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Mechanical Engineering

Department of Engineering Mechanics: Faculty Publications

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Full-Text Articles in Engineering

Moving Screw Dislocations In Piezoelectric Bimaterials, Xiangfa Wu, Yuris A. Dzenis, Wen-Sheng Zou Jul 2003

Moving Screw Dislocations In Piezoelectric Bimaterials, Xiangfa Wu, Yuris A. Dzenis, Wen-Sheng Zou

Department of Engineering Mechanics: Faculty Publications

An explicit solution for a moving screw dislocation in a piezoelectric bimaterial is given by means of complex variables. The electroelastic fields and forces acting on the moving dislocation are obtained in closed form. As special cases, solutions for a moving screw dislocation in a piezoelectric half-plane with a free or rigid surface are obtained explicitly.

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Interfacial Edge Crack Between Two Bonded Dissimilar Orthotropic Strips Under Antiplane Point Loading, Xiangfa Wu, Yuris A. Dzenis, Wen-Sheng Zou Jun 2003

Interfacial Edge Crack Between Two Bonded Dissimilar Orthotropic Strips Under Antiplane Point Loading, Xiangfa Wu, Yuris A. Dzenis, Wen-Sheng Zou

Department of Engineering Mechanics: Faculty Publications

A closed-form solution is obtained for the interfacial edge crack between two bonded dissimilar orthotropic strips loaded by antiplane point loading in form of screw dislocation or line force. Conformal mapping and existing dislocation solutions are utilized for constructing the fundamental solution of the problem. The stress intensity factor (SIF) and the energy release rate(ERR) are obtained explicitly.

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Paper On Measurement Of The Nanomechanical Properties Of Thin Films Using Afam Receives Recognition, Donna Hurley, Joseph A. Turner, Paul Rice, Joshua Wiehn Jun 2003

Paper On Measurement Of The Nanomechanical Properties Of Thin Films Using Afam Receives Recognition, Donna Hurley, Joseph A. Turner, Paul Rice, Joshua Wiehn

Department of Engineering Mechanics: Faculty Publications

NIST researchers are developing atomic force acoustic microscopy (AFAM) methods to quantitatively determine the elastic properties of thin films. The AFAM technique measures the frequencies of an atomic force microscope (AFM) cantilever’s first two flexural resonances while in contact with a material. The indentation modulus, M, of an unknown or test material can then be obtained by comparing the resonant spectra of the test material to those of a reference material. To examine metrology issues for this emerging technique, AFAM results have been compared with those obtained by other methods, such as instrumented indentation. The results show that better agreement …

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Screw Dislocation Interacting With Interface And Interfacial Cracks In Piezoelectric Bimaterials, Xiangfa Wu, Steve Cohn, Yuris A. Dzenis Apr 2003

Screw Dislocation Interacting With Interface And Interfacial Cracks In Piezoelectric Bimaterials, Xiangfa Wu, Steve Cohn, Yuris A. Dzenis

Department of Engineering Mechanics: Faculty Publications

Interface and interfacial cracks interacting with screw dislocations in piezoelectric bimaterials subjected to antiplane mechanical and in-plane electrical loadings are studied within the framework of linear piezoelectricity theory. Straight dislocations with the Burgers vector normal to the isotropic basal plane near the interface or interfacial crack are considered. The dislocations are characterized by a discontinuous electric potential across the slip plane and are subjected to a line-force and a line-charge at the core. An explicit solution for the screw dislocation in piezoelectric bimaterial with straight interface is found based on the solution of a similar problem for infinite homogenous medium. …

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A Semi-Infinite Interfacial Crack Between Two Bonded Dissimilar Elastic Strips, Xiang-Fa Wu, E. Lilla, W.-S. Zou Nov 2002

A Semi-Infinite Interfacial Crack Between Two Bonded Dissimilar Elastic Strips, Xiang-Fa Wu, E. Lilla, W.-S. Zou

Department of Engineering Mechanics: Faculty Publications

This paper is concerned with a semi-infinite interfacial crack between two bonded dissimilar elastic strips with equal thickness. Solutions for the complex stress intensity factor (SIF) and energy release rate (ERR) are obtained in closed form under in-plane deformations. During the procedure, the mixed boundary-value problem is reduced by means of the conformal mapping technique to the standard Riemann–Hilbert problem. In some limiting cases, the present solutions can cover the results found in literature.

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Screw Dislocation Interacting With An Interfacial Edge Crack Between Two Bonded Dissimilar Piezoelectric Wedges, Xiangfa Wu, Yuris A. Dzenis, Wen-Sheng Zou Oct 2002

Screw Dislocation Interacting With An Interfacial Edge Crack Between Two Bonded Dissimilar Piezoelectric Wedges, Xiangfa Wu, Yuris A. Dzenis, Wen-Sheng Zou

Department of Engineering Mechanics: Faculty Publications

This letter is concerned with an interface edge crack interacting with a screw dislocation under antiplane mechanical and in-plane electric loading in a piezoelectric bimaterial wedge. In addition with a discontinuous electric potential across the slip plane, the dislocation is subjected to a line-force and a line-charge at the core. The out-of-plane displacement and electric potentials are obtained in closed-form on the basis of the conformal mapping technique and the solution for a screw dislocation in an infinite piezoelectric bimaterial with a semi-infinite interface crack. The intensity factors (IFs) and energy release rate (ERR) are obtained explicitly.

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Closed-Form Solution For A Mode-Iii Interfacial Edge Crack Between Two Bonded Dissimilar Elastic Strips, Xiangfa Wu, Yuris A. Dzenis Sep 2002

Closed-Form Solution For A Mode-Iii Interfacial Edge Crack Between Two Bonded Dissimilar Elastic Strips, Xiangfa Wu, Yuris A. Dzenis

Department of Engineering Mechanics: Faculty Publications

A closed-form solution is obtained for the problem of a mode-III interfacial edge crack between two bonded semi-infinite dissimilar elastic strips. A general out-of-plane displacement potential for the crack interacting with a screw dislocation or a line force is constructed using conformal mapping technique and existing dislocation solutions. Based on this displacement potential, the stress intensity factor (SIF, KIII) and the energy release rate (ERR, GIII) for the interfacial edge crack are obtained explicitly. It is shown that, in the limiting special cases, the obtained results coincide with the results available in the literature. The present …

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Closed-Form Solution For The Size Of Plastic Zone In An Edge-Cracked Strip, Xiang-Fa Wu, Yuris A. Dzenis Sep 2002

Closed-Form Solution For The Size Of Plastic Zone In An Edge-Cracked Strip, Xiang-Fa Wu, Yuris A. Dzenis

Department of Engineering Mechanics: Faculty Publications

This paper is concerned with the problem of plastic zone at the tip of an edge crack in an isotropic elastoplastic strip under anti-plane deformations. By means of complex potential and Dugdale model, the stress intensity factor and the size of plastic zone are obtained in closed-form. Furthermore, the analytic solutions for an edge crack at the free boundary of a half-space and a semi-infinite crack heading towards a free surface are determined as the limiting cases of the strip geometries.

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Closed-Form Solution For The Size Of Plastic Zone In An Edge-Cracked Strip, Xiangfa Wu, Yuris A. Dzenis May 2002

Closed-Form Solution For The Size Of Plastic Zone In An Edge-Cracked Strip, Xiangfa Wu, Yuris A. Dzenis

Department of Engineering Mechanics: Faculty Publications

This paper is concerned with the problem of plastic zone at the tip of an edge crack in an isotropic elastoplastic strip under anti-plane deformations. By means of complex potential and Dugdale model, the stress intensity factor and the size of plastic zone are obtained in closed-form. Furthermore, the analytic solutions for an edge crack at the free boundary of a half-space and a semi-infinite crack heading towards a free surface are determined as the limiting cases of the strip geometries. 2002 Elsevier Science Ltd. All rights reserved.

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Analysis Of Microdamage Evolution Histories In Composites, Yuris A. Dzenis, Jie Qian Mar 2001

Analysis Of Microdamage Evolution Histories In Composites, Yuris A. Dzenis, Jie Qian

Department of Engineering Mechanics: Faculty Publications

Evolution of microdamage in advanced composites was experimentally studied in this paper. A new method of acoustic emission (AE) analysis of histories of different damage mechanisms was formulated based on a combination of transient AE classification and multiparameter filtering. The capabilities of the method were illustrated on examples of damage evolution in several graphite/epoxy composites. Three characteristic AE waveforms with different frequency spectra were identified based on the transient analysis. Regions occupied by these waveforms in the amplitude–rise time parametric space were identified for the [0]8 and [90]16 unidirectional composites. Multiparameter filtering was applied to extract evolution histories …

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Rate Effects On Mode-I Delamination Toughness Of A Graphite/Epoxy Laminated Composite, Xiangfa Wu, Yuris A. Dzenis Feb 2001

Rate Effects On Mode-I Delamination Toughness Of A Graphite/Epoxy Laminated Composite, Xiangfa Wu, Yuris A. Dzenis

Department of Engineering Mechanics: Faculty Publications

Mechanical properties of composite materials made of high modulus fibers and relatively low modulus polymeric matrix, such as graphite/epoxy laminated composites, are sensitive to loading rate and temperature. Generally, at fixed loading rate, when temperature increases, the fracture toughness of polymers also increases; however, it will decrease with the increase of loading rate at constant testing temperature. Rate effects on fracture toughness are of critical to understand the fracture transition from ductile to brittle of some polymers. However, there have been fewer studies of rate effects on delamination toughness of laminates compared to that of pure polymers. In the present …

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United States Patent: Method And System For Estimating The Tenderness Of A Meat Product, Maria Victoria Spadaro, Rosana Moreira, Jimmy Keeton, D. H. Allen Dec 1999

United States Patent: Method And System For Estimating The Tenderness Of A Meat Product, Maria Victoria Spadaro, Rosana Moreira, Jimmy Keeton, D. H. Allen

Department of Engineering Mechanics: Faculty Publications

A method for estimating the tenderness of a meat product is provided. The method includes determining the stress relaxation coefficient of a meat sample. One or more physical parameters of the meat sample are then determined from the stress relaxation coefficient. Diagnostic sensory characterization data, such as a numerical estimation of the meat's overall tenderness, is then determined for the meat sample. The physical parameters are then correlated to the diagnostic sensory characterization data, to allow the diagnostic sensory characterization data to be estimated solely from the measured physical parameters.

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High-Frequency Response Of Atomic-Force Microscope Cantilevers, Joseph A. Turner, Sigrun Hirsekorn, Ute Rabe, Walter Arnold Aug 1997

High-Frequency Response Of Atomic-Force Microscope Cantilevers, Joseph A. Turner, Sigrun Hirsekorn, Ute Rabe, Walter Arnold

Department of Engineering Mechanics: Faculty Publications

Recent advances in atomic-force microscopy have moved beyond the original quasistatic implementation into a fully dynamic regime in which the atomic-force microscope cantilever is in contact with an insonified sample. The resulting dynamical system is complex and highly nonlinear. Simplification of this problem is often realized by modeling the cantilever as a one degree of freedom system. This type of first-mode approximation (FMA), or point-mass model, has been successful in advancing material property measurement techniques. The limits and validity of such an approximation have not, however, been fully addressed. In this article, the complete flexural beam equation is examined and …

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Diffuse Energy Propagation On Heterogeneous Plates: Structural Acoustics Radiative Transfer Theory, Joseph A. Turner, Richard L. Weaver Dec 1996

Diffuse Energy Propagation On Heterogeneous Plates: Structural Acoustics Radiative Transfer Theory, Joseph A. Turner, Richard L. Weaver

Department of Engineering Mechanics: Faculty Publications

The propagation of diffuse energy on an unwetted flat plate with attached heterogeneities is examined using a statistical, multiple scattering approach. The statistically homogeneous heterogeneities lightly couple the membrane and flexural waves. The problem is formulated in terms of the Bethe–Salpeter equation, which governs the field covariance. It is reduced to a radiative transfer equation in the limit that the attenuations per wave number are small, i.e., when the heterogeneities are weak. This radiative transfer equation governs the diffuse energy propagation as a function of space, time, and propagation direction. Solutions of the radiative transfer equation are presented for the …

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Coupling And Attenuation Of Waves In Plates By Randomly Distributed Attached Impedances, Joseph A. Turner, Richard L. Weaver Apr 1996

Coupling And Attenuation Of Waves In Plates By Randomly Distributed Attached Impedances, Joseph A. Turner, Richard L. Weaver

Department of Engineering Mechanics: Faculty Publications

The average response of an infinite thin plate with statistically homogeneous attached random impedances is examined. The added impedances, which represent typical heterogeneities that might occur on complex shells, provide light coupling between the extensional, shear, and flexural waves. The mean plate response is formulated in terms of the Dyson equation which is solved within the assumptions of the first-order smoothing approximation, or Keller approximation, valid when the heterogeneities are weak. Scattering attenuations are derived for each propagation mode. It is shown that the attenuation of one wave type due to coupling to another is proportional to the modal density …

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Ultrasonic Radiative Transfer In Polycrystalline Media: Effects Of A Fluid–Solid Interface, Joseph A. Turner, Richard L. Weaver Nov 1995

Ultrasonic Radiative Transfer In Polycrystalline Media: Effects Of A Fluid–Solid Interface, Joseph A. Turner, Richard L. Weaver

Department of Engineering Mechanics: Faculty Publications

In previous derivations of the ultrasonic radiative transfer equation (URTE) for the modeling of multiply scattered diffuse ultrasound in polycrystalline media, the boundary conditions appropriate to experiments performed in a water bath were not used. In the present work, this fluid–solid boundary condition is discussed as it applies to the URTE. An interpolation scheme is developed that is consistent with the discrete ordinates method used for the solution of the URTE. Steady-state and time-dependent results are presented for the solution of the URTE with a fluid–solid boundary condition. The steady-state results show that diffusive behavior is exhibited nearer the specimen …

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Time Dependence Of Multiply Scattered Diffuse Ultrasound In Polycrystalline Media, Joseph A. Turner, Richard L. Weaver May 1995

Time Dependence Of Multiply Scattered Diffuse Ultrasound In Polycrystalline Media, Joseph A. Turner, Richard L. Weaver

Department of Engineering Mechanics: Faculty Publications

Time domain results are presented for the multiply scattered longitudinal intensity backscattered from a polycrystalline medium. The results are solutions to the ultrasonic radiative transfer equation (URTE), the derivation of which is based upon radiative transfer theory. Unlike steady-state solutions obtained previously, time domain solutions will more closely correspond to experiments that use tone burst sources. This paper is concerned with the time dependence of the backscattered longitudinal intensity from a polycrystalline medium excited by a normally incident longitudinal wave idealized as an impulsive deposition of energy. It is shown that multiple scattered effects become significant at times on the …

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Radiative Transfer Of Ultrasound, Joseph A. Turner, Richard L. Weaver Dec 1994

Radiative Transfer Of Ultrasound, Joseph A. Turner, Richard L. Weaver

Department of Engineering Mechanics: Faculty Publications

A radiative transfer equation is used to model the diffuse multiple scattering of ultrasound in a medium containing discrete random scatterers. An assumption of uncorrelated phases allows one to write an equation of energy balance for the diffuse intensity. This ultrasonic radiative transfer equation contains single-scattering and propagation parameters that are calculated using the elastic wave equation. Polarization effects are included through the introduction of an elastodynamic Stokes vector which contains a longitudinal Stokes parameter and four shear Stokes parameters similar to the four Stokes parameters used in optical radiative transfer theory. The theory is applied to a statistically homogeneous, …

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Radiative Transfer And Multiple Scattering Of Diffuse Ultrasound, Joseph A. Turner, Richard L. Weaver Dec 1994

Radiative Transfer And Multiple Scattering Of Diffuse Ultrasound, Joseph A. Turner, Richard L. Weaver

Department of Engineering Mechanics: Faculty Publications

A model is presented fro the multiply scattered incoherent field in a continuous polycrystalline elastic medium. Unlike a previous development based upon energy conservation considerations [J. A. Turner and R.L. Weaver, J. Acoust. Soc. Am. 93, 2312 (A) (1993)] for a medium containing discrete random scatterers, the present model has been developed from the wave equation and first principles. Appropriate ensemble averaging of the wave equation leads to Dyson and Bethe-Salpeter equations which govern the mean Green’s function and the covariance of the Green’s function, respectively. These equations are expanded for weak heterogeneity and equations of radiative transfer are obtained. …

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Inhomogeneous Anisotropic Percolation: Two-Dimensional Numerical Threshold Analysis, Yuris A. Dzenis, S. P. Joshi Feb 1994

Inhomogeneous Anisotropic Percolation: Two-Dimensional Numerical Threshold Analysis, Yuris A. Dzenis, S. P. Joshi

Department of Engineering Mechanics: Faculty Publications

Monte Carlo simulations of percolation on a square lattice with anisotropic inhomogeneous probability distribution are reported. Finite-size scaling is used for data analysis. As inhomogeneity increases, the critical probability decreases; whereas the correlation-length exponent remains, within computation errors, the same as in classical two-dimensional percolation.

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