Ultrasonic wave propagation in the corner section of composite laminate structure: Numerical simulations and experiments

Abstract

Two-dimensional finite element simulations and experiments are presented to examine the ultrasonic wave propagation behavior in the corner section of CFRP (carbon fiber reinforced plastics) laminate structures. The numerical model consists of a right-angle corner section of CFRP laminate immersed in water and subjected to the ultrasonic wave incidence from its inner or outer side. The anisotropic stiffness constants of the unidirectional CFRP are identified experimentally and used to model the curved laminate structure. A commercial finite element analysis code is used to compute the reflection waveforms in the pulse-echo mode, and the effect of the laminate stacking sequence and the wave incidence direction is examined. It is shown that the reflection waveforms for the wave incidence from the outer side of the corner qualitatively resemble those for the plane laminate except that the echo signals of the former are substantially weaker. The numerical simulations are shown to well reproduce the qualitative features of experimental reflection measurements performed for the corner sections of 16-ply CFRP laminate. Experimental results indicate that the porosity content of the corner section can be estimated by the amplitude ratio of the surface and the back-wall echoes when a curvature-dependent calibration relation is properly used.

Nondestructive Evaluation of Porosity Content in the Curved Corner Section of Composite Laminates Using Focused Ultrasonic Waves

“…The numerical simulations and the experiments follow the approaches similar to those by Ito et al [20] except that the present study considers the case where the corner section is probed from its inner side by the focused or nonfocused ultrasonic wave. A special attention of this study is paid to the effectiveness of focused ultrasonic waves in obtaining clear echo signals which can be used for porosity characterization.…”

“…Recently, Ito et al [20] performed finite element simulations and measurements of the ultrasonic wave reflection at a curved corner section of the composite laminate structure. Their results indicate that the porosity in the corner section can be evaluated by the amplitude ratio of the surface and bottom echoes of the laminate when it is probed from the outer side of the corner.…”

“…In Ref. [20], the incidence of ultrasonic waves from a nonfocusing transducer was considered. As a consequence, the use of focused ultrasonic waves still remains as a topic to be explored as it can be a potential solution to characterize the porosity in the corner section from the inner side.…”

“…In Ref. [20], the elastic constants of the unidirectional laminate were determined experimentally based on the wave velocities in different propagation directions measured by the double throughtransmission technique [21], and used as the elastic constants of each ply. When the x-axis is taken along the ply thickness direction and the y-axis along the fiber direction, the assumed stress-strain relation of each ply is given by ) are also employed in the present analysis.…”

Influence of porosity on ultrasonic wave velocity, attenuation and interlaminar interface echoes in composite laminates: Finite element simulations and measurements

“…Conventional techniques to evaluate the porosity content have been based on the ultrasonic wave velocity [10][11][12][13][14][15] and attenuation [15][16][17][18][19][20][21][22][23][24][25][26][27] in the stacking direction of composite laminates. In practice, the attenuation is used more frequently than the wave velocity because of its higher sensitivity to the porosity content [2].…”