Plate Wave Characterization of Stiffness Degradation in Composites During Fatigue

Abstract

Cross-ply composite specimens of metal matrix (SCS-6/Ti-6-4 [90/0] s ) and polymer matrix (graphite/epoxy AS4/3502 [0/90] s ) were subjected to tensile fatigue tests to induce stiffness degradaton. Extensional plate wave velocities in the 0, 45, and 90 • directions, together with the quasi-shear wave velocity in the 90 • direction, were used to characterize the degradation of the stiffness constants of each specimen during fatigue. The laminate stiffness constants in the xand y-directions (E x , E y ) and the shear modulus (G xy ) were determined. The laminate stiffness, E x , was also monitored through direct measurement by using an extensometer during fatigue loading. The trend in the stiffness degradation of the titanium matrix composite was identical in both measurement techniques, but the stiffness values calculated from the extensional velocity measurements were higher than those obtained from the extensometer. This discrepancy was shown to be due to microcrack closure during wave velocity measurements when the tensile stress was removed from the specimen. The graphite/epoxy specimens appeared to suffer only a small reduction in their stiffness.

Lamb wave characterization of the effects of long-term thermal-mechanical aging on composite stiffness

“…Karim et al 6 and Mal et al 7 have used inversion techniques to determine the material parameters of composites from experimental Lamb wave data. Recently, Shih et al 8 used Lamb wave velocity measurements to calculate laminate stiffness constants in fatigued composites. Lamb wave techniques have also been used to study composite defects such as delaminations, [9][10][11][12] porosity, 12,13 and fiber misalignment.…”

“…13 Under the normal use environment for many composite aerospace structures, thermal degradation as well as damage due to mechanical fatigue may occur. While studies have been conducted using Lamb waves to examine fatigue damage, [2][3][4][5]8 few studies have been conducted which monitor either thermal degradation or thermal-mechanical aging in polymer matrix composites using ultrasonic nondestructive evaluation techniques. However, ultrasonic Lamb waves have been shown by Seale et al 2 as well as Bar-Cohen et al 14 to be an effective method for characterizing thermal damage in composites.…”

An experimental study on the effects of matrix cracking to the stiffness of glass/epoxy cross plied laminates

“…Also noted, in-plane shear stiffness reduction has been reported due to transverse cracking, showing its applicability as a damage indicator. Shih et al [11] noted that progressive opening of transverse cracks (e.g. from tensile load) caused the guided wave velocity to decrease i.e.…”

Fatigue crack propagation of super duplex stainless steel with dispersed structure and time-frequency analysis of acoustic emission

“…Because cumulate counts and energy include the noise in an acoustic emission test, quantitative evaluation is limited. Studies of fracture mechanism characteristics related to the waveform and the spectra of signals are actively being carried out [9][10][11]. The time-frequency analysis methods, which can represent information about time and frequency domains of signals at the same time, are being tested to study nondestructive evaluation [12][13][14][15][16][17].…”