Deformation Of Nanocomposites Research Articles

Role of cellulose nanocrystals on hysteretic sorption and deformation of nanocomposites

A molecular model of an all-cellulose nanocomposite, with an amorphous cellulose matrix reinforced by cellulose nanocrystals, is built to study the role of cellulose nanocrystal (CN) as a nanofiller in the coupled behavior between sorption and deformation. We find two competitive mechanisms. The first mechanism is the reinforcing effect through CN-matrix mechanical interaction, which constrains the sorption-induced swelling of the matrix and results in a reduction of sorption amount and of hysteresis in both sorption and deformation. The second mechanism is the CN-water interaction, enhancing water sorption in the matrix at the CN-matrix interface, increasing the sorption-induced swelling of the matrix, and increasing the resulting hysteresis in sorption and deformation. The final gain/reduction in sorption, swelling and related hysteresis depends on which of the two effects prevails. These findings shed light on the tailoring of cellulose-based composites for applications involving sorption and deformation.

Simulation of deformation and fracture processes in nanocomposites

The paper studies the processes of deformation and fracture in nanocomposites. The study was curry out by the method of mathematical modeling. The behavior of the nanosystem was described by the molecular dynamics apparatus. A modified immersed atom method was used as a potential. Demonstrated theoretical approaches to the study of the mechanical properties of nanocosposites and the processes of their destruction. Formulas for calculating the stress, strain tensors and displacement veare given. To maintain a constant temperature in the nanosystem, a Nose – Hoover thermostat was used. The destruction of nanocomposites was considered in the process of tension and shear deformation. Pure aluminum, a composite with an aluminum matrix and a filler in the form of spherical iron particles, and a composite with an aluminum matrix and a filler in the form of a cylindrical iron fiber were used as samples. After the filler was introduced into the nanocomposite, the sample was relaxed to ensure its more stable state. The simulation allowed us to establish the basic laws of changes in the atomic structure of the matrix and nanocomposite fillers during deformation and fracture. It is shown that the processes of deformation and destruction of nanocomposites substantially depend both on the structure and types of loading of the material. The results of the research can be used to study the processes of deformation of nanocomposite materials with promising functional properties.

Reversible Loss of Bernal Stacking during the Deformation of Few-Layer Graphene in Nanocomposites

The deformation of nanocomposites containing graphene flakes with different numbers of layers has been investigated with the use of Raman spectroscopy. It has been found that there is a shift of the 2D band to lower wavenumber and that the rate of band shift per unit strain tends to decrease as the number of graphene layers increases. It has been demonstrated that band broadening takes place during tensile deformation for mono- and bilayer graphene but that band narrowing occurs when the number of graphene layers is more than two. It is also found that the characteristic asymmetric shape of the 2D Raman band for the graphene with three or more layers changes to a symmetrical shape above about 0.4% strain and that it reverts to an asymmetric shape on unloading. This change in Raman band shape and width has been interpreted as being due to a reversible loss of Bernal stacking in the few-layer graphene during deformation. It has been shown that the elastic strain energy released from the unloading of the inner graphene layers in the few-layer material (∼0.2 meV/atom) is similar to the accepted value of the stacking fault energies of graphite and few layer graphene. It is further shown that this loss of Bernal stacking can be accommodated by the formation of arrays of partial dislocations and stacking faults on the basal plane. The effect of the reversible loss of Bernal stacking upon the electronic structure of few-layer graphene and the possibility of using it to modify the electronic structure of few-layer graphene are discussed.

Novel high-performance nickel/poly(ether ether ketone) nanocomposites

The present investigation deals with the preparation and characterization of nanocomposites of poly(ether ether ketone) (PEEK) containing nanosized nickel filler up to 3 wt% loading. Characterization of the developed nanocomposites has been carried out by various advanced analytical techniques. Thermogravimetric analysis study depicts that the prepared nanocomposites exhibit enhanced thermal stability. Dynamic mechanical analysis (DMA) technique has been utilized to investigate the viscoelastic deformation of nanocomposites. From DMA studies, it has been demonstrated that with the increase in nano-nickel content, the stiffness of nanocomposites decreases and a very minute change in glass transition temperature ( Tg) has been noticed. The resulting nanocomposites show the optimum improvement in Young’s modulus, tensile strength, flexural strength and flexural modulus. Scanning electron microscopy study reveals that he dispersion of nano-nickel particulates is uniform throughout the PEEK matrix.

Effect of Silicon Carbide Nanoparticle Additions on Microstructure and Mechanical Behavior of Maleic Anhydride Compatibilized High Density Polyethylene Composites

Maleated high density polyethylene (mPE) loaded with 2, 4, 6 and 8 wt% SiC nanoparticles (SiCnp) were prepared by injection molding. The effect of SiCnp additions on the microstructure and mechanical properties of mPE were studied using X-ray diffraction (XRD), polarizing optical microscopy (POM), heat deflection temperature (HDT), tensile and Izod impact measurements. XRD and POM results showed that the SiCnp additions reduce the crystallite thickness and spherulite size of mPE. HDT measurements revealed that SiCnp additions enhance the thermal stability of mPE considerably. Tensile test showed that the addition of 2 wt% SiCnp improves the Young's modulus and yield strength of mPE at the expenses of elongation at break and impact strength. SEM fractography was used to reveal the failure deformation of nanocomposites after impact test. The low impact strength of mPE/SiCnp nanocomposites was related to the absence of particle cavitation and matrix fibrillation. The impact fracture deformation of such nanocomposites is discussed.

Establishing fundamentals of the mechanics of nanocomposites

The paper proposes a basic approach to study the mechanical properties of nanocomposite materials with polymer matrix and the deformation of nanocomposites and structural members made of them. The notions of homogenization and continualization are discussed with reference to nanocomposite materials. Four main tasks for nanocomposite mechanics are defined: (i) description of the properties of nanoformations, (ii) description of the properties of the matrix (binder), (iii) description of phenomena at the matrix-nanoformations interfaces, and (iv) determination of the effective properties of nanocomposites to change over to the mechanics of structural members. Particular attention is given to the interface conditions between the matrix and reinforcement. The role of lower and upper bound estimates is pointed out. The basic models of linear or nonlinear micro-and nanocomposites are considered. These models are used in a numerical analysis. The analysis makes it possible to observe and describe the peculiarities of the processes of fracture, deformation, and wave propagation in nanocomposite materials with polymer matrix. The numerical results are presented in the form of plots

Size Effects on the Plastic Deformation of Nanocomposites Prepared from SiCN and SiCNAlYO Nanopowders Synthesized by Laser Pyrolysis

ABSTRACTThe aim of this work was to synthesise nanopowders by laser pyrolysis in order to elaborate Si3N4-SiC nanocomposites exhibiting a high ductility at high temperature. The synthesis of SiCN and SiCNYAlO nanopowders with a good thermal stability has been developed from a liquid mixture based on hexamethyldisilazane with a gaseous precursor (silane, SiH4) and ammonia. Si3N4-SiC nanocomposites exhibiting almost theoretical density have been elaborated by hot pressing under 35 MPa at 1600°C either from SiCNYAlO nanopowders or from SiCN nanopowders mixed with commercial sintering aids nanopowders (6 wt% yttria and 3 wt% alumina) in ethanol and de-agglomerated by milling with Si3N4 balls. The densification behaviour is better for nanopowders containing in-situ additives. In addition, using prealloyed powders enables to simplify the elaboration process since the mixing step of the nanopowders is eliminated. The nanocomposites elaborated from the mixture (SiCN + commercial sintering aids) exhibit a different microstructure, depending on the drying process (under vacuum or in an oven) of the nanopowders after the mixing step: When drying was performed in a confined atmosphere, a noticeable amount of Si2N2O was detected in addition to β-Si3N4 and the average grain size was 60 nm, whereas the crystalline phases were α- and β-Si3N4, when the slurry was dried under vacuum and the average grain size was 200 nm. The creep behaviour of the two grades was assessed under compressive loading in air and the deformation appears strongly influenced by this change of the microstructure: A strong ductility was observed for the smallest grain size: a deformation as high as 45 % was measured under a compressive load of 180 MPa at 1350°C under air.