Composite Structures最新文献

Polyurea coatings have been widely promoted in explosion and ballistic impact protection applications due to their excellent hyper-elasticity performance. In rail transportation, high-speed trains face potential impact threats from track ballast, which can affect the strength performance of the base material. To address these challenges, we examined the ballistic performances of aluminum alloy plates with polyurea coatings under large-scale impact (>30 mm). Four different configurations of target plates were investigated: A, P-A, A-P, and P-A-P. We fabricated samples and performed dynamic impact tests using an air cannon system to demonstrate the feasibility. Results show that ballistic performance is significantly improved by applying polyurea coatings on aluminum alloy plates. In particular, the growth rate of limit velocity of configuration A-P, P-A, and P-A-P to that of configuration A are 5.5 %, 19.4 %, and 22.8 %, respectively. The enhancement mechanism was further uncovered through stress wave propagation analysis and lateral energy diffusion effect. Explicit formulas for predicting the limit velocity and residual velocity were derived and demonstrated with reasonable accuracy over a wide range of parameter spaces. The observed enhancement in ballistic performance through polyurea coatings on aluminum alloy plates offers promising ways to design and implement more resilient and impact-resistant high-speed train structures.

Although prestressed shape memory alloy (SMA) has shown a great performance in flexural retrofitting of slender RC columns, its shear strengthening effect for squat RC columns has been barely studied. This study explores the shear strengthening and damage control effects of iron-based SMA (Fe SMA) for squat RC columns. The heat-activated prestressing of Fe SMA was evaluated first at material level, then applied to component level structural testing of RC columns. The four circular RC columns with different retrofitting schemes were tested under quasi-static lateral cyclic loading. The specimens strengthened with carbon fiber-reinforced polymer (CFRP) sheet and Fe SMA strip exhibited satisfactory global responses without showing significant shear failure. From the visual inspection and non-destructive damage assessment, the prestressed Fe SMA was found to be superior in delaying damage accumulation in concrete compared to CFRP.

This paper presents a novel Finite Element (FE) simulation approach to examine the mode I fracture of thick adhesive joints used particularly in the trailing edge of the wind turbine blades. The approach involved FE models of the DCB specimens focusing on aspects overlooked in the existing literature. There has been limited investigation on residual stresses caused by thermal mismatch between composites and adhesives. Similarly, the impact of generating notches/pre-cracks in the adhesive layer during the preparation of Double Cantilever Beam (DCB) specimens on residual stresses has received minimal attention. Additionally, the Cohesive Zone Model, commonly used for simulating elastoplastic adhesives, may be inadequate due to its inability to account for the plastic deformation of the adhesive. In the present work, the pre-cracks were virtually generated in DCB FE models so that their effect on the stresses within the joint could be examined, making it a novel contribution to the field. The components were assigned with appropriate thermal expansion coefficients, and a simulation of the cool-down process was conducted to determine the thermal residual stresses. Furthermore, the Drucker-Prager plasticity criteria were used to capture the elastoplastic behaviour of adhesives in the FE simulations. Concurrently, the T-stresses were assessed through numerical investigations. For validation, experiments were conducted on DCB specimens made of two cross-ply composite laminates bonded with a ∼ 10 mm thick layer of an epoxy-based adhesive. A good agreement between computational and experimental results was observed, confirming the effectiveness and reliability of the proposed approach.

Shear-thickening fluids (STFs) effectively enhance the impact-energy absorption of Kevlar fabrics and offer an extensive range of applications for human-safety protection. To precisely depict the impact-energy absorption mechanism and stress transfer behavior of multiphase STF/Kevlar composite fabrics under high strain rates, this study introduces a yarn-interface-friction constitutive model that accounts for the strain rate-thickening effect of STFs. The model is incorporated into a mesoscale numerical simulation to enhance computational accuracy. Theoretical models (impact-pit morphology, yarn-strain, and fabric-strain energy models) are employed to evaluate the off-plane displacement, strain distribution, and impact-energy absorption during impact imprint tests. The established simulation model shows high similarity (0.99) to the impact imprint profile curve and reveals that the strain energy and interfacial friction energy of the composite fabrics contribute primarily to energy dissipation during the impact process. Furthermore, in all specimens, C-STF/Kevlar (CNTs reinforced STF/Kevlar) exhibits reduced off-plane displacement, increased primary-yarn stress, and a higher capacity for impact kinetic-energy absorption. The proposed interface-friction constitutive model can accurately predict the deformation and energy absorption levels of the composite fabrics at various strain rates, thereby offering effective simulation guidance for the preliminary design of composite fabrics.

Self-healing polymers are used to improve the durability and strength of materials and provide them with a longer service life. The authors propose a new optical method for evaluating the self-repair efficiency in polymers containing microcapsules. The non-destructive method measures spatial profiles of a hole series obtained after a material puncture. Spatial images of holes acquired by optical coherence tomography were processed to get a surface profile. The reduction of the average volume or depth of the holes compared to the reference material allows self-healing efficiency calculation. For the presented method, tests were carried out to measure the self-repair efficiency of test materials with 5% and 10% mass of repair capsules compared to Ethe reference polymer without capsules. The volumetric efficiencies of self-repair obtained from 30 holes of each material, acquired 8 h after the puncture, were computed as 51.6% and 58.3% for the two repaired material types, respectively.

To validate the proposed removal mechanism of 2D SiC_f/SiC composite, single- and double-grit scribing experiments were conducted on the fiber woven surface (WS) and stacking surface (SS) along the 0°, 45°, and 90°. The results indicate that transverse fibers mainly undergo shear, tensile, and bending fractures. The removal modes of normal fibers are shear and bending fractures. The longitudinal fibers are damaged by tensile (cut-in side) and bending (cut-off side) fractures, accompanied by fiber peel-off. The removal forms of the matrix include crack propagation, ductile scratch, powdery removal, and brittle peel-off. The order of scribing force is F_SS0 > F_WS45 > F_SS90 > F_WS0. The maximum and minimum scribing force occur on SS0 and WS0, respectively, due to the powdery removal of matrix and fibers + matrix peel-off. The 2nd grit scribes the matrix layer and fiber tip in a very low depth to cause powdery and ductile removal, which exhibit the different material removal mechanism with the 1st grit. The scribing damage formed by 1st grit greatly reduces the force required by the 2nd grit for the same material removal volume. The coupling effect among grits in multi-grit scribing and grinding cannot be ignored.

This research investigated the shear behavior of concrete beams reinforced with Carbon Fiber Reinforced Polymer (CFRP) bars and grids as longitudinal reinforcements and stirrups, in experiment and finite element (FE) methods. Five concrete beams were tested under a monotonical load and experienced shear failure as expected. The test variables including stirrup ratio and grid dimension were considered to investigate the interaction between grid and concrete, and the influence between the horizontal and vertical fibers of the grid. It found that reducing the grid dimension with the constant stirrup ratio could effectively improve the stress distribution of the grid and the shear capacity of the beam. The grid dimension greatly determined the shear capacity of specimens when the stirrup ratio changed in a small range. The horizontal fibers of the grid had anchoring effects on the vertical fibers and directly carried the tensile stress from concrete at the top and bottom of the beam. In FE analysis, the fiber composite layer was adopted to simulate the CFRP grid. The load-midspan deflection of specimens and strain development of the grid in the FE model showed good agreement with the tests. In parameter analysis, the grid configuration with the horizontal fiber arranged in the middle or upper part of the section was recommended.

Tremendous challenges still remain in clinical bone tissue defect repair associated with higher morbidity, recurrence, and longer hospital stays. To combat these problems, bone tissue engineering has begun with artificial scaffold biomaterials and has ushered in a booming development with the rise of additive manufacturing techniques. This review provides a cutting-edge review on recent research progress in mechanics and biology of structural scaffold biomaterials, from the multidisciplinary perspective of starting with mechanical properties of natural bone materials. For mechanical properties, most of the research focuses on the static compression, fatigue or permeability properties of structural scaffold biomaterials. Developments at biological properties are critically discussed with an emphasis on promoting osteogenic capacity. However, biomimetic or composite strategies are commonly adopted in the design of structural scaffold biomaterials, which is lack of design for individualized demand. From the perspective of clinical personalized serve, a new paradigm of individualized demand-guided structural scaffold biomaterials design paradigm (DSBDP) is proposed, and its purpose is to progresses clinical bone defect repair biomaterials by regulating the balance among structure, mechanics and biology of biomaterials. This paper not only reviews state-of-the-art progress of structural scaffold biomaterials, but also puts forward the possible development direction of structural scaffold biomaterials through interdisciplinary research.

Three-dimensional woven composites (3DWCs) have received widespread attention due to their advantages, such as integral near-net molding of complex components and high damage tolerance. However, 3DWCs exhibit significant variations in mechanical behavior under various influencing factors, which poses challenges in selecting appropriate application scenarios. In recent years, there has been rapid development in the performance analysis and modeling strategies for 3DWCs, leading to substantial results. This paper provides a comprehensive overview of the mechanical properties and damage mechanisms of 3DWCs under various influencing factors, aiming to facilitate the selection of 3DWCs for different engineering applications and to complement the existing database of mechanical properties.