Detecting Defects in Composite Polymers by Using 3D Scanning Laser Doppler Vibrometry

Area of Science:

• Materials Science
• Non-Destructive Testing
• Vibrational Spectroscopy

Background:

• Composite polymers are susceptible to discontinuity-like defects.
• Traditional evaluation methods may be destructive or lack sensitivity.
• Local defect resonance (LDR) offers a promising approach for defect detection.

Purpose of the Study:

• To analyze the application of 3D scanning laser Doppler vibrometry for nondestructive evaluation of defects in composite polymers.
• To investigate the phenomenon of local defect resonance (LDR) for enhancing defect detection.
• To characterize vibration propagation and interaction with structural inhomogeneities in composites.

Main Methods:

• Utilized 3D scanning laser Doppler vibrometry to map vibration patterns.
• Employed Fast Fourier Transform (FFT) analysis for vibration components (in-plane x, y; out-of-plane z).
• Applied acoustic stimulation with a frequency-modulated harmonic signal (50 Hz to 100 kHz).

Main Results:

• Identified identical resonance frequencies for all vibration components (x, y, z) in a reference plate with a defect.
• Observed predominant compression/tension deformations (x, y components) in impact-damaged carbon fiber reinforced plastic.
• Demonstrated enhanced inspection by analyzing averaged total vibration patterns at resonance frequencies.

Conclusions:

• 3D scanning laser Doppler vibrometry combined with LDR is an effective nondestructive evaluation technique for composite polymers.
• Analysis of vibration components and resonance frequencies provides reliable defect characterization.
• The LDR technique is nondestructive, as defect-induced deformations are below material tensile strength.