Mechanical Properties Of Polymers And Composites Pdf
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Right from the early days, polymer materials have been discovered as being beneficial for various applications but a poor understanding of these materials greatly handicapped their usage. However, with a change in this trend, polymer materials have gradually displaced other materials in most applications.
- Composite material
- Polymer Matrix Composites: Properties, Production, and Applications
- Mechanical properties of polymer composites reinforced by silica-based materials of various sizes
- Polymer Matrix Composites: Properties, Production, and Applications
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In this work, a new method for evaluating the elastic properties of the interfacial region is developed by examining the fracture behavior of carbon nanotube reinforced poly methyl methacrylate PMMA matrix composites under tension using molecular dynamics simulations. The effects of the aspect ratio of carbon nanotube reinforcements on the elastic properties, i.
The feasibility of a three-phase micromechanical model in predicting the elastic properties of the nanocomposites is also developed based on the understanding of the interfacial region. The outstanding electrical, mechanical and thermal properties of carbon nanotubes CNTs 1 , 2 have made them among the most promising materials in a wide range of applications such as nano-sensors and atomic transportation 3 , 4.
In order to facilitate the development of reinforced polymer composites and the design of the materials, the bulk mechanical properties of the materials must be determined. Although some experiments have been conducted on material properties of CNT reinforced composites 7 , 8 , 9 , scattered data on the nano-reinforced composites have been reported in literature 10 , 11 , The main reasons for the inconsistency are attributed to drawbacks in the uniform alignment of CNT reinforcements and forming proper interfacial bonding between matrix and CNTs during the mixing process of the composites.
Molecular dynamics MD simulations, however, can provide alternative methods to generate detailed information, such as stress-strain behavior and the interfacial interactions between matrix and CNTs. In addition, MD simulation studies may enable interpretations of experimental results and even a route to new designs of laboratory tests.
Frankland et al. Zhu et al. Molecular simulations conducted by Mokashi et al. In the abovementioned molecular studies, the effect of CNT reinforcements on mechanical properties of polymer composites has been investigated. However, mechanical properties reported in the studies are scattered and may not be directly used in a continuum-based framework for design purposes as some effects are still obscure such as the geometries of CNTs. The major reason for the inapplicability of the results in a continuum framework is because the interfacial separation and sliding between reinforcements and matrices owing to the weakened bonding formed between CNTs and polymer matrices have not been accounted systematically.
In view of the above problem, analytical approaches based on continuum micromechanics models in conjunction with molecular simulations have been developed to study the contribution of the interphase zone in the overall elastic properties of nanocomposites 21 , 22 , 23 , 24 , 25 , They reported that the interfacial shear stress of between CNT reinforcements with an outer diameter of 1. In another study 23 , CNT pull-out from the polymer matrix was modeled with MD simulations to investigate the effects of the matrix density, chemical cross-links in the interface and geometrical defect in CNTs on the interfacial shear strength of CNT reinforced polyethylene composites.
Although the simulation studies on the pullout of CNT reinforcements from polymer matrices evidences the load transfer capability from polymer matrices to nanotubes, they do not provide mechanical properties of the nanocomposites and the interfacial region such Young's modulus and yield stress.
In this regard, other models were developed to measure the properties. Tsai et al. They developed a three-phase micromechanical model comprising the CNTs, effective interphase and polyimide polymer.
Yang et al. In the study, the constitutive relations were modified to study the interfacial separation by adopting a linear spring layer between the filler and matrix. Wang 26 developed a continuum modeling of the van der Waals vdW interactions between CNTs and polymers as mechanical spring elements by fitting the molecular mechanics results.
Based on the model, the interaction can be modeled as an external pressure on the tube walls. It is noted that the constitutive relations modified in the proposed models for the interfacial region are limited to a linear spring layer between reinforcements and matrix only in the radial direction. Because of the limitation of the models, the effect of bonding, debonding and relative sliding between fibers and matrix on the mechanical properties cannot be modeled properly.
On the other hand, since the interfacial shear stress between CNT reinforcements and matrix through the vdW interactions along the nanotubes axial direction was ignored in the proposed models, the prediction of mechanical properties of the CNT-composites cannot be reliable and properly identified.
Furthermore, changes in the adhesion behaviors at large strains caused by nonlinear effects between CNT fibers and surrounding polymer matrix in both radial and longitudinal directions were also neglected in the models. The effect of the aspect ratio of CNT fibers on the elastic properties of the interfacial region and the overall stiffness of the nanocomposites is investigated in details.
The feasibility of a developed three-phase micromechanical model in prediction of elastic properties of the nanocomposites based on the understanding of the interfacial region is examined through a verification process with molecular simulation results. A simulation unit cell with a size of 8. The PMMA polymer is generated by 10 repeated monomer units. The constant-strain energy minimization method is applied to calculate the elastic modulus of the polymer system. After an initial energy minimization, a small strain of 0.
The application of the tensile strain is accomplished by uniformly expanding the dimensions of the simulation cell in the direction of the deformation and re-scaling the new coordinates of the atoms to fit within the new dimensions. After each increment of the applied strain, the potential energy of the structure is re-minimized keeping the lattice parameters fixed. The total potential energy and the interaction energy are then measured in the minimized structure. This process is repeated for a series of strains.
Finally, the variation of the measured potential energies versus applied strain is used to calculate the effective Young's moduli of the interfacial region and composite as. Molecular unit cell model of PMMA matrix with a size of 8. The principle of the proposed method is based on a calculation of the interaction energy from the energy difference between the total internal energy of the composite and the sum of the energies of individual molecules:. It is noteworthy that in the absence of covalent chemical bonding, the interfacial bond strength comes from the electrostatic and vdW forces in the molecular system.
In order to examine the effectiveness and applicability of the method, we conduct the same process of applying tensile strain in the x-direction to a unit cell of amorphous PMMA polymer with a size of 8. In the study, the equilibrium distance between CNTs and polymer matrix, which varies from 0. The mass density of the PMMA polymer matrix is set to 1. The mass density of the polymer matrix is 1. For example, Young's modulus of the nanocomposite increases from 3.
Hence, the proposed method enables a direct derivation of the mechanical properties, i. The method also allows the consideration of the influence of nanoscale effects on the mechanical properties since all parameters affecting the amount of the interfacial energy, such as relative sliding between CNT reinforcements and matrix and the transverse deformation of nanotubes, are included in the variation of the interaction potential energy.
The diameter of the 5, 5 CNT reinforcements is 0. The mass density of PMMA polymer matrix is set to be 1. In simulations of nanocomposite unit cells reinforced by CNTs with an infinite length, periodic boundary conditions are imposed in all directions and no end effect of the CNTs such as a cap or hydrogenation is considered, as depicted in Figure 5.
Thus, the embedded CNT has infinite length. Molecular unit cell model of PMMA matrix with a size of 5. In addition, the Young's modulus of the nanocomposite with an infinite long CNT reinforcement significantly increases to While the Young's modulus of the nanocomposite significantly enhances by increasing the length-to-diameter ratio of CNTs, the Young's modulus of the interfacial region relatively experiences a slight increase from 0.
The Young's modulus of the interfacial region with an infinite long CNT reinforcement increases to 2. The mechanical behaviors observed in molecular simulations can be interpreted by developed micromechanical continuum models. Micromechanical models provide simple approaches to predict overall properties of composites using geometries and properties of individual phases that constitute the materials.
Two-phase micromechanical models, such as the Mori—Tanaka method 27 , 28 , assume that only matrix and reinforcement phases exist in a composite material and they are perfectly bonded to each other.
Although the models are precise enough when the size of reinforcements is in the order of micrometers or higher, the reinforcement and adjacent polymer region were not accurately described Hence, they are inaccurate in predicting properties of the composites with shorter reinforcements.
Due to the aforementioned drawbacks, the effective interface model that considers three phases co-existence i. The effective interface model was used to predict the elastic properties of composites with effective reinforcements with an interface of the same shape as the effective fibers as illustrated in Figure 6.
The effective interface has a finite size surrounding the reinforcement, which is referred to as an interphase or an interfacial region. Based on this model, the bulk elastic stiffness of composite E c is predicted as. T f and T fi are the dilute strain concentration tensors given by In Eq.
The key result of Eshelby is to show that within a fiber the strain is uniform. We now apply the three-phase theory in investigation of mechanical properties of CNT-PMMA composites based on the derivation of the interfacial region developed in the previous section. In order to use the micromechanical model, the Young's moduli of the interfacial region and PMMA polymer matrix are taken from molecular simulation results presented in Tables 1 and 2. The Young's modulus of a 5, 5 CNT reinforcement is also measured to be 1.
It is noteworthy that in calculation of the Young's modulus of the CNT, the nanotube is supposed to be a solid bar with a cross sectional area of. From Figure 7 , an excellent agreement between results obtained from the effective interface model and MD simulations is obtained.
The percentage difference decreases to 7. For infinite long CNT fiber, the stiffness of the composite is respectively obtained to be Hence, it is expected that the effective interface model is applicable to nanometer-sized reinforcements.
It is noteworthy that the key point in a successful application of the effective interface model is to determine mechanical properties of the interfacial region using molecular simulations. A new method for the measurement of the elastic properties of the interfacial region between the CNT reinforcements and the PMMA polymer matrix is proposed.
The effect of the aspect ratio of CNT fibers on the elastic properties of the nanocomposites and the interfacial region between nanotubes and the polymer matrix is explored. Simulation results demonstrate that the Young's modulus of a PMMA polymer matrix composite reinforced by an infinite long 5, 5 CNT significantly increases to An effective continuum interface model based on the results from the interfacial region was developed and its feasibility in prediction of elastic properties of the nanocomposites is justified through a verification process with molecular simulation results.
First, a two two-dimensional model of PMMA polymer with 10 repeated monomer units is constructed. An energy minimization is performed by using the conjugate-gradient method 32 on the molecule to achieve a reasonable three-dimensional model. Partial charges of atoms were assigned using Qeq method Next, a number of the PMMA molecules are packed into a cubic lattice corresponding to a predefined density of 1. The module builds molecules in a cell with a Monte Carlo fashion, by minimizing close contacts between atoms, whilst ensuring a realistic distribution of torsion angles for a given force-field.
In this work, we choose COMPASS force-field 34 , which is the first ab initio force-field that enables accurate and simultaneous prediction of a broad range of molecules and polymers. In the nonbonding terms, van der Waals interaction energy and coulombic interaction energy terms are included for the force-field.
A potential cutoff of 1. In order to find a global minimum energy configuration, we utilize the approach by Li and Mattice 35 in the refinement procedure.
Polymer Matrix Composites: Properties, Production, and Applications
Mechanical properties of polymer composites reinforced by silica-based materials of various sizes
The increase of environmental awareness has led to interest in the use of materials with eco-friendly attributes. In this study, a sandwich composite was developed from polyester and kenaf fiber with various orientation arrangements. The tensile, flexural, and Izod impact tests of the sandwich composites were evaluated by using a universal tensile tester and an impact tester.
A composite material also called a composition material or shortened to composite , which is the common name is a material which is produced from two or more constituent materials. Within the finished structure, the individual elements remain separate and distinct, distinguishing composites from mixtures and solid solutions. Typical engineered composite materials include:. There are various reasons where new material can be favoured. Typical examples include materials which are less expensive, lighter or stronger when related to common materials.
At present, to prepare pure CNTs materials is quite difficult and the mechanical properties of the materials are limited in a low level. Because of their extraordinary mechanical properties and high aspect ratio, CNTs are considered to be ideal candidates for polymer reinforcement.
Polymer Matrix Composites: Properties, Production, and Applications
Not a MyNAP member yet? Register for a free account to start saving and receiving special member only perks. Materials as a field is most commonly represented by ceramics, metals, and polymers. While noted improvements have taken place in the area of ceramics and metals, it is the field of polymers that has experienced an explosion in progress.
Polymer composites have good mechanical, friction, durability, and wear performance after being reinforced with waste or nanofiller. These features make them flexible in many structural applications. This study was carried out to improve the mechanical performance of polymer composites using silica-based, waste, and nanomaterials.
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