The Experts below are selected from a list of 105 Experts worldwide ranked by ideXlab platform

Andrea Prota - One of the best experts on this subject based on the ideXlab platform.

  • numerical assessment of the impact behavior of honeycomb sandwich structures
    Composite Structures, 2013
    Co-Authors: Costantino Menna, Alberto Zinno, Domenico Asprone, Andrea Prota
    Abstract:

    Abstract Composite sandwich structures are widely used in the high-performance applications where weight reduction is one of the most attractive design parameters. However, structural sandwich components have low resistance to out-of-plane impact due to the thin outer composite skins and the highly deformable cores. The present Paper deals with a finite element study on the impact response of sandwich panels, obtained combining phenolic resin-based glass fiber reinforced plastics as skins and phenolic resin-impregnated Aramid Paper honeycomb structure (Nomex) as core. The numerical analysis has been performed using the LSDYNA software enabling to account for the main sandwich failure modes occurring during impact. The honeycomb core structure and composite skins have been modeled by means of solid and shell elements respectively. The properties of the finite element model have been calibrated on a series of experimental outcomes in order to achieve numerical parameters for both composite facesheet and orthotropic honeycomb material models. The major concerns are related to damage mechanisms, influence of strain-rate effects and energy absorbing capability. The model is validated using the results from experimental impact tests performed on different initial impact conditions. Good agreement was obtained between numerical and experimental results in terms of impact damage and force–displacement trend.

  • statistical finite element analysis of the buckling behavior of honeycomb structures
    Composite Structures, 2013
    Co-Authors: Domenico Asprone, Costantino Menna, Andrea Prota, Ferdinando Auricchio, Simone Morganti, Alessandro Reali
    Abstract:

    Abstract The main key performance factors of honeycombs are represented by the ability to withstand through-thickness compression and to absorb energy by plastic deformation of the cell walls. The knowledge of the constituent material properties, including the sensitivity of these structures to material defects, and of the folding mechanism occurring during the crushing mode represents a basic step to perform reliable finite element analyses able to accurately reproduce the behavior of such structures. The present Paper reports a comprehensive study of the compressive response of hexagonal honeycomb structures made of phenolic resin-impregnated Aramid Paper (Nomex®); the compressive response is numerically investigated and compared with experimental results. A shell model of a representative single cell made of expanded Nomex has been created using the implicit ABAQUS finite element solver. Imperfections due to the manufacturing process are taken into account including material imperfections (elastic modulus variability) and geometrical defects (thickness variability). Imperfections are included in the model by defining different material and thickness properties for each element according to a pre-defined statistical distribution. The effects of imperfections on the honeycomb structure behavior are investigated. The predicted structural response, numerically obtained using different sets of imperfections, shows a good correlation with experimental results.

Jiaojun Tan - One of the best experts on this subject based on the ideXlab platform.

  • dissolving and regeneration of meta Aramid Paper converting loose structure into consolidated networks with enhanced mechanical and insulation properties
    ACS Applied Materials & Interfaces, 2021
    Co-Authors: Meiyun Zhang, Jiaojun Tan, Yanwei Luo, Bin Yang, Shaowei Ruan
    Abstract:

    Aramid Paper has been widely used in high-voltage motors and transformers due to its excellent insulation property and thermal durability. However, the smoothness and chemical inertness of Aramid fibers lead to a loose structure (voids) of Aramid Paper, which limits its potential applications in harsh environments, such as high-frequency and high-voltage circuits. This work reports a simple and efficient method to improve the mechanical and insulation properties of meta-Aramid Paper via controllable dissolving and regeneration of Aramid fibers. To obtain a dense and robust structure, the pristine meta-Aramid Paper was immersed in a dimethyl sulfoxide/potassium hydroxide (DMSO/KOH) mixture to make Aramid fibers swelled and dissolved, followed by regeneration in water vapor, eventually generating densified Aramid Paper with fewer voids and enhanced insulation and mechanical performance. Optimum conditions resulted in Aramid Paper with the best comprehensive performance, and the tensile strength, Young's modulus, and electrical breakdown strength of the consolidated Aramid Paper were 22.85 MPa, 0.72 GPa, and 15.3 kV/mm, respectively, which were significantly higher than those of the pristine Aramid Paper (12.53 MPa, 0.41 GPa, and 8.36 kV/mm). Meanwhile, such treatment did not cause any chemical structure change, and thus it still retained the excellent thermal resistance (Td > 430 °C) of Aramid fibers. This simple method can effectively regulate the surface porosity and the mechanical and breakdown strength of Aramid Paper, as well as provide a generic method for postprocessing and enhancing Aramid Paper.

Costantino Menna - One of the best experts on this subject based on the ideXlab platform.

  • numerical assessment of the impact behavior of honeycomb sandwich structures
    Composite Structures, 2013
    Co-Authors: Costantino Menna, Alberto Zinno, Domenico Asprone, Andrea Prota
    Abstract:

    Abstract Composite sandwich structures are widely used in the high-performance applications where weight reduction is one of the most attractive design parameters. However, structural sandwich components have low resistance to out-of-plane impact due to the thin outer composite skins and the highly deformable cores. The present Paper deals with a finite element study on the impact response of sandwich panels, obtained combining phenolic resin-based glass fiber reinforced plastics as skins and phenolic resin-impregnated Aramid Paper honeycomb structure (Nomex) as core. The numerical analysis has been performed using the LSDYNA software enabling to account for the main sandwich failure modes occurring during impact. The honeycomb core structure and composite skins have been modeled by means of solid and shell elements respectively. The properties of the finite element model have been calibrated on a series of experimental outcomes in order to achieve numerical parameters for both composite facesheet and orthotropic honeycomb material models. The major concerns are related to damage mechanisms, influence of strain-rate effects and energy absorbing capability. The model is validated using the results from experimental impact tests performed on different initial impact conditions. Good agreement was obtained between numerical and experimental results in terms of impact damage and force–displacement trend.

  • statistical finite element analysis of the buckling behavior of honeycomb structures
    Composite Structures, 2013
    Co-Authors: Domenico Asprone, Costantino Menna, Andrea Prota, Ferdinando Auricchio, Simone Morganti, Alessandro Reali
    Abstract:

    Abstract The main key performance factors of honeycombs are represented by the ability to withstand through-thickness compression and to absorb energy by plastic deformation of the cell walls. The knowledge of the constituent material properties, including the sensitivity of these structures to material defects, and of the folding mechanism occurring during the crushing mode represents a basic step to perform reliable finite element analyses able to accurately reproduce the behavior of such structures. The present Paper reports a comprehensive study of the compressive response of hexagonal honeycomb structures made of phenolic resin-impregnated Aramid Paper (Nomex®); the compressive response is numerically investigated and compared with experimental results. A shell model of a representative single cell made of expanded Nomex has been created using the implicit ABAQUS finite element solver. Imperfections due to the manufacturing process are taken into account including material imperfections (elastic modulus variability) and geometrical defects (thickness variability). Imperfections are included in the model by defining different material and thickness properties for each element according to a pre-defined statistical distribution. The effects of imperfections on the honeycomb structure behavior are investigated. The predicted structural response, numerically obtained using different sets of imperfections, shows a good correlation with experimental results.

Michael Holzapfel - One of the best experts on this subject based on the ideXlab platform.

  • Prediction of impact damage on sandwich composite panels
    Computational Materials Science, 2005
    Co-Authors: Aktay Levent, F Johnson Alastair, Michael Holzapfel
    Abstract:

    Sandwich structures are extensively employed in the aerospace and automobile industries. The understanding of their behaviour under impact conditions is extremely important for the design and manufacturing of these engineering structures since impact problems are directly related to structural integrity and safety requirements. This Paper investigates the damage behaviour of composite sandwich panels with Aramid Paper honeycomb (NOMEX) and polyetherimide (PEI) foam cores under transverse impacts at high velocities. A numerical model was developed using the dynamic explicit finite element (FE) structure analysis program PAM-CRASH. For both sandwich structures numerical analysis reproduces physical behaviour observed experimentally in high velocity impact tests.

Yang Hao - One of the best experts on this subject based on the ideXlab platform.

  • argon low temperature plasma modification of chopped Aramid fiber and its effect on Paper performance of Aramid sheets
    Journal of Applied Polymer Science, 2017
    Co-Authors: Fan Xie, Yang Hao, Guodong Liu
    Abstract:

    Chopped Aramid fiber was modified by an argon low-temperature plasma treatment to enhance the interfacial strength of Aramid Paper. The water contact angle of the Aramid fiber and the tensile strength, tearing strength, and evenness of the Aramid sheets were investigated under different conditions, and the parameters of the argon low-temperature plasma modification, like gas pressure, discharge power, and discharge time, were optimized. The chemical structure and surface morphology of the fiber after plasma modification were characterized by X-ray photoelectron spectroscopy, atomic force microscopy, and scanning electron microscopy. The strengthening mechanism of Aramid Paper by low-temperature plasma modification was also studied. It was found that the argon low-temperature plasma treatment introduced some new polar groups onto the fiber surface and increased the fiber surface wettability and roughness. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2017

  • highly improved mechanical strength of Aramid Paper composite via a bridge of cellulose nanofiber
    Cellulose, 2017
    Co-Authors: Fan Xie, Yang Hao
    Abstract:

    A novel Aramid Paper composite based on pretreated meta-Aramid fiber via the addition of cellulose nanofiber (CNF) was fabricated, and the mechanical strength and interfacial strength of the Aramid Paper composite were investigated. The results indicated that modified fibers showed higher roughness and more available hydrophilic groups. Besides, compared with the pristine Aramid Paper, it turned out that the tensile index, tear index and interlayer bonding strength of the Paper composites with CNF increased by 2.04 times, 2.36 times and 3 times, respectively. In addition, tensile energy absorption (TEA) was also improved by an increment of 99.7% with 20 wt% CNF. These apparent evidences can be accounted for the following mechanisms. On the one hand, enhanced mechanical properties of Aramid Paper composite were derived from the strong hydrogen bonding or dipole–dipole coupling interaction between Aramid fiber and CNF. On the other hand, significant reinforcement of interlayer bonding strength can be attributed to the pivotal bonding bridge and filling agent between Aramid chopped fibers (ACFs) and fibrid, which could improve interfacial adhesion of Paper sheet. The thin film structure like “spider web” or “silk” from SEM images indicated the CNF was used as a bridge actually.