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

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

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

A powerful tool to understand, demonstrate and explain the limits of the pulsed technique in terms of detectability and localizability of AM keyhole pores has been assessed by comparing the active thermographic approach (both experimental and FEM simulations) to Computed Tomography results; 
✓ µCT results demonstrate that the intended defect geometry is not achieved; indeed a network of voids (microdefects consisting of small sharp-edged hollows with a complicated, almost fractal, inner surface) was found;
✓ both Exp-PT and FEM results explains clearly why no indication of defect related to the thermal contrasts could be found during the investigation of an uncoated surface. However, the application of further data evaluations focusing on the thermal behavior and emissivity evaluation (PPT post data processing) enable the detection of some defects;
✓ coating facilitates a closer inspection of inner defects, but inhomogeneities of the coating could impair the spatial resolution and lead to the emergence of hotspots (the FEM simulation reached its limit with this extreme geometry where a 25 µm thin disc is considered at a 1 cm thick specimen in millisecond time resolution);
✓ both Exp-PT and FEM results allow the conclusion that very short pulses of 200 ms or shorter should be sufficient to detect these defects below, but near the surface; besides a short duration of the thermal phenomenon it should be emphasized, about 0.04 s (high frame rate camera);

Capability of active thermography to detect and localize pores in Metal Additive Manufacturing materials

Temperature distribution induced by laser radiation is a very important parameter for an efficient and safe application of lasers in different ceramic processing techniques. This paper presents the results of an infrared thermography application for monitoring temperature distribution on a ceramic surface during Nd:YAG laser irradiation with different fluences and 8ns pulse duration. The FLIR, E40 and SC7200 infrared cameras were used with the aim of recording the maximum temperature in the irradiated zones. It was expected that infrared thermography could give some information related to the heat affected zone and possible damage to the base material. However, the results have shown that infrared cameras, even those with high performance such as SC7200, cannot record the maximum temperature value at the moment of laser operation, but only the average temperature of the bulk sample material after laser pulses. The results of the numerical simulation have confirmed the value of the thermographic measurements. The micro-structure and micromorphology of the ceramic surface before and after the laser treatment were analysed by optical and SEM as well as by examining the roughness of the irradiated and non-irradiated surfaces, while the micro-mechanical changes were analysed by comparing the micro-hardness of the irradiated and non-exposed surfaces.

/pdf/monitoring-of-a-ceramic-surface-temperature-field-induced-by-93o1wylci8.pdf

Monitoring of a ceramic surface temperature field induced by pulsed Nd:YAG laser

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

D Dalibor Filipovic

Papers

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