Laurence J. Jacobs

Bio: Laurence J. Jacobs is an academic researcher from Georgia Institute of Technology. The author has contributed to research in topics: Rayleigh wave & Ultrasonic sensor. The author has an hindex of 43, co-authored 279 publications receiving 6636 citations. Previous affiliations of Laurence J. Jacobs include Columbia University & ExxonMobil.

Modeling elastic wave propagation in waveguides with the finite element method

Abstract: This paper reports on the application of guided waves techniques to nondestructively determine the structural integrity of engineering components. Specifically, this research uses a commercial finite element (FE) code to study the propagation characteristics of ultrasonic waves in annular structures. In order to demonstrate the accuracy of the proposed FE technique, the propagation of guided waves in a flat plate is examined first. Next, the propagation of guided waves in thick ring structures is investigated. Finally, these FE results are compared to analytical and experimental results. The results of this study clearly illustrate the effectiveness of using the FE method to model guided wave propagation problems and demonstrate the potential of the FE method for problems when an analytical solution is not possible because of “complicated” component geometry.

Experimental characterization of fatigue damage in a nickel-base superalloy using nonlinear ultrasonic waves

Abstract: This research develops a robust experimental procedure to track the evolution of fatigue damage in a nickel-base superalloy with the acoustic nonlinearity parameter, β, and demonstrates its effectiveness by making repeatable measurements of β in multiple specimens, subjected to both high- and low-cycle fatigue. The measurement procedure developed in this research is robust in that it is based on conventional piezoelectric contact transducers, which are readily available off the shelf, and it offers the potential for field applications. In addition, the measurement procedure enables the user to isolate sample nonlinearity from measurement system nonlinearity. The experimental results show that there is a significant increase in β linked to the high plasticity of low-cycle fatigue, and illustrate how these nonlinear ultrasonic measurements quantitatively characterize the damage state of a specimen in the early stages of fatigue. The high-cycle fatigue results are less definitive (the increase in β is not as...

Review of Second Harmonic Generation Measurement Techniques for Material State Determination in Metals

Abstract: This paper presents a comprehensive review of the current state of knowledge of second harmonic generation (SHG) measurements, a subset of nonlinear ultrasonic nondestructive evaluation techniques. These SHG techniques exploit the material nonlinearity of metals in order to measure the acoustic nonlinearity parameter, $$\beta $$ . In these measurements, a second harmonic wave is generated from a propagating monochromatic elastic wave, due to the anharmonicity of the crystal lattice, as well as the presence of microstructural features such as dislocations and precipitates. This article provides a summary of models that relate the different microstructural contributions to $$\beta $$ , and provides details of the different SHG measurement and analysis techniques available, focusing on longitudinal and Rayleigh wave methods. The main focus of this paper is a critical review of the literature that utilizes these SHG methods for the nondestructive evaluation of plasticity, fatigue, thermal aging, creep, and radiation damage in metals.

Time-frequency representations of Lamb waves.

Abstract: The objective of this study is to establish the effectiveness of four different time-frequency representations (TFRs)—the reassigned spectrogram, the reassigned scalogram, the smoothed Wigner–Ville distribution, and the Hilbert spectrum—by comparing their ability to resolve the dispersion relationships for Lamb waves generated and detected with optical techniques This paper illustrates the utility of using TFRs to quantitatively resolve changes in the frequency content of these nonstationary signals, as a function of time While each technique has certain strengths and weaknesses, the reassigned spectrogram appears to be the best choice to characterize multimode Lamb waves

Assessment of material damage in a nickel-base superalloy using nonlinear Rayleigh surface waves

Abstract: A reliable laser-based ultrasonic technique is developed to measure the second order harmonic amplitude of a Rayleigh surface wave propagating in metallic specimens. Rayleigh waves are experimentally generated with a wedge transducer and detected with a heterodyne laser interferometer. The capability of this system to measure the nonlinear contribution present in Rayleigh surface waves is demonstrated, and these results are interpreted in terms of a parameter developed for Rayleigh surface waves which corresponds to the nonlinear parameter of a longitudinal wave, β. The proposed measurement technique is used to assess damage in nickel-base high temperature alloy specimens, and the evolution of material nonlinearity under various loading conditions is quantitatively measured in terms of the increasing amplitude of the second order harmonic. These results show that there is a significant increase in the second order harmonic amplitude at monotonic tensile loads above the material’s yield stress, and that du...

Art of electronics

Abstract: Our goal is always to offer you an assortment of cost-free ebooks too as aid resolve your troubles. We have got a considerable collection of totally free of expense Book for people from every single stroll of life. We have got tried our finest to gather a sizable library of preferred cost-free as well as paid files. Whatever our proffesion, the art of electronics can be excellent resource for reading. Find the existing reports of word, txt, kindle, ppt, zip, pdf, as well as rar in this site. You can definitely check out online or download this book by below. Currently, never miss it. This is really going to save you time and your money in something should think about. If you're seeking then search around for online. Without a doubt there are several these available and a lot of them have the freedom. However no doubt you receive what you spend on. An alternate way to get ideas would be to check another the art of electronics. GO TO THE TECHNICAL WRITING FOR AN EXPANDED TYPE OF THIS THE ART OF ELECTRONICS, ALONG WITH A CORRECTLY FORMATTED VERSION OF THE INSTANCE MANUAL PAGE ABOVE.

Ultrasonic Guided Waves in Solid Media

Abstract: Preface Acknowledgments 1. Introduction 2. Dispersion principles 3. Unbounded isotropic and anisotropic media 4. Reflection and refraction 5. Oblique incidence 6. Waves in plates 7. Surface and subsurface waves 8. Finite element method for guided wave mechanics 9. The semi-analytical finite element method (SAFE) 10. Guided waves in hollow cylinders 11. Circumferential guided waves 12. Guided waves in layered structures 13. Source influence on guided wave excitation 14. Horizontal shear 15. Guided waves in anisotropic media 16. Guided wave phased arrays in piping 17. Guided waves in viscoelastic media 18. Ultrasonic vibrations 19. Guided wave array transducers 20. Introduction to guided wave nonlinear methods 21. Guided wave imaging methods Appendix A: ultrasonic nondestructive testing principles, analysis and display technology Appendix B: basic formulas and concepts in the theory of elasticity Appendix C: physically based signal processing concepts for guided waves Appendix D: guided wave mode and frequency selection tips.