Search Results (84)

Polyethylene storage tanks are widely used for storing water and chemicals due to their lightweight and corrosion-resistant properties. Despite these advantages, their structural performance under seismic conditions remains a concern, mainly because of their low mechanical strength and weak bonding characteristics. In this study, a method of external strengthening using fiber-reinforced polymer (FRP) laminates is proposed and explored. The research involves a combination of laboratory testing on carbon fiber-reinforced polymer (CFRP)-strengthened polyethylene strips and finite element simulations aimed at assessing bond strength, anchorage length, and structural behavior. Results from tensile tests indicate that slippage tends to occur unless the anchorage length exceeds approximately 450 mm. To evaluate surface preparation, grayscale image analysis was used, showing that mechanical sanding increased intensity variation by over 127%, pointing to better bonding potential. Simulation results show that unreinforced tanks under seismic loads display stress levels beyond their elastic limit, along with signs of elephant foot buckling—common in thin-walled cylindrical structures. Applying CFRPs in a full-wrap setup notably reduced these effects. This approach offers a viable alternative to full tank replacement, especially in regions where cost, access, or operational constraints make replacement impractical. The applicability is particularly valuable in seismically active and densely populated areas, where rapid, non-invasive retrofitting is essential. Based on the experimental findings, a simple formula is proposed to estimate the anchorage length required for effective crack repair. Overall, the study demonstrates that CFRP retrofitting, paired with proper surface treatment, can significantly enhance the seismic performance of polyethylene tanks while avoiding costly and disruptive replacement strategies. Full article

Carbon fiber-reinforced polymers (CFRP) are widely used composite materials in structural applications, where their mechanical performance is significantly influenced by interfacial shear strength (IFSS). The single fiber fragmentation test (SFFT) is a common technique for characterizing IFSS, but its reliance on optical microscopy makes it time-consuming and impractical for opaque matrices. This study presents an alternative methodology based on acoustic emission (AE) analysis, enabling the estimation of fragment lengths through statistical modeling. The AE technique captures the energy released during fiber fragmentation, represented as AE bursts, whose accurate detection is crucial. A signal-processing approach based on progressive simplification enhances burst detection. To refine the estimation of fragment lengths, a gamma distribution is fitted to experimental data, accounting for observed asymmetry in optical measurements. Results indicate that this approach achieves an IFSS determination error of 14.16% at a 95% confidence level. This study demonstrates the feasibility of using AE for IFSS characterization in SFFT and contributes to future research on AE applications in composite materials. Full article

The combination of fiber reinforced polymer (FRP) and engineered cementitious composite (ECC) has emerged as a promising method for strengthening reinforced concrete (RC) structures. By embedding FRP within an ECC to form a composite reinforcement layer, the advantages of both materials can be effectively harnessed, and the dense ECC matrix can be employed to safeguard FRP from adverse environments. Significantly, the interface bonding property constitutes the key for the two materials to collaborate effectively. In light of the research gap related to the bonding performance of embedded FRP strips in ECC joints, this study conducted a bench-scale investigation into the pull-out behavior of carbon FRP (CFRP) strips within an ECC. The relationship between the average bonding strength (2.84 MPa~4.77 MPa) and the embedded length of FRP strips was established. Additionally, the pull-out mechanism of FRP strips within an ECC matrix was utilized to elucidate the influence of the embedded length on the distinct behavior of FRP strips within an ECC. An analytical method for predicting the full-range behavior of embedded FRP strip–ECC joints by using a trilinear bond–slip relationship was introduced. Four key parameters of the trilinear bond–slip relationship for embedded FRP strip–ECC joints were provided to meet the requirements of future engineering applications. Full article

Self-piercing riveting (SPR) has become a highly promising new method for connecting dissimilar materials in multi-material vehicle bodies, while the joint’s forming quality which largely affects its connection performance lacks sufficient research. This study conducted a detailed numerical investigation on the forming quality of carbon-fiber-reinforced polymer (CFRP)/aluminum alloy (Al) SPR joint and proposed a novel multi-objective optimization strategy. First, the finite element (FE) model of CFRP/Al SPR joint forming was established and then verified to monitor the forming process. Second, based on FE numerical simulation, the action laws of rivet length and die structural parameters (die depth, die gap, and die radius) on the joint’s forming quality indicators (bottom thickness and interlock value) were systematically studied to reveal the joint’s forming characteristics. Finally, taking the rivet length and die structural parameters as design variables and the above forming quality indicators as optimization objectives, a hybrid Taguchi–Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) method was proposed to conduct the multi-objective optimization of the joint’s forming quality. According to the outcomes, the bottom thickness and interlock value of the joint were respectively increased by 10.18% and 34.17% compared with the baseline design, achieving a good multi-objective optimization of the joint’s forming quality, which provides an effective new method for efficiently predicting and improving the forming quality of the CFRP/Al SPR joint. Full article

This study investigates the interfacial bond behavior of clay brick masonry strengthened with carbon fiber-reinforced polymer (CFRP) through single-side shear tests. Two specimen types (single bricks and masonry prisms) were tested under varying parameters, including bond length, bond width, mortar joints, and end anchorage. Experimental results revealed cohesive failure within the masonry substrate as the dominant failure mode. Mortar joints reduced bond strength by 12.1–24.6% and disrupted stress distribution, leading to discontinuous load–displacement curves and multiple strain peaks in CFRP sheets. Increasing bond width enhanced bond capacity by 16.3–75.4%, with greater improvements observed in single bricks compared with prisms. Bond capacity initially increased with bond length but plateaued (≤10% increase) beyond the effective bond length threshold. End anchorage provided limited enhancement (<14%). A semi-theoretical model incorporating a brick–mortar area proportion coefficient (χ) and energy release rate was proposed, demonstrating close alignment with experimental results. The findings highlight the critical influence of mortar joints and provide a refined framework for predicting interfacial bond strength in CFRP-reinforced masonry systems. Full article

A shape-controllable laser-engraving treatment (LET) and aramid pulp (AP)-reinforced resin pre-coating (RPC) were used on a titanium (Ti) alloy surface to construct micro-/nano-aramid pulp and epoxy (MAPE) coatings for greater bonding strength with carbon fiber-reinforced polymers (CFRPs). The array pits of regular hexagon on the Ti alloy surface were engraved and vertical spaces between the array pits were created to place the AP-reinforced epoxy for stronger mechanical interlocking. The specimen treated with laser engraving (side length of 0.3 mm) and AP-reinforced RPC yielded the greatest bonding strength of 27.1 MPa, 67.4% higher than the base strength. The failure modes of the Ti-CFRPs composites changed from debonding failure at the Ti/epoxy surface to fiber-damaged failure of the laminated CFRPs panels. The shape-controllable LET and simple AP-reinforced RPC were confirmed as the most feasible and effective combined methods for use on titanium alloy surfaces for manufacturing stronger Ti-CFRPs composites, which exhibited the potential for application in other metal–matrix-bonding composite systems. Full article

The key structural components of a wind turbine blade, such as the skin, spar cap, and shear web, are fabricated from fiber-reinforced composite materials. The spar, predominantly manufactured via resin infusion—a process of resin injection and curing in carbon fibers—is prone to initial defects, such as pores, wrinkles, and delamination. This study suggests employing the pultrusion technique for spar production to consistently obtain a uniform cross-section and augment the reliability of both the manufacturing process and the design. In this context, this study introduces carbon fiber-reinforced polymer (CFRP/CFRP) and glass fiber-reinforced polymer (GFRP/CFRP) test specimens, which mimic the bonding structure of the spar cap, utilizing pultruded CFRP in accordance with ASTM standards to analyze the delamination traits of the spar. Delamination tests—covering Mode I (double cantilever beam), Mode II (end-notched flexure), and mixed mode (mixed-mode bending)—were performed to gauge displacement, load, and crack growth length. Through this crack growth mechanism, the interlaminar fracture toughness derived was examined, and the stiffness and strength changes compared to CFRP based on the existing prepreg manufacturing method were analyzed. In addition, the interlaminar fracture toughness for GFRP, which is a material in contact with the spar structure, was analyzed, and through this, it was confirmed that the crack behavior has less deviation compared to a single CFRP material depending on the stiffness difference between the materials when joining dissimilar materials. This means that the higher the elasticity of the high-stiffness material, the higher the initial crack resistance, but the crack growth behavior shows non-uniform characteristics thereafter. This comparison provides information for predicting interlaminar delamination damage within the interior and bonding area of the spar and skin and provides insight for securing the reliability of the design life. Full article

The focus of this paper is on estimating the stress concentration factor of circular hollow section KK-joints with different geometric parameters and subsequently assessing the effectiveness of carbon fiber-reinforced polymer (CFRP) wrapping for repairing joints with cracks. Different geometric parameters, such as θ (brace inclination angle), γ (the ratio of the outer diameter to the wall thickness of the chord), and τ (the thickness ratio of the brace to the chord), were studied to investigate changes in stress concentration using numerical simulation. The results indicated that the stress concentration factor was most sensitive to changes in θ, followed by γ. Subsequently, the effect of crack length and depth was analyzed to simulate cracks in joints subjected to reciprocating load. The results showed that changing D from T/16 to T/2 (where T is the thickness of the chord) can cause more stress concentration, with an average of 8.37%. Next, damaged joints were wrapped in carbon fiber-reinforced polymer as a repair. Analysis of the effects of different layers and directions of polymer wrap revealed that even six layers of wrapping effectively reduced the stress concentration compared to the initial model. Finally, based on the results of parametric analysis and nonlinear fitting, a calculation formula for the stress concentration factor suitable for KK-joints under axial loads is proposed. Full article

This study investigates the optimization of carbon fiber-reinforced polymer (CFRP) sheet dimensions and anchorage configurations to enhance the flexural performance of concrete beams while maintaining cost-effectiveness. Eight beam specimens, incorporating variations in CFRP length, width, and anchorage systems, were tested under a three-point bending setup. A systematic approach was employed to evaluate key structural performance metrics, including normalized ultimate load capacity, energy absorption index, and relative deflection index, while minimizing material usage. The results revealed that the W.L.2U configuration, featuring full-length and full-width CFRP sheets with double U-wraps, delivered the highest performance, achieving a 161% increase in ultimate load capacity, an 822% improvement in energy absorption, and superior deflection. Comparative analysis highlighted critical trade-offs between material efficiency and performance, with configurations with full-width and half-length, such as W.0.5L, balancing efficiency and load-bearing enhancements. This study demonstrates that optimizing CFRP configurations, particularly in terms of length, width, and anchorage, is essential for maximizing structural performance while minimizing material usage, offering practical insights for cost-effective and performance-driven structural retrofitting applications. Full article

This study investigates the tensile behavior of carbon-fiber-reinforced polymer (CFRP) and textile-reinforced mortar (TRM) under various design variables to enhance understanding and application in construction structures. TRM reinforced with CFRP grids is highly effective for strengthening existing structures due to its lightweight nature, durability, ease of installation, and corrosion resistance. The research aims to evaluate how design parameters such as the CFRP grid type, mortar matrix strength (influenced by the water-to-cement ratio), specimen length, and grid width affect TRM’s mechanical properties. Through the direct tensile test using a universal testing machine, TRM specimens were subjected to load until failure, with data collected on stress–strain relationships, crack patterns, and strengths. Specimens included untreated CFRP grids (Groups KC, Q47, and Q85) and sand-coated CFRP grids (Specimens AQ47_7 and AQ85_7), each tested under controlled laboratory conditions. The results indicate that crack formation significantly influenced load transfer mechanisms within the specimens, with longitudinal strands bearing load as cracks propagated through the mortar matrix. The presence of sand-coated CFRP grids notably enhanced interfacial bond strength, leading to increased cracking strength and ultimate strength compared with their untreated counterparts. The findings underscore the importance of the surface treatment of CFRP grids for improving TRM performance, with implications for enhancing structural integrity and durability in practical applications. The results provide valuable insights into optimizing TRM design for better crack control and mechanical efficiency in infrastructure. Full article

Due to increasing mobility and energy conservation needs, improving bus and coach safety without adding weight is essential. Many crashes with fatal outcomes for vehicle occupants are associated with the rollover of the vehicle, revealing the structural weakness of the steel pillars between windows, which must resist high levels of bending during rollovers. This study aims to reinforce these pillars with expired carbon fiber prepreg from the aircraft industry, improving safety and reducing environmental waste. To manufacture the pillars, shot-blasted hollow S275 steel tubes with a side length of 25 mm and a thickness of 1.5 mm were used. Bidirectional GG600T woven carbon fiber, CF, and aircraft-grade recycled carbon fiber-reinforced plastic, rCFRP, prepreg M21EV/IMA/3 were used as composite reinforcements. The first composite was made from a CF weave using the rigid epoxy resin Sicomin^® 8500/Sicomin^® SD8601. The rCFRP composite was frayed, and a new composite was made with the same rigid epoxy resin. Both composites were joined to the steel tube using a tough structural adhesive (SikaPower^® 1277). A third composite was obtained using the frayed rCFRP and the structural adhesive as a polymer matrix. All composites were treated with an APPT (atmospheric-pressure plasma torch) before being joined to the steel pillar with the structural adhesive. The comparison of the three reinforcements showed that the steel reinforced with the recycled prepreg composite manufactured with the rigid adhesive performed best, with a 50% increase in specific bending strength and only a 32% increase in weight. It also absorbed 71% more energy, which shows that this novel option for upcycling can noticeably increase the crashworthiness of structures. Full article

Carbon-fiber-reinforced polymer (CFRP) laminates have gained attention for their potential to reduce carbon emissions in construction. The impact of carbon-fiber-reinforced polymer (CFRP Laminate) on carbon emissions and the influence of elasto-plastic analysis on this technique were studied in this research. This study focuses on how CFRP can affect the environmental footprint of reinforced concrete structures and how elasto-plastic analysis contributes to optimizing this strengthening method. Four flat RC slabs were created to evaluate this technique in strengthening. One slab was used as a reference without strengthening, while the other three were externally strengthened with CFRP. The slabs, which were identical in terms of their overall (length, width, and thickness) as well as their flexural steel reinforcement, were subjected to concentrated patch load until they failed. The strength of two-way RC slabs was analyzed using a concrete plastic damage constitutive model (CDP). Additionally, CFRP strips were applied to the tension surface of existing RC slabs to improve their strength. The load–deflection curves obtained from the simulations closely match the experimental data, demonstrating the validity and accuracy of the model. Strengthening concrete slabs with CFRP sheets reduced central deflection by 17.68% and crack width by 40%, while increasing the cracking load by 97.73% and the ultimate load capacity by 134.02%. However, it also led to a 15.47% increase in CO₂ emissions. Also, the numerical results show that increasing the strengthening ratio significantly impacts shear strength and damage percentage. Full article

Corroded steel pipelines are particularly vulnerable to failure due to ground movement, which highlights the need to improve their seismic resistance through reinforcement methods. This paper establishes a three-dimensional finite element model of a corroded steel pipeline subjected to a reverse fault, which considers the effects of the corrosion position and depth, winding thickness, and length of carbon fiber-reinforced polymer (CFRP), to investigate the stress, strain, elliptic deformation, and failure modes of the pipeline before and after CFRP reinforcement. Results indicate that the main failure mode of the intact and corroded pipeline crossing the reverse fault is local buckling. Corrosion intensifies the response of the cross-fault pipeline, accelerates its failure occurrence, and promotes transformation from a single failure mode to multiple failure modes. For CFRP reinforcement, an increase in CFRP winding thickness can effectively inhibit the growth of the pipeline’s compressive strain, thus reducing the buckling potential. Each additional CFRP layer can further enhance the overall buckling resistance but at a decreasing rate. Similarly, longer CFRP winding improves buckling resistance though the effectiveness per meter decreases. Therefore, it is recommended that the thickness and length of CFRP winding on the pipeline should be optimized to obtain the best reinforcement at a reasonable cost. Full article

A carbon fiber-reinforced polymer (CFRP) is a common material utilized for the enhancement in reinforced concrete (RC) constructions. Previous research indicates that the bonding performance between a CFRP sheet and concrete determines whether the bonding of CFRP material is effective. However, the majority of existing research on the bonding performance of the CFRP–concrete interface is concentrated on static loading conditions. In order to clarify the effect of dynamic load on the bonding performance of the CFRP sheet–concrete interface, this study adopts the double-sided shear test method to carry out dynamic experimental research. The test findings reveal that the damage pattern of the CFRP sheet–concrete interface remains consistent across different loading rates. The ultimate bearing capacity increases as the strain rate increases. As the strain rate increases from 10⁻⁵ s⁻¹ to 10⁻² s⁻¹, the effect of bond length on ultimate bearing capacity increases by about 7%. As the strain rate increases, both the maximum strain of CFRP and the maximum interfacial shear stress demonstrate a corresponding increase, with respective increase rates of 60% and 20%. The effective bond length decreases by about 20% when the strain rate rises from 10⁻⁵ s⁻¹ to 10⁻² s⁻¹. Finally, a formula for calculating the dynamic effective bond length of a CFRP sheet, grounded in the Chen and Teng formula, has been proposed and verified. Full article

Aiming at evaluating the bond strength of fiber-reinforced polymer (FRP) rebars in ultra-high-performance concrete (UHPC), boosting machine learning (ML) models have been developed using datasets collected from previous experiments. The considered variables in this study are rebar type and diameter, elastic modulus and tensile strength of rebars, concrete compressive strength and cover, embedment length, and test method. The dataset contains two test methods: pullout tests and beam tests. Four types of rebar, including carbon fiber-reinforced polymer (CFRP), glass fiber-reinforced polymer (GFRP), basalt, and steel rebars, were considered. The boosting ML models applied in this study include AdaBoost, CatBoost, Gradient Boosting, XGBoost, and Hist Gradient Boosting. After hyperparameter tuning, these models demonstrated significant improvements in predictive accuracy, with XGBoost achieving the highest R² score of 0.95 and the lowest Root Mean Square Error (RMSE) of 2.21. Shapley values analysis revealed that tensile strength, elastic modulus, and embedment length are the most critical factors influencing bond strength. The findings offer valuable insights for applying ML models in predicting bond strength in FRP-reinforced UHPC, providing a practical tool for structural engineering. Full article