Nicholas B. Shevchenko

A study on the induction heating of conductive fiber reinforced composites

A unified approach, considering three possible heating mechanisms: fiber (Joule losses) and fiber crossover junction (dielectric hysteresis and contact resistance), to identify dominant heating mechanisms during induction processing of conductive fiber reinforced composites is presented. Non-dimensional parameters were proposed to identify the relationships between heating mechanisms and process and material parameters. Parametric studies showed that junction heating mechanisms dominate fiber heating for the material systems considered, with the exception of relatively low contact resistance (< 10 3). Results for dielectric hysteresis and low contact resistance were consistent with individual models in the literature. A design map relating the three mechanisms is presented that can help identify the dominant heating mechanism, given the properties of the composite.

A study on the induction heating of carbon fiber reinforced thermoplastic composites

Recent work in the literature has identified a new heating mechanism during induction processing of carbon thermoplastic prepreg stacks: contact resistance between fibers of adjacent plies. An experimental methodology has been developed to estimate the contact resistance through heating tests based on the properties of the composite and geometry of the specimen. Measured values indicate comparable resistance values at the contact region, compared to resistance in the fiber direction, for AS-4/PEI prepreg stacks under vacuum pressure. The measured values can serve as inputs for induction heating models and process models of carbon thermoplastic prepreg stacks.

Preparation and characterization of Dy nanoparticles

A technique of pure nanoparticle preparation has been explored by forming first small metal particles under high pressure sputtering and then embedding them into a sputtered film matrix. The tandem deposition method is used where the sputtered matrix is deposited at an argon pressure of 5 mTorr and the particles are formed within a specially designed gun at a pressure of 1 Torr and then deposited. The particle-matrix compositional limitations of reactivity and miscibility are thus reduced. The new technique was applied to dysprosium metal particles in an aluminum matrix. The absence of the antiferromagnetic transition for particles with sizes of 4–12 nm was observed. The 4 nm particles behaved superparamagnetically, while the larger 12 nm particles showed coercivities over twice as large as that of the bulk material at cryogenic temperatures. The success of the technique is demonstrated by having been able to carry out the study on the dysprosium-aluminum system that normally reacts, preventing the existe...

Effect of preparation conditions on the hysteresis behavior of granular Fe-SiO2

Abstract The hysteresis behavior of Fe χ (SiO 2 ) 1- χ granular films was studied as a function of preparation conditions. The films were prepared by dc and rf magnetron sputtering over the composition range χ v = 0.1–0.9 volume fraction of Fe. The Tandem deposition method and deposition from a composite target both with and without titanium sublimation, were used to prepare the films. A typical granular structure was observed, with grain size in the range 2–20 rim. X-ray diffraction and selected area diffraction showed an α-Fe (bcc) type structure. Magnetic properties showed that by varying the deposition method and some of the sputtering parameters (sputtering rate, argon flow, film thickness and substrate temperature), it is possible to switch from a relativeIy magnetically hard sample ( H c ∼ 700 Oe) to a soft sample ( H c ∼ 20 Oe). A dramatic increase in H c has been observed at cryogenic temperatures. This result, along with the Mossbauer data, suggests a shell/core granule morphology with an Fe and/or (Fe-Si) core surrounded by Fe-Si-O.

Development of a numerical model to predict in-plane heat generation patterns during induction processing of carbon fiber-reinforced prepreg stacks

A numerical model is proposed to describe in-plane heat generation spatial response during induction processing of carbon fiber-reinforced thermoplastics. The model is based on a unified approach that considers three possible heating mechanisms: fiber heating (Joule losses in fiber), noncontact junction heating (dielectric hysteresis), and contact junction heating (Joule losses at junctions). A lumped meshing scheme is used to construct a numerical representation for cross-ply and angle-ply orientations of 2-ply prepreg stacks. Heat generation patterns are calculated based on voltage and current conservation laws and verified with induction heating of AS4 carbon fiber-reinforced polyetherimide (AS4/PEI) prepreg stacks. Excellent agreement is found except at very low angle-ply orientations where the predicted heating patterns show significant deviations from the experiment results. A sensitivity analysis is also performed to assess the relationship between heating patterns and material and process parameters. The results show that the stack angle between plies and intrinsic prepreg microstructure can significantly affect the heating patterns.

Effects of preparation conditions on the hysteresis behavior of granular Fe–SiO2

The hysteresis behavior of Fex(SiO2)1−x granular films was studied as a function of preparation conditions. The films were prepared by dc and rf magnetron sputtering over the composition range of xv=0.1–0.9, where xv is the volume fraction of Fe. The tandem and composite target deposition methods, both with and without titanium presputtering, were used to prepare the films. Typical granular structure was observed in these films, with grain size in the range of 2–20 nm. X-ray diffraction and selected area diffraction showed a bcc α-Fe-type structure. Magnetic measurements showed that by varying the deposition method and some of the sputtering parameters including sputtering rate, argon flow, film thickness, and substrate temperature, it is possible to switch from a relatively magnetically hard sample (Hc∼650 Oe) to a soft sample (Hc∼20 Oe). For the former sample, a dramatic increase in Hc has been observed at cryogenic temperatures. This result, along with the Mossbauer data, suggest a shell/core granule m...

Granular thin film deposition by simultaneous spark erosion and sputtering

We have investigated a new method of preparing granular thin films, which are composed of fine metallic particles embedded in a uniform matrix material. By our method, fine metallic particles are created by spark erosion in an inert gas environment and directly deposited onto a cooled substrate. Magnetron sputtering is employed concurrently thereby building up the matrix. Using such a deposition method, granular thin films are created without the need of any heat treatments and can be made with virtually any material and composition. Furthermore it is even possible to create granular thin films from miscible phases. The size of the particles can be controlled by varying the pressure under which the spark erosion is conducted up to a few Torr of Ar. We have applied our method to the case of magnetic particles in a nonmagnetic matrix. Preliminary transmission electron microscope measurements on Fe particles in a Cu matrix showed 10-nm-diam. Fe particles. Selected area diffraction patterns show that the film...

Preparation of Dy and Mn nanoparticles

Abstract We have recently extended our studies on nanoparticles to rare earth and Mn particles. The nanometer scale Dy and Mn particles have been prepared using a new method in which particles are first formed from high purity constituent materials in an inert gas atmosphere and then embedded into a matrix by planar magnetron sputtering. The Dycontaining samples consisted of particles with diameters on the order of 10 nm, which were separated by the matrix material. A strong relationship was observed between the particle size and the magnetic ordering temperature with the absence of antiferromagnetic transition observed at 176 K in the bulk. This method allows for the synthesis of a wider variety of materials by reducing the problems of miscibility and reactivity between the particles and the matrix material.

Effect of preparation technique on the structural and magnetic properties of granular Fe‐SiO2 (abstract)

Previous studies have shown that large coercivities, exceeding 2 kOe, can be obtained in Fe‐based ceramic granular films. The coercivities were also found to be sensitive to the type of matrix material used, being higher in the SiO2 matrix. In this study the hysteresis behavior of FeX(SiO2)1−X granular films was studied as a function of the preparation technique. The films were prepared by dc magnetron sputtering over the composition range of xv=0.1–0.9 volume fraction of Fe. Tandem deposition both with and without titanium sublimation, and deposition from a composite target were used in preparing the films, which resulted in different oxygen environments. Coercivity measurements were found to be strongly composition dependent, with maximum values up to 700 Oe at xv≊0.5 of Fe, for all sets of samples. Typical granular structure was observed, with grain size in the range of 5–20 nm, with the smaller size obtained from composite targets. X‐ray diffraction and selected area diffraction showed a structure of ...

The Application of Spark Erosion to the Synthesis of Thin Films Containing Ultrafine Particles

We have investigated a new method of preparing granular thin films, which are composed of fine metallic particles embedded in a uniform matrix material. By our method, fine metallic particles are created by spark erosion in an inert gas environment and directly deposited onto a cooled substrate. Magnetron sputtering is employed concurrently thereby building up the matrix. Using such a deposition method, granular thin films are created without the need of any heat treatments and can be made with virtually any material and composition. Furthermore it is even possible to create granular thin films from miscible phases. The size of the particles can be controlled by varying the pressure under which the spark erosion is conducted up to a few Torr of Ar. We have applied our method to the case of magnetic particles in a nonmagnetic matrix. Preliminary TEM measurements on Fe particles in a Cu matrix showed 10 nm diameter Fe particles. SAD patterns show that the film is composed of only the Fe and Cu phases. Similarly for the Gd-Ag system, 10 nm Gd particles were observed in an Ag matrix. Gd-Ag compounds that would be expected to form were not observed. Magnetic measurements for these systems agreed with the nanometer scale microstructure that was observed.