Robert L. Sierakowski

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.

Preliminary assessment of electrothermomagnetically loaded composite panel impact resistance/crack propagation with high-speed digital laser photography

This reports documents the baseline development of high-speed laser photography based assessment technique to determine effects of material resistance to puncture or fracture. A series of ballistic experiments were performed to at the Dynamic Event Imaging Laboratory at the Munitions Directorate, Air Force Research Laboratory site at Eglin, AFB, Florida. These experiments were performed to assess the effectiveness of laser photography to document the formation and propagation of cracks in composite materials with and without electromagnetic loading. These experiments were the first fully operational use of a novel and unique experimental capability for high-speed digital laser photography. This paper details the development of the experimental procedures and initial results of this exciting new tool. This report documents the experiments performed and the instrumentation developed along with recommendations for additional research.

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.

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.

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.

A Study of Composite Strengthening Through Application of an Electric Field

Abstract : This paper studies effects of an electric field on the mechanical response of unidirectional carbon fiber polymer matrix composites. The existing experimental evidence suggests that exposure of a composite material to the electromagnetic field leads to changes in the materials strength and resistance to delamination. We have analyzed the effects promoting this phenomenon: coupling of mechanical and electromagnetic fields and Joule heat effects and develop an experimental setup for impact tests of the composites carrying an electric current. Experimental results of low velocity impact tests on unidirectional carbon fiber polymer composite plates carrying a DC electric current show that electrified composites fail at higher impact load. Moreover, a larger electric field leads to a larger impact load that may be sustained by the composite. Finally, analysis of the Joule heat effects reveals that it is not a primary mechanism for the strengthening phenomenon observed in the experiments.

Analysis of electric field induced changes on the response of carbon fiber polymer matrix composites

Our recent studies 1-3 show that application of an electric current to carbon fiber reinforced polymer matrix composites may lead to an increase in the maximum impact load and reduction of the impact damage. In general, the influence of the electric field on the mechanical response of electrically conductive composites is characterized by a complex array of factors, which manifest themselves at both macro- and microscales. With respect to carbon fiber polymer matrix composites that we are interested in, a number of basic factors can be distinguished: (i) coupling of the mechanical and electromagnetic fields if both mechanical and electromagnetic loads are applied; (ii) electric current induced heating; (iii) change in the failure mechanisms in the presence of the electromagnetic field. Mathematically speaking, to study the interaction of mechanical and electromagnetic fields in composites one has to solve a coupled system of equations of motion, Maxwell’s electrodynamic equations, and heat transfer equations. Within this framework we have developed a mathematical model to study the response of carbon fiber polymer matrix composite plates to the applied electric current and mechanical loads. A particular emphasis has been placed on the investigation of coupling between electromagnetic, mechanical and associated thermal loads and analysis of the stresses and deformation caused by coupled loads.

Beams Columns and Rods of Composite Materials

A beam, column or rod is a long thin structural component of width b, height h and length L, where b/L ≪ and h/L ≪ 1, as shown in Figure 4.1

Heat transfer and thermal stress analysis in electrified CFRP composites

Our recent studies 1,2 demonstrate that application of an electric current to carbon fiber reinforced polymer (CFRP) matrix composites may lead to an increase in the maximum impact load and reduction of the impact damage, whereas a prolonged application of the current has a rather detrimental effect due to current induced heating. In this paper we discuss thermal effects in electrified composites due to applied electric current. In particular, electric induced heating and thermoelastic deformation of electrified carbon fiber polymer matrix composite plates are investigated. I. Composites with coupled electrical, thermal, and mechanical response Carbon fiber polymer matrix composites that constitute the focus of this work consist of electrically conductive fibers and dielectric polymer matrix, and are electrically anisotropic and conductive at the macroscale. Their mechanical behavior in the presence of an electromagnetic field is characterized by a complex array of factors, among which are coupling of the mechanical and electromagnetic fields when both mechanical and electromagnetic loads are applied; Joule heating produced in conductive phases and its effects; changes in the failure mechanisms induced by the electromagnetic field. Some of these factors are either uniquely attributed to the carbon fiber polymer matrix composites, or have distinct characteristics in the composites. For instance, it is well known that the properties of polymer matrix composites are adversely affected by the heating. At temperatures above glass transition, a rapid degradation of the matrix occurs, which leads to deterioration in composite strength and elastic moduli. Thus, thermal effects cannot be ignored in evaluation of the mechanical behavior of composites subjected to even moderate electromagnetic fields and the corresponding problems need to be formulated considering interaction of mechanical, electromagnetic, and thermal fields. Mathematically speaking, in the most general case the problem of electro-thermo-mechanical coupling reduces to solving of equations of motion, Maxwell’s electrodynamic equations, and heat transfer equations. Here we discuss briefly the field equations for mechanically and electrically anisotropic composites subject to the mechanical and electromagnetic loads, which will provide theoretical background for the experimental studies and analysis presented in the following sections. Some of the details of the current discussion and derivations may be found in 3 . Equations of motion for conductive solids in the presence of an electromagnetic field have the form

Low Velocity Impact of Electrified Assembled CFRP Composite Plates

The present work is a continuation of our ongoing efforts focused on the investigation of the effects of an electromagnetic field on the impact response of carbon fiber polymer matrix composites. In this work we present new experimental results on the low velocity impact of electrified assembled carbon fiber polymer matrix unidirectional and crossply composites. Assembled plates consisted of two 16-ply unidirectional or 16-ply crossply composite plates attached to each other; 32-ply unidirectional and 32-ply cross-ply “monolithic” composite plates were considered as well. The impact tests results on these electrified two-plate assemblies of composite plates confirmed the conjecture established earlier for the “monolithic” unidirectional composite plates that an increase in the magnitude of the applied electric current leads to a sharp increase in the maximum impact load sustained by unidirectional composites. Furthermore, application of an electric current results in a reduction of the visible damage of the two-plate assembly.