Modeling the effects of beam size and flaw morphology on ultrasonic pulse/echo sizing of delaminations in carbon composites

Abstract

The size and shape of a delamination in a multi-layered structure can be estimated in various ways from an ultrasonic pulse/echo image. For example the −6dB contours of measured response provide one simple estimate of the boundary. More sophisticated approaches can be imagined where one adjusts the proposed boundary to bring measured and predicted UT images into optimal agreement. Such approaches require suitable models of the inspection process. In this paper we explore issues pertaining to model-based size estimation for delaminations in carbon fiber reinforced laminates. In particular we consider the influence on sizing when the delamination is non-planar or partially transmitting in certain regions. Two models for predicting broadband sonic time-domain responses are considered: (1) a fast "simple" model using paraxial beam expansions and Kirchhoff and phase-screen approximations; and (2) the more exact (but computationally intensive) 3D elastodynamic finite integration technique (EFIT). Model-to-model and model-to experiment comparisons are made for delaminations in uniaxial composite plates, and the simple model is then used to critique the −6dB rule for delamination sizing. ABSTRACT. The size and shape of a delamination in a multi-layered structure can be estimated in various ways from an ultrasonic pulse/echo image. For example the -6dB contours of measured response provide one simple estimate of the boundary. More sophisticated approaches can be imagined where one adjusts the proposed boundary to bring measured and predicted UT images into optimal agreement. Such approaches require suitable models of the inspection process. In this paper we explore issues pertaining to model-based size estimation for delaminations in carbon fiber reinforced laminates. In particular we consider the influence on sizing when the delamination is non-planar or partially transmitting in certain regions. Two models for predicting broadband sonic time-domain responses are considered: (1) a fast "simple" model using paraxial beam expansions and Kirchhoff and phase-screen approximations; and (2) the more exact (but computationally intensive) 3D elastodynamic finite integration technique (EFIT). Model-to-model and model-to experiment comparisons are made for delaminations in uniaxial composite plates, and the simple model is then used to critique the -6dB rule for delamination sizing.

Nondestructive evaluation of forced delamination in glass fiber-reinforced composites by terahertz and ultrasonic waves

“…3(a) compared with the surrounding regions. We apply one common approach, the so-called 50% rule or À6 dB drop method, to estimate the size of the delamination [34,35]. This method locates the pixel with the highest value in the C-scan image and assigns this a value of 100%, then colors all pixels red that have a value of at least 50% of the maximum.…”

Ring burst test of filament wound composites for environmental resistance

“…To measure the size of the inside damage, the general 50% rule for delamination sizing was applied. 18 The colored area in Figures 16-18 signifies solely the inside damage of the specimens. The images were processed by ImageJ software to count the number of colored pixels and measure the damage area Intensity of reflected ultrasonic wave dB ð Þ ¼ 20 log ðpeak%Þ ð20Þ…”

Computational modeling of micro-crack induced attenuation in CFRP composites

“…As such, mechanical properties are specified by mass density U and five independent elastic constants, with stress W ij and displacements u i related via the constitutive relation W ij =c ijkl u k,l . Wave motion within the laminate is governed by the elastodynamic field equation, expressed in partial differential equation (PDE) form as (1) with continuity of displacements and tractions at the ply interfaces imposed as boundary conditions. [2] Work presented here obtains solutions to eq.…”

“…An established tool for detection of large-scale ply delamination is pulseecho ultrasound, which looks for a strong reflection from the separated ply interfaces. [1] In addition to the detection of large-scale ply delamination, NASA is interested in detecting the presence of ply micro-cracks prior to advancement to delamination. It was hypothesized by NASA, supported by experimental evidence, that monitoring ultrasound attenuation in the CFRP structure might be a means to detect the presence of micro-cracks.…”