Application of nonlinear ultrasonic analysis for in situ monitoring of metal additive manufacturing

Peipei Liu, Liu Yang, Kiyoon Yi, Tribikram Kundu, Hoon Sohn

Research output: Contribution to journalArticlepeer-review

7 Scopus citations


Nonlinear ultrasonic techniques have the benefit of high sensitivity to micro or early-stage defects. Among the various nonlinear techniques, the newly proposed sideband peak count (SPC) technique investigates defect-induced nonlinearity by counting the spectral sidebands from a broadband ultrasonic response in the frequency domain. In this study, SPC analysis is transformed into the time–frequency plane through synchrosqueezed wavelet transform (SWT) for transient nonstationary ultrasonic signals. The proposed new SPC technique was then adopted for in situ porosity monitoring in directed energy deposition (DED)—a typical metal additive manufacturing process. Porosity is one of the most critical defects in DED and has detrimental effects on the mechanical properties and fatigue performance of products. For in situ porosity monitoring, a fully noncontact ultrasonic measurement was achieved with a laser ultrasonic system, and its detectability was improved by laser polishing. Time and frequency windows were properly selected to suppress the effects of wave characteristic variations on the SPC analysis in the SWT domain. The performance of the proposed technique was verified by monitoring porosity in stainless steel 316L samples manufactured in the DED process. The test results demonstrated that the proposed nonlinear technique is much more sensitive to porosity than conventional linear techniques, and hence, is more suitable for in situ porosity monitoring.

Original languageEnglish (US)
Pages (from-to)1760-1775
Number of pages16
JournalStructural Health Monitoring
Issue number3
StatePublished - May 2023


  • Nonlinear ultrasonic
  • directed energy deposition
  • laser ultrasonic
  • porosity inspection
  • sideband peak count
  • synchrosqueezed wavelet transform

ASJC Scopus subject areas

  • Mechanical Engineering
  • Biophysics


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