The prerequisite for more competent and cost effective aircraft has led to the evolution of innovative testing and
evaluation procedures. Non-destructive testing and evaluation (NDT & E) techniques for assessing the integrity of an
aircraft structure are essential to both reduce manufacturing costs and out of service time of aircraft due to maintenance.
Nowadays, active - transient thermal NDT & E (i.e. thermography) is commonly used for assessing aircraft composites.
This research work evaluates the potential of pulsed thermography (PT) and/or pulsed phase thermography (PPT) for
assessing defects (i.e. impact damage and inclusions for delaminations) on GLARE and GLARE type composites.
Finally, in the case of the detection of inserts - delaminations C-Scan ultrasonic testing was also used with the intention
of providing supplementary results.
An imaging technique of the hand vein tree is presented in this paper. Using the natural human circulatory system and a controlled armband pressure around the arm, a lock-in thermography technique with an internal excitation is carried out. Since the stimulation frequency is inversely proportional to the inspection depth, the subcutaneous layer requires the use of a very slow frequency. Thus, a sawtooth waveform is preferred to minimize the duration of the pressure applied to the armband during the experiment. A frequency of approximately 0.03 Hz and a pressure range between 100 and 140 mmHg, according to the diastolic and systolic blood pressure, are used as stimulation. Then, dorsal hand amplitude and phase images are obtained with IR_view (Klein, 1999), a tool specifically designed to analyze infrared images.
The hand vein structure is thermally mapped by an infrared camera operating in the middle wavelength infrared range (MWIR) at room temperature. Parasitic frequencies are avoided by keeping the hand fixed. The resulting images show a gradient of temperature between surrounding tissues and the back-of-hand veins. The vascular signature segmentation is extracted from the amplitude and phase images by using a Fast Fourier Transform image processing technique. This work could be used for vein localization for perfusion or for the early diagnosis of vein diseases such as primitive varicose and deep vein thrombosis (DVT). A hand vein signature database for identification purposes is also possible.
Inspection of aerospace components has always been a challenge. Infrared thermography has demonstrated to be a useful tool for this matter. In this paper, we offer a comparative study involving three active techniques: pulsed thermography, lock-in thermography and vibrothermography. Some of these techniques have proven to be more effective than others for a specific type of system. We compare the experimental results from these three techniques as applied to two typical aerospace parts: honeycomb structures and Glare. The later is perhaps the most challenging of all as will be pointed out. Some insights are provided regarding the most suitable technique for a number of typical situations.
While other non-destructive testing methods hardly reveal microscopic open cracks, ultrasound excited vibrothermography provides very promising results by converting mechanical waves into local heat by friction. This phenomenon enhances thermal gradients in temperature maps as compared to conventional techniques. To detect temperature gradients caused by hidden cracks, high temperature and spatial resolution infrared cameras are usually used.
Recently, it has been shown that the HVOF (High Velocity Oxy Fuel)-spraying of tungsten carbide or cobalt coatings onto steel substrates, seems to be a suitable alternative to the non-environmentally friendly chromium coating material. However one major issue with these thermal-sprayed coatings is the possibility of the appearance of microscopic cracks when they are submitted to excessive bending loads. If the open cracks spread through the whole coating thickness (typically 100 to 200 ?m), they might also propagate at the coating-substrate interface causing the coating to delaminate in between adjacent open cracks. The latter disbonding phenomenon is therefore strongly dependent on the distance between adjacent open cracks. Therefore, a non destructive technique enabling the detection of cracks and the evolution of their density is critical to preserve the components integrity.
The aim of this work is to investigate the ability of ultrasound excited vibrothermography to detect such cracks. To do so, we investigated tungsten carbide coatings where cracks were artificially generated using a controlled bending test. Results on different samples are presented and discussed.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.