Applied Composite Materials最新文献

The experimental and numerical study of Jute—Basalt hybrid composites was performed under low-velocity impact (LVI) considering the low cost and higher specific strength and stiffness. Hybrid composites were fabricated using the vacuum infusion method to improve fiber volume fraction to reduce the air defect. The LVI tests were conducted on the Instron 9350 model at three impacting energies of 10 J, 20 J, and 30 J to study the impact force, absorbed energy, maximum displacement, and damaged area. The failure behaviour of impact-tested specimens of the natural fiber composites obtained from CT Scan was validated by three–dimensional numerical modelling using the VUMAT subroutine in ABAQUS/Explicit. The experimental and numerical results showed that the peak force and absorbed energy were significantly improved and adding basalt fabric enhanced the peak performance of jute composite. The simulation results helped to understand the delamination phenomenon which was not visible in the samples after the test. Experimental results were validated with numerical simulation results considering the 10, 20, and 30 J energy level. The peak force of B-JFRP was improved due to hybridization and the damage resistance of it could be seen as the impactor was unable to perforate at 30 J fully. The alternating stacking sequence helped in minimizing the use of basalt fabric and enhanced the overall performance of the hybrid composite. Biodegradable hybrid natural fiber composites are a promising category for developing lightweight and impact-resistant structural materials for marine applications, wind turbine, and defense industry applications.

In this article, a comprehensive overview of microwaves-based non-destructive testing (NDT) techniques for carbon fibre- and glass fibre-reinforced polymer composites is presented. These lightweight composites have been widely employed in aerospace, naval, automotive, construction, electronics and wind energy industries. Monitoring the structural integrity is critical for the maintenance and repair of such heterogeneous composite structures. Traditional ultrasonic methods do not always identify defects or damage in such structures. In that case, microwave NDT techniques can provide a complementary modality. The microwave NDT has been adopted for material characterisation, quality assessment and damage detection. Wider applications will be expected, as more low-cost microwave components become commercially available.

Thermo-mechanical response of [90_n/0_m]_s carbon/epoxy and glass/epoxy cross-ply laminates in 4-point bending is analyzed experimentally and analytically. Intralaminar cracks in surface 90°-plies and local delaminations introduced in one of the 90°-plies at large deflections reduce the laminate bending stiffness and make the laminate asymmetric due to differences in the damage state in the layers. The latter leads to residual thermal curvature that increases with intralaminar crack density and with growing local delaminations. In the present study optical microscopy was used for crack density quantification. It was also found experimentally that small local delaminations develop in the initial stage of damage evolution and under increasing load they grow rapidly from the existing and newly created crack tips. The effect of damage on residual curvature and the bending stiffness was analyzed using an analytical method, where the concept of the effective stiffness of damaged ply is used in the classical laminate theory. Analytical results were validated with a 3-D FEM simulation of the damaged laminate in a 4-point bending test. In the literature a phenomenon that the microdamage in laminate layers causes redistribution of in-plane thermal stresses is often overlooked. The present paper shows that the used analytical approach gives an accurate description of experimental results regarding two independent sets of data: the residual curvature; and the laminate bending stiffness with evolving micro-damage. The present study also renders a better insight in the mechanics of the phenomena and allows estimation of the extent of local delaminations that is difficult to measure in tests.

Wet Fiber Placement (WFP) is a manufacturing technology for continuous fiber-reinforced composites. It serves as an alternative to Automated Fiber/Tape Placement processes, offering cost-effective machinery and the programmability advantage of 3D printers. By bypassing pre-impregnated products, WFP enables the blending of preferred resins and fibers, providing enhanced geometric flexibility and material versatility. Two major challenges go along with this process strategy: (1) the freshly impregnated rovings tend to adhere to any surface they come in contact with, while (2) the impregnated rovings are slack and must be pulled rather than pushed all the way from the creel to the point where they leave the placement system. After placement, the generated “in-line prepreg” is consolidated and cured in a compression molding process, using an elastomeric/metallic, thickness-adaptive tool that can be used to process different workpieces with different thicknesses and workpieces with locally differing thicknesses in the same mold. This paper introduces a CNC system tailored for WFP, emphasizing the end effector’s components like pultrusion rollers, dancer modules, a cutting unit, and pre-consolidation elements. Despite successful roving placement, accuracy concerns persist, suggesting the need for sensor synchronization and cutting path optimization. Initial prepreg compression molding trials showcased thickness adaptability with minimal fiber displacement, offering potential for topology optimization, albeit demanding further parameter study to enhance product quality.

Axial compressive strength is a key design parameter for CFRP structures. One of its limiting factors is the non-linear shear behaviour of the unidirectional ply. We investigate the estimation of this behaviour from those of its constituents by computational homogenisation with an hexagonal unit cell and different random microstructures with smooth and clustered fibre distributions. A random microstructure without clusterings predicts the shear modulus most closely. However, the modelled shear responses converge at higher loadings so that an hexagonal model is sufficient to estimate the non-linear shear behaviour and in turn give accurate estimations of measured compressive strength.

The production costs of aircraft primary structures made of carbon fibre reinforced polymer (CFRP) are significantly higher than for comparable metal-based structures. Today substantial effort is made to achieve a sufficient reproducibility and parts’ quality in manufacturing processes of CFRP structures. Especially the sub process vacuum bagging for infusion processes is still expensive. One of the reasons is the complex positioning of the flexible auxiliary materials which have to be stacked on the preform. During the positioning on doubled-curved surfaces these materials tend to form wrinkles, which can lead to defects of the composite part. Yet, a defined description of the wrinkling behavior of the auxiliary materials on doubled-curved surfaces does not exist. In this work a characterization of the wrinkling behavior on doubled-curved surfaces is investigated for the auxiliary materials of the Vacuum Assisted infusion Process (VAP^®): release film, perforated peel ply, flow media, membrane and vacuum foil. Therefore, an experimental test method is derived similar to established hemisphere deformation test methods. The wrinkling behavior for the specific VAP auxiliary materials is empirically determined on differently curved surface geometries. It is shown that the draping behavior can be characterized by partial wrinkle-free surfaces between the wrinkles. A material specific threshold is derived to determine the appearance of wrinkles. The work shows that a characterization of the draping behavior of auxiliary materials on doubled-curved surfaces is possible. With the gained knowledge the potential for an increase of the vacuum bagging reproducibility is given.

Fibre reinforced composites are widely used in marine structures, from small boats to tidal turbines. However, there are some specific features of the marine environment, notably continuous contact with seawater and hydrostatic pressure loading, which require special attention during material selection and design. This paper first describes test procedures developed over the last 30 years to address these conditions in order to identify and validate lifetime prediction models. Surface vessels and underwater applications are discussed. Then, considerations for future applications are described, with particular emphasis on sustainability and environmental impact.

Corrosion-induced defects, extensive and unavoidable in marine structures, pose significant threats to structural integrity and safety. This study aims to assess mechanical response and investigate the failure mechanism of composite-repaired circular hollow section (CHS) steel tubes. A feasibility analysis is conducted through verifying the axial compression performance of a uniformly corroded tube and an Aramid fiber-reinforced polymer (AFRP) strengthened perfect tube. Subsequently, mechanical responses of the corroded and AFRP-repaired tubes are studied, accompanied by parametric studies to comprehensively evaluate the influence of corrosion region, and the depths and densities of corrosion pits. Consequently, critical damage modes of the AFRP patches are explored using a user-defined material subroutine developed based on Hashin failure and Yeh delamination damage criteria. Numerical predictions indicate that composite patches improve the structural residual strength, but not necessarily enhance the structural ductility under diverse failure patterns. In addition, AFRP patches contribute to improving the overall structural load-bearing capacity by alleviating local buckling or regional collapse. Moreover, fiber compression damage emerges as the dominant mode. Premature failure of putty agent initiates stress concentration, intensifies subcritical damage, aggravates critical damage, and expedites final failure.

Carbon fibre reinforced thermoplastic tubular structures can be post-formed into desired curvatures via rotary draw bending (RDB) at elevated temperatures. During this process, a rigid internal mandrel is required to support the walls of the tubes to maintain their ovality and minimise unwanted geometrical distortions. This paper investigates four internal mandrel designs for post-forming carbon fiber reinforced polyamide 6 (CF/PA6) thermoplastic tubes. Mandrel designs include silicone rod, bullet, wire, and coil spring, were evaluated through RDB-forming experiments with [± 60°]₄ CF/PA6 tubes formed to 90° bends. The designs were evaluated for their effectiveness on minimising distortions resulted from induced stresses during post-forming by measuring the post-formed tube diameter and extrados strains. The mandrel designs were also evaluated for their usability when integrated into the RDB process. Results from optical measurements and micro-computed tomography showed the spring mandrel outperformed others, producing tubes with the least geometrical distortions and no defects during the forming process. As compared to other designs, the spring mandrel is a reusable unibody design that is easy to assemble and remove from the tubes.

C/Mullite composites were fabricated through sol impregnation-drying-heating (SIDH) route using the sol with a high solid content in our previous work, and the composites showed desirable performance. However, it was found that thermal stress caused by sintering shrinkage of mullite matrix is one of the main factors leading to the performance regression of the composites. In present study, the sintering characteristic of Al₂O₃-SiO₂ sol was modified to reduce the thermal stress caused by the sintering shrinkage of mullite matrix, optimizing the performance of the composites. The results showed that the sintering shrinkage of mullite matrix was reduced about 25% after heat treatment at 1600ºC by modifying the sintering characteristic of sol, resulting in that the thermal stress caused by sintering shrinkage of mullite matrix was reduced effectively. Therefore, the strength, modulus and fracture work of the composites were increased by about 19.4%, 24.5% and 24.9% to 318.4 MPa, 62.0 GPa and 6958 J/m², respectively. Furthermore, thermal stability of the composites was also improved obviously in Ar and vacuum environment.