Olesya I. Zhupanska

Effects of an electromagnetic field on the mechanical response of composites

The existing experimental evidence suggests that exposure of a composite material to an electromagnetic field leads to changes in the materials strength and resistance to delamination. In this work, the mechanical response of transversely isotropic graphite/epoxy composite plates in the presence of an electromagnetic field is studied. The interacting effects of the in-plane steady and slowly varying electric current, external magnetic field, and mechanical load as well as the effects of mechanical and electrical anisotropies are investigated. It is shown that an electromagnetic field may significantly enhance or reduce the deformed state of the composite plate depending on the direction of its application and its intensity.

Axisymmetric contact with friction of a rigid sphere with an elastic half-space

The problem of normal contact with friction of a rigid sphere with an elastic half-space is considered. An analytical treatment of the problem is presented, with the corresponding boundary-value problem formulated in the toroidal coordinates. A general solution in the form of Papkovich–Neuber functions and the Mehler–Fock integral transform is used to reduce the problem to a single integral equation with respect to the unknown contact pressure in the slip zone. An analysis of contact stresses is carried out, and exact analytical solutions are obtained in limiting cases, including a full stick contact problem and a contact problem for an incompressible half-space.

The Effect of Orientational Distribution of Nanotubes on Buckypaper Nanocomposite Mechanical Properties

This study is concerned with the effects of single-wall carbon nanotubes’ orientational distribution in the buckypaper on the overall mechanical properties of a buckypaper nanocomposite. A micromechanical model that includes prescribed orientational dependence and anisotropy of nanotubes is considered. The model is based on the Mori-Tanaka approach. The validity of the model is discussed in the context of rigorous classical bounds. The results show that all five transversely isotropic effective moduli of buckypaper nanocomposites show strong dependence on the degree of nanotubes’ alignment.

Mechanical Response of Composites in the Presence of an Electromagnetic Field

The existing experimental evidence suggests that exposure of a composite material to the electromagnetic field leads to changes in the material’s strength and resistance to delamination. In this work, the mechanical response of transversely isotropic graphite/epoxy composite plates in the presence of an electromagnetic field is studied. Interacting effects of the in-plane steady and slowly varying electric current, external magnetic field and mechanical load, as well as effects of mechanical and electrical anisotropies are investigated. It is shown that electromagnetic field may significantly enhance or reduce the deformed state of the composite plate depending on the direction of its application and its intensity.

Reliability Analysis of Wind Turbine Blades for Fatigue Life under Wind Load Uncertainty

This study presents a methodology that analyzes the fatigue reliability of a composite wind turbine blade considering wind load uncertainty. To facilitate the reliability analysis of wind turbine design, the turbulent random wind field has been simulated and characterized by two random variables, 10-minute mean wind speed and 10-minute turbulence intensity factor. The well-known Weibull distribution of 10-minute mean wind speed has been validated by statistically analyzing measured wind speed data. A log-logistic distribution is first proposed to represent the distribution of 10-minute turbulence intensity factor. By using both the mean wind speed and the turbulence intensity factor, the chaotic characteristic of a random wind field can be accurately rendered. The uncertainties of parameters determining the Weibull and log-logistic distribution are further studied such that the spatiotemporal wind uncertainty can be accurately represented. A hierarchical expanded wind uncertainty representation method is proposed for reliability analysis of wind turbine blades. A comprehensive procedure, including random wind simulation, aerodynamic analysis, composite structural analysis and fatigue damage calculation has been realized to predict the fatigue life of a simulated blade model. The reliability of a 5-MW reference wind turbine blade is evaluated to investigate the effect of the spatiotemporal wind uncertainty towards fatigue life.

A Study of Impacted Electromechanically Loaded Composite Plates

Experimental results suggest that exposure of composite materials to the electromagnetic field leads to increase in the materials strength and impact resistance to delamination. The factors contributing to this phenomenon are related to deformation of composites due to coupling of mechanical and electromagnetic fields and/or changes in the material properties associated with microscopic processes resulted from the application of an electromagnetic field to the composite material (Joule heating effects, fiber-matrix interface changes). As a step to building a comprehensive model involving all these factors, in this work an analysis of impacted composite plates in the presence of the electromagnetic load is presented.

Mechanical properties of microcrystalline cellulose: Part II. Constitutive model

An elastic/viscoplastic model with non-associated flow rule for microcrystalline cellulose powder PH-105 with mean particle size 20 μm is formulated using experimental data from a number of triaxial tests. The model reproduces the major aspects of the complex powder response that is governed by plastic (dependent on history of the loading) effects, time effects (both creep and relaxation) and irreversible volumetric changes (it is practically the compressibility that was observed in the experiments on the microcrystalline cellulose powder with mean particle size 20 μm). Constitutive parameters and functions of the presented model (the elastic parameters, yield function and viscoplastic potential) were determined directly from the experimental data. Finally, the validity of the model has been discussed.

Micromechanical modeling of metal-ceramic composites for high temperature applications

This paper is concerned with the evaluation of the overall temperature-dependent elastic, thermal, and thermo-elastic material properties of metal-ceramic composites for high temperature applications. Effective properties of an aluminum/zirconia composite are obtained using micromechanics models and finite element analysis of representative volume elements (RVEs). RVE microstructures consisting of mono-sized spherical reinforcement particles embedded in a unit cube matrix were generated using a random sequential adsorption algorithm and event driven molecular dynamics simulation. The adopted algorithm allowed generating microstructures with high volume fractions of reinforcement particles up to 61%. Finite element analysis was performed to determine effective properties of the composite over a wide temperature range. The obtained computational results for effective elastic, thermal, and thermal expansion properties are consistent with the known analytical bounds.

A Markov Chain Approach to Analysis of Cooperation in Multi-Agent Search Missions

We consider the effects of cueing in a cooperative search mission that involves several autonomous agents. Two scenarios are discussed: one in which the search is conducted by a number of identical search-and-engage vehicles, and one where these vehicles are assisted by a search-only (reconnaissance) asset. The cooperation between the autonomous agents is facilitated via cueing, i.e. the information transmitted to the agents by a searcher that has just detected a target. The effect of cueing on the target detection probability is derived from first principles using a Markov chain analysis. Exact solutions to Kolmogorov-type differential equations are presented, and existence of an upper bound on the benefit of cueing is demonstrated.

Impact Damage Assessment in Electrified Carbon Fiber Polymer Matrix Composites

In this work we present experimental and theoretical results on the low velocity impact of electrified carbon fiber polymer matrix unidirectional and cross-ply composites. A particular emphasis is given to the analysis of the influence of Joule heating on the alteration of the mechanical response of electrified composites. The results show that a short term current application leads to an increase in the impact resistance of electrified composites whereas a long term application of a DC current has a detrimental effect. A mathematical model to study the time dependent Joule heating in composites has been developed. The role of the current density and other material parameters has been elucidated.