Rakesh Chandra

Micromechanical damping models for fiber-reinforced composites: a comparative study

Abstract The paper incorporates some micromechanical investigations for the prediction of damping coefficients of two-phase continuous fiber reinforced composite. The effect of the shape of fiber cross-section and fiber volume fraction on the various damping coefficients viz. η11, η22, η33, η12, η13, and η23 is studied through the application of viscoelastic correspondence principle to the model based on Eshelbys method and Mori–Tanaka approach. The damping coefficients expressed as loss factors are predicted using several other micromechanical models like, Unified micromechanics, Haplin–Tsai, Hashin, and Tsai. Loss factors for composite reinforced with cylindrical continuous fiber are also determined by 2D micromechanical FEM/strain energy approach and compared with the predictions made by other methods/theories.

A study of damping in fiber-reinforced composites

Abstract Damping contributions from the viscoelastic matrix, interphase and the dissipation resulting from damage sites are considered to evaluate composite material damping coefficients in various loading modes. The paper presents the results of the FEM/Strain energy investigations carried out to predict anisotropic-damping matrix comprising of loss factors η11, η22, η12 and η23 considering the dissipation of energy due to fiber and matrix (two phase) and correlate the same with various micromechanical theories. Damping in three phase (i.e., fiber–interphase–matrix) composite is also calculated as an attempt to understand the effect of interphase. The contribution of energy dissipation due to sliding at the fiber–matrix interface is incorporated to evaluate its effect on η11, η22, η12 and η23 in fiber-reinforced composite having damage in the form of hairline debonding. Comparative studies of the various micromechanical theories/models with FEM/Strain energy method for the prediction of damping coefficients have shown consistency when both the effect of variable nature of stress and the fiber interaction is considered. Parametric damping studies for three phase composite have shown that the change in properties of fiber, matrix and interphase leads to a change in the magnitude of effectiveness of interphase, but the manner in which the interphase would affect the various loss factors depends predominately upon whether the hard or soft interphase is chosen. Analysis of the effect of damage on composite damping indicates that it is sensitive to its orientation and type of loading.

Mechanical Properties of Polymer Concrete

Polymer concrete was introduced in the late 1950s and became well known in the 1970s for its use in repair, thin overlays and floors, and precast components. Because of its properties like high compressive strength, fast curing, high specific strength, and resistance to chemical attacks polymer concrete has found application in very specialized domains. Simultaneously these materials have been used in machine construction also where the vibration damping property of polymer concrete has been exploited. This review deals with the efforts of various researchers in selection of ingredients, processing parameters, curing conditions, and their effects on the mechanical properties of the resulting material.

Interphase Effect on Fiber-Reinforced Polymer Composites

A mathematical model has been developed for the prediction of elastic moduli of three-phase fiber-reinforced composite. This model considers composite materials consisting of three phases, namely, fiber, interphase and matrix, and incorporates the effect of fiber packing. In the present paper, the interphase is assumed to be a homogeneous and isotropic material. The elastic moduli E 11, E 22, G 12 and G 23 have been evaluated and damping coefficients η 11, η 22, η 12and η 23 have been predicted by application of a correspondence principle using this developed model. The effect of interphase volume fraction on loss factors has been evaluated. Prediction of elastic moduli and loss factors has been carried out with a weak and a strong interphase. The calculated results show that the interphase volume fraction and its properties have a very significant effect on loss factor of fiber-reinforced polymer composite. Evaluation of material properties based on the finite element method is presented using representative volume element approach. Results using the developed model are in good agreement with those obtained by FEM and other methods.

Experimental Evaluation of Damping of Fiber-Reinforced Composites

Anisotropic behavior of damping in fiber-reinforced composites is well established. An attempt is made to measure all the six loss factors for glass fiber-reinforced epoxy (three in normal and three in shear) experimentally using free decay method. Different types of specimen such as beam, tubular and cuboidal in shape made from glass fiber-reinforced epoxy are tested under different loading conditions. The six loss factors (η 11 , η 22 , η 33 , η 12 , η 13 and η 23 ) so determined are compared with the analytical results.

Molecular dynamics simulation of polymer/carbon nanotube composites

In this paper, we present classical molecular dynamics (MD) simulations of model polymer/CNT composites constructed by embedding a single wall (10,10) CNT into two different amorphous polymer matrices: poly(methyl methacrylate) and poly{(m-phenylene-vinylene)-co-[(2,5-dioctoxy-p-phenylene) vinylene]}, respectively, with different volume fractions. The simulation results support the idea that it is possible to use CNTs to mechanically reinforce an appropriate polymer matrix, especially in the longitudinal direction of the nanotube. The comparison of the simulation results with the macroscopic rule-of-mixtures for composite systems showed that for strong interfacial interactions, there can be large deviations of the results from the rule-of-mixtures. In order to verify this study, results obtained have been compared with those given by Elliott and Han (2007).

Mechanical and thermal properties of graphene–carbon nanotube-reinforced metal matrix composites: A molecular dynamics study:

Single layer graphene sheets and carbon nanotubes have resulted in the development of new materials for a variety of applications. Though there are a large number of experimental and numerical studies related to these nanofillers, still there is a lack of understanding of the effect of geometrical characteristics of these nanofillers on their mechanical properties. In this study, molecular dynamics simulation has been used to assess this issue. Two different computational models, single layer graphene sheets–copper and carbon nanotube–copper composites have been examined to study the effect of nanofiller geometry on Young’s modulus and thermal conductivity of these nanocomposites. Effect of increase in temperature on Young’s modulus has also been predicted using molecular dynamics. The effect of nanofiller volume fraction (Vf) on Young’s modulus and thermal conductivity has also been studied. Results of thermal conductivity obtained using molecular dynamics have been compared with theoretical models. Results show that with increase in Vf the Young’s modulus as well as thermal conductivity of single layer graphene sheets–Cu composites increases at a faster rate than that for carbon nanotube–Cu composite. For the same Vf, the Young’s modulus of single layer graphene sheets–Cu composite is higher than carbon nanotube–Cu composite.

Molecular dynamics simulation of functionalized SWCNT–polymer composites

The analysis of the influence of functionalization on the mechanical properties of the carbon nanotubes (CNTs) has been poorly addressed, especially when compared with the extensive amount of work on pristine CNTs. This article analyzes the effect of carboxylic (COOH), ester (COOCH3), silane (COSiCH3), and vinyl (CH = CH2) groups attached on the surface of single-walled carbon nanotube (SWCNT) on elastic properties of polypropylene (PP) composites reinforced with functionalized SWCNTs along the axial direction of the CNTs by using MD approach. Effect of CNT aspect ratio and volume fraction on the elastic moduli has also been studied. The results show that although chemical functionalization of SWCNTs has been considered as a means to increase the load-transfer efficiency in a nanotube–polymer composite, this functionalization has, in fact, degraded most of the macroscopic elastic stiffness components of the composite materials considered in this study. The decrease in longitudinal modulus of functionalize...

Flexural Fatigue-Life Assessment and Strength Prediction of Glass Fibre Reinforced Polymer Concrete Composites

The paper presents the results of an investigation conducted to assess the fatigue-life and prediction of flexural fatigue strength of polymer concrete composites based on epoxy resin as binder material. Three point flexural fatigue tests were conducted on polymer concrete specimens using MTS servo controlled actuator, to obtain the fatigue lives of the composites at different stress levels. One hundred and thirty-seven specimens of size  mm were tested in flexural fatigue. Forty-three static flexural tests were also conducted to facilitate fatigue testing. It has been observed that the probabilistic distribution of fatigue-life of polymer concrete composite (PCC) and glass fibre reinforced polymer concrete composite (GFRPCC), at a particular stress level, approximately follows the two-parameter Weibull distribution, with statistical corelation coefficient values exceeding 0.90. The fatigue strength prediction model, representing S-N relationship, has been examined and the material coefficients have been obtained for GFRPCC containing 0.5% and 1.0% glass fibres. Design fatigue lives for GFRPCC containing different contents of glass fibres have been estimated for acceptable probabilities of failure and compared with those of PCC.

Molecular level analysis of carbon nanofiber reinforced polymer composites

The present study focuses on modeling of carbon nanofibers (CNFs) and evaluating the effect of their reinforcement in polypropylene (PP) matrix. A novel approach for modeling of CNF has been explained in this study. Molecular dynamics (MD) simulation has been used to study the effect of CNF volume fraction (Vf) and aspect ratio (l/d) on mechanical properties of CNF–PP composites. Materials Studio 5.5 has been used as a tool for finding the modulus and damping in composites. CNF composition in PP was varied by volume from 0 to 16%. Aspect ratio of CNF was varied from l/d = 5 to l/d = 100. Results have also been obtained for longitudinal loss factor (η11). To the best of the knowledge of the authors, till date there is no study, either experimental or analytical, which predicts η11 for CNF–PP composites at nanoscale. Hence, this will be a valuable addition in the area of nanocomposites. Results show that with only 2% addition by volume of CNF in PP, E11 increases by 748%. Thereafter, the increase is at a lower rate. Increase in E22 is very less in comparison to the increase in E11. With increase in CNF aspect ratio (l/d) till l/d = 60, the longitudinal loss factor (η11) decreases rapidly. Thereafter, the decrease is smaller. Results of this study are in agreement with those predicted by Shinichi et al.