared with experimental data to show the performance of the proposed model.

Cyclic Cohesive Zone Model for Simulation of Fatigue Failure Process in Adhesive Joints

Progressive failure process of adhesive joint under cyclic loading is of particular interest in this study. Such fatigue failure is described using damage mechanics with the assumed cohesive behaviour of the adhesive joint. Available cohesive zone model for monotonic loading is re-examined for extension to capture cyclic damage process of adhesive joints. Damage evolution in the adhesive joint is expressed in terms of cyclic degradation of interface strength and stiffness. Mixed-mode fatigue fracture of the joint is formulated based on relative displacements and strain energy release rate of the interface. A power-law type variation for each of these cohesive zone model parameters with accumulated load cycles is assumed in the presence of limited experimental data on cyclic interface fracture process. The cyclic cohesive zone model (CCZM) is implemented in commercial finite element analysis code and the model is validated using adhesively bonded 2024-T3 aluminium substrates with epoxy-based adhesive film (FM73M OST). The CCZM model is then examined for cyclic damage evolution characteristics of the adhesive lap joint subjected to cyclic displacement of Δδ = 0.1 mm, R=0 so as to induce shear-dominant fatigue failure. Results show that the cyclic interface damage started to initiate and propagate symmetrically from the both overlap edges and degradation of interface strength and stiffness started to accumulate after 0.5 cycles of displacement elapsed. The predicted results are consistent with the mechanics of relatively brittle interface failure process.

Unloading Behavior Study on FRP-Concrete Interface under an Exponential Softening Law

Loading behavior studies on FRP-concrete interface are refined enough. Because of the complexity of the problem, there exist relatively few unloading behavior studies. Occurrence mechanism of unloading needs to be clarified. Through a combination of theory and finite element method, this paper studied the unloading behavior involved in interfacial failure process under an exponential softening law, clarified when and where unloading occurred and estimated the effect of unloading.

The failure mechanisms of TBC structure by moiré interferometry

In order to study the interface failure process and the mechanical properties of thermal barrier coatings (TBCs), the moiré interferometry technique is used to measure the deformation fields of the TBC specimen subjected to three-point bending load. By changing the object lens in the moiré interferometer, both the macro-scale and micro-scale deformation fields can be measured. In the measurement, a cross type moiré grating with frequency 1200lines/mm is replicated to the TBC sample. The interface moiré patterns at different load parameters can be obtained with the moiré interferometer. And the corresponding displacement and strain distributions are calculated using the moiré patterns. Besides, with aid of the experimental results from moiré interferometry, crack opening displacement (COD) and J-integral of the TBC specimen can be measured. Moreover, the initiation and propagation of the crack in TBCs are observed using scanning electronic microscope and optical microscope, respectively. The failure mode of the TBC is summarized.

Meso-mechanical interfacial behavior of elbow steel fiber reinforced concrete

The strain distributions near the interface when the elbow steel fiber is pulled out from the half-mould concrete matrix are directly measured using a combined method of single fiber pull-out test and digital image correlation. Meanwhile, the real-time processes of the bonding, debonding and sliding at the interface are observed. The micro-mechanism of the strain localization in the failure process of interface when debonding occurs and the strengthening mechanism at the imbedded fiber are discussed. The experimental results show that the meso-scale strain localization gives rise to the localization of shear damage near the fiber interface. This strain localization characterized by the debonding process near the interface occurs, develops and moves gradually at an apparently regular interval. At the elbow part of the imbedded fiber, the peak value of the shearing stress occurs. But the primary debonding does not occur at this place because the strength of the shear damage is increased at the local area of the elbow part in the concrete, displaying an apparent reinforced effect at the end of the fiber.