Showing papers on "Thermography published in 2016"

Infrared thermography of welding zones produced by polymer extrusion additive manufacturing

Abstract: In common thermoplastic additive manufacturing (AM) processes, a solid polymer filament is melted, extruded though a rastering nozzle, welded onto neighboring layers and solidified. The temperature of the polymer at each of these stages is the key parameter governing these non-equilibrium processes, but due to its strong spatial and temporal variations, it is difficult to measure accurately. Here we utilize infrared (IR) imaging – in conjunction with necessary reflection corrections and calibration procedures – to measure these temperature profiles of a model polymer during 3D printing. From the temperature profiles of the printed layer (road) and sublayers, the temporal profile of the crucially important weld temperatures can be obtained. Under typical printing conditions, the weld temperature decreases at a rate of approximately 100 °C/s and remains above the glass transition temperature for approximately 1 s. These measurement methods are a first step in the development of strategies to control and model the printing processes and in the ability to develop models that correlate critical part strength with material and processing parameters.

Infrared thermography: A non-invasive window into thermal physiology

Abstract: Infrared thermography is a non-invasive technique that measures mid to long-wave infrared radiation emanating from all objects and converts this to temperature. As an imaging technique, the value of modern infrared thermography is its ability to produce a digitized image or high speed video rendering a thermal map of the scene in false colour. Since temperature is an important environmental parameter influencing animal physiology and metabolic heat production an energetically expensive process, measuring temperature and energy exchange in animals is critical to understanding physiology, especially under field conditions. As a non-contact approach, infrared thermography provides a non-invasive complement to physiological data gathering. One caveat, however, is that only surface temperatures are measured, which guides much research to those thermal events occurring at the skin and insulating regions of the body. As an imaging technique, infrared thermal imaging is also subject to certain uncertainties that require physical modelling, which is typically done via built-in software approaches. Infrared thermal imaging has enabled different insights into the comparative physiology of phenomena ranging from thermogenesis, peripheral blood flow adjustments, evaporative cooling, and to respiratory physiology. In this review, I provide background and guidelines for the use of thermal imaging, primarily aimed at field physiologists and biologists interested in thermal biology. I also discuss some of the better known approaches and discoveries revealed from using thermal imaging with the objective of encouraging more quantitative assessment.

Thermographic measurements of the commercial laser powder bed fusion process at NIST

Abstract: Quantitative understanding of the temperatures, gradients and heating/cooling rates in and around the melt pool in laser powder bed fusion (L-PBF) is essential for simulation, monitoring and controls development. The research presented here aims to detail experiment design and preliminary results of high speed, high magnification, in-situ thermographic monitoring setup on a commercial L-PBF system designed to capture temperatures and dynamic process phenomena.,A custom door with angled viewport was designed for a commercial L-PBF system which allows close access of an infrared camera. Preliminary finite element simulations provided size, speed and scale requirements to design camera and optics setup to capture melt pool region temperatures at high magnification and frame rate speed. A custom thermal calibration allowed maximum measurable temperature range of 500°C to 1,025°C. Raw thermographic image data were converted to temperature assuming an emissivity of 0.5. Quantitative temperature results are provided with qualitative observations with discussion regarding the inherent challenges to future thermographic measurements and process monitoring.,Isotherms around the melt pool change in size depending on the relative location of the laser spot with respect to the stripe edges. Locations near the edges of a stripe are cooled to lower temperatures than the center of a stripe. Temperature gradients are highly localized because of rough or powdery surface. At a specific location, temperatures rise from below the measurable temperature range to above ( 1100°C) within two frames ( 11.7 m/s.,Several works are detailed in the Introduction of this paper that detail high-speed visible imaging (not thermal imaging) of custom or commercial LBPF processes, and lower-speed thermographic measurements for defect detection. However, no work could be found that provides calibrated, high-speed temperature data from a melt-pool monitoring configuration on a commercial L-PBF system. In addition, the paper elucidates several sources of measurement uncertainty (e.g. calibration, emissivity and time and spatial resolution), describes inherent measurement challenges based on observations of the thermal images and discusses on the implications to model validation and process monitoring and control.

Methodology for High-Throughput Field Phenotyping of Canopy Temperature Using Airborne Thermography.

Abstract: Lower canopy temperature (CT), resulting from increased stomatal conductance, has been associated with increased yield in wheat. Historically, CT has been measured with hand-held infrared thermometers. Using the hand-held CT method on large field trials is problematic, mostly because measurements are confounded by temporal weather changes during the time required to measure all plots. The hand-held CT method is laborious and yet the resulting heritability low, thereby reducing confidence in selection in large scale breeding endeavours. We have developed a reliable and scalable crop phenotyping method for assessing CT in large field experiments. The method involves airborne thermography from a manned helicopter using a radiometrically-calibrated thermal camera. Thermal image data is acquired from large experiments in the order of seconds, thereby enabling simultaneous measurement of CT on potentially 1,000s of plots. Effects of temporal weather variation when phenotyping large experiments using hand-held infrared thermometers are therefore reduced. The method is designed for cost-effective and large-scale use by the non-technical user and includes custom-developed software for data processing to obtain CT data on a single-plot basis for analysis. Broad-sense heritability was routinely greater than 0.50, and as high as 0.79, for airborne thermography CT measured near anthesis on a wheat experiment comprising 768 plots of size 2 x 6 m. Image analysis based on the frequency distribution of temperature pixels to remove the possible influence of background soil did not improve broad-sense heritability. Total image acquisition and processing time was ca. 25 min and required only one person (excluding the helicopter pilot). The results indicate the potential to phenotype CT on large populations in genetics studies or for selection within a plant breeding program.

Damage detection in CFRP by coupling acoustic emission and infrared thermography

Abstract: Acoustic emission (AE) and infrared thermography (IT) are simultaneously combined to identify damage evolution in carbon fibre reinforced composites. Samples are subjected to tensile static loads while acoustic emission sensors and an infrared camera record the acoustic signals and the temperature variations respectively. Unsupervised pattern recognition procedure is applied to identify damage mechanisms from acoustic signals. Thermodynamic arguments are introduced to estimate global heat source fields from thermal measurements and anisotropic heat conduction behavior is taken into account by means of homogenization technique. A spatial and time analysis of acoustic events and heat sources is developed and some correlation range in the AE and IT events amplitude are identified.

Review of Active IR Thermography for Detection and Characterization of Defects in Reinforced Concrete

Abstract: Active thermography methods enable structural investigations of reinforced concrete elements taking into account many different testing problems. The goal of this review is to provide an overview on the state-of-the-art regarding the use of active infrared thermography (IRT) for detection and characterization of defects in reinforced concrete. The paper will provide the physical background, equipment being used, as well as post-processing methods that are used to analyse sequences of thermograms. This work also presents the fields of applicability of IRT with a focus on the aspects related to reinforced concrete structures, as well as the advantages, limitations and potential sources of errors of IRT employment. Additionally previous non-destructive testing (NDT) studies that employed thermography techniques with natural excitation are briefly presented. A review of the future trends of thermal imaging are also included in this work. It can be concluded that while IRT is a useful tool for the characterisation of defects in the building sector, there is great prospect for the development of more advanced, effective and accurate approaches that will employ a combination of thermography approaches.

A Review of Raman Thermography for Electronic and Opto-Electronic Device Measurement With Submicron Spatial and Nanosecond Temporal Resolution

Abstract: We review the Raman thermography technique, which has been developed to determine the temperature in and around the active area of semiconductor devices with submicron spatial and nanosecond temporal resolution. This is critical for the qualification of device technology, including for accelerated lifetime reliability testing and device design optimization. Its practical use is illustrated for GaN and GaAs-based high electron mobility transistors and opto-electronic devices. We also discuss how Raman thermography is used to validate device thermal models, as well as determining the thermal conductivity of materials relevant for electronic and opto-electronic devices.

Ultrasonic analysis and lock-in thermography for debonding evaluation of composite adhesive joints

Abstract: Glass-fiber reinforced thermosetting plastic adhesive joints were characterized through ultrasonic imaging and lock-in thermographic analysis for assessing the adhesion quality before being subjected to static tensile mechanical tests and to accelerated aging cycles. The mapping of each sample has been obtained. Visual testing were performed on all specimens after the mechanical tests in order to obtain a comparison with ultrasonic and lock-in thermography technique. A quantitative analysis has been carried out to evaluate the ability of lock-in thermography in investigating inadequate bonding and obtaining the validation of the technique by the consistency of the results with the well-established ultrasonic testing.

Detection of Perforators Using Smartphone Thermal Imaging.

Abstract: Thermal imaging detects infrared radiation from an object, producing a thermogram that can be interpreted as a surrogate marker for cutaneous blood flow. To date, high-resolution cameras typically cost tens of thousands of dollars. The FLIR ONE is a smartphone-compatible miniature thermal imaging camera that currently retails at under $200. In a proof-of-concept study, patients and healthy volunteers were assessed with thermal imaging for (1) detecting and mapping perforators, (2) defining perforasomes, and (3) monitoring free flaps. Preoperative, intraoperative, and postoperative thermograms can assist in the planning, execution, and monitoring of free flaps, and the FLIR ONE provides a low-cost adjunct that could be applied to other areas of burns and plastic surgery.

Veterinary applications of infrared thermography.

Abstract: Abnormal body temperature is a major indicator of disease; infrared thermography (IRT) can assess changes in body surface temperature quickly and remotely. This technology can be applied to a myriad of diseases of various etiologies across a wide range of host species in veterinary medicine. It is used to monitor the physiologic status of individual animals, such as measuring feed efficiency or diagnosing pregnancy. Infrared thermography has applications in the assessment of animal welfare, and has been used to detect soring in horses and monitor stress responses. This review addresses the variety of uses for IRT in veterinary medicine, including disease detection, physiologic monitoring, welfare assessment, and potential future applications.

Automatic detection and analysis of photovoltaic modules in aerial infrared imagery

Abstract: Drone-based aerial thermography has become a convenient quality assessment tool for the precise localization of defective modules and cells in large photovoltaic-power plants. However, manual evaluation of aerial infrared recordings can be extremely time-consuming. Therefore, we propose an approach for automatic detection and analysis of photovoltaic modules in aerial infrared images. Significant temperature abnormalities such as hot spots and hot areas can be identified using our processing pipeline. To identify such defects, we first detect the individual modules in infrared images, and then use statistical tests to detect the defective modules. A quantitative evaluation of the detection and analysis pipeline on real-world, infrared recordings shows the applicability of our approach.

Detection and Inspection of Steel Bars in Reinforced Concrete Structures Using Active Infrared Thermography with Microwave Excitation and Eddy Current Sensors.

Abstract: The purpose of this paper is to present a multi-sensor approach to the detection and inspection of steel bars in reinforced concrete structures. In connection with our past experience related to non-destructive testing of different materials, we propose using two potentially effective methods: active infrared thermography with microwave excitation and the eddy current technique. In this article active infrared thermography with microwave excitation is analyzed both by numerical modeling and experiments. This method, based on thermal imaging, due to its characteriatics should be considered as a preliminary method for the assessment of relatively shallowly located steel bar reinforcements. The eddy current technique, on the other hand, allows for more detailed evaluation and detection of deeply located rebars. In this paper a series of measurement results, together with the initial identification of certain features of steel reinforcement bars will be presented.

Active Microwave Thermography for Defect Detection of CFRP-Strengthened Cement-Based Materials

Abstract: Nondestructive testing (NDT) of rehabilitated cement-based materials (RCMs) with carbon-fiber-reinforced polymer (CFRP) composites is quite important in the transportation and infrastructure industries. Among various NDT methods, active microwave thermography (AMT) has shown good potential. This method uses microwave energy to heat a structure of interest, and subsequently the surface thermal profile is measured using a thermal camera. In this paper, the application of AMT for defect detection (unbond, delamination, and crack) in CFRP composites used in RCMs is presented. More specifically, the effect of defect size and depth and polarization on the resultant surface thermal profile with defects is first studied through simulation. The effect of polarization on detection of defects with regard to the orientation of CFRP fibers is also experimentally investigated. Finally, a quantitative analysis of the measured results based on the thermal contrast and signal-to-noise ratio (SNR) for all the three aforementioned defect types is presented. The results show that the SNR is improved when utilizing perpendicular (compared with parallel) polarization, and that the maximum effective heating time is $\sim 60$ s, even for small defects.

Infrared thermography for civil structural assessment: demonstrations with laboratory and field studies

Abstract: A detailed investigation of infrared thermography (IRT) for civil structures is presented by considering different technologies, data analysis methods and experimental conditions in the laboratory and also in the field. Three different types of infrared (IR) camera were compared under active IRT conditions in the laboratory to examine the effect of photography angle on IRT along with the specifications of cameras. It is found that when IR images are taken from a certain angle, each camera shows different temperature readings. However, since each IR camera can capture temperature differences between sound and delaminated areas, they have a potential to detect delaminated area under a given condition in spite of camera specifications even when they are utilized from a certain angle. Furthermore, a more objective data analysis method than just comparing IR images was explored to assess IR data, and it is much easier to detect delamination than raw IR images. Specially designed laboratory and field studies show the capabilities, opportunities and challenges of implementing IRT for civil structures.

Simultaneous measurement of the in-plane and in-depth thermal diffusivity of solids using pulsed infrared thermography with focused illumination

Abstract: We extend the flash method to retrieve simultaneously the principal in-plane and the in-depth thermal diffusivities of anisotropic solids using focused Gaussian illumination. A complete theoretical model allows calculating the temperature rise of an anisotropic and semitransparent sample. The surface temperature distribution has a Gaussian shape along the principal axes, whose radii give the principal in-plane thermal diffusivities. On the other hand, the time evolution of the spatially averaged surface temperature gives the principal in-depth thermal diffusivity. Measurements performed on opaque and semitransparent samples, covering a wide range of thermal diffusivities, validate the method. It is especially suited to characterize the principal components of the thermal diffusivity tensor of anisotropic plates from a single and fast measurement.

A Technique for Coupled Thermomechanical Response Measurement Using Infrared Thermography and Digital Image Correlation (TDIC)

Abstract: An integrated infrared thermography and 3-D digital image correlation (TDIC) technique has been developed which allows for simultaneous measurement of spatial and temporal distributions of temperatures and displacements. For this, a novel technique was developed to calibrate the IR thermal cameras with a stereo-vision digital image correlation (DIC) system using the standard pin-hole stereo calibration model. This method fuses thermal and displacement information and compensates for the difference in camera resolutions. Several high temperature black and white paints were evaluated to determine their characteristics including the temperature-dependent emissivity of each paint, the mixed emissivity of both paints in the speckle pattern, and optical thickness. The advantages of evaluating linked full-field temperatures and strain measurements through the TDIC technique are demonstrated through measurements obtained on an E-glass/vinyl ester/balsa wood sandwich composite subjected to simultaneous one-sided heating and compressive loading.

Evaluation of Workpiece Temperature during Drilling of GLARE Fiber Metal Laminates Using Infrared Techniques: Effect of Cutting Parameters, Fiber Orientation and Spray Mist Application.

Abstract: The rise in cutting temperatures during the machining process can influence the final quality of the machined part. The impact of cutting temperatures is more critical when machining composite-metal stacks and fiber metal laminates due to the stacking nature of those hybrids which subjects the composite to heat from direct contact with metallic part of the stack and the evacuated hot chips. In this paper, the workpiece surface temperature of two grades of fiber metal laminates commercially know as GLARE is investigated. An experimental study was carried out using thermocouples and infrared thermography to determine the emissivity of the upper, lower and side surfaces of GLARE laminates. In addition, infrared thermography was used to determine the maximum temperature of the bottom surface of machined holes during drilling GLARE under dry and minimum quantity lubrication (MQL) cooling conditions under different cutting parameters. The results showed that during the machining process, the workpiece surface temperature increased with the increase in feed rate and fiber orientation influenced the developed temperature in the laminate.

Is It Possible to Detect Activated Brown Adipose Tissue in Humans Using Single-Time-Point Infrared Thermography under Thermoneutral Conditions? Impact of BMI and Subcutaneous Adipose Tissue Thickness.

Abstract: Purpose To evaluate the feasibility to detect activated brown adipose tissue (BAT) using single-time-point infrared thermography of the supraclavicular skin region under thermoneutral conditions. To this end, infrared thermography was compared with 18-F-FDG PET, the current reference standard for the detection of activated BAT.

Investigation on the damage evolution in the impacted composite material based on active infrared thermography

Abstract: A novel method was proposed to investigate the damage evolution of the impacted composite laminate using active infrared thermography in this work. This method was comprised of the following procedures. Firstly, the infrared images, containing the damage information under different fatigue cycles, were obtained through fatigue test and damage detection test. Then, the damage area of the impacted composite laminate being inspected under different fatigue cycles was acquired through such infrared image processing as image enhancement, image segmentation and quantitative identification. Finally, an expression, indicating the relationship between the fatigue cycles and the damage area, was fitted by the least square method. Four specimens were implemented to validate the effectiveness of the proposed method via the proposed procedures. The results indicate that the proposed method can effectively reveal the damage evolution. I.e. the expressions can be accurately fitted and the corresponding accuracy can be as high as 0.98186, 0.95067, 0.9797 and 0.99316 respectively.

Analysis of building facade defects using infrared thermography: Laboratory studies

Abstract: One of the main problems facing the inspection of facades by means of passive infrared thermography, in order to identify and evaluate defects or pathologies, is the definition of the most appropriate moment to perform the inspection. Most studies focus on the Delta- T value as a criterion for the identification and evaluation of defects. Nevertheless, the identification of defects will primarily depend on the heat flux, since the way defects appear on the thermogram is determined by their type and by the direction of the flux. This study set out to analyse this problem by studying the behavior of the Delta- T and contrast functions in defects in ceramic tiles and mortar. Accordingly, test samples were made with induced defects during the manufacturing process, to simulate the detachment problems that occur with ceramic tiles of different thicknesses and cracks of different depths. The test samples were assessed during direct and inverse heating cycles. The results showed that it is possible to detect differences in behavior when varying the thickness of the ceramic tiles and the depth of the cracks by considering the Delta- T and contrast functions. In consequence, the inspection moment should be defined according to the behavior of the gradient temperature, the type of the defect and the direction of the heat flux.