Computational modeling of micro-crack induced attenuation in CFRP composites

Abstract

A computational study is performed to determine the contribution to ultrasound attenuation in carbon fiber reinforced polymer composite laminates of linear elastic scattering by matrix micro-cracking. Multiple scattering approximations are benchmarked against exact computational approaches. Results support linear scattering as the source of observed increased attenuation in the presence of micro-cracking. Center for NDE, Iowa State University, Ames, IA 50014 2 NASA Langley, Hampton, VA 23681 ABSTRACT. A computational study is performed to determine the contribution to ultrasound attenuation in carbon fiber reinforced polymer composite laminates of linear elastic scattering by matrix micro-cracking. Multiple scattering approximations are benchmarked against exact computational approaches. Results support linear scattering as the source of observed increased attenuation in the presence of micro-cracking.

Micro-crack ultrasound scattering in anisotropic composite laminates

“…An example of application to scattering by a distribution of micro-cracks in a 16 ply unidirectional laminate is presented, where 112 cracks are randomly distributed in a 4.85 mm wide volume (320 cracks/cm) using an algorithm described in [2]. The micro-cracks are assumed perpendicular to and extend between neighboring ply interfaces.…”

“…Matrix micro-cracking is considered a precursor to a more advanced damage state, hence a means to quantitatively assess levels of microcracking would serve early damage detection. Experiments as reported in [1,2] indicate that an increase in ultrasound attenuation accompanies micro-cracking. The present work seeks to determine if the observed attenuation is attributable to linear elastic wave scattering, as opposed to, say, increased non-linear frictional losses.…”

“…A micrograph showing matrix micro-cracking can be seen in [2]. To keep the scope of the computation supportable by a laptop PC, the BIE analysis is limited to a 2D field dependency.…”

“…Adopting the Cartesian spatial Fourier transform representation for the solution, Fourier integral expressions of the infinite space Green function are obtained (4) where k 3 =0, and k 2 is expressed as a function of k 1 through a relation imposed on the wave vector k by eq.(1). The summation on D denotes distinct modes of propagation, corresponding to 6 allowable functions k 2 D (k 1 ): 3 modes of motion propagating in either +x 2 or -x 2 direction, which along material symmetry axes correspond to longitudinal and two polarizations of shear motion. The integrand of eq.…”

“…(4) as an incident field on the interfaces bounding the m th ply in eq. (7) (8) where the summation over D+ or D-denotes inclusion of wave modes propagating in the +x 2 or -x 2 directions, respectively, and k 1 dependence is implied. The Green function response is evaluated by performing a numerical integration of eq.…”