Interphase Parameters Research Articles

Non-isothermal kinetics of cold crystallization in multicomponent PLA/thermoplastic polyurethane/nanofiller system

The effect of platy and tubular nanofillers (NF) in combination with thermoplastic polyurethane (TPU) on cold non-isothermal crystallization (NIC) of poly(lactic acid) (PLA) was studied by differential scanning calorimetry. The data were processed using a recently proposed method of evaluating NIC kinetics. The results indicate that the NF/TPU combination leads to crystallization behaviour of the PLA matrix which is dissimilar from that of the NF-free blend and neat PLA. Addition of organophilized montmorillonite (C30) results in a dual effect on PLA crystallinity—stimulation at lower concentrations and suppression at higher loadings. In the case of halloysite nanotubes (HNT), this effect is practically absent. Crystallinity of injection-moulded samples is significantly increased by cold NIC. This indicates a synergy originating in a complex effect of NF/TPU, e.g. NF-induced changes in morphology and interphase parameters supporting the solid annealing process. TPU partially eliminates negative effect of high NF contents on cold crystallization rate. This effect is more marked in the remelted samples where the rate increases for all NF loadings. This is probably caused by absence of as-prepared crystallites in combination with higher mobility of PLA chains due to presence of TPU. The observed differences between C30 and HNT could be attributed to differences in size, shape, and specific surface. The results indicate that synergistic and antagonistic effects of NF/polymeric modifiers on mechanical and other material parameters are also significantly determined by the effects on crystallization of the matrix.

Development of cubic orthogonal skeleton or three perpendicular plates system for prediction of Young’s modulus in polymer nanocomposites assuming the interphase

Kolarik proposed a model for Young’s modulus of polymer particulate composites based on the cubic orthogonal skeleton or three perpendicular plates (3PP) system. However, this model commonly underestimates the modulus of polymer nanocomposites, because it does not take into account the interphase properties. In this paper, the Kolarik model is developed for polymer nanocomposites assuming the interphase role. The original and the developed models are compared with the experimental data, and also, the effects of material and interphase properties on the predicted modulus are discussed. The predictions of the developed model display fine agreement with the experimental results from literature assuming acceptable interphase. Similarly, the developed model shows the logical effects of material and interphase parameters on the modulus. For example, the modulus improves by reduction of nanoparticle size which increases the interfacial area between polymer chains and nanoparticles. The appropriate outputs of the developed model confirm the correct expansion of Kolarik model for modulus of polymer nanocomposites.

Elastic and yield behaviors of recycled polypropylene-based composites: Experimental and modeling study

Abstract In this work, stiffness and yield behaviors of recycled polypropylene (PP) based composites have been investigated by means of dynamic mechanical analysis (DMA) and split Hopkinson pressure bar (SHPB). It was found that the mechanical behaviors of non-recycled and recycled PP composites depend on temperature and frequency/strain-rate as well as on filler content and recycling cycle. For modeling the elastic modulus and yield stress, two new approaches were proposed. We extended a statistical stiffness model for neat polymers with temperature and frequency/strain-rate dependences by incorporating a Mori-Tanaka based approach and a two-population model to predict the elastic modulus of PP composites. By considering the initial modulus of neat PP and filler aspect ratio with reprocessing dependences, the predicted elastic modulus not only depended on the test temperature and frequency/strain-rate but also depended on the filler content and recycling number. To predict the yield behavior, we extended the modified cooperative model with temperature and strain rate dependences for neat polymers by incorporating a three-phase approach and a two-population model. In particular, the internal stress for neat PP and the interphase parameter B for PP-based composites were considered with reprocessing dependences. Predicted yield stresses by this new approach not only depended on the strain rate and temperature but also depended on the filler content and reprocessing number. A good agreement was found between experimental results and predictions.

Natural Convection Heat Transfer About a Vertical Cone Embedded in a Tridisperse Porous Medium

This work studies the natural convection heat transfer about a vertical cone embedded in a tridisperse porous medium with constant wall temperature. The three-velocity three-temperature formulation is used to derive the governing partial differential equations. The coordinate transformation and the order-of-magnitude analysis are then used to obtain the nonsimilar boundary layer partial differential equations. The cubic spline collocation method is then used to solve the nonsimilar boundary layer partial differential equations. The effects of two inter-phase heat transfer parameters, three modified thermal conductivity ratios, and two permeability ratios on the heat transfer and flow characteristics of the tridisperse porous medium are studied. Results show that increasing the three modified thermal conductivity ratios or the two permeability ratios tends to increase the natural convection heat transfer rate of the vertical cone in a tridisperse porous medium. Moreover, the thermal non-equilibrium phenomena between the three phases of the tridisperse porous medium are affected by the streamwise coordinate and the two inter-phase heat transfer parameters. The thermal non-equilibrium effects between the three phases of the tridisperse porous medium become significant as the two inter-phase heat transfer parameters or the streamwise coordinates are small.

Influence of interphase properties on the effective behaviour of a starch-hemp composite

Elasticity behaviour of a fully biopolymer composite is studied using both numerical and experimental approaches. Hemp fibre-starch composite is thermomoulded using a varied content of hemp fibres. On one end, mechanical testing reveals loss of stiffness due to limited load transfer with the increase of fibre content. On the other end, two-phase theories predict a reinforcement trend due to contrast of phase properties. In order to meet both ends, a numerical study is performed to study sensitivity of the predicted mechanical response to geometrical and mechanical considerations. Filler content, arrangement and interphase properties are some of the major studied effects. Interphases are accounted numerically to exhibit the mismatch of load transfer due to imperfect interface behaviour. Finite element results are discussed based on geometrical and mechanical considerations using a sensitivity analysis. Identification of interphase parameters for the tested experimental conditions is attempted successfully. The three-phase model is able to detect where the two-phase system approximation is valid. In addition, strong interphase properties are identified despite the apparent loss of stiffness. Such loss turns to be related to fibre clustering, which makes thermomoulding processing not suitable to achieve fibre volume contents above 10% if not combined with an energetic mixing stage.

THERMOELASTOPLASTIC AND VIBRATION CHARACTERISTICS OF COMPOSITES WITH INTERPHASES

ABSTRACTThis paper addresses the problem of predicting the behaviors of a compositematerial, which consists of a matrix and a spherical inclusion coated by a multilayeredinterphase, under thermal and/or mechanical loading variations and basedon the micromechanics principles. The multi-layered interphase, which in generalincludes different properties for each layer, is modeled by applying the multiinclusionmodel. The considered damage mode, which is represented by theprogressive debonding of the particle from the interphase, is assumed to becontrolled by a critical energy criterion and the Weibull’s distribution function. Theeffects of the interphase parameters such as its thickness and the properties of eachlayer on the effective thermomechanical properties and the vibration characteristicsof composites with multi-layered interphases are presented and discussed. Thenatural frequencies give information about the resonance avoidance whereas modeshapes give information about observability and controllability of different structures.Therefore, the natural frequencies and mode shapes as vibration characteristics areinvestigated based on Euler and Timoshenko theories.

Numerical Study on Effects of Interphase in Natural Short Fiber Reinforced Polymer Composite Based on Cohesive Zone Model

Natural short fiber reinforced polypropylene (PP) composite has great significance both in commercial and environmental and is widely used in motor industry. Its local inhomogeneity and interphase both affect the macroscopic properties of the composite. These phenomena are still difficult to observe and study accurately in the experiment. A cohesive zone model (CZM) based numerical simulation method is presented in this paper. The three-phase (matrix-interphase-fiber) model considering some different factors was developed to study the effects of interphase parameters on the mechanical properties of the composite.

The Effect of Interphase Modulus and Thickness on Stress Transfer of Short-Fiber-Reinforced Composites

In this paper, the stress distribution of short-fiber-reinforced composites (SFRC) using representative volume element (RVE) approach based on the finite element analysis (FEA) was presented. A three-phase model was built, in which loads were applied to the matrix. The influences of interphase parameters like Young’s modulus and thickness were studied. The FEA confirms that interphase Young’s modulus and thickness control stress distribution in SFRC. The stress concentration at the fiber interface becomes greater with high interphase Young’s modulus and thin interphase thickness. The FEA results were also compared with those obtained by analytic method.

Effect of Silicone Carbide on the Elastic Properties of Starch‐Based Composites: A Three‐Phase Model

AbstractThe effect of a rigid filler on the elastic properties of starch‐based composites is investigated. Thermomolding of the targeted composite is conducted using a starch matrix with varying silicone carbide content. Mechanical testing reveals that the composite's Young modulus cannot be rationalized using two‐phase analytical models. The effect of a weak interphase region is highlighted using a finite‐element model that assumes the generation of virtual microstructures. Numerical results are discussed by describing the influence of the structural and interphase parameters on the composite's elastic modulus. Identification of optimal interphase parameters quantitatively demonstrates the weak adhesion between intrinsic phases for all studied filler fractions. magnified image

Analytical Investigation and Comparative Assessment of Interphase Influence on Elastic Behavior of Fiber Reinforced Composites

Interfacial interactions and interphases play a key role in all fiber reinforced composites. However, a clear distinction must be made between interface and interphase. Interphase becomes interface if its thickness decreases to zero. In most of the available micromechanical models the interface is considered perfect (no interphase). However, such a condition is hardly fulfilled in real composites. It is possible to find the volume of interphase by using DSC or identification of interphase region using SEM or some other sophisticated instrument techniques as it is a region created between the two main phase of a composite. All these techniques require special technical skill. In the present study attempt is made to identify the existence of the interphase region in fiber matrix composites using SEM. It was also decided to develop an equation for volume fraction and thickness of interphase by considering the composite as three-phase RVE. Developed equations of interphase volume fraction was used by considering the soft and stiff interphase parameters. Comparisons were made to study elastic behavior of fiber reinforced composites in longitudinal and transverse directions with available experimental data and published model in the literature and they are in good agreement.

Effective properties of biopolymer composites: A three-phase finite element model

The effective Young’s modulus of starch–zein biopolymer composite is studied using a finite element model. This model handles the fact that starch–zein interface is not perfect in the sense that elasticity properties across the interface are altered. The motivation here is to predict the right modulus of elasticity near the interface for any zein content. In that way, the finite element model requires zein, starch and interphase properties to be implemented for the computation of the composite Young’s modulus as a function of zein content. The main variables are the interphase thickness and modulus. The comparison between the predicted and experimental results shows, firstly, that the effective composite properties are not correctly estimated using standard models with perfect interface hypothesis. Secondly, the three-phase model is able to suggest optimal interphase parameters in order to fit the experimental data obtained using three-point bending test. Finally, the optimal interphase parameters (thickness and modulus) vary as a function of zein content.

Evaluation of influence of interphase material parameters on effective material properties of three phase composites

In this paper, evaluation of effective material properties of different types of three phase composites (reinforcement, matrix and in between interphase) using numerical homogenization techniques (representative volume element (RVE) approach) based on finite element method is presented. The influence of interphase parameters like stiffness and volume fraction of interphase on effective material properties of transversely randomly distributed uni-directional fiber composites and randomly distributed spherical particle composites is studied. The RVEs, required for transversely randomly distributed uni-directional fiber composites and randomly distributed spherical particle composites, are generated using a modified random sequential adsorption (RSA) algorithm with periodicity on opposite boundary surfaces. The numerical results are compared with analytical methods like asymptotic homogenization method for regular arrangement of uni-directional fiber composites.

Polymerization of vinyl monomers in separated Winsor II (w/o) and Winsor I (o/w) microemulsion phases. Part 1: preparation and characterization of polymerizable vinyl-monomer-containing microemulsions

Classical toluene-based (w/o, water in oil) single-phase Winsor IV inverse microemulsions containing toluene/(sodium bis(2-ethylhexyl) sulfosuccinate (AOT)/water/acrylamide (AAm)/sodium dodecyl sulphate (SDS) and containing, besides AAm, also an oil-soluble vinyl monomer (butyl acrylate (BA), styrene (S), or ethyl acrylate (EA)) were titrated by aqueous titrating systems (TS) composed from water (TA), aqueous solutions of acrylamide (TB), aqueous solutions of sodium dodecyl sulfate (TC), and/or aqueous solution of acrylamide and sodium dodecyl sulphate (TD). The amount of TS absorbed by the inverse microemulsion during titration (i.e., before transformation of Winsor IV inverse microemulsion to the two-phase Winsor II (w/o) (microemulsion phase + aqueous phase) and/or before phase inversion to the Winsor I (o/w) (microemulsion phase + oil phase) microemulsions, depended only slightly on the nature of the oil-soluble vinyl monomer. It was found, however, that the ratios of intra-phase and inter-phase compositional parameters such as toluene/AOT and AOT/SDS of the single-phase Winsor IV (w/o) inverse microemulsions considerably affected the value of the volume fractions of the aqueous phase, Φaw2, necessary for the formation of a two-phase Winsor II (w/o) and/or Winsor I (o/w) microemulsion systems. The composition of the titrating systems TS influenced the Φaw2 values at which the phase separation, and/or phase inversion of the single-phase Winsor IV (w/o) inverse microemulsion, were observed. Thus, the following sequence TAS1 < TA ≪ TC < TB < TD of titrating systems (ordered according to the obtained Φaw2 values) was found.

Enhancing the Properties of Composites by Controlling Their Interphase Parameters

The interfacial interaction between reinforcement and polymer is of crucial importance for the performance of composites. In recent years, special attention has been focused on the exploration and comprehensive description of the relationship between the surface properties of the polymer and fiber, adhesion, and of the resulting mechanical properties.

Boundary element analysis for composite materials and a library of Green's functions

With the rapid development of advanced composite materials and the wide application of such materials in engineering, it is desirable to model problems involving these materials by computer and to use powerful numerical methods like the finite element method (FEM) and the boundary element method (BEM) for analysis. In this paper, a BEM is developed to analyze two-dimensional micromechanical behavior of fiber-reinforced composites based on models for both perfectly-bonded and imperfectly-bonded materials in a unit cell. For composites with perfect bond between matrix and fibers, it is shown that our predictions coincide satisfactorily with comparable quantities obtained in physical experiments and by FEM analysis. For imperfectly-bonded composites, it is found that variation of the interphase parameters (thickness, stiffness) causes pronounced changes in the overall effective moduli and also in the state of stress in the composites. Also in this paper, the idea of a library of Green's functions for fiber-reinforced composites is discussed. With such a library, users could quickly generate data useful in design with very little knowledge of methods for computational modeling in general or of the BEM in particular.

Theoretical study of interphase heat and mass transfer in saturated porous media

Transient convective heat and mass transfer between the solid and fluid phases of a saturated porous medium has been considered in the present study. A geometrically simple model that is capable of predicting retardation of the species has been developed. The equations governing species transport in the liquid and solid phases of the porous medium are coupled due to heat and mass transfer at their interface. The species concentration in the liquid phase is determined by analytically solving the system of differential equations along with experimentally motivated values of the interphase parameter. The following problems have been separately considered: (1) transient heat transfer between a heated fluid and an initially cold matrix; (2) mass transfer of a radioactive nuclide from a contaminated matrix into a clean fluid; (3) transport of a radioactive nuclide present in a fluid flowing through an initially clean matrix; (4) effect of a non-zero dispersion length. Results show that interphase transport between the solid and fluid is an important factor in retarding species transport in the porous region as a whole. Equilibrium in species concentration between the two phases is seen to be attained only under special conditions.

Characterization of interphase conditions in composite materials

Abstract A mixed experimental—numerical method is presented which can be used to characterize interphases in composite materials. This method is marked by using measured field quantities, such as displacements and strains, and finite element simulations of the experiments to fit interphase parameters using an iterative minimum variance estimation algorithm. Field quantities are measured using marker fields in the vicinity of the interphase. The markers are applied using the electron beam of a scanning electron microscope (SEM). A marker grid, consisting of dots with a diameter of 0.2 μm, is placed on the surface of unidirectional glass fibre-reinforced epoxies. The displacement field is determined by calculating the relative displacements of the markers during transverse tensile experiments in a SEM. Subsequently, the experiment is modelled using the finite element method. The positions of the border markers of the marker grid define the geometry of the model, and the displacements of these markers the boundary conditions. A mathematical interphase model is included. The parameters, quantifying the mechanical behaviour of the interphase, are fitted using the iterative parameter estimation procedure. Based on the presented results, it can be concluded that the method is a promising tool for the characterization of interphases.

Multiparameter statistical determination of single fibre interphase properties

Abstract To evaluate the properties of the fibre interphase, statistical analyses are conducted on a previously generated database containing ultrasonic NDE output stresses calculated for various interphase properties. A multivariate correlation technique is used to examine relationships between interphase properties and NDE output stresses. Also, linear and non-linear regression techniques are used to solve the inverse problem of evaluating the interphase properties from the stress database. As an example, the interphase thickness parameter is shown to be predicted through linear and non-linear multiple regression with high accuracy. It is shown that knowledge of other interphase parameters, such as density, can help to improve estimates of interphase thickness. The methods are not specific to the inverse problem under study; on the contrary, they can be applied to the general NDE inverse problem.

Determination of interphase properties of fiber composites from phase velocities of ultrasound

Average values of the in situ mechanical properties of the interphases in an unidirectional fiber-reinforced composite were deduced from measured values of the phase velocities of ultrasonic signals. The composite was modeled by a hexagonal array of fibers in a matrix, and the interphases are represented by a spring-layer model. For deformation in planes normal to the fiber direction there are two unknown interphase parameters. For known values of the mechanical and geometrical properties of the fibers, the matrix, and the interphases, the effective elastic constants were obtained by finite element calculations in a representative cell. When the interphase parameters were unknown, the finite element procedure was measured in an iterative mode to obtain the interphase parameters by systematic comparison between calculated and measured values of the effective elastic constants of the composite.

The meaning of the critical length concept in composites: Study of matrix viscosity and strain rate on the average fiber fragmentation length in short‐fiber polymer composites

AbstractComputer modeling is used in order to provide a theoretical understanding of the concept of critical length in composites, and of the factors influencing the critical aspect ratio. The effects of interphase and matrix properties have been investigated. We have identified the interphase parameters which minimize the critical length. Contrary to the assumption that the critical aspect ratio is related to interfacial shear strength and fiber strength only, we find a significant dependence on matrix viscosity and strain rate, for fixed interphase properties. We therefore conclude that the fragmentation test, which relates the measured critical aspect ratio to a value for the interfacial shear strength, has to be reinterpreted in terms of more parameters than those simply present in the Kelly‐Tyson formalism. Moreover, the significance of the concept of critical length for tailoring mechanical properties of composites needs to be reassessed.