Łukasz Figiel

Mechanical behavior of carbon fiber reinforced polyamide composites

The purpose of this work is to compare tensile, compressive and interlaminar shear properties of different carbon reinforcement/polyamide composites obtained by interfacial polymerization and hot compression molding techniques. Two types of composite matrices were studied: polyamide 6 and polyamide 6/6, both reinforced by fabric and unidirectional carbon fibers. The effects of the fiber volume fraction and the matrix on mechanical properties were analyzed through tensile, interlaminar shear and compressive tests. In general, the results have shown a slight increase of the composite elastic modulus, tensile and compressive strength with the increase of carbon fiber content. The microscopic damage development within selected composites during the loading has been observed through optical and scanning electron microscope techniques and has shown that shear failure at the fiber/matrix interface has been mostly responsible for damage development, initiated at relatively low stress.

Mechanical and thermal fatigue delamination of curved layered composites

Abstract The main aim is to present computational model of delamination of two-layer composite laminate subjected to the cyclic loads, both mechanical and thermal. Numerical fatigue delamination problem is solved by the linear elastic fracture mechanics theory applied together with the classical finite element method, which is done thanks to the commercial engineering analysis package ANSYS. As a result, fatigue delamination growth is predicted for the boron/epoxy–aluminium composite under cyclic compressive shear and periodic temperature changes by the numerical approximation of the curves representing stress and temperature variations versus fatigue cycle number. Computational implementation of the Monte-Carlo simulation technique in the recent versions of this program will enable in the nearest future probabilistic approach to fatigue processes in some random composites.

Exceptional oxygen barrier performance of pullulan nanocomposites with ultra-low loading of graphene oxide

Polymer nanocomposites are increasingly important in food packaging sectors. Biopolymer pullulan is promising in manufacturing packaging films or coatings due to its excellent optical clarity, mechanical strength, and high water-solubility as compared to other biopolymers. This work aims to enhance its oxygen barrier properties and overcome its intrinsic brittleness by utilizing two-dimensional planar graphene oxide (GO) nanoplatelets. It has been found that the addition of only 0.2 wt% of GO enhanced the tensile strength, Youngs modulus, and elongation at break of pullulan films by about 40, 44 and 52%, respectively. The light transmittance at 550 nm of the pullulan/GO films was 92.3% and haze values were within 3.0% threshold, which meets the general requirement for food packaging materials. In particular, the oxygen permeability coefficient of pullulan was reduced from 6337 to 2614 mL μm m(-2) (24 h(-1)) atm(-1) with as low as 0.05 wt% of GO loading and further to 1357 mL μm m(-2) (24 h(-1)) atm(-1) when GO concentration reached 0.3 wt%. The simultaneous improvement of the mechanical and oxygen barrier properties of pullulan was ascribed to the homogeneous distribution and prevalent unidirectional alignment of GO nanosheets, as determined from the characterization and theoretical modelling results. The exceptional oxygen barrier properties of pullulan/GO nanocomposites with enhanced mechanical flexibility and good optical clarity will add new values to high performance food packaging materials.

Computational modelling of large deformations in layered-silicate/PET nanocomposites near the glass transition

Layered-silicate nanoparticles offer a cost-effective reinforcement for thermoplastics. Computational modelling has been employed to study large deformations in layered-silicate/poly(ethylene terephthalate) (PET) nanocomposites near the glass transition, as would be experienced during industrial forming processes such as thermoforming or injection stretch blow moulding. Non-linear numerical modelling was applied, to predict the macroscopic large deformation behaviour, with morphology evolution and deformation occurring at the microscopic level, using the representative volume element (RVE) approach. A physically based elasto-viscoplastic constitutive model, describing the behaviour of the PET matrix within the RVE, was numerically implemented into a finite element solver (ABAQUS) using an UMAT subroutine. The implementation was designed to be robust, for accommodating large rotations and stretches of the matrix local to, and between, the nanoparticles. The nanocomposite morphology was reconstructed at the RVE level using a Monte-Carlo-based algorithm that placed straight, high-aspect ratio particles according to the specified orientation and volume fraction, with the assumption of periodicity. Computational experiments using this methodology enabled prediction of the strain-stiffening behaviour of the nanocomposite, observed experimentally, as functions of strain, strain rate, temperature and particle volume fraction. These results revealed the probable origins of the enhanced strain stiffening observed: (a) evolution of the morphology (through particle re-orientation) and (b) early onset of stress-induced pre-crystallization (and hence lock-up of viscous flow), triggered by the presence of particles. The computational model enabled prediction of the effects of process parameters (strain rate, temperature) on evolution of the morphology, and hence on the end-use properties.

Analysis of a compression shear fracture test for curved interfaces in layered composites

The goal of this paper is computational analysis of a compression shear fracture test, proposed for interface fracture toughness determination and crack propagation analysis in curved layered composites. The main difficulty of the test is that crack surfaces come into contact. Thus, friction is an energy absorbing mechanism, that superimposes with other irreversible phenomena––an energy released during crack extension. Numerical analysis using contact finite elements is paid to the near crack-tip displacements and stresses. The comparison between finite element method and analytically determined stresses is made. This study shows that energy release rate of the composite considered strongly depends on the interfacial friction coefficient.

Effective elastoplastic properties of the periodic composites

The article presented deals with the homogenization of composite materials with elastoplastic constituents. The transformation field analysis (TFA) approach is presented and applied to compute the effective nonlinear behavior of multicomponent periodic composite structure. Computational implementation of the method consists in special utilization of the program ABAQUS, which makes it possible to homogenize n-component periodic composites with relatively general configuration of the periodicity cell. Numerical example of homogenization of a three-component periodic composite shows the comparison between the nonlinear behavior of a real composite and of a homogenized one in a specific boundary problem defined on its representative volume element (RVE).

Influence of Interphase Properties on the Macroscopic Response of Single- and Double-Walled CNT/Epoxy Nanocomposites: A Numerical Study

A concept for improving the impact resistance of carbon fibre reinforced plastic (CFRP) laminates by using a carbon nanotube (CNT)/epoxy surface coating is presented. An initial parametric numerical study shows the effects of interphase properties on the macroscopic stress-strain behaviour of carbon nanotube/epoxy nanocomposites. Finite element (FE) simulations carried out for fully aligned single-walled CNTs (SWCNTs) and double-walled CNTs (DWCNTs) investigated the influence of properties of the polymer/CNT interphase and the interwall phase of DWCNTs. They reveal that a high shear stiffness of the CNT/polymer interphase is essential to take the full advantage of the load-bearing ability of the inner wall of the DWCNT, and thus enhance the mechanical performance of the nanocomposite. Furthermore the interphase shear stress distributions in interwall and CNT/polymer interphase of a DWCNT point out the relationship between CNT/epoxy interphase damage propagation and shear stress in the interwall phase.

Nonlinear multiscale modelling of CNT/polymer nanocomposites

Abstract The objective of this chapter is to present a combined experimental–computational approach to develop a reliable nonlinear multiscale model for the prediction of the nonlinear finite deformation of carbon nanotube (CNT)/epoxy nanocomposites under compressive loading. For this, CNT/epoxy samples of low CNT concentrations and random CNT distribution and orientation were prepared and tested under quasistatic compressive loading. The results were then modeled using the concept of the three-dimensional representative volume element along with the Monte Carlo methodology for morphology reconstruction and a physically based constitutive polymer model for the epoxy matrix. The developed nonlinear nanocomposite model accounts for the finite strain deformation of the matrix, interfacial interactions between the CNT and the matrix, and the nanotube waviness. Predictions of the model are discussed in the context of the most influential nanocomposite parameters and the comparison with experimental results.

Multiscale Finite Element Modelling of Gallery Failure in Epoxy-Clay Nanocomposites

A multiscale finite element (FE) methodology is applied to study failure behaviour of an intercalated epoxy-clay nanocomposite. A 2D FE model of the nanocomposite is built to capture nanocomposite morphology and gallery failure mechanism. Intercalated morphology is reconstructed using a random dispersion of clay tactoids within the epoxy matrix, while the galleries are modeled using cohesive zone elements. The nanocomposite response is predicted by numerical homogenization technique. The effects of cohesive law parameters (particularly the fracture energy) and clay volume fraction on the macroscopic behavior of the nanocomposite are investigated. The analysis shows that gallery failure is the main cause of strength reduction of the nanocomposite. Moreover, the strength reduction is found to increase with the clay content, which is in a qualitative agreement with available experimental results.

A Two-Scale FE[sup 2] Approach for Simulation of Forming Processes for Polymer Nanocomposites

A two‐scale FE2 computational approach for forming simulations of polymer nanocomposites is presented in this work. The approach connects seamlessly the macroscopic length scale at which the forming process occurs with the length scale, where the nanocomposite morphology is defined. The entire approach is implemented in a commercial Finite Element (FE) software ABAQUS. Plane strain simulations show that the FE2 procedure enables to track the nanocomposite morphology during forming. Hence, the procedure can help to optimize process conditions such as temperature or strain rate, to enhance the nanocomposite morphology and end‐use properties.