Bicycle frames made of carbon fibre are extremely popular for high-performance cycling due to the stiffness-to-weight ratio, which enables greater power transfer. However, products manufactured using carbon fibre are sensitive to impact damage. Therefore, intelligent nondestructive evaluation is a required step to prevent failures and ensure a secure usage of the bicycle. This work proposes an inspection method based on active thermography, a proven technique successfully applied to other materials. Different configurations for the inspection are tested, including power and heating time. Moreover, experiments are applied to a real bicycle frame with generated impact damage of different energies. Tests show excellent results, detecting the generated damage during the inspection. When the results are combined with advanced image post-processing methods, the SNR is greatly increased, and the size and localization of the defects are clearly visible in the images.

https://corpus.ulaval.ca/jspui/bitstream/20.500.11794/16365/1/sensors-17-02679.pdf

Nondestructive evaluation of carbon fiber bicycle frames using infrared thermography

The present study was conducted in order to evaluate the efficiency of personal body microclimate cooling systems based on a phase change materials and its effects on physiological strain in soldiers during exertional heat stress in hot environment. The results are obtained in the experiment conducted in the climatic chamber in the Institute of Hygiene, Military Medical Academy in Belgrade. Ten male soldiers were voluntarily subjected to exertional heat stress tests consisted of walking on treadmill (5.5 km/h) in hot conditions (40 °C) in climatic chamber. The subjects performed first test while wearing a field camouflage uniform without any cooling system (CONTROL group) and in second test they used additional microclimate cooling system with paraffin wax consist of n-hexadecane (C16H34), in a form of cooling packs (COOL group). As indicators of thermal strain, mean skin (Tsk) and tympanic (Tty) temperature were determined. Simultaneously, thermal effects of phase change materials were measured by thermal imaging camera. The exercise in hot conditions induced a physiological response to heat stress, manifested through increased body core and skin temperatures. The results confirmed that the cooling vest worn over the field uniform was able to attenuate the physiological strain during exercise, compared to the identical exposure in the “control” group. The results of thermal imaging also indicate that heat generated inside the body is the main factor that will affect the phase change material melting time.

/pdf/efficacy-of-a-novel-phase-change-material-for-microclimate-3v98nr5oyc.pdf

Efficacy of a novel phase change material for microclimate body cooling

Composite materials find wide ranging applications due to their high strength-to-weight ratio. Due to this increasing dependence on composite materials there is a need to study their mechanical behavior in case of damage. There are several ENDT and SHM methods for the assessment of the mechanical properties each with their set of advantages and disadvantages. The paper presents a comparative study of three distinct damage detection methods (infrared thermography, neutral axis method based on optical strain sensor measurements and terahertz spectroscopy) for the detection of delamination and temperature induced damage in a simple GFRP beam-like structure. The terahertz spectroscopy is a specialized technique suitable for detecting deterioration inside the structure, but has limited application for in-service performance monitoring. Similarly the infrared thermography technique in the active domain may be used for in situ monitoring but not in in-service assessment. Both methods allow the visualization of the internal structure and hence allow identification of the type and the extent of damage. Fibre optic sensors (especially FBG) due to their small diameter and no need of calibration can be permanently integrated within the sample and applied for continuous dynamic strain measurements. The measured strain is treated as an input for neutral axis (NA) method, which as a damage sensitive feature may be used for in-service monitoring but gives absolutely no information about the type and extent of damage. The results for damage detection based on proposed comparative studies give a complete description of the analyzed structure.

Damage Assessment in Composite Beam Using Infrared Thermography, Optical Sensors, and Terahertz Technique

Nondestructive thermal examination can uncover the presence of defects via
 temperature distribution profile anomalies that are created on the surface as
 a result of a defect. There are many factors that affect the temperature
 distribution map of the surface being tested by Infrared Thermography.
 Internal defect properties such as thermal conductivity, heat capacity and
 defect depth, play an important role in the temperature behavior of the
 pixels or regions being analyzed. Also, it is well known that other external
 factors such as the convection heat transfer, variations on the surface
 emissivity and ambient radiation reflectivity can affect the thermographic
 signal received by the infrared camera. In this paper we considered a simple
 structure in the form of flat plate covered with several defects, whose
 surface we heated with a uniform heat flux impulse. We conducted a
 theoretical analysis and experimental test of the method for case of defects
 on an aluminum surface. First, experiments were conducted on surfaces with
 intentionally created defects in order to determine conditions and boundaries
 for application of the method. Experimental testing of the pulsed flash
 thermography (PFT) method was performed on simulated defects on an aluminum
 test plate filled with air and organic compound n-hexadecane, hydrocarbon
 that belongs to the Phase Change Materials (PCMs). Study results indicate
 that it is possible, using the PFT method, to detect the type of material
 inside defect holes, whose presence disturbs the homogeneous structure of
 aluminum.

/pdf/application-of-pulsed-flash-thermography-method-for-specific-2dsn9omqrq.pdf

Application of pulsed flash thermography method for specific defect estimation in aluminum

Composite materials find wide ranging applications due to their high strength-to-weight ratio. Due to this increasing dependence on composite materials there is a need to study their mechanical behavior in case of damage. There are several ENDT and SHM methods for the assessment of the mechanical properties each with their set of advantages and disadvantages. The paper presents a comparative study of three distinct damage detection methods (infrared thermography, neutral axis method based on optical strain sensor measurements and terahertz spectroscopy) for the detection of delamination in a simple GFRP beam-like structure. Each of the methods have their own set of advantages and disadvantages. The terahertz spectroscopy is a specialized technique suitable for detecting deterioration inside the structure, but is not suitable for in performance monitoring. Similarly the infrared thermography technique in the active domain may be used for in situ monitoring but not in in-service assessment. Both methods allow the visualization of the internal structure and hence allow identification of the type and the extent of damage. Fibre optic sensors (especially FBG) due to their small diameter and no need of calibration can be permanently integrated within the sample and applied for continuous dynamic strain measurements. The measured strain is treated as an input for neutral axis (NA) method, which as a damage sensitive feature may be used for in-service monitoring but gives absolutely no information about the type and extent of damage. The results for damage detection based on proposed comparative studies give a complete description of the analyzed structure.

Assessment of delamination in composite beam using infrared thermography, optical sensors and terahertz technique

The paper presented testing of surface defects by pulse video thermography techniques. Such techniques rely on transient infrared radiation from the sample heated by the short duration flux initiated by flesh. Experimental measurements are realized by infrared sensor (FLIR camera). Testing results are considered for the samples with controlled designed defects beyond observed surfaces. The effects of response through the transparent wall are measured as infrared visible radiance. Researches with controlled samples are performed to verify visibility threshold of defect dimensions and forms, for possible use as modulation transfer function of defects hidden beyond the surfaces of thin metal walls. Dimensionless coefficients are derived for method estimations as the results from experimental research.

/pdf/experimental-research-of-limits-for-thermal-modulation-26xhtchgc8.pdf

D Ljubisa Tomic

Papers

Application of pulsed flash thermography method for specific defect estimation in aluminum

Experimental research of limits for thermal modulation transfer function