Application Of Micromechanical Models Research Articles

Micromechanics of Ti3C2Tx MXene reinforced poly(vinyl alcohol) nanocomposites

The key to effective mechanical reinforcement in polymer nancomposites lies within the stress transfer mechanisms and the distribution of the nanofillers within a polymer matrix. In this work, the micromechanics of Ti3C2Tx MXene-reinforced poly(vinyl alcohol) (PVA) nanocomposites have been studied in detail. Ti3C2Tx MXene/PVA nanocomposites were prepared by solution blending. The spatial orientation of Ti3C2Tx MXene in the nanocomposites was characterized by polarized Raman spectroscopy and the orientation factor was correlated to the effective Young's modulus of the flakes through well-established micromechanical theories. The mechanical properties of the nanocomposites were evaluated by tensile testing. A 27% increase in Young's modulus and a 24% improvement in tensile strength were achieved by addition of only 0.6 wt% Ti3C2Tx. Efficient stress transfer from the polymer matrix to Ti3C2Tx MXene in bulk nanocomposites has been observed through strain-induced Raman band shifts for the first time. The effective Young's modulus of the MXene nanoplatelets was calculated to be in the order of 300 GPa, in good agreement with the values derived from the application of micromechanical models.

Homogenization of Elastic Properties of Short Fiber Reinforced Composites Based on Discrete Microstructure Data

AbstractSince the microstructure of short fiber reinforced composites is inhomogeneous, the application of micromechanical models is useful, that take into account their characteristics like the fiber orientation and the aspect ratio of fibers. Two different methods are considered in this work: A two‐step approach is utilized to get approximately the upper and lower bounds of the elastic properties. Furthermore, an approximation for the elastic properties is calculated by the self‐consistence method. Both methods use discretely microstructural information including the length, the diameter and the orientation of each single fiber. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Inverse determination of modeling parameters to consider inhomogeneities of semicrystalline thermoplastics in structure simulations

Two semicrystalline thermoplastics, an isotactic polypropylene (iPP, LynedllBasell Moplen HP501L) and a polyethylene-high-density (PE-HD, LynedllBasell Hostalen GC7260), were selected to approve a new approach. The developed approach allows the inverse determination of the amorphous and crystalline mechanical as well as the crystalline geometric constituents’ properties. Commonly, these properties are unknown in structure simulations, and hence, the application of micromechanical models to the inhomogeneous microstructure of semicrystalline thermoplastics is restricted. Rather, a homogenous microstructure is assumed, and only one Young’s modulus and Poisson’s ratio are used in calculations. Thus, the quality and reliability of simulations are limited. In the current study, a new approach was exemplarily conducted for the inverse determination of the required properties by combining a Mori–Tanaka mean field approach with a genetic optimization algorithm. Conclusive results were achieved for both polymers. According to the results, the attained geometric parameters for the crystalline constituents resemble the aspect ratio of the spherulite diameter and the long period of the real crystalline microstructure, and the mechanical properties of the amorphous and crystalline constituents are located within reasonable bounds.

On using micromechanical models to describe dynamic mechanical behavior of asphalt mastics

The applicability of micromechanical models in describing the dynamic mechanical behavior of asphalt mastics is explored. The complex sets of equations from the “generalized self-consistent scheme” (GSCS) are simplified using an order of magnitude analysis. The simplification provides a better perspective and insight into how the model operates and predicts. For asphalt mastics, it is found that the stiffness ratio is sensitive only to the Poisson’s ratio of the binder and the volume fraction of the fine aggregates. The results from the model when compared with experimental data indicate that the theoretical predictions fall short of the experimental values. This is because the GSCS model in its original complex form as well as in the simplified form is unable to capture the effects of all the variables involved in the increase of the stiffness ratio of the mastics. The concepts of percolation theory are incorporated to obtain a modified form of the model. This modified model fits the experimental data of asphalt mastics well when appropriate values of two adjustable parameters, namely, the volume fraction at percolation threshold and the maximum volume fraction of the filler are used.

Application of micromechanical model to high strain rate superplastic materials

Application of micromechanical model to high strain rate superplastic materials

CVD SiC fiber-reinforced barium aluminosilicate glass—ceramic matrix composites

Unidirectional CVD SiC (SCS-6) monofilament reinforced BaO Al 2O 3 2SiO 2(BAS) glass—ceramic matrix composites have been fabricated by a tape lay-up method followed by hot pressing. The glass matrix flows around fibers during hot pressing resulting in nearly fully dense (95–98%) composites. Strong and tough composites having first matrix cracking stress of 250–300 MPa and ultimate flexural strength as high as 900 MPa have been obtained. Composite fracture surfaces showed fiber pullout with no chemical reaction at the fiber/matrix interface. From fiber push out, the fiber/matrix interfacial debond strength and the sliding frictional stress were determined to be 5.9 ± 1.2 MPa and 4.8 ± 0.9 MPa, respectively. The fracture surface of an uncoated SiC (SCS-0)/BAS composite also showed fiber/matrix debonding, fiber pullout, and crack deflection around the fibers implying that the SiC fibers may need no surface coating for reinforcement of the BAS glass-ceramic. Applicability of micromechanical models in predicting the first matrix cracking stress and the ultimate strength of these composites has also been examined.