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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]

This study used a static bidirectional multifunctional loading system. The system conducted bidirectional compression tests on scaled specimens of slurry masonry schist under freeze–thaw cycling conditions. This study aimed to investigate the influence of bidirectional stress coupling with freeze–thaw cycles on the mechanical properties of slurry masonry schist. The results indicate that lateral pressure can increase the peak stress of slurry masonry schist, while freeze–thaw cycles have an adverse effect on the material's internal pore structure, counteracting the gain effect of lateral pressure. This study also employed acoustic emission (AE) technology to analyze the evolution of slurry masonry schist failure characteristics. The findings reveal that freeze–thaw cycles accelerate the failure of slurry masonry schist during loading, and lateral pressure to some extent mitigates the damage development of slurry masonry schist. The synergistic effect of lateral pressure and freeze–thaw cycles alters the fracture mode of slurry masonry schist. Acoustic emission signal localization demonstrates numerous AE localization points in the interface transition zone, forming a coherent signal band where cracks propagate toward complete interface penetration. The crack extension process of the slurry masonry schist was investigated using the digital image correlation (DIC) method. The results indicated that macroscopic cracks formed in the strain localization zone, resulting in fracture damage to the specimens, with interfacial debonding identified as the primary failure mode for slurry masonry schist structures. [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]

Basalt fiber-reinforced polymer (BFRP) has high mechanical strengths as a repairing material but exhibits low ductility. This paper investigates the damage process of reinforced concrete beams repaired using BFRP sheets, aimed at understanding the underlying mechanisms of achieving structural ductility when BFRP sheets are used. The damage process was assessed using digital image correlation (DIC) and acoustic emission (AE) techniques applied to monitor surface and internal damages of three full-scale concrete beams subjected to four-point bending. A beam was first loaded to crack, then repaired with BFRP sheets, and finally reloaded to failure. Surface strain fields and cracks were monitored using a DIC method, and cracking events were monitored using AE sensors deployed at different positions of the beams. The AE signals were analyzed to assess the damage process. The test results indicated that (1) tensile cracks predominated throughout the loading process; (2) the BFRP sheets hindered the widening of cracks and promoted the generation of fine cracks; and (3) the development of concrete cracks promoted interfacial debonding at steel-concrete and BFRP-concrete interfaces. A combination of different types of cracks and interfacial debonding helped the repaired beam achieve ductile flexural behaviors.

ObjectiveIn view of the failure of type-I steel sandwich plate interfaces, this paper analyzes their interface fatigue debonding characteristics. MethodsBased on the cohesive force model and considering the time history, damage evolution equations and convergence criteria of 3D structural nodes with multiple degrees of freedom, an interface fatigue debonding simulation program suitable for 3D complex structures is developed. The accuracy of the developed program is verified through a comparison with the experimental results of welding joint debonding, and the interface fatigue debonding behavior of type-I steel sandwich plates is simulated numerically. ResultsThe results show that the maximum simulation error between the 3D interface fatigue debonding test and debonding experimentis only 14.05%. When an type-I sandwich plate is subjected to out-of-plane load, the debonding failure at the interface mainly manifests as surface crack propagation in the direction of the extended weld. When the crack propagation reaches about 70% of the length of the plate, the crack begins to penetrate through the web to form a penetrating crack.ConclusionThe interface fatigue debonding program developed herein can effectively evaluate the interface fatigue debonding life of type-I steel sandwich plates, giving it certain guiding significance for practical engineering applications.

Introducing Neutral Polymeric bonding agents (NPBA) into the Nitrate Ester Plasticized Polyether (NEPE) propellant could improve the adhesion between filler/matrix interface, thereby contributing to the development of new generations of the NEPE propellant with better mechanical properties. Therefore, understanding the effects of NPBA on the deformation and damage evolution of the NEPE propellant is fundamental to material design and applications. This paper studies the uniaxial tensile and stress relaxation responses of the NEPE propellant with different amounts of NPBA. The damage evolution in terms of interface debonding is further investigated using a cohesive-zone model (CZM). Experimental results show that the initial modulus and strength of the NEPE propellant increase with the increasing amount of NPBA while the elongation decreases. Meanwhile, the relaxation rate slows down and a higher long-term equilibrium modulus is reached. Experimental and numerical analyses indicate that interface debonding and crack propagation along filler–matrix interface are the dominant damage mechanism for the samples with a low amount of NPBA, while damage localization and crack advancement through the matrix are predominant for the ones with a high amount of NPBA. Finally, crosslinking density tests and simulation results also show that the effect of the bonding agent is interfacial rather than due to the overall crosslinking density change of the binder.

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]

Patching is a common technology used in repairing asphalt-pavement potholes. Due to the differences in material properties between patched- and unpatched-asphalt mixtures, significant strain and stress concentrations could be induced; thus, further cracks and interfacial debonding distress could be caused. As a remedy, the strain and stress concentrations can be alleviated by utilizing optimum patching shapes. Therefore, this paper employed finite element methods (FEM) to deeply analyze the mechanical performance of patched-asphalt pavements embedded with different patching shapes. Three patching shapes, these being rectangular, stair, and trapezoid, were considered for use in pavement pothole repairs based on two- and three-dimensional finite element models. In the two-dimensional models, Top-Down and Bottom-Up crack propagations were simulated to assess the anti-damage performance of the patched pavements with different patching shapes. In addition, the thermal stress behaviors within patched-asphalt pavements were simulated using the two-dimensional model to analyze the performance of the patched pavements during the cooling process in construction. In addition, interface-debonding performance was simulated for the patched-asphalt pavements using three-dimensional models. In light of the simulation results, engineers are expected to better understand the mechanism within patched pavements and to improve the quality of the pavement patching. [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]

Introducing Neutral Polymeric bonding agents (NPBA) into the Nitrate Ester Plasticized Polyether (NEPE) propellant could improve the adhesion between filler/matrix interface, thereby contributing to the development of new generations of the NEPE propellant with better mechanical properties. Therefore, understanding the effects of NPBA on the deformation and damage evolution of the NEPE propellant is fundamental to material design and applications. This paper studies the uniaxial tensile and stress relaxation responses of the NEPE propellant with different amounts of NPBA. The damage evolution in terms of interface debonding is further investigated using a cohesive-zone model (CZM). Experimental results show that the initial modulus and strength of the NEPE propellant increase with the increasing amount of NPBA while the elongation decreases. Meanwhile, the relaxation rate slows down and a higher long-term equilibrium modulus is reached. Experimental and numerical analyses indicate that interface debonding and crack propagation along fillerematrix interface are the dominant damage mechanism for the samples with a low amount of NPBA, while damage localization and crack advancement through the matrix are predominant for the ones with a high amount of NPBA. Finally, crosslinking density tests and simulation results also show that the effect of the bonding agent is interfacial rather than due to the overall crosslinking density change of the binder. [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 deformation behavior of hot-roll-bonded Mg/Al laminated metal composites (LMCs) is investigated, focusing on the crack formation around the interface. The material demonstrates a positive strain rate sensitivity mainly arising from the Mg matrix. A diffusion layer was formed at the Mg/Al interface with a serrated morphology during the two-pass rolling process, which consists of the Al3Mg2 and Mg17Al12 phases. The mechanical responses of the LMCs are evaluated using uniaxial tension, interfacial debonding tests (in normal and shear modes), and microstructure characterization techniques, which clarify the interfacial heterogeneity. The fracture constants of the interface were calibrated and incorporated in the finite element models to predict the failure modes of heterogeneous Mg/Al interface under three-point bending. With the increased thickness ratio of the Mg layer, the damage accumulation rate decreases at the interface and increases in the Mg matrix. As a result, the failure mode transferred from interface failure to matrix fracture. The findings of the present work provide new insight into the failure mechanism in laminated metal composites under bending conditions and can provide theoretical guidance for the plastic forming of such materials.

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]

The extended finite element method (XFEM) was employed for the computational modeling of internal defects within a bond layer. Furthermore, a cohesive zone model (CZM) was implemented to characterize the behavior of the bond layer in response to interactions at both the bond layer/steel plate and bond layer/asphalt paving layer interfaces. The coupling of XFEM and CZM was used for a comprehensive analysis of crack propagation within the bond layer as well as the assessment of phenomena associated with interfacial debonding and delamination. The feasibility and accuracy of the XFEM–CZM coupling method were verified by comparing it with the virtual crack closure technique (VCCT), CZM, XFEM–VCCT, and experiments. A double cantilever beam experimental model was established to simulate the process of interlayer-type cracks expanding from the inside of the bond layer to the interface between the bond layer and the upper and lower layers, causing debonding. This was undertaken to analyze the damage failure mechanism of interlayer-type cracks in asphalt paving layers of steel bridge decks; to discuss the impacts of the initial crack length, the interface stiffness, the interface strength, and the thickness of the bond layer on the performance of the overall interlayer bond strength; and to carry out the significance analysis. The results showed that the initial crack length, interface stiffness, and bond layer thickness had different effects on the expansion path of interlayer cracks. The interlayer strength decreased with an increase in the initial crack length and interface stiffness, increased with an increase in the interface strength, and decreased with an increase in the thickness of the bond layer. The interface stiffness had the most significant effect on the strength. [ABSTRACT FROM AUTHOR]

Multilayer adhesive bonded structures/materials (MABS) are widely used as structural components, especially in the field of aerospace. However, for MABS workpieces, the facts that the weak echo of the deep interfacial debonding defects (DB) caused by the large acoustic attenuation coefficient of each layer and this echo, which generally aliases with the excitation wave and the backwall echo of the surface layer, pose a great challenge for the conventional longitudinal wave ultrasonic nondestructive testing methods. In this work, an ultrasonic resonance evaluation method for deep interfacial DBs of MABS is proposed based on the ultrasonic resonance theory and the aliasing effect of ultrasonic waves in MABS. Theoretical and simulation analysis show that the optimal inspection frequency for II-interfacial DBs is 500 kHz when the shell thickness is 1.5 mm and the ethylene propylene diene monomer (EPDM) thickness is 1.5 mm, and the optimal inspection frequency is 250 kHz when the shell thickness is 1.5 or 2.0 mm and the EPDM thickness is 2.0 mm. Verification experiments show that the presence of a DB in the II-interface causes a resonance effect, and in the same inspection configuration, the larger the defect size, the more pronounced this effect is. This resonance effect manifests itself as an increase in the amplitude and an increase in the vibration time of the A-scan signal as well as a pronounced change in the frequency of the received ultrasonic wave. In addition, the increase in the excitation voltage further highlights the ultrasonic resonance effect. Four imaging methods – the integrations of the signal and the signal envelope curve, the maximum amplitude of the fast Fourier transform (FFT) of the signal, and the signal energy – were used for C-scan imaging of ultrasonic resonance evaluation of MABS’s deep interfacial DBs and all these methods can clearly show the sizes and locations of the artificial defects and internal natural defect. The normalized C-scan imaging method proposed in this study can further highlight the weak changes in the signals in the C-scan image. The research results of this study have laid a solid theoretical and practical foundation for the ultrasonic resonance evaluation of MABS.

This study used a static bidirectional multifunctional loading system. The system conducted bidirectional compression tests on scaled specimens of slurry masonry schist under freeze–thaw cycling conditions. This study aimed to investigate the influence of bidirectional stress coupling with freeze–thaw cycles on the mechanical properties of slurry masonry schist. The results indicate that lateral pressure can increase the peak stress of slurry masonry schist, while freeze–thaw cycles have an adverse effect on the material’s internal pore structure, counteracting the gain effect of lateral pressure. This study also employed acoustic emission (AE) technology to analyze the evolution of slurry masonry schist failure characteristics. The findings reveal that freeze–thaw cycles accelerate the failure of slurry masonry schist during loading, and lateral pressure to some extent mitigates the damage development of slurry masonry schist. The synergistic effect of lateral pressure and freeze–thaw cycles alters the fracture mode of slurry masonry schist. Acoustic emission signal localization demonstrates numerous AE localization points in the interface transition zone, forming a coherent signal band where cracks propagate toward complete interface penetration. The crack extension process of the slurry masonry schist was investigated using the digital image correlation (DIC) method. The results indicated that macroscopic cracks formed in the strain localization zone, resulting in fracture damage to the specimens, with interfacial debonding identified as the primary failure mode for slurry masonry schist structures.

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.

The strength and toughness of sealing glass are currently unable to meet increasingly severe application conditions, and composites are an effective way to solve this problem. The size of reinforcement particles significantly affects the material properties, while the underlying mechanism still eludes deeper understanding. In this paper, the influence of the embedded alumina size is investigated from the perspectives of mechanical and fracture properties by mechanical tests, fracture toughness tests and the finite element method. The results of the experiment and simulation indicate that the fracture energy is mainly consumed by interface debonding and particle breakage, and the former consumes more energy. Materials with large particles have better mechanical properties, while those with small particles have better fracture properties. This difference could be ascribed to the curvature of the particles rather than the size. Therefore, an ideal reinforcement particle shape with both mechanical and fracture advantages is proposed. The results shed light on the nature of particle enhancement and point out a new direction for the design of sealing glass composites.

Room temperature vulcanised (RTV) silicone rubber coatings effectively enhance the insulation properties of electrical equipment. However, RTV coatings are prone to internal defects caused by the coating process and the effects of aging during service, which can lead to debonding of the coatings. Internal debonding defects are challenging to detect and can ultimately lead to accidents due to a reduction in the insulation capacity of the equipment. To visualize the internal defect morphology of RTV coatings and quantify the defect size, an ultrasonic pulse-echo-based method for detecting and imaging debonding defects is proposed. The method involves the development of a finite element model to investigate how ultrasonic waves propagate in RTV coatings and the influence of ultrasonic probes and inspection conditions on defect echoes. Furthermore, an ultrasonic detection system specifically designed for RTV coating debonding defects is constructed. This system utilizes wavelet packets in the time-frequency domain to analyze the echo signals in both normal and defective regions. The three-dimensional reconstruction of the debonding defect morphology is accomplished by integrating ultrasonic echo amplitude and position information. Finally, the size of the debonding defects is quantified using an adaptive threshold segmentation method. The findings indicate that ultrasound waves reflected in RTV materials propagate as spherical waves, with the acoustic energy primarily concentrated near the acoustic axis. As the propagation distance increases, the sound beam disperses along the axis and extends beyond the transducer, resulting in a decrease in the sound field's directionality. The developed visual reconstruction method in this study offers the capability of three-dimensional visualization for defects present within RTV coatings, including their length, width, and depth. The accurate determination of defect size is achieved through the utilization of the adaptive threshold segmentation method, yielding an average error rate of 5.7 % across different defect types. In comparison, the maximal interclass variance method (OTSU) and the fuzzy C-means (FCM) method produced results with error rates of 9.8 % and 7.9 %, respectively. The research presented in this paper enables precise assessment of debonding defect severity and establishes a reliable foundation for on-site inspection, operation, and maintenance of RTV coatings.

Patching is a common technology used in repairing asphalt-pavement potholes. Due to the differences in material properties between patched- and unpatched-asphalt mixtures, significant strain and stress concentrations could be induced; thus, further cracks and interfacial debonding distress could be caused. As a remedy, the strain and stress concentrations can be alleviated by utilizing optimum patching shapes. Therefore, this paper employed finite element methods (FEM) to deeply analyze the mechanical performance of patched-asphalt pavements embedded with different patching shapes. Three patching shapes, these being rectangular, stair, and trapezoid, were considered for use in pavement pothole repairs based on two- and three-dimensional finite element models. In the two-dimensional models, Top-Down and Bottom-Up crack propagations were simulated to assess the anti-damage performance of the patched pavements with different patching shapes. In addition, the thermal stress behaviors within patched-asphalt pavements were simulated using the two-dimensional model to analyze the performance of the patched pavements during the cooling process in construction. In addition, interface-debonding performance was simulated for the patched-asphalt pavements using three-dimensional models. In light of the simulation results, engineers are expected to better understand the mechanism within patched pavements and to improve the quality of the pavement patching.

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]

Copyright of Railway Standard Design is the property of Railway Standard Design Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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]

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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]

Understanding of cracking opening behavior is important for the prediction of residual strength and lifetime of silicon carbide fiber-reinforced silicon carbide ceramic–matrix composites at elevated temperatures. Under tensile loading below the proportional limit stress, multiple matrix cracking modes in the longitudinal and transverse yarns of a two-dimensional plain-woven silicon carbide fiber-reinforced silicon carbide composite appear in the matrix with debonding at the fiber/matrix interface. Crack opening displacement is a key parameter to characterize the crack opening behavior in silicon carbide fiber-reinforced silicon carbide composites and is affected by the multiple matrix cracking modes. In this article, a damage-based micromechanical crack opening displacement model for two-dimensional plain-woven silicon carbide fiber-reinforced silicon carbide composites is developed considering different matrix cracking modes. Two typical matrix cracking modes in a two-dimensional plain-woven silicon carbide fiber-reinforced silicon carbide composite, that is, cracking mode III with cracking in the matrix of the longitudinal and transverse yarns and cracking mode V with cracking only in the matrix of the longitudinal yarns, are considered. Micro stress field in the fiber, matrix of the longitudinal yarns, and transverse yarns are obtained. The crack opening displacement and related damage parameters are determined. Relationships between composite's crack opening displacement, constitutive properties, woven parameters, and damage state are established. Experimental crack opening displacements of cracking modes III and V in a two-dimensional plain-woven melt-infiltration silicon carbide fiber-reinforced silicon carbide composite from the published literature are predicted. For cracking mode III with partial interface debonding, the crack opening displacement increased nonlinearly with applied stress; and for cracking mode V with complete interface debonding, the crack opening displacement increased linearly with applied stress. [ABSTRACT FROM AUTHOR]

In this study, an extended layerwise/solid-element (XLW/SE) method is developed for the thermo–chemo–mechanical (TCM) coupling problem of an aero-engine turbine blade with thermal barrier coatings (TBCs). The method consists of two parts, the extended layerwise (XLW) method and the three-dimensional (3D) solid-element (SE) method, which are adopted to formulate the governing equations of TBCs and substrate, respectively. Then, according to the compatibility conditions of displacement, temperature, concentration and internal force equilibrium at the TBCs/substrate interface, the governing equation of the final blade structure is assembled. Through a time integration, the dynamic responses of displacement, temperature and concentration can be calculated. In addition, the fluid–structure coupling analysis is conducted by using COMSOL. The nonuniform thermal load is imported into the XLW/SE method to calculate the mechanical response of blade structure. Finally, the corresponding computing program is compiled with C++. In numerical examples, the TCM coupling analysis is conducted on the blade structure with and without interfacial debonding and delamination damages. To validate the effectiveness of the proposed method, the dynamic TCM responses of the XLW/SE model is compared with those of a 3D elastic model generated by COMSOL, which shows that the two models are in good agreement. [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]

In the traditional integrity analysis of solid rocket motors, solid propellants failure and propellant-liner interface debonding were intentionally differentiated. This empirical distinction of failure regions based on the macroscopic phenomenon neglects their physical correlation, consequently increasing both experiment quantity and simulation complexity. Here, by experiments and simulations, propellant-liner interface debonding is shown to be induced by propellant breakage, i.e., the substrate failure. In experiments, interface debonding and propellants failure share the same cavitation and stringing processes in crack initiation, and the measured break strain of solid propellants and fracture energy of interface satisfy a similar temperature/strain-rate dependent shifting phenomenon. The finite element model can well predict both the strain field and the stress-strain response of interface debonding by using the parameters calibrated by tensile tests of solid propellants, verifying that interface debonding is induced by propellants breakage. Overall, failure envelopes of both propellants and interfaces satisfy a similar peak-position shifting phenomenon but different peak-value shifting phenomena. The time-temperature superposition of HTPB polymer binders induces the peak-position shift, and strain concentration and relaxation of propellants in the crack front induce the peak-value evolution. This study is promising to unify and simplify the solid propellants failure and interface debonding in the integrity analysis.

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]