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In this paper, a new micromechanical hysteresis loop constitutive model of C/SiC composites with different interphases was developed considering the probabilistic‐statistical matrix fragmentation process. The lengths of matrix fragmentation were divided into three types, that is, long matrix fragments (LMFs), medium matrix fragments (MMFs), and short matrix fragments (SMFs). The distributions of the LMFs, MMFs, and SMFs with increasing tensile stress were determined using the probabilistic‐stochastic model by assuming the two‐parameter matrix strength distribution. The micro stress field of the LMFs, MMFs, and SMFs upon unloading and reloading was obtained and adopted to determine the corresponding stress‐strain relations. The interaction of matrix fragmentation lengths, especially for the LMFs with large debonding energy (LDE) and SMFs, was considered in the closed‐form constitutive model and hysteresis‐based inverse tangent modulus (ITMs) damage parameter. Synergistic effects of the fiber volumes, peak stresses, and interface debonding energy on the interface damage state, mechanical hysteresis loops, and related ITMs with small debonding energy and LDE were also analyzed. Comparisons of the mechanical hysteresis loops using the new hysteresis models considering matrix stochastic fragmentation and hysteresis models considering constant matrix fragmentation were also discussed. Experimental cyclic tensile hysteresis loops and unloading/reloading ITMs of C/(PyC)/SiC and C/(PyC+SiC)/SiC composites with different interphase thickness (i.e., t = 300, 600, 1000, and 2000 nm) were predicted using the developed constitutive model. Evolution of the unloading/reloading interface slip ratio was analyzed for different tensile peak stresses. [ABSTRACT FROM AUTHOR]

The composition and thickness of the interphase are critical factors affecting the strength of SiC/SiC materials. Therefore, SiC/(BN/PyC)/SiC ceramic matrix composites with varying PyC thicknesses were fabricated, and the mechanism by which thickness influences the mechanical properties of the materials was investigated. During the fracture process of the composites, debonding and crack deflection predominantly occurred at the BN/PyC interface. The PyC interphase thickness emerged as a critical factor influencing the mechanical performance of composites. The residual stresses within the PyC and its adjacent SiC matrix were determined by analyzing shifts in Raman peak positions. The findings indicate that a reduction in PyC thickness leads to an increase in residual compressive stress within the PyC and a corresponding increase in residual tensile stress within the SiC matrix, which increases the interfacial shear stress and improves the mechanical properties of the composites. [ABSTRACT FROM AUTHOR]

Bimetallic lined pipe (BLP) has been increasingly used in offshore and subsea oil and gas structures, but how to identify the invisible inner defects such as liner wall thinning and interface debonding is a challenge for future development. A nondestructive testing (NDT) method based on pulsed eddy current testing (PECT) has been proposed to face these difficulties. The inspection of the BLP specimen (AISI1020 base tube and SS304 liner) is implemented from outside of the pipe by using a transmitter–receiver-type PECT probe consisting of two induction coils. By simplifying the BLP specimen to stratified conductive plates, the electromagnetic field interaction between the PECT probe and specimen is analytically modeled, and the probe inspection signals due to liner wall thinning and interface debonding are calculated. In order to highlight the weak response (in microvolts) from the liner, the inspection signals are subtracted by the signal, which is calculated in the case of only having a base tube, yielding differential PECT signals. The peak voltage of the differential signal is selected to characterize the liner wall thinning and interface debonding due to its distinguishable and linear variation. Experiment verification is also carried out on a double-walled specimen simulated by a combination of a Q235 casing pipe and SS304 tubes of different sizes. The experimental results basically agree with the analytical predictions. The peak value of the PECT signal has an ascending and descending variation with the increase in the remaining liner wall thickness and debonding gap, respectively, while the negative peak value shows opposite changes. The peak value exhibits a larger sensitivity than the negative peak value. The proposed method shows potential promise in practical applications for the evaluation of the inner defects in BLP lines. [ABSTRACT FROM AUTHOR]

This paper presents a multiscale progressive fatigue damage model to predict the fatigue life of composite laminates. The multi-level damage model was employed considering the interfacial debonding effect, and effective material properties were calculated through homogenization. Damage variables and damage slopes were defined at the constituent level, and fatigue damage parameters were obtained using the residual stiffness data with the chaotic firefly algorithm. The model was implemented into ABAQUS, then validated with flat-bar and pin-loaded specimens of AS4/3501-6 composite. The numerical results corresponded well with the experimental data and showed the ability to capture the failure propagation of composite laminates. [ABSTRACT FROM AUTHOR]

Polymer infiltration and pyrolysis (PIP), as a preparation route for ceramic matrix composites, employs the polymer-to-ceramic transformation inside the preforms to gradually buildup the matrix. The effects of the structural transformation on the residual stress and on the interface debonding behavior of PIP derived Si 3 N 4 whisker reinforced SiCN (Si 3 N 4w /SiCN) composites are analyzed. Accordingly, the Si 3 N 4w whisker in the composites are under residual compressive stress after the formation of the polymer-derived ceramic matrix. An increase in the pyrolysis heating rate from 1 to 10 ℃/min effectively lowers the residual stress from 195.8 to 91.3 MPa. Interface fracture energies of Si 3 N 4w /SiCN derived from the debonding behavior significantly rise from <11.91 to 21.82 J/m2 with the annealing temperature from 900 to 1400 ℃. The residual stress and interfacial behavior are related to the in - situ densification/shrinkage and structural rearrangement during pyrolysis and annealing. [ABSTRACT FROM AUTHOR]

SiC fiber-reinforced SiC matrix composites (SiC f /SiC) containing BN interphase were fabricated via CVI and MI. For fiber-treated SiC f /SiC composites, cracks that initiate in the matrix tend to deflect between the fiber and the BN interphase when it reaches the fiber/matrix region, and the interface debonding and sliding occurs between the BN interphase and the matrix when fibers are pulled out. The mechanical properties of fiber-treated SiC f /SiC composites are significantly improved. The roughness and chemical properties are analyzed for the treated and as-received SiC fibers. The relationship between the surface chemical composition and roughness of fibers and the fiber/interphase adhesion force is discussed. The composites prepared from the treated fibers are confirmed to have stronger fiber/interphase adhesion force, which is caused by the improvement of surface roughness, the decrease of SiO 2 on the fiber surface, and the interinfiltration of BN and excess C on the treated fiber surface. [ABSTRACT FROM AUTHOR]

Injection over‐molded short/continuous fiber reinforced composites are a unique class of materials for fabricating lightweight components having complex geometries in automotive manufacturing due to their higher specific mechanical properties, lower assembly cost, and short production cycle time. The influence of interface temperature on the low‐velocity impact response of short/continuous fiber‐reinforced polypropylene was experimentally investigated by varying the melt temperature. The over‐molded specimens fabricated at an interface temperature considerably higher than the melting point of polypropylene exhibited a 12% enhanced peak load with less impact damage compared with specimens over‐molded at a lower interface temperature. Optical analysis of impacted specimens over‐molded at lower interface temperature revealed interface debonding and insert delamination. Whereas insert delamination alone was observed for the specimens fabricated at higher interface temperature. The specimens over‐molded at high interface temperature exhibited less impact energy absorption and high compression strength after impact because of their strong interfacial adhesion. Highlights: Impact energy absorption is less if melt temperature is high in injection over‐molding.Higher melt temperature enhances interface bonding by raising interface temperature.Interface debonding and insert delamination are the dominant impact failure modes.The compression strength after impact has increased with higher melt temperature.Impact and compression strength after impact is governed by the interfacial strength. [ABSTRACT FROM AUTHOR]

The mechanical properties of metal matrix fiber-reinforced composites depend on many aspects of their structure in a complicated way. In this paper, we propose a phase-field-cohesive-zone framework to study interface debonding, matrix cracking, and their competition in metal matrix fiber-reinforced elastoplastic composites by numerical simulation. This approach combines an explicit cohesive zone model for interface debonding and a phase field model for matrix cracking. The features of this framework are: (1) crack propagation and branching can be simulated without the need to track the cracks; (2) the interface debonding is described by the cohesive zone model, and is not directly interfered by the phase field in the bulk; (3) the cohesive interface has zero thickness instead of being regularized; (4) any reasonable cohesive law of interest is readily incorporated with very few constraints; (5) the competition of the two failure mechanisms, namely, matrix cracking and interface debonding, is captured. Accuracy of this framework is verified with existing analytical and numerical results. The proposed framework shows a potential in investigating various complicated crack behaviors in composites. [ABSTRACT FROM AUTHOR]

The dynamic thermomechanical analysis on stiffened composite plates with damages are investigated in this article based on the extended layerwise method (XLWM) and three-dimensional finite elements method; a thermomechanical extended-layerwise/Solid-element method (TELW/SE) is established. In TELW/SE, the thermomechanical extended-layerwise method (TELW) and thermomechanical three-dimensional solid elements are used to simulate plate and stiffeners, respectively. The final governing equations are assembled by using the interface conditions to ensure the compatibility of displacements and temperature, together with the internal force equilibrium. Several typical damages in stiffened composite plates can be described accurately in the proposed method, such as delamination, transverse crack and stiffener/plate interface debonding. [ABSTRACT FROM AUTHOR]

In the present work, stress-dependent matrix crack opening behavior of SiC/SiC composites was analyzed considering stochastic fragmentation in fibers. The stochastic matrix multiple fragmentation model was adopted to determine the fragmentation lengths of three different types, the accompanying interface debonding process was assessed by the fracture mechanics theory, and stochastic fiber fragmentation was determined by the global load sharing (GLS) criterion. Considering the aforementioned multiple micro-damage mechanisms, matrix crack opening displacements (CODs) in different matrix fragmentation states were determined using a micromechanical technique. Relationships between CODs and the constituent properties of SiC/SiC composites with fiber fragmentation were established. The crack opening behavior of SiC/SiC composites was also analytically predicted. Effects of fiber stochastic fragmentation on crack opening-related damage parameters were examined. [ABSTRACT FROM AUTHOR]

Interphase plays an important role in the mechanical behavior of SiC/SiC ceramic-matrix composites (CMCs). In this paper, the microstructure and tensile behavior of multilayered (BN/SiC) n coated SiC fiber and SiC/SiC minicomposites were investigated. The surface roughness of the original SiC fiber and SiC fiber deposited with multilayered (BN/SiC), (BN/SiC) 2 , and (BN/SiC) 4 (BN/SiC) 8 interphase was analyzed through the scanning electronic microscope (SEM) and atomic force microscope (AFM) and X-ray diffraction (XRD) analysis. Monotonic tensile experiments were conducted for original SiC fiber, SiC fiber with different multilayered (BN/SiC) n interfaces, and SiC/SiC minicomposites. Considering multiple damage mechanisms, e.g., matrix cracking, interface debonding, and fibers failure, a damage-based micromechanical constitutive model was developed to predict the tensile stress-strain response curves. Multiple damage parameters (e.g., matrix cracking stress, saturation matrix crack stress, tensile strength and failure strain, and composite's tangent modulus) were used to characterize the tensile damage behavior in SiC/SiC minicomposites. Effects of multilayered interphase on the interface shear stress, fiber characteristic strength, tensile damage and fracture behavior, and strength distribution in SiC/SiC minicomposites were analyzed. The deposited multilayered (BN/SiC) n interphase protected the SiC fiber and increased the interface shear stress, fiber characteristic strength, leading to the higher matrix cracking stress, saturation matrix cracking stress, tensile strength and fracture strain. [ABSTRACT FROM AUTHOR]

When ceramic-matrix composites (CMCs) are under tension-tension cyclic fatigue loading, stochastic matrix cracking evolves with applied cycles and the closure of cracks occurs upon unloading. Evolution, opening, and closure of matrix cracking affect the reliability and safety of CMC components during operation. The objective of this paper is to establish the relationship between the hysteresis loops, cracking evolution, opening, and closure based on a new hysteresis constitutive model. Multiple micro damage parameters, e.g., unloading/reloading inverse tangent modulus (UITM/RITM), interface reverse slip ratio (IRSR), and interface new slip ratio (INSR), are developed to characterize the hysteresis loops with cracking evolution and closure. Upon unloading, the closure of matrix cracking decreases the UITMs and IRSR of the tension-tension fatigue hysteresis loops; upon reloading, the opening of matrix cracking increases the RITMs and IRSR of the tension-tension fatigue hysteresis loops. Experimental tension-tension fatigue hysteresis loops in different CMCs are predicted for different peak stresses and cycles. Effects of fiber volume, interface properties, peak stress, and stress ratio on ITM, IRSR, and IRSR are discussed. The developed approach can be used for cracking evolution, opening, and closure identification in CMCs. [ABSTRACT FROM AUTHOR]

In this work, we shall implement a novel modeling approach to simulate interface debonding and bulk cracking in realistic 3D printed fiber reinforced composites. The materials are firstly manufactured with the Selective Laser Sintering of PA12 polymer powder embedding glass fibers and additive particles. An in-situ compression test on a cylindrical sample is conducted. X-ray Computed Tomography (XRCT) technique is employed to obtain experimental fracture images and to provide a complete 3D description of the morphology of each component for constructing a completely Realistic 3D microstructure mesh Model (R3M). Meanwhile, an Extended Phase Field Model (EPFM) is presented considering gradient plasticity and interfacial debonding mechanisms. Following that, numerical simulations are conducted, by using the EPFM and R3M, to investigate the fracture behavior in the fiber reinforced composite. In contrast to existing works, a qualitative comparison of fracture phenomena in experiments and simulations is conducted. Anisotropic behavior of the 3D printed fiber reinforced composite is observed both in the experiments and simulations. Our results reveal that the EPFM can well capture the experimental damage phenomena, including fiber/matrix debonding, fiber breaking and pore connecting in 3D printed fiber reinforced composites, by employing the R3M where the microstructure directly arises from the experimental XRCT. • An extended phase-field model (EPFM) with gradient plasticity and interface is proposed. • XRCT technique is employed to provide mesh models and experimental fracture results. • Numerical simulations for 3D printed fiber reinforced composites are carried out. • The proposed EPFM can well capture the experimental fracture phenomena. [ABSTRACT FROM AUTHOR]

[Display omitted] • Microstructures and default defects of propellants are identified and quantified based on micro CT measurements. • Microscopic damage analysis uses representative volume elements integrated with cohesive zone theory. • A novel damage model, calibrated with microscopic damage, demonstrates satisfactory predictive capabilities. Solid Rocket Motors (SRMs) rely on solid propellants, directly impacting the energy capacity of launch vehicles. High energy density material (HEDM) propellant exhibits superior energy density owing to the incorporation of a substantial quantity of energetic particles. However, the elevated particle fill ratio makes the formation of pores more prevalent during the manufacturing process of propellants. These pores, representing default defects, are indispensable factors in the investigation of mechanical properties of propellants. This study investigated default defects effects on HEDM propellants, analyzing both microscopic and macroscopic perspectives. Utilizing micro-CT imaging, the microstructure and default defects were characterized. Subsequently, using the cohesive zone model (CZM), microscopic damage evolution was depicted with the representative volume element (RVE) model, allowing in-depth analysis. Furthermore, a damage constitutive model, based on microscopic damage, was developed, with its softening function calibrated using microscopic damage evolution characteristics. Implemented into ABAQUS via user-defined material subroutine (UMAT), this model enabled the prediction of the mechanical response of HEDM propellants with different defects. The results demonstrate that the developed model accurately predicts the mechanical responses of HEDM propellants with different defects, showcasing the potential of macro-microscopic approaches in analyzing propellants with default defects. [ABSTRACT FROM AUTHOR]

This study presents experimental and numerical studies of the initiation and propagation of interface debonding between the substrate and thin-bonded cement-based overlay under fatigue testing. The overlay material is mortar incorporating amorphous metallic fibres (30 kg/m 3 ) and/or rubber aggregates (30%), while the substrate is a plain mortar. Uniaxial tensile tests were carried out on overlay materials and substrate-overlay interface to obtain a residual normal stress-crack opening relationship (σ-w law) and residual normal stress and substrate-overlay interface debonding relation respectively. Three-point bending fatigue tests were carried out on the composite beam to analyse the structural behaviour of repaired beam. The propagation of debonding along the substrate-overlay interface was monitored by using the Digital 3D Image Correlation (DIC) technique. Three-point bending fatigue test was modelled by finite element method (FEM) using CAST3M, developed by French Atomic Energy Commission. Direct tension test results show reduction in tensile strength and improvement in strain capacity (1.5 times of control mortar) for rubberised mortars. For fibre-reinforced mortars, post-peak residual tensile strength is significantly enhanced. Rubberised fibre-reinforced mortars show positive synergetic effects both in the improvement of residual post-peak strength and strain capacity (3.5 times than control mortar). Results show that the rubberised fibre-reinforced thin-bonded cement-based overlay proved to be very effective in restraining crack opening, by transferring stresses through the crack, and enhancing the fatigue resistance of repair system, by limiting interface debonding propagation upto 50%. Experimental results of composite beams are in good agreement with modelling results. [ABSTRACT FROM AUTHOR]

A novel glass-ceramic spray deposition (GCSD) method was developed to modify the yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) surface and to enhance the bond strength between Y-TZP and resin cement. Five different experimental groups were characterized, non-treatment (NT), airborne particle abrasion (AB), GCSD without etching (GS), GCSD with 5% HF etching (GSE5), and GCSD with 9.5% HF etching (GSE9), to determine the optimal method for improving the bond strength. Scanning electron microscopy and an argon ion milling system were used to investigate the surface and cross-sectional microstructures. The changes in the surface characteristics of Y-TZP were analyzed via contact angle analysis, atomic force microscopy, X-ray diffraction, and energy-dispersive X-ray spectrometry. The bond strengths were determined using shear bond strength test. The results revealed that GCSD could produce a dense and uniform lithium disilicate glass-ceramic coating layer and infiltrate the Y-TZP surface. This coating resulted in superior micromechanical interlocking and increased hydrophilicity, thereby enhancing the bond strength between Y-TZP and resin cement (P < 0.05). The study findings indicated that GCSD accompanied by 5% HF etching for 100 s is optimal for strengthening the Y-TZP/resin cement bond, thereby providing a novel solution for dental bonding systems. [Display omitted] [ABSTRACT FROM AUTHOR]

In the present study, the interface debonding area between face sheets and the foam cores of the sandwich panels were inspected using the thermography method for the five groups of the samples. These samples were manufactured with different processes divided into two main groups; one‐step manufacturing process and two‐step manufacturing process. All of the specimens were subjected to the three‐point bending test after thermography detection technology. The one‐step manufactured samples presented the highest flexural strength and minimum discontinuity. Integrated infusion process in comparison with other processes shows about 40% superiority in mechanical properties at least. The results showed that Indentation beneath the loading roller is the initial failure mode of the one‐step manufactured samples. In addition, the main failure mode of the two‐step manufactured samples is the core shear mode. [ABSTRACT FROM AUTHOR]

In this paper, the time-dependent damage evolution in carbon fiber-reinforced silicon carbide ceramic-matrix composites (C/SiC CMCs) under creep fatigue loading at elevated temperature was analyzed using a micromechanical approach. Synergistic effects of creep fatigue peak stress level and damage in the matrix and the interface on time-dependent damage evolution in C/SiC composites were analyzed. Next, relationships of time-dependent creep fatigue damage mechanisms, damage parameters, environmental temperature and duration were determined. Then, the effects of composite constituent properties, creep fatigue damage state, environmental temperature, and duration on time-dependent damage evolution in C/SiC composites were analyzed. Furthermore, time-dependent composite strain response and interface debonding and oxidation state in C/SiC composite under different creep fatigue peak stress levels were predicted. Under creep fatigue loading, the composite internal damage evolution contributed to the increased time/temperature-dependent composite peak strain. Hysteresis-based damage parameters were developed and utilized to monitor C/SiC composite internal damage evolution. Under creep fatigue loading, the hysteresis area and width increased with oxidation duration to a peak value and remained constant, and the hysteresis modulus decreased with oxidation duration. [ABSTRACT FROM AUTHOR]

• An adaptive phase-field model is proposed to predict the damage in viscoelastic composites. • The B-spline version of finite cell method is applied to simplify the mesh generation. • Nitsche-based method is adopted to weakly impose the dirichlet boundary condition. • A 1-D analytical solution of the bi-material bar is derived for validation. • The proposed model can capture the complex crack patterns efficiently and accurately. The damage of viscoelastic composites is a significant topic in industrial fields. Under external loads, the debonding of the coupling interfaces between the filler particles and the matrix can greatly reduce the reliability of viscoelastic composites. This study proposes a thermodynamically consistent phase-field model with the aim of predicting the quasi-brittle fracture of particle-reinforced linear viscoelastic composites. The main novelties of our model are as follows: (i) The quasi-brittle viscoelastic phase-field model and finite cell method (FCM) are integrated to predict viscoelastic composites with complex geometries, without creating boundary conforming meshes; (ii) An additional interface phase-field is introduced to smoothly transition the interface properties, while the governing equations are established in the framework of finite cell method by weak imposition of the Dirichlet boundary conditions. Based on the Mori-Tanaka method, we also derive a one-dimensional bi-material bar with adhesive interface to validate the effectiveness of the proposed model. The influence of two diffused formulas (Heaviside-like function and quadratic function) for the critical energy release rate of interface on the choice of length scale parameters are discussed in detail. Three cases of particle debonding are designed to demonstrate that the proposed model is capable of capturing the crack nucleation, propagation and intersection in the representative volume element (RVE) of viscoelastic composite. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] Various failures of laminates under low-velocity impacts without penetration are simulated systematically with a limited number of inputs, all measurable following existing standards without any data calibration. No iteration is required to determine any of the failures investigated in this work. Any two adjacent lamina (primary) layers are inserted with a matrix (secondary) layer, whose stresses are modified through two modification coefficients (MCs). The MCs are determined through peak loads of double cantilever beam and end-notched flexure tests on unidirectional laminates, and their weak sensitivity to sample dimensions is shown. Delamination is reproduced by deleting failed secondary-layer elements. The homogenized stresses of fiber and matrix obtained by Bridging Model are converted into true values through the author's true stress theory to estimate constituent-induced intralaminar failures, such as fiber breakage, matrix crack and interface debonding, against the monolithic fiber or matrix strengths measured independently. Primary- layer elements attaining a fatal failure (fiber breakage or matrix crack accompanied with a critical strain condition) are deleted before an impact termination corresponding to separation of the impactor from target. The predicted delamination areas and impact force, displacement and energy histories for the laminates of three lamination angles under different impact energies agree well with our measured counterparts, validating the efficiency of the simulation. [ABSTRACT FROM AUTHOR]

In this study, the discrete lattice simulation of multi-scale fracture growth in layered media is conducted and validated against fracturing laboratory observation and field micro-seismic monitoring. The results reveal that the perforation can substantially influence hydraulic fracture initiation and extension. The vertically-oriented-perforation induced fracture will effectively initiate with moderate near-wellbore complexity, promoting fracture crossing at bedding interfaces. The interlaced design of perforation cluster can alleviate the stress shadow effect and facilitate uniform fracture propagation. The far-field fracture complexity are related to the bedding interfacial properties: more tensile interfaces tend to arrest induced fractures and restrict their vertical growth, while more fracturing fluid will be diverted into the permeable interfaces of lower shear strength. The complex fracture networks has the potential to trigger fault reactivation or serve as conduits for underground water, thus causing induce seismicity or aquifer contamination. The findings can enrich the understanding of multi-scale fluid-solid coupling mechanisms and further help us prevent geological hazards. • Complex fracture networks are sensitive to tensile and shear strength of bedding layers • Multiscale fracture growth models using discrete lattice method are validated against laboratory and field observation • Perforation geometry and arrangement can influence fracture initiation and extension, and interface slip mechanism [ABSTRACT FROM AUTHOR]

Under cyclic fatigue loading, hysteresis loops appear in fiber-reinforced ceramic-matrix composites (CMCs) due to composite's internal damage mechanisms. Loading/unloading inverse tangent modulus (ITMs) of the hysteresis loops reflect the composite's internal damage state and can be used an effective tool to monitor composite's fatigue damage evolution and fracture. In this paper, characterization of cyclic fatigue hysteresis loops of CMCs using ITMs are investigated. Loading/unloading ITMs are derived using a micromechanical hysteresis constitutive model considering fatigue damage mechanisms of matrix cracking, interface debonding, wear and slip, and fiber's failure. Relationships between composite's fatigue hysteresis loops, ITMs and interface slip state (i.e., interface reverse slip ratio (IRSR) and interface new slip ratio (INSR)) are established. Experimental fatigue hysteresis loops, ITMs, and IRSR/INSR of cross-ply SiC/CAS and SiC/MAS composites from the literature are predicted, and the effects of fiber's volume fraction, matrix crack spacing, and interface debonding energy on composite's fatigue hysteresis loops, ITMs, and IRSR/INSR are analyzed. [ABSTRACT FROM AUTHOR]

For China Railway Track System (CRTS) I twin-block slab tracks, the interface between the sleeper and track slab is susceptible to damage under the coupled effect of long-term train load and external environment factors. In order to analyze the damage behavior and identify the type of debonding at the interface, this paper established a three-dimensional finite element model and introduced the cohesion zone model and concrete damaged plasticity model to simulate the interface damage and the inner-layer damage of the track slab, respectively. The interface debonding induced by the temperature effect was analyzed, and the debonding types were identified based on the obtained vertical vibration responses of the sleeper surface under the train load. The results reveal that the damage mainly occurs on the bottom and lateral sides at the interface under the temperature load. The track model can be refined further to obtain higher analysis accuracy with acceptable calculation time using the sequential loading method. The 26 damage features derived from the time domain, frequency domain, and time–frequency domain are in good representativeness in reflecting the damage information hidden in the vibration signals. Among them, the peak values (maximum vertical acceleration of the sleeper) are 55.0, 56.7, 60.3, and 61.6 m/s2 for no debonding, debonding on the lateral side, debonding at the bottom, and debonding on the longitudinal side of the interface under train load, respectively. Moreover, the identification accuracy of the debonding type can reach 93.75% combining the particle swarm algorithm and support vector machine. It indicates that the proposed identification method is effective and reliable to provide theoretical guidance for developing scientific maintenance and repair strategies for twin-block slab tracks. [ABSTRACT FROM AUTHOR]

In-situ tensile damage and fracture behavior of original SiC fiber bundles, processed and uncoated SiC fiber bundles, SiC fiber bundle with PyC interphase, SiC/SiC minicomposites without/with PyC interphase are analyzed. Relationships between load-displacement curves, stress-strain curves, and micro damage mechanisms are established. A micromechanical approach is developed to predict the stress-strain curves of SiC/SiC minicomposites for different damage stages. Experimental tensile stress-strain curves of two different SiC fiber reinforced SiC matrix without/with interphase are predicted. Evolution of composite's tangent modulus, interface debonding fraction, and broken fiber fraction with increasing applied stress is analyzed. For the BX™ and Cansas-3303™ SiC/SiC minicomposite with interphase, the composite's tangent modulus decreased with applied stress especially approaching tensile fracture; the interface debonding fraction increased with applied stress, and the composite's tensile fracture occurred with partial interface debonding; and the broken fiber fraction increased with applied stress, and most of fiber's failure occurred approaching final tensile fracture. [ABSTRACT FROM AUTHOR]

To ensure the reliability and safety of ceramic-matrix composites (CMCs) hot-section components used in the aero engines, it is necessary to perform the strain response of CMCs at intermediate temperatures (600 to 1000 °C) under stress-rupture with stochastic loading. In this paper, the strain response of SiC/SiC composite under stress-rupture with stochastic load at intermediate temperatures is investigated. Multiple damage mechanisms of matrix cracking, interface debonding and oxidation, and fiber's oxidation and fracture are considered. Matrix crack spacing, interface oxidation and debonding length, fiber's broken probability, and intact fiber's stress are determined using micromechanical damage models. Experimental strain response and internal damage evolution of SiC/SiC composite under constant and stochastic stress are predicted. Effects of stochastic stress level and stochastic time, material properties, damage state and environment temperature on composite's strain response and stress-rupture life are discussed. When stochastic stress level and environment temperature increase, the composite's strain at the stochastic stress increases, the time for the interface complete debonding and oxidation decreases, and the stress-rupture life decreases. [ABSTRACT FROM AUTHOR]

Interface debonding may occur in the multilayered TRISO fuel particle and fully ceramic microencapsulated (FCM) dispersion nuclear fuels during their operation, exerting a great influence on their thermomechanical behaviors. In this study, a multiphysics coupling analysis on the performance of a TRISO particle and FCM fuel cell with the interface debonding effect considered is carried out. Interface debonding is dealt with the cohesive zone model (CZM) method. The implemented fuel performance models include temperature and burnup-dependent thermomechanical properties, gap heat conduction, thermal expansion, creep, irradiation swelling, fission gas production and release. The multiphysics coupling models and method are verified against International Atomic Energy Agency (IAEA) benchmarks. The effect of interface debonding between inner pyrolytic carbon (IPyC) layer and silicon carbide (SiC) layer on the performance of individual TRISO particle in traditional High Temperature Gas Reactors (HTGRs) is analyzed under zero traction boundary condition on the outer surface. The approach is then applied to simulate the effect of interface debonding between the SiC layer and outer pyrolytic carbon (OPyC) layer of the TRISO particle on the performance of a representative cell of the FCM fuel. It is shown that interface debonding can significantly affect the temperature distribution in the fuel and the stress magnitude in the SiC layer and matrix. The tensile stress in SiC layer in FCM fuel cell is unrealistically large when the interface bond strength is infinite, and the SiC/OPyC interface debonding reduces the tensile stress in the SiC layer to maintain its own structure strength, which provides the basis to reduce the SiC/OPyC interface bond strength in the manufacturing process of the FCM fuel. [ABSTRACT FROM AUTHOR]

In this paper, stress rupture of fiber-reinforced ceramic-matrix composites (CMCs) subjected to different stochastic loading spectrums at intermediate temperatures (600 to 1000 °C) is investigated. Under stress rupture at stress level higher than the first matrix cracking stress, multiple damage mechanisms of matrix cracking, fiber/matrix interface debonding, interphase and fiber oxidation, and fiber fracture are considered to analyze evolution of composite strain. Four different stochastic loading spectrums are considered in the analysis of damage evolution and lifetime of fiber-reinforced CMCs under stress rupture loading. Relationships between stochastic loading stress, frequency, time, interface debonding and oxidation length, fiber failure probability, and stress rupture lifetime are established. Effects of stochastic loading stress and time, fiber volume, matrix crack spacing, interface debonding energy, interface shear stress, and temperature on composite strain, interface debonding and oxidation length, and the fiber failure probability versus time are analyzed. Experimental stress rupture strain and lifetime of SiC/SiC composite under constant stress and stochastic loading spectrums are predicted. When the stochastic loading stress, frequency, and temperature increase, the stress rupture lifetime and the time for the interface complete debonding and oxidation all decrease. [ABSTRACT FROM AUTHOR]

In this paper, the stress-dependent matrix multiple fractures of fiber-reinforced ceramic-matrix composites (CMCs) with fiber oxidation and fracture is investigated. The shear-lag model is combined with the fiber oxidation and fracture models, and the fiber/matrix interface debonding criterion is adopted to determine the micro-stress field of the damaged fiber-reinforced CMCs. The effects of the fiber volume, interface shear stress, interface debonding energy, oxidation temperature and time on the stress-dependent matrix multiple fractures, interface debonding and oxidation, and fiber fracture are discussed. When the fiber volume fraction and the interface shear stress in the debonding region increased, the matrix first cracking stress and saturation cracking stress increased, the saturation matrix cracking space decreased, and the matrix multiple fracture evolution rate increased. When the interface debonding energy and the interface shear stress in the oxidation region increased, the matrix cracking density increased. When the oxidation temperature and oxidation duration increased, the matrix cracking density decreased. The experimental matrix multiple fractures of unidirectional C/SiC, SiC/SiC, mini-SiC/SiC, SiC/CAS, SiC/CAS-II, and SiC/borosilicate composites are predicted. [ABSTRACT FROM AUTHOR]

In this work, plaster molds for investment casting, reinforced with short polypropylene fibers, were prepared and their properties and fracture surface features were investigated. Fiber contents ranging from 0.10 to 0.50 wt% were introduced into a powder mixture of gypsum and mullite (ratio of 3:7) as reinforcements in order to prepare thin-walled plaster molds with high strength and permeability. The strength of green and fired plaster mold specimens was tested, the permeability was also tested, and their fracture surfaces were observed by scanning electron microscopy (SEM). The results show that the strength of the molds increases initially and then decreases with increasing fiber content. The green flexural strength of the specimens containing 0.20 wt% polypropylene fibers reached the maximum, c.a. 1.94 MPa, increased by 36.6%, and particularly, there was a slight increase in their fired strength, a maximum value of 0.45 MPa, in comparison with the fiber-free specimen. This low increase in the fired strength the reinforced specimen will produce a favorable effect on the collapsibility of shells in the casting cleaning process. In addition, the fired permeability of fiber-reinforced fired specimens exhibited significant enhancement, compared to that of the unreinforced ones. With increasing fiber content, the permeability of specimens increased from 8.6 to 11.5%. The improvement of green permeability was limited substantially. SEM observations indicate that the failure of the green specimens is a result of brittle fracture of the plaster substrate and/or fiber debonding from the matrix during loading. On the contrary, in fired specimens, the failure occurs by holes in the plaster substrate resulted from fiber ablation in the matrix during the firing process. The arrangement of polypropylene fibers can also affect the fracture behavior of molds. This proposed approach can reduce mold thickness without loss of strength and provide defined judgment basis for fracture features. [ABSTRACT FROM AUTHOR]

The present study investigated the time-dependent deformation, damage, and fracture tendencies of fiber-reinforced ceramic-matrix composites (CMCs) that were exposed to stress-rupture loading at average environmental temperatures. The composite micro stress field and tensile constitutive relationship of the damaged CMCs were examined to characterize their time-dependent damage mechanisms. The relationships between stress-rupture lifetime, constant peak stress level, time-dependent composite deformation, and evolution of internal damages are established. The effects of composite material properties, composite damage state, and environmental temperature on stress-rupture lifetime, time-dependent composite deformation, and evolution of the internal damages of SiC/SiC are analyzed. SiC/SiC was monitored at various constant peak stress levels to predict their experimental stress-rupture lifetime, time-dependent composite deformation, and internal damage evolution. When the fiber volume increases, the stress-rupture lifetime increases, the time-dependent composite strain and the debonding fraction at the interface decrease, and the oxidation fraction at the interface increases. When the saturation space between the matrix cracking increases, the time-dependent composite deformation and the debonding fraction at the interface decrease, and the time for complete debonding and oxidation at the interface increases. When the constant peak stress level and environmental temperature increase, the stress-rupture lifetime decreases, the time-dependent composite deformation and the debonding fraction at the interface increase, and the oxidation fraction at the interface decreases. [ABSTRACT FROM AUTHOR]

Detachment of bonded tiles undermines the aesthetics, functionality, and safety of innumerable buildings world-wide. The plate-type interfacial debonding mechanisms that are the root cause of tile detachments are difficult to observe and monitor because they are hidden by opaque external layers. This invisibility, together with the brittle nature of tile detachments, raises questions regarding the triggering, the two-dimensional evolution, and the stability features of the interfacial failure. The present study adopts a combined experimental–numerical approach to address these questions. Through the use of transparent tiles, the full process of tile detachments under a concentrated pullout load is novelly captured on video. The experimental force displacement curves reveal that the interfacial mechanism becomes unstable at critical points. Numerical modeling based on an inhouse specially tailored finite element formulation is used to further explore and interpret the experimental findings. Comparisons between the experimental and numerical results show the numerical model's ability to closely follow the debonding evolution and capture the variety of experimentally observed phenomena. [ABSTRACT FROM AUTHOR]

In this paper, the effect of pre-fatigue loading on tensile damage and fracture of fiber-reinforced ceramic-matrix composites (CMCs) is investigated using a micromechanical approach. Under cyclic fatigue loading, the fiber/matrix interface shear stress degrades with applied cycles due to the damage mechanism of the interface wear. The micro stress field of the damaged composite including matrix cracking, fiber/matrix interface debonding, and fiber failure is obtained for the fiber and the matrix axial stress and the fiber/matrix interface shear stress in the interface wear region, interface debonding region, and the interface bonding region, respectively. The fracture mechanics approach, stochastic matrix cracking model, and global load sharing (GLS) criterion are used to determine the interface debonding length, matrix cracking density, and fiber failure probability at higher applied stress level considering the damage mechanism of the interface wear. The effects of fiber volume, matrix cracking, fiber/matrix interface shear stress, fiber strength, pre-fatigue peak stress, and number of cycles on pre-fatigue tensile damage and fracture of SiC/SiC composites are analyzed. The experimental tensile damage and fracture of SiC/SiC composites with and without pre-fatigue loading are predicted for different interface properties. [ABSTRACT FROM AUTHOR]

In this paper, a time-dependent vibration damping model of fiber-reinforced ceramic-matrix composites (CMCs) is developed. Considering time and temperature dependent interface damages of oxidation, debonding, and slip, the relationships between composite vibration damping, material properties, internal damages, oxidation duration and temperature are established. The effects of material properties, vibration stress, damage state, and oxidation temperature on time-dependent composite vibration damping and interface damages of C/SiC composite are discussed. The time-dependent composite vibration damping decreases with fiber volume, matrix crack spacing and interface shear stress, and increases with vibration stress. The experimental composite vibration damping and internal damages of 2D C/SiC composite for different oxidation duration t = 2, 5 and 10 h at elevated temperatures T = 700, 1000 and 1300 °C are predicted. When the oxidation duration was short (i.e., t = 2 h), the composite vibration damping decreased with temperature; however, when the oxidation duration was long (i.e., t = 5 and 10 h), the composite vibration damping decreased with temperature below 1000 °C, and increased with temperature to 1300 °C. [ABSTRACT FROM AUTHOR]

In this paper, the cyclic fatigue hysteresis of carbon fiber reinforced silicon carbide (C/SiC) and SiC/SiC ceramic–matrix composites with different fiber preforms at room and elevated temperatures is investigated. The evolution of fatigue hysteresis dissipated energy versus applied cycle number for unidirectional C/SiC (σ max = 240 MPa at room temperature and σ max = 250 MPa at 800℃ in air atmosphere), cross-ply C/SiC (σ max = 105 MPa at room temperature and 800℃ in air atmosphere), 2D C/SiC (σ max = 387 and 425 MPa at room temperature), 2.5D C/SiC (σ max = 180 MPa at room temperature, σ max = 140 MPa at 800℃ in air atmosphere, and σ max = 230 MPa at 600℃ in inert atmosphere), 2D SiC/SiC (σ max = 130 MPa at 600℃, 800℃, and 1000℃ in inert atmosphere, σ max = 80 MPa at 1000℃ in air atmosphere, σ max = 100 MPa at 1000℃ in steam atmosphere, σ max = 140 MPa at 1200℃ in air and in steam atmospheres, σ max = 90, 120 MPa at 1300℃ in air atmosphere), and 3D SiC/SiC (σ max = 100 MPa at 1300℃ in air atmosphere) is analyzed. The change rate of the fatigue hysteresis dissipated energy between C/SiC and SiC/SiC composites is compared. The fatigue hysteresis dissipated energy decreases with applied cycle number for unidirectional, and cross-ply C/SiC composite at 800℃ in air, and 2.5D C/SiC composite at 600℃ in inert; and the fatigue hysteresis dissipated energy increases with applied cycle number for 2.5D C/SiC composite at 800℃ in air, 2D SiC/SiC composite at 600℃, and 800℃ in inert. [ABSTRACT FROM AUTHOR]

In this paper, a time-dependent tensile constitutive model of long-fiber-reinforced unidirectional ceramic-matrix minicomposites is developed considering the interface and fiber oxidation. The relationship between the time-dependent tensile behavior and internal damage is established. The damage mechanisms of time-dependent matrix cracking, fiber/matrix interface debonding, fiber failure, and the oxidation of the interface and fiber are considered in the analysis of the time-dependent tensile stress–strain curve. The fracture mechanic approach, matrix statistical cracking model, and fiber statistical failure model are used to determine the time-dependent interface debonding length, matrix crack spacing, and the fiber failure probability considering the time-dependent interface and fiber oxidation. The effects of the fiber volume, fiber radius, matrix Weibull modulus, matrix cracking characteristic strength, matrix cracking saturation spacing, interface shear stress, interface debonding energy, fiber strength, fiber Weibull modulus, and oxidation time on the time-dependent tensile stress–strain curves, matrix cracking density, interface debonding, and fiber failure are discussed. The experimental time-dependent tensile stress–strain curves, matrix cracking, interface debonding, and fiber failure of four different unidirectional SiC/SiC minicomposites for different oxidation time are predicted. The composite tensile strength and failure strain increase with the fiber volume, fiber strength, and fiber Weibull modulus, and decrease with the oxidation time; the fiber/matrix interface debonding length increases with the fiber radius and oxidation time and decreases with the interfacial shear stress and interface debonding energy; the fiber/matrix interface oxidation ratio increases with the interfacial shear stress, interface debonding energy, and oxidation time and decreases with the saturation matrix crack spacing. [ABSTRACT FROM AUTHOR]

In this paper, the effect of interface damage on the tensile damage and fracture of fiber-reinforced ceramic-matrix composites (CMCs) after thermal fatigue loading is investigated. The damage mechanisms of matrix cracking, fiber/matrix interface debonding and wear, interface and fiber oxidation, and fiber failure after thermal fatigue loading are considered in the tensile stress-strain behavior prediction. The relationships between the thermal fatigue temperature, applied cycle number, composite internal damage, and tensile damage and fracture are established. The effects of thermal fatigue temperature, thermal cycle number, fiber volume, interface shear stress, fiber strength, and fiber Weibull modulus on the tensile damage and fracture of fiber-reinforced CMCs subjected to the thermal fatigue loading are analyzed. The experimental tensile stress-strain curves of different C/SiC composites with and without thermal fatigue loading are predicted. When the thermal fatigue temperature and applied cycle number increase, the composite tensile strength and failure strain decrease, the interface debonding ratio, interface oxidation ratio, and broken fibers fraction increase at low applied stress level. [ABSTRACT FROM AUTHOR]

In this paper, the synergistic effects of the stochastic loading stress and time interval on the stress-rupture damage evolution and lifetime of fiber-reinforced ceramic-matrix composites (CMCs) at intermediate temperatures are investigated. The relationships between the stochastic loading stress and stochastic time interval, internal damage evolution, macro strain, broken fiber fraction, and stress-rupture lifetime of fiber-reinforced CMCs are established. The effects of the stochastic loading stress and stochastic time interval, constituent properties, damage condition, and environment temperature on the stress-rupture time, strain evolution, and internal damage of SiC/SiC composite under stress-rupture loading are discussed. The experimental stress-rupture behavior of SiC/SiC composite under constant and stochastic loading condition are predicted. The stress-rupture lifetime decreases with increase of stochastic stress level, stochastic time interval, and environmental temperature, and increases with the fiber volume and interfacial shear stress in the slip region. [ABSTRACT FROM AUTHOR]

The paper focuses on the debonding between a cement-based overlay and a concrete substrate under a mechanical loading. Two categories of substrate surface preparation were considered: Sawing the Substrate and Sand Blasting of the casting surface of the substrate. Untreated substrate surface used in its original state was taken as the Reference Surface. The overlay material investigated was a cement-based mortar. Direct tensile tests perpendicular to the overlay-substrate interface were carried out at the age of 28 days and the results (tensile strength, residual post peak behavior) are presented and discussed. Attention was paid to the Sand Blasted surface which is a more realistic model of practical field conditions. The debonding propagation under monotonic and fatigue loading was monitored for sand blasted surfaces using the Digital Image Correlation technique. Results indicate that both surface preparation technique has its own efficiency level and gives different roughness. Among the techniques used, greater bond strength improvement was observed with the sawn substrate surface than with the sandblasted one. Moreover, under cyclic loading, major debonding along the interface occurs from the first cycle to the 20000th cycle and is negligible thereafter. [ABSTRACT FROM AUTHOR]

Due to the difficulties in micro stress calculation of interface, most failure analysis models of macro composite structure mainly focus on the failure modes of fiber and matrix, which have not taken interface debonding into consideration. In this paper, a high-efficient failure analysis model is proposed to realize quick investigation of interface debonding as well as fiber and matrix failure in macro composite structure under complex stress condition. Stress amplification factors are adopted to realize the rapid calculation of micro stress at interface according to the macro stress of composite. Three-point bending tests with elaborate designed stacking sequences are carried out to extract the critical interfacial normal strength and shear strength used in this model. In the failure analysis of micro unit cell this model shows high accuracy in the prediction of interface debonding both in the failure modes and failure locations compared with cohesive zone model. To further inspect its capability in the analysis of macro composite structures, open-hole compression tests of quasi-isotropic laminates are carried out. Good agreements in the interface debonding mechanisms are obtained between numerical prediction and experimental results. [ABSTRACT FROM AUTHOR]

In this paper, the matrix multi-fracture of SiC/SiC ceramic-matrix composites (CMCs) is investigated using the critical matrix strain energy (CMSE) criterion. The BHE shear-lag model is used to analyze the micro-stress field of the damaged composite, and the fracture mechanics method and the CMSE criterion are adopted to determine the fiber/matrix interface debonded length and matrix multi-fracture density. The temperature-dependent fiber/matrix interface shear stress, Young's modulus of the matrix, the matrix fracture energy, and the fiber/matrix interface debonded energy are considered in the micro-stress field analysis, fiber/matrix interface debonding criterion, and matrix multi-fracture model. The effects of fiber volume fraction, fiber/matrix interface shear stress, fiber/matrix interface frictional coefficient, fiber/matrix interface debonded energy, matrix fracture energy, and temperature on the matrix multi-fracture of SiC/SiC composite are discussed. When the fiber volume fraction and matrix fracture energy increase, the first matrix cracking stress and matrix saturation cracking stress increase; when the fiber/matrix interface shear stress and interface frictional coefficient increase, the first matrix cracking stress, saturation matrix cracking stress, and saturation matrix cracking density increase with the decrease of the fiber/matrix interface debonded length; when the fiber/matrix interface debonded energy increases, the saturation matrix cracking stress decreases and the saturation matrix cracking density increases due to the decrease of fiber/matrix interface debonding ratio. The experimental matrix multi-fracture and fiber/matrix interface debonding curves of unidirectional SiC/SiC composite at elevated temperatures are predicted. The predicted results agree with experimental data, which proves the efficiency of the developed matrix multi-fracture model. [ABSTRACT FROM AUTHOR]

• A micromechanics-based multiscale damage model for 3D woven composites (3DWCs) is proposed. • Interface properties exhibit different effects on tensile and compressive damage mechanisms of 3DWCs. • The interaction of different damage modes controls the overall trend of the tensile strength of 3DWCs. • In contrast, the better the interface properties, the higher the compressive strength of 3DWCs. A multiscale damage model is proposed based on a micro-mesoscale bridging model and a multiscale kinking model, which can predict the damage development processes of 3D woven composites (3DWCs) under different loading conditions using only few material parameters. At the microscale, the various mesoscopic damage modes of yarns, including tensile fiber breakage, compressive fiber kinking and transverse inter-fiber crack, can be simply divided into matrix- and fiber-dominated damage. Using this multiscale damage model, a numerical comparative study is conducted to investigate the effect of interfacial properties on the mechanical performances and damage mechanism of 3DWCs. The numerical results indicate that the interfacial properties exhibit different effects on the tensile and compressive strengths and damage mechanisms of 3DWCs. The interaction of different damage modes controls the overall trend of the tensile strength of 3DWCs. There is an optimum point for the tensile strength of 3DWCs at different interfacial fracture toughness. Beyond the optimum point, the tensile strength of 3DWCs is negatively correlated with interfacial properties. Unlike the tensile loading case, the better the interfacial properties, the later fiber kinking occurs, resulting in higher compressive strength of 3DWCs. [ABSTRACT FROM AUTHOR]

The bonding interface is prone to debonding under environmental implications and long-term operational vibrations, which may severely affect the structural integrity. In this paper, considering the complex intermodal dynamic characteristics caused by interface debonding, a local defect internal resonance method is proposed for the first time to solve ultrasonic damage identification for adhesive interface debonding. Firstly, based on a two degree of freedom (2-DOF) nonlinear model of local defects in the bonding interface, the multi-scale method is used to explain the mechanism of the internal resonance of local defects and the conditions for the generation of the internal resonance. By analyzing the saturation phenomenon peculiar to the 2:1 internal resonance of local defects in the spectrum, the adhesive interface debonding identification experiment of a bonding aluminum plate is carried out. The effectiveness of the local defect internal resonance method is verified by theoretical analysis and experimental results. The experimental results show that the debonding damage produced a V-shaped combination of excitation amplitude and frequency which can produce internal resonance characteristics. Further, the local defect internal resonance method is found to be effective in solving adhesive interface debonding detection. • A local defect internal resonance method is proposed to solve damage identification of adhesive interface debonding. • The frequency response of nonlinear systems with two degrees of freedom is obtained using multi-time scale method. • Established the steps for detecting bonding interfaces by the local defect internal resonance method. • The LDIR method can improve the detection ability of the interface debonding in adhesive structures. [ABSTRACT FROM AUTHOR]

In this paper, the mechanical hysteresis and damage evolution in C/SiC ceramic matrix composites (CMCs) under cyclic tension‐tension fatigue loading at room and elevated temperatures in air and in inert atmosphere and different loading frequencies are investigated. The fatigue hysteresis loops models considering multiple matrix cracking modes are developed to establish the relationships between fatigue hysteresis loops, fatigue hysteresis dissipated energy, and fiber/matrix interface shear stress. The evolution of fatigue hysteresis dissipated energy and interface shear stress vs applied cycles is analyzed. It was found that the interface shear stress degradation rate increases with fatigue peak stress, and loading frequency from 40 to 375 Hz. [ABSTRACT FROM AUTHOR]

Abstract The prediction of stresses in an adhesive layer is helpful in revealing the mechanism of debonding failure in plated beams. This study proposes an improved analytical model for the stress analysis of an adhesive layer in a plated beam. The beam and the soffit plate are individually modelled as a single Timoshenko sub-beam with separate rotations, while the adhesive layer is modelled as a two-dimensional elastic continuum in plane stress, which considers different adherend-adhesive interface stresses. The internal forces of the adhesive layer are assumed to satisfy the Timoshenko beam theory, and the shear deformation and bending moment of the adhesive layer can be considered. The internal forces and displacements of the adhesive layer are fully considered in the displacement compatibility equations, and deformable interfaces are assembled so that the effect of interface stresses on local deformation is captured. Based on equilibrium equations and displacement continuity, the governing differential equations of beam forces are derived, and then the analytical solutions of interface stresses and stresses along the thickness of the adhesive layer are obtained. Comparisons of the results of the finite-element analysis and the existing four-parameter model solutions show that the present model is reasonable. The influence of adhesive thickness on stress distributions in adhesive layers is also investigated. [ABSTRACT FROM AUTHOR]

Abstract A numerical micromechanics study is performed to investigate the effect of using graphene nanoplatelets (Gnp) with theoretical maximum properties and reduced graphene oxide (rGOnp) on the mechanical properties and damage mechanism of graphene based nanocomposites. Here we consider brittle matrix cracking and interface debonding as the main damage mechanisms. The results showed that the competition between both mechanisms is affected by nanoplatelets/matrix modulus-mismatch, volume fraction, interface strength and orientation. Gnp showed improved modulus, however, with inferior strength and fracture strain compared to rGOnp. This is due to the large modulus-mismatch of Gnp, which resulted in increasing the stress concentration, matrix cracking and coalescing at lower loads. On the other side, the lower stress concentration of rGOnp allowed for higher load accumulation and increased interface debonding. Applying stronger interface properties was found to suppress the interface debonding, improving strength and fracture strain. Further, aligned nanoplatelets lead to a simultaneous improvement in modulus, strength and fracture strain. This is due to the improved load transfer and activation of toughening mechanisms observed for bioinspired nacre like structures. [ABSTRACT FROM AUTHOR]

A three-dimensional continuum damage model is proposed to analyze the damage and perforation resistance behaviors of bonding-patch and scarf-patch repaired composite laminates under projectile impact load. Coupling with modified 3D-Hashin failure criteria, a linear-exponential law due to fiber pull-out failure and an exponential law are used to predict tensile and compressive softening processes of materials, respectively. A cohesive interaction based on triangle traction–separation law and mixed-mode fracture energy method is applied for interface debonding damages between patch/lamina, patch/patch and lamina/lamina. Comparisons are made between numerical results and several available test data for different impact offsets. The perforation resistance and interface debonding damage mechanisms are extensively discussed using finite element analysis. Further, perforation resistance behaviors of laminate with six different patch-repair patterns are assessed. Effects of initial velocity of projectile on residual velocity and energy-absorption are discussed. A residual velocity error within 7.3% and energy-absorption error within 9.2% is found between simulations and tests. Consistent failure modes including fiber fracture, matrix cracking, delamination and interface debonding are also identified. As the projectile invades patches, interface debonding damage in patches is accumulated rapidly, especially for larger impact offset. The combined patch-repairs show a reduction of at the most 48.3% in velocity and higher ballistic limit velocities which implies better perforation resistance capacity. The energy-absorption almost increases with increasing the initial velocity and a decreasing trend in average energy-absorption is found with the increase of impact offset. [ABSTRACT FROM AUTHOR]

Abstract In this paper, a hysteresis energy dissipation based damage model for fiber-reinforced ceramic-matrix composites (CMCs) subjected to multiple loading stress levels is developed. Considering the combination effects of multiple loading sequences and multiple fatigue damage mechanisms, i.e., matrix cracking, fiber/matrix interface debonding and interface wear, the evolution of the fiber/matrix interface debonding and sliding, fatigue hysteresis loops, fatigue hysteresis dissipated energy and fatigue hysteresis modulus changing with increasing applied cycles are analyzed. The effects of fiber volume fraction, matrix crack spacing, fatigue peak stress and fatigue stress range on the damage development inside of CMCs are discussed. The difference of the fiber/matrix interface shear stress existed between the interface wear region and new interface debonded region affects the fiber/matrix interface debonded length and loading carrying ability of intact and broken fibers. The damage evolution for C/SiC and SiC/SiC composites subjected to multiple fatigue loading sequences are predicted using the hysteresis energy dissipation damage model. Under multiple loading stress, the fatigue hysteresis dissipated energy increases when high peak stress and stress range increases due to the increase of fiber/matrix interface sliding range. However, when the low peak stress increases, the evolution of fatigue hysteresis dissipated energy depends on the interface debonding and sliding state. Graphical abstract Image 1 Highlights • Multiple loading fatigue damage of fiber-reinforced ceramic-matrix composites (CMCs) is investigated. • A hysteresis energy dissipation based damage model is developed. • The influences of fiber volume fraction, matrix crack spacing, fatigue peak stress and fatigue stress range are discussed. • The developed hysteresis damage model is validated. [ABSTRACT FROM AUTHOR]

Highlights • Complex failure mechanisms within and across the phases of meso-scale multi-phase materials can be captured. • An auxiliary phase field is introduced to regularize interface material properties in addition to the one for crack. • The complex fracture mechanisms are obtained without any additional ad-hoc criterions or crack tracking strategies. Abstract In this paper, a new phase field method is proposed for modelling of progressive failure in multi-phase materials. Material properties of the interface between inclusion and matrix are regularized by an auxiliary interface phase field. In addition, crack initiation and propagation are simulated by using another crack phase field. Different failure mechanisms such as interface debonding, matrix cracking and the interaction between these two failure mechanisms are modelled in a unified framework. For general application of the framework, an image processing method is employed to identify the individual phases for a given multi-phase material. The proposed method is implemented into the commercial software ABAQUS through a user subroutine UEL (user defined element). The derived method is validated through an example of a single fiber reinforced composite system. Moreover, a procedure for choosing parameters of the proposed phase field model is discussed. Further, the validated method is applied to fracture analysis of a multi-phase concrete structure and complex failure mechanisms within and across the phases are captured. [ABSTRACT FROM AUTHOR]

In this paper, a thermomechanical fatigue hysteresis-based damage evolution model for fiber-reinforced ceramic–matrix composites has been developed. Upon unloading and reloading, the fiber/matrix interface debonded length, interface counter-slip length, and interface new-slip length change with increasing or decreasing applied stress, which affects the stress–strain fatigue hysteresis loops and fatigue hysteresis-based damage parameters. The reloading/unloading stress–strain relationships when fiber/matrix interface partially or completely debonding are determined as a function of interface debonding/sliding, peak stress, applied cycle number, and thermal cycle temperature. The relationships between thermomechanical fatigue loading parameters (i.e. peak stress, applied cycle number, and thermal cyclic temperature), fiber/matrix interface debonding/sliding lengths, and fatigue hysteresis-based damage parameters (i.e. fatigue hysteresis dissipated energy, fatigue hysteresis modulus, and fatigue peak strain) have been established. The effects of fiber volume fraction, peak stress, matrix cracking space, and thermal cyclic temperature range on damage evolution under the out-of-phase thermomechanical cyclic loading have been discussed. The differences in damage evolution between in-phase/out-of-phase thermomechanical fatigue and isothermal fatigue loading at the same peak stress have been analyzed. The damage evolution of cross-ply SiC/magnesium aluminosilicate composite under the out-of-phase thermomechanical and isothermal fatigue loading has been predicted. [ABSTRACT FROM AUTHOR]