Monitoring of jute/hemp fiber hybrid laminates by nondestructive testing techniques

Abstract

Abstract:Damage following static indentation of jute/hemp (50 wt.% total fiber content) hybrid laminates was detected by a number of nondestructive testing (NDT) techniques, in particular, near (NIR) and short-wave (SWIR) infrared reflectography and transmittography, infrared thermography (IRT), digital speckle photography (DSP), and holographic interferometry (HI), to discover and evaluate real defects in a laminate with a complex structure. A comparative study between thermographic data acquired in the mid-(MWIR) and long-wave infrared (LWIR) spectrum bands, by pulsed (PT) and square pulse (SPT) thermography, is reported and analyzed. A thermal simulation by COMSOL ® Multiphysics (COMSOL Inc., Burlington, MA, USA) to validate the heating provided is also added. The robust SOBI (SOBI-RO) algorithm, available into the ICALAB Toolbox (BSI RIKEN ABSP Lab, Hirosawa, Japan) and operating in the MATLAB ® (The MathWorks, Inc., Natick, MA, USA) environment, was applied on SPT data with results comparable to the ones acquired by several thermographic techniques. Finally, segmentation operators were applied both to the NIR/SWIR transmittography images and to a characteristic principal component thermography (PCT) image (EOF s ) to visualize damage in the area surrounding indentation.

Detection of incipient defects in book bindings. A functional use of the infrared vision combined with optical and nuclear magnetic resonance (NMR) spectroscopy techniques

“…4a was obtained with the first exposure (texp = 3 s) 10 s after switching off the electric heater. Also the second texp lasted 3s, while the initial ambient temperature was, also in this case, equal to T = 23 °C [49]. The cusps of fringes indicating damages due to conservation problems and biological attacks, are identified in Fig.…”

Non-destructive Investigation of Paintings on Canvas by Continuous Wave Terahertz Imaging and Flash Thermography

“…A perspective of the present work will be the use of the robot in combination with thermographic measurements, as well as the application of a pseudo-static reconstruction algorithm before the advanced image processing procedure. A short-wave IR camera (SWIR) can also be used both in reflection and in transmission modes considering both the semi-transparent nature of the object itself, and the possibility to perform a digital subtraction procedure between the reflectogram and the transmittogram with the aim of detecting the weaker areas of the canvas [60].…”

Thermographic Non-Destructive Evaluation for Natural Fiber-Reinforced Composite Laminates

“…A hemispherical nose of 12.7 mm diameter was used for static indentation tests. Three specimens (see Figure 2) were tested at different loads, which were applied in displacement control with 1 mm/min cross-head speed [22]. Table 2 shows the specific values obtained for the specimens [23].…”