RESEARCH INTERESTS:

Professor Jacobs' research focuses on the development of quantitative methodologies for the nondestructive evaluation of structural materials. This multidisciplinary work advances the efficacy of wave-based techniques by integrating elastodynamics, mechanics of materials, optics, instrumentation and digital signal processing methods. The core of his research program is a state-of-the-art optics (laser ultrasonics) laboratory that was developed by Dr. Jacobs and his students. This facility has enabled Professor Jacobs, his students, and a number of faculty colleagues to develop a quantitative understanding of a wide range of physical phenomena.

optical setup
Laser Interferometer (in-plane and out-of-plane)

optical setup
Laser Interferometer (in-plane and out-of-plane)

optical setup
Laser Interferometric Probe (in-plane and out-of-plane)

optical set up
Laser Interferometer (out-of-plane only)

contact set up
Contact Ultrasonics Setup

CURRENT RESEARCH PROJECTS:

 Dr. Jacobs’s research has been funded by the National Science Foundation (NSF), Federal Highway Administration (FHWA), Georgia Department of Transportation (GDOT), Office of Naval Research (ONR), National Aeronautics and Space Administration (NASA), Air Force Office of Scientific Research (AFOSR), General Electric Power Systems, Defense Advanced Research Projects Agency (DARPA), and Exxon-Mobil. His general research areas are listed below:

 

1. Quantitative damage characterization of structural materials with nonlinear ultrasonic techniques.

Traditional ultrasonic techniques are effective in detecting macro-flaws or gross changes in material properties, but are ineffective in measuring micro-damage.  In contrast, nonlinear ultrasonic techniques, have the potential to characterize micro-damage, and thus lead to an accurate prediction of remaining life of structural components. This research is developing advanced ultrasonic models that will be integrated with physically based micro-structure models, while an experimental portion is validating these ultrasonic models, and providing inputs for the proposed diagnosis scheme. Representative Publications:

1.      Meurer, T., Qu, Jianmin and Jacobs, L.J., “Wave Propagation in Nonlinear and Hysteretic Media – A Numerical Study,” International Journal of Solids and Structures, Vol. 39, No. 21-22, pp. 5585-5614, 2002.

  1. Kim, J.Y., Qu, J., Jacobs, L.J., Littles, J.W., and Savage, M.F., “Acoustic Nonlinearity Parameter due to Microplasticity,” Journal of Nondestructive Evaluation, Vol. 25 (1), pp. 29-37, 2006.
  2. Herrmann, J., Kim, J.Y., Jacobs, L.J., Qu, J., Littles, J.W., and Savage, M.F., “Assessment of material damage in a nickel-base superalloy using nonlinear Rayleigh surface waves,” Journal of Applied Physics, Vol. 99 (12), 124913, 2006.
  3. Kim, J.Y., Jacobs, L.J., Qu, J., and Littles, J.W., “Experimental characterization of fatigue damage in a nickel-base superalloy using nonlinear ultrasonic waves,” Journal of the Acoustical Society of America, Vol. 120 (3) pp. 1266-1273, 2006.
  4. Bermes, C., Kim, J.Y., Qu, J., and Jacobs, L.J., “Experimental characterization of material nonlinearity using Lamb waves,” Applied Physics Letters, accepted for publication, 2006.

 

2. Health monitoring of civil infrastructure including the development of procedures to characterize microstructure and distributed damage in cement-based materials with diffuse and coherent ultrasonic waves.

The major hypotheses of this research are that recent advances in ultrasonic techniques can allow the in situ measurement of critical parameters to characterize both the structure and the degradation in cement pastes, mortars, and concretes and that these parameters can be related to the material’s stiffness, strength, and durability. Building on the success of recent advances in advanced ultrasonics and in medical imaging, this research concentrates on three areas: (1) development of physics-based predictive, analytical and numerical models; (2) utilization of new sensor and measurement technologies; and (3) the application of advanced signal processing methodologies. Representative Publications:

  1. Owino, J.O. and Jacobs, L.J, “Attenuation Measurements in Cement-based Materials using Laser Ultrasonics,” Journal of Engineering Mechanics, Vol. 125, No. 6, pp. 637-647, 1999.
  2. Jacobs, L.J. and Owino, J.O., “Effects of Aggregate Size on Attenuation of Rayleigh Waves in Cement-Based Materials,” Journal of Engineering Mechanics, Vol. 126, No. 11, pp. 1124-1130, 2000.

3.      Becker, J., Jacobs, L.J. and Qu, J., “Characterization of Cement-Based Materials using Diffuse Ultrasound,” Journal of Engineering Mechanics,  Vol. 129, No. 12, pp. 1478-1484, 2003.

4.      Punurai, W., Jarzynski, J., Qu, J., Kurtis, K.E., and Jacobs, L.J., “Characterization of Entrained Air Voids in Cement Paste with Scattered Ultrasound,” NDT&E International, Vol. 39 (6), pp. 514-524, 2006.

5.      Punurai, W., Jarzynski, J., Qu, Jianmin, Kurtis, K.E., and Jacobs, L.J., “Characterization of dissipation losses in cement paste with diffuse ultrasound,” Mechanics Research Communication, accepted for publication, 2006.

6.      Punurai, W., Jarzynski, J., Qu, Jianmin, Kim, J.-Y., Jacobs, L.J., and  Kurtis, K.E., “Characterization of multi-scale porosity in cement paste by advanced ultrasonic techniques,” Cement and Concrete Research, Vol. 37, pp. 38-46, 2007.

 

3. Structural health monitoring using guided Lamb waves and time-frequency representations, with an emphasis on quantitative techniques to locate and size cracks and other defects in plate-like components.

The objective of this research is to develop automated methodologies that use multi-mode and dispersive Lamb waves to quantify damage. The measurement procedure uses both laser techniques and attached PZT sensors to generate and detect Lamb waves in plates.  Experimentally measured time-domain Lamb waves are first transformed into the time-frequency domain with a time-frequency representation (TFR) such as the reassigned spectrogram or the chirplet transform. These TFRs resolve the individual modes of the plate and generates its dispersion curves and thus enable quantitative characterization of damage. Representative Publications:

 

1.      Niethammer, M., Jacobs, L.J., Qu, Jianmin, and Jarzynski, J., “Time-Frequency Representation of Lamb Waves,” Journal of the Acoustical Society of America, Vol. 109, No. 5, pp. 1841- 1847, 2001. 

  1. Luangvilai, K., Punurai, W. and Jacobs, L.J., “Guided Lamb Wave Propagation in a Composite Plate/Concrete Component,” Journal of Engineering Mechanics, Vol. 128, No. 12, pp. 1337-1341, 2002

3.      Benz, R., Niethammer, M., Hurlebaus, S. and Jacobs, L.J., “Localization of Notches with Lamb Waves,” Journal of the Acoustical Society of America, Vol. 114, No. 2, pp. 677-685, 2003.   

4.      Kotte, O., Niethammer, M. and Jacobs, L.J., “Lamb Wave Characterization by Differential Reassignment and Nonlinear Anisotropic Diffusion,” NDT&E International, Vol. 39, pp. 96-105, 2006.

5.      Kuttig, H., Niethammer, M., Hurlebaus, S. and Jacobs, L.J., “Model-based Analysis of Dispersion Curves,” Journal of the Acoustical Society of America, Vol. 119 No. 7, pp. 2122-2130, 2006.   

 

4. Application of guided circumferential waves for structural health monitoring.

This research considers guided circumferential waves and their applications in characterizing radial cracks in circular annulus.  The main focus of this research is to develop methodologies that can determine the crack location and size.  To locate the crack, a time-frequency representation technique (the energy density of the short time Fourier transform or spectrogram) is used to discern the arrival time of a given mode at a given frequency for both the incident and backscattered waves.  By calculating the time delay of a specific mode in the spectrogram, the distance between the receiver and the crack can be determined.  Thus the crack is located.  For sizing the crack, a time domain counterpart of the Auld’s formula is derived.  By using the time domain Auld’s formula, the backscattering energy coefficient can be obtained directly from experimental measurements, as well as calculated from the synthetic, numerical data.  By comparing the experimentally obtained and numerically calculated backscattering energy coefficients, the size of the crack can be determined. Representative Publications:

  1. Valle, C., Qu, J. and Jacobs, L.J., “Guided Circumferential Waves in Layered Cylinders,” International Journal of Engineering Science, Vol. 37, pp. 1369-1387, 1999.
  2. Kley, M., Valle, C., Jacobs, L.J., Qu, J. and Jarzynski, J. “Development of Dispersion Curves for Two-Layered Cylinders using Laser Ultrasonics,” Journal of the Acoustical Society of America, Vol. 106, No. 2, pp. 582-588, 1999. 
  3. Qu, Jianmin, Berthelot, Y.H. and Jacobs, L.J., “Crack Detection in Thick Annular Components using Ultrasonic Guided Waves,” Journal of Mechanical Engineering Sciences, Vol. 214, Part C, pp. 1163-1171, 2000, Winner of the 2000 Water Arbitration Prize. 

4.      Valle, C., Niethammer, M., Qu, J. and Jacobs, L.J., “Crack Characterization using Guided Circumferential Waves,” Journal of the Acoustical Society of America, Vol. 110, no. 3, pp. 1282-1290, 2001.   

5.      Qu, Jianmin and Jacobs, L.J., “Cylindrical Waveguides and Their Applications in Ultrasonic Evaluation,” in Ultrasonic Nondestructive Evaluation: Engineering and Biological Material Characterization, T. Kundu, Editor, CRC Press, pp. 311-362, 2003. 

6.      Qu, J. and Jacobs, L.J., “Guided Circumferential Waves and Their Applications in Characterizing Cracks in Annular Components,” Materials Evaluation, Vol. 61, No. 1, pp. 85-93, 2003.

 

 

5. Development of ultrasonic sensors including embedded piezoelectric sensors, focused air-coupled ultrasonic sensors, and non-contact optical sensors.

The objective of this research is to design, assemble and test miniature acoustic sensors for condition monitoring of structural components. This research also develops multi-scale sensing, modeling and data fusion for condition assessment and life prediction of this new energy infrastructure. The outcome will be structural and environmental sensing integrated with quantitative, multi-scale models via sensor-sensor and sensor-model fusion strategies for both damage assessment and estimation of remaining life for specific structural elements. Representative Publications:

 

1.      Stolzenburg, J.C., Doane, J., Jarzynski, J. and Jacobs, L.J., “Non-contact Method to Measure Material Properties of Layered Media,” NDT&E International, Vol. 36, No. 7, pp. 523-533, 2003.

2.      Blum, F., Jarzynski, J. and Jacobs, L.J., “A Focused Two-dimensional Air-coupled Ultrasonic Array for Non-contact Generation,” NDT&E International, Vol. 38, pp. 634-642, 2005.

3.      Junge, M., Qu, J., and Jacobs, L.J., “Relationship between Rayleigh wave polarization and state of stress,” Ultrasonics, Vol. 44 (3), pp. 233-237, 2006.

4.      Hurlebaus, S. and Jacobs, L.J., “Dual-probe laser interferometer for structural health monitoring,” Journal of the Acoustical Society of America, Vol. 119, No. 7, pp. 1923-1925, 2006.