Interfacial Bond Behavior Research Articles

Experimental study on the interfacial bond behavior of UHPC filled circular stainless steel tubes

As the interfacial bond property is of great significance to derive the composite action between stainless steel tube and UHPC for the Ultra-High Performance Concrete Filled Stainless Steel Tubular (UHPCFSST) columns, the push-out tests were conducted in this program, which includes 8 specimens having different stainless steel tube diameter and tube thickness. Based on the test results, the damage patterns and the full range load-slip curves are analyzed in detail, and the interfacial bond stress constitutes at different loading stages were also identified and evaluated. On top of that, the longitudinal strain of the stainless steel tube was analyzed based on elastic theory to derive the non-dimensional bond stress distribution law along the steel-concrete interface. The comparison between test results and the predictions from current code specification or the available empirical formulas indicate a large discrepancy and inconsistency. Therefore, the bond strength and corresponding slippage value of UHPCFSST columns were predicted by a new equation based on regression analysis. The research discovery obtained from this study provides theoretical significance and practical value for improving the design theory and application of UHPCFSST columns in practical engineering.

An efficient deep learning approach for ultimate bond strength estimations of corroded bar and concrete

Abstract The corrosion behavior of the reinforced concrete structure depends heavily on the interfacial bond behavior between steel and concrete. Over the years, the deterioration of integrated reinforced steel has weakened this bond and potentially led to structural problems. Conventional methods of bond strength evaluation, such as pullout and bond beam tests, is frequently intrusive and tedious. Therefore, there is a growing need for non-intrusive, effective, and reliable forecasting algorithms capable of assessing bond deterioration caused by corrosion. Traditional algorithms for predicting bond strength make it difficult to capture the complex nature of steel-concrete bonds. The present study proposes two different deep learning algorithms, i.e., convolutional neural networks (CNN) and long short-term memory (LSTM), for predicting maximum bond strength in the presence of corrosion. The predictive model is based on a comprehensive dataset comprising 218 datasets from previous studies encompassing diverse input and output variables for predicting the models. The models were trained and tested using the given data to improve early predictions of corrosion-induced bond degradations. The predictive model’s effectiveness was assessed by applying various performance metrics. From this study, the CNN model exhibits higher accuracy and efficiency with mean absolute error, root mean square error, and mean absolute percentage error of 0.25, 0.28, and 95.72, respectively, for predicting ultimate bond strength estimations. The findings of this study provide an accurate and robust prediction model to improve the reliability and safety of the concrete structure by enhancing the residual load-bearing capacity of the concrete structure that has undergone corrosion.

Corrosion failure analysis of interfacial bond performance in circular seawater sea-sand concrete encased weathering steel structures

This paper investigated the bond-slip behavior of circular seawater sea-sand concrete encased weathering steel (CSSCEWS) structures after chloride-induced corrosion. Electrochemical corrosion tests and push-out tests were conducted on fifteen designed CSSCEWS specimens. The results revealed that the corrosion ratio and steel section type distinctly influenced the interfacial bond performance. Both the ultimate and residual bond strengths decreased with the increase of the corrosion ratio, and the decline rate slowed down gradually. Compared to the uncorroded specimens, the average damage ratio of the ultimate strength of the specimens with a corrosion ratio of 8% is 25.9%, while the average damage ratio of the residual strength is 49.1%. The bond toughness continuously decreased with prolonged corrosion, while the bond stiffness and energy dissipation index first increased and then decreased. Additionally, formulas for calculating the corroded bond strengths of CSSCEWS specimens were proposed. Considering the strength damage due to corrosion and the stiffness damage due to slip, a three-stage bond-slip constitutive model was proposed. Finally, this model was applied to the nonlinear spring elements in finite element modeling to effectively simulate the interfacial bond behavior during the loading of corroded CSSCEWS specimens.

Long-term effects including shrinkage and interfacial creep on bond behavior of concrete-filled steel tubes (CFST): Experiment and design

Concrete-filled steel tubes (CFST) are widely used in significant projects due to their high performance stemming from full utilization of combined material advantages. The interfacial bond behavior is the foundation of their high performance, but will deteriorate during the long-term service. Due to the difficulties on carrying out long-term experiments and decoupling the multi-constitutive component bond strength including chemical adhesion, micro-interlocking and friction, there is still a lack of research on long-term interface constitutive models, restricting the safe design of CFST structures throughout their full-lifecycle. Here, push-out tests were carried out on CFST specimens considering long-term effects spanning 850 days including concrete age and duration of long-term interfacial load. The steel plate-concrete specimens, reversed push-out tests and interfacial normal pressure calculation were used to decouple the components of bond stress. the CFST interface database considering long-term effects was established and the mechanism of long-term effects have been revealed. As the duration increases, the bond stress decreases at the beginning, and thereafter stabilizes where the friction component dominates. Compared to that without interfacial load, long-term interfacial load accelerates the damage to chemical adhesion and micro-interlocking at initial stage, but the difference of their effects on bond stress is not significant in the later stage. On this basis, a long-term interfacial constitutive model for its full-lifecycle safe design and a simplified numerical method for long-term effects on bond behavior have been proposed.

Interfacial bond behavior of steel fibers embedded in manufactured sand-based ultra-high performance concrete

The interfacial bond region between matrix and fibers is a non-negligible weak link that can significantly affect the mechanical properties of manufactured sand-based ultra-high-performance concrete (UHPMC). This study investigates the interfacial bond characteristics between steel fiber-UHPMC matrix using single-fiber pullout tests. Four variable parameters were considered: manufactured sand (MS) replacement ratio, stone powder content, fiber embedment length, and steel fiber geometry. Additionally, the microstructure of the steel fiber-UHPMC matrix interface was evaluated using backscattered electron microscopy (BSEM) and scanning electron microscopy (SEM). The results indicate that two typical failure modes including fiber pullout slip failure (in straight and hooked-end fibers) and fiber rupture failure (in corrugated fibers) were observed. The analysis of interfacial evaluation indicators shows that increasing the MS replacement ratio from 25 % to 100 % results in a decreasing trend in peak load, peak tensile stress, and energy consumption. Peak bond strength decreases with increasing embedment length. With the increase in stone powder content, the peak load, peak bond stress, and energy consumption increase initially and then decrease. Additionally, the interfacial failure mechanisms between straight/hooked-end steel fibers and the UHPMC matrix were further elucidated through bond-slip behavior characterization and microstructure analysis. Finally, a design-oriented bond-slip model was developed to predict the interfacial pull-out behavior of steel fiber -UHPMC matrix, showing favorable agreement between predicted and test results. These findings contribute to understanding the interfacial pullout behavior of steel fibers-UHPMC matrix, providing data reference for the performance optimization of UHPMC.

Multi-scale experimental investigation on the structural behaviour of novel nanocomposite/natural textile-reinforced mortars

Natural fibre composites present a very appealing area of research for the structural strengthening of masonry structures. Natural fibres possess several drawbacks, such as low initial stiffness and poor interfacial bond behaviour with inorganic matrices that hinder their functions. Such challenges were overcome by applying an innovative nanocomposite-based impregnation system that was pre-engineered and presented by the authors previously. In this paper, a full experimental study involving pullout, tensile tests and large-scale testing via diagonal compression test was carried out to evaluate the structural efficiency of the developed system. Remarkable improvement at yarn-to-matrix level upon nanocomposite coating was observed. At a medium bond length, yarn rupture was observed, highlighting the great anchorage provided by the nanocomposite coating within the matrix. Coupons cast with the developed system demonstrated outstanding composite behaviour and multicracking under tensile loading. Finally, wallets strengthened with the developed system displayed multiple cracks and maintained high shear capacity (40–60 % of τmax) at remarkably large displacements developed at later stages of the test. Such ductility is crucial for retrofitting masonry structures, especially in seismic areas.

CFRP-RC fracture strength prediction: A novel approach using deep learning

Externally bonded carbon fiber-reinforced polymer (CFRP) composites have been widely adopted for strengthening and repairing aging concrete structures. However, premature fracture at the CFRP-concrete interface remains a significant concern, necessitating a better understanding of the interfacial bond behavior and fracture mechanisms. Traditional experimental studies and numerical simulations have limitations in accurately capturing the complex nonlinear factors influencing this fracture behavior. This paper explores the novel application of machine learning (ML), specifically artificial neural networks (ANNs), for predicting the fracture strength of CFRP-reinforced concrete (CFRP-RC) members. ANNs enable mapping the intricate relationships between input parameters (e.g., CFRP/concrete properties, geometric configurations) and fracture responses through iterative training on experimental data. Key aspects include comprehensive data collection, preprocessing techniques, feature selection methods like mean impact value (MIV) analysis, and neural network architecture design. The paper highlights successful ANN applications in predicting CFRP-RC bond strength, shear capacity, and overall fracture behavior. A systematic approach is proposed for developing robust ANN models tailored to CFRP-RC fracture prediction, encompassing data curation, input variable screening, network training/validation, and model interpretability analyses. By leveraging ML’s ability to handle multifaceted nonlinearities, this data-driven framework offers a powerful alternative to traditional methods, potentially enhancing the design, analysis, and performance evaluation of CFRP-strengthened concrete structures.

Impacts of interfacial bonding between concrete substrate and cast/sprayed HPFRCC on flexural behaviour

The performance of repair materials is greatly enhanced by the integrity of the rehabilitation system, which depends on the behaviour of the boundary or interface bond between the repair material and the concrete substrate. The effects of the implementation of repair materials (casting or spraying), the spraying direction and the roughness of the concrete substrate on the interfacial bond behaviour were experimentally investigated through four-point bending tests on prisms of size 300 × 76.2 × 40 mm. As a first step, 2 cm thick concrete substrates were fabricated with five different types of surface roughness. After 28 days of curing, the repair material (a high-performance (high-ductility) fibre-reinforced cementitious composite (HPFRCC)) was sprayed or poured into specific moulds. The HPFRCC was developed using local materials and had a tensile strain capacity of 3.7%. The spraying direction and surface roughness of the concrete substrate were found to impact the ultimate deflection rate significantly; upward spraying produced the lowest deflection rate and downward spraying the highest. Because beams are often repaired from the lower part and spraying is in the upwards direction, the casting method must be used because of the negative effect of gravity on the interfacial bonding between the concrete substrate and the repair material.

3D meso-scale modeling of bond behavior between helical strand and concrete

Excellent interfacial bonding is the foundation for the strand and concrete working together. Helical structure of strand causes its rotation during the pull-out process, which makes it difficult to quantify the bond-slip at the interface. A three-dimensional (3D) meso-scale numerical model is first established to investigate the bond behavior at strand-concrete interface in this study. A refined modeling method is proposed to build a helical strand with the longitudinal helix shape and transverse flower-like shape. The heterogeneous concrete composed of three-phase composite material is built based on the random aggregate model. The interaction between strand and concrete is implemented by the surface-to-surface contact strategy. The rationality of the proposed model is verified by the experimental results. The effects of the helical structure of strand, the lay length of strand, aggregate content and eccentricity of strand on interfacial bond behavior are discussed. The results indicate that considering the helical structure of strand and heterogeneity of concrete can more accurately describe the stress distribution at the strand -concrete interface. The proportion of twisting slip is lower than that of longitudinal slip in the whole pull-out process, and its proportion increases first and then decreases. The interfacial bond strength increases first and then decreases with the increase of lay length of strand and aggregate content, and it reaches the best when the lay length is 14 time of diameter with the aggregate content of 45 %.

A multiscale experimental study of CFRP-UHPFRC interfacial bond behaviour: Failure mechanisms and a fibre volume dependent bond-slip law

Carbon fiber reinforced polymer (CFRP) materials are being increasingly used with ultra high performance fiber reinforced concrete (UHPFRC) to construct composite structural members making use of their unique properties. As the interfacial bond behaviour between CFRP and UHPFRC plays a key role in the design of such members, it was investigated in detail by multiscale experiments of single shear pull-off tests of 26 CFRP-UHPFRC bonded joints with different bond lengths and widths of CFRP laminates and 0.5–4% volume fraction (Vsf) of straight high-strength steel fibers (length = 13 mm, diameter = 0.2 mm). 12 CFRP-normal strength concrete (NSC) bonded joints were also tested for comparison. The surface strain evolution and the interfacial debonding process were captured and analysed by the digital image correlation (DIC). The complex microscale failure mechanisms, such as the mortar cracking, the CFRP-UHPFRC interfacial debonding, and the steel fibers’ slipping and pulling out of the mortar, were visualised and analysed by the 3D micro X-ray Computed Tomography (μXCT) scanning. It was found that the debonded layer of mortar under the laminates was much thinner than that in the CFRP-NSC bonded joints, due to the lack of coarse aggregates in UHPFRC. The peak pulling forces for the specimens with Vsf = 0.5%, 1%, 2%, and 4% were 9%, 21%, 28%, and 29% higher than those without steel fibers, respectively. An empirical bond strength model and an interfacial bond-slip model were proposed based on the test results, accounting for Vsf, the material properties, and the laminate to UHPFRC width ratio. Finally, the proposed bond-slip model was applied in finite element modelling to simulate the flexural behaviour of an FRP-UHPFRC composite deck in the literature, with the interfacial debonding failure and the ultimate loads successfully predicted.

Identifiability of the parameters contained in a cyclic cohesive zone model for CFRP-to-steel bonded joints

The application of externally bonded CFRP reinforcements has shown its effectiveness in reducing crack growth and extending fatigue life of steel elements subjected to cyclic loadings. Failure usually occurs due to cohesive debonding within the adhesive interface and therefore the interfacial behavior is crucial in guaranteeing the effectiveness of the bonded system. The adoption of cohesive zone models represents a valid approach for the description of interfaces between two adherends (i.e. CFRP and steel substrate), providing a useful tool for the analytical and numerical investigation of CFRP-to-steel bonded systems. An important issue generally associated with the use of a cohesive model is the correct calibration of its parameters, necessary to guarantee a reliable use of the model. Therefore, this work proposes a robust inverse analysis procedure to investigate the identifiability of the parameters governing the fatigue behavior of an exponential cyclic cohesive zone model. Single-lap direct shear tests are considered for the numerical investigation of the interfacial bond behavior. The input data chosen for the inverse algorithm are the axial strain measurements in a discrete number of points along the bonded interface and the values of relative displacement between the two adherends measured at peak and valley of each cycle at the specimen loaded end (i.e. the global slip). Virtual data perturbed by different levels of noise are used and a meta-model reduction technique is adopted to reduce the computational cost of the forward operator and to solve the inverse problem in a stochastic context through a Monte Carlo like procedure.

Interfacial bond behavior between normal OPC concrete and self-compacting geopolymer concrete enhanced by nano-SiO2

This study investigated the interfacial bond performances between ordinary Portland cement concrete (OPCC) and self-compacting geopolymer concrete (SCGC). The studied factors include nano-SiO2, repair material type, curing time, casting direction, and interface pretreatment method. The interfacial bond performances were assessed by Bi-surface shear and drying shrinkage tests. The evolutions in elemental compositions, hydration products, and microstructure in the matrix and interface were verified by BSE/EDS, XRD, and FTIR tests, respectively. ANOVA analysis was conducted to quantitatively analyze the influences of each factor from a statistical approach. The results demonstrated that the bond strength of SCGC increased by 24.5% to 31.7% compared to conventional OPCC. Meanwhile, geopolymers exhibited more compact microstructures but higher drying shrinkage (εsh,u=891 µε). While nanofillers significantly amplified the cracking potential of geopolymers, which was attributed to the higher early-stage autogenous shrinkage instead of drying shrinkage. The SCGC showed a high enrichment degree of calcium at the interface, indicating that more calcium-rich products were formed. In contrast, the use of nano-SiO2 in SCGC caused the enrichment of Na, Al, and Si at the interfacial regions, which provided extra nucleation sites for the polymerization of (C, N)-A-S-H gels. The nano-SiO2 enhanced the intensity of the hydroxide ion and Si-O-T band and promoted the formation of (C, N)-A-S-H gels. The ANOVA analysis proved that the repair material, nano-SiO2, and interface treatment were significant factors to affect the interfacial bond strength. In addition, geopolymer-based repair materials were less sensitive to the casting direction, which differed from the conventional self-compacting OPCC.

Experimental and numerical simulation research on the flexural performance of beams reinforced with GFRP bars and three-sides UHPC layer

This paper presents the results of the experimental investigation and numerical investigation conducted to study the flexural response of reinforced concrete beams reinforced with glass fiber reinforced polymer (GFRP) bars using three-sides ultrahigh performance concrete (UHPC) layer. The interface treatment of bubble wrap was applied in the internal surface of UHPC layer to ensure the enough interfacial bond behavior between UHPC layer and original concrete. Three tested beams, including two beams reinforced with three-sides UHPC and a reference beam, were studied through four-point bending tests and the effectiveness of flexural strengthening scheme associated with three-sides UHPC layer was evaluated. The results showed that the cracking load and ultimate load of beams reinforced with UHPC increased by 36.7%, 55.3%, and 30.0%, 42.7%, respectively, relative to the reference beam. The employment of UHPC layer could effectively control the development of surface crack width in beams. In addition, parametric studies were conducted to investigate the effects of the height of the UHPC, the thickness of the UHPC on both sides, and the longitudinal length of the three-sided UHPC layer using finite-element (FE) analysis. The results of numerical simulation were good agreement with the experimental results, indicating that the proposed finite element model could accurately predict the flexural responses of beams.

Development of ultra-light foamed insulation materials and interfacial bond behavior with fiber-reinforced alkali-activated composites

Due to the complex construction process, short service life and serious environmental pollution, the traditional insulation engineering and formwork engineering have caused great challenges and obstacles to the realization of the " dual carbon " goal. This study developed a new green external insulation system that integrates insulation and formwork based on alkali activation technology. The preparation technology of ultra-light foam insulation material (ULFIM) and the interface design method between ULFIM and fiber reinforced alkali-activated composite material (FRAC) were proposed. The effects of rice husk ash (RHA) and polyethylene (PE) fiber content on the dry density, thermal conductivity, compressive strength, volumetric water absorption, and pore structure parameters of ULFIM were studied. The effects of groove width, groove depth, groove spacing, and groove density on the interfacial bond behavior of FRAC-ULFIM were discussed. The microstructure of ULFIM and the interface transition zone morphology of FRAC-ULFIM and FRAC-extruded polystyrene (XPS) were observed using scanning electron microscopy (SEM), and the mechanism of influencing factors on the corresponding indicators were revealed. The results showed that adding an appropriate amount of RHA and PE fiber had a significant positive effect on improving the performance of ULFIM. In the past, the optimal dry density and thermal conductivity of ULFIM were only 191.5 kg/m3 and 0.0494 W/(m·K), respectively, and the compressive strength at 7 d could be as high as 0.49 MPa. In addition, interface shear performance test results have shown that the "bridging effect" of PE fiber can effectively improve the shear strength and ductility of FRAC-ULFIM, which was 23.7% higher than the interface shear strength of FRAC-XPS under the same conditions. The groove treatment increased the interfacial shear strength of FRAC-ULFIM from 74.59 kPa to 266.37 kPa, with a maximum increase rate of 257.11%. The proposed new green external insulation system has significant potential application value.

Test and analysis of the interfacial bond behaviour of circular concrete-filled wire-arc additively manufactured steel tubes

Interfacial bond behaviour of the circular concrete-filled wire-arc directed energy deposition (DED) steel tubes was investigated experimentally, in which wire-arc DED, commonly referred to as wire-arc additive manufacturing (WAAM), represents a metal 3D printing method. Firstly, a 3D laser scanning was employed to generate the 3D models of the WAAM steel components to obtain the geometric features. A parameter relating to the surface undulation was proposed to evaluate the roughness of the WAAM steel tubes. The results of tensile testing undertaken to obtain the mechanical properties of the WAAM material were summarised. Twelve push-out specimens were tested to obtain the load-slip response and bond strength, while the influence of surface undulation, diameter-to-thickness ratio and interface length was also assessed, respectively. The test results demonstrated that: 1) after reaching the peak load, a slowly descending region appeared until a relatively stable residual load was achieved; 2) the average bond stresses of the push-out specimens were greater than those of the push-out specimens fabricated by conventional steel tubes and even checkered steel tube. Comparisons of the bond strength of the push-out specimens against existing structural design standards indicated the design guidelines of various codes were quite conservative. There needs to consider the influence of the surface undulation of the WAAM steel tube. Finally, based on the nonlinear regression of the test data generated in the present study, an empirical equation was proposed for the prediction of the average bond strength for concrete-filled WAAM steel tubes.

Mechanical Properties and Durability of Textile Reinforced Concrete (TRC)-A Review.

Textile reinforced concrete (TRC) is an innovative structure type of reinforced concrete in which the conventional steel reinforcement is replaced with fibre textile materials. The thin, cost-effective and lightweight nature enable TRC to be used to create different types of structural components for architectural and civil engineering applications. This paper presents a review of recent developments of TRC. In this review, firstly, the concept and the composition of TRC are discussed. Next, interfacial bond behaviour between fibre textile (dry and/saturated with polymer) and concrete was analysed considering the effects of polymer saturation, geometry and additives in polymer of the textile. Then, the mechanical properties (including static and dynamic properties) of TRC were reviewed. For static properties, the mechanical properties including compression, tension, flexural, shear and bond properties are discussed. For dynamic properties, the impact, seismic and cyclic properties were investigated. Furthermore, the durability of TRC under different environmental conditions, i.e., temperature/fire, humidity and wet-dry cycles, freeze-thaw, chemical and fatigue were discussed. Finally, typical engineering applications of TRC were presented. The research gaps which need to be addressed in the future for TRC research were identified as well. This review aims to present the recent advancement of TRC and inspire future research of this advanced material.

Influence of temperature on the SMA-PDMS interfacial bond behavior and its modeling with temperature dependent trapezoidal cohesive law

Soft actuators composed of shape memory alloy (SMA) wires embedded in polydimethylsiloxane (PDMS) matrix are potential in shape-morphing structures and soft robots. However, the SMA-PDMS interface is inevitably subjected to high temperatures during actuation due to Joule heating of the SMA, which affects its bond properties. However, knowledge of how temperature impacts SMA-PDMS interfacial bond properties is still insufficient. This paper conducted fiber pull-out experiments at various interface temperatures to monitor and trace the debonding process with high-speed camera. Results show that the maximum debonding load, critical debonding displacement, and friction load are in exponential decay with interface temperature. Notably, interfacial strength degradation exceeds 50 % when the interface temperature increases from 25 °C to 100 °C, and the traction-separation behavior of SMA-PDMS interface shifts from trapezoidal to triangular as the interface temperature increases. A finite element model was developed to simulate the debonding behavior of SMA-PDMS, in which the interface was modeled using the cohesive zone model with temperature-dependent trapezoidal constitutive law. Simulation results agree well with experiments. Stress distribution during the interface debonding process was also analyzed and discussed. The work demonstrates the importance of accounting for interface bond strength degradation caused by temperature in the design of SMA-PDMS soft actuators.

Combined corrosion and inclination effects on pullout behavior of various steel fibers under wet-dry cycle deterioration

The interfacial bond behavior of corroded fibers in cracked steel fiber reinforced concrete (SFRC) is critical for understanding its structural deterioration performance, while available research focused on aligned straight or hooked-end fibers. This study investigated the combined effects of corrosion and inclination on the pullout performance of various steel fibers bridging artificial cracks exposed to wet-dry cycles of chlorides. Three deformed steel fibers, i.e., hooked-end (H), crimped (C), and milled-cut (M) fibers, with three angles of 0°, 30°, and 45° were examined under both uncorroded and corroded conditions. After corrosion, the average bond strength of H fibers was enhanced due to increased roughness and compact rust layer if the high inclination-induced fracture was avoided, while that of C and M fibers was decreased at various angles because of loose and porous rusts. The highest bond strengths of corroded H, C, and M fibers were discovered at 30°, 30°, and 0°, as a result of the combined mechanisms of snubbing effect, matrix spalling, or corrosion-induced fracture. The ultimate displacement of all fibers increased with angles due to increased matrix spalling area and fiber plastic deformation. The inclination effect of corroded fibers was more significant on energy absorption capacity than average bond strength, regardless of fiber type. A degradation model that describes the snubbing and matrix spalling effects, as well as the corrosion-induced deterioration and fracture was developed, based on which the critical inclination angle was found to decrease with increasing embedded length and decreasing tensile strength.

Structural behavior of CFRP-strengthened steel beams at different service temperatures: Experimental study and FE modeling

The structural performance of externally bonded carbon fiber-reinforced polymer (CFRP)-strengthened steel beams can be affected by different service temperatures. This study carried out three-point bending tests on thirteen beams, including two un-strengthened steel beams and eleven CFRP-strengthened steel beams, at temperatures ranging from −20 °C to 60 °C. CFRP plates with two different lengths (i.e., 300 mm and 600 mm) were used for the strengthening. The load–deflection curves, ultimate failure loads and the strain evolutions in CFRP plates were measured and compared. The results showed that the steel beams strengthened with 300 mm CFRP plates were failed due to plate-end debonding at all temperatures, and the debonding load decreased with the temperature increase. In contrast, the steel beams strengthened with 600 mm CFRP plates were failed due to CFRP rupture at −20 °C to 45 °C but plate-end debonding at 60 °C. A finite element (FE) model was proposed for predicting the experimental results, in which the temperature-dependent interfacial bond behavior was properly considered based on the results from the previous CFRP-to-steel double-lap shear tests. The FE model was extensively validated through the comparisons between the experimental and FE results of load–displacement curves and CFRP strain distributions at various load levels.

Pullout damage analysis of steel fibers under dynamic load based on numerical simulation

FRC is constantly subjected to dynamic loads during its service period, and dynamic pullout behavior of the fibers and the coupling effect between fibers can significantly affect the crack initiation and propagation of FRC. In this paper, based on the single fiber pullout behavior of experimental and numerical results, the failure process of the twin fibers dynamic pullout test was simulated by RFPA3D program with discontinuous and heterogeneous characteristics. The influence of fiber embedding length and fiber spacing on the interfacial bond behavior were analyzed in details. The internal damage degree, crack propagation, and interfacial shear stress of all test series were quantitatively characterized. The results indicate that the specimens with various fiber embedding lengths and fiber spacings present distinct damage evolution patterns. The decrease of the peak of AE events is followed by an increase, when the fiber embedding length is increased. In addition, the fiber spacing has a large influence on the distribution and transmission of interfacial shear stress. With the increase of fiber spacing, the peak of interfacial outside shear stress increases, while the peak value of interfacial inside shear stress gradually decreases. Meanwhile, the AE-accumulative energy presents a trend of decreasing first and then increasing.