Abstract
Detection of precursor damage followed by the quantification of the degraded material properties could lead to more accurate progressive failure models for composite materials. However, such information is not readily available. In composite materials, the precursor damages—for example matrix cracking, microcracks, voids, interlaminar pre-delamination crack joining matrix cracks, fiber micro-buckling, local fiber breakage, local debonding, etc.—are insensitive to the low-frequency ultrasonic guided-wave-based online nondestructive evaluation (NDE) or Structural Health Monitoring (SHM) (~100–~500 kHz) systems. Overcoming this barrier, in this article, an online ultrasonic technique is proposed using the coda part of the guided wave signal, which is often neglected. Although the first-arrival wave packets that contain the fundamental guided Lamb wave modes are unaltered, the coda wave packets however carry significant information about the precursor events with predictable phase shifts. The Taylor-series-based modified Coda Wave Interferometry (CWI) technique is proposed to quantify the stretch parameter to compensate the phase shifts in the coda wave as a result of precursor damage in composites. The CWI analysis was performed on five woven composite-fiber-reinforced-laminate specimens, and the precursor events were identified. Next, the precursor damage states were verified using high-frequency Scanning Acoustic Microscopy (SAM) and optical microscopy imaging.
Highlights
The early detection and quantification of embryonic precursor damage in composites are currently challenging due to lack of an online ultrasonic method
The phase shifts observed in the coda part of the wave signals are independent or decoupled from the first arrival of the Lamb wave modes
Was to device andachieved prove thebyapplicability of acoda reliable damage detection method. This was achieved by analyzing the coda part of the guided wave signals which are usually discarded in the conventional damage detection methods used in Structural Health Monitoring (SHM)
Summary
The early detection and quantification of embryonic precursor damage in composites are currently challenging due to lack of an online ultrasonic method. [1,2] These damages can be visualized using off-line laboratory-based nondestructive evaluation (NDE) methods, for example, X-ray tomography [3], Scanning Acoustic Microscopy [4], Ultrasonic immersion scanning [5], etc. It is realized that the conventional ultrasonic guided-wave-based Structural Health Monitoring (SHM) at low frequencies (~100–~500 kHz) are not sensitive to these precursor damages, and often demands sophisticated pattern recognition algorithms for signal processing, offline. These statistical signal processing algorithms sometimes result in heavy computational burden.
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