Aleksandra M. Vinogradov

Electro-mechanical properties of the piezoelectric polymer PVDF

Abstract A consistent experimental program has been developed to investigate the mechanical and electrical properties of polyvinylidene fluoride (PVDF). The results of the study indicate that this piezoelectric polymer can be characterized as an orthotropic, thermorheologically simple material with constant piezoelectric strain coefficients over the experimental range of stresses, frequencies and temperatures. The mechanical properties of PVDF are time-dependent and, under certain loading and temperature conditions, can be treated using the principles of linear hereditary viscoelasticity.

State-of-the-Art Developments in the Field of Electroactive Polymers

The paper presents a brief review in the field of electroactive polymers. it outlines the main classes of electroactive polymers, their properties and applications. Current efforts to synthesize electroactive polymers with novel or improved characteristics along with the challenges, opportunities and future research directions in the subject area are discussed.

Constitutive model of piezoelectric polymer PVDF

The paper concerns the development of a time dependent constitutive model of polyvinylidene fluoride (PVDF), a thin film piezoelectric polymer. Experimental evidence indicates that PVDF thin films can be characterized as orthotropic materials with different material properties in regard to the orientation of the aligned molecular chains of the polymer. Based on the experimental results, the constitutive equations of linear hereditary viscoelasticity are used to characterize the mechanical properties of PVDF.

Accomplishments and future trends in the field of electroactive polymers

The paper provides a summary review of the accomplishments and challenges in the field of electroactive polymers (EAP). It consists of three parts. The first part outlines the main classes of EAP, their properties and applications. Efforts to enhance the functional performance of EAP are discussed. The second part summarizes the development and use of electroactive polymer based composites. Challenges, opportunities and future research directions in the field are discussed in the third part. The issues of particular interest concern accurate material characterization of electroactive polymers, their time dependent behavior, constitutive modeling, and cyclic loading effects that determine the long-term functionality, integrity and durability of electroactive polymers. Research efforts in these focus areas are necessary to ensure effective integration of EAP in multifunctional material systems.

Structure-material relations in the buckling problem of asymmetric composite columns

Abstract The paper examines the effects of material composition and properties on the non-linear buckling response of asymmetric laminated structures. The problem is studied through the analysis of asymmetric laminated columns composed of an arbitrary number of different material layers. The non-linear buckling behavior of the columns subjected to combined compression and bending is examined depending on parameters such as the number, orientation and stacking sequence of the layers that make up the laminate. The analysis demonstrates that, under certain conditions, asymmetric laminated columns subjected to combined compression and bending exhibit bifurcation. In such cases, the onset of lateral deformations of the columns is delayed until the applied moment–force system attains its critical value. Based on the analytical solution of the non-linear buckling problem under consideration, the potentials for maximizing the critical load and controlling the buckling characteristics of laminated composites through tailoring their material properties are analyzed.

Creep-Fatigue Relationships in Electroactive Polymer Systems and Predicted Effects in an Actuator Design

The paper concerns the time-dependent behavior of electroactive polymers (EAPs) and their use in advanced intelligent structures for space exploration. Innovative actuator design for low weight and low power valves required in small plants planned for use on the moon for chemical analysis is discussed. It is shown that in-depth understanding of cyclic loading effects observed through accelerated creep rates due to creep-fatigue interaction in polymers is critical in terms of proper functioning of EAP based actuator devices. In the paper, an overview of experimental results concerning the creep properties and cyclic creep response of a thin film piezoelectric polymer polyvinylidene fluoride is presented. The development of a constitutive creep-fatigue interaction model to predict the durability and service life of EAPs is discussed. A novel method is proposed to predict damage accumulation and fatigue life of polymers under cyclic loading conditions in the presence of creep. The study provides a basis for ongoing research initiatives at the National Aeronautics and Space Administration Kennedy Space Center in the pursuit of new technologies using EAP as active elements for lunar exploration systems.

Time-Dependent Response of Thin-Film Piezoelectric Polymer Polyvinylidene Fluoride

A summary of recent research results regarding the time-dependent response of a thin-film piezoelectric polymer polyvinylidene fluoride is presented. At present, polyvinylidene fluoride and its copolymers comprise the principal commercially available group of polymers that exhibit strong piezoelectric properties. In this paper, the mechanical response of polyvinylidene fluoride has been studied on the basis of a comprehensive experimental program. It is shown that, within certain limits, the material can be treated as linearly viscoelestic. However, under long-term conditions involving superimposed static and oscillatory loads, the polymer tends to exhibit nonlinear creep behavior that depends on the magnitude of mean stresses, stress amplitudes, and frequencies. The findings reported are of immediate practical significance given that polyvinylidene fluoride thin films are typically employed as sensors or actuators designed to function in vibratory environments.

Buckling resistance of composite wind turbine blades

The paper concerns the buckling analysis and optimization of composite wind turbine blade substructures. Attention is focused on the compression response of a laminated web element under the action of combined compression and bending. The study is based on general assumptions regarding the properties, number and stacking sequence of the layers. Buckling and postbuckling responses of the web element are studied, and the critical buckling condition is obtained based on nonlinear analysis. It is shown that the buckling resistance of the web element can be enhanced by tailoring the material composition and properties of the laminate.

Coupled Durability and Functionality of Piezoelectric Polymers

The main characteristic of piezoelectric polymers is coupling of their mechanical and physical properties. In this view, progressive material degradation of the polymers under cyclic loading conditions is an important factor in terms of both their long-term integrity and functional performance. The study reported herein demonstrates that the piezoelectric polymer polyvinylidene fluoride (PVDF) tends to exhibit accelerated creep rates under superimposed static and cyclic loads. Creep acceleration under such conditions has been observed even in the range of stresses well below the viscoelastic linearity limit. In the paper, the effects of material degradation caused by creep-fatigue interaction in PVDF are discussed. The study includes efforts to develop a constitutive viscoelastic material model taking into account damage evolution due to synergistic creep-fatigue interaction effects. The model is based on the principles of continuum damage mechanics and linear viscoelasticity.Copyright

Vibrocreep and Cyclic Damage of Polymers

The paper concerns the time-dependent response of polymer systems subjected to superimposed static and cyclic loads. An overview of recent experimental results regarding the cyclic creep response of two polymers, Nylon 6/6 and polyvinylidene fluoride (PVDF) is presented. It is shown that both materials have demonstrated accelerated creep rates due to cyclic loading effects. This phenomenon, defined as “vibrocreep”, is essentially nonlinear, since the material response under combined static and cyclic loads does not represent a simple superposition of the responses to static and fully reversed cyclic loads applied separately. Further, a nonlinear constitutive model, describing the interaction between creep and cyclic damage evolution in polymers is formulated. This constitutive model combines the concepts of linear viscoelastic theory of hereditary type with damage characterization using a damage function. It is shown that the damage function depends on the number of loading cycles and can be determined experimentally. In the paper, experimental results validating the developed constitutive model are presented.Copyright