Damage Signature of Fatigued Fabric Reinforced Plastics in the Pulsed Ultrasonic Polar Scan

Abstract

This study investigates the use of both the amplitude and time-of-flight based pulsed ultrasonic polar scan (P-UPS) for the nondestructive detection and evaluation of fatigue damage in fabric reinforced composites. Several thermoplastic carbon fabric reinforced PPS specimens (CETEX), loaded under various fatigue conditions, have been scanned at multiple material spots according to the P-UPS technique in order to extract material degradation in a quantitative way. The P-UPS results indicate that shear dominated fatigued carbon/PPS goes with a reduction of shear properties combined with large fiber distortions. The P-UPS results of the tension-tension fatigued carbon/PPS samples on the other hand reveal a directional degradation of the stiffness properties, reaching a maximum reduction of −12.8 % along the loading direction. The P-UPS extracted damage characteristics are fully supported by simulations, conventional destructive tests as well as visual inspection. The results demonstrate the excellent capability of the P-UPS method for nondestructively assessing and quantifying both shear-dominated and tension-tension fatigue damage in fabric reinforced plastics.

The Ultrasonic Polar Scan for Composite Characterization and Damage Assessment: Past, Present and Future

“…Such a directional stiffness reduction is visible as a stretching (along the direction of loading) of the UPS contours. This is explicitly demonstrated in Figure 11 for a woven C/E laminate (ultimate tensile strength of 770 MPa), which was fatigued along ϕ = 0˝: 314,111 load cycles with stress range 0-625 MPa at a frequency of 5 Hz [33]. The P-UPS experiment yielded a stiffness reduction of 12.8% along the loading direction, which is in good agreement with extensometer data yielding a stiffness reduction of 11% [33].…”

“…Until now, linear wave phenomena were used in the U(B)PS methodology for detecting, assessing and analyzing a range of damage features [24,29,30,33]. However, it is well-known from literature that nonlinear wave phenomena show an increased sensitivity to early stage damage features as well as to certain classes of contact defects [42][43][44][45].…”

Recent Advances in the Ultrasonic Polar Scan Method for Characterizing (Degraded) Fiber Reinforced Plastics

“…This is explicitly demonstrated in Figure 8 for a woven C/E laminate which was fatigued along φ = 0°. The UPS experiment yields a stiffness reduction of 12.8% along the loading direction, which agrees well with extensometer data giving a reduction of 11% [18]. …”

Numerical study of the Time-of-Flight Pulsed Ultrasonic Polar Scan for the determination of the full elasticity tensor of orthotropic plates

“…The importance of this case cannot be underestimated as in practical and realistic applications the fiber direction is often unknown. This is especially true for composite materials which show a distortion of the fiber orientation as a consequence of mechanical loading, potentially resulting in a shift of the main symmetry axes [11,12]. Figure 8c shows a TOF P-UPS simulation of a [0 • ] 8 C/E composite plate at f c d = 5 MHz.mm, for a random orientation of the main symmetry axes.…”

“…In reality, however, the symmetry of the composite sample under investigation, and especially the orientation of its main axes of symmetry, is often unknown a priori. Moreover, when the symmetry orientation of the investigated composite is well defined for an intact sample, mechanical loading during operation could induce a substantial change in fiber direction [11,12]. An approach that uses a consecutive treatment of single scan data at fixed individual azimuthal φ-angles therefore lacks the versatility of acquiring and analyzing the required information in samples of arbitrary symmetry.…”