Search Results (1,470)

Reinforced concrete two-way slabs are important elements in the construction field, and their impact response under drop-weight impact is a complex mechanical issue that can cause the collapse of heavy structures. Previous research has documented the analysis of conventional steel-reinforced concrete slabs under impact loads. However, the investigation of layered hybrid concrete composite flat solid slabs reinforced with carbon-fiber-reinforced polymer (CFRP) rebars is an innovative subject. This paper examines the structural behavior of layered novel hybrid concrete composite flat solid slabs with a combination of reactive powder concrete (RPC) in the top layer and normal concrete (NC) in the bottom layer, reinforced with internal CFRP or traditional steel bars in the tension zone, under an impact load test. For this purpose, ten full-scale square flat solid slab samples with a 1550 mm length and a 150 mm depth were fabricated and divided into eight layered hybrid concrete samples with 50% RPC and 50% NC and two samples cast with NC only. The impact tests were carried out using a hardened steel cylindroconical impactor (projectile) with a height of 650 mm and a diameter of 200 mm, a flat nose diameter of 90 mm, and a total mass of 150 kg released from two different heights of 5 and 7 m. The variables considered were the types and ratios of reinforcement, as well as the free-drop weight and height. The experimental results obtained showed that layered RPC flat solid slabs are superior in resisting and sustaining impact forces and also have fewer scattered parts when compared to NC flat solid slabs. Additionally, the flat solid slab samples reinforced with CFRP bar grids were overall more resistant to impact loads, by an average of 19%, compared to flat solid slabs with steel bars and showed lower deflection, by an average of 10%, compared to the other flat solid slabs. Full article

Stress shielding is a problem for traditional metal bone fixation plates made of magnesium and titanium alloys. This problem can be solved by using composite materials with a low elastic modulus. This study analyzed the effect of carbon fiber reinforced PEEK (CFRP) composites on stress shielding under static loading using finite element simulations. Callus formation times relative to the healing period were gradually imposed according to the elapsed time, considering 1% and 75% as healing stages. The Inventor© 3D CAD 2024 software was used for modeling, and the ANSYS© FEA R2023 software was used for analysis. The results showed that metal fixation plates made of titanium and magnesium alloys transferred less stress to the bone than the CFRP fixation plate. In particular, the use of the CFRP fixation plate resulted in a higher peak stress and a more uniform stress field in the bone, especially in the bone-plate contact area, where the risk of stress shielding is higher in the 1% and 75% healing phases. Full article

In the aerospace field, the riveting process is one of the main methods for connecting the Carbon Fiber Reinforced Polymer/Plastic (CFRP). During the riveting process, components are prone to problems such as damage to CFRP hole walls and reduction in joint strength. To this end, this paper proposes two new bushing structures based on riveting. The riveting damage behavior and mechanical properties of composite materials under three riveting methods: non-bushing, non-boss bushing, and boss bushing were compared. Furthermore, the tensile and hysteretic mechanical properties of CFRP under different riveting structures were studied. The results show that the stress distribution around the hole is more uniform than that of the non-bushing riveting method, and the delamination damage at the hole wall is significantly reduced. In the tensile test, the maximum tensile loads of the non-boss bushing and the boss bushing increased by 2.49% and 5.03% compared to the non-boss bushing schemes. In addition, the tensile failure modes of the three schemes also showed different failure modes due to different riveting forms. The failure mode of the non-bushing riveting scheme is rivet shear failure, and the failure mode of the bushing riveting scheme is rivet pull-off failure. In the hysteretic test, the maximum tensile loads of the non-boss bushing and the boss bushing increased by 5.49% and 12.03% compared to the non-bushing scheme. The failure mode of the three schemes is rivet pull-off failure. The bushing structure not only enhances the connection strength, but also improves the damage to the CFRP hole wall. This study provides a new understanding of the design and optimization of CFRP riveted connection structures. Full article

In this study, we took a closer look at the thermal recyclability of CFRP composites used in the manufacture of high-pressure cylinders. Thermal analysis was used to determine the minimum temperature at which stable resin decomposition begins. The aim was to find temperature parameters and retention times with which the pyrolysis process is as economically viable as possible, and the recovered fibers retain optimum mechanical properties. The surface morphology of fibers annealed in both inert and oxidizing atmospheres was examined. In addition, the mechanical strengths under static as well as dynamic conditions of the newly manufactured laminates containing the recovered fibers were investigated. During research, it was found that reusing fibers is very difficult. The recycled carbon fibers were successfully compressed in an epoxy matrix in the form of a pre-impregnated carbon mat with the presence of air. The presence of oxygen during the thermal degradation of the composite severely damaged the surface and structure of the carbon fiber, causing composites made from these fibers to be mechanically weaker by more than 247%. Full article

Carbon fiber reinforced polymer (CFRP) composites have very high specific properties, which is why they are used in the aerospace, wind power, and sports sectors. However, the high consumption of CFRP compounds leads to a high volume of waste, and it is necessary to formulate mechanical recycling strategies for these materials at the end of their useful life. The recycling differences between cutting-end mills and high-energy ball milling (HEBM) were evaluated. HEBM recycling allowed us to obtain small recycled particles, but separating their components, carbon fiber, epoxy resin, and CFRP particles, was impossible. In the case of mill recycling, these were obtained directly from cutting a CFRP composite laminate. The recycled materials resulted in a combination of long fibers and micrometric particles—a sieving step allowed for more homogeneous residues. Although long, individual carbon fibers can pass through the sieve. Ultrasonication did not significantly affect HEBM recyclates because of the high energy they are subjected to during the grinding process, but it was influential on end mill recyclates. The ultrasonication amplitude notably impacted the separation of the epoxy resin from the carbon fiber. The end mill and HEBM waste production process promote the presence of trapped air and electrostatics, which allows recyclates to float in water and be hydrophobic. Full article

Effectively evaluating the effectiveness of bridge strengthening is a necessary means to ensure the normal operation of existing strengthened bridges, especially when evaluating the effectiveness of bridge strengthening without interrupting normal traffic. Based on a distributed long-gauge Fiber Bragg Grating (FBG) sensor, this paper derived the macro-strain influence line (MSIL) formula for a simply supported beam bridge under a moving vehicle load, studied the changes in the MSIL at the bottom of the beam under the vehicle load before and after the prestressed CFRP plate strengthening, and proposed a rapid evaluation method for the strengthening effect based on the amplitude of the MSIL as the evaluation index for the strengthening effect. Finally, the prestressed CFRP-strengthened steel beam was tested under the moving vehicle load. The theoretical analysis and the experimental results confirm that under the load of moving vehicles, the macro-strain–time history amplitude of the strengthened steel beams under different prestressed tensioning conditions is different. The amplitude of the macro-strain time history of the strengthened bridge is reduced compared to before strengthening, and the local strengthening effect of the bridge can be monitored by the amplitude change in a single sensor. The change in global stiffness can be evaluated by monitoring the MSIL obtained from multiple long-gauge strain sensors. Full article

Prestressed spun high-strength concrete (PHC) piles are commonly used in various types of structures, including bridges, buildings and marine infrastructures. However, piles installed in aggressive environments are vulnerable to corrosion of the steel, which can lead to rapid degradation of the piles. As a corrosion-resistant material, carbon fiber-reinforced polymer (CFRP) is considered an alternative to steel tendons for durability enhancement. In this study, a new pile system with CFRP was proposed. Experimental tests of three full-scale piles and a numerical analysis of eight piles with various parameters were performed to investigate the flexural performance of CFRP prestressed spun high-strength concrete pile. The proposed piles were loaded under four-point bending after prestressing. The experimental and numerical results verified the feasibility of the proposed system, and the CFRP pile exhibited twice of flexural capacity of that of steel-reinforced piles. The flexural performance of the CFRP PHC pile was significantly affected by the reinforcement ratio, prestressing level and modulus of the CFRP. An analytical approach predicting the flexural capacity of the CFRP PHC pile was proposed based on the parametric study. Ninety percent accuracy was achieved for the proposed analytical approach. The presented study can significantly promote the application of CFRP in pile foundations and improve the durability of PHC piles. Full article

The use of hybrid materials as a combination of fibre-reinforced plastic (FRP) and metal is of great interest in order to meet the increasing demands for sustainability, efficiency, and emission reduction based on the principle of lightweight design. These two components can therefore be joined using the intrinsic joining technique, which is formed by curing the matrix of the FRP component. In this study, for the hybrid joint, unidirectionally pre-impregnated semi-finished products (prepregs) with duromer matrix resin and micro-alloyed HC340LA steel were used. In order to conduct a detailed investigation, the damage mechanisms of intrinsically produced fibre metal laminates (FMLs), a new clamping device, and a novel pressing tool were designed and put into operation. The prepregs were prestressed by applying a preloading force using a specially designed prestressing frame. Hybrid specimens were then produced and subjected to nanoindentation and a shear tensile test. In particular, the effect of the residual stress state by varying the defined prestressing force on the damage mechanisms was studied. The results showed that no fracture patterns occurred in the interface of the specimens without preloading as a result of curing at 120 °C, whereas specimens with preloading failed at the boundary layer in the tensile range. Nevertheless, all specimens cured at 160 °C failed at the boundary layer in the tensile range. Furthermore, it was proven that the force and displacement of the preloaded specimens were promisingly higher than those of the unpreloaded specimens. Full article

Fiber-reinforced polymer confinement is considered to be effective in the retrofitting of concrete structures. The current study explores the effectiveness of one- and two-layer carbon fiber reinforced polymer (CFRP) and multiwalled carbon nanotube (MWCNT) incorporated three-layer glass fiber reinforced polymer (GFRP) confinement on concrete cylinders under aggressive exposures, such as acid, alkaline, marine, water, and elevated temperatures. At 1 wt.% MWCNT by weight of the epoxy matrix, mechanical characteristics of the laminate show a significant improvement. In the case of acid exposure, the axial load-carrying capacity of concrete specimens with single-layer CFRP confinement was equal to that of MWCNT incorporated three-layer GFRP confinement (GF₃C₁-AC). The axial strain of GF₃C₁-AC was 23% and 12% higher than one and two-layer CFRP confinement. After exposure at 400 °C, in comparison with one- and two-layer CFRP confinement, the axial strain of MWCNT incorporated three-layer GFRP confined specimens increased by 50% and 20%, respectively, which proved the efficacy of MWCNT as a heat-resistant nanofiller. The ultrasonic pulse velocity (UPV) test indicates that the confinement system protects the concrete core from sudden failure by impeding crack propagation. The test results proved that the MWCNT incorporated FRP system can be considered as a prospective substitute for CFRP systems for retrofitting applications in severe environmental conditions. Full article

An intelligent optimization technique has been presented to enhance the multiple structural performance of PA6-20CF carbon fiber-reinforced polymer (CFRP) plastic injection molding (PIM) products. This approach integrates a deep neural network (DNN), Non-dominated Sorting Genetic Algorithm II (NSGA-II), and Monte Carlo simulation (MCS), collectively referred to as the DNN-GA-MCS strategy. The main objective is to ascertain complex process parameters while elucidating the intrinsic relationships between processing methods and material properties. To realize this, a numerical study on the PIM structural performance of an automotive front engine hood panel was conducted, considering fiber orientation tensor (FOT), warpage, and equivalent plastic strain (PEEQ). The mold temperature, melt temperature, packing pressure, packing time, injection time, cooling temperature, and cooling time were employed as design variables. Subsequently, multiple objective optimizations of the molding process parameters were employed by GA. The utilization of Z-score normalization metrics provided a robust framework for evaluating the comprehensive objective function. The numerical target response in PIM is extremely intricate, but the stability offered by the DNN-GA-MCS strategy ensures precision for accurate results. The enhancement effect of global and local multi-objectives on the molded polymer–metal hybrid (PMH) front hood panel was verified, and the numerical results showed that this strategy can quickly and accurately select the optimal process parameter settings. Compared with the training set mean value, the objectives were increased by 8.63%, 6.61%, and 9.75%, respectively. Compared to the full AA 5083 hood panel scenario, our design reduces weight by 16.67%, and achievements of 92.54%, 93.75%, and 106.85% were obtained in lateral, longitudinal, and torsional strain energy, respectively. In summary, our proposed methodology demonstrates considerable potential in improving the, highlighting its significant impact on the optimization of structural performance. Full article

The reliable anchorage of carbon fiber-reinforced polymer (CFRP) tendons is a critical issue influencing the stable bearing capacity of bridge cables. This study introduces a novel CFRP single-strand extrusion anchoring structure, where the strand is compressed at its end. By integrating this with internal cone filler wrapping, we create a CFRP multi-strand cable composite anchoring system. This innovative design not only minimizes the overall dimensions of the anchoring system but also significantly improves its anchoring efficiency coefficient. An axisymmetric model was developed using ANSYS finite element software. The radial stress distribution and anchorage efficiency coefficient in the anchorage zone of Φ7 CFRP bar and Φ13.6 extrusion die were analyzed with varying parameters, such as chamfering, outer diameter, and length of the extrusion sleeve, and were validated through static load anchorage tests. The results indicate that the highest anchoring efficiency is achieved when four extrusion sleeves with a chamfer angle of 5°, an outer diameter of Φ14.4, and a length of 15 mm are connected in series, reaching a coefficient of 61.04%. Furthermore, this study proposes an anchorage structure where multiple extrusion sleeves are connected in series and sequentially compressed to overcome the limitations of increasing anchorage length for enhancing the anchorage coefficient. The test results demonstrate that with equal total anchorage length, connecting four 15 mm extrusion sleeves in series enhances the anchorage efficiency coefficient by 24.98% compared to a single 60 mm extrusion sleeve structure. Full article

In saline environments, it is difficult for reinforced concrete structures to meet normal durability requirements, which in turn affects the mechanical properties of the members. In this context, this paper proposes a reinforcement method that involves wrapping corroded reinforced concrete columns with CFRP (carbon fiber reinforced polymer) cloth. By conducting axial compression tests on four specimens, key mechanical performance indicators such as failure mode, ductility, and bearing capacity during the entire stress process of the specimens were analyzed, revealing the failure mechanism of CFRP-confined corroded reinforced concrete columns. A refined finite element model of CFRP-confined corroded reinforced concrete columns was established using ABAQUS software. The influence of key parameters such as the number of CFRP wrapping layers, longitudinal reinforcement corrosion rate, and axial compression ratio on the mechanical properties of the specimens was studied, and the influence of each parameter was determined. Furthermore, a formula for the axial compression bearing capacity of CFRP-confined corroded reinforced concrete columns was proposed. The results indicate that in the presence of corroded steel reinforcement, specimens confined with CFRP undergo substantial lateral constraints during the mid to late stages of loading. This approach effectively alleviates the transverse deformation of the concrete. The specimen demonstrated yield bearing capacities and peak loads of 1441 KN and 1934 KN, respectively, representing a 2.2-fold and 2.5-fold increase compared to the non-reinforced specimen. With the increase in the transverse strain of concrete, CFRP begins to play a restraint role, and a more obvious restraint role in the failure stage of members. It is recommended to apply 1–3 layers of CFRP wrapping for a longitudinal reinforcement corrosion rate of 5%, 3–5 layers for a rate of 10%, and 6–8 layers for an overall corrosion rate of 15%. This paper establishes a theoretical framework for investigating the performance characteristics of such columns and offers technical assistance for practical engineering purposes. Full article

This study aims to enhance the ultimate capacity and stiffness of steel–concrete composite beams through external strengthening with prestressed carbon fiber-reinforced polymer (CFRP) plates and post-tensioned CFRP tendons. A 3D finite element model was developed using ANSYS and validated using experiments. The impact of various parameters on the capacity of the beam was investigated, including the level of post-tensioning in the CFRP tendons, tendon profile, degree of shear connection, and beam load level when adding strengthening CFRP tendons. Results indicate that reinforcing composite beams with bonded CFRP plates using post-tensioning tendons with trapezoidal and parabolic profiles can increase maximum load capacity by 37% and 60%, respectively, while maintaining high stiffness. This study also indicates that the optimal strengthening conditions for the composite beam are when the beam is loaded up to 70% of its capacity and has a composite action degree of 100%. Full article

Large-tow carbon fiber-reinforced polymer composites (CFRP) have great application potential in civil engineering due to their low price, but their basic mechanical properties are still unclear. The tensile properties of large-tow CFRP rods and plates were investigated in this study. First, the tensile properties of unidirectional CFRP rods and plates were studied, and the test results of the relevant mechanical properties were statistically analyzed. The tensile strength of the CFRP rod and plate are 2005.97 MPa and 2069.48 MPa. Second, the surface of the test specimens after failure was observed using a scanning electron microscope to analyze the type of failure and damage evolution process. Finally, the probabilistic characteristics of the mechanical properties were analyzed using normal, lognormal, and Weibull distributions for parameter fitting. Quasi-optimality tests were performed, and a probability distribution model was proposed for the mechanical properties of large-tow CFRP rods and plates. Full article

A comprehensive modeling framework for the thermoforming of polymer matrix woven laminate composite was developed. Two numerical indicators, the slip path length and traction magnitude, have been identified to be positively correlated to matrix smearing and wrinkling defects. The material model has been calibrated with picture-frame experimental results, and the prediction accuracy for intra-ply shear and thickness distribution was examined with measurements of the physically formed parts. Specifically, thickness prediction for most locations on the formed parts was accurate within an 11.6% error margin. However, at two points with significant intra-ply shear, the prediction errors increased to around 20%. Finally, a parametric study was conducted to determine the relationship between various process parameters and the quality of the formed part. For the trapezoidal part, orienting the laminate at 45 degrees to the mold axis reduces the likelihood of matrix smear and wrinkling defects. Although this laminate orientation yielded a greater spatial variation in part thickness, the thickness deviation is lower than that for the 0-degree orientation case. Two forming analyses were conducted with ramp rates of 25 mm/s and 80 mm/s to match the equipment’s operational limits. It was observed that higher forming rates led to a greater likelihood of defects, as evidenced by a 15% and 10% increase in the formed part areas with longer slip paths and higher traction magnitudes, respectively. It was discovered that shallower molds benefit from faster ramp rates, while deeper molds require slower rates to manage extensive shearing, stretching and bending. Faster forming rates lead to smaller thickness increases at high intra-ply shear regions, indicating a shift from intra-ply shear to out-of-plane bending due to the visco-plastic effect of the molten laminate and can negatively impact part quality. Lastly, it was shown that a well-conceived strategy using darts could improve the part quality by reducing the magnitude of the defect indicators. Full article