The frequency dependencies of the threshold voltage of electrohydrodynamic instability in nematic liquid crystals were investigated as functions of the dielectric anisotropy (-1.5 O and the homeotropic orientation at all the frequencies (the circular and fingerprint-type domains); c) in the isotropic phase. The threshold voltage in the nemataic phase was shown to be independent of the anisotropy parameters and the orientation of a liquid crystal and to coincide with the threshold of the instability in the isotropic phase. Thus, we came to the conclusion that the instability has the isotropic character in all the cases investigated.

Dielectric Regime of Electrohydrodynamic Instability in Nematic Liquid Crystals

We compare the convenience offered by alternative ways of recording thermal expansion data. Limitations imposed on the values, for every day engineering, of the linear thermal expansion coefficients of laboratory produced carbon fibre reinforced plastics are assessed. It is concluded that the commonly encountered levels of moisture content, voids and effects due to the misalignment and non-uniform distribution of fibres do not provide cause for serious concern in most applications. The practical consequences of thermo-elastic stress are deemed to be more important. It is concluded that provided sensible account is taken of the experience accumulated over the years from the production and application of carbon fibre reinforced plastics, laminate theory may be confidently applied to laboratory data in order to gain a good idea of the behaviour expected from new constructions under normal operating conditions.

The thermal expansion of carbon-reinforced plastics

In this work, a multi-scale modeling approach for simulation of components made from biaxial braided composites has been developed. Based on experimental investigations on the yarn architecture and the mechanical behavior the constitutive behavior of the braided composites was predicted by using a novel approach for FE unit cell modeling. The unit cell results were subsequently used to formulate a nonlinear macroscopic failure model for biaxial braided components.

Experimental Characterization and Numerical Modeling of the Mechanical Response for Biaxial Braided Composites

The amplitude-dependent internal friction in carbon fiber reinforced plastic (CFRP) laminates subjected to fatigue cycling has been measured and analyzed to convert into the plastic strain of the order of 10-8 as a function of effective stress. The microplastic flow indeed occurs in the stress range three orders of magnitude lower than the failure stress, and the stress-strain curves tend to shift to a lower stress as the number of cycles increases, thus indicating a decrease in the CFRP strength. The microflow stress at the plastic strain of 1×10-8 keeps a constant value of about 0.4 MPa in the range less than 103 cycles but then decreases gradually, whereas the Young's modulus evaluated from the resonant frequency is almost constant up to 104 cycles where only transverse cracks are found. Thus we can successfully detect the onset of fatigue deterioration by means of the amplitude-dependent internal friction.

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Amplitude-Dependent Internal Friction Study of Fatigue Deterioration in Carbon Fiber Reinforced Plastic Laminates

The mechanical behavior of carbon nanotube reinforced polystyrene is modeled and tested. The elastic behavior is predicted using the Mori-Tanaka theory for randomly oriented short fiber composites. Simulation of the elastic behavior incorporates modeling the commercially available nanotubes using conventional fiber mechanics and finite element methods on a representative volume element consisting of the nanotube, the interface, and the surrounding matrix. Different strain rates, volume fraction of nanotubes in the polymer, and strain recovery of the composites are experimentally compared to unreinforced polystyrene in order to compare the effect the nanotubes have on the mechanical behavior of the composite material.

Elastic and Viscoelastic Modeling of Carbon Nanotube Reinforced Polystyrene

Hysteresis behaviour during tensile microstrain and constant amplitude load cycling has been studied with CFRP of approximately 50% fibre volume fraction. This hysteresis is explained in terms of the residual strain in the composite caused by the different thermal expansion coefficients of the fibre and matrix. The energy loss during cyclic deformation presented in terms of specific damping capacity was virtually constant after a rapid decrease during the first few cycles. Simultaneous measurement of the acoustic emission energy released showed similar trends. The mode of failure after cyclic loading was markedly different from that obtained by direct tensile loading.

https://iopscience.iop.org/article/10.1088/0022-3727/6/15/301/pdf

F L Matthews

Papers

Hysteresis behaviour in CFRP