Instantaneous frequency and its application to strain extraction in moire interferometry.

Area of Science:

• Experimental Mechanics
• Optical Metrology
• Materials Science

Background:

• Moiré interferometry is a key technique for measuring in-plane deformation.
• Experimental mechanics often requires strain data, which are derivatives of deformation.
• Extracting strain directly from Moiré fringe patterns presents a challenge.

Purpose of the Study:

• To demonstrate that strains correspond to instantaneous frequencies within Moiré fringe patterns.
• To introduce and compare two novel methods for extracting these frequencies: the energy operator and wavelet ridges.
• To evaluate the effectiveness of these methods against traditional approaches.

Main Methods:

• Utilizing instantaneous frequencies of Moiré fringe patterns as a representation of strain.
• Applying the energy operator for pixelwise, on-the-fly strain extraction, noting its sensitivity to noise.
• Employing wavelet ridges for local feature extraction, offering noise insensitivity at the cost of computation time.

Main Results:

• Both the energy operator and wavelet ridges successfully extract strain information from single Moiré fringe patterns.
• The energy operator provides rapid strain analysis but is susceptible to noise.
• Wavelet ridges offer robust, noise-insensitive strain analysis with higher computational demands.

Conclusions:

• The choice between the energy operator and wavelet ridges depends on specific strain analysis needs, balancing speed and noise tolerance.
• These methods provide effective alternatives to traditional techniques for strain determination in experimental mechanics.
• The study validates the proposed methods through application to real fringe patterns and comparative analysis.