Gabriela Petculescu

University of Louisiana at Lafayette | ULL · Department of Physics

No PDF available ABSTRACT We determined the effect of laser speed on the elastic constants of additively manufactured (AM) 316L stainless steel using resonant ultrasound spectroscopy (RUS). The alloy (316L) has biomechanical applications, such as medical implants. AM disks were manufactured at a constant power of 100 W and varying laser speeds of 8...

No PDF available ABSTRACT With the advent of metal Additive Manufacturing (AM), or 3D printing, the focus on evaluating and fine-tuning the fabrication process has become crucial. High-resolution volumetric mapping of elastic properties throughout an AM built sample can be done, “biopsy” style, with the highly adaptable Resonant Ultrasound Spectros...

Velocity and attenuation of shear and longitudinal sound waves were measured as a function of sensitization level in AA5083-H116 and AA5456-H116 aluminum alloys using two different techniques: resonant ultrasound spectroscopy (RUS) and pulse echo (PE). The frequency range for RUS was 0.3 MHz to 1 MHz. For PE, longitudinal 3.5 MHz and shear 1 MHz tr...

Magnetostrictive materials exhibit a strain in the presence of a variable magnetic field. While they normally require large, highly oriented crystallographic grains for high strain values, metal additive manufacturing (3D printing) may be able to produce highly textured polycrystalline rods, with properties comparable to those manufactured using th...

Segregation of atomic species in metastable solid-solution alloys results in a gradual change of the alloy’s properties, sometimes rendering the materials ineffective for the particular task they were designed for. An example of such a case is the sensitization of strong and lightweight Mg-rich aluminum alloys used in marine applications. The ASTM...

Fe1−xMx (M = Ga, Ge, Si, Al, Mo and x ∼ 0.18) alloys offer an extraordinary combination of magnetoelasticity and mechanical properties. They are rare-earth-free, can be processed using conventional deformation techniques, have high magnetic permeability, low hysteresis, and low magnetic saturation fields, making them attractive for device applicati...

Iron is a well-utilized material in structural and magnetic applications. This does not mean, however, that it is well understood, especially in the field of magnetostriction. In particular, the rhombohedral magnetostriction of iron, λ 111 , is anomalous in two respects: it is negative in sign, in disagreement with the prediction of first princi...

The study of Fe–Ga and related alloys is an active frontier research effort. This chapter provides some insightful understanding of the large magnetostriction observed in this family of materials. Excellent agreement between theory and experiment has been achieved for the Fe–Ga zone I composition alloys. Here, Ga atoms are far apart from each other...

Tetragonal magnetostriction (λγ,2) and elastic constants (c′, c44, and c11) for Fe100−xSix were measured as a function of temperature (T). Compositions corresponding to the disordered A2 (x = 5), ordered D03 (x = 19.8), and mixed (x = 11.6) phases, were investigated. The magnetoelastic coupling (−b1) was determined for 77 < T < 300 K and compared w...

This paper presents a comparative study on the tetragonal magnetostriction constant, λγ,2, [ = (3/2)λ100] and magnetoelastic coupling, b1, of binary Fe100-xZx (0 < x < 35, Z = Al, Ga, Ge, and Si) and ternary Fe-Ga-Al and Fe-Ga-Ge alloys. The quantities are corrected for magnetostrains due to sample geometry (the magnetostrictive form effect). Recen...

The contrast between the saturation tetragonal magnetostriction, λγ,2 = (3/2)λ100, of Fe1−xGax and Fe1−yGey, at compositions where both alloys exhibit D03 cubic symmetry (second peak region), was investigated. This region corresponds to x = 28 at. % Ga and y = 18 at. % Ge or, in terms of e/a = 2 x + 3 y + 1, to an e/a value of ∼1.55 for each of the...

In this paper we investigate the magnetostrictive [ (3/2)λ₁₀₀ and (3/2)λ₁₁₁ ] and elastic ( c ^′ and c ₄₄ ) behavior of single crystalline alloys Fe _{100- x} Mo _x for 2< x <12 ; the magnetoelastic coupling constants ( - b ₁ and - b ₂ ) are computed from the meas...

Both components of the tetragonal magnetoelastic constant b₁ : the saturation magnetostriction, λ^γ,2=(3/2)λ₁₀₀ , and the magnetic-field saturated shear elasticity, c^′=(c₁₁-c₁₂)/2 , were investigated over a wide temperature range for the magnetostrictive Fe _1-x-y Ga <sub>x<...

In this paper we investigate the magnetostrictive [(3/2)lambda100 and (3/2)lambda111] and elastic (c' and c44) behavior of single crystalline alloys Fe100-xMox for 2

Temperature dependent magnetoelastic properties of Fe ₁₀₀ _- _xGe_x(5 < x < 18) single crystals have been measured. Tetragonal magnetostriction (3/2) lambda₁₀₀ measurements at x = 5.7, 12.1, 14.9, and 17.7 were performed between 78 K and 426 K and resonant ultrasound spectroscopy measurements were...

In this paper the magnetoelastic characteristics of ternary Fe–Ga–X (X=Ge, Sn) alloys are compared with those of Galfenol (Fe–Ga) within the same range of solute concentration. New magnetostriction and elastic modulus data for Fe–Ga–Ge at six different compositions are presented. The most notable case is that of Fe86.9Ga9.9Ge8.7. Although the tetra...

Saturation magnetostriction measurements along the [100] axis of Fe _100-x Ga _x single crystal rods ( ∼25×6 mm diameter) were observed to have a linear dependence on [100] applied compressive stresses for 20≪x≪30 . This is not expected from linear magnetoelastic theory and indeed is negligible for x=19.5 . An expansion of the m...

In this paper we examine the elastic (c' and c(44)) and magnetostrictive (lambda(100) and lambda(111)) behaviors of Fe100-xGex for 4 < x < 18, quantities used further to find the fundamental magnetoelastic coupling constants b(1) and b(2) at room temperature. The x dependence of b(1) and b(2) for Fe100-xGex is contrasted to those of Fe100-xGax and...

Galfenol, Fe100−x Ga x (∼5<x<∼20), is a unique magnetostrictive alloy that combines high saturation magnetostrictions with robust mechanical properties. [Clark et al., “Magnetostrictive properties of body‐centered cubic Fe‐Ga and Fe‐Ga‐Al alloys,” IEEE Trans. Magn. 36, 3238 (2000)]. These materials can be welded and machined. Additionally, alloys t...

In order to practically exploit the large magnetostriction effects observed in Fe-based alloys, the magnetoelastic interactions in these materials have to be understood. Until now, Fe-Ga alloys have exhibited the largest magnetostriction in non-rare-earth alloys, but they also present a complex phase diagram, which does not allow a simple interpret...

Iron-gallium alloys (known as Galfenol) are one of only a few metal alloys known to exhibit large auxetic or negative Poisson’s ratio behavior. The mechanical properties of Galfenol, including the auxeticity, are strongly dependent on the composition of the alloy. This research seeks to measure the elastic properties of Galfenol through a range of...

A group delay measurement technique is proposed using modally selective Lamb wave transducers for the detection and sizing of delaminations in unidirectional and cross-ply composites. Unlike amplitude or energy based Lamb wave methods, this method is insensitive to transducer coupling. Specifically, modally selective array transducers are used to g...

This work addresses several aspects of damage detection and evaluation in composite laminates, in the general context of structural health monitoring. A group delay measurement technique is proposed using modally-selective Lamb-wave transducers for the detection and sizing of delaminations in woven quasi-isotropic and carbon-epoxy cross- ply compos...

Composite materials, particularly graphite/epoxy laminates, are becoming the materials of choice for major load carrying structures such as the fuselage and wings of commercial airliners. Even though this development has been anticipated for years by workers in the field of quantitative nondestructive testing, it has become apparent that extensive...

The quantitative evaluation of damage in woven composites using mode selective excitation of Lamb waves is reported in this paper. PVDF (polyvinylidene fluoride) comb sensors are used to generate and detect a single plate mode. The top electrode is a single set of equidistant fingers connected in parallel to the same potential while the bottom elec...

Ultrasonic NDI methods have an impressive record of applications on metallic and composite structures. However, limitations arise from the need for a wet couplant between the specimen and the transducer and the rather long inspection times necessitated by point-by-point scanning of large structures. To overcome these constraints, a dry-contact larg...

Sensors based on periodic arrays of coherent piezoelectric sources (comb design) are used to selectively excite and detect Lamb waves in aluminum and AS4/3601 unidirectional carbon-epoxy plates. 110 mum PVDF film poled in the thickness direction is used as piezoelectric material. An algorithm to eliminate the effect of coupling in amplitude measure...

A laser-generated ultrasonic source, to be used with a real-time imaging device, was developed. The ultrasound is generated in the thermoelastic regime, in a composite layer composed of absorbing particles (carbon) and silicone rubber. The composite layer plays three roles: of absorption, constriction and dry-coupling. The central frequency of the...

Elastic shear moduli measurements on Fe100−xGax (x = 12–33) single crystals (via resonant ultrasound spectroscopy) with and without a magnetic field and within 4–300 K are reported. The pronounced softening of the tetragonal shear modulus c′ is concluded to be, based on magnetoelastic coupling, the cause of the second peak in the tetragonal magneto...

Magnetostriction measurements from 77 K to room temperature on oriented (100) and (110) disk samples of Fe93.9Be6.1 and Fe88.7Be11.3 reveal substantial increases in lambda(100) compared to iron. For the 11.3% alloy, lambda(100)=110 ppm, a sixfold increase above that of alpha-Fe. For the 6.1% alloy, lambda(100)=81 ppm, similar to40% and similar to17...

The elastic anisotropy of iron’s most common α‐structure increases significantly when gallium is substituted for a fraction of the iron. Concurrently occurring, the tremendous boost in tetragonal magnetostriction [one order of magnitude above that of pure Fe, 3/2λ100(Fe81Ga19)=400 ppm] makes Fe–Ga alloys important for magnetoelastic applications. M...

Iron-based amorphous metals are investigated as nonferromagnetic amorphous steel alloys with magnetic transition temperatures well below ambient temperatures. Rod-shaped amorphous samples with diameters reaching 4 mm are obtained using injection casting. Amorphous steel alloys are designed by considering atomistic factors that enhance the stability...

Extraordinary magnetostrictive behavior has been observed in Fe-Ga alloys with concentrations of Ga between 4% and 27%. λ₁₀₀ exhibits two peaks as a function of Ga content. At room temperature, λ₁₀₀ reaches a maximum of 265 ppm near 19% Ga and 235 ppm near 27% Ga. For compositions between 19% and 27%, λ₁₀₀ drops sha...

Traveling and standing waves are produced in an open-tube resonator in a controlled ratio. A regenerator/heat-exchanger assembly is placed at the velocity node of the standing wave. The quality factor, Q, and acoustic power along the resonator are measured as the standing wave ratio (SWR), porosity, length, temperature gradient, and position of the...

High-manganese ferrous-based alloys containing 10–20 at. % Mn have been investigated as prospective iron-based structural amorphous metals with magnetic transition temperatures far below the ambient temperature. Many of these alloys are found to have a high reduced glass transition temperature of 0.6–0.63 and large supercooled liquid region of 40–9...

Thesis (Ph. D.)--Ohio University, 2002.

Nonlinear effects on thermoacoustic gain in a single pore are investigated experimentally. By creating a sharp temperature gradient in a uniform cross-section pore, the effect of high displacement amplitudes relative to the stack length is isolated from other high amplitude effects and also from effects due to geometrical discontinuities. The exper...

The elastic anisotropy of iron's most common alpha-structure increases significantly when gallium is substituted for a fraction of the iron. Concurrently occurring, the tremendous boost in tetragonal magnetostriction [one order of magnitude above that of pure Fe, 3/2lambda100(Fe81Ga19)=400 ppm] makes Fe-Ga alloys important for magnetoelastic applic...

Ceperley has discussed the idea that an acoustic traveling wave passing through a regenerator executes a Stirling cycle [P. H. Ceperley, J. Acoust. Soc. Am. 77, 1239?1244 (1985)]. He also emphasized that for an acoustic Stirling device to be useful, the impedance must be high or else viscous losses will dominate. Backhaus and Swift recently found a...

Thermoacoustic stacks of uniform cross section can be characterized completely in terms of the single thermoviscous function F(λ) [W. P. Arnott, H. E. Bass, and R. Raspet, J. Acoust. Soc. Am. 90, 3228–3237 (1991)]. For nonuniform stacks, one must treat thermal diffusion and viscosity separately, and it may be possible to ‘‘tune’’ the performance of...

Thermoacoustic effects in a circular pore with an applied temperature gradient are investigated. A volume-modulation technique is employed to measure the compressibility of a gas in the pore directly. When a temperature gradient is imposed on the pore, the compressibility is sensitive to thermoacoustic effects which depend on both thermal and visco...

Following earlier work [G. Petculescu and L. A. Wilen, J. Acoust. Soc. Am. 103, 2841(A) (1998)], a volume?modulation technique is employed to measure directly the complex compressibility of gas in a stack. When a temperature gradient is imposed on the stack, the complex compressibility is sensitive to thermoacoustic effects which can be measured to...

Continuing experiments designed to look at therrnoacoustic effects in a single pore will be described. A volume-modulation technique is employed to measure the complex compressibility of a gas in the pore directly. When a temperature gradient is imposed on the pore, the complex compressibility is sensitive to thermoacoustic effects which can be mea...

Previous measurements [L. Wilen, J. Acoust. Soc. Am. 101, 3022(A) (1997)] probed the geometry?dependent thermal coupling between a gas and the walls of single pores over a wide range of ratios of the thermal penetration depth to pore size. A volume modulation method was described which allows one to measure the complex compressibility of the pore d...

Elastic constant measurements using Resonant Ultrasound Spectroscopy have been performed on Tl_xCo_ 4Sb_12-ySny skutterudites as a function of temperature and Tl filling ratio, x (y = 0 or 1, for small and large values of x, respectively). In addition to being promising thermoelectric materials (ZT = 0.8 at T = 800 K) [1], these Tl-filled compounds...