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Flax and carbon fibers reinforced polymer composites have high potentials to be used as sustainable building materials. To understand the impact resistance of these fiber composites, the present article studied the impact resistance of unidirectional flax fiber and carbon fiber reinforced polymer (FFRP and CFRP) composite plates. The impact response, damage resistance, and impact tolerance were investigated using drop hammer impact and compression after impact (CAI) tests. The internal damage of FFRP and CFRP due to impact loads was studied using acoustic emission technology. In addition, the development process of impact damage was analyzed. CFRP plates show a higher specific energy absorption rate than that of FFRP, because of the more serious internal damage and brittle fracture tendencies. Matrix cracking was the primary damage in FFRP and CFRP under impact load. Compared with CFRP, FFRP possesses a higher CAI due to less damage. Further expansion of the matrix crack caused by the original impact occurs in the impacted fiber-reinforced polymer composites (FRP) under a compressive load. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Unidirectional carbon fiber-reinforced polymer (CFRP) may exhibit significant mechanical softening in the transverse direction at an elevated temperature. While significant transverse compressive stress exists on CFRP due to the clamping force from anchorage, a CFRP cable may exhibit anchorage failure when suffering an accidental fire disaster. The high-temperature resistance of a CFRP cable anchorage is critical, and clarifying the performance deterioration and failure mechanism of a CFRP cable anchorage system at elevated temperature is fundamental for clarifying its fire resistance. This paper reviews the current research status of the high-temperature resistance of CFRP cable anchorage systems from two aspects, including the high-temperature resistance of the comprising materials and the anchorage system. The reviews on the high-temperature properties of the comprising materials are summarized from two aspects. Firstly, the mechanical performance degradation of bonding epoxy resin at elevated temperatures and the effect of a filler on its mechanical–thermal properties are analyzed. Secondly, the mechanical performances of CFRP composites at elevated temperatures are summarized, with consideration of the stress state of the CFRP cable under the constraint of an anchorage device. The reviews on the high-temperature resistance of the anchorage system also include two aspects. Firstly, the temperature field solution method for the anchorage system is summarized and discussed. Secondly, the current research status of the anchorage performance at elevated temperatures is also summarized and discussed. Based on these reviews, the research shortage of the high-temperature resistance of CFRP cable anchorage systems is summarized, and further research is recommended. [ABSTRACT FROM AUTHOR]

Aramid/carbon fiber hybrid reinforced polymer (A/CHFRP) composites were prepared via compression molding to obtain carbon‐fiber‐reinforced polymer (CFRP) composites with better toughness. Based on the existing theoretical model, the effects of the carbon fiber volume fraction on the properties of the A/CHFRP were studied using thermal gravimetric analysis (TGA), tensile tests, and scanning electron microscopy (SEM) analysis. According to the TGA results, the hybrid fiber improved the thermal stability of the CFRP. With increasing carbon fiber content, the thermal stability of the A/CHFRP composites also increased. The tensile results showed that the A/CHFRP composite with a carbon fiber volume fraction of 22.7% exhibited "pseudo‐ductility," with the failure strain 54.09% higher than that of the CFRP composite. With increasing carbon fiber content, the ductility of the A/CHFRP composites decreased. The elastic modulus of the A/CHFRP composites conformed to the prediction model of the rule of mixtures (ROM). The strength was found to fall in the triangular area surrounded by the ROM and the bilinear ROM and exhibited a positive hybrid effect. The SEM results showed that the tensile failure modes of the A/CHFRP composites were mainly fiber and resin matrix debonding and fiber fracture. Brittle fracture of the carbon fibers was observed in the A/CHFRP composites, while aramid fibers appeared to peel off and silk crimp for ductile failure. Thus, this study provides a theoretical basis for toughening CFRPs. Highlights: The volume ratio of the two fibers affects the hybrid effect of A/CHFRP.The thermal stability of A/CHFRP increases with increasing carbon fiber content.The carbon fiber volume ratio of 22.7% in A/CHFRP exhibited pseudo‐ductility.A/CHFRP exhibiting a failure strain 54.09% higher than that of the CFRP.The strength prediction of A/CHFRP depends on the failure mode. [ABSTRACT FROM AUTHOR]

Ramie-fiber-reinforced polymer composites (RFRP) have the advantages of low price and low energy consumption, but they have high hydrophilicity due to their special chemical composition. In order to study the effect of water absorption on the performance degradation of RFRP in a hydrothermal environment, the authors prepared RFRP sheets by compression molding. Manufactured composites were exposed to a hydrothermal environment with a temperature of 40 °C and a humidity of 50% RH, 85% RH and 98% RH to study the water absorption and diffusion, mechanical properties (tensile properties, flexural properties and shear properties) of the RFRP, and their mechanical properties after drying. The research shows that the equilibrium moisture absorption rate of RFRP is mainly affected by the ambient humidity. The moisture absorption and diffusion of ramie-fiber-reinforced polymer composites (RFRP) in a hydrothermal environment conform to Fick's law. Before reaching the moisture absorption equilibrium (1~2 weeks), the mechanical properties decline rapidly, and then tend to be flat, and the mechanical properties of the RFRP decrease significantly with the increase in humidity; the water molecules reduce the interfacial bonding performance and the modulus degradation degree of RFRP in the hydrothermal environment is greater than that of strength. After the samples were completely dried, the mechanical properties of the RFRP rebounded greatly, but less than the initial value, and the hydrothermal environment produced irreversible changes to the substrates. [ABSTRACT FROM AUTHOR]

Hybrid fiber reinforced polymer composites have attracted widespread attention because they can fully utilize the advantages of two different types of fibers. To produce fiber reinforced polymer composites with excellent impact properties, unidirectional carbon/flax hybrid fiber reinforced polymer composite (HFRP) plates were developed using a filament-winding technique. The effects of the carbon fiber content and hybrid mode (a carbon–flax–carbon or flax–carbon–flax structure) on the impact properties and residual compressive properties of the HFRP plates were studied. Acoustic emission tests were performed to characterize the damage during impact, and the K-means cluster analysis method was used to investigate the HFRP damage development during post-impact compression. The test results indicate the higher carbon fiber contents enhanced their specific energy absorption (SEA), as the impact-induced brittle fracturing of the carbon-fiber layers was more severe. The hybrid mode and impact energy level critically influenced the HFRP SEA behavior. The HFRP plate with flax skin exhibited high SEA at a low impact energy, whereas that with carbon fiber skin exhibited high SEA at a high impact energy along with perforation. A more severe extension of the damage caused by the original impact occurs in the impacted HFRP under a compressive load. • A carbon/flax-fiber hybrid composite with improved impact resistance was studied. • A higher carbon content increases the specific energy absorption. • The hybrid mode and impact level influence the specific energy absorption. • The higher the carbon fiber content, the higher the reduction in the post-impact compressive strength of the HFRP. • The most significant irreversible damage to the post-impact HFRPs was matrix cracking during compression. [ABSTRACT FROM AUTHOR]

A hybrid of flax and carbon fibers was considered as an effective way to enhance the mechanical and hydrothermal resistance of flax-reinforced polymer composites. In this study, hybrid composites based on three layers of cross-ply flax fabrics, two layers of unidirectional carbon fabrics, and an epoxy resin were investigated in terms of the tensile, three-point bending, impact, and water absorption properties. The flax fabric reinforcement of the hybrid composites contributed to an improvement in the toughness, whereas the carbon fabric contributed to an improvement in their hydrothermal resistance and overall strength and stiffness. The hybrid composites with carbon fibers on the surface (CFFFC) exhibited brittle failure in the tensile test, whereas those with alternating layers (FCFCF) exhibited greater plastic deformation. In addition, the failure strain of the CFFFC samples showed a negative hybrid effect, whereas that of the FCFCF samples improved 63.5% compared with that of carbon-fiber-reinforced polymer composites. A positive hybrid effect on the impact performance of hybrid reinforced epoxy composites containing the unidirectional carbon fabric and cross-ply flax fabric was observed. At 40 °C and 80% relative humidity, the diffusion rate of water molecules in the FCFCF samples was 16 times that in the CFFFC samples. • High performance carbon/flax hybrid fiber reinforced epoxy composites with low environmental impact was prepared. • Hybrid mode has a great influence on hybrid effect. • Evaluation of hybrid effect on mechanical, impact and hydrothermal aging properties. [ABSTRACT FROM AUTHOR]

This paper investigates the fundamental mechanical properties of tension, bending, shear, and torsion for unidirectional carbon fiber-reinforced polymer (CFRP) plates. First, the mechanical properties of tension, bending, shear, and torsion for the unidirectional CFRP plates are tested, and the test results of relevant mechanical parameters are statistically analyzed. Secondly, the failure modes and damage evolution processes are analyzed by observing the failure surface using the scanning electron microscope (SEM). Subsequently, the probabilistic characteristics of the statistical results for the mechanical parameters are analyzed. The parameter fitting is performed using the Normal, Log-normal, and Weibull distributions for goodness-of-fit analysis, respectively. Finally, the appropriate probability distribution types for the mechanical performance parameters of CFRP plates are proposed. • Mechanical properties of unidirectional CFRP plates are experimentally investigated for probabilistic characteristics. • The failure modes and damage evolution of CFPR plates under tension, bending, shear, and torsion are analyzed using SEM. • Probabilistic distribution of mechanical properties is discussed using Normal, Log-normal, and Weibull distributions. [ABSTRACT FROM AUTHOR]