Investigation of fiber waviness in a thick glass composite beam using THz NDE

Abstract

Fiber waviness in laminated composite material is introduced during manufacture because of uneven curing, resin shrinkage, or ply buckling caused by bending the composite lay-up into its final shape prior to curing. The resulting waviness has a detrimental effect on mechanical properties, therefore this condition is important to detect and characterize. Ultrasonic characterization methods are difficult to interpret because elastic wave propagation is highly dependent on ply orientation and material stresses. By comparison, the pulsed terahertz response of the composite is shown to provide clear indications of the fiber waviness. Pulsed Terahertz NDE is an electromagnetic inspection method that operates in the frequency range between 300 GHz and 3 THz. Its propagation is influenced by refractive index variations and interfaces. This work applies pulsed Terahertz NDE to the inspection of a thick composite beam with fiber waviness. The sample is a laminated glass composite material approximately 15mm thick with a 90-degree bend. Terahertz response from the planar section, away from the bend, is indicative of a homogeneous material with no major reflections from internal plies, while the multiple reflections at the bend area correspond to the fiber waviness. Results of these measurements are presented for the planar and bend areas.

Ultrasonic Analytic-Signal Responses From Polymer-Matrix Composite Laminates

“…Digital Object Identifier 10.1109/TUFFC.2017.2774776 current importance. Methods have been applied to various NDT modalities such as: X-ray computed tomography (X-ray CT) [4]- [7], terahertz imaging [8], [9], eddy currents [10], [11], ultrasonic guided waves [12], near infrared [13], optical [14]- [17], and ultrasound [18]- [21]. Many of these methods are limited to specific material characteristics or are difficult to deploy due to sample-size limitations or data acquisition constraints.…”

Full wave numerical modelling of terahertz systems for nondestructive evaluation of dielectric structures

“…In order to simulate the operation of the THz devices or the propagation of electromagnetic terahertz waves, full-wave methods (Anastasi, 2008;Deibel and Mittleman, 2006) (e.g. finite element method (FEM), finite difference time domain (FDTD) method) and algorithms based on high-frequency approximation (Melapudi et al, 2006) (e.g.…”

“…Designing the optimum geometry of the terahertz measurement systems and estimating the efficiency of existing and newly developed algorithms for reconstruction of the inner structure of the examined material requires the use of appropriate numerical modelling. In order to simulate the operation of the THz devices or the propagation of electromagnetic terahertz waves, full-wave methods (Anastasi, 2008;Deibel and Mittleman, 2006) (e.g. finite element method (FEM), finite difference time domain (FDTD) method) and algorithms based on high-frequency approximation (Melapudi et al, 2006) (e.g.…”

Experimental fabrication and characterization of out-of-plane fiber waviness in continuous fiber-reinforced composites

“…There have been a number of studies on characterizing fiber waviness using non-destructive testing techniques, such as ultrasonic testing, 12 radiographic testing, 13 electromagnetic testing 14 and shearography, 15 but all with limitations. Among these, the ultrasonic technique developed by Smith et al 12 was the most successful in obtaining a high-resolution waviness profile.…”